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Testing of DPSS laser module

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LAN_403

ConKbot of Doom

Fri Sept 12 2008, 12:20AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

I have recently (tonight) 'revived' a 90mW wikedlasers.com green laser pointer from my scrap bin. The switch had broken, and in the process of dissasembling it, I thought that I had broken the module.

Well tonight I finally removed the switch and replaced it with a wire and hooked up some batteries. Sure enough, laser works fine, a little weaker then I remember though. I havent burned things that I remember it being able to burn before, and it doesnt sting the skin like it used to :p...

but anyway, I'd like to build a driver for the laser module itself, replacing the current driver of course.

At work I have access to a nice Agilent power supply with current limit, so to characterize the laser and figure out what I need to drive it with. I was planning on driving the laser with constant current on the power supply, short the leads, hook up the laser, set the output for 0ma, turn out the output, remove the shunt, and start dialing up the current.

To get 90mW out, the laser diode, is probably ~450-500 mW? so it would be taking on the range of 1W input power, correct? What sort of voltages should I be seeing?

After I figure out what current I want to use, I'll make up a laser driver for it, and I was hoping to add a peltier for cooling. Given the inefficienct, I take it that the optics need cooling and not just the diode? I was planning on clamping the module to an aluminum block, and bolting it down with another block on top. Does this seem like the right way to go for that, or is peltier cooling not that effective unless the diode was meant for it?

Thanks,
Jon

...

Fri Sept 12 2008, 03:22AM

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

You can use a constant current power supply as long as you are 100% absolutely sure that there is 0v on the output when you connect the diode, it doesn't have any spikes at turnon/off, and you never EVER disconnect the diode while the supply is on.

As to the current, a 5mw module will take about 250ma, a 100mw module could draw over an amp

You mainly need to cool diode diode, although the vandata (purple disk hopefully) also needs to be cooled.

Also, generally you can keep increasing power until the slop efficiency drops off. Basically, make a graph of current vs output power and see where the slope of the line starts to drop (graph starts to level off). that is about as high as you want to run it.

Akika

Fri Sept 12 2008, 03:59PM

Registered Member #1449 Joined: Sun Apr 20 2008, 04:10PM
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Posts: 4

My low cost Newwish Laser 100mW laser modules and pointers draw only 600mA, so I think the diode is only 500mW.

lpfthings

Sat Sept 13 2008, 06:54AM

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

The diode in a 100mw DPSS will be over 500mw, since the newwish lasers are quite dodgy and inneficient. I have a really nice >100mw CNI module here I use in my laser display, that uses a cmount diode that draws about 1.2A.

plazmatron

Sun Sept 14 2008, 12:30AM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Regarding the peltier cooling, it is unnecessary for such a small DPSS and may actually decrease performance, as may excessive heatsinking.
The reason is that the YAG crystal needs to be pumped at almost exactly 808nm (emitted by the laser diode).
The diodes are specced to put out 808nm at their stated operating temperatures, and cooling below that temperature (or allowing the diode to heat above) will cause the wavelength to drift (approx 0.25nm per degree C). So if the stated operating temp is 30 C, and you cool down to 0 C, the wavelength will be shorter by 7.5nm, way outside the absorption band of the YAG crystal.

In high powered DPSS lasers, or ultra-stable lab lasers, cooling is employed, but is controlled to within 0.1 C to optimize output, the KTP crystal is also maintained at a constant temperature (several degrees above room temp).

I once bonded a DPSS pointer assembly to a metal case, and found that the output would start quite low, and very slowly creep up to spec over several 10s of minutes. To solve this I bonded a high wattage resistor to the case, to use as a small heater to rapidly bring the case temperature UP to around 25 degrees!

ConKbot of Doom

Sun Sept 14 2008, 03:08PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

Thanks for the information, we have bare photodiodes and a case for them for diffusing sunlight to keep from saturating the diodes. I'll see if I can rig up some sort of output measurment device and test out the beam. Too bad I dont know the laser guys at work as I'm sure they would have something I could use.

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