Abstract: A practical system and method for precisely measuring low-level birefringence properties (retardance and fast axis orientation) of optical materials (26). The system permits multiple measurements to be taken across the area of a sample to detect and graphically display (100) variations in the birefringence properties across the sample area. In a preferred embodiment, the system incorporates a photoelastic modulator (24) for modulating polarized light that is then directed through a sample (26). The beam (“Bi”) propagating from the sample is separated into two parts, with one part (“B1”) having a polarization direction different than the polarization direction of the other beam part (“B2”). These separate beam parts are then processed as distinct channels. Detection mechanisms (32, 50) associated with each channel detect the time varying light intensity corresponding to each of the two parts of the beam.

Abstract: A practical system and method for measuring waveplate retardation. The system employs a photoelastic modulator (22) in an optical setup and provides high sensitivity. The analysis is particularly appropriate for quality-control testing of waveplates (26). The system is also adaptable for slightly varying the retardation provided by a waveplate (26) or any other retarder device in a given optical setup. To this end, the waveplate (26) position may be precisely altered to introduce correspondingly precise adjustments of the retardation values that the waveplate (26) provides. The system is further refined to permit one to compensate for errors in the retardation measurements just mentioned. Such errors may be attributable to static birefringence present in the optical element of the photoelastic modulator (22) that is incorporated in the system.

Abstract: A practical system and method for precisely measuring low-level birefrigence properties (retardance and fast axis orientation) of optical materials (26). The system permits multiple measurements to be taken across the area of a sample to detect and graphically display (100) variations in the birefrigence properties across the sample area. In a preferred embodiment, the system incorporates a photoelastic modulator (24) for modulating polarized light that is then directed through a sample (26). The beam (“Bi”) propagating from the sample is separated into two parts, with one part (“B1”) having a polarization direction different than the polarization direction of the other beam part (“B2”). These separate beam parts are then processed as distinct channels. Detection mechanisms (32, 50) associated with each channel detect the time varying light intensity corresponding to each of the two parts of the beam.

Abstract: A dynamic self calibration process periodically calibrates a system for precisely measuring low-level birefringence properties (retardance and fast axis orientation) of optical materials. Variations in birefringence measurements can be caused by, for example, changes in the environmental conditions ( e.g., ambient pressure or temperature) under which birefringence properties of a sample are measured. In one implementation, the dynamic self calibration process repeatedly calibrates the system at different selected frequencies to compensate for different selected baseline variations.

Abstract: An optical assembly comprising an optical element and a transducer is suspended within an enclosure so that the optical assembly is free to vibrate within the enclosure. In one embodiment, the mechanisms for suspending the assembly do away with any elastomeric material that would cause outgassing in applications where the photoelastic modulator is used in a high vacuum environment. The suspension system also increases the efficiency of the system.

Abstract: An electronic control system that accurately maintains oscillation of an optical assembly at resonance. In the preferred embodiment, a signal control circuit delivers an input signal to an optical assembly. A resonance detector detects the difference in phase between the input signal and a feedback signal from the optical assembly. The phase difference is used to determine whether the optical assembly is at resonance. The signal control circuit is responsive to the resonance detector and modifies the frequency of the input signal to oscillate the optical assembly at its resonant frequency. The electronic control system can also maintain multiple optical assemblies at resonance.

Abstract: Modulated interference effects arising when laser beams are modulated by photoelastic modulators are substantially eliminated by methods and apparatus that extract from the detected beam the modulated, interfering light that emanates from the optical element of the modulator.