New techniques in optical interferometry

Abstract

The first section deals with the optical properties of thin films, especially their reflection and transmission coefficients. Multiple dielectric films, deposited on glass surfaces, can be made to have reflection coefficients up to 0·9 for visible light, with very small absorption losses. Considerably higher reflectivities can be reached with silver films, but the absorption losses are higher and increase with decreasing wavelength. Metallic reflectivity can be increased if one or two dielectric films of appropriate thickness are deposited on the metal surface. The intensity distribution in the reflected and transmitted light in multiple beam interference is discussed and applied to interference filters. `Frustrated total reflection' filters and polarization filters are briefly described.Part II deals with some new developments in the methods of using Fabry-Perot etalons. The resolving power of these instruments is, in practice, limited by geometrical imperfections of the glass or silica surfaces. The theory and practical performance of the double etalon, both with different and with equal spacings, the photoelectric method of recording etalon fringes and the use of etalons in solar spectroscopy are described.Part III deals with standards and testing methods, pure isotope light sources, testing of gauges and of optical instruments, and gives a description of the `wavefront shearing interferometer'.The interferometric study of surfaces forms the subject of Part IV, especially the method of using multiple beam interference fringes. The various forms of the method, using Fizeau fringes and heterochromatic fringes, either in transmission or in reflection, are described and their applications briefly indicated.In the last section some recent modifications of the classical methods of interference refractometry are discussed, and also applications of interferometers of the Mach-Zehnder type to the study of gas flow at high speeds.The method of interference microscopy is outlined and some recent designs of interference microscopes are described.