182. Design of multilayer filters by successive approximations

Abstracts 178-184 nitrous oxide, methane, and propane have been investigated. Although the ultimate limitations of pressure modulation as a detection technique have not yet been completely established, the present results are in qualitative agreement with predictions based o n the earlier studies of Howard, Butch, and Williams. Modulation is of use in distinguishing weak absorption bands from background absorption in the atmosphere. In strong absorption bands, the wings are enhanced in the modulated spectrum ; in weak bands, the modulated spectrum approximates that obtained by conventional methods. Possible applications of pressure modulation are suggested. (Author) James C. Gilfert and Dudley Williams, J. Opt. Soc. Amer. 48, No. 11, 765-769, Nov. 1958. 19 : 30 : 51 178. Antireflexion Coatings for Ge and Si in the Infrared. Very hard and durable single layer antireflexion coatings for Ge and Si have been made which result in a peak transmittance of better than 98 per cent at any desired wavelength in the infrared up to a b o u t 15/~. Silicon monoxide makes an excellent antireflexion coating for Si and Ge in the near infrared, but cannot be used in the 10-/z region where it becomes strongly absorbing. Zinc sulfide has been found to be the most suitable antirefecting material at the longer wavelengths. U n d e r proper conditions zinc sulfide films, which in the past have frequently exhibited unsatisfactory durability, can be prepared as very hard and adherent antireflexion coatings for Ge and Si. The best zinc sulfide films are obtained when the substrate is heated to about 150 °C and cleaned with a d.c. glow discharge just before the evaporation is made. The coatings can stand several hours boiling and several days immersion in water without damage and have been used for periods up to one year without showing any deterioration. (Author) J. T. Cox and G. Hass, J. Opt. Soc. Amer. 48, No. 10, 677, Oct. 1958. 19:51 179. Index of RefraefionofGe. Calvin D. Salzberg and John J. Villa, Z Opt. Soc. Amer. 48, No. 8,579, Aug. 1958. 19 180. Spectral Effects in Interferometry. The infuence on the fringe intensities of sources with known spectral energy density functions is analysed b o t h theoretically and experimentally for double beam interferometers of the MachZehnder type. Simple relations between the spectrum and the fringe intensity and extent of the fringe field are presented. Special attention is given to energy sources consisting of a primary

source used with a monochromator. is demonstrated.

237 Experimental confirmation (Author)

G. D. Kahl and D. B. Sleator, J. Opt. Soc. Amer. 48, No. 8, 525-530, Aug. 1958. 19 181. Light Guide Radiation Pyrometry. A method of calculating and describing transmission characteristics of light guides is developed and applied to rods of synthetic sapphire. The total transmission is shown to be an inadequate measure of the extent to which a calibration curve relating relative signal to temperature is possible for a light guide radiation pyrometer. The angular field of view of synthetic sapphire rod is presented in terms of fractional emergent power per five degree angular increment. It is concluded that the transmission properties presented here, in combination with data for a single point, permit the simple, individual calibration of commercially available light guide radiation pyrometers. (Author) J. Vollmer, G. C. Rein and J. A. Duke, J. Opt. Soc. Amer. 49, No. 1, 75-77, Jan. 1959. 19 : 30 182. Design of Multilayer Filters by Successive Approximations. A relaxation method is used to adjust the thicknesses of the film of a multilayer in order to alter its transmission characteristics in a limited spectral region. This region is used to modify the spectral transmission of a short-wavelength pass multilayer and a broad-band dielectric mirror. The computations also furnish information useful in controlling the thicknesses of the layers in the fabrication of a multilayer. (Author) Philip Baumeister, J. Opt. Soc. Amer. 48, No. 12, 955-958, Dec. 1958. 19 : 32 183. Primary Frequency Standard Using Resonant Caesium. United States. Caesium atoms in a sealed beam tube comprise the heart of a primary frequency standard. New techniques of evacuating the tube, 6 ft long, have made possible a practical and reproducible frequency standard. The complete system generates 9,192.6318 Mc/s (the resonance frequency) from a 5 Mc/s crystal oscillator, whose frequency is automatically corrected by a control loop. Outputs, accurate to 1 in 109 are available at 100 kc/s, and 1, 5, 10 and I00 Mc/s. M.D.A. W. A. Mainberger, Electronics 31, 80-85, 1958. 19 184. Semiconductor P-N Junction Radiation Counter. Letter from B. Salzberg and K. Siegel, Proc. Inst. Rad. Engrs. 46, 1536. Aug. 1958.