JPH01240863A - Method and apparatus for generating speckle pattern - Google Patents

Abstract

PURPOSE:To enable generation of a speckle pattern making a boiling motion depending on none of a lighting optical system and light receiving optical system, by building up a diffusion plate unit with two diffusion plates arranged apart at a specified interval to move the plates relatively. CONSTITUTION:After converged with a lens 11, a laser beam from a laser light source 10 is made to irradiate a diffusion plate 12a. Diffusively transmitted light subjected to a random phase modulation with the diffusion plate 12a further irradiates a diffusion plate 12b. The diffusion plates 12a and 12b are made movable relative to each other within surfaces thereof. Light transmitted through the diffusion plate 12b forms a speckle pattern in a diffraction area or an image area. The speckle pattern thus obtained is detected with a photo detector 15 through a detection opening 14 and a detection output thereof is inputted into a signal processing section 16.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a speckle pattern generation method and apparatus, and more specifically, to irradiating a moving diffuser plate with laser light and emitting light by the transmitted or reflected and diffused laser light. The present invention relates to a method and apparatus for generating a speckle pattern with boiling motion in a diffraction region or an image region.

[Prior Art] Conventionally, methods and devices are known for measuring the moving speed of a diffuser plate by detecting the movement of a speckle pattern obtained by irradiating a moving diffuser with a laser beam. These include, for example, the magazine "Laser Research" (published by the Laser Society), Volume 8.

Described on pages 37 to 45 of No. 2 (March 1980), and pages 3 to 10 of Volume 8, No. 3 (May 1988) of the same magazine. . According to this theory, speckle motion includes translational motion, which moves in a fixed direction as the object moves, and speckle motion, which causes irregular changes in brightness and darkness of the speckled light intensity distribution at that position over time. There is a boiling motion that repeats. Depending on the configuration of the optical system, such as the shape and position of the laser beam used, the position of the object, and the observation position, pure translational motion, only boiling motion, or a coexistence of both can be observed.

Examples of devices that apply this speckle velocity measurement method to measuring blood flow velocity in living bodies include JP-A-80-199430, JP-A-60-203235, and JP-A-60-2032.
3δ and the earlier application by the inventor of the present application, JP-A-62-275
No. 431 and Japanese Patent Application No. 62-75778, etc., and has recently attracted attention as one of the applications of laser engineering to living organisms. When evaluating or calibrating the performance of these devices as a velocity measurement device, such as measurement accuracy, reproducibility, linearity, and velocity dependence, flow models such as fluid in glass tubules are useful because they are models that are closer to blood vessels. Although it is preferable, it is never sufficient due to poor stability of flow velocity, unnecessary tube wall scattering, and influence of flow velocity distribution, etc. In the end, it is possible to easily set a known law any number of times with good reproducibility and always stably. A diffuser plate such as ground glass is often used as a moving light scattering object.

[Problem to be solved by the invention] However, as mentioned above, with a diffuser plate, depending on the laser illumination optical system and light receiving optical system of the device used, the speckle pattern may be in translational motion or boiling motion on the observation surface. do. However, since speckles obtained from living organisms generally undergo boiling motion regardless of the illumination optical system or light receiving optical system, the movement of the speckle pattern formed by the diffuser plate model is difficult to detect changes in speckle light intensity. The signal characteristics may differ from the actual case,
As a result, the current situation is that sufficient modeling is not possible.

Therefore, the present invention has been made to solve such problems, and provides a speckle pattern generation method and apparatus that can generate a speckle pattern that exhibits boiling motion without depending on the illumination optical system and the light receiving optical system. The purpose is to provide

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention comprises two diffusion plates arranged at a predetermined relatively small interval, one of which A configuration was adopted in which a speckle pattern with boiling motion was generated by moving one diffuser plate relative to another diffuser plate at a constant speed within its plane.

[Function] With this configuration, speckle boiling motion can be formed in either the diffraction region or the image region by the movement of the diffuser plate, and the standard model is not affected by the conditions of the illumination optical system and the light receiving optical system. can be formed.

[Example 1] Figure 1 shows the principle of a conventionally known speed measuring device for a moving object using laser speckles.

The laser beam emitted from the laser light source 10 passes through the lens 11
The moving object 12 to be measured is irradiated with the light in a state where it converges once and then diffuses. The laser beam undergoes random phase modulation by the moving object 12, and a moving laser speckle pattern is observed on the observation surface in the diffraction region. Since the speckle pattern moves at a speed proportional to the speed of the moving object 12, the light intensity change due to the movement is detected by the photodetector 15 through the detection aperture 14 on the observation surface 17, and the signal processing section detects the change in light intensity due to the movement. 16, the object speed is measured by performing various types of processing as necessary, such as a correlation function, a power spectrum, a zero crossing number, etc. of the speckle signal.

When this principle is applied to living organisms, for example, in the capillary layer under the skin or red blood cells in normal blood vessels, scatterers are constantly moving in a three-dimensional manner with irregular fluctuations, and the direction is not constant. Due to the occurrence of multiple scattering between surrounding tissues and between scatterers, it must be considered as an engraved object that is completely different from a stationary scattering object like the moving object 12 in FIG. In that case, it is often observed as boiling motion, regardless of the laser irradiation optical system or light receiving optical system used.

Therefore, when evaluating and calibrating the various speed measurement performance of a laser speckle blood flow velocity measurement device applied to a living body, a reference target model is always required, and a device that flows blood through a glass tube is generally used. However, it has drawbacks such as insufficient speed stability and reproducibility, and cannot be used under constant conditions for a long period of time.In the end, something like ground glass, which allows you to easily set the desired speed and can be used stably over and over again, was developed. It is preferable as a reference model. However, forming a boiling speckle pattern with a diffuser plate such as ground glass is limited to cases where the laser irradiation optical system and the light receiving optical system satisfy several conditions. An example of this is shown in Figure 2.
It is shown in Figure 3.

Figure 2 shows an optical system that irradiates an object with the waist position of the irradiated laser beam at 2°, and Figure 3 shows an optical system that aligns the observation plane with the conjugate imaging plane formed by the lens 17 with respect to the waist position 2o of the irradiated laser beam. It is a system. In both cases, boiling motion is formed on the observation plane.

However, in general, the laser irradiation optical system and the light receiving optical system differ depending on the equipment to be evaluated and calibrated, and are not always under the conditions of boiling motion as in the examples of FIGS. 2 and 3. Therefore, it is desirable to be able to generate boiling only on the object side, regardless of the conditions on the equipment side, and to be able to achieve this using a model that is easy to handle, such as ground glass.

Therefore, in the embodiment of the present invention, a configuration as shown in FIG. 4 is used. That is, two diffusion plates 12a and 12b are used as the diffusion plates, which are arranged at a predetermined interval and arranged substantially perpendicular to the optical axis.

In the figure, a laser beam from a laser light source 10 once converges on a lens 11, and then irradiates the front diffuser plate 12a in a diffused state. Thereupon, the diffusely transmitted light that has undergone random phase modulation illuminates the second diffuser plate 12b located further behind. In this way, the light transmitted through the diffuser plate 12b enters the diffraction region,
Alternatively, a speckle pattern is formed in the image area.

Here, for example, if the diffuser plate 12a is moved at a constant speed within its surface 7 and the diffuser plate 12b is fixed stationary, the light diffused and transmitted by the diffuser plate 12a will change at a speed that accompanies the movement of the diffuser plate 12a. In order to have information about the direction, the first
As shown in the figure, translating speckles can be seen on the observation surface, but if the diffuser plate 12b is stationary at a distance d behind it, the diffuser surface of the diffuser plate 12b will be randomly generated as shown in Figure 5. phase modulation, and the diffuser plate 12a
is moving, and the diffuser plate 12b is stationary, so the diffuser plate 12b is stationary.
The phase modulation function of the scattering object, which is determined by the positional relationship between a and 12b, changes every moment.

FIG. 6 specifically shows this. Figure 6 (a
), a certain light ray 1 is scattered at a point 2 on the diffuser plate 12a, becomes a scattered light 1', reaches a point 3 on the diffuser plate 12b, is further scattered there, becomes a diffused light 1', and reaches a point 3 on the diffuser plate 12b. Suppose we move in the direction of.

At this time, consider the case where the diffuser plate 12a moves as shown in FIG. 6(b). If the light ray 1 that enters the incident light flux at the same angle as in Fig. 6(a) is scattered at the point 2 on the diffuser plate 12a, it becomes scattered light 1'. The process continues, but this time the positional relationship between the diffusion plates 12a and 12b is
), the light rays reach the point 5 instead of the point 3 on the diffuser plate 12b, and the light rays scattered here turn into scattered light 7 and travel in the direction of 6. Moreover, since the angle of direction 6 with respect to the optical axis is determined by the surface shape of the scattering points on the diffuser plate 12b,
It changes randomly over time.

If by chance the direction of 6 is parallel to direction 4 in Figure 6(a), as in direction 6', there is a possibility that the speckles will translate, but statistically the probability is very low. low,
As a result, since the relative positional relationship between the diffusers 12a and 12b constantly changes over time, the degree of overlapping of each light beam on the observation surface 17 also changes from time to time, and the interference state changes randomly over time. This will form a boiling motion. If the temporal change in the interference state shifts in a fixed direction with the change in the object, it will be a translational movement, but as shown in FIG.
It can be seen that the translational motion is no longer preserved because the angle of the light beam exiting the diffuser plate 12b changes randomly depending on the positional relationship of the diffuser plate 12b and is not always kept constant. As a result, boiling motion is always formed on the observation surface 17 regardless of the optical system.

Since the boiling motion can be generated based on the principle described above, the laser irradiation optical system also focuses not only on the beam convergence position 20 but also on the positions 21 and 2 before and after it, as shown in Figure 8.
Even if the object is irradiated with 2, very favorable results can be obtained since boiling motion can be formed. Also, two diffusion plates 12a.

The direction of the diffusion surface of 12b is not limited to the example shown in FIG. 5, but may also be configured as shown in FIGS. 7(a) to (C). Also, it is better for the distance d between the diffusion plates to be close to each other, for example, 3m.
It is good if it is less than m, but it is better to adjust it appropriately taking into consideration the light transmittance of the diffusion plates 12a and 12b. However, extremely large distances (for example, 100m+n or 200mm)
(above) is not preferable because the speckles will move in translation.

The light receiving optical system is advantageous because boiling motion can be observed in both image plane detection and diffraction plane detection. Therefore, the boiling motion can be formed without depending on the optical system of the device to be evaluated and calibrated, which is very convenient. Moreover, since the speed of change in light intensity due to boiling motion itself is proportional to the velocity V of the moving object, it is also effective for evaluating linearity. The moving speed of the diffuser plate can be stably and accurately set any number of times at a known speed by controlling a motor or the like. Therefore, this can be a very simple and practical method for generating speckle patterns.

On the other hand, in the two diffusion plates 12a and 12b shown in FIG. 4, the diffusion plate 12a may be fixed and the diffusion plate 12b may be moved. Furthermore, both may be moved independently at any constant speed. The moving direction of the diffuser plates at this time can be arbitrarily selected within each plane, but if the speeds of the diffuser plates 12a and 12b are equal and they are moved in the same direction, the diffusion plates 12a and 12b will move in the same direction. The relative positional relationship is always constant and unchanging, and it can be considered as a single, integrated object. In such a case, speckles may be translated depending on the optical system conditions, so this example should be avoided.

Furthermore, the same effect can be obtained by setting not only two but three or more diffusers, but there are disadvantages such as unnecessary loss of light quantity and complication of the device, so two diffusers are sufficient for practical use. . Furthermore, since the present invention can form boiling motion not only in the diffuse transmission region but also in the diffuse reflection region, it can be effectively used in the optical system of a reflective type apparatus to be evaluated and calibrated.

In addition, the scattering phenomenon caused by two diffuser plates as shown in Figures 5 and 6 is caused by higher-order modulation (double,
(modulation occurs due to triple scattering),
The speed of light intensity change due to boiling motion on the observation plane is generally faster than the boiling motion shown in Figures 2 and 3, which is the normal case, so for example, the correlation between the object speed V and the detected speckle signal Plotting the relationship with the reciprocal of the correlation time τ, which is the time for the function to decay to 1/a, we get the 9th
It will look like the figure. In the same figure, straight line a is
In the case of boiling motion caused by a single scattering object as shown in the figure, a straight line is the case in the embodiment of the present invention. That is, since the rate of change of 1/τC with respect to the velocity V is greater in the straight line, it can be seen that the present invention has the great effect of improving the velocity resolution in measuring the velocity of a moving object. This is a very significant effect in the application of the present invention to evaluation and calibration.

On the other hand, the movement of the speckle pattern is not detected using a detection aperture at a single point, but is detected using a plurality of inter-detection robot patterns 25 made up of patterns such as a plurality of minute apertures 25a and 25b as shown in FIG. If speckle 24
When the speckle moves in translation, a situation occurs in which one speckle moves between two adjacent apertures 25a and 25b with a time delay, and the correlation function of the output signal is originally boiling as shown in FIG. In the case of motion, data such as the curve 26 includes the above-mentioned cross-correlation components, resulting in a straight line 27, making it impossible to perform accurate evaluation.

Therefore, speckles that undergo boiling motion are indispensable for the evaluation and calibration of a speckle utilization device using a multiple-detection robot pattern, and it can be seen that the present invention is very effective and indispensable in this respect as well.

[Effects of the Invention] As explained above, according to the present invention, by simply arranging two diffuser plates in parallel at a relatively short predetermined interval,
It is possible to always form speckle boiling motion in either the diffraction region or the image region, regardless of the conditions of the laser illumination optical system and light receiving optical system of the equipment to be evaluated and calibrated, and the speed of the boiling motion is Since it is proportional to the object speed, the desired speed can be easily controlled.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams explaining the principle of forming a speckle pattern, FIG. 4 is an explanatory diagram explaining a method of forming a speckle pattern according to the present invention, and FIG.
The figure is an explanatory diagram illustrating the state of light diffusion by two diffusion plates, FIG. 6(a). (b) is an explanatory diagram illustrating changes in light rays caused by relative movement of two diffuser plates, and Figures 7 (a) to (c)
8 is an explanatory diagram showing the position of illuminating the diffuser plate, FIG. 9 is a diagram showing the relationship between the velocity and delay of an object, and FIG. 10 is a cross-sectional view showing the deformation of the diffuser plate. An explanatory diagram showing the state of speckle detection using a robot pattern between multiple detections,
FIG. 11 is a diagram showing the relationship between delay time and correlation function. 10... Laser light source 12a, 12b... Diffusion plate 14... Detection aperture 15... Photodetector 16...
・Signal processing unit 17...Observation surface Fig. 8 Fig. 9

Claims (1)

[Claims] 1) A speckle pattern generation method in which a moving diffuser plate is irradiated with a laser beam, and the transmitted or reflected and diffused laser beam generates a speckle pattern with boiling movement in a light diffraction area or an image area. , the diffusion plate is composed of two diffusion plates arranged at a predetermined relatively small interval, and one of these two diffusion plates is moved relative to the other at a constant speed within its plane. A speckle pattern generation method characterized by generating a speckle pattern that undergoes boiling motion. 2) The method according to claim 1, wherein one of the two diffusion plates is kept stationary, and the other is moved within its plane at a constant speed. 3) The method according to claim 1 or 2, wherein the pattern movement of the speckles is detected through a multiple detection aperture pattern having a plurality of microscopic apertures. 4) a laser light source that generates a laser beam; an optical system that projects the laser beam from the laser light source; A diffuser plate is provided, the laser beam is irradiated to the diffuser plate, and one of the two diffusers is moved relative to the other within its plane at a constant speed to produce boiling motion in the light diffraction area or image area. A speckle pattern generating device is characterized in that it generates a speckle pattern.