Microphone detection of pulsed atomic and molecular beams

In a high-vacuum environment a microphone can act as a detector for atomic or molecular beams. Here, the response of the microphone to beams with gaussian temporal profiles is investigated. Using linear response theory, an analytic expression is found for the microphone output voltage for pulsed beams of arbitrary duration. Evaluation of this expression for pulses long compared with the period of oscillation of the lowest-frequency mode of vibration of the microphone diaphragm shows that the output follows the temporal profile of the pulse, with an amplitude proportional to the momentum flux in the pulse. For pulses that approximate delta functions in time, the microphone gives a somewhat distorted, damped sinusoidal response with a peak amplitude proportional to the impulse per area in the gas burst. An experiment was done that demonstrates the response of an electret microphone to a short burst of argon atoms.