Note: For the purposes of this discussion, argon ion and krypton ion lasers are very similar - they are both rare gas ion lasers, their basic principles of operation are similar, and the same basic hardware configuration and power supplies can usually be used. Differences are primarily in gas fill of the plasma tube and the mirrors/prisms for selecting the output wavelength. Keep this in mind since where we describe something for an argon ion laser, most likely it applies to a krypton ion (or mixed gas 'white light') laser as well. However, this doesn't mean you can just replace one type with another or convert an argon ion laser to krypton by cracking open the seal on its tube and refilling it! For more information, see the section: Comparison of Argon and Krypton Ion Tube Characteristics and the chapter: Ar/Kr Ion Laser Power Supplies.
These are the types of lasers generally used for large scale light shows as well as in some types of high performance phototypesetters or other digital imagers, and for use in holography and other optics research. Unlike diode and HeNe types, a serious interest in these also represents a very serious investment of time, money, and caution.
At least the added plumbing shouldn't be much of a problem unless portability is an important consideration! This is not to say it cannot be done, just that you will have to be pretty determined to get that large laser going in an one-bedroom apartment! In any case, you can't just go and plug one of these beasts into the nearest AC outlet. :)
A small air-cooled ion laser is probably a more reasonable toy especially if you have to share the single 3-prong outlet in your place with the family microwave! :-) And, some of these lasers still have outputs that can approach 500 mW (though most are much lower).
The types of small argon ion (krypton ion types would be rare) lasers that are turning up on the surplus market are often from various high performance scanners, recorders, duplicators (not your ordinary office copier), printers, and phototypesetters.
The Xerox 9700 series and older 8700 series (and possibly the 8400 as well) utilized an American Laser Corporation (ALC) 60X argon ion laser. This laser was made to the Xerox "X" standard for a high speed duplicator/printer, hence the X in the part number. The NEC-3030 is also a printer laser and OEM Spectra-Physics (SP) 161 lasers were used in a Times Graphics, Inc. printer. The IBM model 3900, 3835, and 3825 printers (circa 1996) have argon ion lasers and AOMs. Other companies that manufacture or have manufactured equipment containing ion lasers include Dainippon Screens, Hell, and Ricoh.
Many of these older but expensive graphic arts systems are still being maintained and are now being retrofitted with newer technology such as high power IR diode lasers or Diode Pumped Solid State (DPSS) lasers. Therefore, more small air-cooled argon (mostly) ion laser heads and power supplies are showing up on the surplus market at attractive prices. (However, if you would be content with only 532 nm green, there are high quality DPSS lasers showing up surplus from these sources as well. The most common is the Coherent Compass 315M-100 which produces a TEM00 beam with an output power of up to 100 mW. However, red and blue DPSS lasers are still way too expensive for most hobbyists. For more information, see the chapter: Solid State Lasers.)
Some DNA sequencers apparently also contain argon ion and other medium power visible lasers.
For reference, here are the typical wavelengths and expected power output from argon ion laser heads pulled from graphics arts equipment:
Other argon ion lasers that may turn up as pulls from graphic arts equipment include the Uniphase 2202-5BLT, 2202-30BLT, and Spectra-Physics 163, as well as several others.
Note that some lasers that at first appear to have excellent specs may be designed for pulsed (low duty cycle) operation. One example is the HGM Spectrum Compac A Argon Laser. This uses a American Laser 68B tube which would be good for 2.5 W with a proper power supply and adequate cooling but in this case is only designed for relatively low duty cycle pulsed operation. Pulse, cool, pulse, cool, etc. If the price is low enough, it may be worth buying just for the tube (assuming it is still good) but non-trivial modifications will likely be needed for it to run CW.
Additional more detailed information on many of these and other models from ALC, NEC, and SP can be found later in this and subsequent chapters on ion lasers. Also see the section: How to Get a Laser Without Really Trying - Part 2.
However, many older laser printers and related equipment were based on HeNe lasers so don't assume there is an argon ion laser in that dusty thing at the salvage yard (even if quite large) just because it has a laser warning label! (Newer consumer/office type laser printers use relatively low power IR diode lasers.)
Mike Harrison (mike@whitewing.co.uk) has a Web page in the early stages of development which lists graphic arts, industrial, medical, scientific, and other equipment which include internal lasers of all kinds. The page can be updated with your contributions as well. Take the link near the bottom of Mike's Electric Stuff Page (which also has a lot of other interesting topics).
Here are some guidelines for determining if dragging home something bigger than your living room will be worth the trouble:
(From: Lynn Strickland (stricks760@earthlink.net).)
Some of the higher-end stuff from Xerox, ECRM, still have HeNe's in them. The Xerox printers are the kind of machines you'd find at places like Kinko's. (big, expensive ones). Xerox still services some argon ion based units too.
Xerox just yanks the laser heads out after a certain number of operating hours and, last I knew, sells them off on the surplus market. The HeNe's that come out still have quite a few operating hours left in them at that point. For awhile MWK had first dibbs on them, but I don't know what's happening in the last year or two.
(From: Dean Glassburn (Dean@niteliteproducts.com).)
Basically here is the story on Amercian Laser's Lasers. ALC has sold 60X, 68B, 909, and 920 systems in the past. The 60X was used in Xerox graphic arts machines, the 68B, 909, and 920 in medical systems. All these manufactures of the systems that used the tubes have since either gone out of business or found other technology to replace the ion laser systems (e.g., high power diode and DPSS lasers).
About two years ago, ALC's main source of BeO went out of business. Not a major disaster to ALC, because their replacement of those tube types were about 10 a year combined for the 909 and 68B. Ceramic for the 920 was all gone as well as the need for that tube. The current situation is that to get a new tube manufactured there is a 6 to 10 week wait and the cost for the ceramic is twice what it once was, so the tube price new is much higher.
OK that is the current situation. We have sold and rebuilt many ALC systems for use, but the new tube issue always eventually comes up.
The benefits to using these are easy to state: Usually you can find these cheaper than other systems. When working properly, the systems put out good power as designed.
The design limitations are as follows. The 60X was originally designed for 7 to 9 A tube running 488 nm TEM00. This equates to a maximum of 20 mW for 8,000 hours. However, all the 60X systems currently out there are usually old tubes running at a MUCH higher current. To get a higher output of 50 to 100 mw, tube life is very limited. The 909 systems deliver about 5 to 6 watts multimode/multiline. Not the best divergence but not bad either. No fill system on the tube, so life is about 1,000 to 2,500 hours. We have regassed plenty of these and kept them running. As a krypton or mixed gas, life around 600 hours is normal. We usually leave a valve on the tube for regassing. The 68B tubes are usually cracked and cannot be repaired, or run at a low pressure and carbon tracked the bypass. The 920 made a lot of power when running, but it was designed to pump into a Dye laser or a fiber. It is a big bore tube to operate on three-phase 208 VAC at 45 amps, good for about 1,000 hours. You would have better divergence with a flashlight. Changing the optics to reduce the divergence makes a 6 watt, 45 amp laser instead of a 14 watt high divergence laser. Better off with a 909, same output, less power consumed.
However, a word of caution: Just because the connectors look the same or the specs look like the power supply and laser head should be compatible doesn't make it so. Just plugging something together may result in smoke or shortened lifetime. It is a safe bet that if the components actually came from a working system, they will play happily together. On the other hand, if someone just connected a power supply to a laser head that it wasn't designed to drive, tested the combination for a couple of minutes, and sold it as a working system, there could be problems down the road.
Regardless of whether your laser is built like Frankenstein's monster, it WILL likely be missing the cooling fan and in some cases, even the head cover. The typical Patriot style fans are available surplus typically for between $15 and $30. Other type fans or blowers with similar ratings (220 cfm and up) will also work if the airflow direction is correct (i.e., for the ALC-60X, it must be sucking out of the head). In cases where the fan diameter is much larger than the opening in the head above the tube as with the Patriot and ALC-60X, a 1 inch collar will also be needed between them to act as an adapter plenum. For laser heads like the SP-161 where the cover may be missing, replacements (including the fan) may be available from the original manufacturer or companies like National Laser. though the cost may be a good fraction of what you paid for the entire laser! (In the case of the SP-161, the cover is really only needed for safety - the fan doesn't use the cover for mounting.) But, if you are just a bit handy, they can usually be fabricated relatively easily. Any interlocks that are missing will also need to be replaced. I've even heard of people using vacuum cleaners for cooling ion lasers! (Think of the marketing possibilities!)
Also, don't be upset if the running time meter says something like 64,500 hours! This is typical of a graphic arts pull and doesn't reflect on how much time is on the tube itself - which is the only thing that really matters. You can be sure the tube has been replaced more than once but there is probably no way to actually determine how many hours are on the one that is installed.
Where the umbilical cable has been cut (this happens as well since whoever removed the unit may not have realized that the cable could be extracated non-destructively), a proper connector will need to be reattached. If they are the same type at both ends, the wiring is likely 1:1 so an ohmmeter can be used to determine the connections. However, if they are not the same type (e.g., a Jones type at one end and an AMP type at the other), you will need to find the wiring for each one. Ditto if either end is hard-wired. However, in the worst case, a lot of the wiring at the head-end at least can be determined by tracing connections inside the head. WARNING: A cut umbiliacal could also mean there could be compatibility problems as mentioned above if the head and power supply were not from the same piece of equipment and were never tested together. Even if they use the same AMP connector, there could still be problems. For example, an ALC or Omni power supply may melt down attempting to drive an NEC head or vice-versa without some rewiring and other changes (if it is even possible) even though the connectors mate.
Also see the section: Spectra-Physics-161 Laser - More or Less.
In particular:
See the section: On-Line Introduction to Lasers for the current status and on-line links to these courses, and additional CORD LEOT modules and other courses relevant to the theory, construction, and power supplies for these and other types of lasers.
Several modules would be of particular interest for ion lasers. Unfortunately, the on-line manuals (in PDF format) have disappeared from the MEOS Web site. But I have found and archived most of them:
Surprisingly, there is no module speecifically on ion lasers!
If MEOS should complain, these will have to be removed. So, get them while you can! But I doubt they'll complain. And most are also archived at the Wayback Machine Web Site.
I'm sure you've seen the posts on the sci.optics or alt.lasers newsgroups that go something like: "I just got a big laser. What type is it? What can I do with it? Etc." One of these guys is going to look down the bore and get blinded or worse. So I'd also like to see a site up for that reason. Well it turns out there is such a site. There is a excellent laser safety site at: Rockwell Laser Industries.
Note: Since comparisons are made throughout this discussion between argon (and krypton) ion lasers and helium-neon (HeNe) lasers, it is worthwhile to first read the Chapter: Helium-Neon Lasers if you are not familiar with those devices.
The basic design of the argon/krypton laser is conceptually similar to that of the HeNe (or other gas) laser - plasma tube containing the active medium (argon and/or krypton gas) mirrors forming a Fabry-Perot resonator. However, unlike HeNe lasers, the energy level transitions that contribute to laser action come from ions of argon or krypton - atoms that have had 1 or 2 electrons stripped from their outer shells. Spectral lines at wavelengths less than 400 nm come from atoms that have had 2 electrons removed. Longer wavelengths come from singly ionized atoms. There are many possible transitions in the UV, visible, and IR portions of the spectrum. With suitable optics coherent light from a single spectral line or many lines may be produced simultaneously. An adjustable intra-cavity prism can even be included to permit the desired wavelength to be selected via a thumb-screw adjustment.
Beam characteristics in terms of diameter and divergence are similar to those of HeNe lasers. However, the coherence length (without additional optics) tends to be smaller than that of a HeNe laser of similar cavity length. This is because the gain curve for the ion laser transitions is wider than the one for the HeNe laser - around 2.5 GHz compared to 1.5 GHz. So, a larger number of longitudinal modes will be present and the coherence length will therefore be reduced. Coherence lengths quoted by various sources range from 2.5 to 10 cm for typical air-cooled ion lasers.
To excite the ionic transitions and achieve a population inversion, much more current is needed than for a HeNe laser. A 'small' argon laser may use 10 AMPs of current (rather than the 3 to 8 mA typical of a HeNe laser tube). Even at a tube voltage of 100 VDC, this represents about 1000 W of power dissipation. (Think of a typical space heater inside a small box!) High flow rate forced air cooling is absolutely essential - the tube would melt down in short order without it. Larger ion laser tubes may pass more than 100 AMPs of current at up to 400 VDC or more - and require three-phase power and water cooling - figure on utility substation just for your laser!
Thus, while Ar/Kr ion lasers and HeNe lasers are conceptually similar, the approximately 3 orders of magnitude greater tube current and two orders of magnitude greater power dissipation compared to a HeNe laser mean that the construction details are vastly different. You won't find one of these in a laser pointer!
See Typical Cyonics Air-Cooled Argon Ion Laser Tube for the construction of one popular internal mirror type (which bears the most similarity to a HeNe laser tube)! Those from other manufacturers are similar.
The following assumes a small air-cooled Ar/Kr ion tube like that used in the American Laser Corporation 60X/Omnichrome 532 or the Cyonics tube described in the section: Cyonics Argon Ion Tube.
Only a few modern air cooled tubes stand up to 12 A and most models peak out at 10 A, despite what Omnichrome says in their documents. The tubes will invariably come with a 10 A limit sticker. As far as I'm aware, no application ever used the 'special modifications' for 14 A for the Omnichrome 532, these special modifications are going to a tube that is twice as long with 2 huge fans, which is actually the next model up, the 543.
Also see the section: Argon/Krypton Ion Laser Tube Life.
Unlike a HeNe tube, the Ar/Kr ion discharge may not present a large negative resistance once the arc has been struck. Some references suggest that the effective series resistance is on the order of 1 or 2 ohms positive while others indicate that it is a low negative value (or perhaps it depends on the particular tube design and operating conditions). In any case, the tube behaves so much like a dead short that without a regulator or some additional ballast resistance, this argument may be only of academic interest!
If the resistance is positive, tube current can theoretically be controlled by varying the voltage of the supply and a ballast resistor isn't strictly essential as with an HeNe tube just to maintain stability. However, this control would be extremely sensitive to EVERYTHING since a small change in input voltage would result in a large change in current. For example, assuming the effective discharge resistance is 1 ohm for a tube dropping 100 V at 10 A, a 5 percent variation in input voltage would result in more than a 50 percent change in tube current! Furthermore, due to changing conditions as the tube heats, a runaway condition is possible even if the resistance of the discharge is non-negative and must be avoided by using a proper current regulator (or adequate ballast resistance - for testing only).
In any case, if you acquired a head that is missing the HUGE fan - don't be tempted to run it until you have one in place and spinning up a storm (at least not for more than 30 seconds)! Sit a vacuum cleaner on top if you have to but don't skip the cooling!
Large frame Ar/Kr lasers may require 35 A at 400 V running on three-phase 240 VAC, 30 kV or more to start, and gallons-per-minute of tap water cooling!
Think of how much larger the cathode of a HeNe tube is compared to the anode. That much surface area is needed to keep the heating and sputtering at the cathode within acceptable limits. (An HeNe tube WILL lase if hooked up backwards but its life will be significantly shortened.) And that is for a tube using only a few watts compared to a KILOWATT or more for an ion laser.
The typical ion tube has a thick helix of tungsten for its cathode (calling it a 'filament' is really minizing the massive nature of this structure!). The hot cathode results in thermionic emission (the boiling off of electrons from its surface) reducing its work function - the potential (voltage) drop associated with pulling an electron out and away from it to free space. With less voltage drop, less power is dissipated at the cathode itself, there is less damage and less sputtering, as well as a reduced voltage requirement for the power supply. Also see the section: Effects of Improper Filament Temperature.
Also note that the cathode isn't just made out of metallic tungsten - it is specially processed and coated to promote the formation of an sufficiently dense electron cloud so that AMPS of current can be passed through the tube with minimal additional heating at the cathode itself. The AC of the filament supply keeps arc moving in the vicinity of the cathode Even so, if conditions aren't perfect, you can end up with localized heating leading to cathode sag and eventual failure. Repeated attempts at starting, improper gas pressure, contamination, and plasma oscillations can result in erosion of the cathode. An ion tube with a cathode that is not hot enough won't start. One that loses its filament supply during operation will go out - and there may be damage to the cathode in the process.
All in all, what you would gain in not needing a filament transformer, you would lose in having to have a truly HUGE cathode structure to handle the heat dissipation, a much HIGHER voltage power supply, even better then perfect cooling, etc. :-)
This arc temp is well above what would melt glass. There are only 5 or 6 materials that can go into a argon plasma tube and survive the arc: BeO, tungsten, aluminum nitride, pyrolytic graphite and molybdenum. Even the NEC-3030 which has a glass outer bottle, has a BeO tube fused on to handle the plasma and conduct away the heat. If you put enough current through the bore, you get additional wavelengths as the sodium, oxygen. barium, and who knows what else ions start to lase with the argon. Tube materials lasing is not something you want to see despite how pretty it might look. :-) Tubes (and possibly power supplies) don't last long when this happens!
Keep in mind that even the old quartz plasma tubes have beryllium oxide or tungsten bores, and the glass is NOT in contact with the plasma. Beryllium oxide conducts heat 5 times faster then most metals.
You will NOT be able to purchase BeO as it can be an extremely nasty thing if mishandled and you breathe the powder. A small but unknown percentage of people will have their lungs damaged leading to an early death. If somebody gives you a old plasma tube made of BeO or containing BeO components, you should NEVER grind on it, open it, clean it with acid, or breathe the dust it makes when it breaks. When they break, they have to be FLOODED with water, and all the pieces sealed in a plastic bag and sent to a special place for disposal (there should be precisely this warning on the tube somewhere). (And, then you may have to have a Hazmat team come in to clean up your house.) Don't mess with it!
The following were measured with calipers from end-bell to end-bell and then roughly compensated with eyeball for actual bore length:
Given the overall length of these tube, the relatively short bores may seem surprising. The remaining length is taken up with the filament/cathode and support structure, and gas filled spaces of the cathode and anode end-bells. Typical Cyonics Air-Cooled Argon Ion Laser Tube where (although the diagram is not totally to scale) the cathode end-bell is actually longer than the actual bore.
Bore diameters usually range from .55 to .75 mm for small lasers and up to 2 mm for large-frames. Longer tubes require larger bores.
Most of the information below is from the operation manual for a Spectra-Physics large-frame ion laser.
The formula for argon output available from a given ion tube operated below saturation all lines multimode output is:
P = K * (J2) * V
Where:
Notes:
Most lasers in the less then 1 meter class like about 600 Gauss to start. Too much magnetic field in an ALC-60X type tube, can actually kill power, as we have found (--- Steve).
Magnetic fields that envelop the plasma discharge enhances the population inversion, it tends to force free electrons toward the center of the plasma tube bore, increasing the probability of a pumping collision, unfortunately the magnetic field also causes Zeeman splitting of the laser lines, which elliptically polarizes the output, causing partial loss at the polarization sensitive plasma tube windows
The following equation applies to any laser - not just an ion type. Output power can be calculated from:
q * L
Po = T * A * I * (------ - 1)
T + B
Where:
The following are some specific numbers for various lasers (from "Laser Fundamentals" by William Silfast, ISBN 0-521-55617-1):
Here are some others you might run across:
(Photos provided by: Marco Lauschmann (mla@sbk-ks.de). Diagram (don't you just love the fabulous colors? :) from: Sam.)
Cyonics/Uniphase Model 2301 Internal Mirror Ion Tube - Cathode-End showing filament connection studs and mirror mount. Exhaust tube is visible below.
See Typical Cyonics Air-Cooled Argon Ion Laser Tube for some details of its internal construction.
The 2301 is used in the Uniphase model 2011 and older 2201 lasers heads. (There should be a dash number following the 2301 model number: -10 = 10 mW, -20 = 20 mW, etc. The letters following this info determine the wavelength: SL = single blue line (488 mm), GL = single green line (514 nm), VL = 458 nm, BL = all blue (458 nm, 476 nm, 488 nm, and 497 nm), ML = Multiline (all lines).) More complete specifications may be found at JDS Uniphase. Go to "Commercial Lasers", "Argon Gas Lasers".
Typical Spectra-Physics specifications for modern versions of these lasers:
Spectra-Physics Model 091-92 Internal Mirror Ion Tube - Anode-End showing mirror adjustment collar and thermal protector on heat sink.
The basic design is by Dr. Sergei Babin at Novosibersk. They are available commercially as one offs at up to 75 watts. Get yours while they are hot! :)
However, what about a really compact air-cooled argon ion laser only capable of a few mW but made as small as possible?
The problem no matter how you slice it is power dissipation and the bore length required to achieve adequate gain. The smallest commercial argon ion tubes have bore lengths of a little over 75 mm with a diameter of about .5 mm. These may have a lasing threshold as low as 2 A at perhaps 85 V across the tube. Assuming that such a tube could produce 2 mW at a current of 3 A and that amount of power is most that will be needed, the power dissipation of the discharge is reduced to just over 250 W max. For such a tube:
(From: Steve Roberts (osteven@akrobiz.com).)
For CW work, 4 units of 350 cfm Patriot fans for a model 68B, the HGM5 is an ALC-68B with shortened Brewster stems, a bigger gas ballast, and a slightly wider bore, it can be 3 watt CW laser, but is usually ran duty cycled. I have seen ALC-68s do 7 watts on the bench when freshly made. The HGM does run about 500 mW CW and can be pulsed up to 3 watts max for up to say 15 seconds with the existing HGM fan, which is a big squirrel cage type.
The warning label is 5 watts on the HGM5, the medical circuitry clips the power at 3 W.
If you could cool it enough, an ALC-60X size tube can do 2 to 3 watts easily, in fact there is a medical unit that uses a small internal mirror tube at 3 watts using a closed loop water-to-air-cooler in a power-on-demand application at a 5% or so duty cycle. What limits you on an ALC-60X is the glowing red undercooled anode that will open up when you try it - spoken from experience, not conjecture. :-)
Just about every gaseous element has been shown to lase in the IR and some cases visible or UV, but few will lase CW. Xenon is used for resistor trimmers because in its pulsed mode, its green lines are able to be focused tightly, and its per pass gain is much higher then any other gas laser except copper vapor resulting in a compact high power green laser before frequency doubled solid state lasers were available.
The following patents are particularly relevant with respect to small ion lasers:
While patents do not provide all the details needed to construct your own system, they are valuable nonetheless as a starting point for understanding basic principles of operation and system design. Some of the electronics are described in substantial detail.
However, some of these appear to match actual hardware very closely. Of particular interest are the two ALC patents. These outline the principles of operation and provide fairly complete schematics of the power supply for the ALC 60X/Omnichrome 532 laser.
Some information may also be available from the major manufacturers of ion lasers. See the chapter: Laser and Parts Sources for addresses and links.
454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, 528.7 nm.
406.7 nm, 413.1 nm, 415.4 nm, 468.0 nm, 476.2 nm, 482.5 nm, 520.8 nm, 530.9 nm, 568.2 nm, 647.1 nm, 676.4 nm.
Which lines actually lase are sensitive to both tube current and gas pressure and thus the color balance (relative intensity of the various wavelengths) will shift as the tube heats up and with age.
To get an idea of the actual perceived color at each wavelength, see the section: Color Versus Wavelength.
Single-line or multiline: This refers to the output spectral lines in the beam. For ion lasers, several wavelengths can be generated simultaneously. The reflectivity curve of the Output Coupler (OC) mirror and tube current determine which subset of the possible lasing lines are active.
Also see the section: Single-Line and Multiline Output.
Single-mode or multimode: This refers to the axial mode structure of the output beam.
The table below shows the distribution of output wavelengths as a function of the type of optics and tube current for an ALC-60X/Omni-532 compatible argon ion tube (specific model unknown).
Plasma -------- Laser Output Power (mW) --------
Tube Multi- ------ Gaussian TEM00 Mode ------
Current mode ------- Pure Line ------
(Amps) -- All Lines -- 457 nm 488 nm 514 nm Lifetime (MTBF) Hours
---------------------------------------------------------------------------
4 20 10 1.0 7.0 0.0 15,000 - 25,000
6 50 30 2.0 17.6 7.5 8,000 - 15,000
8 110 70 5.0 27.0 23.0 4,000 - 6,000
10 220 130 10.0 44.0 42.0 1,500 - 2,000
12 325 200 15.0 60.0 68.0 1,000 - 1,500
14 430 280 22.0 81.0 98.0 500 - 1,000
Notes:
A laser set up for multiline operation will usually result in highest total output power but there are many applications where a monochromatic beam is required.
multiline operation requires a set of mirrors with reflectivities designed to achieve laser operation for all the desired spectral lines. Any intracavity prisms are removed.
Single-line operation can be implemented in a couple of different ways:
(From: Steve Roberts (osteven@akrobiz.com).)
The typical ion laser etalon is 15 mm diameter, 12 mm thick, fused silica or quartz, coated to reflect about 10% from both sides, usually with as few coating layers as possible. It's heated 10 to 20 °C above room temperature, stable within 0.001 °C. Without temperature control, it won't be very stable. The laser will flash at 2 to 3 Hz as the etalon temperature stabilizes. You peak it on a bright flash.
Even a thick plate of window glass will get you started, the trick is to position it correctly and keep it warm. Trust me, try making a simple holder using a (Newport) MM1 or MM2 and stick a piece of high quality glass or quartz intracavity.
Etalons need to first be adjusted to what is referred to as "Flash". In other words, extremely parallel to the cavity where minute changes in the angle take the cavity in and out of resonance very quickly. They are then walked to a offset angle that sets the choice of single frequency once they heat up.
I have one of these rugs I maintain running 24/7 locked to an iodine cell with a etalon,
For krypton, the lines are 647 nm and 530 nm. Krypton lines are sensitive to pressure and magnetic field strength. All water-cooled ion lasers have axial electromagnets around the bore to concentrate the arc. A krypton laser will have a high/low field switch as well.
The tables below list the relative strengths of all the important lines for a typical 30 watt argon/7 watt krypton laser with:
Normally, optics are selected to support the mission of the laser - i.e., surgery wants only the blue lines; ophthalmology needs green, red, and yellow; Raman Spectroscopy needs 647 and 676 nm; laser shows use argon for blue, green, and violet, and krypton for red and yellow. Mixed gas lasers use optics selected for 55% red, 20% green, and 25% blue and violet. To kill a line, one of the optics is made more then 15% transmissive at that line.
The 488 and 514.5 nm lines are lower then normal on this list - other manufacturers claim more power for these 2 lines. Note: The total power for all wavelengths adds up to more than 30/7 W because these lines are selected with a prism and are not lasing simultaneously which would result in wavelength competition.
Argon lines:
Wavelength Relative Power Absolute Power
------------------------------------------------
454.6 nm .03 .8 W
457.9 nm .06 1.5 W
465.8 nm .03 .8 W
472.7 nm .05 1.3 W
476.5 nm .12 3.0 W
488.0 nm .32 8.0 W
496.5 nm .12 3.0 W
501.7 nm .07 1.8 W
514.5 nm .40 10.0 W
528.7 nm .07 1.8 W
Krypton lines (magnetic field optimal for majority of lines, but not all).
Wavelength Relative Power Absolute Power
------------------------------------------------
406.7 nm .036 .9 W
413.1 nm .07 1.8 W
415.4 nm .02 .28 W
468.0 nm .02 .5 W
476.2 nm .016 .4 W
482.5 nm .016 .4 W
520.8 nm .028 .7 W
530.9 nm .06 1.5 W
568.2 nm .044 1.1 W
647.1 nm .14 3.5 W
676.4 nm .048 1.2 W
(From: Skywise.)
Here's what I have. I gathered it from commercial manufacturer brochures and Jeff Hecht's "The Laser Guidebook".
Argon Ion:
Wavelength (nm) Rel Pwr
----------------------------
1090.0
528.700 0.16
514.533 1.0
501.717 0.2
496.508 0.35
487.986 0.78
488.1
476.488 0.29
472.689 0.10
465.795 0.07
457.936 0.18
454.504 0.06
437.073
363.8
351.4
351.1
334.0
305.5
302.4
300.3
275.4
Krypton Ion:
Wavelength (nm) Rel Pwr
--------------------------
799.300
752.5
687.096
676.457 0.22
657.000
647.100 1.0
631.2 0.03
593.3 0.03
575.3 0.03
568.192 0.31
530.868 0.33
520.832 0.16
484.666
482.518 0.11
476.571
476.244 0.12
468.045 0.14
461.917
457.720
415.4 0.08
413.1 0.53
406.7 0.30
356.4
350.7 0.32
337.4
Depending on gas fill, current, optics, and luck, there may be other weak lines present including: 437 nm (argon), and 457.7 nm, 461.9 nm, 657.0 nm, 687.0 nm, and 799.3 nm (krypton).
As a side note, the color saturation with an ion laser is unbelievable, it's possible to get 16.8 million distinct shades with off the shelf hardware. I know the eye can't resolve that but the results you can see are beautiful.
(From: Tom Yu (tlyu@mit.edu).)
I found the following interesting comments on relative power of the various argon ion lines in my Spectra-Physics 164/166/167/168 manual. (These are the medium-frame 1 meter water-cooled Argon or Krypton lasers that want 3-phase 208 VAC at 40 A per line or so.)
"A more interesting effect in the case of argon, specifically, is that of relative intensity and gain ratios in the case of the two strong lines, 488.0 nm and 514.5 nm. Most of the visible laser transitions in the CW argon-ion laser have approximately the same gain-to-power ratio as 488.0 nm, although they are weaker than that line and generally have less gain. The 514.5 nm line, however, has only about 1/4 the gain of the 488.0 nm line, but has approximately 25% more power output when the gain is sufficient to overcome internal losses. This effect is largely due to the difference in the atomic constants that determine the power-to-gain ratio, owing to the fact that the 514.5 nm upper state comes from a different family of levels than do most of the other transitions."
It seems that this explains nicely why the 514.5 nm line is quite weak at lower powers but quickly becomes as strong as the 488.0 nm line at higher tube currents.
(From: Steve Roberts.)
Here are some additional lasing lines from Alan B. Peterson, In "New Developments and Applications in Gas Lasers" Lee R. Carlson, chair/editor SPIE Volume 737, based on the proceedings of a 1987 conference on gas lasers, pp. 106-111.
Nobel gas ion lines not previuosly reported (nm):
Argon: 307.816, 276.223, 437.594
Krypton: 379.270, 330.473, 322.062, 317.22, 304.692, 302.230
Neon: 372.710, 372.684
Xenon: 377.629, 376.897, 376.226, 373.022, 367.662, 366.675, 365.461, 364.831,
312.569, 310.863, 304.425, 297.051, 295.478, 282.251, 281.968, 276.778
The book has lasing conditions and power but no details about transmission on the optics. A magnetic field up to 1,600 gauss was used, as most of these are III transitions. The experiments used a type SP-171 and a type SP-2020 tube. The author is/was an employee of Spectra-Physics.
The most common white light lasers are large frame ion types with a mixture of argon and krypton for the gas fill.
White light lasers are now even available in air cooled format. All use a mix of argon and krypton. Many are made for a roughly 60:20:20 ratio of red, green, and blue lines for proper white balance. Their reliability is increasing with cost staying a little above normal Ion laser prices. Spectra-Physics, Coherent and Lexel all manufacture tubes for this. And LaserPhysics, Inc. sells the air-cooled version that runs off single phase 220 VAC and does 400+ milliwatts. Most of these lasers are modified for reduced operator skills with sealed mirrors and simplified power supplies. So, yes, they are out there, and laser company reps tell me the demand is going up as people start to use them for lab and industrial applications as well as display.
There are other ion lasers that aren't optimized for best laser show or TV color rendition but for other applications. For example, some biological mixed gas and biological krypton will kill green, lase red, yellow, and blue, With RYB optics, there will never be more than say 4 lines and no green, not 514 nm, not 520 nm, nor 530 nm. The RYB optic will have a 15% or greater transmission from 500 to around 550 nm. The lasing transmissions are about 1.5% for blue, 0.8% for yellow, and 1.2% for red. If it has RYGB optics, there will be about 7 lines. Note that for the laser enthusiast, these have a high novelty value but are less than ideal for for display due to their wavelengths as noted above. With external mirror lasers, the optics sets can be replaced but this may not be ideal if the gas fill ratio and pressure isn't optimal.
CREOL in Florida and quite a few other labs have demonstrated RGB as well in diode pumped frequency doubled YAG lasers so smaller and more practical is just around the corner as soon as ways are found around the materials and quality control problems with solid state laser components. Right now they have to test 4 or 5 crystals for every good one they get.
Note that other technologies can be used for white light lasers. For example:
(From: Colin Evans (c.j.evans@goose.ac.uk).)
A white light laser was developed in this department several years ago. It was based on a helium-cadmium mixture which could lase simultaneously at red, green and blue wavelengths. There was no automatic balance between the three colours and had to be carefully adjusted using the pressure and temperature. Also, I don't know whether the three colours could be regarded as "coherent" in any sense. Advantages are very strict polarization, and narrow parallel beams, neither of which are much use in a projector.
(From: Marco Lauschmann (mq-laser@gmx.de).
The only real white laser I know of used a Bucky-ball (carbon) compound which was optical pumped by the 488 nm line of a argon ion Laser. The emission was a real white light continuum - not like the 488 nm, 514, nm and 647 nm lines of an Ar/Kr ion laser system which looks like white light to the human eye. Researchers at the University of Manchester Institute of Science and Technology have demonstrated that confined buckyballs emit strong white light when excited by blue light from an argon-ion laser. Although work is at an early stage, the group has already identified some possible applications for this new material. They suggest that it may form the basis of a new laser material or new types of optical displays.
Another source for a white light continuum is a Ti:Sapphire regenerative amplifier with a frequency doubler. So, a white light continuum could be produced with 800 nm output of 150 Fs, 500 uJ pulses at 1 kHz from a Ti:Sapphire regenerative amplifier, which extends from 400 to 1500 nm. A 5 cm long piece of fused silica is the non-linear element and was used to generate the continuum. This is only an example - there are systems which deliver a white light spectrum with average power of more than 1 W with repetition rates of 250 kHz or more.
A word of caution. The digital camera does not record with the same range of brightness the eye can perceive visually. Thus the intensities of the laser lines are somewhat "compressed".
Please note that the 530 nm Kr green line is suppressed on YBR Krypton and White Light lasers as it suppresses gain on the 568 nm yellow line. That's why the normally very strong green line at 530 nm is also missing in the spectrum and pictures. Killing the 530 nm line also kills the 528 nm line in argon because the coating is not that selective. This is in addition to the red/yellow pressure branch problem. This laser was shipped initially very high in pressure - these pictures are the result of what happens when the excess gas is "burned off" after many hundreds of hours of operation. What is missing is the picture of the initial state of this laser, which had just the 488 and 482 nm lines lasing with the red lines, which results in a sort of strange magenta color.
(From: Steve Roberts (osteven@akrobiz.com).)
Argon ion lasers are generally shipped with broadband optics installed, they are usually a 100 to 200 layer dielectric stack. The high reflectors are coated for 99.999% reflection at all wavelengths (that the laser may be set up produce - they will still be transparent at others). The OC is what is changed. Wavelength selective output couplers are coated for a minimum 15 to 20% transmission on lines that are *not* supposed to lase, and the transmission for desired lines varies from .5 to to 12 %, depending on the length of the laser. Higher power tubes have more gain and thus use a higher transmission. An air-cooled laser will have transmission in the .5 to 1.5% range, short-frame water-cooled lasers will be in the 2 to 5% range and 25 watt large-frame types will be in the 8 to 12% range. It is possible to adjust the coatings for a given color balance if you have a large number of identical tubes. Ion optics are sold as matched pairs, and loosing half a pair can ensure that you will play musical mirrors and maybe not even lase. However some manufacturers have different OCs you can use with a given HR.
In the case of lasers with a intracavity prism, unless the client pays extra for special optics for a weak line that doesn't have that much gain, a broadband set is still used.
White Light lasers using Ar/Kr mixes are using a mirror coated for 400 to 700 nm broadband high reflectance and an OC that usually kills the 531 nm line of krypton, as these compete with the yellow line for gain, thus killing the yellow if they are allowed to lase. The 647 nm red and 568 nm yellow lines share the same upper state and thus the optics must be tailored for a given red/yellow balance on a given laser tube design at a given gas pressure, thus making these optics even more expensive.
A typical 1/2" diameter large-frame optic is $400 to 500 from the factory PER optic. White Light optics are about $2,000 a set minimum.
Still it's a selected silica filled epoxy with a high Tg. low cost 5 minute epoxy from the drug store or department store wont do it.
If you dare, take a very sharp razor blade and very slowly press its sharp edge in against a unglued older brewster where it joins to the stem and POP! Off comes the now ruined window and a flat undamaged polished face is usually left on the stem. If you stick that window between polarizers in a stress analyzer, it is now very deformed.
(From: Steve Roberts (osteven@akrobiz.com).)
This depends on the line and size of the tube. In a long bore laser, there may be a 10 to 15% gain on some lines while on other lines there will be little or no net gain. Some lines share a given upper state and tube conditions such as pressure and magnetic field determine where they fall. For example, the red and yellow lines of krypton will fight each other. If I recall my Spectra-Physics manual correctly, there are two weak argon lines that can also fight, but I can't remember which ones and it's an insignificant difference in normal operation anyhow.
For a short tube argon, there may be few percent increase in power with single line optics. They are used for spectral purity in a short tube ion laser. For example, each line comes to focus at a slightly different point on the film or drum in a printer or copier which means you would have to filter out one of the lines or use expensive achromatic optics. Or, a particular line is used for spectroscopy and the other one would increase the noise level if not removed.
Narrow band dielectric mirrors are easier to manufacture anyhow so they should be cheaper as well - a win-win situation for many applications.
There are several parameters which must be closely matched to achieve enough resonator gain and make alignment something that doesn't share too many characteristics with Chinese Water Torture. :)
The best option if you really want to do this (realizing that a partial mirror alignment will almost certainly be needed in any case), is to acquire a replacement OC or complete mirror sets designed for your particular model laser. Some companies sell what they claim are 'high output optics' at similarly high prices for this purpose. Unfortunately, I don't know of any reliable way of determining whether a given product will do anything for you or your laser other than waste an afternoon or more in installation and alignment. Specifications are rarely detailed enough to make a decision on technical merit. So, if you are willing to spend the time, at least get a binding money back warranty.
However, where you have something sitting on the shelf or a potentially good deal arises, here are some considerations:
For example, here is a table of OC traansmission percent (100 minus reflectivity) for some typical argon ion lasers:
Output Power OC Transmission Circulating Power
----------------------------------------------------
.1 W 1 % 10.0 W
.5 W 2 % 25.0 W
1.5 W 3 % 45.5 W
4.0 W 5 % 80.0 W
10.0 W 8 % 125.0 W
20.0 W 11 % 182.0 W
The "Circulating Power" is the light flux inside the cavity. While not
really useful (it can't be tapped off for anything practical), these high
values do demonstrate that there is serious activity going on in there (and
the Brewster windows must be able to handle it)!
"I have a XYZ corporation small or medium-frame ion laser. It's old, but it seems to have gas. I didn't get optics with it. I don't even know if it's argon or krypton. Heck, it may be mixed gas. What optics should I buy?"
(From: Steve Roberts (osteven@akrobiz.com).)
Recent experience suggests that just about any 1 meter class ion laser will lase with the following mirror specs, at moderate power with no major sensitivity to alignment. You may or may not get peak possible power, but IT WILL lase, over a wide range of pressures, gas mixes, and magnetic fields. Mode quality is not guaranteed, and we observed everything from TEM00 to doughnut mode to high order multimode. However none of the odd modes such as 1,2 or 2,2 or 3 to 5 were seen and in each case, a round beam was obtained. When doughnut mode was lasing, the band to hole ratio was at least 20 to 1, i.e., a very small hole.
These combinations has been tested on a Lexel 88, Lexel 95, American Laser 68, HGM 5, HGM 20, Spectra-Physics 164/168, and Omni 543. In krypton, argon, and mixed gas. In every case, it lased well but not always on every line.
The HR had a 2 meter radius with 100% reflectivity at desired wavelengths.
The OC had a 2 meter radius with transmission as follows:
There is a second yellow line in Kr. It is never spec'd in manufacturers' data because it is hard to obtain without a prism and special optics. There is also no major demand for it, and its gain is much lower then the 568 nm yellow. But we had it lasing day before yesterday. One tube rebuilder specs his White Light optics for this line and kills 568 nm to obtain a stable yellow for planetarium displays.
530 nm green was killed at the HR during some tests by use of a standard argon or KR OC. In one case, a standard argon HR produced lasing on 2 blues and two yellows in pure krypton. In no case was the 528 nm argon line observed as far as we know, it seems to require a low transmission. (But see the section: How to Get 528 nm in an Argon Ion Laser.) Lasers tested were a mix of Kr only, Ar only and MG lasers. The optic used for the OC was 7.62 mm in diameter. This optic was good for some lasers, but resulted in extra high intracavity powers for others. In some cases performance was better then factory optics. A few larger lasers were tested with a 1 meter mirror at each end and this worked well, but 1 meter mirrors were not recommended for the ALC-68/LExel-88/Omni-543 sized lasers as power was weak due to lack of mode volume.
Argon optics pairs produced poor low power lasing on pure krypton as their transmission was too high, i.e., the Lexel-95 standard argon optics were very poor and resulted in only a faint blue from the same sized krypton.
Thanks to Dale Harder, and Bruce Rodgers, and Dr. S. for access to their lasers. Thanks to Karl at Promethius Photonics for providing the high grade chemicals used in this study.
I wanted 528 nm from an argon ion laser. I'd only seen it once in a huge Laser Ionics tube at very high pressure. Strangely, that tube had a more or less orange glow at the cathode sheath, much more orange then normal. Now I know why. After a year of research and wondering if my prism was walking out of alignment when cranked to the 528 nm position, I found the solution in a old gas laser text the library was throwing out. It turns out you need a trace of neon in the tube to get the right upper state. No wonder 528 is always labeled "special testing required" from the manufacturer.
About that 300 mW claim, all I can say is: Ha Ha Ha Ha Ha Ha Ha....
150 mW yes, 175 yes, 225 to 250, yes on a factory select tube. 300, hum... Rarely and not for long unless it was designed that way. Note where the PSU current limit is set when they claim this. Note that newer high-tech tubes can do this running on 115 VAC. One manufacturer does make a 300 mW sealed mirror retrofit for the 60X. Laser Physics' Reliant series certainly does.
What happened is when large quantities of these units were in use, a few companies made money rebuilding them in quantity. They bought large quantities of pulls for rebuilding. They didn't care which tube they installed in a unit, as long as it met spec and lasted out the warranty. So therefore once in a while you can hit the jackpot on a used laser and get a hot tube. Once in a while you can also pick up a head that was designed for high power.
It's with special multimode optics and a high divergence doughnut mode or worse beam shape on a selected tube. Notice how vendors have power graded pricing, this lines up with the factory catalog of tubes. Note that lasers almost always are shipped doing well above the factory rating when new. Yes this gets you 275 mW or so on a fresh new high power tube at 10 A with brand new optics and a sweet new cathode. To sustain it for any length of time it takes 11 A. But I'd want a iron clad warranty I could enforce.
The idea is buy a hot laser and run it lower then its rated power, and thus enjoy longer life. Thats why you could retune that tube to 110 mW or so, it was derated for longer service and the optics were tuned to run at a fairly constant power over its life. Run it at 60 to 70 mW and enjoy it for a long time.
And, as with any laser, the CDRH safety sticker or catalog listing may not be an accurate indication of useful or possible output power. Actual performance may be a small fraction of what you expected! This is a significant issue with ion lasers since they have many variables affecting output power (compared to internal mirror HeNe lasers, for example, where the output power is pretty much fixed - it isn't affected in a significant way by tube current or often not even much by age and use). The output power of an ion laser is a strong function of tube current and life expectancy is inversely proportional to tube current! So, the rating on the CDRH safety sticker is likely to be much much higher than what could be used with expectations of a reasonable tube life. And, unscrupulous or unknowledgeable people can list the power based on a ridiculously high tube current where life might only be a few hours! Ion tubes that are physically the same size and interchangeable in a laser chassis also can vary by a large factor in power ratings even if they are new depending on manufacturer and model. For tubes with external mirrors, the type of resonator (single-line fixed, single-line with line selecting prism, multiline) as well as alignment and cleanliness, strongly influence output power. At least you can remedy problems with some of these with some basic maintenance or parts replacement. However, age, total operating hours, and possible prior abuse, are also significant factors affecting ion laser performance and there is little you can do to revive a weak tube.
Also see the sections: Locating Laser Specifications and Buyer Beware for Laser Purchases.
(From: Dean Glassburn (Dean@niteliteproducts.com).)
Most of these lasers came from xerox machines which were set up for single line 488 nm TEM00 running at about 6 to 7 amps when installed. New they would do about 15 to 20 mW in that configuration. There were also slightly different tubes (bore diameter) which would preclude higher current densities as the cross sectional area of the active region was smaller. You can and many do install broadband mirrors which would more than double the output. And, you can increase the current as much as 100% (double) as installed, which would give you the higher power limits advertized (and, of course, much shorter tube life). Additionally if the optics were not carefully aligned it was real easy to catch the rubber between the photocell and the front tilt plate when beam walking the laser which would smoke the rubber onto the front optic and beam splitter.
A used laser is just that - and priced accordingly unless the tube meets specifications as originally installed. And some units due to the smaller bore diameter will never attain the higher power levels.
(From: Mike Kenney (MKenny1989@aol.com).)
Nearly all of the 60Xs made for Xerox came with 200 cm, 488 to 505 nm TEM00 optics - very flat and wern't coated for all of the argon wavelengths. That's why if you had a new tube from American Laser with Xerox optics you might get 85 mW at 10 amps. However, with 60 cm, 450 to 530 nm multimode optics, you can get 250 mW at 10 amp. I just sold one with a new tube (not regassed or refurbished) that was putting out 200 mW at 9 amps. The true capability of these lasers is only really understood by American, Omnichrome, and National laser service and that's about it.
(From: Steve Roberts (osteven@akrobiz.com).)
I'd tend to agree, although the hottest 60X I've ever seen on a laser power meter was 225 mW. However when you figure out the uncertainty in the power meter calibration, that tends to jive. Xerox needed a small focal point and the AO used on the sled would tend to diffract out the 514 and 477 nm lines a lot, so the narrow band was needed to get a tight spot. Xerox Sled AOs are carefully AR coated and have a wedge on the backside of the crystal that probably corrects for the diffraction.
My source for used optics was a rebuilder who had Xerox contracts, he bought heads where ever he could get them, and stashed all the old optics in 55 gallon drums. He gave me a couple of hand fulls of optics from each drum and put them in optics shipping boxes from Coherent Auburn division. I'd get a laser off a used xerox sled and reoptic it using something from the barrel batch, or some bought from a laser engineer living in SLC., usually just the OC, and WHAM! 110 to 150 mW and all lines on many of the units. It would take some matching of the optics to get the best power. Tubes with better heatsinks also did better, so I suspect heat transfer plays a part.
I also agree that the factory can dial in the lifetime and power to anywhere they want it. There also were other tubes that I knew were brand new but I could never coax more then 20 mW out of them as well.
The middle of the road optics that I prefer all had 120 cm radius, its a nice tradeoff between beam diameter and divergence compared to the 60-60s, and some customers would gladly sacrifice some power for a tight beam. The hottest 60X I ever saw was a dual side fan 60C that had a TEM01 structure and all lines and was from a HELL Typesetter, it would easy burn holes in the wall. I didn't have a PM with me, but that laser would give my Lexel 88 a run for the money.
The really good high power "X" OCs have a deep cherry red color when viewed in transmission, as opposed to the straw or yellow color of the tailored copier optics. But you can't just go by the color, for example I've seen I've seen optics from Auburn that have a radial gradient, or "bullseye" pattern that performed just as well as the cherries and were almost transparent. Usually just the OC is doctored, its kind of expensive to change anything but the radius on both optics, and that coating is really dialed in. We have a excellent UV/VIS spectrometer here at work and I can barely make out the changes in transmission from a known high power all lines optic except they bleed out much more 514/528 nm green and have reflectivity almost to the UV. The difference is a fraction of a percent in transmission. I can also easily see the 10% or more changes in transmission on a line that is killed.
However the thing I always wanted to read was the document that spec'd the OC transmissions versus wavelengths for all the different factory shipping powers, it would be very interesting. I did once find the curves for the RYB krypton lasers developed for confocal microscopy, and the changes needed for a given power were very minute.
However, it should be possible to estimate the power output of a small ion laser using a simple laser power meter such as the one described in the sections: Sam's Super Cheap and Dirty Laser Power Meter or Simple Laser Power Meter Using Photocell. In fact, about all you really need is almost any type of photodiode (those from old computer mice floppy drives are fine), a working 9 V battery (even if it is tired and puts out only 7 V), a multimeter that measures DC mA, and a 1K ohm resistor (to protect your multimeter should the photodiode be connected backwards or decide to turn into a blob of solder). :)
The approach below makes use of the relative brightness sensitivity of the human eye to provide a reference in comparison to a HeNe laser at 632.8 nm with a known power output. The simple laser power meter can then be used as a relative indicator of ion laser's output at various tube currents. To perform the comparison, the ion laser must have adjustable output (from just above threshold) and the actual power output of the HeNe laser must be known - not just the typically much higher value printed on the CDRH safety sticker.
This same basic approach (with minor modifications) can be used for other types of lasers with variable power output or through the use of a variable laser attenuator or set of neutral density filters.
For a single-line ion laser, use that wavelength. For argon or krypton ion lasers with multiline (all lines) optics, use 488 nm and 647.1 nm respectively, since those wavelengths will be dominant at low power. Multiply the (actual) HeNe power, P(HeNe), by the ratio of the eye's relative sensitivities at 632.8 nm and 488 nm.
So, for a single-line 488 nm or multiline argon ion laser, the output power, P(488)0, will be:
.171
P0 = P(488)0 = P(HeNe) * ----- = P(HeNe) * .895
.191
It may be possible to do this without any instruments by comparing the power determined by comparison with the HeNe laser to values in the chart shown in the section: Argon/Krypton Ion Laser Tube Life. However, depending on your actual current threshold, it is possible for the relative power versus current relationship to be quite different for your tube and optics.
The output couplers on argon lasers are 5 to 7% transmissive, (much greater than the helium-neon output side mirror). (Note: These values are on the high side for short tubes at least compared to the table out of the service manual for a commercial argon ion laser in the section: Substituting Optics Between Lasers. --- Sam) So an argon has more gain and it scales as a semi-log function of current density. The upper limit is the tube material melting - about 100 watts output at present in experimental (very large) tubes. (A HeNe tube peaks in output power and then declines as current is increased.)
However, for a typical small air-cooled argon ion laser, 100 mW beam power out for 1,000 W electrical power in is only about .01 percent efficient which is not quite as 'efficient' as a HeNe laser (e.g., 6 mA at 2,450 V for a typical 10 mW HeNe laser - about .07 percent).
For a mid-size water-cooled argon ion laser - say 4 W out 7,000 W in, the efficiency is somewhat better - about .057 percent. :)
Some specific numbers for maximum output using multiline optics from a few common argon ion lasers:
-------- Tube Input ------- Output
Laser Model Current Voltage Wattage Wattage Efficiency
-----------------------------------------------------------------------
Cyonics-2301-20ML 7 A 100 V .7 kW .02 W .0029 %
Omni-532 10 A 105 V 1.05 kW .13 W .0124 %
Lexel-88 20 A 165 V 3.3 kW 1.5 W .0454 %
Coherent-CR18SG 50 A 550 V 27.5 kW 18.0 W .0654 %
Power outputs (and efficiency) for krypton ion lasers is must lower - perhaps
1/10th to 1/5th of the numbers listed above at the same power input.
So, from this very comprehensive listing, the larger the laser, the more efficient it is likely to be when operated at full power. Note that this doesn't take into consideration the losses in the power supply - figure another 10 to 30 percent reduction in efficiency for that!
The Omni-532 is for all practical purposes a exact drop-in replacement for a ALC-60X. Or, that could be reworded that an ALC-60X is a exact drop-in replacement for an Omni-532. Both lasers were made to the Xerox "X" open standard. While there are minor differences in the electronics, there are major differences in the construction. For example, Omni-532 heads have a cast aluminum alloy L shaped resonator while ALC-60Xs have the traditional rod and end-plate resonators floating on a baseplate.) There are also proprietary differences in the ion tube construction, but their I-V curves are very interchangeable.
Other air-cooled argon/krypton ion lasers are similar but not identical. Keep this in mind where specific component values or designs are described - variations are likely where a different laser is concerned.
An air-cooled tube is a neat little thing about four times the diameter of an average glass HeNe tube. Most have external mirrors and Brewster windows, but many are of the sealed mirror variety. What they all have in common is a heated cathode (like a vacuum tube such as a magnetron) requiring 3.2 volts at 10 to 25 amps. They operate from a range of 4 to 10 AMPs through the arc (Yes, that is AMPs) at around 100 VDC. The tube current is fed to the cathode via a center tap on the filament winding of the transformer to balance the arc on the center of the cathode to avoid plasma etching of the cathode supports. Hence the need for a beefy transformer with #14 or #10 wire on the secondary. Rewound microwave oven transformers work well for this purpose.
The tube is designed for a 100 to 105 V voltage drop, and is ran directly off the rectified and filtered AC line. This makes regulating the tube current a very interesting problem in design because we also have a series injection igniter (similar in function to a HeNe starter) which is a 3" toroid with 80 turns on the secondary and one turn on the primary. A 10 uF cap is charged to 110 or 400 V depending one the model of laser and is dumped directly into the 1 turn primary through an SCR which has a reverse connected fast switching (10 ns) diode across it. You end up with a 500 Khz 30 kV ringing wave pulse applied to the tube, which can blow the arc out as well as ignite it. The winding on the igniter transformer is also #14 wire as it also carries the entire tube current. There is no ballast resistor (as would be found in a HeNe laser power supply) as it would have to dissipate up to 1,000 watts at times. There is a .2 ohm resistor in the anode lead inside the head to sense the current for feedback to the supply, and a beam-splitter sampler that drives a solar cell for the fine loop, which keeps the light level constant to .05% and is used to cancel out noise and oscillations in the beam.
An air cooled tube's current may be regulated in a variety of ways including a series pass-bank of 4 high power NPN power transistors in linear mode, with two 700 V, 20 A PNP transistors ahead of them in switch mode; two 400 V, 25 amp FETs are used in a buck mode converter at 80 Khz; or just a linear regulator. Larger water cooled lasers which run off three-phase and need 20 to 35 amps of tube current use about 100 large NPNs in series/parallel strings for fine adjust and SCR's on the incoming phases for course adjustment.
The fun part starts when you buy the laser, the power supplies are scarce and run about $900 to $1,250 used. When the laser tubes are pulled for a rebuild every 5,000 hours the PSU stays in the photocopier/printer/medical instrument/typesetter or whatever until the whole unit is discarded. So the laser heads show up, but supplies keep their initial value.
A tube is good for 2 to 3 rebuilds, and after 5,000 hours they usually have 1,000 to 2,000 or more hours left for they hobbyist to enjoy. Most of the lasers are built as 150 milliwatt units and ran at 20 milliwatts to enhance lifetime, so even an old laser still has a lot of potential.
There is no book on how to maintain these things either and since it is the Holy Grail of laser hobbyists to own one, maybe it's time they learned how to maintain them, clean the optics, align the mirrors, peak the performance and find out how to avoid paying $3,800 for a used one when you can get one for less then $1.000. I (Steve Roberts) paid $125 for my head, and built my own power supply.
Also see the section: Maintenance, Alignment, and Modifications of the ALC-60X Laser Head for much more detailed information on the ALC-60X/Omni-532 laser.
(The following photos are from Steve Roberts (osteven@akrobiz.com) and Jeff Keyzer (jkeyzer@ucsd.edu).)
The beam exits from the copper tube attached to the square box - which contains a beamsplitter mirror which directs a small amount of light to a solar cell optical power sensor.
If your laser has had its tube replaced at some point (which is very likely), its appearance may differ considerably from the photo (different style heat sink fins, etc.). Some older versions apparently also include a pair of auxiliary electrodes (one at each end of the tube) poking into the Brewster stems outside the bore via glass-metal seals. See the section: About Those Extra Electrodes on Some ALC-60X Tubes.
CAUTION: These are very fragile where the glass to metal seal joins them to the tube body. Try not to put pressure on them. Running the laser at full current with a finger print on the window can damage the quartz face. Do not make the mistake of trying to remove the window to clean it, it will let air into the tube. :-(
WARNING: NEVER measure tube voltage on the tube-side of the transformer. You WILL destroy your multimeter if the starter is working!
CAUTION: The black and red jacks are across a resistor in series with the tube and are at 60 to 100 VDC referenced to the case. You will read a voltage from 0 to 3 VDC on the meter, at .2 V/A.
WARNING: Cross connecting the red and black current jacks to the blue and yellow light jacks can blow up the laser system. Even through a voltmeter, the button is there to remind you and protect you. Like they said in Ghostbusters, don't cross the streams!!! For power supplies on lasers over 20 milliwatts, the light jack is not an accurate measure of power, it is there for you to keep track of performance and for tuning the cavity (for best results use a analog meter while tuning).
Additional photos of the ALC-60X useful in conjunction with maintenance and alignment procedures can be found starting in the section: Maintenance, Alignment, and Modifications of \ the ALC-60X Laser Head.
Also see the Laser Equipment Gallery for for many more detailed views of ALC laser heads and power supplies.
The ALC-60X laser head is a box about 13-1/8" (L) x 6-1/8" (W) x 4-1/2" (H) made of goldish colored (alodyned) aluminum with thick ends plates - actually not part of the box structure but rather the movable parts of the mirror mounts.
The primary structure is composed of three, 3/8" InVar rods placed near 3 of the 4 edges of the box. They are bolted to the fixed portion of the mirror mounts at each end. The rods extend through these plates and another pair of thick plates - the moving part of the mirror mounts. They terminate in the large hex (you have to use a wrench) mirror adjustment screws.
