Watt’s up, Doc?

February 24, 2013

power_test 3

So finally after about a year on the back burner, I finally managed to get some time in on the LASER. I have been slowly acquiring bits for the re-build over the past year, but this is the first real hands on moment I had for a while. One of my more recent acquisitions for the LASER was a 100W power sensor for measuring the output power of the LASER. The idea being that I would use it to monitor the health of the tube and my optical path once I got everything up and running. I also wanted to have an idea of what the real power was of my “free” LASER that had been sitting around for about 3 years before I got my hands on it, and then another year now on my shelf. So while the LASER was relatively new before being relegated to the scrap heap, a lot has happened that could have resulted in a drop in performance of the LASER. I’ve herd stories of the glass tube LASERs dropping in power output, even if just sitting on the shelf for a while… So I’ve been wondering if the same is happening to my LASER.

power_test 4

As a result, today I dusted off the LASER and set it up on one of my work benches at the office. You can see the sensor sitting between the LASER and my “fire wall” in the image above. I had to use some scrap metal here as my firewall because there is no concrete wall behind my workbench. The rest of the set-up is exactly as before, with the key-switch on the safety loop, and a two-way momentary switch for the red aiming and CO2 LASERs. The sensor itself is made by Coherent and bears the model “100W SINGLE SRV”. Unfortunately I can’t find any official specs, so all I have to go on is what the seller has told me. If anyone has any official info on this sensor, I’d love to see it.

power_test 1
According to the seller it is a thermopile sensor [makes sense as that is one of the main types produced by Coherent] and that it generates 0.6mV/W [this is a little off from the current standard offerings from Coherent, but this may be a custom sensor] A thermopile sensor is essentially an array of thermocouples embedded in a ceramic substrate. The substrate is typically designed to maximize absorption at a particular wavelength of light [10.6um in this case] Thermocouples are made by bonding two dissimilar metal wires. One end is exposed to the heat/energy source, and the other is kept cool [ambient in this case] The thermocouple generates a voltage relative to the temperature differential between the hot and cold ends, as such ambient temperature has no effect. on the overall reading.  And in this case the particular thermocouple chosen generates a voltage that is proportional to the power applied.

power_test 2

And there it is, you can see the meter showing 18.686mV which translates to approximately 31W of power. I repeated the measurement several times, and got powers all in the same range, with the highest being a little over 32W. This is in-line with my LASER as it is rated at 30W, so either the LASER is outputting a tad more, or the sensor calibration is a little off [or a combination of both]. Either way it’s a decent reading, and seems to indicate that the power level of my LASER is where it should be.



  1. did you ever find a replacement stepper motor for the Y-Axis?

    • Not one I could get readily, as a single piece. You may find acceptable ones on eBay, but that’s just luck of the draw. I recently started on a total redesign, with my own chassis and rails, because after further investigation the existing one is far too damaged and warped from the fire. As a result I can design to use whatever steppers I can get and fit my needs.

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