Laser interferometer for interferometric length measurements including an automatic-compensating circuit

Claim 1

A laser interferometer for interferometric length measurement including a semiconductor laser for emitting a light beam which energizes, by way of a beam divider, a measuring interferometer for generating a measuring interference light beam, said measuring interferometer having two reflectors and a measuring section, one of said reflectors being operatively associated with a moveable object to be measured, said laser energizing a reference interferometer for generating a reference interference light beam, said reference interferometer serving to control the wavelength of said laser light beam, said reference interferometer comprising a reference section including a fixed reference reflector, said reference interference light beam adapted to energize a reference signal detector, said reference signal detector generating a reference output signal, said reference output signal being fed to a closed loop feedback control circuit, said control circuit adapted to monitor the maximum, minimum, and slope values of said reference signal detector output signal for automatically and continuously adjusting both the supply current and operating temperature of said semiconductor laser during measurment operations while said reference reflector is fixed to thereby adjust the frequency of said laser in order to maintain said reference output signal constant, the interference light beam of the measuring interferometer containing information indicative of a length to be measured and adapted to impinge on an interference signal detector, said interference signal detector generating a measurement output signal which is fed to an evaluating device for determining the length to be measured, said reference section extending parallel to said measurement section a longitudinal distance substantially equal to the length of said measuring section, the lateral distance between said reference and measuring sections being very small relative to the length of said measuring section, said fixed reference reflector being adjustable in the longitudinal direction of said reference section whereby said reference section may be adapted to the length of said measuring section between measuring operations.