JP2005077251A - Method and apparatus for visualizing fine particles by laser beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To hold the uniform intensity of light within a visualizing space without irregularity and to certainly visualize fine particles even if a cutoff substance is present in the visualizing space. <P>SOLUTION: This visualizing apparatus is constituted of a laser beam oscillator 2, the visualizing space 4 substantially surrounded by a plurality of fixed reflecting mirrors 3 arranged in a peripheral direction and a polygon mirror 6 for allowing a laser beam, which is projected from the laser beam oscillator 2, to be incident into the visualizing space 4. The laser beam is allowed to be incident into the visualizing space 4 by operating the polygon mirror 6 while continuously changing an incident angle and the multiple reflection of the laser beam allowed to be incident into the visualizing space 4 is repeated in the visualizing space 4 by a plurality of fixed reflecting mirrors 3 to visualize fine particles present in the visualizing space 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for visualizing various fine particles suspended in the air with a laser beam.

  Particularly in the field of the semiconductor industry, fine particles present in the air in a clean room cause various troubles. In daily life, a huge amount of various fine particles are discharged into the atmosphere every day from automobiles and factories, and these fine particles have an adverse effect on human health.

  For these reasons, in recent years, the necessity of managing fine particles floating in the air has been recognized, and various methods for visualizing fine particles by forming a laser beam into a sheet have been proposed.

  For example, Patent Document 1 below discloses a method of converting a laser beam 20 into a fan-shaped sheet beam 21 by passing the laser beam 20 through a semi-cylindrical lens 22 called a cylindrical lens, as shown in FIG. . Further, as shown in FIG. 3B, there is also known a method for converting laser light 20 into sheet light 21 by using a mirror called a vibrating mirror or galvano mirror 23 that vibrates in a predetermined angle range. Yes. Further, in Patent Document 2 shown below, as shown in FIG. 3C, a laser beam 20 is irradiated onto a polygonal mirror 24 having a regular polygonal column shape, and rotated to form a light film, thereby forming a sheet. A method is disclosed.

  However, in the case of the method described in Patent Document 1, since one laser beam is diffused into a fan-shaped sheet beam, energy is attenuated in inverse proportion to the projection distance, and the same size fine particles Even when the liquid is floating, there is a problem that depending on the floating position, the appearance of the visualized fine particles, that is, the detection sensitivity is different, which is not preferable.

  In the case of the method described in Patent Document 2, since a fan-shaped sheet light is formed by optically scanning (or rotating) one laser beam, the sheet angle can be increased. Although it is possible, there is a problem that a regular polygon mirror having a different number of angles according to the desired sheet angle is required, and if the sheet angle is increased, the light intensity decreases extremely as the distance from the mirror increases. There was a problem. In addition, since there is no time simultaneity at each position of the sheet light, if the movement of the observation target particle has a movement perpendicular to the sheet light, it cannot be detected depending on the phase of the laser beam (if it hits the laser beam) In other words, there is a problem that fine particles that pass through without scattering laser light exist.

In view of the above problems, in Patent Document 3 below, as shown in FIG. 4, a light source 30, a beam expander 31, a guide mirror 32, multiple reflection mirrors 33A and 33B, a beam trap 34, an analog differential camera 35, and a display device 36, and a method of forming sheet light by multiple reflection of the laser light output from the light source 30 between the multiple reflection mirrors 33A and 33B via the beam expander 31 and the guide mirror 32 is disclosed. Yes.
JP 61-29729 A JP-A-4-307346 JP-A-11-153535

  According to Patent Document 3, laser light is formed into a sheet by repeating reflection between multiple parallel reflection mirrors that are spaced apart in parallel. Therefore, if the reflectivity of the mirror is high, the light intensity is less attenuated and incident. It is described that sheet light close to the light intensity of laser light can be obtained.

However, even the sheeting method using multiple reflection according to Patent Document 3 has the following problems.
(1) The cross-sectional intensity distribution of the laser beam is a Gaussian distribution, and the beam cross-section having this Gaussian distribution repeats multiple reflections as it is, so that the light intensity of the sheet becomes striped.
(2) The laser light is not completely parallel light, but spreads as the distance advances and the light intensity attenuates. Therefore, the light intensity of the sheet is different between the vicinity of the parallel mirror incident point and the emission of the parallel mirror. In order to solve this, in the same document, an expanding lens is used, but this expanding lens serves to narrow the beam to a certain point, and it is difficult to make the laser beam infinitely parallel. It is still difficult to make the light intensity distribution of the sheet uniform.
(3) In order to make multiple reflections of one laser beam in one direction, if there is a laser beam blocking object in the visualization space, the laser beam will be blocked by the blocking object. It will not be done.
(4) Since the shape of the particle is not necessarily spherical, it may be difficult to obtain scattered light depending on the direction of the particle when irradiated with light from a certain direction.
(5) It is necessary to terminate the laser beam by capturing the laser beam that has escaped from the parallel mirror with a beam trap.

  Therefore, the main problem of the present invention is that it is possible to maintain a uniform light intensity at a high level without unevenness in the visualization space, and to ensure that the fine particles can be obtained even when a blocking object exists in the visualization space. An object of the present invention is to provide a laser beam visualization method and apparatus having advantages such as visualization.

  In order to solve the above-mentioned problem, as the present invention according to claim 1, a laser beam irradiated from a laser oscillator is formed by forming a visualization space substantially surrounded by a fixed reflecting mirror arranged in the circumferential direction. Is incident on the visualization space while continuously changing the incident angle by the movable reflection mirror, and the laser beam incident on the visualization space is repeatedly reflected by the fixed reflection mirror in the visualization space, There is provided a method for visualizing fine particles by laser light, characterized by visualizing fine particles present in a visualization space.

  As a second aspect of the present invention, the laser light oscillator, a visualization space substantially surrounded by a fixed reflecting mirror disposed in the circumferential direction, and the laser light projected from the laser oscillator are reflected by the reflection. The movable reflecting mirror is made to enter the visualization space, and the movable reflecting mirror is operated to cause the laser light to enter the visualization space while changing the incident angle continuously, and to enter the visualization space. The laser beam visualizing device is characterized in that the laser beam is visualized by repeating multiple reflections by the fixed reflecting mirror in the visualization space, thereby visualizing the particles present in the visualization space.

  According to the first and second aspects of the present invention, the laser beam is incident on the movable reflection mirror while continuously changing the incident angle into the visualization space surrounded by the fixed reflection mirror. By repeating multiple reflections by the fixed reflecting mirror in the visualization space, the fine particles existing in the visualization space are visualized. Therefore, by forming a sheet by scanning the movable reflecting mirror, the light intensity distribution of the beam cross section with a Gaussian distribution is made uniform, and in the visualization space surrounded by the fixed reflecting mirror, the laser beam can travel in all directions. Since the multiple reflection is repeated, it is possible to maintain a substantially uniform light intensity in the visualization space.

  In addition, the direction of the laser beam is always changed by the movable reflection mirror, and the laser beam is changed in all directions due to multiple reflections even in the visualization space, so that the laser beam is blocked even when there is an obstruction in the visualization space. It will not be done. This is a very effective method for a visualization model in which an obstruction exists.

  Furthermore, since the direction of the laser beam is constantly changing in the visualization space, scattered light can be obtained regardless of the direction of particles that are not necessarily spherical.

  In addition, since the laser light repeats multiple reflections in the visualization space until it attenuates, it is not necessary to terminate the laser light.

  Next, as a third aspect of the present invention, the movable reflection mirror is a polygon mirror, and the rotation angle of the polygon mirror continuously changes the incident angle of the laser beam into the visualization space. An apparatus for visualizing fine particles by the laser beam described in 2 is provided.

  According to a fourth aspect of the present invention, the movable reflecting mirror is a vibrating mirror, and the incident angle of the laser beam into the visualization space is continuously changed by the swinging of the vibrating mirror. An apparatus for visualizing fine particles by the described laser beam is provided.

  As a fifth aspect of the present invention, the visualization space is substantially surrounded by four fixed reflecting mirrors arranged in two pairs in parallel. The fine particles by laser light according to any one of claims 2 to 4 A visualization device is provided.

  According to a sixth aspect of the present invention, the visualization space is substantially surrounded by a laser beam according to any one of the second to fourth aspects, wherein the periphery of the visualization space is substantially surrounded by five or more fixed reflecting mirrors arranged in a polygonal shape. A microparticle visualization device is provided.

  As described above, according to the present invention, in the visualization space, it is possible to maintain a uniform light intensity at a high level without unevenness, and fine particles can be obtained even in the case where an obstruction exists in the visualization space. It will be possible to visualize reliably.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a front view of a fine particle visualization apparatus 1A according to a first embodiment of the present invention.

  As shown in FIG. 1, the visualization device 1 </ b> A is substantially surrounded by a laser light oscillator 2 and four fixed reflecting mirrors 3, 3. The visualization space 4 and a polygon mirror 6 that causes the laser beam 5 projected from the laser beam oscillator 2 to enter the visualization space 4 by reflection.

  The laser beam oscillator 2 can use various laser beams used as a visualization laser, and among them, an argon laser beam is preferable. Argon laser light has a plurality of wavelength components in the vicinity of 500 nm. Specifically, it has large peaks of wavelength components at 488 nm and 514 nm. Other than that, it has small peaks at 457.9 nm, 465.8 nm, 476 / 472.7 nm, 496.5 nm, and 501 nm. In particular, since the laser light output from the argon laser oscillator has a high energy density, the intensity of the scattered light generated by the fine particles is large, and the imaging sensitivity can be increased.

  In the illustrated example, the visualization space 4 has a rectangular visualization space formed by four fixed reflecting mirrors 3, 3... Arranged in parallel with each other, but the visualization space 4 according to the present invention is arranged in the circumferential direction. It is sufficient that the space is substantially surrounded by the fixed reflection mirror provided, and the arrangement of the fixed reflection mirrors 3, 3,. For example, as in the second embodiment shown in FIG. 2, the visualization space 4 may be a hexagonal space, or may be a polygonal space larger than that. The fixed reflection mirror 3 is preferably a plane mirror because it is easily available, but a curved mirror may be used. In the visualization space, it is desirable that the part other than the laser light entrance 4a is completely blocked in the circumferential direction, but as shown in FIG. 1, a laser light path from the laser oscillator 2 to the polygon mirror 6 is secured. Therefore, a part (4b) may be opened. That is, a slight opening may be formed as long as it does not affect the multiple reflection according to this effect.

  As the fixed reflection mirror 3, various mirrors exist, and it is desirable to use a dielectric multilayer mirror having a reflection film in which several thin films of high refractive index and low refractive index are alternately stacked. Since this type of mirror uses a derivative, the spectral reflectance can be freely selected, and the reflectance close to 100% can be given to light of a specific wavelength. FIG. 5 is a diagram showing the reflection characteristics of the dielectric multilayer mirror 3 used in this embodiment. In the figure, the horizontal axis indicates the wavelength of the reflected light, and the vertical axis indicates the reflection loss. As shown in the figure, the dielectric multilayer mirror 3 has almost no reflection loss for light in the wavelength region of about 450 nm to 540 nm, and can reflect incident light in a state close to total reflection. As described above, the wavelength of the laser beam output from the argon laser as the light source is included in the range of about 450 nm to 520 nm and can be almost totally reflected by the dielectric multilayer mirror 3. Accordingly, even when multiple reflections are made between the dielectric multilayer mirrors 3, the degree of attenuation of the laser light can be minimized.

  As shown in FIG. 1, for example, the fixed reflecting mirror 3 is assembled by forming a substantially rectangular outer frame 7 by four frame plates 7A to 7D, on the inner surface side of each of the frame plates 7, 7. The fixed reflecting mirrors 3, 3... Are fixedly arranged by the fixing bolts 8, 8, thereby forming a visualization space substantially surrounded by the surroundings. In addition, the laser oscillator 2 is disposed outside the outer frame 7 at an adjacent position, and an opening 4a that is not sealed by the fixed reflecting mirrors 3 and 3 is provided at the corner of the lower portion on the other side of the outer frame 7. The polygon mirror 6 is disposed outside the opening 4a. In the visualization space 4 surrounded by the fixed reflecting mirrors 3, 3..., An opening 4 b for securing a path of the laser beam 5 from the laser beam oscillator 2 to the polygon mirror 6 is formed. The irradiated laser light is projected onto the polygon mirror 6 through the opening 4 b, and the laser light 5 is reflected by the polygon mirror 6 so as to enter the visualization space 4.

  The polygon mirror 6 is a regular polygonal mirror, which is a regular hexagonal mirror in the illustrated example, and is rotated by a driving force of a motor or the like. Therefore, the laser beam 5 projected from the laser oscillator 2 is incident on the visualization space 4 while continuously changing the incident angle by the rotation of the polygon mirror 6, and in the visualization space 4, the fixed reflection mirror 3, By 3 ..., multiple reflections in all directions are repeated without complicated and fixed directivity. Thereby, the visualization space 4 has a substantially uniform light intensity, and the fine particles existing in the visualization space 4 are remarkably visualized.

  Although not shown, when the visualization space 4 is photographed, photographing means such as a camera and a video recording device such as a video deck are provided separately. As this photographing means, an ordinary photographing camera can be used, but it is more preferable to use an analog differential camera. By further including differential processing means for differentiating the signal output from the imaging means, the video signal having a high frequency component scattered by the fine particles is differentially emphasized, so that the sensitivity of visualization can be further increased. Moreover, it is preferable that the imaging means described above is an avalanche multiplication operation type imaging tube. Since the avalanche multiplication operation type imaging tube has a high gain and a wide dynamic range due to the avalanche effect, it is suitable for photographing a fine subject with little change in luminance, and can visualize fine particles with high sensitivity. In particular, by combining with the above-described differential processing means, the output amplitude is not saturated, and the dynamic range of the imaging tube can be used 100%, and an S / N characteristic advantageous for visualization of fine particles can be obtained. .

[Other examples]
(1) In the above embodiment, a dielectric multilayer mirror having a high reflectance is used as the fixed reflecting mirror 3. Although it is ideal to use this dielectric multilayer mirror, in the case of this visualization apparatus, sheet formation is performed primarily by scanning with the polygon mirror 6 and the reflection of the laser beam is reflected until it is attenuated in the visualization space. Since it is repeated, it is possible to make the light intensity uniform to a certain high level even with a normal mirror.
(2) Although the rectangular or hexagonal visualization space 4 is used in the above embodiment, there is no limitation on the space shape. Therefore, it may be a space shape including a circular shape or a curved surface portion in addition to the polygonal shape. However, in the present visualization apparatus, it is desirable to avoid multiple irregular shapes because the greatest feature point is to repeat multiple reflections in all directions within the visualization space.
(3) In the above embodiment, the incident angle of the laser beam 5 to the visualization space 4 is continuously changed by the polygon mirror 6, but instead of the polygon mirror 6, another movable reflection mirror, for example, FIG. The vibrating mirror 23 shown in B) can also be used.
(4) Although the polygon mirror 6 is arranged outside the visualization space 4 in the above embodiment, it may be arranged inside the visualization space 4.

It is a front view of visualization device 1A concerning the 1st form example. It is a front view of the visualization apparatus 1B which concerns on a 2nd form example. It is a figure which shows the conventional visualization method of microparticles | fine-particles. It is a system block diagram of the visualization apparatus concerning patent document 3. FIG. 6 is a diagram showing the reflection characteristics of the dielectric multilayer mirror 3.

Explanation of symbols

  1A, 1B ... Fine particle visualization device, 2 ... Laser light oscillator, 3 ... Fixed reflection mirror, 4 ... Visualization space, 5 ... Laser light, 6 ... Polygon mirror, 12 ... Sheet light

Claims (6)

A visualization space substantially surrounded by a fixed reflection mirror arranged in the circumferential direction is formed, and a laser beam emitted from a laser light oscillator is continuously incident on the visualization space by a movable reflection mirror. Laser that is incident while being changed, and the laser beam incident in the visualization space is repeatedly reflected by the fixed reflection mirror in the visualization space, thereby visualizing the fine particles existing in the visualization space Visualization method of fine particles by light. A laser light oscillator, a visualization space substantially surrounded by a fixed reflection mirror arranged in the circumferential direction, and a movable reflection mirror that causes laser light projected from the laser oscillator to enter the visualization space by reflection The movable reflecting mirror is actuated to cause the laser light to enter the visualization space while changing the incident angle continuously, and the laser light incident on the visualization space is incident on the visualization space in the visualization space. An apparatus for visualizing fine particles by laser light, wherein fine particles existing in a visualization space are visualized by repeating multiple reflection by a fixed reflection mirror. 3. The apparatus for visualizing fine particles by laser light according to claim 2, wherein the movable reflecting mirror is a polygon mirror, and the angle of incidence of the laser light into the visualization space is continuously changed by rotation of the polygon mirror. 3. The apparatus for visualizing fine particles by laser light according to claim 2, wherein the movable reflecting mirror is a vibration mirror, and the angle of incidence of the laser light into the visualization space is continuously changed by swinging the vibration mirror. . The apparatus for visualizing fine particles by laser light according to any one of claims 2 to 4, wherein the visualization space is substantially surrounded by four fixed reflecting mirrors arranged in two pairs in parallel. The apparatus for visualizing fine particles by laser light according to any one of claims 2 to 4, wherein the visualization space is substantially surrounded by five or more fixed reflecting mirrors arranged in a polygonal shape.

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