Importance

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Abstract

An instrument of measuring motion of a vibratory system, such as an ultrasonic bonder, employs a laser (10) that receives within its lasing cavity light transmitted (24) to the object (26) to be monitored and retroreflected (24), so that oscillations within the laser cavity experience interference peaks corresponding to the phase relation between the outgoing and incoming laser beams (24). The interference peaks of the beam within the cavity are counted to provide an indication of motion of the reflecting object. Sensitivity is enhanced by choosing a front reflector (14) of the laser cavity to have a transmissivity at the frequency of interest that is selected to achieve maximum interference peak values. The laser cavity length is selected to cause the laser to have no more than two modes at the output frequency of interest, thereby avoiding beat frequencies that approach the frequency of vibration of the mechanical system of which motion is being observed.

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First Claim