METHOD OF AND DEVICE FOR MEASURING THE ANGLE BETWEEN THE PLANE OF POLARIZATION OF PLANE POLARIZED LIGHT AND A REFERENCE PLANE

摘要

1322470 Investigating polarized beams CARL ZEISS-STIFTUNG [trading as CARL ZEISS] 19 April 1971 [7 March 1970] 23721/71 Heading G4H [Also in Division G1] In a device for measuring the angle "α" between a plane polarized light beam 1 and a reference plane, the light beam 1 is passed via a rotating analyser 2 on to a photo-cell 4 and the resulting electrical signal is processed by a D.C. amplifier 4, a high gain differential amplifier 5 and fed into a digital circuit 7 which also receives a signal representing the reference plane. The reference signal is provided by a light source 11 and detector 10 arranged about an opaque rim 9 on the analyser 2 as shown. The differential amplifier 5 also receives a constant D.C. voltage by means of a variable resistance 6 and as a result has a square wave output in which each square wave pulse is centred about the angle of minimum passage of light through the analyser (Figs. 2a, 2b, not shown). The digital circuit, shown in Fig. 3, provides a digital value for the minimum angle. The circuit comprises two bi-stable flip-flops 16 and 17 which may be turned on "O" or off "L" by positive going signals only. The pulse U 12 representing the reference plane turns on the flip-flop 16 and allows pulses from a pulse generator to pass through an AND gate 18 and an OR gate 19 to a counter 8. Then the positive going signal provided by the side 14 of the pulse U 5 due to the polarized light beam switches off the flip-flop 16 and passes via an AND gate 20 to switch on the flip-flop 17 and the pulses from the pulse generator then have to pass via a 2 : 1 reducer stage before they pass via an AND gate 23 and an OR gate 19 to the counter 8. Finally the negative going side 15 of the pulse U 5 switches off the flip-flop 17 by way of a negative stage 24. Thus the value on the counter 8 is a measure of the position of the angle of the minimum passage of light and is thereby a measure of the angle of the plane of polarization. At the end of each rotation of the analyser 2 after read out of the counter 8, the counter is immediately cancelled through input 25. In an application to an interference microscope, Fig. 4, comprising a light source 30, a collector lens 31, a polarizer 32, a condenser lens 33, a beam splitter 34 a #/2 plate 35, a beam uniter 37, an objective lens 38, a #/4 plate and an eyepiece 41, the object under investigation is held at the object stage 36 with a comparison medium in the paths of the measuring and comparing polarized rays 43 and 42 respectively. The difference of the refractive values of the object under investigation and the comparison medium is then represented by the angle of rotation of the polarized light and it is measured by an arrangement similar to the Fig. 1 embodiment.