# DIY laser power meter?



## jspeybro (Nov 2, 2011)

Hi,

I searched the forum but couldn't really find an answer so let me ask the question.

Does anyone know a rather basic circuit diagram for a laser power meter using a photodiode that allows to change the offset (caused by the operational amplifier(s))?

I'm aware of the power meters from laserbee, but the wavelength range is not right (basic thermopile), I need an InGaAs photodiode to be able to measure the power. Since this is not much different from a normal silicon photodiode, I suppose a circuit for a laser power meter using a silicon photodiode should be fine.
regarding calibration, I have a power meter available to compare it with so it should be possilble to calibrate it, it's just that this power meter is too bulky for the measurements I need to do. Power levels are within class 3B so less than 500mW.

it's ok to use a multimeter to measure the current or voltage (depending on the circuit I guess). 
Preverably, the circuit should allow for battery powered operation (e.g. 3V or 9V), but several DC voltages from -15 to +15V are available as well if that would make things easier.

The main problem is actually that the only power meters that are available with InGaAs sensors, are fiber based, which doesn't work in my application.

any help appreciated.


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## bshanahan14rulz (Nov 2, 2011)

http://laserpointerforums.com/f51/openlpm-free-open-source-lpm-project-68498.html

Mostly thermopile based. Perhaps you can find a thermopile with a better coating for your wavelength.


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## jspeybro (Nov 3, 2011)

Thanks, I'll have a look at that.

Oh, I'm sorry, I forgot to mention that I also don't have a lot of space to put the detector in the beam path, usually this is not more than 1.5cm (thickness of the head) in 1 of the positions that I need to measure the power. 
Most of the space taken by the thermopile is probably the heatsink. I suppose it could be possible to redesign the heatsink to allow it to fit it between the components.


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