I'm designing a low-cost system to record femtosecond laser pulses and characterize the average power and shot-to-shot deviations (of the laser pulses). A photodiode seems to be the economic solution, but I'm running into issues on the ADC side: the laser-induced pulse coming out of the photodiode is on the order of 10's of nanoseconds, requiring expensive ADC solutions to properly record. So I'm searching for analog circuits that might somehow temporally elongate these electrical pulses, allowing me to sample more points across the signal and accurately measure it. Simply adding some capacitance might work, but I'm looking into other solutions (peak/envelope detectors, etc.)
Currently, the pulses I get from my photodetector are about 30-40 ns wide and a few volts (up to 4V) in amplitude.
I'd like to be able to measure RMS/Average power of the laser (which is essentially measuring RMS/Average of the photodiode output) as well as shot-to-shot deviations (this is the real tough one, not sure its possible with my requirements). I want the lowest possible sampling rate (slowest ADC) to save on money. It will probably be in the 10-100 MS/s range
Thanks for your thoughts.