Wedge immersed thermistor bolometers

961,906. Infra-red detectors. BARNES ENGINEERING CO. Aug. 16,1962 [Aug. 29, 1961], No. 31542/62. Heading G1A. [Also in Division H1] A bolometer comprises a wedge shaped lens 1 (Figs. 1, 2 and 3) the aspect ratio of the part spherical front surface 2 of which differs from unity and the tapered surface 3 of which is provided with at least one "immersed" radiation detector 4 preferably consisting of a thermistor "flake" insulated from surface 3 by a layer 9 of arsenic modified selenium. The lens which is preferably made from germanium, is supported in a holder comprising two wedges 6 (also preferably of germanium) spaced by plastic buttons or strips 7 the whole being cemented together with an epoxy cement 8. The leads 5 are connected to the thermistor "flake" through an area of thin deposited gold which also defines the active area. The use of a wedge shaped lens is stated to improve the sensitivity, due to the reduction in "flake" size, by a factor approximately equal to the square root of the aspect ratio of surface 2 (5: 1 in the described embodiment). The bolometer is of particular advantage in instruments in which the product of the aspect ratios of field-stop and entrance pupil departs significantly from unity. A series of such bolometers may be used in an infra-red spectrometer each lens receiving only a narrow band of radiation of a particular wavelength and to prevent "cross-talk" baffles may be employed between each lens. Specifications 881,575 and 945,566 are referred to.