Microelectromechanical system programmable aberration generator for adaptive optics.

Adaptive optics systems and control algorithms can be tested in the laboratory with controlled disturbances. We have a micromachined deformable mirror that we use as a programmable aberration generator. We present a method of programming the actuator amplitudes so that the wave front reflecting from the surface will simulate atmospheric turbulence. We present experimental results that show that we can simulate the Kolmogorov spatial spectrum within the constraints of the useful region of the deformable mirror.

Adaptive optics and ground-to-space laser communications.

The relationships between laser communication system parameters and adaptive optics system parameters are addressed. Improvement in optical signal propagation between space-based receivers and ground-based transmitters is possible with adaptive optics systems that compensate for a few degrees of freedom. Beginning with the relationship between optical signal fade and surge and the atmospheric log-amplitude variance and coupling to expressions that combine adaptive optics systems performance with the reduction in log-amplitude variance, system level examinations of the effects of adaptive optics can be done. Examples are given that show the advantageous reduction in signal fade and surge when adaptive optics are built into the optical system.

Conversion of Zernike aberration coefficients to Seidel and higher-order power-series aberration coefficients.

This Letter describes the derivation of a matrix equation that can be used to determine the Seidel and higher-order power-series aberration coefficients from an aberration function expressed in terms of Zernike coefficients. The elements of the conversion matrix are given in analytic form, and the first 195 nonzero elements are given in a table. Two examples of the use of the conversion formula are presented.

Using the deformable mirror as a spatial filter: application to circular beams.

Adaptive optics correction of a wave front by a deformable mirror that acts as a lossless spatial filter is studied. The decomposition of the wave front into Zernike polynomials provides a means for deriving the rms error of a corrected wave front in analytic form. The spatial filter is given in a functional form related to deformable mirror characteristics. A step filter approximation is derived and the conditions where the approximation holds are examined. An example is provided to demonstrate the utility of the spatial filtering concept for adaptive optics systems analysis.

Practical considerations in gamma camera line spread function measurement.

In recent years the modulation transfer function (MTF) has played an important role in the quantitation of imaging performance of gamma cameras. The most common method of MTF determination requires line spread function (LSF) measurement. This paper reviews methods used for LSF measurements with special consideration given to the practical aspects of LSF measurement and MTF calculation. An analysis of errors in LSF measurements is made and means to reduce or to avoid these errors are discussed. Recommendations regarding practical considerations for LSF measurement and MTF calculation are presented in tabular form for convenience.

Computer simulation study of Siemens star x-ray image artifacts.

In the Siemens star image, exact determination of the first disappearance frequency, which is used to measure the focal spot size, is difficult since the disappearance band has a finite width and the image also has other artifacts. The origin of these artifacts and their appearance was studied by Siemens star image simulation on a digital computer. The simulated images were manipulated by using many different modulation and phase transfer functions. It is shown that the bending of spokes is not related to zero contrast; exact triplet splitting can occur only at the disappearance frequency, and therefore splitting is a valuable indicator of that frequency.