A dual sensor wavefront correction system is adaptable to correcting wavefronts including wavefronts that are severely scintillated. The system includes a Hartmann wavefront sensor as well as a unit shear lateral shearing interferometer (LSI) wavefront sensor. The optical output signals from the Hartmann wavefront sensor are applied to a real reconstructor which provides an estimation of the distortion in the wavefront during most conditions except for conditions of severe turbulence. In order to provide compensation for the phase discontinuities in a scintillated wavefront, a unit shear lateral shearing interferometer (LSI) wavefront sensor is provided. The optical output signals from the unit shear LSI wavefront sensor are processed by a complex reconstructor in order to provide relatively accurate estimates of the tilt signals at the discontinuities. The output of the real reconstructor and the complex reconstructor are combined in a synergistic manner to provide a composite correction signal to the actuators of a deformable mirror. As such, the wavefront correction system has a relatively wide dynamic range and is not blind to discontinuities in the wavefronts as a result of turbulence. A steering mirror may also be provided to optimize the dynamic range of the deformable mirror.
A lateral shearing interferometer wavefront sensor system (10) that employs a double-shear/full aperture approach to correct for branch points in the wavefront of an optical beam (24) that has been aberated. The wavefront sensor system (10) includes a lateral shearing interferometer (12) having a beam splitter (14) that splits the beam (24) into a first split beam (28) and a second split beam (26), a beam shifter (22) that shifts the first split beam (28) relative to the second split beam (26), and a beam combiner (16) that combines first shifted split beam (28) and the second split beam (26) into a combined beam (30). The combined beam (30) provides an interference pattern that includes a plurality of interfered beam portions (76, 78, 82, 84). A deformable mirror (72) includes a plurality of actuators (74) which deform the mirror (72) to correct the beam wavefront. The interfered portions (76, 78, 82, 84) are twice the distance apart between actuators (74),or a double shear such that interfering portions (76, 78, 82, 84) do not align with branch cuts between the actuators (74).
A state space wavefront reconstructor for use in an adaptive optics control system is disclosed. The adaptive optics control system comprises a wavefront corrector having a surface controlled by a plurality of actuators, at least one wavefront sensor adapted to measure at least one wavefront state of the wavefront and generate wavefront sensor output signals indicative thereof, and a state space wavefront reconstructor adapted to receive the wavefront sensor output signals and generate a plurality of correction signals based thereon to be applied to the wavefront corrector. The wavefront reconstructor comprises a wavefront velocity estimator, a state space wavefront estimator, and a wavefront phase reconstructor. A method of compensating for the distortion of an optical wavefront using such a state space wavefront reconstructor is also disclosed.
An improved, adaptive optics control system having a signal-to-noise ratio-tuned wavefront corrector is disclosed. The system comprises a wavefront corrector, a wavefront sensor, a wavefront reconstructor and a wavefront controller. The wavefront corrector has a surface controlled by a plurality of actuators. The wavefront slope sensor has a subaperture separation mechanism for defining a plurality of subapertures through which the distorted wavefront can pass, each subaperture corresponding to an actuator of the wavefront corrector. The wavefront slope sensor produces a wavefront sensor output signal for each subaperture indicative of the distortion of the wavefront. The wavefront reconstructor is adapted to receive the wavefront sensor output signals and calculate corresponding phase estimates based thereon, each phase estimate having a signal-to-noise ratio. The wavefront reconstructor generates a plurality of correction signals to be applied to each of the actuators of the wavefront corrector, each correction signal having a bandwidth. The wavefront controller is adapted to selectively adjust the bandwidth of each correction signal based on the signal-to-noise ratio of the corresponding phase estimate of the actuator to which it is to be applied. A method of optical wavefront distortion correction is also disclosed.
A hybrid curvature/tilt wave front sensor (50) that employs both tilt measurements and curvature measurements of the wave front of a light beam (16). The light beam (16) is split into a first path and a second path. The light beam (16) on the first path is directed to a tilt sensor (12) employing a lenslet array (24) having a plurality of lenses (26). The lenses (26) focus separate portions (32) of the wave front onto a CCD (28) that provides local intensity measurements. A computer (30) receives electrical information of the intensity of the various beam portions (32) and computes a tilt measurement based on this information. The light beam (16) on the second path is directed to a curvature sensor (14) that includes a pair of CCDs (40, 42) positioned at the same distance before and after the focal plane of a lens (52). The intensity measurement of the beam (16) at these locations is sent to the computer (30) which performs curvature measurements on the beam wave front. Algorithms are employed to determine the phase of the wave front based on the tilt and curvature measurements.
A method and apparatus for producing a scintillation-immune adaptive optics reconstructor is disclosed. The present invention includes a wavefront sensor (70) which determines illumination slope and amplitude of a number of subapertures (75). The slope and amplitude information is coupled to a slope weighting function (90), which weights the slopes of each subaperture (75) according to the amplitude of illumination of each subaperture. The present invention determines the variation in light amplitude received by the subapertures (75) and determines a slope of the light amplitude variation. The signal gain of the imaging system is then adjusted depending on the slope of the light amplitude variation, thereby yielding a closed-loop system that compensates for amplitude disturbances caused by scintillations in the images received by the imaging system (10).
