LaserUser.com Forum (formerly RDWorksLab)

I was curious if anyone has some good insight into measuring power output levels. Obviously I've watched Russ's videos, not sure if he still makes that little doohicky (I've love to buy one if so, but no responses so I figure he's busy). As such I've contemplated another possible route via the specific heat of water. I'm thinking I'd get one of those $10-$20 scales capable of hundredths of a gram measurement and then fill a little container with say 50g water. If we know the starting temperature of the water we should be able to calculate the Joules/calories and thus the watts required to turn the missing quantity into vapor.

Example:

Start with 50g water.
Fire laser at whatever level you want to test for 20 seconds into it.
Measure new water mass. (For our example 47.03g)
Joules Used (997.92J) = 4.2J/g (Specific Heat) * 2.97g (Mass 50 - 47.03) * 80c (▲Ht - Ambient 20c to vapor point 100c)
997.92J / 20 seconds = 49.896 Watts

Does this sound reasonable for a test mechanism? Obviously this can't easily be used before the mirror system, but should work quite well on the work table I'd imagine. Thoughts?

I do not know if your method will work or not- I got this from Russ about how to contact him and will work on a way to make this process easier. Gene

Hi Gene
Yes, You Tube canned their message service a few months ago. Add a comment with an email address. Comments always get auto copied to my gmail. I immediately remove the comment so no one's email sits in public view.
I have enough work to do responding to my own emails and comments so I rarely visit the forum. I always answer everything no matter how trivial.

Penetration of long wave IR into water is extremely small. a few microns. Firing a 50-100watt laser at water will heat only the surface molecules. Evaporation will be micro explosive bursts of steam and water mix. You may not get accurate weighings of the steam loss.
This can of course be improved with an unfocussed beam.

Thanks, I'll try that! Still want to test the "Chemistry/Physics" way of measuring power since I'd like to prove to myself all those classes back in the day paid off.

Sounds like a good experiment if you have lots of time but I would not consider the effort practical nor would I expect a high degree of accuracy because of a number of variables you would have difficulty controlling. It would certianly give a result that could show a trend but I would be supcious of the interpruted value of power vs the actual power.

Russ still makes and alrkets his DOHICKY - he email is listed in the post below - send an email and he will get back to ya.
viewtopic.php?f=97&t=3745

Yes, Russ does still make and sell the dohickey.
I just got mine 2 days ago at a cost of $40 (USA) including the shipping.
Do as Gene's post says.
$40 probably cheaper and easier than reinventing the wheel, I mean the dohickey.

If you buy the Dohickey, pay attention to where you buy the digital meter. If you order one that ships direct from China, you could be waiting much longer for the meter to arrive compared to the Dohickey. If I remember right, the Dohickey took a bit more than a week to arrive.

Thanks all, Russ did get back to me after leaving my email in a comment on YouTube and I've sent payment for the dohicky. Regardless I've also ordered myself a scale and will compare/contrast the two power measurement methods and update this thread on what I find. (I expect shipping on all my parts to take 2-4 weeks).