Topic: 200mW DPSSFD Labby not behaving well to modulation

[dtewksbury]

When you say you messed with them, does that mean you took them apart?

This is what I was worried about, I have this laser that has good power, a great beam profile, but just doesn't modulate properly anymore. My worst fear would be that I take it apart and wreck it, that would suck.

Do you think it is OK to take the top off and have a look? I was hoping I could measure the TEC and check that it is working. The reason I think that it isn't is because it doesn't seem to get warm on the outside. I would assume if the TEC was working then it would be pumping heat out, or getting cold if it is heating.....

[James]

It's a bummer these things are not polarized.

An AOM wastes most of the power, but it does work.

James. 

[dtewksbury]

I use PCAOMs a lot at work, they are sort of cool, but I find them a bit temperamental, and often don't get near the 80% efficiency they claim. They are probably OK if you just want to modulate one frequency, but it is certainly easier to modulate the supply (assuming the laser likes that).

[James]

I have both a PCAOM and an AOM.

Yes they throw away lots of power, but they give you an amazingly accurate linearity.

You can use the waste beam elswhere.

If you have a white light, you should not have much of an issue finding the sweet spot on a PCAOM.

If you have to align an Ar and a HeNe, it's a bit trickier.

If I could get a polarized green laser, I'd sure think about using an AOM.

James. 

[BlinkenLights]

you can replace the modulation circut with a FLEXmod from dr lava. that should be an easy fix

[Fanny Pack]

I doubt it is the modulation circuit that is the problem.  I have run into green modules that exhibit the same behavior.  Even connected to a known good driver they just don't modulate well.  I have one module that puts out 100mw but is worthless except for either full on or full off.  When I first got it, it wouldn't even put out a single beam except at full power.  Between off and full power it would have two beams.  I repositioned the diode slightly and was about to get a good beam but with the very slow modulation.  I will probably either put it in a lumia wheel or use it in TTL mode with one of my spare galvo sets.

But anyway, I don't know if it is the diode or the crystal causing the problem.  I know it isn't the TEC because these modules don't have a TEC and one identical unit works just fine... 

[James]

and one identical unit works just fine... 

Wow.

That kinda' makes it sound hit or miss.

James. 

[drlava]

It's true, it's the nonlinearity of the crystals combined with local heating effects of the pump diode.  As you can tell, the laser thermal zones were tuned with output at 100%  If you re-tune them with output power at 60-80% then you will probably get a better modulation curve at that area.  But that's only part of a solution.  the best solution is to use an optical feedback modulation linearizer. 
(inputs: small sample of green light power converted to voltage, modulation control voltage from DAC.  Output: compensatory modulation drive signal to laser modulation input that is processed via rela-time stabilized loop)

If that module doesn't have a TEC then you won't be able to adjust for thermal zones.  It's just the luck of the crystal/diode draw.

[Fanny Pack]

The modules I have is one of those Aixiz 50-80mw tuneable jobs that they are selling at their ebay store.  I have 3 of them.  My original has been working fine since day 1.  The 2nd has the problems I mentioned.  I haven't even tried the 3rd one, yet.  One of these days I need to go through all my stuff and either use it or get rid of it.  I have a bunch of blu rays and red diodes, optics, scanner sets to make a couple more scanners but have never gotten around to it.  I kind of laughed when I won that 20K galvo scanner set at SELEM.  They are still in the plastic bag on my bookshelf.   LOL.

[dtewksbury]

OK well it sounds like this is a common problem. I will investigate further.

[cfavreau]

I have one of  those Axiz modules as well.  It modulates OK... much better than the pointer I have.  It does have a problem with modulation speed.  It has tails where it ramps up and down.  This gives a nice artistic effect though.   

Off topic:  want to sell any scanner sets?  I am looking to build a 2nd projector and would like to have something with a nice small power supply (instead of the G100's with big honkin linear supplies).

[BlinkenLights]

tails are not normally a modulation issue, more commonly thats because your galvo's and your modulation are out of synch (or rather not properly out of synch) 

[James]

That's not entirely true with DPSS lasers.

They do not go black the instant you cut the power.

So it's not just a matter of aligning the color modulation signals with the delay of the scanners.

James. 

[BlinkenLights]

well you can also stop tails with more dwell at the end of lit segments.

[Lazerjock]

I have one of those Axiz lasers too. I modulate it with a Flexmod driver. It seems to work fairly well for what I do. It took me a couple trys to get them set right though. I blew up 2 before I got it right. I would have blown up this one without Dr. Lavas help at SELEM.
Third times the charm (right)?