Abstract: A system for controlling a light beam in an optical setup includes a light source that directs a collimated light beam along a path, through a sample, and toward the active area of a stationary detector. A lens is selectively movable into the path of the light beam for spreading the beam in instances where the path of the beam is altered by the sample between the source and the stationary detector. The detector, therefore, is held stationary. Adjustment mechanisms are provided for increasing the intensity characteristic of the light that reaches the detector to account for a decrease in intensity that occurs when the lens is in the path of the light beam to spread the beam.

Abstract: A method of controlling a light beam in an optical system includes a light source that directs a collimated light beam along a path, through a sample, and toward the active area of a stationary detector. The method includes the step selectively moving a lens into the path of the light beam for spreading the beam in instances where the path of the beam is altered by the sample between the source and the stationary detector The detector, therefore, is held stationary. Adjustment means are provided for increasing the intensity characteristic of the light that reaches the detector to account for a decrease in intensity that occurs when the lens is in the path of the light beam to spread the beam.

Abstract: A support for a vibrating component of an optical assembly that is adjacent to a frame includes an elastomeric rod having one end that is attachable to the component. A rigid sleeve is fastened to the frame and movable relative to the frame. The sleeve has a bore that opens to an inner end of the sleeve and is sized to receive the free end of the rod therein.

Abstract: The sample holder includes support having a thickness and an aperture through the thickness of the support. A tilt mechanism is connected to the support for controlled tilting of the support, and the aperture through the support is configured to have a diameter that increases in a direction through the thickness of the support. This arrangement enables a light beam to pass through the same given area of the sample, irrespective of whether the sample is held perpendicular to the beam or held at a tilted position relative to the beam. In one embodiment, the holder includes an efficient magnetic clamp mechanism for securing the sample to the holder. The holder compactly integrates with tilting mechanisms a sample rotation mechanism.

Abstract: The amount of gain applied to a photodetector such as a photomultiplier tube (PMT) is limited to an amount that does not cause the applied PMT bias voltage to overdrive, hence damage, the PMT. Techniques for limiting the PMT gain are implemented in a way that does not interfere with the precision with which the PMT gain may be established (by selection of a reference level) below that limited level.

Abstract: Provided are methods for determining the birefringence level of optical material such as polymeric film. In one embodiment, the method uses a setup of optical components that has known system reference angle. The sample may be a stretched polymeric film that has a fast axis angle that has a predetermined orientation in the sample. The system is operated to align the direction of the fast axis of the sample with the reference angle of the system and to measure the birefringence level at a location of the sample. As one aspect of the invention, embodiments and methods are described for accurately determining birefringence levels across a very wide range and up to tens of thousands of nanometers.

Abstract: The disclosure is directed to precise measurement of out-of-plane birefringence properties of samples of transparent optical material. Two angled-apart light beams are passed through a selected location of a sample optical element. One of the beams is incident to the sample surface. The characteristics of the beams are detected after passing through the sample, and the information detected is processed to determine the out-of-plane birefringence.

Abstract: Provided are methods for determining the birefringence level of optical material such as polymeric film. In one embodiment, the method uses a setup of optical components that has known system reference angle. The sample may be a stretched polymeric film that has a fast axis angle that has a predetermined orientation in the sample. The system is operated to align the direction of the fast axis of the sample with the reference angle of the system and to measure the birefringence level at a location of the sample. As one aspect of the invention, embodiments and methods are described for accurately determining birefringence levels across a very wide range and up to tens of thousands of nanometers.

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 system and method for precisely measuring low-level linear and circular birefringence properties (retardance and direction) of optical materials (26). 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. This information is combined for calculating a precise measure of the linear and/or circular retardance induced by the sample, as well as the sample's fast axis orientation and direction of circular retardance.

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: 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: A diagnostic system (24) for a PEM (20) provides optically determined information about the retardance characteristics induced by the PEM (20). The diagnostic system (24) is integrated with the PEM (20) so that the PEM (20) performance may be diagnosed or monitored during operation of the PEM (20). Specifically, the diagnostic system (24) is used alongside an optical setup (22) that employs a primary light beam (28) for conventional purposes such as polarimetry, optical metrology, etc. The diagnostic system (24) includes its own diagnostic light source (50) that is directed through the optical element (32) of the PEM (20) at a location remote from the primary aperture (38) of the PEM (20). Thus, the diagnostic system (24) and the primary PEM (20) operation can be undertaken simultaneously, with one not interfering with the other. The output of the diagnostic system reflects the actual retardance characteristic provided by the PEM (20) and can be used as feedback to adjust the PEM control as needed.

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.