What is the interpretation of and the difference between the

total power


total output power

of a pulsed laser? How are these parameters measured and which type of detectors are the most suitable for the measurement.

I used both a "Thermal Power Sensor" with wavelength ranges covering 190 nm to 20 µm, and a "Photodiode" with wavelength ranges covering 400 nm to 11 µm to measure a white-light laser. I certainly do not expect the two sensors to give similar values, however, the photodiode seem to measure the average power while the thermal power sensor measured the total output power.

I would like to know what the working principles of these detectors are, and how they measure the total power and total output power of a pulsed laser.

Your help in this clarification will be much appreciated.


I'm guessing that "thermal power sensor" is another name for a bolometer. That is, an instrument that measures the temperature increase when some part of it absorbs incident radiation.

If that's the case, then the "thermal" sensor most likely has a slow response. It probably is incapable of measuring the peak power of a single pulse, but instead tells you the average power over some longer period of time (e.g., averaged over several seconds.)

A photodiode on the other hand, is a solid state device that responds to individual photons. They can respond very quickly (e.g., on the order of a nanosecond), but some lasers produce pulses that are far shorter than that, so I can't say for sure what your photodiod-based power meter measures. Probably there is a data sheet or a manual that gives a detailed explanation.

  • $\begingroup$ Thank you Solomon for the response and explanation. This is the conclusion I also came to after trying to know more about the detectors. The pulses is in the order of picoseconds. Response time for thermal sensor in the order of a second and the photodiode < 2 microns. The power sensor: thorlabs.com/thorproduct.cfm?partnumber=S425C Power: 2 W. This value was the same irrelevant of selected wavelength. The photodiode: newport.com/p/818-UV--DB Power: 3.77 mW. This value changes according to the power distribution of the spectrum. $\endgroup$ – Tiswell Nov 16 '19 at 22:55

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