Using a large adaptive optical system designed for the correction of a visible wavelength laser, we report the results for the first known compensated laser illumination demonstration of an uncooperative low Earth orbit (LEO) satellite using an active point ahead mirror. The results of these tests using a low-power laser beacon at D/ro equals 25 show improvement of over a factor of 5 in peak energy at the diffraction limited resolution of 0.1 arc sec for stellar images. The amount of light reflected from a large, diffuse LEO satellite was improved by a factor of approximately 2 using the adaptive optical system.
We report on the design and operation of an integrated 1 meter adaptive optics system for compensation of a visible wavelength laser for satellite beamforming applications. A visible artificial laser guide star (frequency-doubled Nd:YAG laser with wavelength of 0.532 micrometers ) is used as the source for the reference wavefront. A shearing interferometer which uses a narrow optical bandwidth and has 500 subapertures is employed to sense wavefront distortion. These measurements are used to compute a conjugate wavefront to the distorted input light. The computed conjugate is then imprinted on a deformable mirror which consists of 500 square mirror segments. The deformable mirror is integrated with a 1 m Cassegrain telescope. The tracking system is designed to track and illuminate low Earth orbit (LEO) satellites. Computer control of both the adaptive optics and tracking systems are done via two terminals, and the entire adaptive optics/tracking system can be run by only two operators. We have used this system for both compensated imaging and compensated illumination applications. In this paper, we will present an overview of the system architecture and discuss computer control of the adaptive optics and tracking systems.
In a program with the Office of Naval Research and the Innovative Science and Technology directorate of BMDO, we have designed, built and tested a large adaptive optical system for the correction of a visible wavelength laser beam. A visible artificial laser guide star (frequency-doubled Nd:YAG laser with wavelength of 0.532 micrometers ) is used as the source for the reference wavefront. A shearing interferometer which uses a narrow optical bandwidth and has 500 subapertures is employed to sense wavefront distortion. The sensor is used to control a 500-segment deformable mirror which is integrated with a 1 m telescope. In this paper, we will present results for the first known compensated laser illumination tests of an uncooperative low Earth orbit (LEO) satellite using an active point ahead mirror. The results of these tests using a first generation low-power laser beacon at D/ro equals 25 show improvement of over a factor of 5 in peak energy at the diffraction limited resolution of 0.1 arc sec for stellar images. The amount of light reflected from a large, diffuse LEO satellite was improved by a factor of approximately 2 using the adaptive optical system. In the Spring of 1994, a custom, high powered illuminator laser will be implemented to facilitate novel active tracking and imaging applications.
We report on the design and fabrication of a high bandwidth interferometer suitable for real- time measurement of the figure of a deformable mirror. The design allows for measurement of mirror figure in terms of optical path differences (OPD) between the surface of the mirror and a static reference wavefront. Measurements are made on a 31 by 31 square grid. This instrument is relevant for atmospheric adaptive optics systems because it provides a method for accurately monitoring the figure of a deformable mirror during real-time compensation of atmospheric turbulence. Measured values of OPD on the mirror surface are output in digital form at approximately 10 kHz and can be used as a feedback signal in a digital control-loop for driving the deformable mirror. The system uses a common 4-bucket or 4-measurement interferometric algorithm to compute OPD. The maximum measurable OPD is +/- 7.5 waves. Tests of the completed interferometer indicate that it can routinely measure the dynamic changes in figure of an optical mirror. Preliminary tests indicate that the measurements are accurate to approximately (lambda) /25.
We report on the operation and performance of a complete integrated 1 m adaptive optics systems for compensation of atmospheric distortion of optical wavefronts. Both visible artificial laser guide stars (doubled Nd:YAG laser with wavelength of 0.532 micrometers ) and natural stars can be used as sources for reference wavefronts. A polarization shearing interferometer which uses a narrow optical bandwidth and has 500 subapertures is employed to sense wavefront distortion. These measurements are used to compute a conjugate wavefront to the distorted input light. The computed conjugate is then imprinted on a deformable mirror which consists of 500 individual square mirror segments. The effectiveness of the compensation is determined from a measured PSF of the system. Both indoor benchtop and atmospheric experiments are under way to test the performance of the integrated system. The results of these tests so far are very promising, yielding short-exposure images at 0.532 microns which contain discernible energy at the diffraction limit of 0.1 arcsec.
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