Applied Physics Letters · 1976 · 34 citations · 2 references
EngineeringMeasurementOptical TestingVibration MeasurementInterferometryOptical MetrologyEducationFiber OpticsOptical InterferometersVibrationsCalibrationInstrumentationOptical SystemsLength MetrologyTime MetrologyOptical MeasurementOptical InterferometryUltrasoundHigh-frequency MeasurementPhase ShiftInterferometer SignalsIntensity ModulationLaser Ultrasound
Optical interferometers are very sensitive if they operate at the point halfway between the peak and minimum of detected intensity. By introducing a 90° phase shift between orthogonal polarizations in the reference beam, the interferometer signals due to each polarization are in quadrature; squaring and summing the signals effectively stabilizes the operating point of the interferometer at the high-sensitivity point, independent of the large low-frequency variations in optical-path difference caused by ambient disturbances. This method has been used to make stable (±0.5 dB) measurements of 2.5-MHz ultrasound pulses of 1-pm displacement.
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