I didn’t find much information about this but I read a couple of papers about using thin water streams to measure power of multi KW lasers. I know water has good absorption of near-mid IR, has any one tried to measure CO2 laser power by heating up a known volume of water for a set time and measuring the temperature difference?
at the very least to check the life of the tube and not have to pay $300 to buy a calibrated power probe.
Ever heard of the russ’ dohicky?
i bought mine half a year ago or something from him.
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yes same idea but I thought with water’s excellent IR absorbtion there would be no need to calibrate a block of aluminium against a known probe since there wouldn’t be much reflection if any.
Sounds like an interesting idea. The volume of the water needs to be very exact though.
true, I was thinking distilled water in a styrofoam container and keep the laser moving in a small circle to avoid any phase transition issues and probably better distribution of the heat.
I wish 
No I just bought an 80W tube to replace my 60W and I was curious to see if I can verify that the tube is functioning properly. I just thought it could be an easier and affordable alternative for general maintenance activities that doesn’t cost as much as the expensive analogue probes or rely on a device that’s calibrated from a one…not that there’s anything wrong with Russ’ dohicky.
perhaps weighing the water using a micro scale would be the best measure of the small volumes needed to make this process quick?
If there was a low cost method to measure the laser power I would certainly go with it just to satisfy my curiosity. I replaced my supposedly 55W tube which had no indication if it’s specification on it with a new branded tube. I would love to know what the power actually is.
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If my tube was not 55W I would simply have knowledge of the fact that it’s not. Given my Laser machine is a China no brand (although it looks the same as the OMTech version) there little chance of contacting the supplier as he is just a middle man. But then I knew all of this when purchasing.
Now that I have a decent brand of tube installed I have more confidence in it being what it is supposed to be, but it would still be a ‘nice to know’ factor.
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I’m going to run some tests and let folks know that if it works and if it’s worth the hassle.
To those not interested in measuring what they do, all the best to you, this a discussion for people interested in testing 
I have Russ’ meter and love it. Primarily because it’s digital, and 100% repeatable. Initially I was going to run an annual test to check on my tube. but after an overheat caused by a faulty in line flow switch, I now test biannual. Run the test five times for each power level and toss the high and low, average the other three and you have something you can drop into Excel and create a power curve.
My QC reject factory tube has a power curve that looks more like a quarter circle, but it did tell me I hit my 80W at a little below the working max mA rating.
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No matter how you do it, the same kind of variables apply
You can move the laser around, but that still doesn’t give you a distribution of the heat within the mass of the water. If the ‘lid’ is open, you lose heat. If you stir it, you lose heat to the stirring device. While you wait for it to distribute, you lose heat. How much heat is directly related to the temperature difference between the surfaces, the more difference the more heat loss.
Simple fact, if there were a good, cheap way of doing this, it would probably be all over the Internet and all of us would be using it.
Cheap, simple way, buy a crystal ball and believe it… 
There is the Mahoney meter
https://bell-laser.mybigcommerce.com/mahoney-co2-laser-power-meter-probe-0-100-watts/
and the dohickey from Russ.
Best options that I know of…
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Great advice, I was worried about all the heat loss and propagation variables as well hence my original question hoping that someone who has a probe has done a side by side. My thought was to come up with an insulated container(styrofoam) with a very small exposed surface area(a tube shape) and volume( big enough to fit the thermocouple and keep it away from the beam).
And you are right about the fact that if it could be done it would have probably been all over the internet, but I’m actually surprised about how little there is about heating water with a co2 laser…you’d think there’d be hundreds of videos…I found exactly 2 
I wanted to order the Mahoney but saw very mixed reviews about Bell Laser. Do you have any experience ordering from them?
I have one of each. Like having a digital volt meter and a mechanical volt meter. Both work well.
Couldn’t find the cost for his ‘dohickey’, but I’m sure it was less expensive than the Mahoney.
My ‘China Blue’ 50 watt measured out at about 44 watts. About right for an 880mm length tube. The power supply is a 60 watt supply.
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The replacement tube for our laser - a Reci W6, was a bit over $2200 in AUD a few years ago… it’s not such a simple toss it out and buy another like the sub 100 watt tubes.
Monitoring its life is useful, to be able to predict the beginning of the end and have a spare ready - considering also that overseas postage is so slow in these Covid days.
Yeah, being able to make periodic checks will give you plenty of heads up to know you need to start shopping. Lets you do a power curve to know your individual tube characteristics as well. My factory QC reject has a power curve that looks more like a quarter circle. Even a 1/4% change at the controller makes a few watts power change on the low end of the curve.
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