SU1732291A1 - Method of surface wave phase velocity measuring - Google Patents

Abstract

The invention relates to the field of measurement of parameters of surface electromagnetic waves (SEW) and is intended for use in optical instrumentation. The method is implemented in a device containing a laser 1, a mirror 5, an input element 7 of a semiconductor, an element 8 that converts sew into a volumetric radiation, a photodetector 10. 9 volumetric emission frequency shifted. A phase difference meter 12 detects a beat phase difference at the photodetectors 10, from which the phase velocity is determined. 1 il. "(/)

Description

The invention relates to the field of optical instrumentation, in particular, to a technique for measuring the optical characteristics of surfaces, and can be used in designing a device for measuring the phase velocity of surface electromagnetic waves (SEW),

The aim of the invention is to carry out measurements in real time, while simultaneously increasing the accuracy of measurements.

The drawing shows a structural-functional diagram of a device for measuring the phase velocity of surface electromagnetic waves.

The scheme contains a laser radiation source 1, a beam splitter 2, a modulator 3 that shifts the frequency of the laser radiation, a laser radiation injection unit A along the propagation path of the surface of the semiconductor, made in the form of a mirror, a turning mirror 5, sample 6 converting sew into volumetric radiation (in the form of a diffraction grating), partially transmissive sew, element 9 converting sew into volumetric radiation (in the form of a diffraction grating), photodetectors 10 and 11, meter 12 phase difference signals.

The device works as follows.

The radiation from the laser source 1 is directed to the element 7 for the introduction of the sew and excites the sew propagating along the surface of the sample. The volumetric radiation received along the surface by the node k propagates collinearly with the sew. When the conversion element 8 which is translucent for the PEV element 8 is reached, the PEV is partially converted into volumetric radiation. A part of the bulk radiation along the surface also diffracts onto the PEV conversion element 8 and propagates along the same path as the volume radiation converted from the PEV. After the splitter, a modulator 3 is installed in one of the laser radiation channels, shifting the frequency of the laser radiation by fiW e) (the value of 1 / LLO should not be less than the time resolution of the photodetector), where CO is the frequency of the laser radiation, and the photoreceiver 10 records the beat signal at the frequency L CO That part of the radiation

five

which passed through the conversion element 8 and the volume radiation traveling along the surface through the sew conversion element 9 will also give a beat signal at the frequency UG) detected by the photoreceiver 11. However, the phase of this beat signal will be different from the phase of the beat signal detected by the photoreceiver 10 by the magnitude D1p, which is determined by the distance 1 between the conversion elements 8 and 9 and the phase velocity of the vacuum generator V, the phase difference of the DC is determined by the difference of the optical path lengths between the conversion elements 8 and 9 for the vacuum generator and for the bulk radiation along the surface and, as can be seen from the drawing, it

20 equals:

YU . (S + LSO) W G)

- - 1 1- - 1,

V СV С

where c is the speed of light. The last approximation is valid with good accuracy, so how do (I "SZ. Hence:

C01 UJl + TftifTc

Thus, by measuring the phase difference of the beat signals, it is possible to determine the phase velocity of the sew,

v with

The time resolution of the device is in the order of (1 / AOD)

and is limited to the bottom only by the time resolution of the photodetectors. This time resolution may be substantially less than the characteristic times of the processes occurring on the surface.

metals and affecting the magnitude of the phase velocity (e.g., oxidation reactions, etc.). Therefore, the measurement of the phase velocity can be carried out in real scale.

of time.

Since a laser is used as a radiation source, the coherence of the waves, with interference-f

which signals are recorded beating signals will always take place. However, the amplitude of the beats will always occur. However, the amplitude of the beats will be the greater, the higher the coherence of the interfering waves. Therefore, the difference between the optical path lengths in the two channels from the splitter to the input element ELV should be made as small as possible.

formula from

S

arr

one

et e and

The method of determining the phase velocity of a surface electromagnetic wave, which consists in directing the coherent volume radiation along the propagation path of the surface electromagnetic wave, converts the surface electromagnetic wave into volume radiation, measure the radiation intensity and determine the phase velocity, characterized in that , in order to measure in real time and increase accuracy, the direction of the propagation of a surface electromagnetic wave directs the bulk radiation, Toe frequency relative to the frequency of a surface electromagnetic wave, surface pre elektromag1732291

five

During the photo-mixing with frequency-shifted bulk radiation, the phase difference between the two waves spatially separated along the propagation direction of the surface electromagnetic wave during photo-mixing is measured, and the phase velocity v is found from the ratio

v ssl / (l + | ulflc),

where (0 is the frequency of the surface electromagnetic wave; c is the speed of light; 1 is the distance between the spatially separated points of conversion of the surface electromagnetic wave into bulk radiation; UCf is the phase difference of the beat signals,

Claims (1)

Claim' Method for determining phase ambulance? of a surface electromagnetic wave, which consists in directing coherent volumetric radiation along the path of the surface electromagnetic wave, converting the surface electromagnetic wave into volumetric radiation, measuring the radiation intensity and determining the phase velocity, characterized in that, in order to measure in real scale time and increase accuracy, along the path of propagation of a surface electromagnetic wave direct volumetric radiation, shifted in frequency relative to the frequency surface electromagnetic wave, the surface electromagnetic wave is converted into volumetric radiation θ 'of two points spatially spaced along the direction of the surface electromagnetic wave propagation t points when photographing with frequency-shifted volumetric radiation, the phase difference of the two corresponding optical beat signals is measured, 10 and the phase velocity v is found from ω, ratios v = cu) 1 / (ϊ + ίήφΐ s), where (О 'is the frequency of the surface electromagnetic wave / s is the speed of light;' 1 is the distance between spaced points conversion surface 20 of the electromagnetic wave in Ob, capacious radiation; Δψ is the phase difference of the beat signals ”ϊ Compiled by I. Konovalov 'Editor V. Bugrenkova Tehred A“ Kravchuk Corrector S, Shekmar _; Order 1581 Circulation Subscription VNIIIPI of the State Committee for Inventions and Discoveries at the USSR State Committee for Science and Technology. 1,13035, Moscow, Zh-35, Raushskaya nab., D. 4/5 Production and Publishing Plant Patent ”, Uzhgorod, st. Gagarina, 101