Don K.'s Laser Page

Most recent update in Sam Goldwasser's laser FAQ (see links) noted on 7/15/2001. Most recent non-Sam link elsewhere 7/14/2001. Most recent update otherwise 4/18/2001.

Get a module or a complete pointer and not a bare diode!

Please, save yourself a few tons of trouble and get a laser pointer or laser diode module from someone who has already taken the time and trouble to get those infamously fussy laser diodes to do what you probably want.

Go here for a partial list of suppliers of working diode lasers. (updated 12/23/2000)These are getting really cheap - some around $5 - 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.

Beam divergence and use of lenses

Meanwhile, you might want to consider some messy limitations about minimum theoretical divergence of laser beams. This is some messy stuff resulting from the wave nature of light.
The minimum divergence rate of a visible red laser beam in milliradians is approximately equal to 1 divided by its initial width in millimeters. Given the very tiny size of the light emitting part of a diode laser, a very considerable beam divergence is expected. This does indeed occur.
This can be largely fixed by placing a convex lens in front of the diode laser, with a distance nearly equal to the lens's focal length. This reforms the beam, giving it a new, wider initial width with a correspondingly lower divergence. You will have to adjust the focus (or lens distance) yourself for best results.
Once you do this, you might wonder what happens with the beam, since the beam from a typical laser diode is not round, but oblong. This occurs because the light emitting part of the laser diode is oblong. At best, the wider dimension of the beam will diverge less than the narrower dimension. The best to be expected from compact lenses around a centimeter in diameter is a beam with initial dimensions (upon leaving the lens) of nearly 1 centimeter in the wider dimension, by a couple or a few millimeters in the narrower dimension. The wider dimension will expand by a millimeter every ten meters or so, while the narrower dimension of the beam will expand by a millimeter every couple or few meters. The divergence may even be greater than this if the lens is of poor quality or not exactly at the optimum distance from the laser diode, or if the beam exits the lens with smaller dimensions than just mentioned above.
The divergence may not be apparent within a few meters of the lens, if the "waist" of the beam occurs at that point. The beam "waist" is a region that sometimes occurs if the lens is trying to make the beam converge at the same rate that the wave nature of light is trying to make the beam diverge. At long distances, the beam *will* diverge, at best, at a rate in milliradians roughly inverse to its initial width in millimeters.
To get less divergence, you need more complex optics or a He-Ne laser, which has a very close-to-ideal round beam. Although a He-Ne laser's beam is fairly narrow and would diverge roughly by a millimeter every meter, this can easily be "fixed". Simply fire the He-Ne through a telescope, into the eyepiece and out the other end. If the telescope is optimally focused, the beam will exit the front of the telescope with a diameter magnified by the telescope's magnification. (Try not to magnify the beam beyond the diameter of any lens it has to go through.) With luck, you could get the beam to have an extremely low divergence of around a millimeter every several 10's or even roughly every 100 meters.

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.

Wavelength, color, and visibility.

One should also consider the wavelength of laser diodes while shopping around for one. Longer wavelengths of almost 700 nanometers are almost infrared, and are not very easily visible. Lasers with such wavelengths are not very bright. Shorter wavelengths closer to the visibility peak of 555 nanometers are more visible and brighter. It is recommended to get a diode laser with a wavelength as close to 555 nanometers as possible, as opposed to longer wavelengths.

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.

Nowadays, laser diodes with wavelengths around 635 nanometers are available. This wavelength is close to that of He-Ne lasers, and is a very visible red wavelength.

Availability of non-red laser pointers and diodes

At this time, no diode lasers with wavelengths below 635 nanometers were easily available. Blue ones are available as high priced samples ($3000 as of 4/18/2001) and violet ones are available at lesser but still high prices.

UPDATE 4/18/2001 on Nichia's violet and BLUE (440 nm typ.) laser diodes:

Nichia's violet and blue laser diode page.
Nichia's blue laser diode page.

the blue laser diode and LED book site.

There are green laser pointers with a very visible 532 nM wavelength. These are frequency doubled neodymium lasers pumped by IR diode lasers and cost a few hundred dollars. Blue ones using a similar process and with at least a similar price can be made.

You might have noticed that supposedly infrared wavelengths slightly over 700 nanometers are not completely invisible. In fact, wavelengths around 800 nanometers are very slightly visible. However, one should be cautious with visible quantities of light in the 800 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.

Links!

Sam Goldwasser's mighty laser FAQ - Approx. 6.3 meg of laser goodies (broken into several parts under 460K) plus about 249 GIF's/JPEG's from Sam Goldwasser. MUST READ! This includes lots of info on HeNe, diode, argon, CO2, dye, copper vapor, and nitrogen lasers. If you have already seen this but not in the past several months to maybe a year, you may want to look again since this document has not stopped growing.

Don Klipstein's mirror copy at misty.com. Most GIFs and some other files "cleaned up" for faster download. V. 5.98 as of 5/16/2001.

Official copy at the University of Pennsylvania. V. 6.06 as of 8/21/2001.

Official copy at repairfaq.org. Version 6.06 as of 8/21/2001.

Official copy at the new site laserfaq.org - with a dark-background color scheme. V. 5.99 as of 5/27 through 8/21 2001.

The whole thing including .GIF, .PDF, .JPG files, etc. in a zip file -
Laser FAQ zip file at the University of Pennsylvania. V. 5.98 as of 5/16/2001, size approx. 9.4 meg at that time, official version with no speed/size cleaning.

Don Klipstein's V. 5.98 speed-cleaned sized-cleaned T3-connected 7.9 meg .zip file at netaxs.com. Based on the UPenn 5/2001 zip.

Now the Netaxs 7.9 meg zip is available via "anonymous" FTP at:

ftp://ftp.netaxs.com/web/people/klipstei/laserfaq.zip
Future availability beyond sometime in July 2002 is not assured and this location is not an official one. All Netaxs locations have been off the official lists at least since early fall of 2000.

Where hobbyists and enthusiasts can get laser goodies. UPDATED 12/23/2000!

Craig Johnson's Diode Laser Page! NEW for Christmas 2000, updated 7/14/2001 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.

M. Csele's Homebuilt Lasers Page

Power boost hacking of cheap laser pointers!

WARNING - LASERS 5 to 499 mW are Class IIIB which are not toys and are subject to all sorts of Federal regulations and may be subject to state and local laws. Lasers over 5 mW may cause permanent eye damage faster than one can blink. You may have serious liability issues operating them where other people and/or animals can be exposed to the beam.

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 circumsances. The laser was a good foot or two away from the solar cell to rule out most of any eadiation 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 ofD 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") 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.

Back up to Don's home page. Written by Don Klipstein.