| Class / Patent application number | Description | Number of patent applications / Date published |
|---|
| 356365000 | With birefringent element | 38 |
| 20080239317 | SYSTEMS, METHODS, AND DEVICES FOR HANDLING TERAHERTZ RADIATION - Methods and apparatus for detecting variations in electromagnetic fields, in particular, terahertz (THz) electromagnetic fields, are provided. The methods and apparatus employ polarization detection devices and controllers to maintain or vary the polarization of modulated signals as desired. The methods and apparatus are provided to characterize electromagnetic fields by directing the electromagnetic field and a probe beam upon an electro-crystal and detecting the modulation of the resulting probe beam. Detection of the modulation of the probe beam is practiced by detecting and comparing the polarization components of the modulated probe beam. Aspects of the invention may be used to analyze or detect explosives, explosive related compounds, and pharmaceuticals, among other substances. A compact apparatus, modular optical devices for use with the apparatus, sample holders, and radiation source mounts are also disclosed. | 10-02-2008 |
| 20080252888 | APPARATUS FOR POLARIZATION-SPECIFIC EXAMINATION, OPTICAL IMAGING SYSTEM, AND CALIBRATION METHOD - A device for polarization-specific examination of an optical system having a detector part that has polarization detector means for recording the exit state of polarization of radiation emerging from the optical system. Also, an associated optical imaging system, and a calibration method for the device. The device includes a polarization detector with a polarizing grating structure. Provided as an alternative is a device for snapshot polarimetry having a birefringent element and downstream polarizer element that adequately polarizes nonquasi-parallel radiation. The device may be used for determining the influence on the state of polarization of UV radiation by a microlithographic projection objective. | 10-16-2008 |
| 20090015834 | OPTICAL SENSORS FOR DOWNHOLE MEASUREMENTS USING BIREFRINGENT MATERIALS - A sensor for measuring in a borehole at least one of orientation, acceleration and pressure, the sensor including: a light source; a birefringent material receiving light from the source; and a photodetector for measuring light transmitted through the birefringent material to measure the at least one of orientation, acceleration and pressure. | 01-15-2009 |
| 20090066952 | APPARATUS AND SYSTEM FOR ELECTRO MAGNETIC FIELD MEASUREMENTS AND AUTOMATIC ANALYSES OF PHASE MODULATED OPTICAL SIGNALS FROM ELECTROOPTIC DEVICES - An apparatus, for measuring an electric field while minimally perturbing the electric field being measured, includes an analyzing stage and a sensor head. The sensor head is optically coupled to the analyzing stage by a laser probe beam transmitted from the analyzing stage. The sensor head includes an electro optic crystal disposed between two gradient index lenses, where the first gradient index lens emits a laser beam transmitted from the analyzing stage to the sensor head, where the electric field is applied and where, the electro optic crystal transforms the laser beam probe into a phase modulated laser beam. The second gradient index lens transmits the phase modulated laser beam back to the analyzing stage, where polarization optics and a photodetector convert the phase modulated laser beam into an electrical signal representing field strength and phase of the electric field. | 03-12-2009 |
| 20090207409 | Measuring Optical Spectral Property of Light Based on Polarization Analysis - Apparatus, systems and techniques for measuring optical spectral property such as the frequency and the optical spectrum of light based on polarization analysis. | 08-20-2009 |
| 20090237663 | METHOD FOR DETECTING EQUATORIAL PLANE - To provide a method for detecting the equatorial plane, capable of detecting directly an equatorial plane that has the optical axis as the axis thereof, in a spherical optically uniaxial crystal. The method for detecting the equatorial plane as set forth in a first form of the present invention is a method for detecting an equatorial plane of a spherical member made from a single crystal of an optically uniaxial crystal having birefringence, comprising: a step for causing light to be incident on the spherical member through a polarizer; and a step for observing the isogyre that is structured by the light that is emitted from the spherical member through an analyzer that has a cross-nicol relationship with the polarizer; wherein the isogyre is an isogyre that is observed when the oscillating direction of the polarizer or the analyzer is near to parallel with the optical axis of the spherical member. | 09-24-2009 |
| 20090262350 | Automated analysis system for detection and quantification of biomolecules by measurement of changes in liquid crystal orientation - The present invention provides systems and methods for data acquisition and image analysis that utilize twisted nematic liquid crystals (“TNLCs”) to create maps of bio/chemical functionality patterned on surfaces. The method involves the acquisition of a series of images of TNLC film that contacts the analytic surface followed by analysis of the series of images to yield maps of twist angle of the liquid crystal across the surface. This analysis technique effectively condenses a large data set (stack of images) into a compact form (map of twist angle), revealing features on the surface that were not apparent in the individual images comprising the original stack. | 10-22-2009 |
| 20090273784 | Stokes parameter measurement device and method - The invention provides a Stokes parameter measurement device and Stokes parameter measurement method that enable high-precision measurement. The Stokes parameter measurement device comprises a polarization splitting device which comprises an optical element formed of a birefringent crystal material and which, by means of the optical element, splits signal light to be measured into a plurality of polarized light beams and adjusts the polarization state of one or more among the plurality of polarized light beams, and a light-receiving portion for performing photoelectric conversion of an optical component of the signal light split by and emitted from the polarization splitting device. | 11-05-2009 |
| 20090279089 | Detection System for Birefringence Measurement - 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. | 11-12-2009 |
| 20090323064 | Measurement of Linear and Circular Diattentuation in Optical Elements - A system for measuring linear or circular diattenuation in an optical element includes a sample rotation stage for securing an optical element sample; a light source module for generating a source light beam and a detector module. The light source module and detector module are arranged with the sample rotation stage between them, thereby permitting the source light beam to propagate through a sample that may be secured in the sample stage and to the detector module. Linear motion control of the light source module and the detector module, as well as tilt control of the light source module, the sample rotation stage and the detector module is provided, thereby to facilitate detection, by the detector module of the modulated light intensity information corresponding to a diattenuation characteristic of the optical sample secured in the sample stage. | 12-31-2009 |
| 20100045983 | Spatially precise optical treatment or measurement of targets through intervening birefringent layers - A treatment pattern (such as a focused spot, an image, or an interferogram) projected on a treatment target may lose precision if the treatment beam must pass through a birefringent layer before reaching the target. In the general case, the birefringent layer splits the treatment beam into ordinary and extraordinary components, which propagate in different directions and form two patterns, displaced from each other, at the target layer. The degree of birefringence and the orientation of the optic axis, which influence the amount of displacement, often vary between workpieces or between loci on the same workpiece. This invention measures the orientation of the optic axis and uses the data to adjust the treatment beam incidence direction, the treatment beam polarization, or both to superpose the ordinary and extraordinary components into a single treatment pattern at the target, preventing the birefringent layer from causing the pattern to be blurred or doubled. | 02-25-2010 |
| 20100103420 | METHOD FOR THE SPATIALLY RESOLVED MEASUREMENT OF BIREFRINGENCE, AND A MEASURING APPARATUS - A method for the spatially resolved measurement of the birefringence distribution of a cylindrically symmetrical blank ( | 04-29-2010 |
| 20100110432 | METHOD AND SYSTEM FOR EVALUATING OPTICAL PROPERTIES OF COMPENSATION LAYER - A compensation layer optical property evaluation method capable of precisely and accurately evaluating the optical properties of the compensation layer without separating the compensation layer from the optical film, namely without causing a breakage of the compensation layer or a change in the optical properties, and to provide a compensation layer optical property evaluation system for use in such a method. The method for evaluating the optical properties of a compensation layer in an optical film comprising at least a polarizer and the compensation layer placed thereon, comprising the steps of: preparing the optical property data that represent the relationship between the ellipticity of polarized light and optical properties of the compensation layer, wherein the optical properties include front retardation R | 05-06-2010 |
| 20100245822 | DIFFERENTIAL POLARIZATION MEASURING EXTENSION UNIT FOR A LASER-SCANNING MICROSCOPE - The invention relates to a differential polarizing laser-scanning microscope (DP LSM) for determining differential polarization quantities of a material, comprising a laser light source (L) for scanning the sample and illuminating it with a coherent and monochromatic light, a microscope unit (ME) with a sample holder for providing a preselected optical magnification and imaging and a polarization state setting unit (PAA) positioned in the illuminating beam path (between the light source and the sample holder). The microscope is further provided with detectors (D | 09-30-2010 |
| 20100321693 | MINUTE MEASURING INSTRUMENT FOR HIGH SPEED AND LARGE AREA AND THE METHOD OF THEREOF - The present invention relates to a minute measuring instrument for high speed and large area and a method thereof, and more particularly, to a minute measuring instrument for high speed and large area which measures properties of a specimen in high speed by a focused-beam ellipsometric part and then minutely remeasures the position showing a singular point by a minute measuring part and a method thereof. | 12-23-2010 |
| 20100328666 | POLARIZATION-INDEPENDENT UP-CONVERSION PHOTON DETECTION APPARATUS - A photon detection apparatus includes an optical divider splitting incident signal light by polarization components, an optical mixer mixing pump light with the signal light output from the optical divider, an up-converter up-converting a frequency of the mixed signal light including the pump light, and an optical detector detecting the up-converted signal light. | 12-30-2010 |
| 20110007316 | Inspection Method and Apparatus, Lithographic Apparatus, Lithographic Processing Cell and Device Manufacturing Method - An inspection apparatus configured to measure a property of a substrate includes an illumination source, a beam splitter, a first polarizer positioned between the illumination source and the beam splitter, an objective lens and an optical device that alters a polarization state of radiation traveling through it positioned between the beam splitter and the substrate and a second polarizer positioned between the beam splitter and a detector. An axis of the second polarizer is rotated with respect to an axis of the first polarizer. Radiation polarized by the first polarizer that reflects off any optical elements between the beam splitter and the optical device is prevented from entering the detector by the second polarizer. Only radiation that passes twice through the optical device has its polarization direction rotated so that it passes through the second polarizer and enters the detector. | 01-13-2011 |
| 20110019189 | SUB-WAVELENGTH STRUCTURES, DEVICES AND METHODS FOR LIGHT CONTROL IN MATERIAL COMPOSITES - A device for enhancing transmission of incident electromagnetic radiation at a predetermined wavelength is presented that includes an aperture array structure in a thin film. The structure includes a repealing unit cell having more than one aperture including a first aperture and a second aperture, wherein a parameter of the first aperture differs from that of the second aperture. The unit cell repeats with a periodicity on the order of or less than said predetermined wavelength, The structure parameters are configured to preferentially support cavity modes for coupling to and enhancing transmission of a predetermined polarization state at the predetermined wavelength. By structuring the unit cell with apertures that differ by appropriate degrees in at least one of dimension, height, dielectric constant of material filling the apertures, shape, and orientation, the devices can be adapted for polarization and/or wavelength filtering- and/or light circulating, weaving, or channeling. | 01-27-2011 |
| 20110019190 | RESISTIVITY TESTING METHOD AND DEVICE THEREFOR - An object is to efficiently measure the resistivity of a transparent conductive film with high accuracy in a non-destructive and non-contact manner. Provided is a resistivity testing device that includes a light emitting device that emits p-polarized emission light having a wavelength selected by a preliminarily performed test-condition selecting method toward a transparent conductive film, formed on a light-transmissive substrate conveyed along a manufacturing line, from a film-surface side at an incidence angle selected by the method; a light detecting device that detects reflected light reflected at the transparent conductive film; and an information processor that calculates an evaluation value related to the amount of light of the reflected light with respect to the wavelength on the basis of the intensity of the detected light and obtains a resistivity from the calculated evaluation value by using a correlation characteristic in which the evaluation value and the resistivity are associated with each other in advance. | 01-27-2011 |
| 20110122409 | OBJECT CHARACTERISTIC MEASUREMENT METHOD AND SYSTEM - The present invention provides a method for measuring object characteristics, wherein the method is capable of overcoming the interference induced bye the phase difference of the background with respect to the measuring system so as to measure the tiny characteristics such as the retardance or azimuth angle of an object accurately. The method is capable of obtaining two sets of light intensity images having retardance of background and the object respectively by simultaneously rotating the retarding elements and analyzer in various rotating angle combinations, and analyzing and calculating upon the polarized light intensities of the images associated with the background and the object so as to obtain actual retardance and azimuth angle of the object without the affect of the background retardance. | 05-26-2011 |
| 20110188040 | Mounting for deviation angle self compensating substantially achromatic retarder - A system, method of configuring, and application a system for introducing a relative phase retardation into orthogonally polarized components of an electromagnetic beam entered thereinto, wherein the system involves a substantially achromatic multiple element retarder system for use in wide spectral range (for example, 190-1700 nm) rotating compensator spectroscopic ellipsometer and/or polarimeter systems. | 08-04-2011 |
| 20120092669 | MEASUREMENT METHOD AND MEASUREMENT SYSTEM FOR MEASURING BIREFRINGENCE - A method measuring the birefringence of an object. A measurement beam having a defined input polarization state is generated, the measurement beam being directed onto the object. Polarization properties of the measurement beam after interaction with the object are detected in order to generate polarization measurement values representing an output polarization state of the measurement beam after interaction with the object. The input polarization state of the measurement beam is modulated into at least four different measurement states in accordance with a periodic modulation function of an angle parameter α, and the polarization measurement values associated with the at least four measurement states are processed to form a measurement function dependent on the angle parameter α. A two-wave portion of the measurement function is determined and analysed in order to derive at least one birefringence parameter describing the birefringence, preferably by double Fourier transformation of the measurement function. | 04-19-2012 |
| 20120154805 | OPTICAL POSITION MEASURING INSTRUMENT - An optical position measuring instrument including a scanning plate and a scale, wherein the scale and the scanning plate are movable relative to one another. The optical position measuring instrument including a grating and a light source that emits a beam toward the grating, wherein the grating receives the beam and splits the beam into two partial beams with orthogonal polarization states. The optical position measuring instrument including a polarizer being arranged in beam paths of the two partial beams, wherein the polarizer has a structure to generate polarization effects on the two partial beam striking the polarizer that are periodically variable, wherein a polarization period of the periodically variable polarization effects is greater than a graduation period of the grating. The two partial beams being reunified into a resultant beam. A detection unit that receives the resultant beam and generates a plurality of displacement-dependent scanning signals. | 06-21-2012 |
| 20120176617 | APPARATUS AND METHODS FOR THE OPTICAL EXAMINATION OF BIREFRINGENT SPECIMENS - A method for optically examining a birefringent specimen, the method comprising the steps of: collecting a specimen using a substantially non-birefringent polymer film having an adhesive surface, such that the specimen is attached to the adhesive surface; and examining, between crossed polars, the specimen attached to the said film. Also provided is a substantially non-birefringent laminate film comprising: a first birefringent polymer layer and a second birefringent polymer layer, the first and second layers being mutually oriented such that the birefringent properties of the two layers cancel each other out; and an adhesive surface; wherein the adhesive surface is an outer surface of the film, and/or is an exposable surface between the first and second layers. A method of manufacturing such a film is also provided. | 07-12-2012 |
| 20130100446 | INSPECTION APPARATUS AND INSPECTION METHOD - The invention is directed to find a false defect from defect candidates and obtain a threshold with which the false defect can be eliminated by the smallest number of review times. Defect candidates are reviewed and selected as a defect or a false defect. By deleting a defect candidate having a characteristic quantity equal to or less than that of the false defect from a map or displaying it in another sign, the false defect can be determined visually. Since the defect candidate having the characteristic quantity equal to or less than that of the selected false defect is deleted from the map or displayed in another sign, the defect candidates unnecessary to set a threshold are not reviewed. The number of defect candidates to be reviewed can be largely reduced as compared with that in the conventional technique. Further, by repeating the above work, the threshold is automatically calculated, and an inspection result map with the threshold is displayed, so that a re-inspection is unnecessary. | 04-25-2013 |
| 20130107258 | Downhole Sensors Using Anisotropic Permittivity | 05-02-2013 |
| 20130265575 | DETECTION APPARATUS, LITHOGRAPHY APPARATUS, CHARGED PARTICLE BEAM APPARATUS, AND ARTICLE MANUFACTURING METHOD - A detection apparatus includes an optical system including a polarization beam splitter and a quarter-wave plate. The optical system illuminates a mark via the polarization beam splitter and the quarter-wave plate in sequence, and directs light reflected from the mark via the quarter-wave plate and the polarization beam splitter in sequence towards a light-receiving element An airtight container configured to enclose therein at least part of the optical system includes, as a partition wall thereof, a light transmitting member arranged in an optical path between the polarization beam splitter and the quarter-wave plate. | 10-10-2013 |
| 20130271763 | INSPECTION DEVICE AND METHOD THEREOF - An optical system configured to visually inspect a target having a variable position with respect to the optical system is provided. The optical system includes a polarizer configured to convert an incident light reflected or diffused from the target into linearly polarized light; a light modulating element configured to modulate a polarization state of the linearly polarized light in response to control signals; and a lens group comprising at least one birefringent element, the birefringent element configured to refract or reflect the modulated linearly polarized light with a first polarization state under a first refraction index to enable inspection of the target at a first object position, and the birefringent element further configured to refract or reflect the modulated linearly polarized light with a second polarization state under a second refraction index to enable inspection of the target at a second object position. | 10-17-2013 |
| 20130335740 | OPTICAL CHARACTERISTIC MEASUREMENT DEVICE AND OPTICAL CHARACTERISTIC MEASUREMENT METHOD - A linearly polarized light reaches a sample S through a polarizer and receives a retardation from the sample S. Then, the light reaches a movable mirror unit and a fixed mirror unit of a phase shifter through a first polarizing plate and a second polarizing plate. Then, the reflected measurement lights pass through an analyzer, and are caused by an imaging lens to form an interference image on the light-receiving surface of a detector. At this time, an optical path length difference between a beam reflected on the movable mirror unit and a beam reflected on the fixed mirror unit is continuously changed the movable mirror unit. Hence, the imaging intensity of the interference image detected by the detector continuously changes producing a synthetic waveform similar to an interferogram. The synthetic waveform is Fourier-transformed, to obtain an amplitude per wavelength and a birefringent phase difference per wavelength. | 12-19-2013 |
| 20140268149 | DEVICE AND METHOD FOR DETECTION OF POLARIZATION FEATURES - An apparatus and method for imaging a section of a medium are disclosed. The section of medium has features (“Polarization Sensitive Features”) which return light according to the polarization of the received light. The disclosed apparatus and method may be configured to measure the irradiance of light returned from the object across the lateral (with respect to the optical axis) dimension. | 09-18-2014 |
| 20150116713 | APPARATUS AND METHODS FOR MEASURING MODE SPECTRA FOR ION-EXCHANGED GLASSES HAVING STEEP INDEX REGION - Apparatus and methods for measuring mode spectra for ion-exchanged glass substrates having a steep index region are disclosed. An interfacing fluid is provided between the coupling prism and the glass substrate. The interfacing fluid thickness is selected so that the variation in modal birefringence with fluid thickness is reduced to an acceptable level. The coupling prism can include a prism coating on the coupling surface so that the substrate-prism interface includes the prism coating. The coupling prism can also include stand-off members that serve to define the thickness of the interfacing fluid. | 04-30-2015 |
| 20150345950 | NON-INTERFEROMETRIC OPTICAL GYROSCOPE BASED ON POLARIZATION SENSING - This patent document relates to optical devices and optical sensing techniques including optical gyroscopes and optically sensing rotation. Sensing of rotation can be used in a wide range of applications, including, e.g., navigation, motion sensing, motion control including object stability control, game console controllers, hand-held devices such as smartphones. Optical gyroscopes can be designed to use rotation-induced changes in the optical interference pattern of two counter-propagating optical beams to measure the rotation. Many optical gyroscopes are based on an optical Sagnac interferometer configuration including various interferometric fiber-optic gyroscopes (IFOGs). Such optical gyroscopes can be designed without moving parts and thus eliminate the wear and tear in other gyroscopes with an oscillating proof mass or a moving component. | 12-03-2015 |
| 20160063790 | AUTHENTICATION APPARATUS AND METHOD - The present invention provides an authentication apparatus operative to determine the authenticity of a polymer film, comprising an optically-based measuring arrangement operative to measure a first effect influenced by a birefringence characteristic of said film and a second effect influenced by another optical characteristic of said film, and wherein said apparatus is operative to: compare a value, or range of values, representative of said first effect with a value, or range of values representative of a specified first effect corresponding to a predetermined birefringence characteristic of an authentic polymer film; compare a value, or range of values, representative of said second effect with a value, or range of values representative of a specified second effect corresponding to a predetermined other optical characteristic of an authentic polymer film; and output an authenticity signal indicative of authenticity or otherwise of said film based upon one or both of said comparisons. There are also provided one or more methods of determining the authenticity of a polymer film. | 03-03-2016 |
| 20160078707 | AUTHENTICATION APPARATUS AND METHOD - The present invention provides an authentication apparatus operative to determine the authenticity of a polymer film, comprising: an optical response modifier operative to modify a first effect influenced by said birefringence characteristic of said to a modified first effect; and an optically-based birefringence measuring arrangement operative to measure said modified first effect; and wherein said apparatus is operative to: compare a value, or range of values, representative of said modified first effect as measured with a value, or range of values representative of a specified first effect as modified by a same optical response modifier and corresponding to a predetermined birefringence characteristic of an authentic polymer film; and output an authenticity signal indicative of authenticity or otherwise of said film based upon said comparison. There are also provided one or more methods of determining the authenticity of a polymer film. | 03-17-2016 |
| 20160084751 | POLARIZED LIGHT IMAGING APPARATUS AND METHODS THEREOF FOR SEPARATING LIGHT FROM A SURFACE OF A SAMPLE ITS DEEPER DIFFUSE LAYERS - A polarized light imaging apparatus is provided. In an embodiment, the apparatus comprises a light source for producing light beams; an illumination optic coupled to the light source for guiding the light beams towards the sample; a linear polarizer coupled to the illumination optic and configured to produce a linearly polarized light towards the sample respective of the light beams; a TIR birefringent polarizing prism (BPP) coupled to the sample to maximize a refraction difference between ordinary waves and extraordinary waves of light returning from the sample; and a detection optic unit coupled to the non-TIR BPP for guiding the light waves returning from the sample towards a single polarization sensitive sensor element (SE), the SE is configured to capture at least one frame of the sample respective of the light waves returning from the superficial single-scattering layer of the sample apart from the deeper diffuse layer. | 03-24-2016 |
| 20160103062 | Polychromatic polarization state generator and its application for real-time birefringence imaging - Apparatus for generating polychromatic polarized light with the polarization ellipse orientation determined by the wavelength. The proposed polychromatic polarization state generator can be used in various configurations of polarized light microscope (called “polychromatic polscope”) for imaging birefringent samples. The polychromatic polscope produces a spectral-modulated visual scene, in which birefringent structures are evident because their appearance is different from the background. New polarized light microscope can subtract the background and produce video-enhanced color image of birefringent structures. The obtained picture can be also mathematically processed in order to obtain a map of quantitative distribution of specimen retardation and orientation of the principal axes. | 04-14-2016 |
| 20160123807 | Absorption Line Optical Filters and Spectrometers - An apparatus is disclosed for filtering of probe light and measurement of probe light frequency. The apparatus includes an optical filter comprised of a medium of rapidly changing circular birefringence. The circular birefringent medium changes the polarization of probe light such that light within a certain frequency bandwidth is rotated between crossed polarizers so it will be transmitted through the second polarizer. The spectrometer rotates the polarization of probe light an amount that is dependent upon probe light frequency. Probe light frequency is deduced by analyzing probe light polarization after it propagates through the birefringent medium. The birefringent medium is constructed from a gaseous substance and a magnetic field, where the gaseous substance has one or more absorption lines near the probe light frequency. The magnetic field permeates the gaseous substance and shifts the frequency of the absorption line(s) by the Zeeman effect. | 05-05-2016 |
| 20160139033 | Device for Compensating for the Drift of a Phase Shift of a Device for Modulating the Polarization State of a Light Beam - A device for analyzing and/or generating a polarization state of a measurement point of a target object includes a polarizer suitable for selecting, in an incident light wave, a light beam which is linearly polarized in a predefined direction; a first birefringent element suitable for having the light beam pass therethrough; a second birefringent element identical to the first element and suitable for having the light beam pass therethrough, the light beam then being directly or indirectly directed toward the object in order to be reflected in the form of a reflected beam. The device includes an optical assembly having one or more optical elements located in an optical path between the first element and the second element, and the optical assembly includes an odd number of mirrors, or, an odd number of half-wave plates, or, an odd number of a mix of mirrors and half-wave plates. | 05-19-2016 |
