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Thread: DIY or cheap Bolometer/Pyrometer (aka Optical power meter) ?

  1. #1
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    Laser Warning DIY or cheap Bolometer/Pyrometer (aka Optical power meter) ?

    Hello,
    i was wondering if there are ways to measure the true optical output power of a photon emitter, as i am thinking of comparing several laser modules of different beam characteristics (and wavelenghts).
    Since the human eye is easily deceived, i would like to have an instrument to do this.
    I have read the articles in wikipedia about this, and searched the net for "DIY Bolometer" and "DIY Pyrometer", but the results showing up are for thermal imaging, not measuring. Or, if they are intended for measuring, it is for furnaces
    and ovens.
    On ebay, only devices for RF (mostly microwavefreqs) power measurement show up.

    How do You guys measure the output power of Your lasers?
    Do You "just trust" the vendor?
    What Instrument is good and affordable?

  2. #2
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    Yes, the device you are searching for is a "Laser Power Meter".

    Not everyone has one, but when we host a Laser Enthusiast's Meeting, there are usually a few people who bring their power meters with them. That way everyone can test their lasers.

    It's a handy device to have, but it's not a requirement. If you don't have one (and many people don't), then yes, you basically have to take the manufacturer at their word when they quote the power output of their laser. Although today it seems most manufacturers are pretty honest when it comes to their output power claims. 15 to 20 years ago this was a major problem, but today it's rather rare (at least in my experience anyway).

    There are different types of power meters, based on your desired accuracy and the range of power you need to be able to measure. Some of the more affordable models use a simple photodiode as a sensor, while others use various thermal sensors to measure the beam power. There was a popular hobbyist power meter that used a Thermo-electric cooler (Peltier device) as the sensor, although I can't remember the name of it at the moment. It was a reasonably accurate unit for the price, though. EDIT: Just remembered the name - The Laserbee.

    The venerable Coherent Lasercheck wand is an affordable and reliable laser power meter that can handle up to 1 watt of power. It includes a wavelength correction factor, so you need to be sure to set the wavelength before you perform your measurement. They used to retail for around $400 on EdmundOptics.com, but you can find them on the used market for half that. (Check ebay)

    For higher power lasers, you'll need to purchase a bench-top laser power meter with a separate measurement head. ThorLabs, Ophir, and Coherent are good companies to start your search, but keep in mind that retail pricing can get pretty steep on these units, so be sure to check the used market for deals.

    I currently own a ThorLabs PM-10, and it's very nice, but I also have two older, home-made meters that were built using calibrated heads - one from Coherent (6.5 watts max power) and one from Ophir (15 watts max power). So long as the calibration on the head is good, you only need a stable voltage source and a digital voltmeter to read the output from the head. All three of these meters read very close to the same.

    I even have an old Coherent Lasercheck stuffed away in a box somewhere, but I haven't tested it against any of my other meters recently, so I don't know if it's still as accurate as it used to be. (I had to change the battery in my Lasercheck, and this can cause the calibration curve to be scrambled.)

    Adam
    Last edited by buffo; 05-03-2022 at 16:36.

  3. #3
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    Search string "DIY Laser Power Meter" using a Peltier Element will get you there for more modest powers.

    I'll post back later with a link to my favorite modern micro-power design.

    The Attached circuit will do it "The Old Hard Way" and is obtained from citeseer.penn.edu. It's saving grace would be using the PT100 series sensors. A more modern op-amp or Diff-amp wouid be called for.

    No one today would build it that way, but since you mentioned bolometer...

    Steve
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    Last edited by mixedgas; 05-04-2022 at 09:50.
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  4. #4
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    Ah, I was searching for VK2SAY, I needed the genius of VK2ZAY,

    http://www.vk2zay.net/article/210

    For very low power levels..

    Steve
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    Quote Originally Posted by mixedgas View Post
    Ah, I was searching for VK2SAY, I needed the genius of VK2ZAY,

    http://www.vk2zay.net/article/210

    For very low power levels..

    Steve
    Nice find, Steve! Thanks.

    I purchased a J. Bauer LaserBee USB Power Meter a few years ago. It worked very well. I compared power readings (in the 40-500 hundred milliwatt range) between it and my far more expensive (but now hard to find) Coherent Radiation's Model 210 power meter and they were in close agreement.

    Here's a link that can direct you in that direction: https://laserpointerforums.com/threa...ock-now.80627/
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    Here's a thread with a lot of links and resources for building DIY laser power meters: https://laserpointerforums.com/threa...rojects.71234/

    The problem is that with any kind of DIY meter, you still need to calibrate it to a proper meter in order to make it accurate. Without calibration, you are basically blind, the reader could be fairly accurate but it could also be entirely bogus, you just don't know, because sensor behavior can vary from batch to batch. So it's best to buy a cheaper meter from a guy that does the calibration for you, like the lasersbee that has been mentioned earlier in the thread.

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