Showing papers on "Adaptive optics published in 1974"

Real-time wavefront correction system

Abstract: An optical imaging system having the capability of detecting and eliminating in real-time phase distortions in a wavefront being imaged by the optical system. The resolution of ground based telescopes is severely limited by random wavefront phase changes and tilts produced by atmospheric turbulence. The disclosed invention was designed to overcome this problem. In the disclosed invention, an AC, lateral shearing interferometer measures in real-time the relative phase differences of the wavefront being imaged by the optical system. Phase differences measured by the shearing interferometer are directed to an analog data processor which, in combination with other circuitry, generates a plurality of electrical signals proportional to the required phase corrections at different areas of the wavefront. The electrical signals are applied to a phase corrector upon which the wavefront is incident to change the relative phase at various locations of the wavefront to achieve a wavefront in which the phase distortion is removed. In one embodiment the phase correction device consists of a mirror having an array of piezoelectric elements which function to selectively deform the mirror to correct phase distortions in the wavefront. In a second embodiment the phase correction device consists of a refractive device which has the capability of having its index of refraction selectively changed in different areas to correct phase distortions in the wavefront.

Phase compensation for thermal blooming.

Abstract: Appropriate correction of the initial phase of a laser beam is shown by numerical computation to be capable of appreciably reducing thermal blooming for a cw beam.

Analog data processor

Abstract: An optical imaging system having the capability of detecting and eliminating in real-time phase distortions in a wavefront being imaged by the optical system. The resolution of ground based telescopes is severely limited by random wavefront phase changes and tilts produced by atmospheric turbulence. the disclosed system was designed to overcome this problem. In the disclosed system, an AC, lateral shearing interferometer measures in realtime the relative phase differences of the wavefront being imaged by the optical system. Phase differences measured by the shearing interferometer are directed to an analog data processor which, in combination with other circuitry, generates a plurality of electrical signals proportional to the required phase corrections at different areas of the wavefront. The electrical signals are applied to a phase corrector upon which the wavefront is incident to change the relative phase at various locations of the wavefront to achieve a wavefront in which the phase distortion is removed. In one embodiment the phase correction device consists of a mirror having an array of piezoelectric elements which function to selectively deform the mirror to correct phase distortions in the wavefront. In a second embodiment the phase correction device consists of a refractive device which has the capability of having its index of refraction selectively changed in different areas to correct phase distortions in the wavefront.

Stellar interferometer for figure sensing of orbiting astronomical telescopes.

Abstract: An interferometric device designed to be located in the focal plane of a large astronomical telescope is presented. The prime application is for the forthcoming large space telescope. The device is to perform interferometry on the optical wavefront arising from a single star after it has propagated through the telescope. The concept of a focal plane figure sensor has been experimentally verified by fabricating and testing an operating laboratory breadboard figure sensor. A set of linear independent control equations are derived that define the operations for utilizing a focal plane figure sensor in the control loops for the positioning of the secondary mirror and for the active control of the primary mirror optical figure. A number of scientific experiments that could be performed with the interferometer are also briefly discussed.

Application Of Local Reference Beam Holography To The Study Of Laser Beam Parameters

Abstract: Local reference beam holography can be used in conjunction with interferometry to determine the complex amplitude distribution in the output of CW and pulsed laser beams. A hologram is recorded of the laser wavefront with a locally generated reference beam from the laser beam to be measured. The wavefront is then reconstructed with a CW laser beam in the usual way. The modulus of the complex amplitude can be measured directly and the phase is measured by interfering the reconstructed wavefront with a uniform phase wavefront. If the laser output is partially coherent the possibility exists of extending this method to determining the mutual intensity function and the complex degree of coherence of the laser wavefront.

Gradient index optics: aspects of design, testing,tolerancing, and fabrication

Abstract: The properties of gradient index optical components were studied. Lens systems composed of materials whose index of refraction varied in a prescribed manner were designed using both third order aberration theory and raytrace analysis. The lenses contained either an axial gradient, where the index varies in the optical axis direction or a radial gradient where the variation is orthogonal to the optical axis. The raytrace was based on a polynomial expansion of the ray path in the gradient index media. Single element collimators with wavefront errors of less than 1/20 were designed. The equivalence of an aspheric surface and a spherical surface bounded by an axial gradient was shown in the design of corrector plates for a spherical primary mirror. Tolerancing analysis of the gradient index profile and the effects of its decentration, tilt, and displacement were also studied for these lenses. The index profiles were measured automatically by an instrument that utilized AC interferometry. Measurements of the gradient, of the dispersion of the gradient, and of the birefringence were made on samples manufactured by Bausch and Lomb. A single element lens with an axial gradient was fabricated from the glass of one sample. The measured wavefront error was 0.75λ at 0.5145μ and 1.0λ at 0.6328μ. These errors were in excellent agreement with those predicted by the theoretical design.