JPH04263225A - Method and instrument for optical measurement - Google Patents

Abstract

PURPOSE:To execute the analysis of the vibration frequency of an object body to be measured in a short time. CONSTITUTION:One probe light I1 which has optical information on the object body O is made incident on a nonlinear optical medium Q and two pump light beans I2 and I3 are made incident on both surfaces of the nonlinear optical medium Q while facing to each other to perform a four-wave mixing process. In this process, the pulse periods of the probe light I1 and pump light beans I2 and I3 generated by a laser beam source S are selected to generate a phase conjugate wave component P1, corresponding to the object image of a specific part of the object body O which vibrates at a specific vibration frequency in specific relation with the pulse periods of the probe light I1 and pump light beams I2 and I3, by the nonlinear optical medium Q, thereby extracting an optical signal showing the spatial distribution of the part of the object body O which vibrates at the specific vibration frequency.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measurement method and apparatus, and more particularly to an optical measurement method and apparatus that can analyze the vibration state of an object to be measured in real time.

0002

2. Description of the Related Art A strobe irradiation method using a holographic interferometer has conventionally been used as a method for optically detecting a region of a vibrating object that is vibrating at a specific frequency.

In the conventional method using a holographic interferometer, as shown in FIG. The object wavefront information of O is written as a hologram.

On the other hand, the strobe method, as shown in FIG.
This method creates a hologram by modulating the object light and reference light into pulses and making them incident on a hologram dry plate.

In FIG. 4, the symbol Ov indicates a specific physical vibration waveform of the object, and the symbol Lp indicates the pulse oscillation timing of the object light and reference light (see FIG. 5).

Assuming that each part of the object vibrates at different frequencies, the pulse oscillation timings of the object beam and the reference beam are synchronized as shown in FIG. 4 among the object wavefronts having various vibration frequency components. Object wavefronts that are present are always holographically recorded, and wavefronts with different vibration frequency components are almost never holographically recorded.

Therefore, when this hologram is irradiated with only the reference light as shown in FIG. 6, only the region of the object wavefront that was vibrating at a specific frequency can be observed as the hologram reproduction light.

Theoretically, by repeating this operation while changing the pulse period of the incident light, it is possible to detect object wavefronts with different frequency components each time, that is, to realize frequency analysis of a vibrating object.

[0009]

[Problem to be solved by the invention] However, with the conventional method, it is impossible to record and read out a hologram at the same time, so it is difficult to determine in real time which part of the vibrating object is synchronized with the incident light. The problem was that it could not be observed.

[0010] Furthermore, there is a thermoplastic plate as a reproducible hologram dry plate that has been widely used in the past. However, this dry plate has the problem that it is not possible to rewrite the hologram in real time, and it takes more than 10 minutes for at least one rewriting.

[0011] Therefore, as described above, when it is necessary to repeatedly record, read, and rewrite a hologram many times, there is a problem in that it takes an enormous amount of time to complete the analysis. That is, it has been virtually impossible to perform frequency analysis of a vibrating object within a short period of time. An object of the present invention is to solve the above problems and provide an optical measurement method and apparatus that can perform vibration frequency analysis of an object in real time and within a short measurement time.

0012

[Means for Solving the Problems] In order to solve the above problems, in the method of the present invention, one probe light having optical image information of an object to be measured is made incident on a nonlinear optical medium, and In a four-wave mixing process in which two pump lights are incident oppositely from both sides of a nonlinear optical medium, the pulse periods of the probe light and pump light are selected to have a predetermined relationship with the pulse periods of the probe light and pump light. A phase conjugate wave component corresponding to an object image of a predetermined portion of the object to be measured vibrating at a predetermined vibration frequency is generated from the nonlinear optical medium, and In addition, in the apparatus of the present invention, a probe light having optical image information corresponding to the vibration state of the measured object is used. and an optical means for making the pump light incident on a nonlinear optical medium; a means for changing the pulse period of the probe light and the pump light; and a predetermined pulse period and a predetermined pulse period of the probe light and the pump light generated from the nonlinear optical medium. A configuration is adopted in which output means is provided for extracting a phase conjugate wave component having object wavefront information corresponding to an object image of a predetermined portion of the object to be measured vibrating at a related predetermined vibration frequency.

[0013]

[Operation] According to the above configuration, when two pump lights and one probe light having object wavefront information are pulse-modulated at a specific frequency and input into a nonlinear optical medium, the four-wave mixing process causes the frequency to change. The object wavefront synchronized with the object wavefront becomes a phase conjugate image and is output in real time. That is, sequentially extracting phase conjugate wave components having object wavefront information corresponding to an object image of a predetermined portion of the object to be measured vibrating at a predetermined vibration frequency having a predetermined relationship with the pulse period of the probe light and pump light. Can be done.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below based on embodiments shown in the drawings.

[0015] Here, four-wave mixing, which is a process of generating phase conjugate waves, will be described using FIGS. 2 and 3.

In FIG. 3, one probe beam I1 and two pump beams I2 and I3 facing each other are superimposed on the object reflected beam to form a nonlinear optical medium (phase conjugate mirror) Q.
Inject it into the

At this time, the probe light I1 and the pump light I2
, to I3, two types of interference fringes are formed in the nonlinear optical medium Q.

The nonlinear optical medium Q as a phase conjugate mirror has the property that its absorption rate or refractive index changes depending on the intensity of incident light, that is, it has a nonlinear optical effect. Typical materials having such a nonlinear optical effect include photoinduced refraction materials and saturable absorption materials. Therefore, interference fringes are reversibly written inside the nonlinear optical medium as an absorptive or refractive index grating (FIG. 2). These different types of gratings are indicated in FIG. 2 by diagonal lines of different orientation.

The two pump lights are subjected to Bragg diffraction by these two types of gratings. This diffracted light propagates in the same direction as the probe light I1. This wave is, in other words, the phase conjugate wave P1 (FIG. 3). The rise time of the phase conjugate wave P1 depends on the writing time of the grating.

At this time, the greater the intensity of the incident light, the faster the grating writing time. On the other hand, the nonlinear optical medium Q
The lattice formed inside disappears with a certain time constant when the incident light is blocked. Therefore, when the incident light intensity is large,
The decay time of the grating will be longer than its writing time.

In this embodiment, the vibration frequency is analyzed using the properties of the nonlinear optical medium Q described above.

FIG. 1 shows the specific configuration of the optical meter used in this example.

As shown in the figure, the laser light from the laser light source LS is split by a beam splitter BS and illuminates the vibrating object O to be measured. The reflected light from the object O, that is, the probe light I1 for the nonlinear optical medium Q, is reflected by the half mirror H.
The nonlinear optical medium Q is irradiated via M2. Further, the laser beam split by the half mirror HM1 is reflected by mirrors M1 and M2 placed symmetrically with respect to the nonlinear optical medium Q, and irradiates pump beams I2 and I3 from both sides of the nonlinear optical medium Q.

[0024] The half mirror HM2 has a nonlinear optical medium Q.
This is for guiding phase conjugate light P1, which will be described later, generated from the output surface S to an output surface S (consisting of an optical reading element, a photosensitive material, etc.). Note that although the object O is of a reflective type, in the case of a transmission type object, the transmitted light of the object O may be used as the probe light I1.

In this embodiment, three beams of light incident on the nonlinear optical medium Q are simultaneously modulated into pulses at a certain frequency.

If there is a component in the vibrating object that vibrates at a frequency synchronized with the incident light, the probe light I1 of that portion always has a constant wavefront. This is the same as the case in FIG.

When the vibration period of the object is shorter than the writing time of the grating, only the object wavefront with a frequency component synchronized with the incident light is efficiently written into the nonlinear optical medium as a hologram. At the same time, this grating is read out in real time as a phase conjugate wave P1 by means of a four-wave mixing method.

Thereafter, by arbitrarily modulating the frequency of the incident light pulse modulation, the written grating can be rewritten into a new grating in real time. Therefore, this time, a part of the object with a different frequency component than before appears as a phase conjugate image.

By repeating the above operations, it becomes possible to analyze the frequency of the vibrating object.

That is, by sequentially changing the frequency modulation of the laser light source LS in a predetermined pattern and capturing the phase conjugate image output from the output surface S each time, the object O vibrating at a predetermined vibration frequency can be obtained. Images of only certain parts can be captured sequentially.

According to the above embodiment, since the hologram of the nonlinear optical medium Q can be rewritten in real time, it is easy to repeat such operations, measurement can be carried out in a short time, and the vibration of the object O can be It has the excellent effect of being able to perform frequency analysis (in this case, spatial distribution of vibration) in a short time and in real time.

[0032] This makes it possible to conduct material tests, structural tests, etc. using vibration frequency analysis within a short time.

[0033] It is also believed that it will become possible to inspect defects hidden inside objects from vibration frequency analysis, which has not been done in the past. For example, the relationship between the object shape, the state of internal defects, and the spatial distribution of vibration of the object is obtained in advance as a statistical database, and based on this, the spatial distribution of vibration to be measured can be determined from the internal defect. It is possible to consider a process that predicts .

[0034]

As is clear from the above, according to the present invention, one probe beam having optical image information of an object to be measured is made incident on a nonlinear optical medium, and two pump beams are made incident on a nonlinear optical medium. In a four-wave mixing process in which the light is incident oppositely from both sides of a nonlinear optical medium, by selecting the pulse periods of the probe light and pump light, the probe light vibrates at a predetermined vibration frequency that has a predetermined relationship with the pulse period of the probe light and pump light. A phase conjugate wave component corresponding to an object image of a predetermined portion of the object to be measured is generated from the nonlinear optical medium, and an optical signal indicating a spatial distribution of a portion of the object to be measured vibrating at a predetermined vibration frequency. Also, the configuration to extract
In the device of the present invention, an optical measurement device for measuring changes in shape of an object to be measured includes an optical means for making probe light and pump light having optical image information corresponding to the vibration state of the object to be measured enter a nonlinear optical medium. , means for changing the pulse period of the probe light and pump light, and the object to be measured vibrating at a predetermined vibration frequency having a predetermined relationship with the pulse period of the probe light and pump light, which is generated from the nonlinear optical medium. Since the configuration includes an output means for extracting a phase conjugate wave component having object wavefront information corresponding to an object image of a predetermined portion of the object, the pulse period of the probe light and pump light is adjusted to a predetermined value by a four-wave mixing process. It is possible to sequentially extract phase conjugate wave components having object wavefront information corresponding to the object image of a predetermined portion of the object to be measured that is vibrating at a predetermined vibration frequency in the relationship, and thereby to obtain information about the vibration state of the object to be measured. Spatial distribution can be extracted and vibration frequency analysis of the measured object can be performed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of an optical measuring device employing the present invention.

FIGS. 2(a) and 2(b) are explanatory diagrams showing the configuration and operation of a nonlinear optical medium used in the present invention.

FIG. 3 is an explanatory diagram showing the characteristics of a phase conjugate wave generated from a nonlinear optical medium.

FIG. 4 is an explanatory diagram showing pulse modulation of light incident on a nonlinear optical medium.

FIG. 5 is an explanatory diagram showing the state of measurement in a conventional device.

FIG. 6 is an explanatory diagram showing the state of measurement in a conventional device.

[Explanation of symbols]

Q Nonlinear optical medium M Mirror HM1, HM2 Half mirror S　Output surface BS beam splitter LS Laser light source

Claims (2)

[Claims] Claim 1: A four-wave mixing process in which one probe beam having optical image information of an object to be measured is made incident on a nonlinear optical medium, and two pump beams are made oppositely incident on both sides of the nonlinear optical medium. By selecting the pulse periods of the probe light and pump light, an object image of a predetermined portion of the object to be measured vibrating at a predetermined vibration frequency having a predetermined relationship with the pulse period of the probe light and pump light is formed. An optical measurement method characterized by generating a corresponding phase conjugate wave component from the nonlinear optical medium and extracting an optical signal indicating the spatial distribution of a portion of the object to be measured vibrating at a predetermined vibration frequency. 2. An optical measurement device for measuring the vibration state of an object to be measured, comprising: an optical means for making probe light and pump light having optical image information corresponding to the vibration state of the object to be measured enter a nonlinear optical medium; means for changing the pulse period of the probe light and pump light; and the object to be measured vibrating at a predetermined vibration frequency that is generated from the nonlinear optical medium and has a predetermined relationship with the pulse period of the probe light and pump light. 1. An optical measuring device comprising an output means for extracting a phase conjugate wave component having object wavefront information corresponding to an object image of a predetermined portion of the optical measuring device.