The original laser invented in 1960 was a solid state laser. It used a synthetic ruby rod (chromium doped aluminum oxide) with mirrors on both ends (one semitransparent) pumped with a helical xenon flashlamp surrounding the rod. The lamp was similar to what is used for indoor and high speed photography. The intense flash of blue-white light raised some of the chromium atoms in the matrix (the aluminum oxide is just for structure and is inert as far as the laser process is concerned) to an upper energy state from which they could participate in stimulated emissions (see the chapter: What is a Laser and How Does It Work? for a brief explanation if this isn't familiar to you. The result was an intense pulse of coherent red light at 694.3 nm - the first ever laser light in the world. Gas and semiconductor lasers followed closely behind but only the SS laser can claim to be first.
It was found early on that these lasers could burst balloons and blow holes in razor blades and someone even attempted to coin a new measure of laser energy to be measured in 'Gillettes' based on how many razor blades could be holed at once. :) And, the popular notion that hand-held death ray weapons would soon follow are based on these sorts of demos of solid state lasers, not on whimpy gas lasers (though the carbon dioxide laser is actually a much more likely candidate being the classic heat-ray of science fiction)!
SS lasers are used in all sorts of applications including materials processing (cutting, drilling, welding, marking, heat treating, etc.), semiconductor fabrication (wafer cutting, IC trimming), the graphic arts (high-end printing and copying), medical and surgical, rangefinders and other types of measurement, scientific research, entertainment, and many others where high peak power and/or high continuous power are required. A high energy pulsed YAG laser has even been used in rocket propulsion experiments (well, at least to send an ounce or so aluminum projectile a few feet into the air using just the pressure of photons!). The largest lasers (with the highest peak power) in the World are solid state lasers. Many of the laser projectors for light shows and for other laser displays use solid state rather than gas lasers like argon or krypton ion. And, that green laser pointer is a Diode Pumped Solid State (DPSS) laser.
The exact wavelength of the strongest lasing lines depends on the actual host material but usually doesn't vary that much. In addition to Nd:YAG and Nd:YVO4 at 1,064 nm, examples that lase at slightly shorter wavelengths include Nd:LSB at 1,062 nm, Nd:Glass at 1,060 nm and Nd:YLF at 1,053 nm. However, the lasing wavelengths of some like Nd:LiNbO3 (niodymium doped lithium niobate, 1,084 nm and 1,092 nm) are longer and further away.
Other materials include holmium doped YAG (Ho:YAG) or Ho:YLF. These lase at around 2,060 and 2,100 nm respectively. In the fiberoptic arena, erbium doped glass (Er:Glass) may be used in optical repeaters and amplifiers at around 1,540 nm. Er:YAG lases at 2,840 nm.
Beyond these, there are not that many examples of widely used commercial solid state lasers though many other materials are capable of the population inversion needed for laser action. The workhorse by far is still Nd:YAG with Nd:YVO4 becoming increasingly important for low to medium power (up to a few watts) 1,064 nm and frequency doubled 532 nm (green) diode pumped solid state lasers.
Energy output is measured in joules (Watt-seconds) per pulse. Multiply this by the number of pulses/second to calculate average power output. To determine the peak power in each pulse requires a knowledge of the pulse shape.
Flashlamp pumped SS lasers are used where high peak power is required as most other pumping methods can't even come close. However, the average power and efficiency may be quite low compared to approaches using high power laser diode pumping (see below).
Power output is measured the same way as for other CW lasers.
Depending on the application, the average power output or peak pulse energy or power may be the relevant measurement of performance.
Note that while this output if frequency doubled to 532 nm (green) would appear CW to the human eye, it would NOT be suitable for laser TV or light show scanning since it really isn't continuous.
(From: Anonymous (localnet1@yahoo.com).)
A (laser) diode pumped Nd:YAG may have a 40% efficiency (operating multimode with good thermal control of the diodes), and the pump diodes themselves have about a 45% efficiency, resulting in a net 18% of efficiency from electrical power to the diodes to output beam power. However, at increased pump powers, thermal issues may cause the efficiency to decrease after a certain point. This decrease is power dependent, as well as resonator and pump assembly design dependent.
Unlike HeNe and Ar/Kr ion lasers, there is little standardization of solid state laser components. Laser rods come in all shapes and sizes - some not even rod-shaped :) with or without mirrors (for use with external mirrors and Q-switch optics). They are also relatively expensive as despite their deceptively simple appearance - partly due to the fact that they are a lot fewer of them than laser diodes or HeNe tubes. A price of $300 for a 75 x 5 mm Nd:YAG rod could be a bargain.
The most common type of solid state lasers to have shown up on the surplus market are the laser head assemblies and pulse forming networks from some versions of the M-60 and M-1 tank rangefinders. Yes, if you come across a blown up M-60 or M-1 battle tank in your local junk yard, there may be a laser in there you can salvage! But don't worry, most of the time, you just have to take the laser. :)
In fact, building a solid state laser if you have a Nd:YAG rod with integral mirrors in-hand is very easy - just add a linear flashlamp of with enough energy in close proximity wrapped in degreased aluminum foil! For small rods, a single-use (disposable) pocket camera flash will even work. See the paper: Micro-Laser Range Finder Development: Using the Monolithic Approach.
My first contact with lasers was in the late 1960s when I inherited a student built ruby laser based on a design from Popular Science magazine archived on the Modern Mechanics blog Web site at Popular Science: PS Builds a Laser and so can you. This used a ruby rod with integral dielectric mirrors about 1/4" x 3" (this is all from memory) and a linear flashlamp with an energy input of up to 400 W-s. Regrettably, I don't know if it ever worked - the lamp fired fine but I was too chicken to turn the capacitor voltage up to its maximum setting for fear of blowing up the flashlamp! Oh well. :( At least, shortly after that, our high school acquired a *real* 1 mW HeNe laser so I played with that some and used it to view the hologram that was part of an issue of, I believe, Scientific American. Not the same as exploding balloons or drilling holes in razor blades, however. :(
The Laser Equipment Gallery has many detailed views of various solid state lasers from the M-60 Tank rangefinder to a high power arc lamp powered system putting out over 100 W CW.
Some people may only the first one to be a true microchip laser due to the small size of the lasing crystal but I include the other two since their designs are similar. However, in all cases, the only reason the lasing chip is so large in comparison to the active volume is due to manufacturing, handling, mounting, and thermal considerations. Thus, in principle, for the 100 mW green laser, a microrod say 1.2 mm long x 0.2 mm in diameter would be all that is actually required. But until laser chips are fabricated like computer chips and a way is found to get rid of the waste heat, much more material must be used. And, it is the thermal problems that ultimately limit performance - these tiny bits of lasing crystal are potentially capable of much more power output than can be obtained without them being damaged from heating. The smallest mass produced microchip laser crystals I know of are the CASIX DPM0101 hybrid vanadate-KTP module used in some green laser pointers: 1x1x2.5 mm. With cooling on all 4 sides, these may be capable of more than the small number of mW required for a pointer. The larger DPM0102 can generate over 50 mW intermittently at least (but the glue used to cement the two crystals may be damaged by the high intensity green light after awhile).
Melles Griot's low to medium power high quality green DPSS lasers now use composite crystals similar to CASIX's but of their own design optically contacted, not glued, so there is no problem with high intracavity flux. They use optics to shape the pump beam and active TEC cooling so these are much better than laser pointers (and of course cost a lot more as well!). I was told that the cavity is something like 1.5 mm in length (unconfirmed) so this is even shorter than the DPM0101 but it probably has a cross-section more than 1x1 mm. The models currently available produce up to 20 mW but they have gone much higher in the lab. See the section: The Melles Griot 58 GCS Series Green DPSS Laser for more info.
Unlike lamp pumped rod based side-pumped SS lasers which may use much of the volume of the laser rod, end-pumped DPSS lasers typically shape and focus the diode pump beam to a very narrow waist to boost the power density in the lasing crystal and to match the TEM00 mode volume of the cavity. This is an extremely efficient process compared to that of a lamp pumped laser. The typical conversion from diode pump light to IR laser output is over 33%. Compare this to a typical efficiency of 1% for a lamp pumped YAG laser. A DPSS laser may have a better than 10% wall plug efficiency for IR and frequency doubling efficiency (from 1,064 nm IR to 532 nm green) may exceed 50 percent.
Since microchip lasers can use so little actual lasing material and the pump diodes are also very small, they can be very compact, and potentially mass produced and inexpensive. In addition to green laser pointers and low to medium power DPSS IR and green lasers based on YAG or vanadate, all sorts of other SS lasing materials can be used. Of particular interest for communications are erbium (Er) doped materials which lase around 1,530 nm, a wavelength which is optimal for fiber-optic cable.
Microchip lasers also don't necessarily need high pump power. Depending on type, cavity design, and pump beam shape, a few mW of pump beam may be enough to exceed the lasing threshold and they have very high slope efficiency (percent increase in laser output versus increase in pump input) as well.
(From: Doug Little (dmlittle@btinternet.com).)
Like other lasing mediums, the output power from a YAG, ruby, or similar solid state rod will rise according to pump energy - but only up to the point where the active lasing medium is saturated (i.e. all the dopant ions are raised to the upper state). Beyond this point, no amount of extra pump energy will make any difference beyond generating unwanted waste heat. Also, a low-% doped crystal will reach this state more quickly, and will have a longer fluorescence period because the laser 'chain reaction' is inhibited by a reduced population of contributing ions - something like sticking carbon rods in a nuclear reactor to slow it down (well, that's how I like to think of it but feel free to flame, grill, or laser zap me if you think it's a bad analogy :-)
(From: Sam.)
Actually, I think it is an excellent analogy. Just think of all those mouse traps in the upper energy state! :)
(From: Doug.)
The saturation thing is a fairly obvious point, but it would be unfortunate to see enthusiasts building some huge 6-lamp device with a tiny pink ruby rod to find that they get the same output as they could achieve with 2 or 3 lamps! :-)
It would also be nice to have a good clear explanation of doping percent differences and what effect this typically has on laser action. It can make a big difference when you are designing a laser that will work properly even with reasonably well known pump energies.
(From: Sam.)
Yes, the last item would be nice. Are you volunteering? :) However, realistically, where the laser rod is surplus, there probably isn't any easy way to determine the doping percent or control it!
(From: Bob.)
There are all sorts of things that limit the amount of output energy or power from a given size crystal including: damage threshold of the laser medium, energy storage capacity of the laser medium, thermal considerations, and optical considerations (such as self focusing and thermal lensing). You can scale any laser, but there comes a point where you have to make the laser bigger to get more energy. Look at the NOVA laser at Lawrence Livermore National Labs: The light starts out in a small laser rod that could be placed in the palm of your hand, then it gets amplified in a chain of laser amplifiers that take up the area of a football STADIUM!
(From: Ed Xavier Gonzalez (ohlaser@flash.net).)
"Short pulse YAGs can do considerable damage, and can possibly ignite insignificant metals without warning. I have (on only one occasion) accidentally ignited some very fine stainless steel powder. I thought that was impossible until I read the MSDS on some commercially available material. Long pulse YAGs will burn very deeply and can do biological damage if not handled with respect (experience talking). Typically, long pulse YAGs mark alumina ceramic and stainless very well without removing much material. The short pulse YAGs will definitely remove material, but have a tendency to ablate rather than mark."
The document: Safety Guidelines for High Voltage and/or Line Powered Equipment should be thoroughly studied before even thinking about working on any of the power supplies for solid state lasers. ALWAYS assume the capacitors are charged - never assume they are safe to touch even if the laser has been left unplugged for weeks!
More information on the specific electrical dangers are outlined below.
There are several potential hazards in dealing with the innards of electronic flash, solid state laser power supplies, and other xenon strobe equipment.
High voltage with high energy storage is an instantly deadly combination. Treat all of these capacitors - even those in tiny pocket cameras with the same respect as a loaded gun or stick of dynamite. Always confirm that they are fully discharged before even thinking about touching anything. On larger systems especially, install a shorting jumper after discharging just to be sure - these types of capacitors commonly recover a portion of their original charge without additional power input. In the case of an SS laser capacitor bank, it doesn't take a very large portion to be fatal. Better to kill the power supply than yourself if you forget to remove the shorting bar when powering up the unit.
Some links:
Reading and following these recommendations and heeding the warnings is especially important when working with high power solid state laser power supplies or xenon strobes of any kind.
For solid state lasers provided as kits of parts (which is probably the most common for types like Nd:YAG or ruby other than the M-60 rangefinder), be aware that the only type that can likely be made to work easily are those that are flashlamp pumped unless you have access to high power laser diodes of the proper wavelength. The rod must be optically polished and coated (HR, OC, or AR as appropriate) - you won't do that in your basement. See the section: Grinding and Polishing a Ruby Rod.
Using broad band sources like halogen lamps or the Sun for pumping is extremely difficult due to the limited range of wavelengths that matches the lasing medium's absorption spectrum and the huge amount of waste heat. And, any claims about CW operation for some of these are often totally bogus as the physics simply prohibits it.
(From: Chris Chagaris (pyro@grolen.com).)
Commercial laser rods are typically finished with the following specifications: Ends flat to l/10 wavelength, ends parallel to 4 arc seconds, perpendicularity to the rod axis to 5 minutes, rod axis parallel to within 5 to [111] direction. These tolerances cannot readably be achieved by the home experimenter. All commercial laser rods also have anti-reflection coatings applied to their ends which must also be done professionally. If the mirrors aren't included or part of the rod itself, they will have to be purchased separately.
The CW pumping of ruby is not impossible but nearly so, with terrible efficiencies. The pumping of ruby or Ti:sapphire to threshold is literally impossible using tungsten-halogen lamps as has been suggested by some uninformed individuals. Ruby's main absorption bands are located at 404 nm and 554 nm and Ti:sapphire's peaks at about 490 nm. Tungsten-halogen lamps have an emission maximum at 840 nm which is very far from the either of these crystal's absorption bands. Radiation output at the blue and green wavelengths is very poor in these types of lamps, hence another major problem.
Finally, ruby has a very high excitation threshold, being a three-level system, despite its fairly long fluorescence lifetime of 3 ms (at 300K). In early experimental tests, a very small ruby rod (2 mm diameter x 50 mm length) was pumped by special capillary mercury arc lamps (good spectral match) and it took an input of 2.9 kW to produce a CW output of 1.3 watts. Only a small portion of the ruby was excited by the filament arc and laser action only occurred in 6 x 10-3 cm3. Using this data, the lamp input power per unit volume of active material to obtain threshold is about 230 kW per cubic centimeter.
While portions are quite technical with many equations, much of it can be read and understood without a fancy college degree. The book has been published in several editions betweem 1976 and 1999. The earlier ones (which may be available at reasonable prices from used technical book sellers) are probably better for pulsed lasers as some material on this topic has been dropped in the latest (5th) edition in favor of more coverage of diode pumped solid state lasers.
Some other relavent publications can be found in the chapter: Laser Information Resources.
There are a number of Web sites with laser information and tutorials.
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.
The basic structure of the SS Laser hasn't changed in any fundamental way since its invention in 1960. A transparent rod (most common shape) doped with a small amount of impurity (the actual lasing medium) is optically pumped by a light source (most commonly one or more linear xenon flashlamps or an array of high power laser diodes) whose spectrum contains significant energy at wavelengths matching one or more of the absorption lines of the lasing medium. One or both mirrors are either an integral part of the laser rod or external. A Q-switch device is often included to compress and boost the energy in the output pulse (pulsed or quasi-pulsed lasers only) with some loss in total energy or average power at the fundamental wavelength. Additional devices such as an intra-cavity frequency harmonic generation crystal (most commonly, doubling - second harmonic generation or SRG) or external Optical Parametric Oscillator (OPO) may be added. Total output energy or average power may actually increase compared to CW operation due to the non-linear behavior of these processes.
Properly selecting the cavity components and driving the pump source properly can make all the difference in terms of output pulse energy, beam quality, and stability.
Matching the PFN to the flashlamp, rod material, and cavity optics is critical in achieving efficient (as these things go) pumping of the laser. For example, just one parameter - the flashlamp pulse duration - can easily determine whether a modest input energy will result in an output beam, whether 10 times this energy will be needed, or whether it the laser will do anything at all. For a given total pulse energy, if the pulse duration is too long, lasing will be erratic or non-existent. Normally, it should be designed to be shorter than the fluorescence lifetime of the lasing medium. As the pulse becomes shorter and shorter, the peak output power and pulse consistency will approach that of a Q-switched laser. However, designing a PFN for a very short pulse is difficult and expensive, and the flashlamp must be derated and its life reduced for very short pulses. Thus, practical direct drive schemes can never compete with Q-switching. The PFN for a typical non-Q-switched Nd:YAG laser will produce a 100 to 200 us pulse which is well matched to the Nd:YAG's 230 us fluorescence lifetime but will result in a series of variable size pulses rather than a single short large one.
See the chapter: SS Laser Power Supplies for more information.
However, most of our attention will be devoted to the common rod shape for lamp pumped solid state lasers and "microchips" for diode pumped solid state lasers.
Other important solid state lasing materials include:
Some additional notes on the comparison of amorphous (glass) and crystalline lasing material:
(From: M. C. D. Roos (roosmcd@dds.nl).)
Straight out of my text-book (1975 and first edition):
"Glass laser hosts are optically isotropic and easy to fabricate, posses excellent optical quality, and are hard enough to accept and retain optical finishes. In most cases glasses may be more heavily and more homogeneously doped than crystals, and in general, glasses posses broader absorption bands and exhibit longer fluorescence decay times. The primary disadvantage of glass are its broad fluorescence line widths (leading to higher thresholds), its significantly lower thermal conductivity (a factor of 10, leading to thermally induced birefringence and distortion when operated at high pulse repetition rates or high average powers), and its susceptibility to solarization (darkening due to color centers which are formed in the glass as a result of the UV radiation from the flashlamps). These disadvantages limit the use of glass laser rod for CW and high-repetition rate lasers."
Nd:YAG has been effectively pumped by various sources including flashlamps (xenon and krypton), krypton CW arc lamps, tungsten-halogen lamps, and high power laser diodes. At current densities of lass than 4,000 A/cm2, both xenon and krypton have a good match with the absorption curve of Nd:YAG laser material. Even some more exotic methods have been used, such as sun-pumped, flashbulb-pumped, and explosively-pumped. The availability of high quality surplus Nd:YAG rods at reasonable prices on the surplus market make this material very attractive to the home-experimenter. Using one of these to make a flashlamp pumped pulsed laser is quite easy.
Nd:YAG, Nd:YVO4, and Nd:YLF are common in diode-pumped lasers. But, the most effective is the newly developed laser crystal Nd:LaSc3(BO3)4 or Nd:LSB. Nd:LSB has has absorption and radiation cross section similar to Nd:YAG but the bands are five time wider. The absorption coefficient of Nd3+ (10%at) in LSB is three times higher than Nd:YAG. LSB can be very heavily doped with Nd3+ (until 50%at), which provides record efficiency in the end-pumped configuration. This is a very high level in comparison with YAG (1.2% before luminescence quenching) or YVO4 3%, and 1.5% YLF. Furthermore, the saturation intensity of Nd:LSB is five times bigger than those of YAG or LSB.
For example, using a microchip 0.5 mm thick and 2 to 3 mm in diameter, is is possible to obtain 0.5 to 50 mW of green output at 531 nm. Q-switch mode in such a microchip is possible with a Cr4+:YAG absorber. On LSB with KTP for SHG grown in Russia, BREMLAS is producing powerful green lasers with cubic inch dimensions. A 10 W green microlaser is under development.
The wavelength for vanadate is more precisely 1,064.3 nm. There is also a weaker line at 1,342 nm.
(Portions from: Juozas Reksnys (rexnys@uj.pfi.lt).)
This most powerful lasing Nd:YAG line is composed from two lines 1,064.17 nm (strong line) and 1,064.4 (week line). At room temperature, the half-width of lasing line is 6.5 cm-1 which exceeds the distance of 2 cm-1 between two lines. Therefore, they are a joint line.
The wavelength of this line depends on temperature. In the practical range of +/-60 °C, it linearly shifts to longer wavelengths during heating by 5x10-3 nm/deg. At 27 °C (300 °K), the center of the lasing line is at 1,064.15 nm.
In addition to the common 1,064 nm wavelength, Nd:YAG has over a dozen other weaker lasing transitions between 1,052 nm and 1,444 nm.
(From: Sam.)
However, the vanadate and YAG wavelengths are close enough (0.15 nm) that a lamp or diode pumped YAG crystal can be used as an amplifier for the output of a vanadate laser in a (MOPA - Master Oscillator Power Amplifier) configuration since the gain bandwidth of YAG is about 0.5 nm.
KGW has a NICE broad absorption spectrum, that makes it a lot easier to work with than YAG BUT its thermal properties are poor.
I have a paper titled "Generation of visible light with diode pumped solid state lasers" by Boller/Bartschke/Knappe/Wallenstein from 1993 that was published in "Solid State Lasers: New Developments and Applications" Edited by M.Inguscio and R. Wallenstein, Plenum Press, New York, 1993. This long paper (17 pages) focuses on NYAB. The authors state: "We report the so far highest 531 nm output power of 130 mW generated with 1.55 Watt of diode pumping."
(From: Milan Karakas (mkarakas@vk.tel.hr).)
I have a Nd:KGW rod 5 mm diameter x 50 mm long. This is a neodymium doped potassium-gadolinium tungstate single crystal. This crystal has a Nd doping of 3% and operates at 1067.2 nm with 4 to 6% efficiency (Q-switched, 6.3 mm x 75 mm at 50 Hz), 3% efficiency CW, and 60% efficiency when diode pumped laser (quasi CW). The lasing threshold is extremely low - 0.2 - 1 J! I have not found reasonably priced optics for this laser (we may use optic for classic Nd:YAG, because wavelength is close) and pump source with low thermal emission (808 nm laser or LED). The rod was inexpensive - $209 USD including DHL shipping and duty.
(From: Bob.)
NYAB is a self-doubling (combined lasing and non-linear crystal) but it has a much lower doubling efficiency than traditional vanadate/KTP or YAG/KTP. The numbers I have seen are on the order of about 30 mW out for 1 W of diode pumping (efficiency is much higher with Ti:Saph pumping, but it's kind of inconvenient to have a such a laser pump a 100 mW 532 nm system, not to mention expensive. :)
The following is from a 1990 paper so better performance is likely: "Work on diode-pumped self-doubling lasers is still in the early phases of development. The most attractive nonlinear gain medium is Nd:YAB, which is a dilute form of the stoichiometric neodymium compound neodymium aluminum borate (NAB). Diode-pumped Nd:YAB lasers with output powers in the milliwatt range have been demonstrated (reference 10.67)"
There are slight variations in the peak wavelengths for different types of Nd doped glasses. These differences are only very slight and should not be of great concern. The following are some glass types and peak emission wavelengths:
Ruby rods for lasers are made synthetically. Aluminum Oxide (Al2O3) with a very small amount of chromium impurity is melted in an induction furnace. A seed crystal (perhaps a natural ruby or a chip off another synthetic crystal) is stuck into the melt on a rod then slowly withdrawn. A cylindrical rod of "ruby" crystal is formed and is slowly pulled out of the melt. This rod is then cut up and ground with diamond machining equipment to form the precisely shaped laser rod. The ends are polished to extreme levels and then treated with whatever optical coatings are desired, depending on the design of the laser (i.e., mirrors directly on the rod or external).
(From: Mark W. Lund (mlund@moxtek.com).)
There are several ways to do this. The first is the easiest, to pull from the melt. You can melt Al2O3 in molybdenum crucibles and pull a crystal directly from the melt. Even single crystal tubes and other shapes having a fixed cross section can be pulled using a technique called "edge defined growth." Unfortunately, because of the incredible temperatures that sapphire melts at any dopants that you might want to use vaporize, so you can't make red or blue material, only water-white material.
If you want colored sapphire or ruby there are two more methods used. The first, Vernuile (sp?), uses a hydrogen-oxygen flame and drops powdered Al2O3 plus dopant through the flame. The flame melts the powder, which falls on the seed crystal and crystalizes. Because only the surface of the crystal is molten the dopant gets incorporated into the bulk. The crystals are called boules, and look vaguely like a pop bottle, with a small neck, opening up into a cylindrical crystal. The stresses are so enormous in these boules that when you snap the neck off the entire crystal breaks into several pieces along the axis of the boule. Most colored sapphire and ruby sold is made this way, including the watch jewels.
The last method used commonly is flux growth. The Al2O3 is dissolved in a molten salt, usually lead oxide plus cryolite, in a platinum crucible. The crystals come out of solution as the melt is cooled just like sugar in hot water. These are the most desirable of the synthetic stones because they look more like natural stones after cutting, and the process is the most expensive.
(From: Fred Perry.)
Actually, Union Carbide in Washougal Washington makes synthetic Ruby and other colored variants of Al2O3 (sapphire) by the Czochralski method. I bought an nice big CZ 'ruby' gemstone from UC at CLEO a few years ago. You are right that it is hard to get dopants to dissolve in the pot; but this is more a limitation on max concentration and hence achieved depth of color than something that can't be done at all. UC in fact makes (sole source - patented) the 'ruby' laser rods that were discussed in another post this week. They are pink, not red.
(From: Mark.)
Hmm, whom am I going to believe, Fred, whom I have a lot of respect for, or me, whom I have to live with? CZ is usually the method of choice if you can grow a crystal, but I have never seen a paper or patent on CZ growth of colored sapphire. I can't imagine going through all the pain and cost of flux growth or Vernuile if you could pull it from the melt. The method of choice for lasers, by the way, was flux growth when I last looked. On the other hand, if anyone could do it it would be Union Carbide, and it has been a few years since I did search the literature.
I can imagine that some kind of sealed high pressure CZ puller could drive the dopants back into the melt.
Of course the dopant level of a ruby laser is much less than a gemstone. How do they grow titanium doped sapphire? Anyone know?
(From: charlesk@vloc.com.)
As Fred pointed out UC grows ruby by Czochralski as does VLOC (without patent violations, mind you) and we do it quite well as pointed out by the Rogers (Thanks for the recommend). Mark, Czochralski is the preferred method for ruby growth for lasers, has been for a while. Now Ti:Sapphire is a different story, probably due to the higher dopant levels as you surmised. Crystal Systems can probably answer that point.
There is more information on the VLOC Web Site.
"Does Nd:YAG material yield interesting gems when cut? Is it actually considered a "gem"? I think I have a piece of scrap material left over after a bunch of laser rods were cut from it. It's interesting to show to people because it appears transparent to slightly yellowish under most fluorescent illumination, but becomes magenta/pink under full-spectrum illumination."
(From: Chris Cox (ccox@slip.net).)
Yes, and gem faceters like it. Nd:YAG is considered a man-made gem material. It will go almost clear under some more recent rare-earth fluorescent lamps (which confused me when I brought some home. ;-)
There are many types of these crystals, which are referred to as "color change" materials in lapidary/gemstone circles.
(From: Uncle Al (UncleAl0@hate.spam.net).)
Ditto glassblowers' didymium glass lenses and the fabulous gem alexandrite, sunlight versus candle light or incandescent illumination (blue in sunlight, red in cool illumination).
See: "Man-Made Gemstones" by Elwell.
Laser crystals make more than passable gems if they are hard enough to retain facetting and especially if they are optically isotropic. Pale laser ruby doesn't look like much, but if you give it a megarad of Co60 gamma (piggyback on a medical sterilization) you get a superlative tawny orange. (Facet first, because warming to above 100 C gives F-center decay and an eerie deep red glow as it returns to pale pink).
(From: A. E. Siegman" (siegman@stanford.edu).)
I also have a vague memory that maybe there was a diamond solid state laser doped with Cr or Fe or a RE at some point way back, but I'm not sure about that, and you'll have to do the digging in some of the standard handbooks of laser transitions to check if this is correct.
If by a "diamond laser" you mean in general "diamond as the host material, doped with something as the laser atoms", well then diamond is just another host, competing with YAG, sapphire, etc It might have some useful attributes in competition with these others -- thermal conductivity, fracture strength, ability to polish -- but the others are already generally pretty good, and diamond isn't likely to be a miracle material in comparison.
An interesting connection between diamond and laser technology is that some diamonds have small internal flaws that are visible because they contain some uncrystallized carbon or other impurities. If you use laser drilling to drill a tiny tunnel in to the hole and vaporize out the impurity, the remaining tunnel and empty void inside the diamond become much less visible because of the high index of diamond, and the diamond's value as a gemstone can be substantially increased. I believe this practice is in routine commercial use.
I recall that in the '60s I had a visitor who was in the diamond industry and wanted to start up a venture to implement this technique. Getting involved in that kind of imaginative venture wasn't my thing at the time (or ever, I'm afraid), so I didn't jump at the chance -- maybe I should have.
Of course there was also the marine researcher who wanted to develop a CO2 laser gun to brand serial numbers on whales as they surfaced, to make marine surveys more accurate -- and the student who wanted to mount a similar laser on a pickup truck to brand cattle on the fly, which I think later actually got tried somewhere, and may in fact be a good idea. And so on.
(From: Harvey Rutt xh.ruttx@x.ecs.soton.ac.uk).)
And in our lab then the guy who wanted to slice mushrooms which apparently difficult commercially (can't keep the knives sharp enough it was claimed), and substantial money was spent on slicing up foamed toffee brittle into bars with lasers (it sticks to the slitting knives...) but the customers didn't like the caramelised taste!
However, RE: diamond.
Aside from the 'technological' issues such as thermal conductivity, toughness and hardness etc there are some more fundamental issues which don't seem to have been mentioned.
If you go for a dopant system, you need solubility of the dopant. Diamond is a strongly covalent lattice, with a very small covalent radius. This will make it hard to get the typical laser ions in in any reasonable amount in the right valence state. Also the crystal field strength and symmetry at the impurity site has to be 'right' to provide appropriate energy levels (Tanabe Sugano diagrams, if I spelled it right); they will be very different in diamond I suspect, and might need different dopants and level schemes. So you might be looking to unconventional, small atom impurities with a liking for covalent sites, like nitrogen which is well known in diamond; but are there any suitable level schemes?
You also need good (low) non radiative relaxation rates from the upper laser state; but diamond must have very high phonon energies (light atoms, strongly bound) which correlate with high non radiative rates. This will be especially bad for IR transitions (its the photon to phonon energy ratio that matters, if less than 5 or 6, trouble usually.)
If you tried to do a diode laser, I assume diamond is an indirect semiconductor like Ge and Si? (I don't know - does anyone?) and I think injection diode lasers are not possible in an indirect gap material - aside from getting adequate doping densities and profiles, but thats mere technology :-)
A colour centre laser? That might be the best bet, if some diamond colour centre has suitable levels. But it must be said the many conventional alkali halide, etc., colour centre lasers were all a bit pathetic and have been dropped.
(From: Professor Siegmen.)
Harvey's comments, as always, informed, to the point, and well put.
Just in case it might be of interest to the OP, I believe there were at one time some experiments on doped s-s lasers in another gemstone material, emerald, and they also seem to have been dropped.
Also, alexandrite (is that considered a gemstone?), which does offer some special advantages and was commercialized by a company called Light Age, spun out of Allied Chemical, though it's not been a roaring success.
A ceramic is formed by using heat and pressure to merge a nano-fine powder of the desired material at slightly below its melting point. The result is not a single crystal but an aggregate of small crystals. Nonetheless, the ratio of crystal volume to grain boundary volume is so large that the lasing behavior is almost identical to that of a single crystal (i.e., the result with Nd:YAG is a homogeneously broadened gain profile just like the crystalline host).
There are a number of benefits to using a ceramic rather than a crystalline host. Some of the most important include:
While performance is not quite as good as with single crystals, it's getting there. Expect a ceramic solid state laser in your future!
Flashlamps are the method of choice where high peak power is required. None of the alternatives can produce the short, high intensity, burst of light needed to pump a solid state laser for the generation of optical output pulses with peak power measured in Megawatts or more. While the xenon flashlamp is most common, other gas fills may be used to tailor the output spectrum to more closely match the absorption bands of the solid state lasing medium. However, none are really that great and most of the light ends up as waste heat that must be removed - one of the major limitations on maximum pulse rate.
Arc lamps were used in the past where CW operation was required. However, a major difficulty with these was the need to remove kWs or 10s of kW of waste heat from the lamp, rod, and cavity components. Circulating water or oil was needed along with a separate 'chiller' unit for cooling. Arc lamps are rapidly being replaced by arrays of high power laser diodes which are at least 10 times more efficient partially because their output is at the precise absorption wavelength of the solid state lasing medium. They can usually be convection or force air cooled and operate from a regular 115 VAC outlet.
Other types of light sources including the Sun and halogen lamps have been used where the physics permits (Nd:YAG, for example), but their efficiency is very low and the heat dissipation problems are significant. Due to the continuous spectrum produced by these sources, the percentage of light that matches the absorption bands of the solid state lasing medium is quite small. And, for the halogen lamp, at most 10 percent of the electrical input power ends up as visible light to begin with (the rest is IR or heat with a bit of UV).
(From: Leonard Migliore (lm@laserk.com).)
There are lots of CW Nd:YAG lasers. Laser markers are, most commonly, CW-pumped Q-switched Nd:YAG lasers. The rod (or slab) is generally immersed in water, with illumination by arc lamps or diodes going through the water. They get very unhappy with even a momentary loss of cooling.
The laser mode is quite sensitive to the amount of heat being pumped into the rod; they only work properly over a narrow range of lamp currents. I don't think you could get any output out of an air-cooled YAG rod before it cracked.
There are many possible configurations. Which one is used may depend on many factors including the type and shape of the lasing medium (rod, slab, etc.), cooling requirements, and cost:
The cavity reflector is often made of polished metal formed or milled to the desired ellipsoidal or other shape. However, some lasers may use a compacted white powder coating on the outside of the glass or quartz flow tube holding the rod and lamp(s) or between flow tubes. The exact composition isn't critical as long as it has a high reflectivity and is stable. One such material contains barium sulfate. See: Labsphere. Search for "white coating". Another one is magnesium oxide. Similar products are available from Edmund Scientific (actually made by Kodak). It is sprayed on from a can. In general, I wouldn't recommend attempting to remove these sorts of coatings unless they are visibly damaged.
A common model of linear flashlamp is the EG&G FXQ-1300-2 which has a total length of 115.8 mm long, 4 mm outside diameter, and 2 mm inside diameter.
For the FXQ-1300-2, above, the rating is 500 V.
For the FXQ-1300-2, the maximum explosion energy is 140 joules at a 100 us pulse duration and 500 joules at 1 ms.
See EG&G 1300 Series Linear Flashlamp Specifications and Links for detailed info on the other models.
Here are some notes on the K factor and its relationship to flashlamp voltage and current:
(From: Don Klipstein (don@misty.com).)
For more, see the section: Flashlamp and Arc Lamp Manufacturers and References.
This data used to be available on the EG&G, now Perkin-Elmer, Web site but for now at least, much of it is gone. If you want more info, request their CDROM which includes complete product specs as well as the EG&G technical papers that used to be at their Web site. A variety of useful information is available for driving flashlamps (and other topics) at Perkin Elmer Optoelectronics under "White Papers".
Mechanical specifications:
Bore Arc Tube Overall
Flashlamp Size Length Diameter Length
Type (mm) (in/mm) (mm) (in/mm)
-----------------------------------------------
FXQ-1300-1 2 1/25 4 3.56/90.4
FXQ-1300-2 2 2/51 4 4.56/115.8
FXQ-1300-3 2 3/76 4 5.56/141.2
FXQ-1301-1 3 1/25 5 3.56/90.4
FXQ-1301-2 3 2/51 5 4.56/115.8
FXQ-1301-3 3 3/76 5 5.56/141.2
FXQ-1302-2 4 2/51 6 4.56/115.8
FXQ-1302-3 4 3/76 6 5.56/141.2
FXQ-1302-4 4 4/102 6 6.56/166.6
FXQ-1302-6 4 6/152 6 8.56/217.4
FXQ-1302-10 4 10/254 6 12.56/319.0
FXQ-1303-2 5 2/51 7 4.56/115.8
FXQ-1303-4 5 4/102 7 6.56/166.6
FXQ-1303-6 5 6/152 7 8.56/217.4
FXQ-1304-3 6 3/76 8 5.56/141.2
FXQ-1304-4 6 4/102 8 6.56/166.6
FXQ-1304-6 6 6/152 8 8.56/217.4
FXQ-1305-3 7 3/76 9 6.06/153.9
FXQ-1305-4 7 4/102 9 7.06/179.3
FXQ-1305-6 7 6/152 9 9.06/230.1
FXQ-1305-9 7 9/229 9 12.06/306.3
Electrical specifications:
All lamps listed are filled to a xenon pressure of 450 Torr. They are designed for convection or forced air cooling. Water cooling is not recommended. Lamps may operate with either series or parallel triggering and are supplied with a trigger wire. Minimum flashing voltage parameters assume an unloaded trigger pulse.
Maximum Minimum
Ko Minimum Average Trigger Explosion
Flashlamp Impedance Flashing Power (W) Voltage (kV) Energy (J)
Type (ohm-A^0.5) Voltage (V) Conv Forced Series Parallel T=100us T=1ms
------------------------------------------------------------------------------
FXQ-1300-1 16.2 400 25 50 12 15 70 250
FXQ-1300-2 32.4 500 50 100 12 15 140 500
FXQ-1300-3 48.3 600 75 150 12 15 210 750
FXQ-1301-1 10.8 400 35 70 12 15 90 300
FXQ-1301-2 21.6 500 70 140 12 15 180 600
FXQ-1301-3 32.4 600 105 210 12 15 270 900
FXQ-1302-2 16.2 500 100 200 12 15 240 780
FXQ-1302-3 24.3 600 150 300 12 15 360 1170
FXQ-1302-4 32.4 700 200 400 12 15 480 1560
FXQ-1302-6 48.6 900 300 600 15 20 720 2340
FXQ-1302-10 81.0 1300 500 1000 15 20 1200 3900
FXQ-1303-2 13.0 500 120 240 15 20 340 1040
FXQ-1303-4 25.9 700 240 480 15 20 680 2080
FXQ-1303-6 38.9 900 360 720 15 20 1020 3120
FXQ-1304-3 16.2 600 225 450 15 20 600 1800
FXQ-1304-4 21.6 700 300 600 15 20 800 2400
FXQ-1304-6 32.4 900 450 900 15 20 1200 3600
FXQ-1305-3 13.9 600 255 510 15 20 660 2160
FXQ-1305-4 18.5 700 340 680 15 20 880 2880
FXQ-1305-6 27.8 900 510 1020 20 25 1320 4320
FXQ-1305-9 41.6 1200 765 1530 20 25 1980 6480
The following are from the EG&G (now Perkin Elmer) "High Performance Flash and Arc Lamps" available at the Perkin Elmer Optoelectronics Web site for that document. (Using the search terms "High Performance" is sufficient.)
Explosion energy:
(Thanks to Doug Little for helping to put the following into a more consistent form.)
The explosion energy is the energy input at which a particular flashlamp is likely to fail after (or during!) a single shot at a given pulse width. As will be seen, longer pulses result in much higher explosion energy values. The calculation for explosion energy takes into account the parameters of the lamp that are fixed (material, construction, diameter, length) and those which change (pulse width, and the resulting current for a given energy). Keeping the equations separate helps clarify the difference between the fixed lamp specification and varying conditions for a given application.
For convenience (or to make this seem more obscure!), the fixed parameters are lumped into a single number called Ke, which could be printed on the flashlamp box because it is a constant for a given flashlamp.
Ke = Q * d * l
Where:
Typical values of Q vary from around 190 to 250 for a typical of xenon lamp, based loosely on the lamp's diameter. Older xenon lamps such as the FX-103C have an estimated Q of 194. The Perkin Elmer catalog gives the following typical values based on lamp bore (I believe this is ID): 8 mm - 246, 10 to 12 mm - 210, 13 mm - 200.
Special fast-risetime lamps (which are probably for dye lasers) basically double this value to 400 to 500. There is no obvious way to tell a fast risetime lamp from others, except perhaps that flash pumped dye lasers tend to be considerably longer than the longest YAG rods, so the lamps will normally be longer too (200 mm arc is getting into dye laser territory).
The second equation calculates explosion energy in joules, based on the lamp's Ke constant and the desired pulse length.
Ex = Ke * (1/3 * t)1/2
Where:
So, explosion energy goes up as the square root of the pulse width.
Here are some approximate guidelines for lamp life versus input energy/explosion energy (Eo/Ex):
Eo/Ex Life Expectancy (Shots) ----------------------------------- 0.1 >106 0.2 >105 0.3 104 - 106 0.4 1,000 - 30,000 0.5 200 - 3,000 0.6 50 - 300 0.7 10 - 75 0.8 4 - 20 0.9 2 - 5 1.0 1 or less
Ko parameter:
The design of the PFN would be trivial if the flashlamp behaved as a simple resistor. Unfortunately, it is a dynamic impedance with a value designated as Ko (units: ohms-amps1/2). The Ko parameter determines the voltage across the lamp as a function of current just like a resistor except that the effective resistance (ER) is a function of current. For example, at 1 A, the ER of the lamp is Ko; at 100 A, it is Ko/10, at 10,000 A, it is Ko/100, and so forth.
V = Ko * |i|1/2
Where:
l p
Ko = 1.28 * --- * (---)1/5
d x
Where:
C, L, and V for optimal PFN design:
Normally, it is desired that the circuit be critically damped. This puts the most energy into the flashlamp in the shortest time without undershoot. For a given flashlamp Ko value, there are unique values for C, L, and V given the desired flash energy and pulse width.
2 * Eo * a4 * T2
C = (-----------------)1/3
Ko4
T2
L = ----
C
2 * Eo
Vo = (--------)1/2
C
Where:
Peak current:
It is important to know the peak current since it affects the spectral output and to assure that it is within the ratings of the lamp.
Vo
Ipk = ---------
Zo + Rt
Where:
For single-shot and low repetition rate flashlamp pumped SS lasers, the flashlamp is used as both the light source and the discharge switch. In these systems, the energy storage capacitor (part of the pulse forming network) is charged to a voltage specified by the desired flash energy. A trigger pulse is then applied either to the outside of the lamp, or in series or parallel with the energy storage capacitor which ionizes the xenon gas in the flashlamp allowing the capacitor to discharge through it.
But for multiple-shot and high repetition rate flashlamp pumped SS lasers, using the flashlamp as the switch is both technically challenging and also hard on the flashlamp.
An alternative that is widely used is to trigger the flashlamp once and then run it at a controlled low current in between pulses. So, it runs more like a low current arc lamp most of the time. A separate "simmer" power supply usually provides both the high voltage trigger pulse and the simmer current. A current of between 50 and 500 mA is typical.
However, what this means is that a separate means must be used to control the main current pulse through the flashlamp. In modern lasers, this may be an Insulated Gate Bipolar Transistor (IGBT), thryristor (SCR or triac), or other similar high current fast acting solid state switch. Where an IGBT is used, very precise control of both the start and end, and thus energy, of the flashlamp can be provided. Older lasers might use thyratron or ignitron tubes.
Basic SS lasers don't need this added complexity. But where the repetition rate is greater than perhaps 1 Hz maintained, up to several hundred Hz, the added complexity of the simmer circuitry becomes worthwhile.
Additional information can be found on the Web sites of manufacturers of flashlamps and arc lamps, and support electronics. For example, see Perkin Elmer Optoelectronics under "Flash Lighting".
There is also general information on xenon flashlamps including guidelines for estimating appropriate voltages and energy levels for glass and quartz flash tubes on Don Klipstein's Flash and Strobe Page. Don's General Xenon Flash and Strobe Design Guidelines Page which also includes some basic design equations.
And, of course, there is tons of xenon strobe information, handy circuits, and complete schematics in Sam's Strobe FAQ (also mirrored at Don's site, above, and other sites Worldwide).
(From: Chris Chagaris (pyro@grolen.com).)
The maximum energy that a flashlamp can withstand is referred to as the 'explosion energy' and it is the energy at which the flashlamp is most likely to fracture. This explosion energy is determined by a number of factors including the type of lamp, size, and current pulse width. If a flashlamp is indeed built for laser pumping it would be of quartz construction but could actually be a number of different models.
For example, a new, EG&G, FXQ-1302-3 (4 mm bore x 76 mm arc length) flashlamp has an explosion energy of 360 joules for a 100 us pulse. As pulse width is increased, explosion energy rises.
In other words, you cannot just buy any old flashlamp driver and expect it to operate your particular flashlamp. I would suggest building your own pulse forming network for your application. It is not overly difficult (although can be very dangerous) if you have some background in electronics. All the formulas to calculate what you'll require are in a booklet available from EG&G or in any good book that deals with solid-state lasers. Capacitors for operating such a small flashlamp are readily available at very reasonable prices.
(From: Don Klipstein (don@misty.com).)
The "EG&G Linear Flashlamp Technical Brief" has a very general rule that has a fair chance of being good for most quartz flashtubes, even someone else's. As for glass? Stay below both half the quartz limit and the tube's regular ratings, and it will probably be OK. See the section: EG&G 1300 Series Linear Flashlamp Specifications and Links.
And EG&G recommends staying below 30 percent of the explosion energy if you want the tube to have a reasonable life expectancy.
For really short pulse width, the limiting factor is ablation - evaporation of the glass or quartz. The vapor decomposes in the arc and you get oxygen among whatever else. The oxygen really increases voltage requirements for flashing. If the electrodes get hot enough, they may react with the oxygen and may remove most of it, but then you may discolor the inner surface of the tube with oxide in addition to any discolorations from silicon or other decomposition products.
I have been through this, and even did some damage to a quartz tube with just a few joules per flash. Heimann DGS0610 (10 mm arc length) does not like voltage much above 300 volts combined with a few joules of energy, nor 1.5 kV at even a fraction of a joule.
When a flashlamp fails, it may do so quietly or with a bang.
Generally, only laser pump flashlamps or similar ones with a lot of flash energy for their size will likely die spectacularly. When lower power flashlamps such as those used in small to medium size photographic strobes crack, they tend to stay in one piece or sometimes break apart surprisingly quietly.
As for failure modes due to abuse:
Even if the ends appear to be identical, check the manufacturers specs to be sure that they are identical - they probably aren't!
(From: Don Klipstein (don@misty.com).)
Some xenon flashtubes do have identical electrodes and can be operated in either polarity. If the flashtube is polarized, wrong-way operation usually shortens the life by sputtering or overheating the anode (being used as a cathode), or by having getter material evaporated from the normal cathode location, drift to what is being used as the cathode and, discoloring much of the tubing along the way - active metal vapors in discharge lamps tend to have some positive ions and will drift to the negative nd.
I have seen some flashtubes have difficulty flashing the wrong way. Usually an extra hundred volts can force an anode to work as a cathode.
Arc lamps may have thermionic emission materials on their cathodes (but not flashlamps). Abusing an anode as a cathode will usually overheat it, often sputter it, and the arc can have an excessive voltage drop (and then conduct less current) which often leads to the arc being less stable, and the arc tube material can overheat around the anode being abused as a cathode. If the arc voltage rises more than the arc current decreases (common), then the whole lamp can overheat - but I think overheating will mostly be around what is being misused as a cathode. Then again, if the lamp discolors from sputtered electrode material then it can absorb light and overheat.
The simplest electrical test is to apply a current limited high voltage to confirm ionization. The required peak voltage will need to be greater than the trigger voltage for the lamp. An easy way to do this is with a neon sign or oil burner ignition transformer on a Variac. Current limiting is built in. An adjustable high voltage power supply with a few hundred K ohms of high voltage ballast resistance can also be used. Since very little current is required, almost any source of HV will do. The start voltage from a helium-neon laser power supply will be sufficient for smaller lamps.
Start at 0 V and turn it up until the lamp fires. For a small (e.g., 2 inch) xenon flashlamp, this will typically be in the 4 to 8 kV range; for a medium size arc lamp, perhaps 10 to 15 kV; large ones may require 30 kV or more. The start voltage will depend on the gas type (xenon or krypton typically), fill pressure, tube inside diameter, and amount of use or abuse.
At these low currents, the operating voltage is probably no where near what it would be at normal current but with this approach, if the lamp fires at all, it is most likely good. The appearance of the discharge at the gas pressure inside the arc lamps is similar to that of a plasma globe - streamers of lightning that move around in response to (internal) thermal gradients and possibly even (external) proximity to conductive materials like fingers. So, if you don't want to use the lamp for a laser, it could be powered from a little HV module and make an interesting display piece. :)
It should be possible to do further testing of arc lamps using an ion laser power supply (but if running for more than a couple seconds, most excellent cooling will be required). This is left for the advanced course.
(From: Chris (ndyaglaser_chrisc@yahoo.com).)
The most important aspect of determining what you have is to be able to differentiate between a flashlamp and an arc lamp. This can be somewhat difficult without a history or printed specifications for the lamps. These linear lamps may look very similar in outward physical appearance but are constructed and used very differently. If one were to use an arc lamp in a flashlamp circuit, there would be disastrous and dangerous results. There is not normally a 'gas mix' in either of these types of lamps but is usually either pure xenon or pure krypton. A spectrometer can be used to determine which gas fill is present. The envelope for the 'better' flashlamps is usually constructed from a type of fused silica (quartz). While passing a continuous high voltage discharge through the lamp, the strong odor of ozone will almost assuredly indicate a fused silica envelope. A glass envelope would not allow the UV to pass and produce the copious ozone odor. Arc lamps are usually krypton filled (to a few atmospheres of pressure) and have at least one pointed electrode for arc stability. Unfortunately some flashlamps may contain one pointed electrode also, but this is not very common. Flashlamps usually have two rounded electrodes but can filled with either xenon or krypton gas at a reduced pressures. To sum things up:
Remember what they say about assumptions though! If you are positive that that you indeed have flashlamps in your possession than the only thing you need now determine is the explosion energy of the particular lamp and the proper operating parameters to prevent proving that explosion energy rating. Energy and time (pulse width) both play a very important role in the safe operation of any flashlamp.
Information is available for driving flashlamps (and other topics) on their Web site, though it may not be an easily located place! Start with "White Papers" and "Datasheets", search for "flashlamps". However, much of the product and technical info that used to be on the EG&G Web site is no longer present but this material is available on the Perkin Elmer CDROM, which includes complete product specifications and technical papers. The CDROM is accessed using your normal Web browser.
Includes specifications on arc lamps and flashlamps as well as Flashlamp System Design Calculator.
General technical information on flashlamps and arc lamps may be accessed under "Resources".
Some very complete technical notes on driving and triggering of flashlamps has been published by ILC Technology (now part of Perkin Elmer). Some of these include:
These were originally published around 1986 so there may be newer versions. As far as I know, they are not currently on-line but should be available in print by contacting ILC.
The most common arc lamps for solid state laser pumping are the xenon and krypton variety. Specifications for a variety of arc lamps used to be available on the EG&G, now Perkin-Elmer, Web site but for now at least, much of it is gone. If you want more info, request their CDROM which includes complete product specs as well as the EG&G technical papers that used to be at their Web site.
Arc lamp power supplies have a lot in common with ion laser power supplies: a relative low voltage (under 50 to several hundred VDC) at high current (many AMPs) and a high voltage trigger required for starting. (However, with their massive cathode - where much of the destructive energy is dissipated - no heated filament is used.) See the chapters starting with: Ar/Kr Ion Laser Power Supplies for general information on systems that are similar to those for arc lamps.
Modern laser diodes are quite efficient and can be designed to produce the precise wavelength needed to match an absorption band of the solid state lasing medium. For Nd:YAG, this is near-IR at 808 nm. These laser diodes are inexpensive (as these things go) at less than $10 a watt for small quantities in chip form. Arrays of diodes mounted side-by-side of 40, 100, or more total WATTs are commercially available. Multiple such laser diode bars may be arranged surrounding a Nd:YAG rod. Laser systems using several hundred watts of laser diode pump power producing 100 W of coherent 1064 nm output or perhaps 40 or 50 W of 532 nm frequency doubled green output are compact, can be plugged into a standard 115 VAC outlet, and require not special cooling.
Power supplies (usually called 'drivers') for high power laser diodes must be designed for absolute current limiting and to compensate for the change in laser diode characteristics with temperature. These types of laser diodes do not have internal monitor photodiodes like their low power cousins so other techniques must be used to regulate output power. Needless to say, preventing damage to these expensive laser diode arrays during power cycling, from power surges, and many other possible dangers, is extremely critical. See the chapters starting with Diode Lasers for more information.
And, if you are wondering... No, LEDs really can't be used since not even a truckload of those super bright Radio Shack LEDs can be focused to achieve the required power density. (Even the brightest produce at most a few mW compared to the minimum of 1/2 W or so used in the smallest DPSS green laser pointer. In addition, being incoherent, their spectral width is much greater than that of laser diodes for a given power, the electromagnetic field intensity is lower.
Lasers (predating laser diodes) have also been used where their output wavelength matched an absorption band of the target lasing medium. However, until the advent of the high power laser diode, such systems were very expensive, had terrible efficiency, and were probably only used for very specialized applications where there were no alternatives.
I have seen a General Photonics laser that put out 5 W, with a 'few' kW of pump power - 2 or 3 or 4 - don't remember exactly how many. :) This was one HELL of a power hungry beast! The reason is that the emission spectrum is not matched to the laser rod. In theory, if you looked at the emission spectrum, you could shift it up or down by controlling the power to the lamp and thus the temperature. But I have no idea where to suggest one find a spectrum for an off the shelf lamp unless you happened to have a spectrophotometer to measure it. :)
My first laser was built with a 3 mm by 60 mm YAG rod, 2 tungsten halogen lamps, an intracavity piece of lithium niobate, and focusing optic. The rod was cooled by a HUGE flow of forced air, and the laser could be run for 5 or 10 seconds at a time before it would overheat. The mirrors were set in homemade mounts using 8-32 screws - NOT what you would call fine adjustment. :) I used a HeNe laser for alignment, then hoped and prayed when it came time to do actual alignment with the thing running, as there was such little time. After about an hour of turning it on, then letting it cool for a minutes, I saw some flashes of green light. Surely no more than microwatts, but then, I was using a very crude, low power YAG in CW mode.... Still one heck of an accomplishment if I do say so myself. :)
(From: sarlock@twcny.rr.com.)
The HR mirror may be dielectric, metal coated, or a corner or half-corner reflector, to name just a few possibilities depending on the lasing wavelength, presence of additional cavity optics (like a Q-switch), and application. The OC mirror will generally be either a dielectric or resonant optic (like the one in the Hughes rangefinder. A resonant optic is basically a multiplate etalon with at least one of its peak reflectances adjusted to coincide with the lasing line). Both mirrors are likely planar so there are no focused regions inside the rod. However, this is not always the case.
Unlike low gain gas lasers, aluminized (metal coated) mirrors may have enough reflectance (greater than 95 percent) to easily reach threshold in a solid state laser. However, in addition to the less than optimal reflectance for the HR, that missing 5 percent is due to absorption, not transmission. Thus,