Laser beam profile measuring device

Abstract

Laser beam profile measuring device (100;200) for measuring a two-dimensional laser light profile, comprising: a plate-like or block-like fluorescence generating element (10; 30) having an incident surface (1a; 21a) on which the laser light is incident and an emission surface (1b; 21b) from which the laser light is emitted, the incidence surface (1a; 21a) and the emission surface (1b; 21b) being opposite each other; a light separation element (3; 23) for separating fluorescence from laser light, wherein the fluorescence is generated in the fluorescence generation element (10; 30) and emitted from the emission surface (1b; 21b); and an imaging element (8) for receiving the fluorescence, wherein the plate-like or block-like fluorescence generating element (10; 30) includes a first film (S1) formed on its incident surface (1a; 21a), and the first film (S1) has a wavelength-to-reflectance characteristic of transmitting a wavelength λ1 of the laser light and reflecting a wavelength λ2 of the fluorescence, wherein the light separation element (3; 23) includes a second film (S2), and the second film (S2) has a wavelength-to-reflectance characteristic of transmitting the wavelength λ2 of the fluorescence and reflecting the wavelength λ1 of the laser light, and wherein the first film (S1) further has a wavelength-to-reflectance characteristic of reflecting a wavelength λ0 between the wavelength λ1 of the laser light and the wavelength λ2 of the fluorescence, while the second film (S2) further has a wavelength-to-reflectance characteristic of reflecting the wavelength λ0.

Description

Technical FieldThe present invention relates to a laser beam profile measuring apparatus. More particularly, the invention relates to a laser beam profile measuring apparatus capable of measuring a two-dimensional beam profile of laser light with high power with high position precision and high accuracy.Technological BackgroundThe following methods are known as a conventional method for measuring a beam profile (two-dimensional light intensity distribution) of high-power laser light of more than 100 mW. The methods include: a method in which laser light is attenuated by a filter or mirror and observed with an image sensor such as CCD and CMOS; a method in which the intensity of transmitted light is measured during partially shielding the light beam with a pinhole, slit or cutter and the beam profile is calculated from a correlation between the light shielding position and the intensity of transmitted light; a method in which a light intensity distribution is measured by two-dimensional scanning with a rod having a small mirror at the tip thereof or a light guide rod formed with a small hole at the tip thereof in the beam; and a method in which a light diffusion plate is irradiated with the laser light and an image of the diffused light is measured from behind by a camera. It is noted that the term "camera" as used herein generally means devices for capturing images. The camera generally includes therein a picture element (for example, an image sensor such as CCD or CMOS) for detecting an image and an optical system (lens and the like) for forming an image on the picture element.The method of attenuating the laser light with the filter or mirror requires some space for inserting the filter or mirror in front of the image sensor. However, a certain position of the beam to be measured prevents the filter or mirror from being inserted. In addition, the employment of the filter or mirror is connected with the fear that the beam profile may be deformed by heat or aberrations. On the other hand, the following problem is encountered in the method for measuring the laser beam during partial shielding of the beam with the pinhole, slit or knife blade. In a case where the beam profile does not have a single (single) maximum (peak) but is complicated, the measurement accuracy can be significantly reduced due to the volume of information acquired by the measurement. The method for performing two-dimensional scanning in the laser beam by means of the rod having the small mirror at the tip or the light guide rod formed with the small hole at the tip thereof suffers from the following drawback. The profile of a fine beam having a size of 1 mm or less cannot be measured because of the size of the mirror attached to the tip of the rod or the size of the hole at the tip of the rod. When mechanically scanning with the rod at high speed, the tip of the rod floats and thus the positional precision can be reduced. According to the method in which the light diffusion plate is irradiated with the laser light so that the image of scattered light is measured with the camera from behind, the scattered light to be measured is diffused a plurality of times, and thus the image is blurred. In particular, in a case where the laser beam size is reduced to 1 mm or less, the measurement accuracy can be significantly reduced.On the other hand, a method is also known in which the laser light is applied to a plate-like fluorescent body (fluorescent plate) and measurement of a two-dimensional intensity distribution of fluorescence emitted therefrom is performed (see, for example, Patent Literatures 1 to 3 and Non-Patent Literature 1). Patent Literatures 1 and 2 propose a method in which the fluorescent plate is irradiated with the laser light from the front side of the fluorescent plate, and the fluorescence from the irradiated surface is observed with a camera from a front side of the fluorescent plate irradiated with the laser or from a back side thereof. Patent Literature 3 and Non-Patent Literature 1 propose a method in which Nd:YAG is used as the fluorescent plate, and report the experimental results. Non-Patent Literature 1 is the report on the results of past experiments, a co-author of which is the inventor.Referring now to Fig. 10, a description will be given of a hitherto proposed method for measuring a beam profile using fluorescence. Laser light to be measured (wavelength: 808 nm) 1103 is applied to a film-like fluorescent body 1101 formed on a surface of a transparent block 1100. A laser light not absorbed by the fluorescent body 1101 passes through an interface 1102 for emitting to the outside. On the other hand, fluorescence 1104 generated from the fluorescent body is reflected by the interface 1102 and is freed from wavelengths other than the fluorescent wavelength by a filter 1105. Thereafter, the resultant light enters the camera 1106 to be focused in an image. Non-Patent Literature 1 also fundamentally discloses the same configuration except that the transmission direction and reflection direction of the laser light are opposite. The literature references cited Nd:YAG as an example of the fluorescent body.Regarding the above-described prior art techniques, advantages of the measurement method using fluorescence over the other measurement methods will be described below. First, the method enables accurate and highly accurate identification of a position in an optical axis direction (z-axis direction) of the laser light to be measured on the fluorescent plate. Specifically, by placing the fluorescent plate at a position where the beam is to be measured, a beam profile at the location of interest is faithfully converted into a fluorescence intensity profile (fluorescent image) that is imaged by a camera for observation and storage. The fluorescence emitted from the fluorescent plate has a wavelength separate from that of the laser light to be easily separated from the laser light by a dichroic mirror (wavelength separation mirror) or the like. Fluorescence can be observed with a high signal-to-noise ratio (S / N)). Since the fluorescence is less liable to scattering or absorption in the fluorescent plate, a fluorescent image is blurless and has high resolution to be measured by a camera with a high degree of accuracy. It is easy to reduce the intensity of the generated fluorescence to 1 / 100 or less of the intensity of incident laser light by adjusting (reducing) the concentration (absorption characteristic) and thickness of the plate fluorescent material and fluorescent body. That is, the fluorescent plate also functions as a kind of neutral filter, so that after the fluorescence is separated by the wavelength separation mirror, the laser light can be observed using the image sensor without signal saturation or signal dropout. Further, the amount of heat generated in the fluorescent plate at this time can be reduced, so that a temperature rise can be suppressed when laser light having high power is directly applied. Thus, the measurement can be stably performed for a long time. Unlike the laser light or the scattered light thereof, the fluorescence is incoherent light that produces fewer speckles. When used with an optical system having a small numerical aperture (NA)), fluorescence in an image can be accurately focused on the image sensor, resulting in a high degree of freedom in selection of the optical system. Further, the fluorescence provides free adjustment of image magnification based on the combination of lenses, which has an advantage of enabling measurement of a fine beam profile with high accuracy by magnification.Patent Literature 4 discloses a laser beam profile measurement device for measuring a two-dimensional laser light profile, comprising a plate-like or block-like fluorescence generating element having an incident surface on which the laser light is incident and an emission surface from which the laser light is emitted, the incident surface and the emission surface facing each other, a light separating element for separating fluorescence from the laser light, the fluorescence being generated in the fluorescence generating element and emitted from the emission surface, and an imaging element for receiving the fluorescence.It is known from Patent Literature 5 that by using a fluorescent reflection film that transmits light having the wavelength λ1of the laser light and reflects light having the wavelength λ2of the fluorescence, the sensitivity of the sensor at the fluorescent wavelength can be increased.Patent Literature 6 discloses a measurement geometry in which a light separation element includes a third film, and the third film has a wavelength-to-reflection characteristic of reflecting the wavelength λ2of fluorescence and transmitting the wavelength λ1of laser light.Citation ListPatent LiteraturePatent Literature 1: Japanese Laid-Open Patent Application JP H06-221 917 APatent Literature 2: Japanese Laid-Open Patent Application JP 2004-245 778 APatent Literature 3: Japanese Laid-Open Patent Application JP 2008-519 263 APatent Literature 4: US 2011 / 0 063 592 A1Patent Literature 5: EP 0 843 363 A1Patent Literature 6: US 2009 / 0 015 830 A1Non-Patent LiteratureNon-Patent Literature 1: Masaki Tsunekane et al., "Provisional for New Measurement Method of High-accuracy 2D Beam Profile" January 11-12, 2015, the 35 th Annual Conference of Laser SocietySUMMARY OF THE INVENTIONTechnical ProblemThe above-mentioned patent literature and non-patent literature do not contain any specific description of the formation of a film formed on a surface of the fluorescent material, fluorescent body, or fluorescent plate (hereinafter, generally referred to as "fluorescent plate") and for controlling the reflection of light having the wavelength of fluorescence generated in the fluorescent plate. When the laser light is applied to and absorbed into the fluorescent plate, the fluorescence generated in the fluorescent plate is generally emitted in all directions. Thus, the fluorescence other than that incident on a camera or image sensor for measuring the beam profile is scattered and lost. Of the scattered fluorescence, a portion of the fluorescence passes out of the device through the surface of the fluorescent plate. Subsequently, the fluorescence in question is often reflected from a surface of an external optical part or a housing surface before it reenters the device through the surface of the fluorescent plate and further enters the above-described camera or image sensor for measuring the beam profile. Re-entry of such scattered fluorescence is associated with the following problem. The fluorescence in question overlaps with light generated in the fluorescent plate and is a measurement object per se, resulting in deformation of the beam profile shape, observation of an actually non-existing image (ghost image), or the decrease of the S / N ratio of measurement due to the increase of the background level. As for the fluorescence generated by the fluorescent plate and scattered in the device but not out of the device, a measure may be taken to prevent the fluorescence in question from being mixed with the fluorescence incident on the camera or the image sensor. For example, the configuration of the wall surface in the device is designed to prevent the scattered light in the device from being reflected from the wall. However, it is difficult to distinguish or separate the fluorescence reflected back from the outside of the device by the fluorescent plate from the fluorescence which is the measurement object per se. This leads to a fear that the measurement accuracy and reproducibility and the reliability of measurement results are seriously deteriorated.The configurations disclosed in Patent Literature 3 and Non-Patent Literature 1 have the following problem. In a case where a laser light having a wavelength near the wavelength of fluorescence enters, an optical element for separating the laser light and the fluorescence fails to perform complete separation between the laser light and the fluorescence, so that the laser light can follow the same optical path as that of the fluorescence with high power, enters a band pass filter, a camera, or an image sensor, and causes damage or damage to the fire.Accordingly, the present invention is directed to solving the problems of the conventional configurations, and an object thereof is to provide highly accurate measurement of the beam profile of laser light with high power by preventing fluorescence generated in the fluorescent plate from scattering to the outside of the device and re-entering the fluorescent plate.It is another object of the invention to ensure that in a case where the laser light having any wavelength enters, the band pass filter, the camera, or the image sensor is prevented from suffering damage or damage to fire.Solution to ProblemsThe invention provides a laser beam profile measuring apparatus according to claim 1 and a laser beam profile measuring apparatus according to claim 2.According to a preferred aspect of the invention, the first film may have a reflectance of 70% or more at the wavelength λ2of fluorescence.According to another preferred aspect of the invention, the first film may have a reflectance of 90% or more at the wavelength λ2of fluorescence.A brief description of an exemplary configuration and functions of a laser beam profile measuring apparatus according to the invention will be provided below with reference to Figs. 1 to 7. FIG. 1 is a diagram showing an exemplary configuration of a laser light reflection separation beam profile measuring device using a 45° prism that reflects the laser light and transmits the fluorescence as a light separating element. FIG. 2 is a diagram showing an exemplary configuration of a laser light transmission-separation beam profile measuring device using a 45° mirror that transmits the laser light and reflects the fluorescence instead of the 45° prism as the light separating element. FIG. 3 is a block diagram schematically showing functions of a first film S 1, a second film S 2, and a third film S 3 according to the invention. FIGS. 4(A) and 4(B) are graphs showing exemplary wavelength-to-reflectance characteristics of the first film S 1 and the second film S 2 suitable for the laser light reflection separation beam profile measuring device. FIGS. 5(A) and 5(B) are graphs showing exemplary wavelength-to-reflectance characteristics of the first film S 1 and the third film S 3 suitable for the laser light reflection separation beam profile measuring device. FIGS. 6(A) and 6(B) are graphs showing exemplary wavelength-to-reflectance characteristics of the first film S 1 and the second film S 2 that are more suitable for the laser light reflection separation beam profile measuring device. FIGS. 7(A) and 7(B) are graphs showing exemplary wavelength-to-reflectance characteristics of the first film S 1 and the third film S 3 that are more suitable for the laser light reflection separation beam profile measuring device.According to an example of the laser light reflection separation beam profile measuring apparatus shown in FIG. 1, a fluorescence generating element 10 includes a fluorescent plate 1 that, upon incidence of a laser light having a wavelength λ 1, absorbs a part of the incident light and generates fluorescence having a wavelength λ 2 therein. In addition, according to an example of the laser light transmission-separation beam profile measuring apparatus shown in FIG. 2, a fluorescence generating element 30 includes a fluorescent plate 21 that absorbs a part of the incident light upon incidence of the laser light having the wavelength λ 1 and generates therein the fluorescence having the wavelength λ 2. An incident surface 1 aof the fluorescent plate 1 and an incident surface 21 aof the fluorescent plate 21 are each formed with a first film S 1 having a wavelength-to-reflectance characteristic of transmitting the wavelength λ 1 of the laser light and reflecting the wavelength λ 2 of the fluorescence. This first film S1 has a wavelength-to-reflectance characteristic as shown in any one of Figs. 4(A) to 7(A). Herein, the phrase "the film has a wavelength-to-reflectance characteristic of transmitting the wavelength of the laser light and reflecting the wavelength of the fluorescence" means that, in terms of the wavelength-to-reflectance characteristic, the film has a lower reflectance at the wavelength of the laser light and a high reflectance at the wavelength of the fluorescence. In other words, the film has high transmittance at the wavelength of the laser light and low transmittance at the wavelength of the fluorescence. Conversely, the phrase "the film has a wavelength-to-reflectance characteristic of reflecting the wavelength of the laser light and transmitting the wavelength of the fluorescence" means that, in terms of the wavelength-to-reflectance characteristic, the film has a high reflectance at the wavelength of the laser light and a low reflectance at the wavelength of the fluorescence. In other words, the film has a low transmittance at the wavelength of the laser light and a high transmittance at the wavelength of the fluorescence. The reflectance of a film is defined as a ratio of an amount of light reflected from the film to an amount of light incident on the film. In the following description referring to the wavelength-to-reflectance characteristic shown in FIGS. 4 to 7, a reflectance of 70% or 90% corresponds to a high reflectance, while a reflectance of almost 0 corresponds to a low reflectance. However, these numerical values of the reflectance are literally cited as examples, and the invention is not limited to these values.In each of FIG. 1 or FIG. 2, the laser light having the wavelength λ1 passes through the first film S 1 formed on the incident surface 1 a, 21 aof the fluorescent plate 1, 21 to enter the fluorescent plate 1, 21. A part of the fluorescence having the wavelength λ2generated in the fluorescent plate 1, 21 goes toward the incident surface 1 a, 21 a, but a majority thereof is returned to an emission surface 1 b, 21 bby reflection by the first film S 1 formed on the incident surface 1 a, 21 a. Namely, the first film S1 prevents a part of the fluorescence generated in the fluorescent plate 1, 21 from permeating through the incident surface 1a, 21a to be scattered and lost in the outside of the device. In addition, when a part of the fluorescence toward the incident surface 1 a, 21 apasses through the first film S 1 to be scattered by the incident surface 1 a, 21 aand to be lost in the outside of the device, and the scattered fluorescence toward the incident surface 1 a, 21 ais reflected back from the outside of the device, most of the reflected fluorescence is similarly reflected from the first film S 1 to the outside of the device. That is, the first film S 1 also prevents a part of the fluorescence scattered to the outside of the device from re-entering the fluorescent plate 1, 21 through the incident surface 1 a, 21 a. This is effective to limit or prevent adverse effects on the beam profile measurement caused by fluorescence scattered to the outside of the device and re-incident on the fluorescent plate. Further, the fluorescence generated in the fluorescent plate does not come out of the device through the incident surface, but is reflected by the first film S 1 toward the inside of the device. This results in an advantage that the fluorescence generated in the fluorescent plate is increased in the amount of light to be observed as an image by the image sensor, so that the apparatus is improved in S / N performance.In a case where the first film S 1 has a reflectance of 70% at the wavelength λ 2 of fluorescence (for example, reflection characteristic of the first film S 1, as in FIGS. 4(A), 5(A), 6(A), 7(A), for example, the amount of fluorescent light scattered from the fluorescent plate 1, 21 to the outside of the device has 30% of the amount of light when the first film S 1 has a low reflectance (for example, a reflectance of nearly 0%). Further, when a part of the fluorescence scattered to the outside of the device is reflected back from the outside to the fluorescent plate 1, 21, 70% of the returned fluorescence is reflected back to the outside from the surface of the fluorescent plate 1, 21. Thus, the amount of light entering the fluorescent plate 1, 21 is reduced to 9% as compared with the case where the first film S 1 has low reflectance. Thus, the adverse effect on the beam profile measurement caused by the fluorescence being scattered to the outside but incident again on the fluorescent plate can be remarkably reduced.In a case where the first film S 1 has a reflectance of 90% at the wavelength λ2of fluorescence (represented by the example of FIG. 8(A) ), the amount of light incident on the fluorescent plate 1, 21 again from the outside of the device is reduced to 1% as compared with the case where the first film S 1 has the low reflectance (for example, a reflectance of nearly 0%). Thus, the adverse effect on the beam profile measurement caused by the fluorescence being scattered to the outside of the device but re-incident on the fluorescent plate can be reduced even further. In addition, the fluorescence generated in the fluorescent plate does not come out of the device from the incident surface, but is reflected by the first film S 1 into the device. This also leads to an advantage that the fluorescence generated in the fluorescent plate is increased in the amount of light to be observed as an image by the image sensor, so that the apparatus is improved in S / N performance.Now, to a case where a second laser light having a wavelength considerably different from the wavelength λ1 of the laser light or, more specifically, a wavelength λ2' near the wavelength λ2 of the fluorescence is incident on the fluorescence generating element. In the example of the laser light reflection-separation beam profile measuring apparatus shown in FIG. 1, a reflection surface 3 bis formed in a 45° prism 3 as a light separating element, and the second film S 2 has a wavelength-to-reflectance characteristic of transmitting the wavelength λ 2 of fluorescence and reflecting the wavelength λ 1 of laser light. Similarly, in the example of the laser light transmission-separation beam profile measuring apparatus shown in FIG. 2, a reflection surface 23 aof a 45° mirror 23 is formed as the light separating element, and the third film S 3 has a wavelength-to-reflectance characteristic of reflecting the wavelength λ 2 of the fluorescence and transmitting the wavelength λ 1 of the laser light. These second film S 2 and third film S 3 on the light separating member respectively emit the laser light through the fluorescence generating member to the outside of the device by reflection and transmission, and respectively guide the fluorescence to the image sensor by transmission and reflection.In an example, the second film S 2 may have a reflectance of nearly 100% at the wavelength λ1of the laser light and a reflectance of nearly 0% at the wavelength λ2of the fluorescence (the wavelength-to-reflectance characteristic of the second film S 2 shown in FIGS. 4(B), 6(B) ). Similarly, the third film S 3 may have a reflectance of nearly 0% at the wavelength λ 1 of the laser light and a reflectance of nearly 100% at the wavelength λ 2 of the fluorescence (the wavelength-to-reflectance characteristic of the third film S 3 shown in FIGS. 5(B), 7(B) ).In the example of the laser light reflection separation beam profile measuring apparatus shown in FIG. 1, we want to focus on the wavelength-to-reflectance characteristics of the first film S 1 and the second film S 2 at a wavelength λ0between the wavelength λ1of the laser light and the wavelength λ2of the fluorescence. In an example of a usual wavelength-to-reflectance characteristic shown in FIG. 4, the first film S 1 has a reflectance of nearly 0% at the wavelength λ0in exact manner as at the wavelength λ1 (in FIG. 4(A) ), while the second film S 2 has a reflectance of nearly 0% at the wavelength λ0in exact manner as at the wavelength λ2 (in FIG. 4(B) ). In this example, when the wavelength λ2' of the incident second laser light is the same as or near the wavelength λ2 of the fluorescence, 70% of the incident second laser light is reflected from the first film S1 to the outside of the device, while the remaining 30% of the light enters the fluorescence generating element. Subsequently, with the wavelength that is the same as or close to that of the fluorescence, the second laser light also passes through the second film S 2 formed on the reflection surface of the light separation element and goes toward the image sensor. The second laser light of which 70% is already reflected by the first film S 1 is attenuated. Thus, there is a possibility that the second laser light may remarkably reduce damage or damage to the band pass filter, the camera, or the image sensor. That is, when the first film S 1 having such a wavelength-to-reflectance characteristic for transmitting the wavelength λ1of the laser light as the measurement object and reflecting the wavelength λ2of the fluorescence is formed on the incident surface 1 aof the fluorescence generating element, the damage to the optical system or the image element of the device can be reduced even if the second laser light having the wavelength that is the same as or near the wavelength λ2of the fluorescence enters the device.However, when the wavelength λ2' of the incident second laser light is the same as or close to the wavelength λ0, almost all of the second laser light goes toward the image sensor when it passes through the first film S1 and the fluorescent generating element 10 and also passes through the second film S2 formed on the reflection surface 3b of the light separating element. This leads to a fear that the intense second laser light enters the band pass filter, the camera or the image sensor, resulting in damage or fire damage to these elements. Thus, in a case where the first film S 1 and the second film S 2 have the wavelength-to-reflectance characteristics shown in FIG. 4, it is necessary to confirm that the wavelength of the incident laser light is not the same as or close to the wavelength λ 0. Otherwise, it is necessary to ensure that the laser light having the wavelength in question cannot enter the device.Similarly, in an example of a laser light transmission-separation beam profile measuring apparatus shown in FIG. 2, an example of common wavelength-to-reflectance characteristics shown in FIG. 5 is as follows. The first film S1 has a reflectance close to 0% at the wavelength λ0 just as a reflectance at the wavelength λ1 (FIG. 5(A)), while the third film S3 has a reflectance close to 100% at the wavelength λ0 just as a reflectance at the wavelength λ1 (FIG. 5(B)). In this example, if the wavelength λ2' of the incident second laser light is the same as or close to the wavelength λ2 of fluorescence, 70% of the incident second laser light is reflected from the first film S1 to the outside of the device, and thus the damage to the device can be reduced just as in the above-described laser light reflection-separation beam profile measuring device. However, when the wavelength λ2' of the incident second laser light is the same as or close to this wavelength λ0, almost all the laser light passes through the first film S1 formed on the incident surface of the fluorescent generating element 30 and then through the fluorescent generating element 30. Thus, the intense second laser light is likely to enter the band pass filter, the camera, or the image sensor, thereby causing damage or fire damage to these elements. Thus, in a case where the first film S 1 and the third film S 3 have the wavelength-to-reflectance characteristics shown in FIG. 5, it is necessary to confirm that the wavelength of the incident laser light is not the same as or near the wavelength λ 0 in question. Otherwise, it is necessary to ensure that the laser light having the wavelength in question cannot enter the device. It is thus desired to provide a device that can prevent the bandpass filter, the camera, or the image sensor from suffering the damage or fire damage when laser light having any wavelength enters therein.In the example of the laser reflection separation beam profile measuring apparatus shown in FIG. 1, the first film S 1 more preferably has a high reflectance at the wavelength λ0between the wavelength λ1of the laser light and the wavelength λ2of the fluorescence, and the second film S 2 also has a high reflectance at the wavelength λ0. As a specific example, FIG. 6(A) shows a wavelength-to-reflectance characteristic of the first film S1, while FIG. 6(B) shows a wavelength-to-reflectance characteristic of the second film S2. Note here that the first film S 1 has a reflectance of 70% at the wavelength λ0that is equal to the reflectance at the wavelength λ2of fluorescence. The second film S 2 has a reflectance of nearly 100% at the wavelength λ0which is equal to the reflectance at the wavelength λ1of the laser light. In a case where the first film S 1 and the second film S 2 have such wavelength-to-reflectance characteristics, how the light path of the laser light varies depending on the wavelength of the second laser light entering the device will be described in sequence. First, when laser light having a wavelength λ1or less enters, the laser light does not go toward the image sensor because, after passing through the first film S 1, all the laser light is reflected from the second film S 2 to the outside of the device. When a laser light having a wavelength greater than λ1 and equal to λ0 or less enters, all the laser light having a wavelength near λ1 passes through the first film S1, while 70% of the light having a wavelength near λ0 is reflected from the first film S1 to the outside of the device. On the other hand, the remaining 30% of the light passes through the first film S1. However, the laser light does not pass to the image sensor because all the laser light having both wavelengths is reflected from the second film S 2 to the outside of the device. When the laser light having a wavelength above λ0 enters, the first film S1 reflects 70% of the incident light regardless of the wavelength, while the remaining 30% of the light goes to the light separating element. Of these, the light having the wavelength equal to or near λ2 also passes through the second film S2 and goes to the image sensor. However, the laser light of which 70% is already reflected by the first film S 1 is attenuated. Thus, the possibility that the laser light may cause damage or fire damage to the band pass filter, the camera, or the image sensor can be remarkably reduced. In the beam profile measuring apparatus having the configuration shown in FIG. 1, the following feature is obtained by configuring the first film S 1 and the second film S 2 having the wavelength-to-reflectance characteristics shown in FIG. 6. When a laser light having any wavelength including the wavelength λ2of fluorescence enters, most of the incident light is emitted to the outside of the device from the first film S 1 or the second film S 2.Thus, the amount of laser light reaching the camera or the image sensor is suitably limited regardless of the wavelength of the incident laser light. Accordingly, the reliability of the device can be improved. The wavelength-to-reflectance characteristic of the first film S 1 shown in FIG. 6 is defined such that the film has a reflectance of 70% at the wavelength λ 0 and the wavelength λ 2. When the first film has a higher reflectance of 90% or nearly 100% as illustrated by the embodiments to be described below, the film can substantially reduce the amount of laser light reaching the image sensor to 0%, regardless of which wavelength the second laser light has. Thus, it can be completely prevented that the band pass filter, the camera, or the image sensor suffer damage or fire damage.Similarly, in the example of the laser light transmission separation beam profile measuring apparatus shown in FIG. 2, it is more preferable that the first film S 1 has a high reflectance at the wavelength λ0at a wavelength λ0between the wavelength λ1of the laser light and the wavelength λ2of the fluorescence, while the third film S 3 may have a low reflectance at the wavelength λ0. The wavelength-to-reflectance characteristics of the first film S 1 and the third film S 3 are shown in FIG. 7 as a specific example. Note that the first film S 1 has a reflectance of 70% at the wavelength λ0that is the same as the reflectance at the wavelength λ2of fluorescence. The third film S 3 has a reflectance of nearly 0% at the wavelength λ 0, which is the same as the reflectance at the wavelength λ 1 of the laser light. In a case where the first film S 1 and the third film S 3 have such wavelength-to-reflectance characteristics, how the light path of the laser light varies depending on the wavelength of the second laser light entering the device will be described in sequence. First, when the laser light having the wavelength λ1or less enters, the laser light does not pass to the image sensor because after passing through the first film S 1, all the laser light also passes through the third film S 3 and is emitted to the outside of the device. When the laser light having the wavelength greater than λ1 and equal to or less than λ0 enters, all the laser light having the wavelength near λ1 passes through the first film S1, while 70% of the light having the wavelength near λ0 is reflected from the first film S1 to the outside of the device. On the other hand, the remaining 30% of the light passes through the first film S1. However, the laser light does not pass to the image sensor because all the laser light having both wavelengths passes through the third film S 3 and is emitted to the outside of the device. When the laser light having wavelength above λ0 enters, the first film S1 reflects 70% of the light regardless of the wavelength, while the remaining 30% of the light goes toward the light separating element. Of these, the light having the wavelength equal to or near the λ2is reflected by the third film S 3 and goes to the image sensor. However, the light from which 70% has already been reflected by the first film S 1 is attenuated. Thus, the possibility that the laser light causes the damage or fire damage to the band pass filter, the camera, or the image sensor is remarkably reduced. In the beam profile measuring apparatus having the configuration shown in FIG. 2, the following feature is obtained by configuring the first film S 1 and the third film S 3 with the wavelength-to-reflectance characteristics shown in FIG. 7. When a laser light having any wavelength enters, most of the incident light is emitted to the outside of the device from the first film S 1 or third film S 3. Thus, the amount of laser light reaching the camera or the image sensor is suitably limited regardless of the wavelength of the incident laser light. Consequently, the reliability of the device can be improved. The wavelength-to-reflectance characteristic of the first film S 1 shown in FIG. 7 is defined such that the film has the reflectance of 70% at the wavelength λ 0 and the wavelength λ 2. When the film has a higher reflectance of 90° or near 100° as illustrated by the embodiments to be described below, the film can reduce the amount of the second laser light that reaches the image sensor to near 0%, whichever wavelength the second laser light has. Thus, it can be completely prevented that the band pass filter, the camera, or the image sensor suffer damage or fire damage. It is assumed that a relation of wavelength λ1of laser light<wavelength λ0<wavelength λ2of fluorescence exists in FIGS. 4 to 7 as well as in FIGS. 8 and 9.Fig. 3 is a block diagram schematically showing functions of the above films. The following feature is obtained by selecting the wavelength-to-reflectance characteristic of the first film S 1 of the fluorescence generating element and the wavelength-to-reflectance characteristic of the second film S 2 or the third film S 3 of the wavelength separating element as illustrated in FIG. 6 or 7. When a laser light having any wavelength enters the beam profile measuring device, the laser light is emitted to the outside of the device from the first film S 1 in combination with the second film S 2 or the third film S 4 before the laser light reaches the image sensor. Meanwhile, only the fluorescence generated in the fluorescent plate impinges on the image sensor and is observed. Here, assume that there is a relation of wavelength λ1of laser light<wavelength λ0<wavelength λ2' of second laser light.Note that an optimum wavelength may be selected as the wavelength λ0according to a central wavelength of the laser light to be measured principally (including the wavelength λ1of the laser light according to the invention), an absorption wavelength range of the fluorescent plate, a fluorescence detection wavelength (including the wavelength λ2of the fluorescence according to the invention), or a fluorescence generation wavelength range. The configurations of the first film S 1, the second film S 2, and the third film S 3 may be respectively designed according to the selected wavelength λ 0 and a required reflectance at the selected wavelength λ 0.Advantageous Effects of the InventionThe inventive beam profile measuring apparatus using the fluorescence is capable of high-accuracy measurement of the beam profile of a high-power laser by inhibiting the fluorescence generated in the fluorescence generating element from scattering to the outside of the apparatus and by inhibiting the scattered fluorescence from re-incident on the fluorescence generating element.According to the preferred embodiment of the inventive beam profile measuring apparatus using the fluorescence, even if a laser light having any wavelength enters the apparatus from the outside, most of the incident light is emitted to the outside of the apparatus through the first film S 1 or the second film S 2 or the third film S 3. This causes a marked reduction in the risk of damage or damage to the bandpass filter, camera or image sensor that may occur in the conventional configuration when the second laser light having the wavelength near the wavelength λ2of fluorescence is made incident on the device. Thus, the apparatus can be improved in reliability.The above-described objects and advantages, as well as other objects and advantages of the invention, will become more apparent from the following description of preferred embodiments of the invention. It should be understood that the following embodiments are merely examples, but the invention is not intended to be limited thereto.Brief Description of the DrawingsFIG. 1 is a diagram showing an exemplary configuration of a laser light reflection separation beam profile measuring device of a laser beam profile measuring device according to the invention; FIG. 2 is a diagram showing an exemplary configuration of a laser light transmission separation beam profile measuring device of the laser beam profile measuring device according to the invention; FIG. 3 is a block diagram schematically showing functions of a first film S 1 and a second film S 2 or a third film S 3 according to the invention; FIG. 4 is a set of graphs showing exemplary wavelength-to-reflectance characteristics of the first film S 1 and the second film S 2 of the laser light reflection separation beam profile measuring device; FIG. 5 is a set of graphs showing exemplary wavelength-to-reflectance characteristics of the first film S 1 and the third film S 3 of the laser light transmission-separation beam profile measuring device; FIG. 6 shows a set of graphs showing more preferred exemplary wavelength-to-reflectance characteristics of the first film S 1 and the second film S 2 of the laser light reflection separation beam profile measuring device; FIG. 7 is a group of graphs showing more preferable exemplary wavelength-to-reflectance characteristics of the first film S 1 and the third film S 3 of the laser light transmission-separation beam profile measuring device; FIG. 8 is a group of graphs showing more preferable exemplary wavelength-to-reflectance characteristics of the first film S 1 and the second film S 2 of the laser light reflection separation beam profile measuring device; FIG. 9 is a group of graphs showing more preferable exemplary wavelength-to-reflectance characteristics of the first film S 1 and the third film S 3 of the laser light transmission-separation beam profile measuring device; and FIG. 10 is a diagram illustrating a conventional example of a beam profile measurement method using fluorescence.DESCRIPTION OF EMBODIMENTSPreferred embodiments of the laser beam profile measuring apparatus according to the invention will be specifically described below based on the accompanying drawings and with reference to many examples of the laser beam profile measuring apparatus.Referring again to FIG. 1, an example of the laser beam profile measuring apparatus according to the invention will be described. As already mentioned above, FIG. 1 shows an exemplary configuration of a laser beam reflection separation beam profile measuring device 100, in particular a positional relationship of components of the device in plan view. A fluorescence generating element 10 of the laser light reflection-separation laser beam profile measuring device 100 has a cylindrical shape having a diameter of 10 mm and includes a fluorescent plate 1 and a support body 2. the fluorescent plate 1 is made of an Nd:YAG crystal having an Nd concentration of 1.0 at % (at %) and a thickness of 0.2 mm. The support body 2 is made of a Nd-less YAG crystal having a thickness of 2 mm. Opposite surfaces (represented by a reference numeral 1 bin FIG. 1 ) of the fluorescent plate 1 and the support body 2 are integrally bonded to each other by thermoplastically bonding without using a binder / adhesive agent. Since these components are made of the same base material YAG, the components do not undergo light reflection at an interface thereof due to different refractive indices when the components are directly connected to each other. Having the same thermal expansion rate, these components are less susceptible to failure such as deformation-induced separation of the fluorescent plate 1 from the support body 2 when the fluorescent plate generates heat. As an example of solving the problem according to the invention, a dielectric film S1 is formed on a laser incident surface 1a of the fluorescent plate 1. The dielectric film has a reflectance of 0.5% in a wavelength range of 800 nm to 900 nm of a laser light 12 which is principally assumed to be measured, and a reflectance of 90% at a 1064 nm wavelength of the fluorescence generated in the fluorescent plate 1 and detected by an image sensor 8. As an example of solving the problem according to the invention, the first film S1 has a structure designed to have a wavelength-to-reflectance characteristic shown in Fig. 8(A), where λ1 is 800 nm, λ0 is 950 nm, and λ2 is 1064 nm. On the other hand, on an opposite surface 2 bof the support body 2 from the surface formed with the fluorescent plate 1, a dielectric film (not shown) having a reflectance of 0.5% is formed in a wide band of 800 nm to 1100 nm, so that the laser light 12 and a fluorescence 13 generated in the fluorescent plate 1 are not reflected. A 45° prism 3 as the light separating element for separating the laser light 12 and the fluorescence 13 is made of 15 mm square quartz and configured by combining two rectangular prisms. On an incident surface 3a of the 45° prism 3, a dielectric film (not shown) having a reflectance of 0.5% in a range of 800 nm to 1100 nm is formed so that the laser light 12 and the generated fluorescence 13 are not reflected. On a surface 3b inclined at 45° in the 45° prism 3, a dielectric film having a reflectance of 99.7% for light at an incident angle of 45° and in a wavelength range of 800 nm-900 nm and having a reflectance of 3% at the wavelength of 1064 nm is formed to transmit the fluorescence at the wavelength of 1064 nm. Note that, as an example of solving the problem according to the invention, the dielectric film S 2 has a structure configured to have a wavelength-to-reflectance characteristic shown in FIG. 8(B), in which λ1is 808 nm, λ0is 950 nm, and λ2is 1064 nm. Further, on a prism face 3c from which the fluorescence 13 is emitted through the face 3b, a dielectric film (not shown) having a reflectance of 0.5% at the wavelength of 1064 nm is formed. On a surface 3d of the 45° prism 3 from which the laser light 12 is emitted at 45° from the surface 3b, a dielectric film (not shown) having a reflectance of 0.5% is formed in a wavelength range of 800 nm to 900 nm.In the laser light reflection separation beam profile measuring apparatus 100 shown in FIG. 1, the laser light 12 having the wavelength 808 nm made incident thereon as an example of the laser light to be measured is passed through the fluorescent plate 1 and the support body 2, and reflected by the 45° prism 3 and emitted to the outside of the apparatus. A part of the laser light 12 transmitted through the fluorescent plate 1 is absorbed by the Nd:YAG of the fluorescent plate 1, where the absorbed light undergoes energy conversion to emit fluorescence therearound, the fluorescence having a central wavelength of 1 μm in proportion to the distribution of the laser light intensity. Of the emitted fluorescence, the 1064 nm fluorescence 13 passes through the 45° prism 3 and through an objective lens 4, a neutral filter 5, a band pass filter 6, and an imaging lens 7 to reach the CMOS image sensor 8. The objective lens 4 and imaging lens 7 are convex lenses made of optical glass known by the preamble of "BK7", and both have a focal length of 50 mm. On the surfaces of these lenses, a dielectric film (not shown) having a reflectance of 0.5% at 1064 nm is formed. The fluorescent plate 1 is located at a focal point of the objective lens 4, while the CMOS image sensor 8 is located at a focal point of the imaging lens 7. In this configuration, a fluorescent image of the fluorescent plate 1 is formed 1:1 on a recording surface (not shown) in the CMOS image sensor 8. The neutral density filter 5 has a transmission of 10% at the wavelength of 1064 nm and thus weakens the fluorescence in order to prevent saturation of the CMOS image sensor 8. The CMOS image sensor 8 can be adjusted for appropriate sensitivity to light by removing the neutral filter 5 when an incident laser light is so weak that fluorescence from the fluorescent plate 1 has low intensity, or by employing more than one neutral filter 5 when the laser light and the fluorescence have higher intensities. The band pass filter 6 has such a characteristic that it does not block at wavelengths other than 1064 nm to prevent the light having wavelengths other than 1064 nm from reaching the CMOS image sensor 8. The band pass filter 6 has a transmission wavelength interval of, for example, 10 nm at the wavelength of 1064 nm.Referring back to FIG. 2, a description will be given of another example of the laser beam profile measuring apparatus according to the invention. As described above, FIG. 2 shows the exemplary configuration of the laser light transmission-separation beam profile measuring device 200, or more specifically, a positional relationship of the components of the device in plan view. A fluorescence generating element 30 of the laser light transmission-separation beam profile measuring apparatus 200 has an incident surface defined by a 6 mm square prism and is substantially composed of a fluorescent plate 21 and a support body 22. A material of the fluorescent plate 21 is transparent Nd:YAG ceramic having an Nd concentration of 0.7 atomic % (at %) and a thickness of 0.05 mm. A material of the carrier body 22 is transparent Nd-less YAG ceramic with a thickness of 2 mm. Opposite surfaces (represented by a reference numeral 21 bin FIG. 2 ) of the fluorescent plate 21 and the support body 22 are integrally bonded to each other by a low-temperature fusion bonding method without using a binder / adhesive agent. As an example of solving the problem according to the invention, a dielectric film S1 is formed on an incident surface 21a of the fluorescent plate 21. The dielectric film has a reflectance of 0.5% in a wavelength range of 800 nm to 900 nm from an assumed laser light 32 to be measured, and a reflectance of 99% at a 1064 nm wavelength of the fluorescence generated in the fluorescent plate 21 and detected by the image sensor 8. As an example of solving the problem according to the invention, the first film S1 has a structure designed to have a wavelength-to-reflectance characteristic shown in FIG. 9A, where λ1 is 800 nm, λ0 is 950 nm, and λ2 is 1064 nm. On the opposite surface 22 bof the fluorescence generating element 30 from the surface formed with the fluorescent plate 21, a dielectric film (not shown) having a reflectance of 0.5% is formed in a wide band of 800 nm to 1100 nm, so that the laser light 32 and a fluorescence 33 generated in the fluorescent plate 21 are not reflected. On a surface 23 aof the 45° mirror 23, a dielectric film S 3 having a reflectance of 99% for light at an incident angle of 45° and in a wavelength range of 1000 nm to 1100 nm and a reflectance of 0.3% in a wavelength range of 800 nm to 950 nm is formed. As an example of solving the problem according to the invention, the dielectric film S 3 has a structure configured to have a wavelength-to-reflectance characteristic shown in FIG. 9B, where λ1is 800 nm, λ0is 950 nm, and λ2is 1064 nm.In the laser light reflection separation beam profile measuring apparatus 200 shown in FIG. 2, the laser light of 808 nm made incident as an example of the wavelength of the laser light to be measured is passed through the fluorescent plate 21 and the support body 22 and further passed through the 45° mirror 23 to be emitted to the outside of the apparatus. When transmitted through the fluorescent plate 21, a part of the laser light is absorbed by the Nd:YAG of the fluorescent plate 21, the absorbed light undergoes energy conversion to emit fluorescence around, the fluorescence having a central wavelength of 1 μm in proportion to the distribution of laser light intensity. Of the emitted fluorescence, a fluorescence 33 of 1064 nm is reflected by the 45° mirror 23 and reaches the CMOS image sensor 8 after transmission through the objective lens 4, the neutral filter 5, the band pass filter 6, and the imaging lens 7. The objective lens 4 has a focal length of 50 mm, while the imaging lens 7 has a focal length of 100 mm. On the surfaces of these lenses, a dielectric film (not shown) having a reflectance of 0.5% at 1064 nm is formed. The fluorescent plate 21 is located at a focal point of the objective lens, while the CMOS image sensor 8 is located at a focal point of the imaging lens 7. A fluorescent image of the fluorescent plate 21 is formed twice enlarged and visualized on a recording surface (not shown) in the CMOS image sensor 8. The neutral density filter 5 has a transmission of 10% at the wavelength of 1064 nm and attenuates the fluorescence in order to prevent saturation of the CMOS image sensor 8. The CMOS image sensor 8 can be adjusted to appropriate sensitivity to light by removing the neutral filter 5 when an incident laser light is so weak that fluorescence from the fluorescent plate 21 has a low intensity, or by employing more than one neutral filter 5 when the laser light and the fluorescence have high intensities. The band pass filter 6 has a characteristic of blocking light having wavelengths other than 1064 nm to prevent light at wavelengths other than 1064 nm from reaching the CMOS image sensor 8. The band pass filter 6 has a transmission wavelength interval of, for example, 10 nm at the wavelength of 1064 nm.In the above examples, TiO 2, Ta 2 O 5, HfO 2, Nb 2 O 3, ZrO 2, MgF 2, YF 3, SiO 2, Al2O3and the like are preferably used as materials for the dielectric films S1, S2, S3and the dielectric films formed on the faces of the fluorescence generating element, 45° prism, 45° mirror and convex lenses for controlling the reflectance for the wavelength. One or more of these materials for dielectrics may be used for forming a single-layer thin film having a specific thickness (such as 0.5 μm or less) or a multi-layer film formed by laminating a plurality of films having different materials in specific thicknesses on each other. This allows a desired reflectance in a certain wavelength range to be given to the formed film. Examples of a method for forming the film include, but are not limited to: a vacuum deposition method in which a material is heated in vacuum to deposit the material on a surface of an object; a sputter deposition method in which a material is shot with ions of different materials to eject the material for deposition on a surface of an object. It is important that an optimum material, an optimum film thickness and an optimum film forming method for obtaining a required reflectance in a required wavelength range are selected.While the above-described examples cite Nd:YAG as an example of the fluorescent plate medium, the scope of the invention is not limited thereto with respect to the fluorescent plate material. Other usable materials are: Yb: YAG which absorbs light at 940 nm and 970 nm and emits fluorescence at 1050 nm; Cr, Yb: YAG which contains Yb: YAG and Cr4 +- ions added to shorten a fluorescence lifetime; Er: YAG which absorbs light near 785 nm or 1.5 μm and absorbs fluorescence of 1.6 μm or 2.9 μm; Tm: YAG which absorbs light of 780 nm or 785 nm and emits fluorescence of 2.01 μm; Ho: YAG which absorbs light near 1.9 μm and emits fluorescence of 2.01 μm; Cr, Tm, Ho: YAG which absorbs light near 780 nm and emits fluorescence of 2.08 μm, and Ce: YAG which absorbs light near 350 nm or 450 nm and emits fluorescence of 550 nm. Further, Cr, Nd:YAG with added Cr 3+- ions which absorbs light in the visible light region and emits fluorescence of 1 μm is also usable. The above-described light energy absorption wavelengths and fluorescence wavelengths are typical examples, and any light energy absorption wavelength or any fluorescence wavelength can be selected from those inherent in the medium according to any object or specification. A fluorescence wavelength to be detected does not always need to be set to a fluorescence peak wavelength of the medium. In order to prevent scattering laser light having a wavelength near the fluorescence peak wavelength, a transmission wavelength of a band pass filter may be set so that the filter detects a fluorescence wavelength having a wavelength other than the fluorescence peak wavelength. While the foregoing examples use YAG as the base material of the fluorescent plate and the support body, the invention is not limited thereto. Quartz and BK7 which are transparent may be used. Otherwise, Y 2 O 3, Lu 2 O 3, LuAG, YAP, Sc 2 O 3, GGG, GSGG, YSGG, YSO, and sapphire having higher thermal conductivity than YAG are also usable. The base material may be a single crystal or transparent ceramic. It is necessary to select a medium capable of absorbing the wavelength of a laser light to be measured. The fluorescent plate and the support body may be bonded together with a transparent binder / adhesive agent or otherwise, by means of optical contact where bonded surfaces are polished with high precision and pressed together. However, from the viewpoint of joining strength, thermoplastically-bonding for joining the surfaces to each other at higher temperatures, diffusion bonding (high-temperature fusion), and low-temperature fusion are more preferred. In order to prevent deformation of the fluorescent plate due to heat generation, the fluorescent plate and the supporting body may preferably be made of equivalent base materials having similar expansion coefficients. However, when the fluorescent plate has a small heat value, the support body may be made of a material different from that of the fluorescent plate. For example, the base material of the fluorescent plate may be YAG and that of the support body may be sapphire having good thermal conductivity. However, it is more desirable that the fluorescent plate has a small thickness in order to improve the positional accuracy of measurement with respect to the optical axis direction of the beam.However, when the fluorescent plate is made thin, a transmission distance of the laser light decreases, so that the generated fluorescence has a lower intensity. Thus, a desired fluorescent intensity can be obtained by increasing the addition amount of fluorescent element to the fluorescent plate.The above description shows the example in which the objective lens 4 and the imaging lens 7 having the same focal length are used to form the fluorescent plate image on the image sensor at a magnification ratio of 1:1, and the example in which the imaging lens 7 having a focal length different from that of the objective lens is used to form the image on the image sensor 8 at a magnification ratio of 1:2. However, lenses having focal lengths different from the above may be used to project an enlarged image or a reduced image onto the fluorescent plate on the image sensor. Imaging optics may use three or more lenses and are not particularly limited. A reflecting mirror may be incorporated in the above imaging optical system to bend the optical path for the purpose of reducing the overall device size. The insertion positions of the neutral filter and the band pass filter are not limited to the above examples. The filters can be used anywhere in the imaging optics.While the above examples illustrate the configuration in which the neutral filter and the band pass filter are disposed in the space between the objective lens and the imaging lens where the light intensity is the lowest. However, the neutral density filter and / or the band pass filter may be disposed at locations different from the above. As far as necessary, more than one neutral-band filter and more than one band-pass filter can be used. The type or attenuation rate of the neutral filter, the transmission wavelength, the transmission wavelength interval, transmittance, and the like of the band pass filter can be selected optimally on the basis of the laser light to be measured, fluorescent plate specifications, and the like. The CMOS or CCD image sensor as the picture element may use a material such as Si, Ge, GaAs, InGaAs and InP having appropriate sensitivities at the wavelength of fluorescence emitted from the fluorescent plate.Industrial applicabilityThe invention is applicable to a wide variety of apparatuses having a function of measuring the beam profile of the laser light.List of reference characters10, 30 Fluorescence generating element 1, 21 Fluorescent plate 2, 22 Support body 1 a, 21 aLaser light incident surface 1 b, 21 b Grenzfläche surface between fluorescent plate and support body S 1 First film S 2 Second film S 3 Third film 12, 32Laser light 13, 33 Fluorescence 3 45° Prism 4 Objective lens 5 Neutral filter 6 Band pass filter 7 Imaging lens 8 Image sensor 1100 Transparent block 1101 Fluorescent body 1102 Grenzfläche surface 1103Laser light 1105 Filter 1106 Camera

Claims

A laser beam profile measuring apparatus (100; 200) for measuring a two-dimensional laser light profile, comprising: a plate-like or block-like fluorescence generating element (10; 30) having an incident surface (1a; 21a) on which the laser light is incident and an emission surface (1b; 21b) from which the laser light is emitted, wherein the incident surface (1a; 21a) and the emission surface (1b; 21b) are opposed to each other; a light separating element (3; 23) for separating fluorescence from the laser light, wherein the fluorescence is generated in the fluorescence generating element (10; 30) and emitted from the emission surface (1b; 21b); and an imaging element (8) for receiving the fluorescence, wherein the plate-like or block-like fluorescence generating element (10; 30) includes a first film (S1) formed on its incident surface (1a; 21a), and the first film (S1) has a wavelength-to-reflectance characteristic of transmitting a wavelength λ1 of the laser light and reflecting a wavelength λ2 of the fluorescence, wherein the light separating element (3; 23) includes a second film (S2), and the second film (S2) has a wavelength-to-reflectance characteristic of transmitting the wavelength λ2 of the fluorescence and reflecting the wavelength λ1 of the laser light, and wherein the first film (S1) further has a wavelength-to-reflectance characteristic of reflecting a wavelength λ0 between the wavelength λ1 of the laser light and the wavelength λ2 of the fluorescence, while the second film (S2) further has a wavelength-to-reflectance characteristic of reflecting the wavelength λ0.A laser beam profile measuring apparatus (100; 200) for measuring a two-dimensional laser light profile, comprising: a plate-like or block-like fluorescence generating element (10; 30) having an incident surface (1a; 21a) on which the laser light is incident and an emission surface (1b; 21b) from which the laser light is emitted, wherein the incident surface (1a; 21a) and the emission surface (1b; 21b) are opposed to each other; a light separating element (3; 23) for separating fluorescence from the laser light, wherein the fluorescence is generated in the fluorescence generating element (10; 30) and emitted from the emission surface (1b; 21b); and an imaging element (8) for receiving the fluorescence, wherein the plate-like or block-like fluorescence generating element (10; 30) includes a first film (S1) formed on its incident surface (1a; 21a), and the first film (S1) has a wavelength-to-reflectance characteristic of transmitting a wavelength λ1 of the laser light and reflecting a wavelength λ2 of the fluorescence, wherein the light separating element (3; 23) includes a third film (S3), and the third film (S3) has a wavelength-to-reflection characteristic of reflecting the wavelength λ2 of the fluorescence and transmitting the wavelength λ1 of the laser light, and wherein the first film (S1) further has a wavelength-to-reflectance characteristic of reflecting a wavelength λ0 between the wavelength λ1 of the laser light and the wavelength λ2 of the fluorescence, while the third film (S3) further has a wavelength-to-reflectance characteristic of transmitting the wavelength λ0.The laser beam profile measuring apparatus (100;200) according to claim 1 or 2, wherein the first film (S1) has a reflectance of 70% or more at the wavelength λ2 of fluorescence,The laser beam profile measuring apparatus (100;200) according to any one of claims 1 to 3, wherein the first film (S1) has a reflectance of 90% or more at the wavelength λ2 of fluorescence.

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