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A nine-aperture, wide-field Fizeau imaging telescope has been built at the Lockheed-Martin Advanced Technology Center. The telescope consists of nine, 125 mm diameter collector telescopes coherently phased and combined to form a diffraction-limited image with a resolution that is consistent with the 610 mm diameter of the telescope. The phased field of view of the array is 1 murad. The measured rms wavefront error is 0.08 waves rms at 635 nm. The telescope is actively controlled to correct for tilt and phasing errors. The control sensing technique is the method known as phase diversity, which extracts wavefront information from a pair of focused and defocused images. The optical design of the telescope and typical performance results are described.

Much confusion about jet noise has come about as a direct result of inadequate facilities and insufficient knowledge and control of test conditions, in many cases giving rise to completely erroneous conclusions. The facility described here has been carefully designed, accounting for the shortcomings of other facilities and being guided by the stringent demands of ongoing jet noise research at Lockheed. The design goal was the capability of testing model jets up to 2000°F at pressure ratios as high as 8, in a free-field environment anechoic at all frequencies above 200 Hz. A comprehensive series of flow visualization and temperature mapping experiments in a one-sixth scale-model anechoic room was conducted. The results dictated the design of the exhaust collector/muffler to provide entrainment and room cooling air in the quantities demanded by the jet operating conditions. In order to optimize the choice of material and anechoic wedge design to achieve the 200-Hz requirement, a special impedance tube was used extensively in performance evaluations. Some features of the facility are (1) an exhaust collector providing air in quantities dictated by the particular jet operating condition with no special forced-air injection or fan installation and (2) a “cherry-picker” crane used to gain access to instrumentation, etc., for maintenance, calibration, and setup, thus eliminating the need for access platforms, etc. The crane is stowed by remote control under an anechoic cover during all test operations. The superior performance of the room is described by intensity/distance plots obtained from a fixed loudspeaker source and moving microphone installation.

An electromechanical model of a deformable mirror was developed as a design tool for adaptive optical systems. The model consisted of a continuous, mirrored face sheet driven with multilayered, electrostrictive actuators. A fully coupled constitutive law simulated the nonlinear, electromechanical behavior of the actuators, while finite element computations determined the mirror's mechanical stiffness observed by the array. Static analysis of the mirror/actuator system related different electrical inputs to the array with the deformation of the mirrored surface. The model also examined the nonlinear influence of internal stresses on the active array's electromechanical performance and quantified crosstalk between neighboring elements. The numerical predictions of the static model agreed well with experimental measurements made on an actual mirror system. The model was also used to simulate the systems level performance of a deformable mirror correcting a thermally bloomed laser beam. The nonlinear analysis determined the commanded actuator voltages required for the phase compensation, and the resulting wavefront error.

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