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CHEAPO green laser pointer 30mW problem

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LAN_403

EEYORE

Sun May 25 2008, 05:28PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hello all,
I just got a cheapo 30mW green laser pointer from DealExtreme.com for 25$. For the first few seconds, it was awsomely bright! Then the output dropped down to half brightness, and then to near nothing. I cooled it down in the freezer for a minute and its back to super brightness. Now I know that 25$ means its "get what you pay for" crap, but I like to tinker and experiment. I could send it back, but likely get another dud. (The site's forum claim you CAN get a good one, and mine is crap). I just dont feel like sending back a 25$ pointer and waiting to get a new one.

Here is my theory: Laser heats up and the laser diode's wavelenght shifts, thus causing the output to drop out. The crystals heat up and shift, thus killing the perfect alignment needed for good green laser output.

Is it possible to re-align the crystals through freezing, and thawing? Will the device expand and contract enough to maybe fix this issue? Seems the laser can go for 16 seconds before light drops down to half power.
Matt

...

Sun May 25 2008, 06:22PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

There are a large number of possible problems with that laser, you might be able to make it run continuously by mounting the optics assembly on a coldplate, but short of completely tearing the laser down and realigning the crystals (and probably replacing the diode) it is never going to be quite right.

My top theory as to the poor performance is that that laser pointer started life as a cheep 2mw laser pointer, and someone decided to turn up the diode current (the internal driver board has a variable resistor just for that) to get 10x the rated output. So instead of running that poor diode at something like 200mw it is trying to put out 2w and the diode itself is just self destructing.

Bjørn

Sun May 25 2008, 07:00PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

What springs to mind is to measure the IR output of the laser and see if that is constant or if it tracks the intensity of the green light. After doing that you would know more about possible causes.

EEYORE

Sun May 25 2008, 07:49PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hello,
thanks for the responses. The diode ought to be run within its specs. They call it a true 30mW, which they explain as un-modified (or so they claim)...The laser now seems to me to like colder temperatures. I know that laser diodes either need to be heated or cooled to keep it at its sweet spot for DPSS use. Seems mine needs to be cooled. (Unlucky I guess)...I do not have any laser power meters to use.

It does seem to last longer and longer as I cool, then use...If left in a hot car, it sure doesnt take long before the lasing drops out. Holding in the path of the cars AC, cools it and thus "revives" again...Aparently, the metal end of the laser is connected to the innerds. Mayybe a heatsink there would prolong the high power green? Im thinking some kinda Al heatink with fins that I can stick on the end? When it works, it sure is impressive!
Horribly cheap...
Matt

uzzors2k

Sun May 25 2008, 09:42PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Mine works great, and I think I bought the exact same type as you did. I've found that the beam from my laser is split into two for the first 10 seconds, then it merges into one after some use. I assume it's caused by the laser warming up, which is odd since your laser's performance improves as it cools down.

EEYORE

Mon May 26 2008, 12:39AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Uzzors wrote ...

Mine works great, and I think I bought the exact same type as you did. I've found that the beam from my laser is split into two for the first 10 seconds, then it merges into one after some use. I assume it's caused by the laser warming up, which is odd since your laser's performance improves as it cools down.

Hello,
I got the true 30mW model. Uses AAA batteries...
I guess I just got unlucky and wound up with the type that needs to be cooled rather than warmed? Seems most people need to warm it up before it starts working. Ive seen alot of IR diodes that either need heat or lack there of to tune to 808nm. There is no room at all inside to add something such as a micro TEC, so I guess that it will just need to cool down for some time. Just sucks when I am outside, as it is 90+degrees here in Florida! Only takes a few seconds to make it go out.
On a side note, it DID melt some black trashbag, and KILLED a tick I found.

Matt

johnf

Mon Jun 02 2008, 05:39AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

My 30mW laser soon stopped after a few minutes and after taking it apart (not the optics) and tracing out the circuit I found that a surface mount transistor there are a npn /pnp pair was out to lunch replacing it with one that I knew the specs of and the other at the same time it worked with 2mW more in output power as maesured on the laser power meter at work. 18 mW before it died 20mW after rebuilding the electronics.
Only drawback now is that the assembly isn't glued to the tube and shifts sometimes loosing contact with the batteries

lpfthings

Mon Nov 24 2008, 01:00PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

You got the "You get what you pay for" part right!

On the other laser forums I frequent, the DX lasers are very popular (Now banned in the US, though).

I have had a few of these, and I have found that they liked to be WARMED UP before they were at full power!
You had a pretty good idea of why it was dropping in power. The crystals used in the DPSS process are quite heat sensitive. A difference in 1 degree C can result in a huge power loss or gain.
The 2 dots is known as "Mode hopping", and like you said, usually happens when the laser gets too hot or cold. That again is caused by the crystals. If you got a magnifying lens on the laser while it was "low powered", you'd probably notice it is also mode hopping, its just a natural occurrence for DPSS lasers, especially the non-temperature controlled ones.

I can confirm these lasers arent "Pot modded", or current modified to be specific. They are good lasers for their price, and some DO actually meet spec ( A friend of mine bought the 100mw model, it was doing about 160mw!)

Dealextreme is a gamble when it comes to lasers, you can get one that is DOA, or one that wayy overpowers what its rated for.

Good luck!

Sulaiman

Mon Nov 24 2008, 09:27PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I recently bought two green laser pens from china (eBay), one 5mW and one 50mW.
I must be lucky as both have no noticeable temperature effects.
I really like the 50mW laser .. my own 'light saber':-D

Update; one month after writing the above, the 5mW green laser pen needs about 1 second 'warm-up' before a nice green beam appears.

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