Topic: 523nm DPSS Laser Does Not Modulate Well

[cfavreau]

To summarize the issue:

My DPSS module does not modulate very well.  It turns on/off very slowly.  When scanning it ramps up.  It turns off fine    I am using TTL modulation right now, so I assume that analog is going to be that much worse.

My module looks like this:



I know it does not say much.  I removed it from a laser pointer that ran on 2xAAA batteries.

When it was in pointer form I noticed that running it for a few minutes would cause it to get hot... so I added a big hunk of aluminum (to keep the temp. fluctuations to a min.) and a fan.. I removed the fan as it didn't make a difference.

I measured the current draw before I removed the driver and it was appx. 290 mA.  I set my driver for 270 mA to be conservative however it took a while ( > 5 minutes) to warm up...  I then set it for 333 mA and found that it worked much much better ... and a bit brighter too.  It still has all the issues though.

Does anyone have any idea of how to improve the response?  Or should I just buy another module?  If anyone has any suggestions for the modules that would be great too.

[Fanny Pack]

Just buy something else.  A laser pen isn't going to do much for you in a projector anyway.

[James]

What the hell? He already has this! Why not work with what you have? If it fails, learn a little and get something else.

James. 

[cfavreau]

I was hoping for something of a bit more technical nature for a response.   I disagree about the pen not belonging... as all they are are laser modules which are found in projectors all the time.  I agree on maybe getting another one.

I would like to know why (actual truth or speculation) the sluggish modulation.  I figured you guys would explain it more along the lines of a software engineer...

Also if anyone has some good suggestions for a DPSS module/pointer/laser that responds well to modulation I would be grateful.  5 to 15 mW range .... < $100.  ... or an 808nm diode, 200 to 300 mW that I can use for the one I accidentally killed last year (5.6mm case).  That one originally cost me an Argon laser many years ago and is of much higher quality.

I do have a 15mW module from Axis however I was saving it for something else.  It has TTL modulation (however I would like analog modulation and the driver I have can be modified to suit a larger module).

Thanks James... that is the direction I was hoping for.

[Fanny Pack]

What the hell? He already has this! Why not work with what you have? If it fails, learn a little and get something else.

What does he have?  Laser pen guts that don't modulate well.

[James]

I would also be interested in this EXACT same line of thinking. I have a couple of greenie pointers too!  :

James. 

[meandean]

  I have a small laser pointer that can produce a healthy output, but only when it's warm. When you start it cold, it's very weak (about worthless), but if I put it in my pocket for awhile it lights up strong quickly- it's very temperature sensitive. Try
heating your unit a little and see what happens- if it behaves like my pointer, you might consider rigging up a simple low temp heater blanket for it.

[James]

Let's not forget that good old resisters are............................... HEATERS!

James. 

[meandean]

 Sadly, temperature regulation is not easy, as the unit runs it needs cooling, but if it sits awhile, it needs warming...

[James]

DrLava knows a lot about this. He has done exactly what this thread inquires about. He's also the guy who designed, made and sells the FlexMod diode driver.

He knows a lot about driving TEC devices for cooling and using resisters to heat other parts.

He's on this forum.

James. 

[cfavreau]

*** Paging Dr. Lava.  If you happen to read this thread, any advice would be very much appreciated.

I noticed the temperature thing too.  Mostly if mine ran too long it would dim because of poor heat dissipation.  I put it in a nice sized chunk of aluminum to help stabilize it.  I have read a little bit about the temperature stabilization over on Sam's laser FAQ.  However the 15 mW laser I have is just in a big heat sink and is not actively stabilized and uses a constant current drive.  It seems to do OK.

I think I can heat it up just by taking it out of the aluminum.  I will try that tonight and see where that goes.  Also I am going to try throwing a bit more current at it.  It might blow up ... it might not.  I have see similar "looking" modules doing 100mW not that I think mine would do that.  I have heard that DPSS lasers can be very non linear so that may be one issue I am dealing with.  I would settle for ALL on quickly .. and ALL off quickly.

[James]

From what I understand, there is a problem with thermal hysteresis in the frequency doubling crystal. The crystal itself does its job with varying efficiency due to temperature..... It is being pumped with a randomly varying amount of IR.... Put the two together and you end up with a crystal that behaves in a very unpredictable way.

Analog modulation of an IR diode should produce results much like any other direct injection diode would.

James.