This paper describes the digital retrieval of a wave aberration when the modulus of pupil function and the point spread function (psf) are known. The Gerchberg-Saxton algorithm is used as the iterative retrieval method with an additional a priori information. Computer simulation in the case of 3rd-order spherical aberration is performed and some effects with regard to the measurement of the psf on the algorithm are demonstrated. It has been shown that the algorithm is considerably influenced by the accuracy of the measurement of the psf.
In the image reconstruction from projections, it is often occured that projections of an object are restricted with respect to angular view. A method to improve the image quality in such a reconstruction is proposed. Using this method, a better image is reconstructed compared with one by ART (Algebraic Reconstruction Technique). Computer simulations are conducted to show the utility of the method.
A servo-stabilized wave-front folding type of interferometer has been constructed for spatial coherence measurements. Sinusoidal phase-modulation is imposed on either wave-front of light in the interferometer in order to facilitate signal processing and servo-signal generation as well. The servo-stabilized optical system makes it possible to obtain reliable results as well as calibrate the measured erroneous phases due to imperfections of the optical components.
This paper reports a measuring method of the flow velocity using a transmission grating. The flow velocity is determined from the velocity measurement of particle images on the transmission grating Placed in front of a photodetector. These images formed by a microscope objective correspond to particles moving in a flowing fluid. By using the present method, the flow velocity distributions in a small flow cell are measured and their results are compared with the data obtained by using the differential laser Doppler method. It is shown that the present method can provide the data which are comparable in sensitivity and accuracy to the data obtained by using the differential laser Doppler method.
A study was made of visual evoked potentials (VEP's) elicited by heterochromatic stimuli. A periodic presentation of stimulus on a field of 2 degree of arc consisted of consecutive 500 msec duration of green, 12 msec of red or yellow, and 500 msec of green followed by 600 msec of dark. Averaged VEP's were recorded for 512 msec interval starting from the onset of the 12 msec red or yellow. Recordings were made for heterochromatic stimuli of equal lightness and unequal lightness. Recordings were also made for lightness induced potentials. The results revealed that the waveform of the VEP is strongly dependent on the lightness level and it is concluded that the assumption adopted for analyzing VEP's by several authors that VEP for an unequal lightness heterochromatic stimulus is linear summation of VEP's for the equal lightness heterochromatic stimuli and for the lightness stimuli may not be correct.
Natural frequencies and the corresponding mode shapes of circular cylindrical shells were experimentally investigated by time-averaged holographic interferometry. The shells used in the experiment had two kinds of boundary conditions, one of which was clamped at one end and free at the other, and the other of which was clamped at both ends. The natural frequencies which were measured ranged from 1137 to 7758 Hz, and the fifty-nine mode shapes were obtained. Some rough tendencies could be identified, although an exact conclusion could not be drawn due to insufficient numbers of experimental samples.
Mutual coherence function of a laser beam spatially modulated by an ultrasonic wave is fomulated in a low frequency region. It is verified theoretically and experimentally that the spatial coherence state of the modulated laser beam can be controlled through the potential voltage across the transducer. More effective controls are realized if a laser beam is doubly phase-modulated by passing it twice in a sound field.
Phase objects are made by exposing a Ronchi grating from a tungsten lamp on Type 649F plates, which are developed in D-19, fixed and bleached in R-9. Development of the edge exposure yields an overshoot on the high-density side of the edge image due to the adjacency effect. It is found that the amount of the overshoot in relief decreases as the bleaching time increases. Experimental results are shown.