SU1002828A1 - Device for checking mirror shape - Google Patents

Description

one

The invention relates to instrumentation technology and can be used, in particular, to control the shape of mirrors.

A device for controlling the shape of mirrors using an amplitude modulation of an optical signal and comprising a laser, a modulator unit, a Michelson interferometer, a photodetector (dissector) and a meter (phase meter) is known.

The conversion of the optical path difference into the phase of an electrical signal carried out in this device provides sensitivity in the order of hundredths of the laser wavelength l used.

A disadvantage of this device is the relatively low sensitivity of the control.

Closest to the invention by technical essence is a device for controlling the shape of mirrors, containing a successive laser, a Mdikelson interferometer, a photodetector, and a meter electrically connected with it. Sensitivity reaches a fraction of the wavelength of the laser 2 used.

The disadvantage of the known interferometer is the small amplitude of the mirror displacement of the optical resonator, which limits the frequency deviation

10 modulations, and hence the control sensitivity.

The aim of the invention is to increase the sensitivity of the control.

15

The goal is achieved by the fact that the device for controlling the shape of the mirrors is equipped with a drum, made to rotate around an axis, perpendicular to the plane passing through the optical axis of the laser, and at least one corner reflector rigidly fixed on the side surface of the drum and located in the optical path of the laser, the menad is its active element and ONE of its mirrors. Figure 1 shows the optical layout of the device for controlling the shape of the mirrors; figure 2 is a view of And figure 1; Fig. 3 is a plot of the law of frequency modulation of laser radiation. The device comprises a laser comprising a flat flat mirror 1, an active element 2 and a translucent mirror 3 Between the deaf flat mirror 1 and the active element 2, one or several are inserted into the optical path of the laser. to the corner reflectors rigidly fixed, for example pasted, on the lateral surface of the drum 5, mounted on the axis 6 of the electric motor (not shown). On the optical axis of the active element 2 behind the translucent mirror 3 a positive lens 7 is installed with the focus of which is combined a diaphragm 8 and a beam splitter 9. A beam divider 9, a lens 10, a reference spherical mirror 11 and a controlled mirror 12 form a Michelson interferometer, the output of which is an aperture 13 and a photodetector AND, for example, a photomultiplier tube connected to the input of the meter 15, which is used as a time meter. The diaphragms 8 and 13 are the center of curvature of the reference mirror 11 and the front focus of the objective 10 optically weighted. In front of the monitored mirror 12, a diaphragm 16 is installed, having freedom of movement in two directions in its plane. The device works as follows. A laser formed by a deaf plane mirror 1, an active element 2 and a translucent mirror 3, generates in the gain band of the active element 2 at a frequency determined by the instantaneous value of the length of the optical resonator and its rate of change. When the drum rotates 5 corner reflectors k, alternately falling into the optical path of the laser, i.e. The optical axis of the laser, enclosed between mirrors 1 and 3, periodically changes the length of the optical resonator, thereby causing the frequency 8284 laser emission to a certain sawtooth law ((curve 17 of the frequency modulation shown in FIG. 3)) The laser radiation is focused by the lens 7 onto the input diaphragm 8 and is split into two beams passing through the reference and measuring arms of the Michelson interferometer using a beam splitter 9. The reference beam reflected from the reference mirror 11 and the measuring beam The lens 10, the aperture 10, and the aperture 1b reflected from the counter-controlled mirror 12 is focused on the output aperture 13 and hit the input of the photodetector 1A. The apertures 8 and 13 serve to protect the input of the photodetector 14 from stray light. Aperture 1b serves to select the set the area of the monitored mirror 12. The optical path difference between the reference beam and the measuring beam in the area of the diaphragm 1b causes a time shift of the modulation law by the value of t (Fig. 3), and hence the frequency shift e-. The reference and measurement signals separated by frequency, simultaneously acting on the input of the photodetector 14, cause a pulse with frequency & at its output. The period T J5 of the beating of the signal of the photodetector AND is measured with a 15 time interval meter calibrated in units of length. The introduction of a rotating drum 5 with corner reflectors 4 into the laser resonator and the use of a 15 time interval meter instead of a phase meter allows a sharp increase in the sensitivity of the interferometer. The geometrical difference in the course of the measuring and reference rays is associated with the period T of the beats by the formula o, acoRT °, where w is the angular velocity of rotation of the drum 5; UQ is the maximum length of the optical resonator; R is the displacement of the axis of rotation of the drum 5 relative to the optical axis of the active element 2; Q is the wavelength of the laser used.

Claims (2)

Invention Formula A device for controlling the shape of mirrors, containing successively located laser, Michelson interferometer, photodetector and electrically connected with it meter, characterized in that, in order to increase the sensitivity of the control, it is equipped with a drum made with the possibility of rotation around an axis perpendicular to the plane passing through the optical axis of the laser, and at least one corner reflector rigidly mounted on the side surface drum and located in the optical path of the laser between its active element and one of its mirrors. Sources of information taken into account in the examination of Mottier F, M. Microprocessorbased automatic heterodyne interferometer, - Optical Engineering, vol. 18, No. 5, September - October, 1979 2. Esulun S.A., Wolff E.G.Advances in interferometric signal analysis. - JSA Transactions, vol, 19, (G 1, November-December, 1979 (prototype). FIG.