any info on building a laser power meter?

[MARKLASE69]

does anyone have plans on building a laser power meter ? any help would be greatly appreciated . thanks

 

[pseudonomen137]

Save up $ and buy one - those are the best plans! Unfortunately, without having 5 figure + setups of calibrated, stabilized sources to even calibrate your meter against, its pretty worthless. There's a reason Coherent can justifiably charge $400 for a few bucks of parts shoved into what looks like a pregnancy tester.

 

[BlueFusion]

LOL

 

[Phazonx]

I know its difficult. But I don't know how to do it.

But I'm sure if you knew how, it would be cheaper than buying one.

 

[likewhat]

It is not difficult at all. I have built several of these, the accuracy when compared to commercial meters was always within 10 percent. The laser check one is only accurate to 5 percent anyways. You can build them for like 20 dollars but everyone assumes they wont be accurate enough (as though they really need a super accurate power figure for popping a balloon) so no one does it. If you are building your own laser or modifying another and are interested in how much the power changes, the relative readings will be extremely precise.

 

[TheMonk]

You can try Sam's Super Cheap and Dirty Laser Power Meter.

http://www.repairfaq.org/sam/laserioi.htm#ioilpm3

 

[pseudonomen137]

It is not difficult at all. I have built several of these, the accuracy when compared to commercial meters was always within 10 percent. The laser check one is only accurate to 5 percent anyways. You can build them for like 20 dollars but everyone assumes they wont be accurate enough (as though they really need a super accurate power figure for popping a balloon) so no one does it. If you are building your own laser or modifying another and are interested in how much the power changes, the relative readings will be extremely precise.

Relative readings... sure. Which leads back to my point of not the high improbability that someone trying to DIY a power meter would have any laser source to act as a good baseline from which to draw accurate relative readings. I guess if you just want to know what order of magnitude a laser's power is, that wouldn't be too tough....

 

[likewhat]

Actually you can pretty easily get absolute power readings within 10 percent without calibrating it, that is what I was trying to say. The relative readings with be dead on because you are just making comparisons.

 

[pseudonomen137]

hm. Care to explain?

 

[likewhat]

Sure.

Photodiodes are light controlled switches essentially where the current that flows through them is proportional to the power of the light hitting them. If you know that relationship and you measure the current flowing through it than you know how much power is hitting it. Now how well you know that relationship will determine how accurately you can know the power, but to be within 10 or so percent isnt very hard. If you wanted to get very accurate (like 1percent) you can get a calibrated photodiode and you will have the absolute response that is measure for THAT exact photodiode.

Here is a link to a really cheap photodiode that costs 9 dollars and has the spectral response curve.

http://jp.hamamatsu.com/products/division/ssd/pd041/pd042/pd045/S2386-44K/index_en.html

There is a really easy circuit that you can build and all it needs is the photodiode, a battery, and a resistor then all you do is measure the current flowing through the photodiode and you can back out the power. Since you have the response curve you can use it for whatever color of light you want.

Obviously these things can saturate so I probably wouldnt shoot a 100 mW pointer into it, but if you had a neutral density filter than you can cut the power down to a reasonable number and measure whatever you want.