SU813133A1 - Device for measuriing crystal rlate thiskness in the process of finishing - Google Patents

Description

(54) DEVICE TO CONTROL THICKNESS

CRYSTAL PLATES IN THE PROCESS OF ARRANGEMENT

reference voltage oscillators, outputs connected respectively to the first inputs of the phase meter and the synchronous detector, the second inputs of which are connected to the outputs of the respective selective amplifiers.

FIG. 1 shows a diagram of the proposed device; in fig. 2, the position of the interference maxima at different thicknesses of the crystal plate (t is the interference order, A- (j is the working wavelength of light); circumferences, ellipses and straight lines denote circular, elliptical and linear polarization of light after the compensator for the length Ar waves; Fig. 3 illustrates the shape and relative amplitude of the electrical signal at the photodetector output as a function of the azimuth of the rotating quarter-wave phase plate for different states of polarization of the light after the compensator.

The device contains a light source 1, a monochromator, the role of which can be performed, for example, a light filter 2, a lens 3, a polarizer 4, a 1 sensor 5, placed in a thermostat b with protective windows 7 and 8, a black-wave Phase plate 9 rotating with a circular frequency ( i) from the electric motor 10, the fixed analyzer 11, the lens 12 and the photodetector 13. The electrical signal from the Lotto receiver 13 is divided into two. One of them through the selective amplifier 14, tuned to the frequency of 2 oh, comes one of the inputs of the phase meter 15. The reference voltage generator supplied to the second input of the gas meter 15 consists of a disk 16 with two holes 17 arranged circumferentially through 180, incandescent lamps 18 and a fluoropole 19. Another electric signal through a selective amplifier 20, tuned to the frequency 4ou, goes to one. from the inputs of the synchronous detector 21. The reference voltage generator supplied to the second input of the synchronous detector consists of the same disk 16, but with four holes 22, circumferentially through 90 ° and radially offset from the holes 17, of the lamp 23. and a photodetector 24.

The compensator 5 consists of two plane-parallel plates of crystalline quartz of the same thickness, enclosed in a frame (not shown in FIG. L) tilting around a horizontal axis. The plates are cut parallel to the optical axis, oriented relative to each other so that their main sections are mutually perpendicular and fixed in the frame so that the main section of one of the plates is parallel

the axis of rotation of the frame, i.e. horizontally. In this case, an increase in the angle of inclination of the compensator corresponds to an increase in the phase difference introduced by it.

The polarization planes of the polarizer 4 and the analyzer 11 should be mutually parallel and form the corners of the main sections of the controlled crystal plate 25 and the compensator plates 5. The device operates as follows.

The intensity of the light flux incident on the photodetector 13 is determined by the following formula: 5 I | O (A - B sin + C COS 4u) t), (1)

where is

0 6 - Sin6;

C - cosS-. 4Here Other - the maximum intensity of the light flux, - the total phase difference of the controlled plate and the compensator at the wavelength X.

Controlled phase plate 25 is placed in thermostat 6. Initially, compensator 5 is added to

0 the fractional part of the order of interference of the controlled plate 25 to a value of 0.25 or 0.75, in which the light coming out of the compensator 5 is polarized in a circle. The criterion for this is the absence of a signal component with a frequency observed on the synchronous detector 21. In this case, the reading of the compensator 5, previously calibrated, gives

Q possibility to determine the fractional part of the order of interference of the crystal plate 25.

The fractional part of the order of interference of the crystal plate 25, and hence the excess of its thickness, is uniquely determined from one indication of the compensator 5, corresponding to the absence of an electrical signal component with a frequency of 4aj, while simultaneously recording the phase of the electrical signal component with a frequency of 2ci.

Thus, the introduction of a quarter-wave phase plate, rotated by a JJ with a constant frequency, and the implementation of a two-channel electron-recording unit makes it possible to significantly simplify the control process and increase its accuracy. i

Claims (2)

1. USSR author's certificate number 344265, cl. G 01 B 11/06, 1972. 2. Authors certificate of the USSR 121240, cl. G 01 B 11/06, 1959 (prototype). S m-Jm-1 Lll Ld  ABOUT LAA L / U7- / IQ / Пffj.) Lal LAL T- / m / rr- / I Vt A A ff Jl / Tt Ha 9nol1 figure 2 s Azimdt phase and p / ae / piil .3