Abstract: In multi-telescope arrays that comprise multiple telescopes, a beam-combining module, and flat mirrors for directing light beams from the multiple telescopes to the beam combining module, a laser metrology system is used for monitoring various pathlengths along a beam path where deviations are likely. Some pathlengths are defined simply by a pair of retroreflectors or reflectors at both ends. Lengths between pairs of retroreflectors are measured and monitored by laser interferometers. One critical pathlength deviation is related to the displacement of the flat mirror. A reference frame is set up relative to the beam-combining module to form and define the coordinate system within which the positions of the flat mirrors are measured and monitored. In the preferred embodiment, a pair of retroreflectors along the optical axis of the beam-combining module defines a reference frame. A triangle is formed by the reference frame as the base and another retroreflector at the flat mirror as the vertex.

Abstract: A large effective-aperture, low-cost optical telescope with diffraction-limited resolution enables ground-based observation of near-earth space objects. The telescope has a non-redundant, thinned-aperture array in a center-mount, single-structure space frame. It employs speckle interferometric imaging to achieve diffraction-limited resolution. The signal-to-noise ratio problem is mitigated by moving the wavelength of operation to the near-IR, and the image is sensed by a Silicon CCD. The steerable, single-structure array presents a constant pupil. The center-mount, radar-like mount enables low-earth orbit space objects to be tracked as well as increases stiffness of the space frame. In the preferred embodiment, the array has elemental telescopes with subaperture of 2.1 m in a circle-of-nine configuration. The telescope array has an effective aperture of 12 m which provides a diffraction-limited resolution of 0.02 arc seconds.

Abstract: A large effective-aperture, low-cost optical telescope with diffraction-limited resolution enables ground-based observation of near-earth space objects. The telescope has a non-redundant, thinned-aperture array in a center-mount, single-structure space frame. It employes speckle interferometric imaging to achieve diffraction-limited resolution. The signal-to-noise ratio problem is mitigated by moving the wavelength of operation to the near-IR, and the image is sensed by a Silicon CCD. The steerable, single-structure array presents a constant pupil. The center-mount, radar-like mount enables low-earth orbit space objects to be tracked as well as increases stiffness of the space frame. In the preferred embodiment, the array has elemental telescopes with subaperture of 2.1 m in a circle-of-nine configuration. The telescope array has an effective aperture of 12 m which provides a diffraction-limited resolution of 0.02 arc seconds.

Abstract: There is described a device for analyzing the wavefront of a light beam exiting the laser to detect any aberrations across the cross-sectional area of the beam from a planar wavefront. A rotating wave plate splits the beam from the laser into two orthogonally polarized beams separated in frequency by a frequency difference in the audio range. A polarization selective interferometer directs these two beams along a test arm and a reference arm. Quarterwave plates in each arm convert the outgoing waves to circular polarization and the return waves back to linear polarization but orthogonal to the input polarization. A linear polarizer at the output oriented at a 45.degree. angle to the polarizations causes the waves to interfere and a detector placed at any point in the output beam detects a beat signal at the audio frequency.

Abstract: Wave front distortions of a laser beam are detected by measuring the distribution of the point spread function of a focussed portion of that beam and by generating moments of that function representing tip, tilt, focus, and astigmatisms of the beam. Signals representing these moments can be used directly for correcting the distortions.

Abstract: An interferometer for detecting defects in the surface of a mirror or inhomogeneities in a medium uses two coherent but orthogonally polarized beams, one of which may be frequency or phase modulated. The two beams are separately directed into a test arm and a reference arm and, upon their return, recombined, and polarization filtered so that they interfere. The interference pattern is detected in a plane in plural, individual detection points. The resulting electrical signals are processed to obtain OPD information at a resolution that is much higher than the wavelength of the beams used. An alternative method using neither phase modulation nor frequency modulation is based on additional, separate point by point detection of the intensities of the individual beams.

Abstract: There is described apparatus for combining a plurality of pulsed laser beams into a single beam by a rotating mirror assembly. A rotor supports a plurality of individual mirrors arranged in a plurality of axially spaced planes, one plane for each beam. The mirrors in successive planes are angularly and radially spaced relative to mirrors in the other planes. Incident beams are pulsed successively in synchronism with rotation of the mirrors. Each beam in succession is reflected by a mirror in successive planes along a common axis to form a single reflected beam.

Abstract: A laser beam is split into two components which remain coherent, are differently frequency-shifted, orthogonally polarized and recombined. The recombined beam is expanded and directed into polarization type beam splitter directing one component into a reference branch, the other one into a test branch. Both branches return the component beams which are combined and polarization filtered so that they may interfere on account of local optical path differences. Brightness oscillations are photoelectrically detected in individual points of a plane intercepting the interference beam and referenced as to phase against a reference oscillation derived from a particular point in that plane. The phase differences are electronically acquired point-by-point for generation of a contour map or its equivalent of the optical path differences as between a test object in the test branch and a reference object in the reference branch.