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

USA As Represented by Secretary of the Navy

Athanasios Gavrielides

Phillip R Peterson

David A Cardimona

John H Erkkila

Thomas M Shay

Thomas B Simpson

Craig A Robin

Mohinder P Sharma

Justin Spring

Jia M Liu

A method and system whereby a narrow linewidth coherent laser source when transmitted as a plurality of output signals and subsequently detected at a distance appears to produce the uniform illumination characteristics of an incoherent source thereby suppressing laser speckle and environmentally induced scintillation effects. A master oscillator source is split into N signals, each of which is independently phase modulated by frequencies designed to minimize a derived apparent incoherence factor. The signals are then either directed to an object to be illuminated so that they overlap at the object or first recombined and directed to the object.

Apparent incoherence method

An injection-locked semiconductor laser process that improves the modulation bandwidth and reduces the broadband noise of an injection-locked semiconductor laser. Injection locking of a semiconductor laser can significantly improve its broadband modulation characteristics. By adjusting the frequency offset between the master laser and the slave laser, improved modulation bandwidth of the modulation response can be emphasized. The intrinsic modulation bandwidths can be enhanced above the theoretical limit for the free-running laser. The improved modulation characteristics are accompanied by reduced broadband relative intensity noise.

Bandwidth enhancement and broadband noise reduction in injection-locked

Whenever any laser is interfaced with any type of optics there is always backscatter back into the laser. For diode lasers this backscatter makes it emit chaotic radiation where the frequency spectrum is broad and contains many different frequencies. This means that the laser has limited use as a source of information transfer in fibers. This weakness can be overcome, by driving the laser with an external cavity filled with a Kerr material. The addition of a Kerr material in the external cavity suppresses the chaos, or coherence collapse. Thus the new apparatus of laser plus external cavity filled with a Kerr material increases the stability of the diode laser.

Backscatter absorption for laser diodes

An intensity sensitive optical switch is described which comprises a nonlinear thin film Kerr material deposited on a conducting surface.

Thin film multistable angular optical switch

Multibeam coupling in a Kerr medium of nonlinear characteristics and finite response time is disclosed together with two different frequency spectrum examples of its use. In the first spectrum example, the modes are equally spaced and in the second spectrum the frequency separations are all unequal. In either case, as the beams propagate, both input spectra eventually reach a saturation characterized by a cascading of energy into the lowest frequency if the Kerr constant is positive. The direction of cascading of energy transfer is reversed to the highest frequency if the Kerr constant is negative. The examples disclosed include a typical Kerr medium and are representative of a multimode, equally spaced laser source and an unequally spaced source. For the equally spaced case, the optimum medium response time for conversion of Gaussian spectra is disclosed. If the frequencies are unequally spaced general conditions to be satisfied are disclosed, along with examples.

Laser line narrowing and frequency shifting

An optical parametric amplifier system is used to illuminate an object of interest with a signal beam, and parametrically mix the signal beam from the object with a pump beam to produce a down converted idler beam which maintains an image of the object of interest but which has a frequency which equals the difference between the frequencies of the pump beam and the signal beam. A signal laser is used to illuminate the object of interest, while a pump laser produces the pump beam. A beam combiner mirror produces a combined output by receiving and combining the pump beam and the signal beam. Finally, a nonlinear crystal receives and down converts the combined output of the beam combiner mirror to produce the idler beam by parametrically mixing the signal beam with the pump beam. When a KDP nonlinear crystal is used, the crystal optic axis may be rotated with respect to the direction of propagation of the idler beam to spectally score and amplify the image of the object of interest.

Optical parametric amplifying variable spatial filter

A bandpass filter is comprised by a plurality of reflection gratings operating in a Wood's anomaly region and arranged in serial relationship. Specifically, the gratings are serially arranged in two substantially parallel rows with the gratings in the first row offset laterally from the gratings in the second row. Further, the input to each grating is at substantially the same angle of incidence such that the output of one grating is the direct input to the next succeeding one of the gratings.

Bandpass filter formed by serial gratings operating in a Wood's anomaly

A method and apparatus for detecting small angular deviations of an input beam which utilizes a pair of diffraction gratings in series, both of which are operating in the Wood's anomaly region. As a result, the output intensity of the doubly diffracted input beam is at a maximum. Any deviation from the Wood's anomaly region by the input beam will substantially reduce the intensity of the output. This intensity variance is detected and utilized as an indication of a small angular deviation of the input beam.

Method and apparatus for detecting small angular beam deviations

An optical beam mode controlled high power laser system having a resonator which incorporates therein as one of the reflective elements a high efficiency diffraction grating. Impinging upon the diffraction grating is not only the high power resonator laser beam, but also an injected mode controlling laser beam of preselected wavelength. Each beam is directed at the diffraction grating at a predetermined angle in order for the grating to direct away therefrom a combined beam of radiant energy having high power and being locked to the preselected wavelength of the injected laser beam. It is this high power laser beam of preselected wavelength which is output from the laser system.

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Albuquerque, NM, United States of America

Athanasios Gavrielides