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Some FAQs about green DPSS lasers

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Well, I've noticed that we keep seeing the same questions about DPSS (mostly green) lasers over and over again, so I'm starting this thread to post permanent answers to some of them..

The first thing I'll do is link to the section of Sam's Laser FAQ dealing with DPSS lasers: Sam's Laser FAQ - Solid State Lasers

This link contains the answers to just about any questions regarding DPSS lasers.

If you're still wondering after reading that section of Sam's then here are some common FAQs:

[highlight]Q: Why does my green DPSS laser seem dimmer/brighter at first and then change power gradually over the first few minutes of use?[/highlight]

A: DPSS lasers are much more complex than diode lasers like DVD burner diodes or blu-ray diodes. Because of this, a warmup period is required for the internal parts of the laser to reach a stable temperature (most manufacturers state a warm-up of 5-15 min.). While this warm-up is occurring, the power output and beam undergo large fluctuations, but as the warm-up progresses they become more and more stable until it finally reaches the optimum temperature for operation. This is normal with all DPSS lasers and is not a defect.

[highlight]Q: What is the optimum temperature for my DPSS laser to operate at?[/highlight]

A: It varies from laser to laser since no two DPSS lasers are perfectly identical. The reason that there is an optimum temperature for stable operation is that as the pump diode inside the laser heats up and the rest of the laser heats up around it, the internal alignment changes due to expansion from the heat. These subtle changes are what cause instability. At some point during these changes an optimum alignment is achieved. At this point the laser is at it's peak intensity. Going much above or below this point will alter the intensity and sometimes the beam shape of the output. How much depends on the individual laser and no two are exactly alike.

A good rule of thumb to avoid damaging the laser is to not allow the case temperature to exceed 50C. *Also, being too cold will cause a sharp decrease in output and if it is extremely cold the laser may not work at all. Most typical green laser pointers do not have adequate heatsinking for the laser inside, and so their output may never be entirely stable. Lab-style DPSS lasers typically have several features (thermal and optical control devices) built in to ensure long-term output stability. Due to cost and space constraints, these features are left out of DPSS laser pointers, resulting in a comparative lack of stability..

[highlight]Q: Why does the beam from my DPSS laser seem to change brightness and shape randomly?[/highlight]

A: What you are witnessing is a phenomenon called mode-hopping. Describing why this happens is extremely complicated (more info can be found here: http://laserpointerforums.com/f44/some-facts-about-mode-hopping-28456.html).
Mode-hopping that occurs during the warmup phase, during operation above/below optimum temperature, or during operation while powered by an unstable source like low batteries is not the result of a defect. Mode-hopping that occurs randomly seemingly for no reason at all is the result of misalignment of the internal parts of the laser and is considered a defect. Ideally a TEM00 beam is most desirable. This is a beam with a single spot, brighter in the center than the edges, also known as "perfect gaussian power distribution"

[highlight]Q: Why, after my DPSS laser suddenly stopped working, do I see just a dim red light coming from the aperture?[/highlight]

A: DO NOT LOOK INTO THE APERTURE!!!!!!! This dim red light is actually being produced by an extremely powerful infrared laser. Since IR light is invisible, all we can see is the dim red light. Don't be fooled by the dimness, even in a 5mW DPSS laser the IR output is guaranteed to be at least 200mW, which is more than enough to fry your eyes. The reason that you can see this is because some of the internal parts of the laser have gone out of alignment..

[highlight]Q: How do I refocus my green laser pointer?[/highlight]

A: Focusing commercially made green modules/pointers can be extremely difficult. The lens assembly usually requires a spanner wrench to turn it without scratching the lens, and is usually glued in place. With green pointers in most cases the beam diameter exiting the aperture is narrow enough to permit burning, so truthfully I don't recommend attempting to refocus them to burn things. If you're not happy with the divergence of your laser, you can try to refocus to correct this. Once you have broken the glue bond and loosened the lens assembly enough to turn it, then refocus it using this calculator to obtain the desired divergence value: pseudonomen137's JScript mRad Calculator

By measuring the beam diameter at the aperture and again at a given distance, you can calculate the divergence in mRad.

These are just some of the top questions that I see asked here frequently.. I encourage anyone to add to this with other questions and/or answers they may have or may have seen..
 
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rog8811

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[highlight]Q: My laser has suddenly stopped working, what is wrong with it?[/highlight]

A: Always assume it is flat batteries in the first instance, replace with fresh batteries. Make sure you put them back in the right way round. As a rule of thumb green lasers need the negative end of the battery toward the laser module (where the light comes out). Most other types and colours will have the positive end toward the module.

Q: I have measured the voltage of my batteries, they seem ok but laser still not working, any ideas?

A: Did you test the battery voltage under load, ie with the laser turned on? A green laser will draw between 200 and 300ma which will drag the battery voltage down if they are well used. Try fresh batteries.

Q: I have put new batteries in, they are the right way round, laser is still not working, why?

A: Check that all battery contacts are clean and shiney, also check that the threads that you unscrew to get the batteries in and out are clean and shiny as most lasers use the barrel/joining threads of the laser as part of the circuit.

Q: I have done all of the above why is my laser still not working?

A: I don't know but I do know some people who may be able to help.

http://www.laserpointerforums.com/forums/YaBB.pl?board=b_repairs

Be sure to post all important information about what you have done so far.

[highlight]Q: How can I turn my 5mw green laser into a 100mw burner?[/highlight]

A: You can't, in the early days of green lasers it was possible to get a much higher output by messing with the driver. Any mods made to current lasers will almost certainly result in the death of the pump diode.

Some owners of 5mw green lasers have been able to get a higher output by replacing the 2 X 1.5v batteries with a rechargable 3.7v battery and a spacer. I will admit to doing this myself and the laser is still working, I would not recommend doing this mod to a higher priced, higher powed laser as it may fry the crystals or the pump diode.

It boils down to "if you must have 100mw, buy a 100mw laser".

From my site ;)

Regards rog8811
 
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ElektroFreak said:
[highlight]Q: Why, after my DPSS laser stopped working, do I see just a dim red light coming from the aperture?[/highlight]

A: DO NOT LOOK INTO THE APERTURE!!!!!!! This "dim" red light is actually being produced by an extremely powerful infrared laser. Since IR light is invisible, all we can see is the dim red light. Don't be fooled by the dimness, even in a 5mW DPSS laser the IR output is guaranteed to be at least 200mW, which is more than enough to fry your eyes. The reason that you can see this is because some of the internal parts of the laser have gone out of alignment..
But doesn't the question imply that the laser has been switched off and is not powered in any way? Which I would make a logical assumption that nothing will be powered up at all, including the IR diode.
 

rog8811

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But doesn't the question imply that the laser has been switched off and is not powered in any way?
That is not how I read it, I see my laser has stopped working but when I press the button  I see a red glow....


Regards rog8811
 
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lamborgini8 said:
[quote author=ElektroFreak link=1234903304/0#0 date=1234903304][highlight]Q: Why, after my DPSS laser stopped working, do I see just a dim red light coming from the aperture?[/highlight]

A: DO NOT LOOK INTO THE APERTURE!!!!!!! This "dim" red light is actually being produced by an extremely powerful infrared laser. Since IR light is invisible, all we can see is the dim red light. Don't be fooled by the dimness, even in a 5mW DPSS laser the IR output is guaranteed to be at least 200mW, which is more than enough to fry your eyes. The reason that you can see this is because some of the internal parts of the laser have gone out of alignment..
But doesn't the question imply that the laser has been switched off and is not powered in any way? Which I would make a logical assumption that nothing will be powered up at all, including the IR diode.[/quote]


I had meant after a green pointer stops working because it is broken.. I reworded the question a bit to help make it more clear..

PS Thanks for your post Rog!
 
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Is it possible to change the pump Diode (with one from a DVD burner) of my 5mW green ?
(this is an ebay thingy.. Something I won't feel Too bad about killing, but killing it will be sad still)

And also,
How would I be able to PWM my green laser (i cannot just PWM the driver power supply , as the laser obviously wont work..),
Would You suggest I desolder the pump Diode, and put a Transistor inbetween the Diode and the driver circuit ?



Or can I just use an LM317 Driver to drive the diode (IR one that goes into the lens mount with the green crystal in it), and modulate the power supply to the diode.

Then I will be able to PWM the output form a micro-controller, or does the driver circuit use feedback from the diode ?...
in which case it wont work..

This is all part of my RGV pointer attempt
 
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It is possible to change the pump diode in a green pointer, but not with a DVD burner diode. It requires an 808nm diode to make the crystals produce green.

Depending on how fast you want to modulate, you can modulate the supply to the LM317, but special cicuitry id required to modulate directly at the diode. If you use the circuit you've provided, you might blow the diode due to the fact that the signal will not be 100% clean. The signal that reaches the diode must be clean with absolutely no overshoot. You'd need to add filter circuitry after the transistor to make sure that the signal is clean, but the filter needs to be specially designed so that you can modulate at a high rate of speed.
 

HIMNL9

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I suggest you to use a mosfet, or modulate the adj pin of the LM317, instead ..... more safe
 

Nefarious

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Hmm... this only partially answers the problem I have with one of my greenies (got extremely dim and weak after a day of use, supposed to be 200mw)... I guess the answer would be mode hopping? and theres no way to fix it? :thinking:
 




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