Stress testing cheap pens - do they ever die?

Hi all,

I have been given a few pen lasers this holiday season and I was curious to see what kind of duty cycles they would be capable of. I researched and couldn't really find any kind of solid documentation or answer so decided to test myself. I am lead to believe all three of the pens tested were bought from deal extreme - they're the Matt black type with dimples on the battery compartment, and "laser pointer" embossed on the pocket clip, with a silver tip and momentary push button.

First I tested one of the two 532nm lasers, could be anything from 5-50mW I honestly have no idea. Using a small clip to hold the button on, and using a black torch as a beam stop I noticed a few interesting things:-

-In typical DPSS fashion the beam took some time to brighten up and become properly visible - this is in a room at about 14 degrees C, so a tad on the cold side.
-using an infrared thermometer (the pistol grip type with a red laser pointer) I observed almost no heat increase across the entire barrel of the laser for a full 6 minutes of on time. The beam stayed stable the whole time.

Afterwards I unscrewed the laser and did a thorough temperature check. the battery compartment, batteries, lens and diode (pointed the thermometer through the aperture) were all no hotter than 18 degrees C.

I did the same test with the second 532 nm pointer, albeit with a faulty button so the test was harder to conclude - but I saw the same results.

I then tried with the 405nm pointer - again I have no idea of power, the beam is visible in a dark setting if you hold it up to your cheek. the 405nm, being non DPSS didn't want any time to heat up and stayed stable the entire 8 or so minutes I had it on, but rose in temperature a tad more than the DPSS greens, sitting at a barely tepid 20 degrees C at its hottest parts.

Conclusion? Firstly, I was surprised that after a minute the pointers did not start to burn up. I won't even run my SKY laser for more than a minute, never mind 6. Second, the absurdly long duty cycle makes these, at least for me, good for star pointing, provided the DPSS green manages to warm up at all on a cold, clear night. Set a clip round its button, tripod it and I could probably point objects out for long periods until the batteries died. Great for groups.

I hope this was helpful and I appreciate it won't apply to every pen laser so please don't go burning out those wildly overspec or pot modded pens.

Your environment probably works to your favor. If you do the same test over here (30C ambient) the results can vary

I'm sure it does. Never mind he laser though, I don't function properly in 30C temps!

More and more new members impressing the old guys! Good information! What about battery life? Or were you using a lab PSU. that would eliminate some variables from your experiment...

+1 for good work

:beer:
-Matt

I was just using normal batteries. They weren't Duracell, but they still hold a good charge. I'm no doubt going to try again at some point with Duracells, and probably in lower temperatures to see if the DPSS lasers heat up enough to actually work as star pointers. If they don't it's back to the drawing board (I'm funny about using my expensive lasers too much outside; should someone call the police and I end up getting lasers taken off me, I'd much rather it happen to cheap pens than proper lasers)

Thanks for the rep, by the way.

So, as a follow up, I did a few more experiments with the green pens. We all know that DPSS is quite sensitive to temperature, but I wanted to find out exactly how it would affect practical application, within reason of course.

Gradually cooling one of the pens down to outside temperature (about 4 degrees C at most) I then took it outside and powered on. Surprisingly, the output started off low, warmed up within a minute to being very bright, and then over the course of 6 or so minutes, gradually dimmed to a point where the beam wasn't very visible. It then appeared to stabilise somewhat. Temperature of the laser did not change much as far as I could see and measure.

To make sure I hadn't knackered it or run the batteries down, I brought it inside (still on) and in the warmer room the output brightened again, but seemed more unstable in that the dot flickered slightly.

I repeated the test with a second pen, but this one was taken straight from room temperature outside and left on for another 6 or so minutes. Output decreased as the laser cooled down but was more gradual as it had retained more heat from the room. Temperature of the laser again appeared to have not moved much, and certainly hadn't increased despite continuous use. In simple terms, with colder climates, these lasers get colder rather than warmer, even under constant use.

Back inside and in the warmer room, the laser started to increase in output again, and using an electric radiator to warm it up a little more it got very bright and once again the dot became more stable, and the beam very visible, when the diode was at 30 degrees C.

I did these tests with two sets of Duracells to eliminate crap battery syndrome. My conclusion is that - although we all know DPSS lasers don't like the cold - they seem to dislike CHANGES in temperature most of all, whether it's up or down. In both tests I did the output of the lasers reduced but eventually stabilised, and, under a truly dark sky would still prove useful for star pointing. My observations are that these type of pen lasers have, to all intents and purposes, an unlimited duty cycle in colder climates and will run for long periods fairly happily, but, rather like an old diesel you might not want to stop them for very long while actually out in the cold.

And, even at just a few degrees below room temperature, they showed no real evidence of burning up. So for me these pen lasers get a big +1.

FYI my Ebay 405 pens run around 60mw and my 532 green ebay pens run around 35mw

Thanks for the Information. The beams of both are visible, rather surprisingly in the 405's case in a darkened room, and will probably work wonders when an incense stick is lit. (I'll try when I'm back at home).

This thread interests me, because I've had a few lasers go LED, and have also grossly abused some of my lasers.

I've had three (four, sort of) lasers turn LED:

- a Laser 301 that died after being run constantly for 2 to 3 minutes. It warmed up a little, but I know for a fact that unit had minimal heatsinking and that the diode module was actually separated from the host by a layer of plastic. But, see about my other 405nm's later)

- My Skylasers HL405-500mW. I never LPM'ed mine but from what I gather many of these from Offroadfreak's GB 2 were overspec so they must have been overdriving the diodes a bit. When I did my laser rainbow setup last summer the HL405 was run up to ~5 minutes at a time, and got warm in the process. It also accidentally turned on once when being carried in a pocket; the beam shutter was closed so I didn't notice immediately. It wasn't quite hot, but it was getting there so I suspect this laser's death was due to excessive runtimes. From what I understand the heatsinking in Skylasers is somewhat light.

- The Lazerer LZCS 650nm @ 200mW. According to the power certificate it was overspec at 267mW. It used an open can diode and I did have to open up the front end a few times to correct focus issues due to the heatsink shifting within the host. I guess any kind of particles at all can kill those. When it died it dimmed over the course of a couple of seconds. I think it was still lasing a little, but was otherwise LED. I think it was probably being overdriven as well.

- Lastly, I have an SD-303 (looks/handles same as Lazerer LZCS) 405nm that apparently went zombie on me. I don't think it was ever run very long. It is definitely still lasing, but appears to be 10mW or less in power as I can feel no heat from it at all, even when focused to a point. The diode output profile is strange, it looks cool actually, I'll try to remember to post a picture of it. Part of it is incoherent and gives off blue and even a little green light. The rest seems to still lase, as the laser speckle is there, but it looks like a multi-mode situation is going on and it flickers and mode-hops a lot. From a distance and slightly unfocused, there is also faint golden glow. This laser appears to be stable, and deliberate 10+ minute suicide runs haven't damaged it further. (the LZCS does have a function, if small, heatsink.)

Wall of text but there is the baseline for abuse leading to failure. Here is what I don't understand:

- I have another Laser 301, the plastic insulated kind, that has been run so long that it got hotter than hell, never mind the insulation. This has happened more than once. It's also been dropped dozens of times. No idea how, but apparently it is still at 100% output, there hasn't been any reduction in heat or burning power at all.

- My Lazerer 450nm has gotten warm/hot a couple of times due to the button having no resistance left. I was carrying it in a pocket and it had been turned on. I have lots of holes in my pockets because of this laser. I can only carry it with the key turned off now. It's also suffered the usual drops etc., more than my other lasers. I'm pretty sure the diode is the OSRAM PL450 though, and from what I gather these are very hard to kill, even deliberately.

- I abused my ebay Laser 301 532nm units by running them 10+ minutes just to see what they would do. They were dirt cheap and I figured they would give some kind of warning before dying since they were DPSS. They still are DPSS actually, they eventually would mode hop a bit, but none of them died and the only thing wrong with them today is that the cheap plastic lenses are scratched. The laser cavity itself works just fine.

The 405nm's (PHR diodes?) seem most prone to dying but even then you can't tell, it seems very random. I'm surprised at how durable the cheaper lasers can be, especially the 532's. Not sure how the ebay-type 650nm lasers hold up.

Not sure what else I can say about that, all of my other lasers are working normally and show no signs of damage.

My ebay 650 nm pen is still fine and I tape its power button down for 10 minutes at a time to do photo stuff. Out of my 3 ebay pens (a 405, 532, and 650) only the 532 gets warm with continued use, and I assume thats because its actually a IR diode probably in the 300-400 mW range being used to pump the DPSS.

I'm hoping I can keep my lasers alive for a while. I only use them at night while I walk and I generally have a song playing on repeat on my Zune, so i'll usually run a unit for about 5 minutes, and then leave it off for the same amount of time. It's been really cold at night recently, so I haven't had an issue with my lasers getting even a scant bit warm, but I still keep them a 5 minutes on and 5 minutes off. I'm curious to see how long my PL-E Pros can go before getting a little warm when the temperature isn't so cold.

Marco Polo said:

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You either have extraordinarily bad luck or 405 diodes are as fragile as I've been reading. On the contrary I hear 445s are virtually bombproof?

Interesting accounts, though. I sure hope I get good use out of my lasers before they go pop... but I'd rather they didn't go pop at all! :can:

A final question, if I may - what exactly is a laser "going LED"? I figure the diode basically craps itself but what happens to the light, is it no longer coherent anymore? Can it be used as an ordinary handheld light thereafter?

trencheel303 said:

You either have extraordinarily bad luck or 405 diodes are as fragile as I've been reading. On the contrary I hear 445s are virtually bombproof?

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I was talking about lasers to someone today and about how if one is into lasers there are exciting times ahead. I was explaining why I think certain diodes are prone to failure while others are not. The explanation (hypothesis) I came up with I came up with is that reader/burner diodes were never intended to be viewed or used for any type of display. How bright they look was never supposed to matter; all they were meant to do was read or burn discs and the diodes just needed to be run at or maybe even below spec to do that and avoid heat issues. They don't need to be overdriven or stressed to function in a disk drive, and their maximum continuous run time is limited to the time it takes to burn a DVD or Blu-ray.

Thus, these diodes (i.e. 405's, certain reds, 780nm IR's) weren't designed with excess capacity or durability in mind. Why should Nichia or whoever spend money to do that when they would never see a return on that R&D investment? In most cases, the disk drive mechanism will fail, or the computer be obsolete, before diode life ever became an issue. And if, on the off chance, it did become an issue, optical disk burners are cheap enough that you would just buy a new drive.

Enter laser/pico projectors. Completely different ballgame; a projector light source must be BRIGHT and it has to run for hours, maybe even days or more, at a time. The light source must be able to do this reliably, on demand, without issue. It must be able to tolerate occasional high temperature excursions due to poor cooling, as could happen if a curtain or similar object fell onto the unit and blocked the air flow. To me, this explains why the Opnext 638nm, and the OSRAM 450nm and 520nm diodes are so hard to kill. What else could it be? They have to run at high power, for long time periods, and they need some heat tolerance, otherwise they would be useless in a projector.

A final question, if I may - what exactly is a laser "going LED"? I figure the diode basically craps itself but what happens to the light, is it no longer coherent anymore? Can it be used as an ordinary handheld light thereafter?

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It stops lasing, but still emits a dimmer, incoherent light of similar wavelength to its lasing wavelength. Or maybe not necessarily, that zombie 405nm emits some blue, green, and even yellowish. Once the diode turns LED it's done for and can't be fixed. Usually the result of damage to the mirrors/facets due to excessive heat or current, but can also happen if the laser beam is reflected and focused back into the diode. It's a disappointing event.

Ive thought about this too. Your right about that.
I got a m140 that runs for 2-3 mins sometimes. I even fell 6 feet with it my hands and while gasping it. I broke my fall with my hands and that sucker slapped the ground with some force. still runs like a champ. as for the DPSS they are some of the most snobby I have used.

Marco Polo said:

...The explanation (hypothesis) I came up with I came up with is that reader/burner diodes were never intended to be viewed or used for any type of display. .....

Enter laser/pico projectors. Completely different ballgame; a projector light source must be BRIGHT and it has to run for hours, maybe even days or more, at a time.......

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