Review of the Yellow (593.5nm) DPSS Laser Module

* IMPORTANT: Pricing is accurate as of 10-26-10. Please visit the Currency Calculator for the latest currency conversion rates from British pounds to US dollars.

Yellow beam lasers in pointer format have not existed - until now {September 2004}, anyway.
This is a yellow laser module, emitting just over 6 milliwatts of laser radiation at 593.5nm (5,935Å); just a bit longer in wavelength than the sodium line at 589.2nm. The color could best be described as a "very strong urine yellow"; though there are probably some more gentle terms that could be used to describe the color - like...er...uh..."sunset yellow".
It uses a mechanism similar to that used by green laser pointers: an infrared laser diode is fired into a crystal of material that lases at two longer wavelengths in the infrared, who's light is then fired into a frequency-doubling crystal, producing the yellow laser beam you see.
This is known as DPSS (Diode Pumped Solid State).

This laser module emits just over 6mW of laser radiation at 593.5nm, making it a CDRH Class IIIb instrument.

It comes in a flashlight-like (torch-like) case, and features a key switch on the back to help prevent unauthorised use. It feeds from two C cells, so the total battery lifetime will be significantly longer than a pen-style yellow DPSS laser pointer of the same power output that uses two AAA cells.

SIZE



To use the laser module, just turn the key switch on the tailcap 90 degrees left or right from the position it was in when you inserted it, aim it at something you wish to point out, and press & release the blue plastic button on the barrel to turn the laser on for as long as you need the yellow laser spot. A red LED emission indicator above the switch will come on.

Press and release the blue plastic button again to turn the laser module back off.

Intermittent (momentary) operation is also available by pressing the button more lightly (before it clicks) and holding it that way for as long as you need the laser spot. Releasing the button turns the laser off.

If the red emission LED above the switch comes on but no laser beam is emitted, check to see that the beam shutter at the front of the laser is not closed and blocking the beam. If it is, slide it to the left (as the laser is facing you and the blue switch is at the top). This shutter has a fairly stiff action to it; you'll have to make a purposeful effort to move it - it won't just slide back and forth on its own.

Turn the key switch off and remove the key to prevent unwanted activation.

The interlock key is *supposed* to be stubby; see the photograph directly below.






To change the batteries in your spiffy new yellow DPSS laser module, remove the key from the tailcap if necessary and set it aside, unscrew and remove the tailcap, and set it aside too.

Tip the two used C cells out of the barrel and into your hand, and dispose of or recycle them as you see fit. Or stomp on them, if you like to break things. ;-)
If the cells are rechargeable, pop them in the charger instead of throwing them away or stomping on them.

Insert two new C cells into the barrel, flat-end (-) negative first. This is the opposite of how batteries are installed in most flashlights (but is the same way batteries are installed in most pen-type laser pointers), so please pay attention to polarity here. Be certain the button-end (+) of each cell faces outward when you're changing the batteries.

Screw the tailcap back on, insert and turn the interlock key in the tailcap, and be done with it.

Current consumption measures 869mA, using my DMM's 2A scale.




This is a laser module, not a flashlight. So I won't whack it against a steel rod, run over it, try to drown it in the loo ("toilet", "toilet stool", "john", "can", or "commode" for US viewers), throw it, stomp on it, or subject it to other abuses that a flashlight might have to endure.

Yellow diode lasers are a lot different than those common red lasers you see all the time.

In a 640nm red laser pointer, there's a red-emitting diode and a lens to collimate (focus) the beam.

In a 593.5nm yellow DPSS laser (pointer or larger size), there's a BIG infrared laser diode that generates laser light at 808nm, this is fired into a crystal containing the rare-earth element "neodymium". This crystal takes the 808nm infrared laser light and lases at 1,064 and 1,342nm (yes, deeper in the infrared!). This laser light comes out of the Nd:YV04 (neodymium yttrium vanadium oxide) crystal and is then shot into a second crystal (containing potassium, titanium, & phosphorus, usually called KTP) that roughly doubles the frequency to 593.5nm - the bright orangish yellow color you see. This light is then collimated (focused) by a lens and emerges out the laser's "business end". Just before the lens, there's a filter that removes any stray IR (infrared) rays from the pump diode and the neodymium crystal. You don't want that stuff in your yellow beam, trust me.

From a laser engineer who emailed me, comes the following text:

The technology behind the yellow laser is a bit more involved than in the green laser,
involving a process called sum frequency generation. It uses the same
components that the green laser has, but the coatings are much different.

There are two particular "tricks" in making a sum frequency laser. The
first is to get a single laser crystal (the Nd:YAG or Nd:YVO4) to lase
simultaneously at two different wavelengths, both 1064 nm and 1342 nm.
While we do this with gas lasers (Argon and Krypton) frequently, this is
pretty rare with solid state. The relative powers of the two have to
be in a reasonable range for the sum frequency process to work. The
two waves are introduced in to the KTP crystal, which generates the 593.5nm output.

This is why yellow DPSS lasers are so much more expensive than red diode lasers. Lots of itty bitty parts, and they all need to be very carefully aligned by hand. If the polarisation is "off", one or both crystals need to be turned.
With red diode lasers, you just slap in the diode and slap a lens in front of it.

This laser module includes an interlock key switch on the tailcap, and a beam attenuation shutter on the front of the unit. If your unit does not appear to function, check these first before calling Bluesky Marketing about the laser.
Note: The interlock switch key can become slanted in its keyhole; the laser still functions in this condition and you need not go out of your way to correct it at once.

The bezel at the business-end of this laser unscrews to allow you to clean the lens if necessary.
To clean the lens, unscrew and remove the bezel, and set it aside. Use a Q-tip or other cotton swab and alcohol (disk- or tape-head cleaner will work well for this purpose - do not use rubbing alcohol if it contains water or glycerine). Dip the swab in the alcohol, shake it so it's not dripping, and clean the lens. Turn the swab over to the dry end or use a new swab to dry the lens. Then, screw the bezel back on. Dispose of the used swab(s) properly; you don't want to use them on this laser again.

You can also use a Sima Lens Pen to clean the lens of this laser.


The entire head assembly comes off too. Although this does not expose the laser itself, the beam will be significantly wider (approximately 5° wide) in this configuration, different beam modes can be seen as the laser warms up, and if you view the lens off-axis, faint red (671nm) & green (532nm) flashes may be seen. This indicates the KTP crystal does emit some red & green radiation as the laser warms up, but this effect is short-lived, the red & green radiation is faint (probably less than 1µW (0.001mW) total), and does not affect the yellow output.

(Update 04-25-07): The two lenses exposed by removing the bezel and beam attenuation shutter are AR (antireflective) coated. I neglected to mention this in September 2004 when I received this laser, but it was there all along.


Here's the beam on a ceiling from ~5 feet away, when the entire head assembly is removed. Light is not white and orange as depicted in these photographs.

There is some visible fluctuation of laser power output for perhaps the first ten seconds, then it appears to stabilise.

Every year, I laser the Westlake Mall Christmas tree lighting ceremony and the Bon Marche Star lighting ceremony (both ceremonies are on the day after Thanksgiving just three blocks from here in downtown Seattle) with a green laser pointer; this year I'll laser these ceremonies with this yellow laser module and see what happens.

UPDATE: 10-01-04
I'm no longer going to be in this area, so it is very, very unlikely I'll be able to laser these ceremonies this year or in years to come.

The output power level of these laser modules can be had much lower (less than 1mW) so the laser complies with UK (United Kingdom) regulations regarding laser pointers available to the general public in that country. Lasers like this come in pen-style housings, and use two AAA cells for power.

This laser module is CDRH Class IIIb; lower powered versions for European and UK users are CDRH Class II.

The label on this laser reads:

PEAK POWER <500mW WAVELENGTH 473nm-1064nm
CLASS IIIb LASER PRODUCT


Here's a photograph of the sticker on this laser:



This is a Class IIIb laser product, as it produces a bit greater than 6mW of laser radiation at 593.5nm in the visible portion of the spectrum.

I ran its output through a diffraction grating (13,500 lines per inch) to look for lines at 532nm, 671nm, 808nm, 1,064nm, and 1,342nm; and did not see them or (for the three IR lines) did not image them through a digital camera. I know the diffraction grating will deflect radiation up to at least 910nm, so I know at very least the 808nm line from the pump diode is being filtered out. The 1,064nm line probably is too, but I don't know if the 1,342nm line is being filtered out or not. I'll have to find a glass prism and try the experiment again.




TEST NOTES:
Sample of the yellow DPSS laser module was provided by Paul of Bluesky Marketing, and was received on 09-16-04.
The main website for Paul's laser modules is www.megagreen.co.uk.

VERY IMPORTANT: You can purchase yellow DPSS laser pointers with less than 1mW of total radiated power (CDRH Class II) if you live in Europe or the UK. Lasers like this come in pen-style housings, and use two AAA cells for power. Expect to pay £179.00 ($329.43 as of 10-25-04) for a yellow DPSS laser module like this.

VERY, VERY IMPORTANT: Paul was given explicit written permission (not just implied oral consent) to use in any manner he sees fit any of the photographs on this and other web pages on this website that contain his products. So please do not be alarmed if you see any of my photographs on any of his websites.


UPDATE: 09-16-04I have decided to rate this product 4 stars, and give it a place in this website's Trophy Case.
The primary reason it did not receive 4 1/2 stars (the highest rating I can give to a DPSS laser) is because the beam power fluctuates visibly (which translates to a significantly large variation) during warmup.


UPDATE: 09-22-04I have used this product every single day since I received it, and carried it in my EDC bag on no fewer than three occasions. It endured a light sprinkle on two occasions, and only the barrel was lightly wetted. It was carried head-down in the bag, with just the barrel exposed. I will not amend my water-resistance text or change the rating I gave this product. There appears to be no environmental protection (such as O-rings), but this product was never intended to be used in foul weather anyway.



UPDATE: 09-24-04
I have continued to use this product daily, and to carry it in the EDC bag on the floorboard of my electric Rascalator thing, and have no problems to report, and no rainfall on the barrel to report either. I'm still using the original set of batteries I installed in it on 09-16-04. Figure it gets at least 5-10 minutes of "on" time every day.




UPDATE: 09-27-04
I got a reading of 2.099mW using a solar cell, a DMM (with the solar cell connected to the DMM and the meter set to read low milliamps), and a mathematical formula that translates the meter reading to milliwatts of output power. The mathematical formula I used was:
(current in milliamps as shown on meter)*1239.7/593.5/0.97




UPDATE: 10-03-04
I have heard that this may be a CNI product.
I have no way to verify this of course, but it's a possibility anyway.




UPDATE: 12-02-04
I have heard from a reliable source, the following:

From what I understand, they've put the production of yellow modules on hold indefinitely after producing very few of them, perhaps less than 10 units, so you have a very special laser there.



UPDATE: 01-03-05
I ran this laser through my 13,500 lines/inch diffraction grating and the visible-blocking goggles I got from Ebay in November 2004, and came up with the following photograph:



Note the very, very faint green spot in the upper right.
None of the IR lines were present in the photograph.



UPDATE: 06-29-05
I measured an output of 2.64656mW using a laser power meter (yes, specifically designed for that purpose) I received this afternoon.



UPDATE: 09-01-05
I thought it looked a bit brighter, so I decided to measure it. I measured an output of 4.1988mW using a laser power meter. Indeed it was considerably more powerful.



UPDATE: 11-06-05
I measured an output of 4.3475mW at 593.5nm using a laser power meter specifically designed for that purpose. It's still a Class IIIa device, but it's getting really close to the Class IIIb area where I can no longer call it a "pointer" and would have to start calling it a "module".



UPDATE: 11-18-05
I measured an output of 4.9125mW at 593.5nm using a laser power meter specifically designed for that purpose.


UPDATE: 11-18-05
No, you aren't seeing things. Yes, a same-day update.
I measured an output of 6.1125mW at 593.5nm using a laser power meter specifically designed for that purpose. It has now reached CDRH Class IIIb limits (any laser outputting a beam power of over 5 milliwatts continuous wave), so I must now call it a "module" on this website.



UPDATE: 11-21-05
I have confirmed that this is indeed a CNI product.



UPDATE: 12-18-06
I observed not just green flashes, but red flashes too when the head was removed and the laser was viewed off-axis as it warmed up. I added "red &" to the appropriate locations above, so my evaluation is accurate.




UPDATE: 12-19-06
I just attempted to capture these flashes via spectrometer, and I was not successful.


UPDATE: 02-17-07
Power output was measured at 5.35mW.



UPDATE: 03-03-07

Beam cross-sectional analysis, with collimating lens removed.
Image made using the ProMetric System by Radiant Imaging.






UPDATE: 04-21-07
The tailcap interlock key can be defeated if desired (or if necessary, such as if you lose the key).
To do this, follow these three simple steps:


1: Unscrew & remove the tailcap.
2: Inside the tailcap, you'll see a white plastic disk with a hole in it. Remove it.
3: Screw the tailcap back on.

The laser will now operate without the key.




UPDATE: 04-23-07
If the laser functions intermittently after this modification, just place a small amount of ordinary kitchen aluminum foil in the tailcap before screwing it back on.




UPDATE: 04-26-07
Power output measures 5.075mW.




UPDATE: 05-16-07
WMP movie (.avi extension) showing this yellow laser (with IR filter removed) spinning the vanes of a Crooke's Radiometer.
It is approximately 4.0 megabytes (4,226,784 bytes); dial-up users please be aware.
It will take no less than twenty minutes to load at 48.0Kbps.

I cannot provide it in other formats, so please do not ask.




UPDATE: 06-07-07
From an email I received from the laser expert I loaned this laser to, comes this:


Mostly appears to me roughly "sodium yellow", close to "usual yellow LED
yellow", despite the wavelength of this laser being maybe 4 nm longer,
enough to make me think it should look just a bit more orange than that.

In some but not most conditions, the color apears to me a more orangish color, just a bit more yellow than a Crayola "yellow-orange" crayon.
Such conditions:


1. Diffusing the light over a wide area and viewing it less brightly -
often but not always makes it appear to me more a very yellowish shade of
orange than an orangish shade of yellow.


2. Moving the beam rapidly along a surface illuminated somewhat by higher
color temperature light, such as daylight.


3. Shining the beam onto a surface illuminated brightly by higher color
temperature light, such as an 8-inch globe around four 13 watt 4100K
("cool white") PL-13 compact fluorescents. Then the color appears to me
almost, but not quite, as orange as a yellow-orange Crayola crayon.
I suspect that I would see the beam similarly orangish when using this
laser in brighter daylight.


4. Occasionally, probably short of usually, when illuminating very
brightly lit surfaces (such as diffused lightbulb surfaces or nearby
brightly illuminated surfaces) when the light source has color temperature
as low as about 2800 K.


Keep in mind that the sodium wavelengths centered around 589.3 nm can
look similarly orangish to me under some conditions of high ambient
lighting with color temperature near or above 4100 K.


At this moment, it mostly appears to me "very orangish yellow", slightly
more orange than "sodium orange-yellow" and most yellow LEDs, about the
color of more amberish yellow LEDs.





UPDATE: 07-12-07
Power output measures 4.475mW on a laser power meter specifically intended for this purpose.
I noticed that the laser appeared very slightly brighter, so I decided to measure it.





UPDATE: 07-12-07
No, you aren't seeing things.
Yes, a same-day update.
This laser is true CW (continuous wave), not quasi-CW or pulsed. I verified this two ways: I rapidly waved it around to see if a broken line appeared (it did not), and I tested it with an oscilloscope to detect pulsed operation at faster speeds than an optical detection method can reveal.






UPDATE: 03-21-09

This photograph of its beam showing TEM10 (Transverse Electromagnetic Mode 10) operation was taken with the collimating lens assembly removed, and at a range of approximately ten feet.

A laser who's beam is TEM00 (by far, the most common) would have a single, mainly circular beam. Here, let's show you with this chart:





UPDATE: 11-24-09
An "on the spot" power measurement came up with 3.68750mW; measured on a laser power meter.




UPDATE: 10-26-10
I converted this eval. to BBCode so that I coupld post it on a couple of BBSs about lasers & lights.









PROS:
Durable, hefty casing
Natural, flashlight-like feel in the hand
Uses batteries that are common and relatively inexpensive
Unique, attention-getting color that's radiant and unusual for a handheld laser
Beam is "clean", with no visible speckling or artifacts around it
Three safety features built in that don't impede normal operation
LED emission indicator so you know if it's on even if the beam shutter is closed
Continuous operation available via the pushbutton switch
Unique, attention-getting color...o wait I said that already.



CONS:
Visible fluctuations in power output during warmup
Uses an unexpectedly large amount of current (869mA) - large batteries compensate for this however
Fragile interior construction - like all DPSS lasers. Will not figure into my rating
Not water-resistant - but most other DPSS lasers aren't either. Will not figure into my rating






MANUFACTURER: CNI
PRODUCT TYPE: Yellow DPSS laser module
LAMP TYPE: DPSS Laser
No. OF LAMPS: 1
BEAM TYPE: Very narrow; it's a laser, remember? ;-)
SWITCH TYPE: Pushbutton click on/off/momentary on barrel
BEZEL: Metal; an aperture (hole) is in it to allow laser beam to emerge
BATTERY: 2xC cells
CURRENT CONSUMPTION: 869mA
WATER- AND VODKA-RESISTANT: No (*very* light sprinkle-resistance at maximum)
SUBMERSIBLE: FOR GOD SAKES NOOOO!!!!!

ACCESSORIES: Key for key switch
SIZE: 7.75" L (not including key) 1.4" D
WARRANTY: Unknown/not stated


PRODUCT RATING:

Update 08-15-11: Performed repeat spectroscopy of it.

"WATER- AND PEE-RESISTANT"

This would have to be the first laser reviewed with this feature :beer:

I love yellow lasers.

Cool... I like how you showed the 671 and 532nm emissions. I always wondered how much 532 my Rigel was putting out even when it was doing "full on 593.4".

BTTT: Added two short-term stability analyses.

BTTT: Added one long-term stability analysis.