Abstract: Reliable and economical passive thermal compensation in both focus (parallel to the optical axis) and lateral position (perpendicular to the optical axis) is disclosed for optical apparatus, including spectrographs. In the preferred embodiment, to maintain the position of the lens along the optical axis, two or more polymer spacers are used between the lens mount and a floating flange to which the lens is attached. The polymer spacers have a thermal coefficient of expansion such that when the temperature increases the lens is moved toward the detector array by the spacers to compensate for the normal increase of the lens-detector spacing with temperature. Flexure mounts, which bend by a predetermined amount in a known direction when the temperature changes, are preferably used to connect the lens mount to the floating plate, thereby moving the lens in a direction lateral to the optical axis.

Abstract: Various optical probe configurations are particularly suited to the monitoring of a process flow through the wall of a containment vessel. A probe body extends through, and is sealed to, the wall of the containment vessel. The probe body has an inner wall terminating in a distal end with a window, enabling light from the process flow to pass therethrough and into the probe body. In one embodiment, one or more lenses are disposed within the probe body to focus the light into a focal point, and a restriction of the inner wall of the probe body is used to create a narrow aperture at the focal point. In an alternative embodiment, a plug transparent to the light of interest is sealed to the inner wall of the probe body. As a further alternative, the elements include a second window creating a cavity with the distal window, and a port into the cavity accessible from outside the window for sampling purposes.

Abstract: An external cavity diode laser system which finds utility in many application areas, is particularly suited to fiber-coupled Raman Spectroscopy. A holographic transmission grating is disposed in the optical path to transmit elements of the beam having the nominal wavelength and reject beam elements of differing wavelengths. In a fiber-coupled arrangement, the lens used for focusing the exit beam from the module onto the entrance of the fiber acts as a spatial filter of the light dispersed by the transmission grating. In this configuration, the combination of the transmission grating and the focusing of the exit beam operates as a bandpass filter. The transmission grating is preferably oriented such that the elements of differing wavelengths are dispersed perpendicular to the long dimension of the diode. The module may further include a half-wave retarder supported between the external cavity and transmission gratings to rotate TM polarization orientations to TE polarization orientations.

Abstract: A volume-phase optical grating, preferably supported between substrates and prisms, uses large-angle input and output light beams to provide a very high degree of dispersion and improved separation of closely spaced wavelength channels. The average refractive index of the grating medium is also less than that of the supporting substrates and prisms, thereby providing improved uniformity and reduced sensitivity to the state of light polarization. The device therefore finds utility as a wavelength multiplexer, demultiplexer or optical spectrum analyzer in fields such as optical communications and optical signal processing. The grating itself may be constructed by conventional interferometric or holographic techniques, and may be a reflection or transmission device. In a system configuration, optical fibers may be used to carry the multiplexed or demultiplexed optical signals. Optoelectric detectors may also be used to detect different wavelengths and convert the optical signals into electrical counterparts.

Abstract: Methods and apparatus are disclosed for calibrating remote optical probe configurations of the type wherein a spectrum emitted by a sample is delivered to a spectrograph for analysis using fluorescence, Raman detection or other dispersive techniques. The invention may be used to calibrate the spectrograph wavelength axis, the system spectral response or intensity axis, and the wavelength of the laser used for excitation. A collection optical fiber having a first end for receiving wavelengths emitted by the sample has a second end for delivering the wavelengths to a base unit containing the spectrograph. A calibration optical fiber is used to deliver an optical calibration signal to a point proximate to the first end of the collection optical fiber, and an optical element is used to direct the optical calibration signal into the collection optical fiber so that the spectrograph receives both the wavelengths emitted by the sample and the optical calibration signal.

Abstract: In an improved optical switch, light from an input optical fiber is directed to one of a plurality of output optical fibers on a selective basis. The output fibers are contained in a bundle, preferably within a removable connector, thereby easing removal and maintenance. The input fiber also preferably forms pair of a bundle within a removable connector. The means for selectively directing the light from the end of the input fiber to the end of one of a plurality of the output fibers may include a pivot upon which at least the input optical fiber is mounted, or an electro-optic Bragg cell without moving parts. One or more lenses are preferably used between the end of the input optical fiber and the ends of the output fibers to assist in directing the light. A preferred arrangement incorporates two lenses, positioned so that the end of the output fiber and the end of a selected input fiber are each located at the focal point of one of the lenses.

Abstract: A compact, preferably monolithic optical element converts an incident beam of light into a dispersed exit beam. A transmissive optical grating is supported between two reflective surfaces such that a beam is reflected to pass through the same grating at least twice to form the exit beam. In the preferred embodiment the grating is a volume hologram cemented between two optically transmissive substrates which include outwardly oriented surfaces that are parallel to one another and to the grating, and the internal reflections occur at these surfaces. Mirrors may also be used. A preferred method of grating formation is also disclosed.

Abstract: An optical-fiber breakage detection system continuously monitors the integrity of a laser-guiding fiber, whether the laser itself is on or off. If an interruption is detected, the system may cut off, lock out, or reduce laser power, as appropriate. An optical element such as a beamsplitter is used to introduce an optical test signal into one end of the fiber so that the signal is carried by the fiber to the other end where the test signal is detected and employed to perform a desired function. In the preferred embodiment, the test signal is modulated and encoded to minimize false shut-downs. The source of the optical test signal is preferably disposed at the first location and carried by a second fiber to the remote location, enabling the test signal to be compared directly to the test signal as detected.

Abstract: In an optical measurement system of the type wherein a source of excitation radiation is directed along an excitation path to stimulate an optical emission from a sample along a collection path, the use of polarization-based beam splitting enables optical shutters to control selective polarization of the excitation and/or collection paths while maximizing overall optical alignment accuracy. In a preferred embodiment, polarization-based beam-splitting optics are disposed in one or both of the excitation and collection paths to divide that path into two orthogonally polarized paths, and a controllable optical blocking element is disposed in at least one of the orthogonally polarized paths, such that control of over transmission of that path results in control over polarization.

Abstract: Calibration wavelengths are injected into an optical detection system preferably at a point after laser rejection filtration, enabling the known spectral content of the calibration radiation to pass through and into a spectrograph. In a preferred embodiment, at least some of the wavelengths used for calibration are derived through the excitation of a noble gas such as neon, thereby conveniently and economically providing a full-spectrum calibration line set. The feed from the laser source used to illuminate the sample is also preferably introduced into the collection path, enabling both the calibration wavelengths and laser line to be detected and used in calibration. The invention is applicable to spectral analysis systems in general, including non-Raman systems and systems which do not require a laser notch pre-filter stage.

Abstract: A fiber-optic spectroscopic probe minimizes unwanted sources of luminescence through the use of one or more non-luminescing beam-redirecting elements operative to aperture share the optical collection path. Preferably, the beam-redirecting element is reflective, and may take the form of a spot mirror on an otherwise optically transparent window to fold at least a portion of the excitation radiation into the optical collection path or a mirror having a centralized aperture may be used to introduce the excitation radiation into the optical collection path. In either case, the excitation radiation may first pass through a dispersive element in a bandpass filter configuration. Several complete fiber-optic-based probe head designs are disclosed along with results indicating reduced luminescence, spurious fluorescence, in particular.

Abstract: An optical probe assembly, which may be used with or without optical fibers for remote operation, incorporates a leak-detecting capability. A source such as a laser is used for optically exciting at least a portion of a sample substance, causing wavelengths characteristic of the sample to be emitted along a collection path for reception by spectral analysis means. The same laser or a different source is employed for optically exciting a point within a test region, causing wavelengths characteristic of any substances contained or entering into the test region to merge with those of the sample within the collection path.

Abstract: A fiber-optic probe uses imaging optics between the remote ends of the excitation and collection fibers and the sample under investigation to enhance working distance and efficiency. In one embodiment a plurality of collection fibers are disposed circumferentially around a central excitation fiber, enabling a conventional focussing lens arrangement to be used for imaging purposes. The assembly may optionally include a rotationally symmetric diffraction grating to cause the excitation energy to assume an annulus superimposed over the image of the collection fibers. The excitation and collection fiber may alternatively be physically spaced apart from one another sufficient to permit one or more optical elements to be disposed in either or both of the excitation and collection paths, depending upon the application.

Abstract: The collection of spectral information is enhanced through the formation of multiple zones of excitation and emission. In one embodiment, a plurality of the zones are located within a sample substance, thereby increasing the efficiency of sample spectrum collection. In another embodiment, a reference substance is positioned so as to enclose at least one of the excitation/collection zones. The reference substance adds a known spectrum to the collection path, enabling analytical instrumentation to compare the sample and reference spectra for calibration purposes. In a further embodiment, one of the zones may be positioned within a sealed volume, and compositional changes in the sealed volume may be detected and used for leak-detection purposes.

Abstract: A dispersive grating, preferably in the form of a volume-phase holographic optical element, or HOE, is used as a beam combiner in an optical measurement probe of the type used to analyze induced radiative effects such as Raman or fluorescence detection. Although a reflective grating may be used, a transmission grating of holographic derivation is used in the preferred embodiment. Although the grating may define an area substantially equivalent to the cross-section or aperture of the collection path, a grating which consumes a fraction of the collection aperture may instead be utilized, thereby allowing collected light to pass around the grating to further enhance the efficiency of detection. As a further advantageous option, the grating may be fabricated with `power,` that is, with the capability of collimating excitation energy that has been focused onto the grating surface.

Abstract: Methods and apparatus for synchronous spectral line imaging are disclosed for use in conjunction with any of a number of radiative analysis techniques such as Raman or fluorescence detection. Light emitted points on a sample are separated into wavelength components and directed onto a two-dimensional image sensor such that the wavelength components impinge along one dimension of the sensor. The other dimension of the sensor is used in conjunction with spatial position relative to the sample, with at least certain of the steps being repeated for the different sample points so as to form the spectral line image. In terms of apparatus, the invention preferably utilizes at least one optical fiber having an input end to receive the light emitted by the sample and an output end to deliver the emitted light to the two-dimensional image sensor. The use of a flexible optical fiber facilitates the movement of the light received from the sample, movement of the received light relative to the sensor, or both.

Abstract: A multimode optical fiber is used in a confocal light-collection arrangement. A confocal aperture is supported in intimate proximity with respect to the first end of the fiber, preferably within two core diameters from the first end of the fiber. In the preferred embodiment, the confocal aperture is formed directly onto the first end of the fiber using, for example, photolithography or photoablation of a thin metallic film adhered directly to the light-collection end of the multimode fiber.

Abstract: Laser band-pass filter and/or band-reject filters are located at the end of an optical measurement probe by placing an appropriate Bragg grating proximate to the tip, and within, one or both of the optical fibers that make up the probehead. Thus, where an optical fiber is used to carry excitation energy of a nominal wavelength to a sample, the distal tip of this fiber will have included therein an optical filter to selectively pass energy of the nominal wavelength. Similarly, where an optical fiber is employed to carry stimulated emission from the sample to an analytical instrument such as a spectrometer, this fiber will have included within it at its distal tip an optical filter to selectively reject energy associated with the nominal wavelength.

Abstract: A combined optical diffuser and light concentrator uses a layer of optically transmissive material having a first surface to receive light at a range of angles of incidence and a second surface from which the light emerges at a range of angles of emergence, the second surface including a relief pattern featuring a multiplicity of minute projections, the shape and distribution of the projections resulting in diffused light at a range of angles of emergence narrower than the range of angles of incidence. The projections may be produced in accordance with various techniques, including the processing of a photoresist layer exposed to a random speckle pattern or microlithography, including e-beam/x-ray sources.

Abstract: Apparatus for gathering a frontal facial image of an individual observing a display area includes a light-conductive waveguide, transferring the image from a first light-redirecting region to a second light-redirecting region to output the image. The element is supported at least partially in front of the display, such that the input region overlies the display area, and all portions of the element overlying the display area, including the input region, are sufficiently transparent so as not to substantially interfere with the individual's observation of the display. In a preferred embodiment, at least the input region is a holographically derived optical grating, and the element is a transparent panel constructed of glass and/or plastic.