JPWO2020179049A1 - Laser beam profile measuring device - Google Patents

Abstract

The beam profiler has a plate-shaped or block-shaped fluorescence generating element having an incident surface on which the laser beam is incident and an emitting surface on which the laser beam is emitted, and a laser that emits fluorescence generated in the fluorescence generating element and emitted from the emitting surface. It includes an optical separation element that separates from light, an image element that receives fluorescence, and a mask that is located in the optical path of fluorescence between the optical separation element and the image element. The mask may be provided so as to cover the central portion including the center of the fluorescent optical path, and shield the laser beam and its stray light. The mask may be a metal plate, and the metal plate has a shielding portion that covers the central portion and a rim portion provided around the shielding portion, and a hole is formed between the shielding portion and the rim portion. It is good. Alternatively, the mask may include a transparent substrate and a film formed on one surface of the substrate. The beam profiler makes it possible to measure the beam profile of a high-power laser with high accuracy by eliminating the effect of ghosting due to stray light of the laser beam that is not separated by the wavelength separation mirror.

Description

The present invention relates to a laser beam beam profile measuring device, and more particularly to a laser beam beam profile measuring device capable of measuring a two-dimensional beam profile of a laser beam having high light intensity with high position accuracy and high accuracy.

As a conventional method for measuring the beam profile (two-dimensional light intensity distribution) of high-power laser light exceeding 100 mW, a method of dimming the laser light with a filter or a mirror and observing it with an image sensor such as CCD or CMOS, a pin. A method of measuring the transmitted light intensity while blocking a part of the beam with a hole, slit, or knife edge and calculating it from the correlation between the light blocking position and the transmitted light intensity, a rod with a small mirror at the tip or a small hole at the tip. We know how to measure the intensity distribution by scanning an open light guide rod two-dimensionally in the beam, and how to irradiate a plate that scatters light with laser light and measure the image of the scattered light from behind with a camera. Was being. In addition, in this specification, a camera means the whole apparatus for taking an image. Generally, a camera includes an image element (for example, an image sensor such as a CCD or CMOS) for detecting an image and an optical system (a lens or the like) for forming an image on the image element.

On the other hand, a method of irradiating a plate-shaped phosphor (fluorescent plate) with a laser beam and measuring the two-dimensional intensity distribution of the fluorescence emitted from the plate-shaped phosphor (fluorescent plate) with a camera or an image sensor has also been known (for example, Patent Documents 1 to 3). Non-Patent Document 1). Patent Documents 1 and 2 propose a method of irradiating a laser beam from the front of a fluorescent plate and observing the fluorescence from the irradiated region with a camera from the front surface of the irradiated fluorescent plate or the back surface of the fluorescent plate. There is. Further, Patent Document 3 and Non-Patent Document 1 propose a method of using Nd: YAG as a fluorescent plate, and report the results of experiments. Non-Patent Document 1 is a report of past experimental results in which the inventor is one of the co-authors.

A beam profile measurement method using fluorescence, which has been conventionally proposed, will be described with reference to FIG. 7. The laser beam (wavelength 808 nm) 1103 to be measured is irradiated on the film-shaped phosphor 1101 formed on one surface of the transparent block 1100. The laser light that is not absorbed by the phosphor 1101 passes through the interface 1102 and is emitted to the outside. On the other hand, the fluorescence 1104 generated from the phosphor is reflected at the interface 1102, light other than the fluorescence wavelength is removed by the filter 1105, and is incident on and imaged on the camera 1106. Non-Patent Document 1 also has the same basic configuration except that the directions of transmission and reflection of the laser beam are opposite. Nd: YAG is shown as an example of the phosphor.

Among the above-mentioned prior arts, the method using a fluorescent material, a fluorescent substance or a fluorescent plate (hereinafter collectively referred to as “fluorescent plate”) is described below in that it is superior to other measuring methods. First, the position of the measured laser beam in the optical axis direction (Z-axis direction) can be specified exactly and with high accuracy by the position of the fluorescent screen. That is, by placing the fluorescence plate at the position where the beam is to be measured, the beam profile at that location is faithfully converted into a fluorescence intensity profile (fluorescence image), which can be imaged with a camera for observation and storage. Since the fluorescence generated from the fluorescent plate is far from the wavelength of the laser beam, it can be easily separated from the laser beam by a dichroic mirror (wavelength separation mirror) or the like, and can be observed with a high signal-to-noise ratio (S / N). Since fluorescence is less affected by scattering and absorption in the fluorescence plate, the fluorescence image can be measured with a camera with high resolution and high accuracy without causing blurring. The light intensity of the generated fluorescence can be easily reduced to 1/100 or less of the light intensity of the incident laser light by devising (thinning) the material, phosphor concentration (absorption characteristics), and thickness of the fluorescent plate. Is. That is, since the fluorescent plate also functions as a kind of dimming filter, it is possible to observe the fluorescence without causing saturation or destruction of the signal by using an image sensor after separating the fluorescence with a wavelength separation mirror. Further, since the amount of heat generated by the fluorescent plate can be suppressed to be small at this time, the temperature rise can be suppressed even if a high-power laser beam is directly incident, and stable measurement can be performed for a long time. In addition, since fluorescence is incoherent light unlike laser light and its scattered light, interference fringes such as speckles and filters do not occur, and even if an optical system with a small aperture (NA) is used, it can be seen on the image sensor. The degree of freedom of the optical system is high because the image can be accurately formed. Further, the magnification of the image formation can be freely set by combining the lenses, and there is an advantage that the measurement can be performed with high accuracy by enlarging a minute beam profile.

Japanese Unexamined Patent Publication No. 6-221917 Japanese Unexamined Patent Publication No. 2004-245778 Japanese Patent Publication No. 2008-591263

Masaki Tsunebu et al., "Proposal of New High-precision 2D Beam Shape Measurement Method", January 11-12, 2015, Laser Society of Japan Academic Lecture 35th Annual Conference, Lecture Proceedings 12pIX03, Laser Society of Japan

However, in the method using the fluorescent plate described above, it is difficult to manufacture a wavelength separation mirror that achieves the transmittance or reflectance of 100% of the laser light, so that the laser light having an energy of about 1 to 5% is usually used. , Reflects or transmits through the wavelength separation mirror without being separated. This laser beam (that is, the stray light of the laser beam) follows the same optical path as the fluorescence and heads toward the image sensor. Normally, the filter located between the wavelength separation mirror and the image sensor has a bandpass characteristic that selectively transmits only light having a wavelength of fluorescence. In the case of a filter having such a bandpass characteristic (bandpass filter), the filter is designed to significantly attenuate light having a wavelength other than the wavelength of fluorescence received by the image sensor from 1/10000 to 1/10000. There is.

The stray light of the laser light reflected or transmitted through the wavelength separation mirror is also attenuated by the bandpass filter, but the intensity of the fluorescence generated from the fluorescent plate is very high depending on the emission characteristics of the fluorescent plate, the wavelength of the laser light, and the wavelength of fluorescence. It is weak, and the fluorescence intensity and the stray light intensity of the attenuated laser light may be comparable on the image sensor. In that case, since the stray light of the laser beam is observed as a ghost on the image sensor in addition to the fluorescent image, there is a problem that the fluorescent image cannot be measured correctly. In particular, when the wavelength of the laser light and the fluorescence (transmission wavelength of the bandpass filter) are close to each other, the incident laser light component may not be attenuated so much by the bandpass filter due to the characteristics of the bandpass filter, which is caused by the stray light of the laser light. There was a problem that the influence of ghost could not be removed.

In addition, when the intensity of the laser beam is strong and the laser beam is finely focused and incident, or when the laser beam is irradiated in a pulse shape over time and the peak intensity of the pulsed light is high, the wavelength separation mirror is reflected or Even if the stray light of the transmitted laser light is 1%, there is a problem that the band pass filter, the camera, or the image sensor may be damaged because the central portion has a high light intensity.

Therefore, the present invention is intended to solve such a problem of the prior art, and eliminates the influence of ghost due to stray light of the laser beam that is not separated by the wavelength separation mirror, and obtains a high-power laser beam profile with high accuracy. The purpose is to make it possible to measure.

Another object of the present invention is to prevent the bandpass filter, the camera, or the image sensor from being damaged by the stray light of the laser beam.

In order to solve the above-mentioned problems, the present invention has the following configurations.
The present invention is a beam profile measuring device that measures a two-dimensional light intensity distribution of laser light, and has a plate-shaped or block-shaped fluorescence having an incident surface on which the laser light is incident and an exit surface on which the laser light is emitted. A generation element, a light separation element that separates fluorescence generated in the fluorescence generation element and emitted from the emission surface from the laser beam, an image element that receives the fluorescence, and the light separation element and the image element. The mask comprises a mask located in the light path of the fluorescence in between, and the mask is provided so as to cover a central portion including the center of the light path of the fluorescence, and shields the light having the wavelength of the laser light.

In one of the preferred embodiments of the present invention, it is preferable to further include an imaging optical system located between the optical separation element and the image element.

Further, in one of the preferred embodiments of the present invention, the mask includes a transparent base material and a film formed on one surface of the base material and shielding light having a wavelength of the laser light. It is good.

Further, in one of the preferred embodiments of the present invention, the mask includes a film formed on one surface of a lens constituting the imaging optical system to block light having a wavelength of the laser light. good.

Further, in one of the preferred embodiments of the present invention, the mask may be a metal plate having a shielding portion covering the central portion.

Further, in one of the preferred embodiments of the present invention, the mask is a metal plate having a shielding portion covering the central portion and a rim portion provided around the shielding portion, and the shielding portion and the shielding portion. It is good to have a hole between the rim and the rim.

Further, in one of the preferred embodiments of the present invention, the mask may be in the shape of a circle, an ellipse, a straight line, a triangle, a square, a rectangle, or a polygon having five or more angles.

Further, in one of the preferred embodiments of the present invention, it is assumed that the shielding portion of the mask is in the shape of a circle, an ellipse, a straight line, a triangle, a square, a rectangle, or a polygon having five or more angles. good.

Generally, the laser beam and its stray light are coherent light, and have a strong directional property, and have the highest intensity at the center of the optical path in the optical path between the optical separation element and the image element. Therefore, a mask located in the fluorescence optical path between the optical separation element and the image element is provided so as to cover the central portion including the center of the fluorescence optical path so as to shield the light having the wavelength of the laser beam. By configuring, the influence of the stray light of the laser beam is effectively removed. As used herein, "shielding" means not transmitting light of a wavelength of laser light, and includes either reflecting, diffusing, or absorbing light.

On the other hand, fluorescence, which is incoherent light, has no directionality and spreads to the surroundings when emitted from the fluorescent plate, and a part of the spread fluorescence passes through an optical path between the optical separation element and the image element. The spread fluorescence is greater than the mask provided to cover the central portion including the center of the fluorescence path. Therefore, despite the installation of the mask, the fluorescence that has passed around the mask is correctly imaged on the image element. As a result, the influence of ghost can be removed and the fluorescence image can be measured correctly. As described above, the present inventor has obtained the idea of shielding only the laser beam by utilizing the difference in the properties of the laser beam and its stray light (coherent light) and the fluorescence (incoherent light). The present invention has been completed.

On the other hand, the mask located in the optical path of fluorescence between the light separation element and the image element shields the stray light of the laser light, so that the stray light of the laser light damages the bandpass filter, the camera or the image sensor. There is also an advantage that it can be prevented.

The above-mentioned objects and advantages of the present invention as well as other purposes and advantages will be more clearly understood through the description of the following embodiments. However, the embodiments described below are examples, and the present invention is not limited thereto.

It is a figure which shows one structural example of the laser beam profiler by this invention. It is a figure which shows the structural example of a laser beam profiler. It is a schematic diagram which shows the structural example of a mask. It is a schematic diagram which shows the other structural example of a mask. It is a figure which shows the other structural example of a laser beam profiler. It is a figure which shows the other structural example of a laser beam profiler. It is a figure explaining the conventional example of the beam profile measurement method using fluorescence.

Hereinafter, preferred embodiments of the laser beam beam profile measuring apparatus according to the present invention will be described in detail with reference to the drawings with reference to a plurality of examples of the laser beam beam profile measuring apparatus.

The outline and function of the configuration example of the beam profile measuring apparatus according to the present invention will be described below with reference to FIGS. 1 to 6. Here, FIG. 1 is a diagram showing a configuration example of a laser light transmission separation type beam profiler using a wavelength separation mirror that transmits laser light and reflects fluorescence as a light separation element and a mask made of a metal plate. FIG. 2 is a diagram showing a configuration example of a laser light reflection separation type beam profiler using a wavelength separation mirror that reflects laser light and transmits fluorescence as a light separation element and a mask made of a metal plate. 3 is a schematic diagram showing a configuration example of a mask made of a metal plate, FIG. 4 is a schematic diagram showing another configuration example of a mask made of a metal plate, and FIG. 5 is a mask of the metal plate shown in FIG. The figure shows another configuration example of the laser light transmission separation type beam profiler in which the above is replaced with another mask, and FIG. 6 shows the laser light transmission separation type in which the metal plate mask shown in FIG. 1 is replaced with another mask. It is a figure which shows the other structural example of a beam profiler.

In the example of the laser light transmission separation type beam profiler 100 shown in FIG. 1, when the laser light having a wavelength λ1 is incident from the incident surface 1a, the fluorescent plate 1 absorbs a part of the laser light and generates fluorescence having a wavelength λ2 internally. .. The generated fluorescence 13 is emitted from the emission surface 1b while spreading to the surroundings. The fluorescent plate 1 corresponds to the fluorescence generating element in the present invention. Here, an example in which the wavelength λ1 of the laser beam is 808 nm and the wavelength λ2 of the fluorescence for which the fluorescence image is to be observed is 1064 nm among the fluorescence generated in the fluorescent plate 1 will be described below.

The fluorescence plate 1 may form a fluorescence generation element bonded and integrated with a support (not shown). For example, the fluorescence generating element may have a square prismatic shape with an incident surface of 6 mm square. The material of the fluorescent plate 1 is, for example, Nd: YAG translucent ceramic, and the Nd concentration is 0.7 at. %, The thickness may be 0.05 mm. The material of the support (not shown) may be, for example, YAG translucent ceramic containing no Nd and a thickness of 2 mm. The facing surfaces (indicated by reference numeral 1b in FIG. 1) of the fluorescent plate 1 and the support (not shown) may be joined and integrated by a low temperature fusion method without using an adhesive.

In the laser light transmission separation type beam profiler 100 shown in FIG. 1, the laser light 12 having a wavelength of 808 nm incident as an example of the laser light to be measured passes through the fluorescent screen 1 and further passes through the wavelength separation mirror 2. It is discharged to the outside of the device. However, since it is difficult for the wavelength separation mirror 2 to achieve 100% transmittance of the laser light 12, a part of the laser light 12 (usually a laser light having an energy of about 1 to 5%) uses the wavelength separation mirror 2. It is reflected and becomes stray light 14 of laser light. Here, two stray lights reflected from the two surfaces transmitted by the laser beam 12 of the wavelength separation mirror are shown. The wavelength separation mirror 2 corresponds to the optical separation element in the present invention.

On the other hand, when passing through the fluorescent plate 1, a part of the laser beam 12 is absorbed by Nd: YAG of the fluorescent plate 1 and converted into energy to generate fluorescence centered on a wavelength of 1 μm proportional to the laser light intensity distribution. However, the 1064 nm fluorescence 13 is reflected by the wavelength separation mirror 2, passes through the objective lens 5, the imaging lens 6, and the bandpass filter 8 and then reaches the CMOS image sensor 3. The objective lens 5 and the imaging lens 6 are, for example, convex lenses made of quartz, and the focal length of the objective lens 5 may be 50 mm and the focal length of the imaging lens 6 may be 100 mm. The fluorescent plate 1 is arranged at the focal position of the objective lens 5, and the CMOS image sensor 3 is arranged at the focal position of the imaging lens 6, and the fluorescent image of the fluorescent plate 1 is doubled on the light receiving surface (not shown) inside the CMOS image sensor 3. It is magnified and imaged and visualized. The CMOS image sensor 3 corresponds to the image element in the present invention. Further, the objective lens 5 and the imaging lens 6 correspond to the imaging optical system 7.

The bandpass filter 8 is designed to significantly attenuate the light other than 1064 nm so that the light other than 1064 nm does not reach the CMOS image sensor 3. The transmission wavelength width of the bandpass filter 8 at 1064 nm is, for example, 10 nm. However, as already described, especially when the intensity of the laser beam incident on the fluorescent plate 1 is strong and the intensity of the fluorescence 13 reaching the CMOS image sensor 3 from the fluorescent plate 1 is very weak, the stray light of the laser beam having a wavelength of 808 nm is assumed. Even if 14 is attenuated by the bandpass filter 8, the intensity of the stray light 14 of the laser beam reaching the CMOS image sensor 3 may be about the same as the intensity of the fluorescence 13, which is the correct fluorescence as a ghost. Observing the image on top of it has been a conventional problem.

Therefore, a mask 4 is provided in the optical path of the fluorescence 13 between the wavelength separation mirror 2 and the CMOS image sensor 3. The mask 4 is provided so as to cover the optical path of the fluorescence 13, that is, the central portion including the center of the imaging optical system, and is configured to shield the light having a wavelength of 808 nm of the laser light. Therefore, the stray light 14 of the laser beam reflected from the wavelength separation mirror 2 is shielded by the mask 4 and is prevented from reaching the CMOS image sensor 3.

A configuration example of the mask will be described in detail with reference to FIGS. 3 and 4. The mask 4 may be a metal plate having a shielding portion 41 covering a central portion including the center of the fluorescent optical path. For example, a shielding portion 41 is formed by punching or cutting a metal plate having a thickness of about 1 mm made of aluminum, an aluminum alloy, copper, a copper alloy, or stainless steel to make a hole. Can be done.

With reference to FIG. 3, the mask 4 of the metal plate has a shielding portion 41 and a rim portion 43 provided around the shielding portion 41, and a hole 42 is provided between the shielding portion 41 and the rim portion 43. It may be an open configuration. The mask 4 of the metal plate may have a bridge 45 connecting the shielding portion 41 and the rim portion 43 in order to support the shielding portion 41. 3A and 3B show different configuration examples of bridges supporting the shielding portion 41, FIG. 3A shows one bridge, FIG. 3B shows two bridges, and FIG. 3C shows three bridges. Each has a bridge.

The metal plate mask 4 is advantageous in that it can be manufactured most easily and inexpensively. When the material of the mask 4 is aluminum, the surface may be further subjected to white alumite treatment to reflect light, and conversely, black alumite treatment may be performed to absorb stray light of laser light. When absorbing light, it is preferable to use a material having high thermal conductivity, for example, aluminum, copper or a copper alloy, because the temperature of the light-shielding portion 41 rises.

As described above, the mask 4 of the metal plate as shown in FIG. 3 can be configured by making a hole 42 around the shielding portion 41, but since only air exists in this hole, it goes into the optical path of fluorescence. The optical path length of the entire imaging optical system does not change depending on the installation of the mask 4. Therefore, in addition to the advantage that it is not necessary to readjust the optical system even if the mask 4 is inserted in the optical path of fluorescence, a plurality of masks having shielding portions 41 having various shapes or sizes are prepared. There is also an advantage that the mask can be arbitrarily selected and inserted according to the measurement target, which is highly practical.

The mask may be provided so as to cover the central portion including the center of the fluorescent optical path, and the shape of the mask is not particularly limited. The shape of the mask may be, for example, a circle, an ellipse, a straight line, a triangle, a square, a rectangle, or a polygon having five or more angles. In the example shown in FIG. 3, the shape of the shielding portion 41 corresponds to the shape of the mask 4, and in these examples, the shape of the mask is a circle. The shape of the rim portion 43 is not related to the shape of the mask in the present invention.

Other configuration examples of the mask will be described with reference to FIG. FIG. 4A is an example in which the shape of the shielding portion 51 is rectangular, FIG. 4B is an example in which the shape of the shielding portion 53 is rectangular, and FIG. 4C is an example in which the shape of the shielding portion 55 is straight. Are shown respectively. Also in these examples, the shapes of the shielding portions 51, 53, 55 correspond to the shapes of the mask, and the shape of the rim portion 43 does not relate to the shape of the mask in the present invention. Including these examples, when the shape of the mask is a straight line, a square, a rectangle, or a polygon having five or more angles, one side of the mask is the p-polarization direction in the wavelength separation mirror 2. It should be aligned so that it is parallel to. Such a configuration in which the mask is aligned is advantageous because the stray light of the laser beam reflected on the front surface and the back surface of the wavelength separation mirror 2 can be efficiently removed.

Generally, the shape and size of the mask may be determined in consideration of the shape and size of the laser beam 12 scheduled to be incident, the size of the imaging optical system 7, and the like. Since the laser beam 12 is considered to travel substantially linearly without spreading from the fluorescent plate 1, the shape of the shielding portion 41 of the mask 4 may be the same as the shape of the fluorescent plate 1 (for example, a circle), and the shielding portion 41 may have the same shape. The size may be substantially the same as or slightly larger than the size of the fluorescent screen 1.

The area of the shielding portion 41 is preferably 1/3 or less of the area of the lens of the imaging optical system. The larger the area of the shielding portion 41, the higher the shielding effect of the laser light, but as the ratio of the shielding portion 41 increases, the CMOS image sensor 3 passes through a region (for example, a hole) other than the shielding portion 41 of the mask 4. Since the amount of fluorescence light reaching the area is reduced, the observed fluorescence intensity distribution (laser light intensity distribution) becomes darker and the S / N decreases. Further, since the laser light 12 is considered to travel substantially linearly without spreading from the fluorescent plate 1, the laser light reflected by the wavelength separation mirror 2 covers the central portion including the center of the fluorescent optical path 41. It should be noted that even if the area of is increased to a certain area (for example, an area slightly larger than the area of the fluorescent plate 1), the shielding effect of the laser beam does not change much, but the fluorescent image becomes darker. Is.

With reference to FIG. 1 again, in the laser light transmission separation type beam profiler 100 shown in FIG. 1, the mask 4 is provided at any position in the optical path of the fluorescence 13 between the wavelength separation mirror 2 and the CMOS image sensor 3. However, it is preferable that the imaging optical system 7 is provided at a position close to the front and back. If the mask 4 is too close to the CMOS image sensor 3, the portion shaded by the mask 4 becomes a shadow and is reflected on the CMOS image sensor 3, which may affect the measurement of the fluorescence image. More preferably, the mask 4 is provided immediately before the coupled optical system 7 on which the fluorescence 13 is incident. In such an arrangement, even when the intensity of the stray light 14 of the laser beam is strong, the objective lens 5, the imaging lens 6, and the bandpass filter 8 constituting the imaging optical system 7 are damaged by the laser beam. It is more advantageous because you can avoid receiving it.

Next, another example of the beam profile measuring apparatus for laser light according to the present invention will be described with reference to FIG. FIG. 2 shows a configuration example of the laser light reflection separation type beam profiler 200.

In the example of the laser light reflection separation type beam profiler 200 shown in FIG. 2, when the laser light of wavelength λ1 is incident from the incident surface 21a, the fluorescent plate 21 absorbs a part of the laser light and generates fluorescence of wavelength λ2 internally. .. The generated fluorescence 13 is emitted from the emission surface 21b while spreading to the surroundings. The fluorescent plate 21 corresponds to the fluorescence generating element in the present invention. Here, an example in which the wavelength λ1 of the laser beam is 808 nm and the wavelength λ2 of the fluorescence for which the fluorescence image is to be observed is 1064 nm among the fluorescence generated in the fluorescent plate 21 will be described below.

The fluorescence plate 21 may form a fluorescence generation element bonded and integrated with a support (not shown). For example, the fluorescence generating element may have a cylindrical shape with a diameter of 10 mm. The material of the fluorescent plate 21 is, for example, Nd: YAG crystal, and the Nd concentration is 1.0 at. %, The thickness may be 0.2 mm, and the material of the support (not shown) may be, for example, a YAG crystal containing no Nd, and the thickness may be 2 mm. The facing surfaces (indicated by reference numeral 21b in FIG. 2) of the fluorescent plate 21 and the support (not shown) may be joined and integrated by a thermocompression bonding method without using an adhesive.

In the laser light reflection separation type beam profiler 200 shown in FIG. 2, the 808 nm laser light 12 incident as an example of the wavelength of the laser light to be measured passes through the fluorescent screen 21 and is reflected by the wavelength separation mirror 22. , Discharged to the outside of the device. However, since it is difficult for the wavelength separation mirror 22 to achieve 100% of the reflectance of the laser light 12, a part of the laser light 12 (usually a laser light having an energy of about 1 to 5%) uses the wavelength separation mirror 22. It is transmitted and becomes stray light 14 of laser light. The wavelength separation mirror 22 corresponds to the optical separation element in the present invention.

On the other hand, when passing through the fluorescent plate 21, a part of the laser light is absorbed by Nd: YAG of the fluorescent plate 21, energy is converted, and fluorescence having a wavelength of 1 μm proportional to the laser light intensity distribution is generated toward the surroundings. However, the 1064 nm fluorescence 13 passes through the wavelength separation mirror 22, passes through the objective lens 25, the imaging lens 26, and the bandpass filter 8, and then reaches the CMOS image sensor 3. The objective lens 25 and the imaging lens 26 may be, for example, a convex lens made of optical glass known by the general name “BK7”, and the focal lengths of the lenses may both be 50 mm. Further, the fluorescent plate 21 is located at the focal position of the objective lens 25, and the CMOS image sensor 3 is located at the focal position of the imaging lens 26. In this configuration, the fluorescent image of the fluorescent plate 21 is 1: 1 and the light receiving surface in the CMOS image sensor 3. Imaged above (not shown).

The configuration and position of the mask 4 may be the same as the configuration and position of the mask 4 in the example of the laser light reflection transmission type beam profiler 100 shown in FIG. The function of the mask 4 in the laser light reflection separation type beam profiler 200 shown in FIG. 2 is the same as the function of the mask 4 in the example of the laser light transmission separation type beam profiler 100 shown in FIG. The explanation is omitted. The laser light reflection separation type beam profiler 200 also achieves the laser light transmission separation type beam profiler 100 shown in FIG. 1, except that the functions of reflection and transmission of the laser light 12 and the fluorescence 13 by the wavelength separation mirror 22 are different. It is possible to achieve the same effect as the effect of

Next, another example of the beam profile measuring device of the laser beam will be described with reference to FIG. FIG. 5 shows a configuration example of the laser light transmission separation type beam profiler 300. In the configuration example shown in FIG. 5, as an alternative to the mask 4 of the metal plate in the laser light transmission separation type beam profiler 100 shown in FIG. 1, the transparent base material 61 is formed on one surface of the base material 61. Further, a mask 4 including a film 63 that shields light having a wavelength of laser light is used. Other components are the same as the components of the configuration example shown in FIG.

The material of the transparent base material 61 may be a glass material such as quartz or BK7, an inorganic crystal material such as sapphire, a plastic such as acrylic, or the like, and the film 63 may be a metal film or a dielectric film. The material of the metal film may be gold, silver, nickel, aluminum, an aluminum alloy, copper, a copper alloy, chromium, or the like, or a laminate thereof may be used. The material of the dielectric film may be TiO ₂ , Ta ₂ O ₅ , HfO ₂ , Nb ₂ O ₃ , ZrO ₂ , MgF ₂ , YF ₃ , SiO ₂ , Al ₂ O _3, or the like. Using one or more of these metallic or dielectric materials, a single-layer thin film of a specific thickness (eg 0.5 μm or more) or multiple films of different materials were laminated to a specific thickness. A multilayer film may be formed. As a method for forming the film 63, a vacuum vapor deposition method is performed in which a portion of the surface of the base material 61 other than the portion where the film 63 is formed is masked, and then the material is heated in a vacuum to adhere to the surface of the base material 61. Alternatively, there is a sputter method in which another ion is struck against the material to flick the material off and adhere to the surface of the base material 61, but the method is not particularly limited. Further, in the case of a metal film, it may be attached to the surface of the base material 61 via an adhesive, an adhesive film or the like.

The shape and size of the film 63 may be the same as the shape and size of the shielding portion 41 or the shielding portions 51, 53, 55 of the mask 4 in the laser light transmission separation type beam profiler 100 shown in FIG. The function of the mask 4 in the laser light transmission separation type beam profiler 300 shown in FIG. 5 is the same as the function of the mask 4 in the example of the laser light transmission type beam profiler 100 shown in FIG. Is omitted. The laser light transmission separation type beam profiler 300 can also achieve the same effect as that of the laser light transmission separation type beam profiler 100 shown in FIG. When the mask 4 in which the film 63 is formed on the transparent base material 61 is used, the bridge 45 is not required as compared with the mask 4 of the metal plate shown in FIG. 3, so that the area of the portion through which fluorescence is transmitted is large. And the S / N can be improved.

Next, another example of the beam profile measuring device of the laser beam will be described with reference to FIG. FIG. 6 shows a configuration example of the laser light transmission separation type beam profiler 400. In the configuration example shown in FIG. 6, the laser beam transmission separation type beam profiler 100 shown in FIG. 1 is formed on one surface of the objective lens 5 constituting the imaging optical system 7 as an alternative to the mask 4 of the metal plate. The mask 4 including the film 73 that shields the light having the wavelength of the laser light is used. Other components are the same as the components of the configuration example shown in FIG.

The film 73 formed on the surface of the objective lens 5 may be a metal film or a dielectric film similar to the film 63 formed on the surface of the base material 61 in the laser beam transmission separation type beam profiler 300 shown in FIG. , Detailed explanation about the material and the composition of the film is omitted. Further, in the method of forming the film 73, after masking the portion of the surface of the objective lens 5 other than the portion forming the film 73, the material is heated in a vacuum to adhere to the surface of the objective lens 5. There are methods such as a spattering method in which another ion is struck against the material to flick the material off and adhere to the surface of the objective lens 5, but the method is not particularly limited. Further, in the case of a metal film, it may be attached to the surface of the objective lens 5 via an adhesive, an adhesive film, or the like.

The laser light transmission separation type beam profiler 400 also achieves the same effect as that achieved by the laser light transmission separation type beam profiler 100 shown in FIG. 1 and the laser light transmission separation type beam profiler 300 shown in FIG. be able to.

In the above example, Nd: YAG is mentioned as an example of the fluorescent plate 1, but the material of the fluorescent plate 1 is not limited to this, and in addition, it absorbs light of 940 nm and 970 nm and fluoresces at 1030 nm. Yb: YAG that emits Yb: YAG, or Cr, Yb: YAG in which Cr ⁴⁺ ions are added to Yb: YAG for the purpose of shortening the fluorescence lifetime, and 1.6 μm or 2.9 μm that absorbs light in the vicinity of 785 nm or 1.5 μm. It may be Er: YAG that emits the fluorescence of 780 nm or 785 nm, or Tm: YAG that absorbs light of 780 nm or 785 nm and emits 2.01 μm of fluorescence. Ho: YAG may be used, and Cr, Tm, Ho: YAG may be used to absorb light in the vicinity of 780 nm and emit fluorescence of 2.08 μm. Ce: YAG may be used to absorb light in the vicinity of 350 nm and 450 nm and emit fluorescence of 550 nm. But it may be. Further, Cr, Nd: YAG to which Cr ³⁺ ions that absorb the visible light region and emit fluorescence of 1 μm may be added. The absorption wavelength and the fluorescence wavelength described above are typical examples, and may be selected from the absorption wavelength band and the fluorescence wavelength peculiar to the medium according to the individual purpose and specifications. The fluorescence wavelength to be detected does not necessarily have to be set to the fluorescence peak wavelength of the medium, and the transmission wavelength of the bandpass filter 8 may be set so as to detect at a wavelength away from the fluorescence peak wavelength. Further, in the above examples, YAG was used as the base material of the fluorescent plate and the support (not shown), but the present invention is not limited to this, and if it is a transparent material, glass such as quartz or BK7 is used. also may a material having a high thermal conductivity than YAG _Y 2 _{O 3} and _{Lu 2 O 3, LuAG, YAP} , Sc 2 O 3, GGG, GSGG, YSGG, YSO, or sapphire. Further, the crystallinity of the base material may be a single crystal or a translucent ceramic. Further, as the fluorescent plate, in addition to the above-mentioned inorganic materials in which transition metals and rare earth ions are dispersed, II-VI semiconductor nanoparticles such as ZnS, ZnSe, and ZnTe may be dispersed and fixed in glass or plastic. A medium that absorbs the wavelength of the laser beam to be measured may be selected. A transparent adhesive may be used to bond the fluorescent plate 1 and the support (not shown), or optical adhesion (optical contact) in which the surfaces to be bonded are ground and pressed against each other with high precision without using an adhesive. However, in terms of adhesive strength, thermocompression bonding, diffusion bonding (high temperature fusion) and low temperature fusion are more preferable. In order to avoid deformation of the fluorescent plate 1 due to heat generation, it is more preferable that the fluorescent plate 1 and the support (not shown) are the same base material having a similar expansion coefficient, but if the heat generation is small, the support (not shown). The base material different from the fluorescent plate 1, for example, the base material of the fluorescent plate 1 may be YAG and the support may be sapphire having good heat conduction. Further, it is desirable that the thickness of the fluorescent plate 1 is thin in order to improve the measurement position accuracy in the optical axis direction of the beam. However, if the fluorescent plate 1 is made thin, the distance through which the laser beam is transmitted decreases and the intensity of the generated fluorescence decreases. Therefore, it is preferable to increase the amount of the fluorescent element added to the fluorescent plate 1 so that the desired fluorescence intensity can be obtained. ..

In the above example, an example in which an image of the fluorescent screen 1 is formed on the image sensor 3 at a ratio of 1: 2 using lenses having different focal lengths on the objective lens 5 and the imaging lens 6, and the objective lens 25 and the imaging lens 26 are formed. An example is shown in which an image of the fluorescent screen 1 is imaged on the image sensor 3 at a ratio of 1: 1 using a lens having the same focal length. However, other lenses having different focal lengths may be used to magnify or reduce the image on the fluorescent screen 1 and project it on the image sensor 3, which is an imaging optical system using three or more lenses. It may be an imaging optical system using one lens simply, and is not particularly limited. Further, the lens may be a double-sided spherical lens, a plano-convex lens, a bonded achromatic lens, or an aspherical lens.

Further, regarding the position of the bandpass filter 8, the configuration in which the bandpass filter 8 is placed immediately after the imaging optical system 7 having the lowest light intensity is shown in the above example, but it may be placed at a position different from such a position. It may be arranged between the objective lens 5 of the image optical system 7 and the imaging lens 6. Alternatively, a plurality of filters may be used as needed. Further, as the CMOS or CCD image sensor used as the image element, it is preferable to select a material such as Si, Ge, GaAs, InGaAs, or InP, which has an appropriate sensitivity in the wavelength of the fluorescence emitted by the fluorescent plate.

Industrial application field

The present invention can be widely applied to various devices having a function of measuring a beam profile of a laser beam.

1, 21 Fluorescent plates 1a, 21a Incident surface of laser light 1b, 21b Emission surface of laser light 12 Laser light 13 Fluorescent 14 Stray light of laser light 2, 22 Wavelength separation mirror (light separation element)
3 Image sensor 4 Mask 5, 25 Objective lens 6, 26 Imaging lens 7 Imaging optical system 8 Bandpass filter 41, 51, 53, 55 Shielding part 42 Hole 43 Rim part 45 Bridge 61 Base material 63, 73 film

Claims (8)

A laser beam beam profile measuring device that measures a two-dimensional profile of laser light.
A plate-shaped or block-shaped fluorescence generating element having an incident surface on which a laser beam is incident and an emitting surface on which the laser beam is emitted.
An optical separation element that separates the fluorescence generated in the fluorescence generating element and emitted from the emitting surface from the laser beam, and
The image element that receives the fluorescence and
A mask located in the fluorescent optical path between the optical separation element and the image element,
Including
The mask is provided so as to cover a central portion including the center of the fluorescent optical path, and shields light having a wavelength of the laser light.
Laser beam profile measuring device. The beam profile measuring apparatus for laser light according to claim 1, further comprising an imaging optical system located between the optical separation element and the image element. The beam profile measurement of a laser beam according to claim 1, wherein the mask includes a transparent substrate and a film formed on one surface of the substrate to shield light having a wavelength of the laser beam. Device. The beam profile measuring apparatus for laser light according to claim 2, wherein the mask includes a film formed on one surface of a lens constituting the imaging optical system to block light having a wavelength of the laser light. .. The beam profile measuring device for laser light according to claim 1, wherein the mask is a metal plate having a shielding portion covering the central portion. The mask is a metal plate having a shielding portion that covers the central portion and a rim portion provided around the shielding portion, and a hole is formed between the shielding portion and the rim portion. The beam profile measuring device for laser light according to claim 1. The beam profile measuring apparatus for laser light according to claim 1, wherein the shape of the mask is any of a circle, an ellipse, a straight line, a triangle, a square, a rectangle, or a polygon having five or more angles. The laser beam according to claim 5 or 6, wherein the shape of the shielding portion of the mask is any of a circle, an ellipse, a straight line, a triangle, a square, a rectangle, or a polygon having five or more angles. Beam profile measuring device.

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