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Powering a Laser Diode and what to do with it...

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Turkey9

Mon Nov 28 2011, 04:37AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

Hello all,
I got my hands on a piece of test equipment that is basically a high power laser diode and a coil of fiber optic material exiting in a normal fiber optic cable (the orange sleeved kind). The warning label of the back of the thing says: GaAIAs Diode CW 20W max class IV laser product. The warning label also says "Invisible Laser Radiation." What kind of diode is this? UV or IR? Can I assume that the diode is actually 20W CW max or is that just a ceiling they put of class IV lasers? The thing is mounted on a college-dictionary-sized heat sink so I imagine it is closer to the 20W spec than anything else. The device has a lot of fancy control circuitry that looks to be controlled through a computer serial port. What kind of drive circuitry is this thing going to need?

Lastly, what can I do with a laser this size other than burn things? I was thinking a small laser cutter if the beam is IR.

Thanks for your help and I can post pictures if that would help!

EDIT** I opened up the device again and found that the laser is a SDL-6460. I also found a datasheet that says it is 915nm and 17W. The threshold current is 6A with a operating current of 28A and operating voltage of 2V. The actual diode is already coupled to some polarizing fiber optic cable. How to I drive this thing? Does it just need at least 6A @2V to run?

Thanks!
Jesse

Daedronus

Mon Nov 28 2011, 08:48AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

Just keep the optic and use a constant current power supply to power it.
You will also need to actively cool it. Peltier or a water cold plate.
A simple computer heat sink will not do, since the diode is not meant to work much higher then 25 degrees Celsius (unlike our everyday processors that run quite hot)

Conundrum

Mon Nov 28 2011, 09:49AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

I seem to recall that these are pulsed diodes.
Yes, they also need extreme cooling as said.

Interestingly the newer optical drives are starting to use >500mW diodes, in order to burn Lightscribe disks and other media at 52x.
The 8x Bluray writers use a 600mW diode due to the diminshing returns of writing at such a high speed; these diodes can be turned fully on and off at speeds of up to 40 MHz so are ideal for pulsed laser holography.

Turkey9

Mon Nov 28 2011, 04:11PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

It's already mounted on a peltier so I'll probably keep it at that.

When I investigated the power supply board, I found two 150W dc-dc converter boxes hooked in parallel. They are rated for 24V in and 5V out. They have four .02 ohm sense resistors in parallel with the output for a total of .005ohm. The positive output goes straight to the diode and the negative output looks like it goes through a high power filter inductor and then to the diode. Is it alright to have 5V going to this diode or is there some circuitry in there that I'm missing that divides it down again? When you say a constant current supply, do you mean a supply that provides constant 28A at any voltage or one that will only supply 28A @ 2V? Sorry for all the questions, I don't want to accidentally burn this diode out.

The DC-DC blocks have an enable pin on them so I think it might have been used pulsed even though the data sheet rates everything at CW.

klugesmith

Mon Nov 28 2011, 07:26PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1715

Be careful with that thing.
915 nm is in the worst range of wavelengths for retinal hazards.
It's transmitted and focused just (about) like visible light, but is invisible so there's no aversion reflex.
Operating your laser when the far end of the fiber (or its specular reflection) is in your field of view could cause permanent eye injury without immediate pain.

From

:
"Class IV lasers emit high power, in excess of the limit for Class IIIB devices, and require stringent controls to eliminate hazards in their use. Both the direct beam and diffuse reflections from these lasers are damaging to the eyes and skin, and are potential fire hazards depending upon the materials that they strike. Most laser eye injuries involve reflections of Class IV laser light, and consequently all reflective surfaces must be kept away from the beam, and appropriate eye protection worn at all times when working with these lasers. Lasers of this category are employed for surgery, cutting, drilling, micromachining, and welding."

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