Hughes Aircraft Company

Raytheon Company

United States of America As Represented by the Secretary of the Air Force

Hughes Electronics Corporation

David Fink

Mario P Palombo

Dave Goran

Maurice Halmos

Point-ahead laser pointer-tracker systems with stabilization and wavefront correction in both transmit and receive directions provide arrangements for sensing the wavefront correction required in two different directions, one in the received target image direction for good image quality in the tracker and the other in the point-ahead direction for good beam quality on the target. In the several embodiments, a marker beam is aligned with the target image. Wavefront aberration correction signals are produced by an output wave sensor that senses the wavefront of the marker beam in the received target image direction and the wavefront of the source laser beam in the point-ahead transmit direction. The alignment is maintained by use of the output wave sensor signals together with signals from the tracker of the target and current aimpoint positions. These signals, compared in selected pairs, control mirrors in various legs of the optical system to put the current aimpoint on the desired aimpoint and to align the marker beam along the received target image direction.

Point-ahead laser pointer-tracker systems with wavefront correction in both transmit and receive directions

A system (80) for controlling deformations of optical components adapted for use with laser system aperture sharing elements (16) and deformable mirrors. The inventive system (80) includes a control loop (12, 40, 24, 20, 46, 28, 74, 78, 60, 34) for determining a desired temperature pattern. The control loop (12, 40, 24, 46, 28, 74, 78, 60, 34) provides a control signal (45) corresponding to the desired temperature pattern to a heat map applicator (18, 46, 47, 59, 60). The heat map applicator (18, 46, 47, 59, 60) applies the desired temperature pattern to the optical component (16) in response to the control signal and the optical component (16) is selectively deformed in response thereto. In a specific embodiment, the control loop (12, 40, 24, 20, 46, 28, 74, 78, 60, 34) is a closed loop control system that includes an interferometer (74). The interferometer (74) provides a first shape of the optical component (16) to a comparator circuit (20) that compares the first shape to a desired shape corresponding to the desired temperature pattern for determining the control signal. An alternative closed loop control system (12, 40, 24, 20, 46, 28, 74, 78, 60, 34) includes an infrared energy detector (12) that determines a current temperature pattern and generates the control signal in response thereto for converting the current temperature pattern to the desired temperature pattern. The heat map applicator (18, 46, 47, 59, 60) provides an electromagnetic beam (50, 52) that is swept across the optical component (16) to impart the desired temperature pattern on the optical component (16). In another illustrative embodiment, the control loop is an open loop control system that includes a complimentary electromagnetic energy beam that is swept over the optical component to form a heat pattern complimentary to the temperature pattern imparted to the optical component by a high power laser beam such that the total heat deposited on the optical component is uniform.

Heat maps for controlling deformations in optical components

A laser rangefinding system (12) that utilizes multiple pulse, multiple return, modal range processing for clutter rejection. A laser source (16) emits a series of laser beam pulses (42), and each reflected return from objects (46) in a scene for each of the pulses is recorded. Each return signal above a predetermined threshold is added as a count to a count table within a selected bin representing the range of the return signal. After all of the analog return signals are recorded, the range bin with the most counts is selected as the range of a target.

Multi-pulse, multi-return, modal range processing for clutter rejection

Deleterious feedback reflections from a power amplifier into a laser master oscillator are eliminated by interposing a nonreciprocal frequency shifter between the oscillator and amplifier, which shifts the laser frequency by more than twice the bandwidth of the laser oscillator resonant cavity.

Optical feedback eliminator

Disclosed is a scanning device (10) having a very fast raster scan and a small angle field of view. The scanning device (10) incorporates a rotating polygon scanning wheel (12) in which a beam of light (24) is reflected off of a first facet (14') of the wheel (12). A reflected beam (32) from the first facet (14') is directed through an optical subsystem that reverses the scanning direction of the beam and redirects the beam onto a second facet (14') of the scanning wheel (12). Since the subsystem optics reverses the scan of the beam, the second facet (14') scans the beam in an opposite direction to that of the first facet (14') and only the difference between the two scans remains. In a first embodiment, the optical subsystem magnifies or demagnifies the beam such that the angle of scan is enlarged or reduced, and thus the second scan will not completely cancel the first scan. Consequently, a very narrow field of view of a particular scene can be scanned very quickly. In an alternate embodiment, the size of the scan is altered by either altering the convergence or divergence of the beam between the two scanning reflections to achieve the small angle scan. In yet another embodiment, the small angle scan is achieved by substantially, but not entirely, reversing the scan direction.

Method of obtaining a narrow field of view scan

A laser configuration is disclosed that generates linear, repeatable, and one-directional frequency modulated chirps by means of a laser cavity whose effective length is varied by employing a combination of a moving special optical element that engages the laser beam twice on each pass of the laser beam through the cavity plus other optical elements such that the laser beam is returned back upon itself, thus rendering ineffective certain errors of position or orientation associated with the motion of the special optical element that otherwise would disturb the established optical alignment of the laser cavity. Equivalent results are obtained with a ring laser by applying similar and corresponding optical features.

Cavity modulated linear chirp laser

A spectral line selector for a laser comprises a diffraction grating that images a waveguide exit plane back into the waveguide with an essentially exact reproduction of the waveguide output intensity and phase distribution and with a predetermined wavelength. The selector also comprises lenses disposed between the waveguide exit at a point between the exit opening and the grating, the lenses providing a magnification and a phase compensation to the beam passing therethrough such that the phase of the beam returned to the waveguide matches that of the exiting beam. Thus, coupling losses due to clipping of the returned beam at the entrance to the waveguide bore and coupling losses due to a mismatch of the returning field phase to that of the waveguide mode are made essentially zero.

High resolution spectral line selector

The present invention provides various embodiments of laser systems for generating 'chirp' signals. In the broadest sense, a diffraction grating is placed within a laser cavity on the face of a carrier and the motion of the carrier in its own plane causes the laser to chirp. Typically, the diffraction grating is placed in the end-reflector position of the optical path of the resonant cavity associated with the laser. By putting the diffraction grating on the outer peripheral rim of a wheel and rotating the wheel, a sequence of either up-chirp or down-chirp signals can be generated continuously. Similarly, the desired 'chirped' signals can be generated by using a diffraction grating oriented radially on the face of a rotating wheel. The system also contemplates the simultaneous generation of both an up-chirp signal of one polarization and a down-chirp signal of an orthogonal polarization by using a pair of lasers and a single wheel carrying the diffraction grating on either its outer peripheral rim or its face disposed in the end-reflector positions of the lasers for simultaneously generating both the up-chirp and down-chirp signals. An optical system including a reflective mirror, a one-half waveplate, and a polarizing beamsplitter are provided at the output of the two laser system for combining the up-chirp signal and down-chirp signal for simultaneous outputting.

Diffraction grating driven linear frequency chirped laser

Frequency modulated radar transmitters with a repetitive linear increase in frequency with time, referred to as 'frequency chirps', are required for many radar applications. The present invention provides a simple way of obtaining such a chirped frequency modulation for a laser radar transmitter or the like. The principle is to translate an optical wedge in the direction of its wedge gradient at constant velocity across the optical path of a laser resonator. The resulting increase or decrease in the effective optical length of the resonator causes frequency chips. In a first embodiment of the present invention, a rotating phase plate on the face of a rotating wheel with the added phase varying linearly with angular position around the wheel is placed within a laser's resonator cavity to tune the optical pathlength of the cavity and thereby the longitudinal mode of the resonator to produce the chirp. This embodiment can be used in either a reflective or a transmissive mode. In a second embodiment of the present invention, the outer peripheral rim of a spiral wheel having a spirally increasing or decreasing radius is used, whereby the rim functions as a mirror, is disposed within the laser resonator. Rotating the wheel changes the optical pathlength of the resonator and causes the longitudinal modes of the resonator to tune so as to generate the required chirp sequence. Lastly, various systems are proposed for eliminating various types of errors in the system as well as for generating both up-chirps and down-chirps sequentially and/or simultaneously.

Phase plate or spiral phase wheel driven linear frequency chirped laser

A method and apparatus for frequency shifting an optical beam where the frequency shifted beam remains both spatially and temporally coherent with no spread in frequency and can be continually tuned in frequency shift over a wide range without any change in beam pointing or beam quality with time. This is achieved by changing the effective optical path length of the resonant cavity of a laser by translating an optical wedge, such as a prism, across the optical path in the direction of the wedge gradient. In a first embodiment, a rotating helical phase plate is used to linearly increase the optical path of a transmitted or reflected beam with time, thereby frequency shifting the exiting beam. In another embodiment, the rim of a wheel with a spirally increasing or decreasing radius is used in which the outer periphery of the wheel is a mirror. Spinning the wheel at a constant rotational speed increases or decreases the optical path of a reflected beam linearly with time, thereby frequency shifting the reflected beam. The helical phase plate can be used in either a transmissive mode or a reflective mode, whereas the spiral wheel is used primarily in a reflective mode.

Optical frequency shifter

A waveguide coupler comprises a curved end reflector mirror that images a waveguide exit back into the waveguide with an essentially exact reproduction of the waveguide output intensity distribution. The coupler also comprises a lens disposed near the waveguide exit at a point between the exit and the mirror, the lens providing a phase compensation to the beam passing therethrough such that the phase of the beam returned to the waveguide matches that of the exiting beam. Thus, coupling losses due to clipping of the returned beam at the exit/entrance to the waveguide bore and coupling losses due to a mismatch of the returning field phase to that of the waveguide mode are made essentially zero. Other embodiments of the coupler are presented wherein the phase compensating lens is positioned at locations other than adjacent to the waveguide exit, or wherein no inversion of the imaged field field distribution occurs, or wherein the beam is not caused to be focused at the center of a lens, or wherein one waveguide is coupled to another waveguide having a similar sized or a dissimilar sized bore.

Zero loss waveguide coupler

This invention forces a multi-spectral line laser to operate on a single spectral line by modifying the gain of the medium instead of the standard approach of modifying the loss of the cavity. The spectral line selected by the system of the present invention is always the same identical spectral line. There are no ambiguities in knowing which line has been selected as there are with other methods. The invention involves a system for using more than one type of gain media within the laser cavity. Each medium gives rise to a distinct set of spectral line frequencies at which it has gain. Only occassional coincidences will occur at which spectral lines from two or more media fall within a linewidth of each other. Where these coincidences do not occur, the gain for a spectral line is only proportional to the amount of the individual medium present and will be below threshold. Where the coincidences do occur, the total gain is proportional to the total amount of gain for all of the involved media and the line will lase. Spectral lines that are within one operating linewidth of one another may be achieved by the use of two different types of gain media within the laser cavity. The most promising embodiment of the present invention is to use the same type of gain media but with different isotopes, which would, in many but not all cases, allow a physical mixing of the media within the resonant cavity. Each medium or isotope gives rise to a different and distinct set of spectral line frequencies at which the system has gain. Only occasional coincidences will occur at which spectral lines from two or more media fall within a linewidth of each other. Where these coincidences do not occur, the gain for a spectral line is only proportional to the amount of the individual medium present and will be below threshold. Where the coincidences do occur, the total gain is proportional to the total amount of all the involved media and the line will lase.

Single spectral line laser

This disclosure describes an optical system which serves to multiply the change in the path length of an optical system. The system employs an even number of pairs of mirrors which are displaceable along a line or lines parallel to an axis. Each segment of the optical path is between mirrors which are oppositely displaceable, so that the length of each segment is increased by an amount equal to twice the displacement of the mirror pairs.

Optical path length multiplication system

A first embodiment includes a set of diffraction gratings on the face of a wheel, each grating being set at an angle to select a different spectral line. The wheel is rotated, and as each grating moves into the end-reflector position of the laser's optical path, the laser is fired. Alternate embodiments include a small spinning fold mirror that reflects the beam in a circle about the axis of the laser. Such embodiments include (a) a circular array of diffraction gratings arranged about the laser axis such that the tilt of the gratings and the orientation of the grooves vary as one goes around the circle and successively fires the laser at each grating; (b) both a circular array of mirrors and a corresponding array of diffraction gratings such that the grooves of all of the gratings are parallel and the gratings are all tilted in the same direction; and (c) two spinning fold mirrors and two circular arrays of mirrors giving a double fold plus a single diffraction grating wherein the optical paths are not parallel but arrive at the grating at different angles for selecting different spectral lines.

Rapidly switchable line selector for pulsed lasers

A method and apparatus are disclosed for mounting an interferometer cavity such as a laser so that constant interferometer resonant frequency is maintained in spite of environmental vibration and other external acceleration forces. The invention can be used alone or in combination with prior art frequency stabilization systems, such as shock mounts and active feedback type stabilization systems.

Growing community of inventors

Los Angeles, CA, United States of America

David Fink