A holographic optical element transforms a spectral distribution of light to image points. The element comprises areas, each of which acts as a separate lens to image the light incident in its area to an image point. Each area contains the recorded hologram of a point source object. The image points can be made to lie in a line in the same focal plane so as to align with a linear array detector. A version of the element has been developed that has concentric equal areas to match the circular fringe pattern of a Fabry-Perot interferometer. The element has high transmission efficiency, and when coupled with high quantum efficiency solid state detectors, provides an efficient photon-collecting detection system. The element may be used as part of the detection system in a direct detection Doppler lidar system or multiple field of view lidar system.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority under 35 U.S.C. .sctn.119(e) of U.S. Provisional patent application No. 60/091,733 filed Jul. 2, 1998, entitled "Holographic Optical Element Apparatus, Article of Manufacture, and Method for Converting Incident Electromagnetic Radiation Distribution to Points," which is hereby incorporated by reference.
An improvement is provided for a system that identifies particles such as microorganisms in fluid by directing a laser beam (52) forwardly through a tiny detect zone (46) in the fluid and detecting the pattern of light scatter by a particle as it passes through the detect zone. The improvement includes a holographic optical element (60) positioned forward of the detect zone to intercept light scattered in multiple directions by the particle. The holographic optical element is divided into discrete areas, or sections, that each directs intercepted scattered light toward a selected photodetector (74, 90, 92) of a linear array (62) of photodetectors. A converging lens (106) reduces the required diffraction angles of the sections of the holographic optical element. This arrangement avoids the need to custom mount and connect numerous individual photocells, and enables simplified high speed readout of the photodetectors.
A target plate (Z) according to the invention for positioning components, in particular pipes (R1, R2), has a holographic optical element as a holographic diffusor. By means of the diffusor, radiation striking the target plate (Z) in the form of a reference beam (RS) can be guided very accurately and virtually without loss into a defined solid angle region (d.OMEGA.). Furthermore, the diffusor may have stochastically distributed structures and thus illuminate the solid angle region (d.OMEGA.) homogeneously. By means of the target plate (Z), the visibility of the incident reference beam (RS) is increased, and the reference beam (RS) can also be detected independently of position.
In the case of a method of detecting wind velocities by means of a Doppler-lidar system (10), a laser beam of a defined frequency generated by means of a laser (11) is emitted by a transmitting device (12) toward a space area and the light backscattered from the space area is received by means of a receiving telescope (13). For determining a Doppler shift, an interferogram is generated by means of an interferometer (16), the intensity distribution of the interferogram being directly measured by means of a photodetector (17). The measured intensity distribution is compared with one or more reference patterns which had previously been determined for defined parameters and are filed in a memory device (18a). From the comparison, the Doppler shift is determined as a measurement for the wind velocity. The Doppler-lidar system (10) comprises an analyzing unit (18a, 18b) for implementing the method, having a comparison unit (18b) for the comparison of reference patterns with the measured interferogram.
A remote sensing system and method for instrumenting the entries to manhole enclosures, in order to provide a platform and means for sensing environmental parameters within and around the enclosures and wirelessly transmitting those parameters to a distant site. The system comprises a housing with sensor for monitoring environmental parameter in the vicinity of the manhole. A microcontroller in the housing sends the parameters to a radio module, which transmits the parameters to a communication device for alerting a user that a manhole has been tampered with.
This invention relates to a gas velocity sensor such as an air velocity sensor for use on an aircraft such that the velocity of the aircraft can be determined. There is provided a gas velocity sensor comprising an electromagnetic radiation source operable to illuminate a gas; a photodetector operable to detect electromagnetic radiation scattered from the gas; an optical path linking the gas to the photodetector; an interferometer positioned on the optical path, the interferometer having an input for receiving electromagnetic radiation scattered by the gas and an output for producing an interference pattern when the interferometer is illuminated; and a spatial filter positioned on the optical path on the output side of the interferometer, the spatial filter having regions that are relatively transparent and relatively opaque that form a structure corresponding to an interference pattern produced by the interferometer.
