Why is the surface of my detector damaged when it is supposed to handle much higher power?
Tuesday, September 14, 2021
So your laser power detector is supposed to be good up to 110W and you damaged its surface with a 30W laser? Sounds familiar?
Why is this happening? Let’s find out!
Maximum average power vs. maximum power density
When choosing the most adequate power meter to measure the power of your laser, you should not only look for the maximum average power that the detector can take, but also the maximum power density that it can handle.
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In other words, not only how many Watts can be absorbed by the surface of the detector without damaging it, but also how much power by cm² that you can apply on the absorber.
Therefore, when we list the different capabilities of our power meters, we always specify damage thresholds for both average power and power density. Understanding your laser power detector spec sheet is important and actually quite simple once you know the terminology.
Of course, the beam size and shape will impact the power density of your beam. Hence, when the power density of your laser is close to the damage threshold of the detector, we recommend expanding your beam on the absorber surface to avoid damaging it.
Expanding the laser beam
Our general recommendation is to expand the beam to cover between 40% to 60% of the detector’s active area. Expanding the laser beam and centering it on the absorber will result in better performance since the heat will be completely absorbed and transferred to the power meter. It will also help you achieve more accurate measurements. Read this blog article to learn our expert tips on how to make the most accurate power measurements.
Beam shape
Also, the shape of the beam is important to take into account. Having a Gaussian beam versus a flat-top beam will result in more power concentrated in the center of the beam. Therefore, the power density will be higher in that location.
The rule of thumb when you calculate your laser's power density is to double it for Gaussian beams and triple it if you have a beam with hotspots. This must be taken into account when choosing the right detector as well as how much you need to expand the beam.
Gentec-EO offers different power meter models that will fit most applications needs, and we are always happy to work with you on projects that push back the limits of laser power measurement. You won't find them in our off-the-shelf offering, but we've made instruments that can handle more than 120 kW of average power, and large-area calorimeters for extremely high intensity pulses, in the kilojoules range! From the largest aperture size (up to 280 mm and more) to the high-density power absorbers (up to 100 kW/cm²), we can help you find the measurement solution you need.
Our product finder is a very helpful tool to identify the best measurement instruments for your laser. Give it a try! Also, feel free to contact your local representative for help.
