Go here for a partial list of suppliers of working diode lasers. (updated 7/5/2003) These are getting really cheap - some around $5 and a few for even $1 - and are now the way to go if you just want a laser to play with.
If you already have a separate or bare laser diode (as opposed to a "module" which is ready to connect to batteries), please return it if possible. They are easily ruined. Complete laser pointers are now available at impressively low prices!
Laser diodes are rather fussy. The "junction" or main light-emitting working part of a typical laser diode is about the size of a bacterium and can overheat within a microsecond if its limits are exceeded. Furthermore, the minimum current to achieve laser operation ("laser threshold") can easily be near or over 80 percent of the "fatal dose" of current.
The light-emitting area of a laser diode typically emits more light than a similar area of the surface of the sun. Since more power must go into this area than into a similar size piece of the sun just to get things working at all, it should be understandable that things can easily go wrong.
Laser diodes can be damaged by exceeding the maximum safe optical output, which may be hardly at all over the rated optical output. Damage can occur in this way even if no other limits are exceeded or reached. Excessive amounts of light can fry particularly vulnerable subregions of the bacterium-sized working region. This is probably how most instant damage occurs. Please note that laser diodes make laser light more easily and more efficiently at lower temperatures, and it is sometimes possible for a laser diode to be ruined by a given current at low temperatures that it survives at warmer temperatures. Most diode laser modules have feedback systems based on the photodiode included in the laser diode to stabilize beam output. The feedback system must be free of overshoots, even during power-up and power-down.
Laser diodes are easily ruined by static electricity. Static electricity can briefly exceed maximum safe forward currents even if barely noticed. If static voltage should be applied in reverse polarity, things are even worse.
Yes, some laser diodes have survived worse than looking at them the wrong way. Some are better-built and/or more conservatively rated than others. You may get lucky and be able to just throw something together and have it work. Maybe, maybe not...
If you already have a laser diode that you can't return, and you want to push your luck, then go to Sam Goldwasser's laser FAQ (see links below or jump in here). Good luck, try only at your own risk to get a laser diode to work.
Diode lasers generally don't have ideal beam characteristics, but they are fairly easy to focus to the degree that the beam does not widen by more than a millimeter or two per meter. Most diode laser "pointers" and collimated diode laser modules should achieve this.
As the wavelength gets closer to 555 nM, the visibility becomes greater,
while the color becomes closer to a yellowish green.
Wavelengths less than 555 nanometers are more blue and less visible than
555 nM.
Wavelengths less than 400 nanometers are ultraviolet.
"Brightness per milliwatt" as a function of wavelength would be roughly the Photopic Function.
Brightness/visibility of the beam's path through air:
Usually, the beam's path through clean air is visible mostly from Rayleigh scattering. The percentage of light scattered by a given length of path traced by the beam is inversely proportional to wavelength raised to the 4th power.
Sometimes scattering by dust is more significant, and that is essentially independent of wavelength. However, many people want lasers whose beams are visible from the side in clean air.
Since a laser beam shows a visible path mainly in dark rooms or outdoors at night, perceived brightness of the beam's trace through air depends mainly on scotopic vision. This is usually true even when the color of the beam is visible - in which case "mesopic vision" is operating. Mesopic vision is a combination of photopic and scotopic vision, with photopic vision providing a sensation of color and scotopic vision providing most of the sensation of illumination.
So, a reasonable predictor of visibility of the beam's path tracing through clean air, is output power times the scotopic function, divided by wavelength to the 4th power.
Following is a table of scotopic function divided by wavelength to the 4th power, normalized to have maximum value of 1, for some common laser wavelengths (6.324E10 times scotopic function divided by wavelength^4):
Wavelength/Laser 6.324E10*V'(lambda)*lambda^-4 -------------------------------------------------------------------- 405 nm violet diode laser .0435 441.6 nm He-Cd violetish blue .580 458 nm deep blue DPSS .781 473 nm turquoise-blue DPSS .897 488 nm main green-blue argon wavelength .986 532 nm green DPSS .617 543.5 nm green He-Ne .428 593.5 nm orange-yellow DPSS .0264 594.1 nm orange-yellow He-Ne .0253 612 nm red-orange He-Ne .0062 632.8 nm red common He-Ne .00105 635 nm less-common red diode laser .00087 647.1 nm red krypton laser .000307 650 nm common low cost red diode laser .00024Since photopic vision and scattering by dust will remain to a small extent, visibility of beam path will be greater for longer wavelengths and less for shorter wavelengths than the above chart indicates.
Visibility of beam path through air for red lasers can easily be a a few times what the above chart indicates, but is still low.
Commercially available laser pointers whose output is a laser diode wavelength as of this time have only been red, with the only exception being a very expensive violet one that just became available. In recent years lower cost red diode laser pointers have had wavelength mainly close to 645-650 nm.
Laser pointers of other colors using DPSS technology have been available for a few years, though they cost more than red diode laser pointers.
The most common and least expensive non-red laser pointers are 532 nm green DPSS ones. As of early June 2007, green laser pointers generally cost near or over $35, mostly well above $35.
UPDATE 3/26/2009: Radio Shack now sells a green laser pointer, with catalog number 63-132. Craig Johnson reviews it here.
More expensive still, generally costing at least a few hundred dollars, are "yellow" (very orangish shade of yellow) 593.5 nm DPSS laser pointers and 473 nm blue ones (color is a "turquoise" cyanish shade of blue).
Other DPSS wavelengths/colors are known, but less easily achieved than 473 nm blue, 532 nm green, and 593.5 nm orangish yellow.
He-Ne laser pointers have been known to be marketed, as far as I know only in 632.8 nm red, and only before red diode laser pointers became easily available at low prices.
UPDATE 6/23/2007: Violet diode laser pointers are starting to become available, but at high prices. Four examples:
1. A modified product, availability probably limited at best: This flashlight retrofitted with a violet laser diode.
2. A commercial product reviewed here.
3. A commercial product reviewed here. This is a very hazardous laser module of "pointer style" producing reportedly around .27 watt of laser radiation.
4. A commercial product reviewed here.
Those considering laser devices of "pointer style" and in Class IIIb range should do so after gaining sufficient experience with laser pointers in the Class IIIa or Class II range, which are legally allowed for retail sale in USA. Extensive practice leading to avoidance of accidents makes for safety when using similar products that have more power.
Please beware of major uptick in regulations when laser beam power gets to 5-plus milliwatts - Class IIIb. There is 21 CFR 1040.10 and .11, along with some patches of state/local legislation affecting usage of lasers 5 milliwatts or more.
UPDATE 12/27/2004 - I got a 4 mW 532 nm "greenie"! (green laser using frequency-doubled neodymium laser wavelength produced by a rod/crystal "pumped" by an infrared laser diode) It is one that I got from Roithner Laser with the catalog number GPL-105.
According to Roithner, the output power of this item can be anywhere from 2 to 5 mW, and according to my tests mine produces slightly over 4 mW.
It is noticeably brighter than the cheap 645 nm red ones. 4 mW of 532 nm theoretically looks about 5 times as bright as 5 mW of 645 nm and about 3 times as bright as 5 mW of 632.8 nm! Even if you get one that produces only 2 mW, it should outshine any 5 mW red laser of any common type.
As for the color, it usually looks not quite a deep pure green but a very slightly yellowish green, sort of "between pure green and lime green". It is slightly less yellowish than the green line of mercury. If you look at a CD reflecting the light of a compact fluorescent lamp and see a bright green band among the colored bands, a 532 nm laser has a shade of green slightly less yellowish than that but still yellowish in comparison to "emerald green".
The beam of my "greenie" is slightly visible when viewed from the side in a dark room. I did not see this effect with a 5 mW 645 nm red laser.
The beam quality of my 532 nm green laser pointer was much better than that of any cheap red laser pointer that I ever tested, but was slightly worse than that of a He-Ne laser.
Look for more on green and other laser pointers including dangerous high power ones in the Craig Johnson links towards the bottom of the Links section below.
UPDATE - Craig Johnson has a page on one that produced 190 milliwatts! This is an extremely dangerous one that can easily cause permanent eye damage in as little as a few milliseconds. If the beam reflects from shiny glass, plastic or other shiny smooth objects, it can be powerful enough to possibly cause permanent eye damage faster than one can blink! It even has a slight burning capability!
However, I believe that orange, yellow and green lasers should be no more dangerous and at least a little safer than red ones of the same brightness as opposed to the same power. This is because a red laser needs more power to match the brightness of an orange, yellow or green laser.
If you want to try blocking any infrared output yourself, use a "dielectric interference" bandpass filter for the wavelength that you want to use. Too may other filter types pass the infrared wavelengths in question, including many dichroic filters, nearly enough all stage lighting filter gels, and most to nearly all colored transparent acrylic sheets such as colored "Plexiglas" or colored "Lucite".
DO NOT STARE INTO A DPSS LASER POINTER WITH VISIBLE OUTPUT ATTENUATED BY A FILTER UNLESS INFRARED CONTENT IS KNOWN TO NOT EXIST AT AN EYE-HAZARDOUS LEVEL!
1064 nm and longer wavelengths of infrared are widely considered completely invisible at any eye-safe level. Do not expect to see it through a filter that attenuates the visible output, although safely seeing a dim red glow for other reasons (pumping diode output or weak fluorescence caused by the visible beam) is possible.
You might have noticed that supposedly infrared wavelengths slightly over 700 nanometers are not completely invisible. In fact, wavelengths around 800, even 900 nanometers are very slightly visible. However, one should be cautious with visible quantities of light in the 800-900 nanometer range, since large quantities of light that could be hazardous to the eye might be involved in order for such light to be easily visible.
Don Klipstein's mirror copy at misty.com. Some GIFs and some other files "cleaned up" for slightly faster download. Updated on 9/1/2009 to a "later V. 9.10" having been updated on 8/15/2009, despite saying early on 3/1/2009.
Official copy at the University of Pennsylvania. V. 9.80 as of 8/21/2009 through 9/1/2009.
Official copy at repairfaq.org. V. 9.80 as of 8/21/2009 through 9/1/2009.
Official copy at Drexel University. V. 9.10 as of 3/1/2009 through 9/1/2009.
The whole thing including .GIF, .PDF, .JPG files, etc. in a zip file -
Laser FAQ zip file at
the University of Pennsylvania. This is a "later V. 9.10" having an update
date of 8/15/2009 despite an early notation of 3/1/2009, as of 9/1/2009, maybe
updated since. Size approx. 45 meg at that time, official version.
Where hobbyists and enthusiasts can get laser goodies. UPDATED 3/2/2002.
The laser section of the table of contents of Craig Johnson's main page.
Craig Johnson's Diode Laser Page! NEW for Christmas 2000, updated 1/27/2007 and subject to more updates. Includes test reports of a green laser pointer, existence of a blue one, a very informative close-up photo, as well as easily and cheaply hacking up some cheap pointers to 7-10 milliwatts! Read all warnings and disclaimers here and there before hacking!
See below this link section for hacking results on my end.
UPDATE 6/23/2007! Craig Johnson evaluates a newly available VIOLET laser!
GREEN laser pointers are here!
Craig Johnson's Page on a
15 milliwatt green laser pointer! (added in his site 5/30/2003)
Craig Johnson's Page on a
50 milliwatt green laser pointer! (Added in his site 6/20/2003 updated
7/30/2003)
Craig Johnson's
page on an EXTREMELY DANGEROUS 190 mW 532 nm green laser pointer!
He reviews many other green ones.
UPDATE 10/13/2004: - Craig Johnson's page on orange-yellow 593.5 nm DPSS laser pointers!
UPDATE 6/2/2006 ("born" in mid-2005): - Craig Johnson's page on a blue 473 nm DPSS laser pointer!
Craig Johnson's Main Page (mostly LEDs and flashlights rather than lasers).
DANGER - the 15 mW and especially the higher power
lasers can cause permanent eye damage faster than a human can react!
Glass objects, shiny plastic objects and many other shiny objects, even ones
that are not metallized, can produce reflected beams of the 190 mW unit that
are strong enough to cause permanent eye damage faster than one can react!
Use of lasers 5 mW or more is regulated in the USA and forbidden by law in
public places in some areas (check state and local laws)!
M. Csele's Homebuilt Lasers Page. Updated 3/29/2007.
Homemade
TEA (Transverse Electrode Atmospheric) Laser at Sparkbangbuzz!
This is a variation of a nitrogen laser. The lasing medium is air at
atmospheric pressure! No mirrors are needed!
The beam is not a true coherent laser beam, but it is reasonably narrow and
the radiation is actually laser radiation.
CAUTION - High voltage is required, and the laser beam is invisible ultraviolet. Also, these lasers involve spark gaps that produce nitrogen oxides and ozone, possibly in quantities unhealthful to breathe for more than a few minutes - you may need good ventillation if you operate such a laser for more than a few minutes! The sparking can also be very loud!
UPDATE 12/27/2000 - I tried hacking some cheap bullet style laser pointers as suggested by Craig Johnson. I have been getting some amazing solar cell readings on one of these hack jobs indicating at least 6.9 milliwatts absolutely worst case of consistently reproducible readings, and more likely 7.3 mW! Your mileage may and probably will vary but 6.9-plus mW is known achieved without doing anything really extreme! All you need to do is get some spares of the right bullet style laser pointer, and then not get in trouble! :)
Actual solar cell readings were 3.6 mA easily consistently reproduced and occaisionally 3.8 mA under favorable circumstances. The laser was a good foot or two away from the solar cell to rule out most of any radiation not in the laser beam. The wavelength seemed to be 648 nm and was nominally 650.
UPDATE - try removing the bullet tip "plain lens" for more output since this seems to catch and block a small portion of the beam. All milliwatt figures in this section are for with this tip removed from the pointer.
UPDATE 1/2/2001:
CAUTION - One of my "better" samples of this pointer with the usual three batteries and with the bullet tip removed hit 5.4 mW with fresh, non-tired batteries. This power level sagged to 4.4 mW in about a minute. But let it be known that just by removing the bullet tip makes some of these pointers sometimes slightly exceed the 5 mW limit of Class IIIA. Use with caution. Lasers over 5 mW are in a legal class of definitely not a toy - serious federal regulations apply and serious state/local laws may apply.
UPDATE 1/2/2001 - My pointer with 4 batteries managed 9.2 mW for a few seconds with well-rested batteries, sagging to 7.2 mW within a minute as the batteries got tired.
NOW FOR RESULTS OF MORE ADVENTUROUS HACKING! (1/2/2001)
I tried attaching clip leads to the spring and the case of one of these pointers. This went to a variable voltage DC power supply. I cranked it up to 4.9 volts, which was the highest I dared to go.
Results - power output was 10.6 mW, but this sagged to 10.2 mW within a minute as the laser diode heated up.
WARNING - 10-plus mW has a significant risk of causing permanent eye damage faster than one can blink or react if the beam enters someone's eye. A 10 mW laser is definitely not a toy!
WARNING - Such abuse may ruin the laser pointer. The laser diode may degrade within minutes, possibly within a minute from overheating. In addition, thermal stress may break things in the laser diode assembly. There is also a threshold of instant damage ("catastrophic optical damage" occurring in less than a microsecond) which may be somewhere around 10 milliwatts of laser output power.
CAUTION - non-regulated power supplies may have the voltage change significantly between an unloaded condition and a loaded condition. If the voltage with a light load is safe, the no-load voltage may charge up a capacitor in the supply past the threshold of a rapid damage mode! I recommend attaching a light bulb that draws 75-300 mA to the output of any unregulated supply to guard against the voltage rising past some critical level when you release the button on the laser pointer.
CAUTION - if you remove the diode assembly from the pointer, beware that any metal part of the diode assembly that the laser diode chip is attached to may need to be pressed against a larger piece of heat-conductive metal to keep the laser diode from overheating.
This modification is sometimes known as the "pot mod". The pushbutton switch cap can be popped off with a sharp knife or a utility knife blade. This exposes a very small potentiometer or "pot" that can be turned with a very small screwdriver. Turning it counterclockwise (to the left) increases output power.
Do not turn the pot all the way up - it is recommended to at least back it down a little, otherwise the wiper of the pot may fail to make contact.
It may be a good idea to back the pot down enough to get somewhat noticeably less than maximum possible output, so that current flowing through the pump diode is limited by the circuitry rather than by resistance of the batteries. One should also verify that current draw of this laser is less than 500 milliamps, preferably less than 400 milliamps - and beware of ammeters having enough resistance to have combination of ammeter and battery resistance being the limiting factor.
Adjusting the pot with the laser on can short the pot and a resistor in series with one of the pot's leads, resulting in extreme output and possibly damaging the pump diode.
This modification can achieve 15-plus milliwatts of output. Adjusting the pot for maximum possible output can achieve output of 20-plus milliwatts, sometimes over 30 milliwatts. I would do this modification conservatively to achieve longer life of the pump diode.
More extreme modifications are known, such as replacing resistors and placing a short from the wiper of the pot to the positive battery connection. Output as high as 100 milliwatts has been achieved with such extreme modifications. However, life of the pump diode is likely to be significantly shortened, especially if current draw exceeds 500 milliamps.
DANGERS AND WARNINGS!
1. Boosting output past 5 milliwatts makes this laser a Class IIIb one, subject to serious laws and regulations, as well as serious policies at many workplaces and most schools, colleges and universities. USA regulations for Class IIIb lasers include appropriate labelling, and an emission indicator, a key switch, a turn-on delay, and generally to not use such lasers in public with some exceptions.
2. If a green laser beam much over 5 milliwatts enters one's eye, there is a significant chance that permanent eye damage will occur faster than one can react or blink. If the beam power involved is around or over 15 milliwatts, then this will *probably* cause permanent eye damage.
After what I say in the above disclaimers, as best as I know the main USA Federal regulations affecting lasers are 21 CFR 1040.10 and 21 CFR 1040.11.
It appears to me likely that the USA's FAA imposes some regulation upon at least some lasers being fired into the sky.
There is also Federal legislation affecting lasers. One example is an early 2,000's Federal law against firing lasers at flying aircraft. As far as I know, that law has no exemptions for lasers that can be rightfully fired into the sky, or for ones of output power low enough to not be dangerous. The penalties are very severe.
There are also state and local laws.
Laws are different in countries other than the USA. In the USA, laser pointers are legal to retail-market if they are visible and have total output power under 5 mW. But in the United Kingdom, these have to be under 1 mW.