Optical sensors

Could someone help me find some information reg. Optical sensors in a microphone for the audible range and also as an air pressure sensor for a meteorological measuring station.

The answers I need are
– the pressure arrangement i.e. what P and P0 respectively (P and P0 is the pressure difference)
– the frequency range needed for meaningful measurements
– the suitability of the suggested principle.

Do a search for window laser bounce listening, where you point a laser at a window. The vibrations in the glass caused by sound create modulation of the laser. Its the same principal as an optical microphone.