Abstract

The paper gives a general survey of the main institutions where research in optics is carried on in Great Britain. A more detailed account is given of the activities of the Light Division, National Physical Laboratory, the Optics Department, British Scientific Instrument Research Association, and the Technical Optics Section, Imperial College of Science and Technology.

© 1962 Optical Society of America

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Figures (9)

Fig. 1
Fig. 1

N.P.L. spectropolarimeter. In this spectropolarimeter, two crystalline quartz prisms, cut with the optic axis at right angles to the prism base, are used both to disperse the radiation and to polarize it. The optical system closely resembles a double monochromator, wavelength scanning being provided by the rotation of two plane mirrors about a common axis. The optical rotation of the specimen is recorded in terms of current; this is derived automatically from an electronic system utilizing two Faraday cells with cores of fused silica. The wavelength range of the instrument is 200 mμ to 600 mμ, and the output noise level is less than 0.001° over most of this spectral range.

Fig. 2
Fig. 2

Cut-away model of absolute radiometer developed in the Light Division, N.P.L., for fundamental measurement of radiant power. The radiation is totally absorbed in a blackbody receiver. The heat so produced is measured by comparison with heat produced electrically in an in-built resistive element.

Fig. 3
Fig. 3

Increment–decrement threshold equipment, in the Light Division, N.P.L., for studying the properties of the underlying receptor mechanisms of human vision. Screening has been removed. The equipment has so far been used for studying the form of the spectral response functions of the eye, their summation properties with respect to wavelength, luminance, and time, and the effect of various sources of scattered light in the eye on visual performance.

Fig. 4
Fig. 4

Light Division, N.P.L., has developed the use of diffraction gratings for precise linear and angular measurement. In the tool room lathe shown above the linear movement of the tool saddle and the rotatory movement of the work-piece are monitored by suitable gratings and accurately related by a servo system.

Fig. 5
Fig. 5

Two examples of the position-sensitive photocell (“Wallmark diode”) as developed at B.S.I.R.A. for use in optical instruments.

Fig. 6(a)
Fig. 6(a)

The experimental prototype of an electrical autocollimator utilizing the position-sensitive photocell.

Fig. 6(b)
Fig. 6(b)

The collimator with cover removed. (by courtesy of W. Ottway & Co. Ltd)

Fig. 7
Fig. 7

Taking a sample from the melt of a new glass in the B.S.I.R.A. furnace room.

Fig. 8
Fig. 8

An interferometer for the measurement of optical frequency response. Light from an entrance slit is collimated by the test lens and is incident on the interferometer assembly as shown. A shear is introduced between the two beams leaving the interferometer by means of the shear plates S1 and S2. Fringes are then formed between the overlapping portions of the two sheared beams, any given shear corresponding to a definite spatial frequency. The light flux in the overlapping portion is caused to vary sinusoidally by the reciprocating movement (which has a linear velocity in each direction) of a small-angle prism P in one arm of the interferometer. The ac component of the electrical signal produced when the total light flux is incident on a photomultiplier is fed, after amplification, to an ac pen recorder. The amplitude of the ac signal relative to that in the nonsheared pupils gives a modulus of the frequency response function for the particular value of the spatial frequency. Continuous variation of the shear by rotation of S1 and S2 enables the frequency response curve to be recorded. A point to be noted is that because each beam is reflected from the beam splitter BS and the mirrors M1 and M2 there is automatic compensation for tilt between the two emerging beams.

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