Abstract: Provided are systems and methods for precisely measuring birefringence properties of optical elements, especially those elements that are used in deep ultraviolet (DUV) wavelengths. The system includes two photoelastic modulators (PEM) (126, 128) located on opposite sides of the sample (136). Each PEM is operable for modulating the polarity of a light beam that passes though the sample. The system also includes a polarizer (124) associated with one PEM, an analyzer (130) associated with the other PEM, and a detector (132) for measuring the intensity of the light after it passes through the PEMs, polarizer, and analyzer. Described are techniques for determining birefringence properties across a wide range. For example, a dual-wavelength source light embodiment is provided for measuring relatively high levels of birefringence.

Abstract: A system and method for exploiting the dependance of a photoelastic modulator's (PEM's) resonance frequency on temperature (attributable to driving amplitude and to ambient temperature) to generally improve the performance of PEMs. In one embodiment there is provided a method and system for efficiently driving a series of multiple PEMs. To this end, each of the PEMs in a stack are separately tuned, as by controlling the power dissipated in each PEM, so that the resonance frequencies of all of the PEMs converge to a common frequency. Thus, all of the PEMs are simultaneously at resonance to ensure maximum efficiency and to maintain a selected total retardation amplitude. In another embodiment of the present invention, a single-element PEM is controlled in a manner to account for the subtle changes in the PEM's resonance frequency.

Abstract: An improved system for mounting an optical assembly of a photoelastic modulator (PEM) to permit free vibration of the optical assembly without introducing any stress or strain on the optical element. Moreover, the mounting system, which includes a mounting block (50), elastomeric mount (32), support flanges (36, 38), and a mounting rail (40), facilitates accurate and easy assembly of the optical element into its enclosure (26).

Abstract: Purging of a light beam path in an effective manner that minimizes the affect of the purging requirement on system throughput. In one embodiment, the invention is incorporated into a birefringence measurement system that has several components for directing light through a sample optical element and thereafter detecting and analyzing the light. The segment of the beam path through the sample is isolated to reduce the volume that requires continual purging.

Abstract: A holder for optical elements, or samples, in an optical setup. The holder is readily adjustments to accommodate samples of various sizes, such as cylindrical shaped samples of various diameters. The holder provides stable support for the sample, irrespective of the size of the sample and maximizes the area of the sample through which a light beam may pass as part of the analysis of the optical properties of the sample.

Abstract: Provided are systems and methods for precisely measuring birefringence properties of optical elements, especially those elements that are used in deep ultraviolet (DUV) wavelengths. The system includes two photoelastic modulators (PEM) (126, 128) located on opposite sides of the sample (136). Each PEM is operable for modulating the polarity of a light beam that passes though the sample. The system also includes a polarizer (124) associated with one PEM, an analyzer (130) associated with the other PEM, and a detector (132) for measuring the intensity of the light after it passes through the PEMs, polarizer, and analyzer. Described are techniques for determining birefringence properties across a wide range. For example, a dual-wavelength source light embodiment is provided for measuring relatively high levels of birefringence.

Abstract: A practical system and method for measuring waveplate retardation. The system employs a photoelastic modulator in an optical setup and provides high sensitivity. The analysis is particularly appropriate for quality-control testing of waveplates. The system is also adaptable for slightly varying the retardation provided by a waveplate (or any other retarder device) in a given optical setup. To this end, the waveplate position may be precisely altered to introduce correspondingly precise adjustments of the retardation values that the waveplate 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 that is incorporated in the system.

Abstract: The disclosure is directed to systems and methods for precisely measuring birefringence properties of large-format samples of optical elements. A gantry-like configuration is employed for precise movement of birefringence measurement system components relative to the sample. There is also provided an effective large-format sample holder that adequately supports the sample to prevent induced birefringence therein while still presenting a large area of the sample to the unhindered passage of light.

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 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 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.