Diode (and other) Lasers: The good, the bad, and the blown.
Last updated 01-29-07 (Red 635nm laser pointer has come back to life - I know, I just took a spectrum of it)



LASER POINTERS: WHAT ARE THEY?
By now, most of you reading this have either used or seen a solid-state (diode) laser pointer before. These are typically battery operated, most come in either pen-shaped or bullet-shaped cases, and a few come with different kinds of pattern projection heads.

First appearing in the late 1980s, they have gone from $500.00 handheld units in the pockets of high-ranking executives to the point where they can be found for ONE DOLLAR APIECE if you look hard enough!
The early models produced a deep red, somewhat dim (by today's standards) laser beam. They would typically generate between 1 and 3 milliwatts at 680 to 685nm (very deep, amost ruby laser red) and would operate for an hour or so from several size "N" or "AA" cells in series. Although the commercially successful laser pointer dates back farther than this, some earlier versions used a subminiature helium neon plasma tube and step-up circuitry and aren't covered here.

Now to clarify a few things here. A laser diode (the active element in all solid-state pointers) is NOT just a glorified LED. They function like most any common laser, in that inside the tiny chip is an active medium (something that glows), a resonator cavity, and a pair of mirrors.
These components are for the most part, microscopic. The typical light-producing region in a laser pointer's diode is about the size of a bacterium, whereas the light producing portion of an LED is at least 10,000 times larger. This is one reason why a laser pointer's light can be foucussed into a very tiny spot, something that simply cannot be done with an LED, regardless of what kind it is or who made it.
Laser diodes by themselves are also incredibly delicate, and can be destroyed just by looking at them the wrong way. This is one of the main reasons you should buy a laser pointer or other complete module instead of a bare laser diode if you want to mess with laser technology.

At first, all diode-type laser pointers used 5mm can-style laser diodes; however today's cheaper, mass-produced models use a bare diode on a "C" mount, like the one in the picture at right. The actual laser beam comes from the small dark chip sitting on top of the silvery, larger block near the top of the picture, and is focused by a tiny lens in the end of the laser pointer.

Until the last couple of years, most cheap pointers (that is, anything you could buy for under $40 or $50) were all 670nm deep red types. Only the very expensive models had a brighter, more orangish color output. Now, you can find these orangish-red 635nm models for under $20, and 650nm (pure red, but brighter than 670nm) laser pointers can regularly be found for a dollar or two on Ebay!

Laser pointers come in hundreds of different types, with dozens of different case styles and "extras". For the sake of this document, the ones I am using are the bullet-style (fits on a keychain and uses LR-44 button-cell batteries) and the pen-style (clips into pocket, and uses at least 2 "AAA" cells). I have personally owned, used, and destroyed dozens of laser pointers over the years. Most have been those with wavelengths in the 670-685nm range, and those with wavelengths between 645nm and 660nm.


A 635nm RED LASER POINTER FOUND ON EBAY:.
I found this 635nm red laser pointer on Ebay in November 2003, so like any good flashaholic might, I bought it.



It uses two AAA cells for power, and draws 41mA on the DMM's 2A scale. The beam it produces is nice, and is characteristic of other good red diode laser modules, consisting of a central band with dimmer areas above and below it. This beam pattern is perfectly normal, and does not in any way indicate a problem with the laser pointer.



Here is a picture of the beam on a wall about 8 feet away, with photoflash. I used the camera's 3x optical zoom here. I did not use the additional digital zoom available on the camera, because it's {vulgar term for feces}ty. :-\

I fired this laser at the uninhabited top of a building approximately 3/4 of a mile away (the most distant target I can use here without resorting to a telescope or binoculars) after dark and with virtually no previous dark adaption to my eyes, and was easily able to see the spot with the naked eye. This is with a considerable amount of city light pollution, so the laser spot should be visible even farther away in a truly dark area.

My spectrometer is broken, so I eyeballed the wavelength. It's somewhere around 637nm to 638nm; right where this laser diode ought to be. They can vary between 635nm and 640nm; this is a normal variation for this kind of laser diode.

(Edit 10-02-05): This laser appears to have gone tits-up. I tried several sets of batteries, and confirmed the batteries were good by testing them in another product that uses AAA cells. This laser meters as an open circuit, confirming that the laser diode, the switch, or the resistor has failed open.


(Edit 01-29-07): The laser appears to be operational again. So I took a spectrum of it.


Spectrometer plot of this 635nm red laser pointer
Ocean Optics USB2000 Spectrometer on loan from WWW.TWO-CUBED.COM.
Power output measures 2.178mW on a laser power meter specifically designed for this purpose.


GREEN LASER POINTERS - BRIGHTER AND FARTHER:

A green laser pointer works a lot differently than a typical red one. Because science has not yet created laser diodes that can create green laser light by themselves, a clever work-around is used to get green. In this case, a high-powered infrared laser diode is fired at a neodymium-doped crystal, which absorbs the 808nm infrared light and lases at 1064nm. This longer-wave light is then thrown at another crystal which converts the 1064nm light into 532nm (exactly doubled in frequency). So the green light that shoots out the end of the pointer has to go through several steps and through several rather expensive crystals. This is why green laser pointers still cost well over $200, and sometimes closer to $350 or even $400!


A red and a green pointer being fired at the standard LED Museum test target.
The beam from the green is actually smaller than the red, but its brightness causes its camera image to bloom. You can tell the difference in brightness not only by the actual spots, but by the reflections they cast on the styrofoam block on the bench.


This picture shows one effect of the green laser: it causes some unexpected fluorescence in some unexpected materials. In this picture, the laser is shown being discharged through a common Christmas decoration - one of those liquid-filled "snow globes". The otherwise clear liquid fluoresces a bright yellow-orange color, yet when red laser light is shined through it, the liquid is not turbid at all and almost no scattered beam can be seen.

For the truly curious - or destructive among you, go to http://repairfaq.ece.drexel.edu/sam/laserpic/glpdpics.htm#glpdtoc to see somebody actually mutilate and dissect one of these laser pointers. A much more technical explanation of how they actually work is at www.repairfaq.org/sam/lasersam.htm. I certainly cannot afford to disembowel mine - it could be years before I can afford another. So let's let someone else do it and share in his misery and triumph.
Note: some of the pictures of laser butchery are rather sad, so keep a box of tissue handy.

A source of inexpensive 5mW green pointers is at http://www.gothlust.com/laser240.html or send an e-mail to freeman@dimensional.com if you have any questions regarding your potential purchase.
This is the type of green laser I have tested here (and this is where I purchased it from) so I know the source is good, and the laser lives up to expectations.


FEEDING THE HUNGRY, HUGRY BEAST:
If you buy a green laser pointer, especially a CW (continuous wave) model, expect to spend a lot on alkaline "AAA" cells; lasers like this are notoriously power-hungry. After the first three or four sets of alkalines, I bought a set of NiMH batteries and a charger specifically for this instrument.

Initial results have shown a set of Radio Shack #23-527 600mAH cells lasted somewhere between 1:20 and 1:40 of actual laser on time in varying usage patterns ranging from intermittent brief activations to periods where it was on for ten out of every fifteen minutes. I pulled the batteries well before they were fully discharged - the laser was still maintaining good power levels and probably would have worked satisfactorily for another 10 to 30 minutes. But it had become somewhat unstable with beam power fluctuating +-20% or so over very short terms, so that's when I figured it was a good idea to dump the batteries and put them to bed for the night.

This discharge time is consistent with a device drawing somewhere in the range of 350 to 400mA. Once I get a loaner meter, I'll measure the current consumption of this pointer using both alkaline and NiMH cells.
The Radio Shack charger made specifically for these NiMH cells will charge them basically overnight.
Fresh as flowers in just eight hours. :)

Update 01-24-01:
Using nearly-new NiMH cells (previous use <5 minutes), the pointer starts out drawing 360mA, and ends up drawing 384mA once it fully warms up and stays at full output power.

Update 01-25-01:
Using brand spanking new alkalines, the maximum curent is 399mA, which the pointer reaches after a brief warmup period.

Attempting to hack the pointer and obtain higher optical power was mostly futile - the best I got was 6.04 milliwatts using three batteries, and this peak was short-lived. Most of the time, the pointer peaked out between 5.04 and 5.14mW, then dropped to around 4.9mW as the guts inside warmed up.

Current measurements: with 2 alkaline cells (the way it's supposed to be), 399mA. With 3 cells, 401mA. Not much of a change there.
With two NiMH cells, it draws 384mA and consistently produces 4.68 milliwatts of laser power after a brief warmup.

From a cold start (68°F), it gives 3.3mW, quickly rising over the next 20 or 30 seconds as the internal guts warm up. If the pointer is kept above 85°F or so, the warmup time is negligible, and it appears to start at or near maximum power.

Update 06-15-01:
For some as of yet unknown reason, my green pointer has begun to produce almost 10mW of bright green light, mutating itself into a deadly Class IIIb instrument. Well, not *deadly*, but definitely dangerous to the eye. How or why it has done this is as of yet unknown. Maybe something inside the resonator got bumped into a more favorable position, or maybe the diode driver is croaking???



This picture shows one very visible effect of the green laser pointer - its ability to throw a clearly visible beam where a red pointer will not. (Output was 4.68mW for this photo)

In this picture, both a red "bullet style" pointer and this green model were fired in the same direction, but only the beam from the green laser was visible.

The camera was set up by the computer, and the laser was fired from across the room (about 15 feet) to get this picture.

I have since obtained a second green laser pointer, this time a GLP-4 pulsed type.

This is a fairly early 2nd generation green laser pointer model, made in late 1998 (the first ones appeared commercially as extremely expensive $1,000 to $2,000 devices as early as 1996); and it pulses its beam at about a 265Hz rate with a duty cycle of approximately 75%.
The picture below was taken while holding both pointers, shooting them at the ceiling, and waving them about in tandem.

Note the distinctly dashed line the GLP-4 produces. Earlier models like this were probably too power hungry to run in true CW mode, so pulsed operation helps lengthen an already very short battery life.


The newer (November 2000) GLP-5 is the spot on the left.
The older (December 1998) GLP-4 is the weaker spot on the right.

This picture may be a bit misleading if taken on its own merits however; as my 3rd generation GLP-5 has developed a "problem" that causes it to emit anywhere between 9.5 and 11.6 milliwatts under some conditions and after warming it in the hand. In this picture, it was outputting somewhere between 6.5 and 7.0 milliwatts, while the GLP-4 has an *average* output power of 2.2mW with a 75% duty cycle.

When both pointers are started cold (all components around 18°-20°C), they both have beams with similar brightness to the eye; although the meter says the GLP-5 is about 30% more intense. The "defective" pointer usually has its jump in power after the head has warmed to over 30°C or so either by external means (warming in the hands) or by using it intermittently for about a minute.

Actual "cold" readings:
GLP-4: 1.977mW
GLP-5: 2.572mW

Actual "hot" readings:
GLP-4: 1.543mW
GLP-5: 8.722mW (briefly topped 11.62722 milliwatts!)

Current drain on batteries:
GLP-4: 370mA
GLP-5: 400mA

The GLP-4 has a pulse rep rate of approximately 265Hz, not 30Hz as is commonly believed. As stated earlier, the duty cycle is approximately 75%.

The GLP-5 is missing (as of early 2003), so I cannot do any comparisons or additional testing with it.


(Update 10-23-04): My GLP-5 vanished in late-2002, and never did turn up. Now that I've moved, I can chalk this one up as a total loss.



SAFETY CONSIDERATIONS WHEN SHOPPING FOR GREEN LASER POINTERS:
One particular kind of green laser pointer represents a possible danger. This model is imported into the USA often without a proper manufacturer certification or labeling. The pointer, reportedly imported from Russia, emits a green beam from a diode-pumped frequency-doubled Nd:YAG laser operating at 532 nm. The beam is actually a train of 40 ns pulses of 0.5 µJ/pulse energy emitted at approximately 1.7 KHz. This equates to an average power of about 0.85 mW. But the per-pulse energy far exceeds recommended eye exposure limits for a Class IIIa laser product.

Another green DPSS laser pointer imported from China emits 5 mW in a CW beam .
The pointer has no labeling, and unscrewing the front end cap removes the IR filter!
In this case, the combined 1064nm and 532nm beams exceed 15 mW; clearly a Class IIIB emission.

Another kind of CW pointer starts out with a Class IIIA beam, but jumps up to a Class IIIB, approaching 10mW at times. See above. In this case, the "problem" is very likely a fluke, as I have not heard of this happening to any other green pointer, not even from Sam the laser guru who would likely be the first to hear about it.

NOTE: The pointers sold by freeman@dimensional.com (this is where I bought mine) are NOT of this "bad" type where the filter could be removed, and you should not be concerned about this when buying a pointer from this particular source.

When the front cap on one of these is unscrewed, you will see the cap only has a hole in the center; the IR filter is safely tucked away inside the laser head between the output coupler and the collimating lens, where prying screwdrivers, pins, or razor blades can't get to it.

The picture on the left shows what you should see when the cap is removed - the collimating lens glued on; with the blue-green colored filter itself buried deep inside the pointer.



All "good" pointers will (or should) have a removable end cap, as you see on the picture to the right. This is to allow for cleaning of the lens when it becomes soiled. But when removing this part also removes a crucial safety component, that's when it's time to worry and maybe think about returning or exchanging the pointer for a safer model or confining its use to a laboratory setting and treating it like a Class IIIb instrument.

Notice in this example, you do NOT see a square of blue-green material over the opening in the cap - this is the way they should be, just a hole.

If you find a blue-green glass thing in this cap, you should quit using the laser immediately, or confine its use to a laser lab environment only!



UNORTHODOX USES FOR A GREEN LASER POINTER
A fan of the website suggested that while stargazing, the pointer can be used to point out stars, planets, and other astronomical phenomena to anyone standing at your side. The visibility of the beam to an observer not looking directly over your shoulder will depend in great part on how much atmospheric pollutants there are; if there was a recent heavy rain <3 hours previous) followed by clearing, the laser beam will probably not be visible to anyone except you, the shooter. However, if the weather has been fair and calm for several days or more, there should be enough junk in the air to make the beam quite visible to anyone confined to a small region around you.


Take a 5mm high-brightness yellow LED, and shove it head-
first into the aperture of your green laser pointer.

Then take a high-brightness red (a Hewlett-Packard 623nm
model works well here) and attach it to the leads of the
yellow LED, then turn the laser on.

What happens?

If you did this correctly, the red LED should light up
very clearly; bright enough to use as a pilot light!
If nothing happens, reverse the leads on the red LED.


NOTE: Do not push the LED in so far that it touches the laser's lens, and don't remove the end cap on the laser. If the yellow LED doesn't fit the hole (too loose or too tight), hold it in position with your hand, turn the laser on, and move the LED about slightly until the red LED glow becomes bright.


The green laser beam also seems to be an indicator of how much manganese is present in antique glass - such as insulators, glass blocks, bottles, and similar articles. When the beam passes through glass containing more manganese than was originally needed for clarifying the object, the beam will appear to have a yellowish or yellow-orange glow as it passes through the glass.


LASER DIODES... FROM PLAIN JANE TO THE TRULY BIZARRE:
When you think of the phrase "laser diode" you probably think of these things. You can find them in all kinds of products, from grocery store scanners to that CD walkman you dropped and busted in the driveway last week.
The diodes pictured at right are your typical deep red, visible light types used in good laser modules, some types of laser pointers, and laser scanners used in the grocery store. They have two seperate components inside: the actual laser diode itself, and a photodiode that is used to "watch" the brightness and allow a special circuit to adjust the current to compensate for day-to-day variations all laser diodes encounter.




The wide picture shows you what the laser beam from a typical red laser diode would look like if you just grabbed one and hooked it up to a power supply. You don't just automatically get a nice, tight beam like you do from a gas (tube-type) laser. Instead, you have to place a lens in front of the laser's output window, and adjust it to obtain the correct focus. This is called "collimation". You can see the result of that in the second photo.

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BLUE LASER POINTERS? YOU BET!!
Like the green laser pointer described above, blue laser light cannot yet be generated directly by a cheap diode. An infrared laser pumps a crystal, which pumps another crystal, in order to get blue light with a typical wavelength of 473nm (about the same color as an average Nichia blue LED, but with a bit less of a white color to it). Because the optics used for generation of blue laser light are less efficient and more expensive than those used for green, blue DPSS laser modules are still horrendously expensive.

Blue diode laser pointers (actually,
DPSS like the green pointers) are also
available if you look hard enough, but
at much greater cost than even green.
Expect to spend over $2,000.00 if you
absolutely, positively, must have a blue
laser pointer.
A model similar to the one pictured at
left was recently offered on Ebay for a
grand or so.


The vast majority of these blue lasers aren't in the shape of pen-style pointers; but instead the laser head is in a small, usually rectangular box which is connected to a seperate power supply & cooling controller via a thin umbilical containing wires for laser diode power & feedback, and TE cooler power & feedback.
One model sold by DeHarpporte Trading is advertised as being able to be battery powered, but most of these will probably plug into a household outlet to get power.


UPDATE: 06-13-01:
Nichia America is now making directly-injected VIOLET diode lasers at 5 and 30 milliwatts (405nm), and they now have a directly injected BLUE laser diode (5mW at 440nm) with a lifetime of 500 hours. The blue diodes cost $3,000 each, not including driver electronics or beam forming optics. (!)



Information on these diodes is available at: http://www.nichia.co.jp/vlaserhome-e.htm

Violet lasers really are out there... these pictures are of a Nichia violet laser diode fitted with a collimator, so it behaves like your regular red pointer.

Pictures were used by permission of the laser's owner.
The first one is of the device itself. The second is of the collimated beam hitting a styrofoam box, and the last one is of the image created when the laser was installed in a Black Widow type home laser light show unit in leiu of the red diode that came with it.



A Melles-Griot HeNe head that a fan of the website sent me a year or two ago. This is a typical HeNe tube, similar to the type you can scavenge out of grocery store price scanners, older model laser disk drives, measuring devices, medical equipment, and other devices that used HeNe lasers before laser diodes came down in price.
Measured power output of this tube tops out at 6.8 milliwatts, and its wavelength is 632.8nm.


A green HeNe tube I bought from MWK Industries in the mid-1990s. This is a 19" laser head - a laser tube & ballast resistor encased in a metal tube and outfitted with the standard HV connection. Stated power output was 0.23mW, but it has since degraded, and now only produces approximately 10-12 microwatts. Wavelength of this laser is 543.5nm. Smoke was used to allow the beam to be seen. After running for only about a minute, it starts sputtering, so it's getting pretty close to the end, awww the poor thing.

The power supply I used for both tubes is a Melles-Griot adjustable that I bought with the green tube. It can provide up to 7mA which is needed for the larger green HeNe tube.


Here's an explanation of how regular diode lasers are made.
And here's an explanation of how VSCELs are made.


UPDATE: 12-24-03:
I received a cute little 12V helium neon laser from a fan of the website today, and here is the proof:


Here is the laser & power supply itself. It's approximately 6" long, 1.25" wide, and 2.25" high. It's quite small for a HeNe plasma laser with integral power supply. :-)
It reportedly outputs 1mW at 632.8nm, in the orangish-red part of the spectrum.
And it feeds from 10-14 volts DC at 900mA.

The integral power supply outputs 1,250VDC at 4mA. So it can power the Siemens tube that comes with it or any other tube that can use this kind of power if you tap into the two high voltage terminals. Don't make those wires too long now; the added capacitance will make an external tube harder to start. There's nothing wrong with the tube that comes with it, so leave it in there if you can.


Here's a picture of the laser beam coming out the business end.
That blue light at the bottom is an LED in a computer mouse; and is not produced by the laser or any other lighting devices in the vicinity. Smoke was used to allow the beam to show up more clearly in this photograph.


And here's a picture of its beam spot on a wall approximately 6 feet away. It is a bit out of focus; the main (brightest) beam is a small, round spot.
This laser produces a bright primary beam, and a dim, wider (higher divergence) secondary beam. This is perfectly normal for a small HeNe laser like this, and does not in any way indicate a problem with the laser. At the lower left of the primary beam spot in this picture, you can see the larger, dimmer secondary spot.

The laser & power supply unit appears to reach a peak temperature of 144°F after approximately 4 hours of "on" time. This temperature was measured with a non-contact IR thermometer. Input voltage (loaded) is 11.95 volts DC; which is right where it ought to be. Unloaded (open circuit) voltage is 12.18 volts; no surprise there.

The tube appears to sputter when started, but this is easily remedied by taking the cover off and rotating the tube slightly in its power supply cradle (spring-like electrodes that contact the anode and cathode ends of the tube). For the amount of time I expect to use this laser (a few times a week), this is not a problem even if it has to be done every time.


THE FUTURE OF THIS PAGE:
As you can see, work has finally resumed on this page. It will soon be split into more edible sections before it grows too large.
Eventually, you will read about diodes, power supply pitfalls, and things that $250 green pointer (or your $1 red one) can actually be used for. And although most of the lasers on this page will be diode types, don't be surprised to find other types (like pictures and descriptions of a HeNe I was recently sent).
The use of photos will no doubt create some minor problems for users of 14.4K and 28.8K modems, but for this type of material, pictures really can be worth 1,000 words.


PLEASE DON'T THROW AWAY THOSE ABANDONED, HOMELESS LASERS!
I am always looking for small (<500mW) lasers, especially those in visible wavelengths. Diode laser modules, DPSS lasers in green and blue, small-frame argon heads + power supplies; Helium-Cadmium lasers, and Helium Neon tubes or heads in red, orange, yellow, and green; and of course, laser pointers in all shapes and sizes would all be welcome additions to my small home laboratory.

Because I'm on a fixed disability income of around $300 a month, everything but the smallest diode lasers are out of reach for me, so your older, unused, or abandoned lasers would be very welcome here.

If you have lasers that are unused, older, or just don't work quite like they used to that need a new home, please contact me at ledmuseum@gmail.com or send it to:

The LED (and Laser) Museum
c/o Craig Johnson
32820 20th Ave S. Unit 4
Federal Way, WA, 98003-9428
USA
Ph. 1-253-653-1743

If there should appear an anonymous laser showing up meowing on my doorstep, it will automatically be assumed it was sent for the purpose of posting test results & pictures on these pages.
Thank you in advance.

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