Hi

I am measuring the spectrum of Relative Intensity Noise (RIN) in a laser. I think I am doing the right calculation, but if someone could comment on that, it would be great.

On the FFT spectrum, we get a voltage (in mV) vs frequency (in kHz). I first divide the voltage by 1000 and multiply the frequency by 1000.

I note the frequency bin spacing. Also in oscilloscope mode, I measure the DC level (in V).

For each frequency, I divide the voltage by the DC level, then I square that, and I divide the result by the frequency spacing. At this point the unit is 1/Hz.

Then I take the square root and I multiply by 10^6 to get the RIN spectrum in uW/W/sqrt(Hz), because the voltage is proportional to the laser power.

It looks physically acceptable, but I just want to check that I am not missing a factor of 2 or a factor of sqrt(2) or something else.

All comments are welcome, thanks!

JC