"An actinometer is a chemical system or a physical device by which the number of photons in a beam absorbed into the defined space of a chemical reactor can be determined integrally or per time" [Pure Appl. Chem., Vol. 76, No. 12, pp. 2105–2146, 2004].
Therefore, it can be used for the absolute calibration of pulsed laser energy meters. However, there are plenty chemical substances available with certain advantages and drawbacks.
What is the most simple and accurate method to calibrate in the 532 nm (or 565 nm) spectral range with a ns pulsed laser?
Has anyone typical values for the achieveable accuracy from the own laboratory experience which he might share?
Thanks in advance!
First, let me say I agree with Michael's observations about actinometry. Remember, the device and technique was invented by John Herschel (son of William Herschel the famous astronomer who discovered of IR radiation) back in 1825. Back then, there were few ways to measure optical power. Electronics didn't exist. Analytical chemistry was in its infancy, but it offered a way to measure optical power when little else was available.
Since you're asking the question, I assume you're wondering if your meter is correct and you'd like to verify its accuracy. But, measuring laser energy can be problematic. First, you must be careful not to exceed the power or energy density ratings of the detector (actinometer, bolometer, pyroelectric, thermopile, PIN, etc.). It's easy to reach very high levels even with a low power beam if it is focused. You'll get the best reproducibility when you can illuminate as large an area on the detector as practical.
How you verify your meter's accuracy really depends on just what type of detector you are using. Frequently, for a bolometer, there are calibration ports where you can input a measured DC voltage and current. Hence, you know the excitation power and you can generate a calibration curve. Because you can calibrate a bolometer in this way, right in the laboratory, and they are very simple and robust, they are very popular as a primary reference. Bolometers work quite well for CW or pulsed lasers.
For a pulsed source, it's easy to measure pulse repetition frequency quite accurately. With a known PRF and your bolometer, you can measure average power. From there you can determine average pulse energy. If you're looking for peak pulse power, that's a whole different ball of wax. But I assume that's not the case here.
If you have something other than a bolometer detector or one without calibration ports, your best bet is to cross correlate against another well calibrated bolometer. Of course, you could always send your detector back to the manufacturer to be re-calibrated (where they will probably check it against a bolometer). But, that might not be the best option for you.
Anyway, the whole point about the bolometer is that you can use fundamental quantities like voltage, current, temperature, heat capacity, etc. that are readily measurable to a very high degree of precision with simple laboratory instruments. Actinometry is a very indirect route that cannot offer the same degree of precision and accuracy.
I hope this helps!
Thank you Michael and Patrick, that was interesting and helpful input for us!
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