Development of radio astronomy, since its birth, has been closely dependent on that in the instrumental technology. A large variety in size and shape of radio telescopes are being used. A simple parabolic areial has an advantage of simpleness while the limitation in the resolution is its main disadvantage. Improvements in the accuracy of construction and thus the usefulness in the shorter wave-lengths are the recent trends. Aperture synthesis and image synthesis provide a possibility of very high resolution by trading off sensitivity and flexibility. Use of multiple element for the former and multiple cabling network for the latter improves the sensitivity to equal a filled aperture of the same size, yet with more flexibility. Recent trends and problems in these improvements are discussed in detail.
Several methods of filtering the Fraunhofer diffraction plane in the double diffraction system have been studied to measure the optical phase distribution of large variation at one time. “Sine amplitude filter” and “grid cut off filter of gradient pitch” are found to be suited for “widerrangeschlieren method.” These methods are more excellent on the range width and accuracy of measuring the optical phase distribution than conventional schlieren or interference method. They are applied to analyses of strain and principal stress. Using reflection and transmission arrangements placed a polarizer before a sample can discriminate the effect due to variation of absolute refractive indices of a strained material from the effect due to variation of its thickness.
The light absorbing filter made by the deposition of absorbing film on to glass plate have the useful property. The filter's optical density can be readily controlled to be uniform independent of the thickness of the glass plates. The absorbing films for this purpose were prepared by evaporating chromium-oxide in vacuo. The optical constants of the films in the visible region were obtained from the measured values of transmittance and reflectance. Then the conditions of the double-layer anti-reflection which reduce the reflection of the absorbing films to zero at the wavelength of 550μp were calculated as a function of thickness of the films. Using these results, the spectral reflectance of the evaporated chromium-oxide films with the anti-reflection coatings of cerium-oxide and magnesium-fluoride was calculated and compared with the experimental results.
The sensitivity improvements on LiF phosphors as thermoluminescent dosimeters were made with the method of thermal treatments. In the investigation of thermal treatment method, the atmosphors used were air, nitrogen and argon gasses. The thermoluminescent yields of the phosphor which were treated at 600°C in argon gass for 500hr were given about 95% as compared with the yields of Harshaw TLD-100 LiF phosphors. In case of thermal treatments in air, LiF phosphors treated at 400°C had good sensitivity for exposure of ionizing radiation.. But the treated crystals in air contained OH ion and its transmission decreased in comparison with original crystals. It was reported that poor sensitivity of treated phosphors in air at higher temperatures is caused by the killer action of OH ion for thermoluminescence phenomena and the decrease of transmission.
An analog technique is described for improvement of signal-to-noise ratio by average response, computation. A device composed of a conventional multi-track magnetic tape recorder and simple electronic circuits, in which all the computation is carried out in analog form, has been constructed. The principle of operation is on the basis of accumulating the recurrent data on a magnetic tape through a summing amplifier successively. The results obtained show that this technique allows the accumulation of data as many as one hundred times for any signal containing the frequency components lower than 10cps. and retrieval of weak signals concealed by noise is accomplished to an accuracy of 0.5 percent. The sources of restricting the computational accuracy are also discussed in detail.
Theoretical and experimental analyses on the images reconstructed from acoustic holograms are conducted. The sound waves are used to construct the acoustic holograms, with the frequencies of 10kHz_??_20kHz. The optical reconstruction is made to use laser light (6328Å). The virtual and the conjugate images are observed. The relation between the light intensity levels converted from the acoustic fields and the reconstructed images is discussed. The effect of the scanning lines produced by the scanning of a microphone to the reconstructed images is analyzed. An improvement of the reconstructed images is done eliminating the spectrums of the scanning lines. The effects of the limitation of the hologram plane and frequency-chaging of the sound waves to the reconstructed images are also analyzed. Further, the basic consideration on the three dimensional information storage in the acoustic holagrams is made.