Greetings, I've been looking for a way to create a microphone capable of picking up high frequencies (up to about 100kHz). Electrets dont tend to go that high and piezo crystals even detuned will only give a limited band. I had the idea of bouncing a laser off a sheet of reflective material. The light can either be picked up directly, by pulsing the beam with a square wave and taking the phase shift as a form of pulse width modulation, or with a sine wave and using the doppler shift (I'll have fun experimenting with all these methods). What I dont have any clue about is the material and what properties it should have. What kind of thickness, surface area, tension etc. would I need? Would there be a resonant frequency? Is it even possible for the frequency range in question?