A far infrared filter monochromator with reststrahlen crystals has been constructed for use irr the region between 50μ and 150μ. In order to cover this region, , NaCl, KCl, KBr, KI and KRS-5 crystal plates are employed. The filtering system is characterized by setting two of the reststrahlen plates at crossed position to eliminate short wave radiation and to reduce the degree of polarization. This kind of monochromator has simple construction and provides fairly large energy for the longer wavelength region where energy is scarce. The performance of the monochromator has been examined by measuring specimens of which transmittance was already measured with a grating monochromator and satisfactory agreement between data by two instruments has been obtained.
A gas laser interferometer has been devised by utilizing coherent property of beams from opposing ends of a gas laser. With this interferometer under various conditions, several interference experiments are made with interference fringes that appear by superposition of two beams from opposing ends of Gihe laser. Some characteristics of gas laser can be obtained from the study of these interference fringes. For example, the existence of spatial coherence between the said two beams; possibility of observation about the conditions of spatial coherence and wavefront seen in mode patterns by superposing and shearing the beams; formation of ring-type interference fringes and its interpretation; and the phase reversal occurring here and there in the mode pattern and its demonstration
It is shown that the optical transfer function of a focal spot of an X-ray tube can be defined and treated in quite the same way as other blurring elements. Optical transfer functions of the, focal spots are measured photoelectrically with an X-ray fluorescent screen. The line spread func-n tion of the focal spot in X-ray intensity distributions is reproduced on the fluorescent screen in. the form of light emissions when a metal slit is placed between the focal spot and the fluorescent: screen as an object, and the light image on the fluorescent screen is Fourier-transformed optically by an area type masking method with a direct scanning apparatus described in a previous paper6). Optical transfer functions of the focal spot which have negative components along some directions: correspond to photographs of a Siemens' star which shows spurious resolutions. The line spread function calculated from optical transfer function data agrees with the one obtained by the photographic method within experimental errors. Field characteristics of the focal spot due to the geometry of the X-ray tube are obtained theoretically and experimentally, and good agreement between the results by these two treatments shows that field characteristics can be determined by simple calculations in some specified fields. It is suggested that field characteristics can be effectively applied to practical radiographic techniques for clinical purposes.
In this part, several methods for quantitative measurement based on the optical double diffraction of the phase distribution in material are described. 1) When a sharp cut-off amplitude filter (i.e., mask) is scanned at a constant velocity in Fraunhofer diffraction plane of the specimen observed, the density distribution of photographic film obtained by photographing the image of a specimen corresponds to the distribution of phase gradient in material. 2) When a linear graded amplitude filter (optical wedge) is inserted in the diffraction plane, the phase distribution can be calculated by the photometric result of the image intensity distribution. Since the result is obtained by a single photographic operation, it is very convenient to measure the time dependent phase distribution or analyze the stress and strain of a specimen in motion. 3) When the phase difference of a specimen is very small as compared with the wavelength, the phase distribution can be presumed approximately from Hilbert transformation of the image intensity which is yielded in a system with half stop. 4) When a polychromatic light source is adopted instead of a monochromatic one and a prism is placed in front of specimen, a coloured image pattern can be obtained. The colour distribution in the image is equivalent to the distribution of phase gradient in the specimen. Of course the analysis of stress and strain is possible by these methods as well as by the mask scanning method described in Part I. Especially the following consideration is given in Appendix. When the phase distribution has a singly periodic sinusoidal construction, the distribution can be determined quantitatively by the photometric observation of the average intensity in the image plane.
Image transfer properties of optical fiber are different in two cases of static and dynamic transfers. In the case of static image, a knife edge is conceived as the object and the transfer function is defined as the Fourier transform of differential of the image, and from results of calculations, a conclusion is drawn that the transfer function obtained on dynamic image is a measure of the quality of static image. If viewed dynamically, the case of flare can be treated with ease as a case of an ordinary optical imaging system. Results of some simple experiments agree well with those obtained by calculation.