Patent Publication Number: US-2023134268-A1

Title: Laser light source device and laser processing apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of PCT International Application No. PCT/JP2021/024928 filed on Jul. 1, 2021, designating the United States of America, which is based on and claims priority of Japanese Patent Application No. 2020-125757 filed on Jul. 22, 2020. The entire disclosures of the above-identified applications, including the specifications, drawings and claims are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to a laser light source device and a laser processing apparatus. 
     BACKGROUND 
     Conventionally, a laser light source device that includes a laser element in which a plurality of light emitters are integrated is known. 
     For example, Patent Literature (PTL) 1 discloses a laser light source device that includes such a laser element, a fast-axis collimator, a diffraction grating, and a partially reflecting mirror in this order along an optical path. In this laser light source device, an external resonator is configured between the laser element and the partially reflecting mirror. 
     In such a laser light source device, a plurality of laser beams emitted from the plurality of light emitters are incident on the diffraction grating at different incident angles. The plurality of laser beams have different oscillation wavelengths in accordance with the incident angles. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Unexamined Patent Application Publication No. 
       
    
     SUMMARY 
     Technical Problem 
     Optical feedback efficiency is used as an index that indicates the extent to which a plurality of laser beams that are reflected by a partially reflecting mirror return to a plurality of light emitters. In a conventional laser light source device, the diffraction efficiency of a diffraction grating varies for the plurality of laser beams because the plurality of laser beams are incident on the diffraction grating at different incident angles and have different oscillation wavelengths. Therefore, it is difficult to control the optical feedback efficiency of each of the plurality of light emitters and, for example, there is a variation in the optical feedback efficiency among the plurality of light emitters. Consequently, the oscillation stability of the plurality of laser beams decreases, for example. 
     The present disclosure provides a laser light source device and the like that enables the optical feedback efficiency of each of a plurality of light emitters to be controlled. 
     Solution to Problem 
     A laser light source device according to the present disclosure includes: a first light emitter that emits a first laser beam; a second light emitter that emits a second laser beam; an optical element that converges the first laser beam and the second laser beam; a wavelength dispersing element on which the first laser beam and the second laser beam that have exited from the optical element are incident, the wavelength dispersing element causing an optical axis of the first laser beam and an optical axis of the second laser beam to coincide with one another, and then transmitting the first laser beam and the second laser beam; and a partially reflecting mirror that returns a portion of the first laser beam and a portion of the second laser beam that have exited from the wavelength dispersing element by reflection, and transmits a remaining portion of the first laser beam and a remaining portion of the second laser beam that have exited from the wavelength dispersing element, wherein a reflectance of the partially reflecting mirror is wavelength-dependent. 
     A laser processing apparatus according to an aspect of the present disclosure includes the above-described laser light source device. 
     Advantageous Effects 
     The present disclosure can provide a laser light source device and the like that enables the optical feedback efficiency of each of a plurality of light emitters to be controlled. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other advantages and features will become apparent from the following description thereof taken in conjunction with the accompanying Drawings, by way of non-limiting examples of embodiments disclosed herein. 
         FIG.  1    is a schematic diagram illustrating the configuration of a laser light source device according to Embodiment 1. 
         FIG.  2    is a graph showing a simulation result of external optical feedback amplitude and ASE amplitude of a plurality of laser beams of a laser light source device according to a comparative example. 
         FIG.  3    is a graph showing a reflection spectrum of a partially reflecting mirror according to Embodiment 1 and a reflection spectrum of a partially reflecting mirror according to the comparative example. 
         FIG.  4    is a schematic diagram illustrating a laser processing apparatus according to Embodiment 1. 
         FIG.  5    is a perspective view illustrating the configuration of a plurality of laser elements included in a laser light source device according to Embodiment 2. 
         FIG.  6    is a perspective view illustrating the configuration of a plurality of laser elements included in a laser light source device according to Embodiment 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to the Drawings. It should be noted that each of the embodiments described below shows a specific example of the present disclosure. Accordingly, the numerical values, shapes, materials, constituent elements, the arrangement and connection of the constituent elements, steps, the order of the steps, etc. shown in the following embodiments are mere examples, and therefore are not intended to limit the present disclosure. 
     It should be noted that the respective figures are schematic diagrams and are not necessarily precise illustrations. Accordingly, the scaling, etc., depicted in the figures is not necessarily accurate. Additionally, in the figures, elements that are substantially the same are given the same reference signs, and overlapping descriptions thereof are omitted or simplified. 
     Embodiment 1 
     (Configuration of Laser Light Source Device) 
     First, the configuration of laser light source device  1  according to the present embodiment will be described with reference to  FIG.  1   . 
       FIG.  1    is a schematic diagram illustrating the configuration of laser light source device  1  according to the present embodiment. 
     As illustrated in  FIG.  1   , laser light source device  1  is a light emitting device that includes laser element  10 , optical element  20 , wavelength dispersing element  30 , and partially reflecting mirror  40 . Laser element  10 , optical element  20 , wavelength dispersing element  30 , and partially reflecting mirror  40  are arranged in this order along the optical path of a plurality of laser beams L 100  that are emitted from laser element  10 . In  FIG.  1   , behavior of the plurality of laser beams L 100  is indicated by arrows. 
     Laser light source device  1  is a light emitting device that outputs output beam Lo according to the so-called direct diode laser (DDL) system which directly uses laser beams that are emitted from laser element  10 . Laser light source device  1  that uses the DDL system is characterized in that it is highly efficient because a laser beam is not converted and it enables processing using a laser beam ranging from ultraviolet to infrared by selecting the material (e.g., semiconductor material) of laser element  10 . 
     In the present embodiment, laser light source device  1  outputs output beam Lo in the violet to blue range (i.e., having a wavelength in a range of from 380 nm to 480 nm). More specifically, output beam Lo is a light having a peak wavelength in the violet to blue range. Such laser light source device  1  is used for fine processing of a material, such as metal or resin, for example. 
     Next, constituent elements included in laser light source device  1  will be described. 
     Laser element  10  is a semiconductor laser that has a multi-emitter structure in which a plurality of light emitters  100  are integrated in a single device, and outputs the plurality of laser beams L 100 . Specifically, laser element  10  is a nitride-based semiconductor laser that is formed using a nitride-based semiconductor material, and outputs, for example, laser beams L 100  in the violet to blue range. 
     The plurality of light emitters  100  are composed of 38 light emitters  100 , namely, first light emitter  101  to thirty-eighth light emitter  138 . Here, light emitters  100  are described when first light emitter  101  to thirty-eighth light emitter  138  do not need to be distinguished. It should be noted that the plurality of light emitters  100  may be composed of more or less than 38 light emitters  100 . 
     As illustrated in  FIG.  1   , laser element  10  is a laser bar that is elongated in one direction. 
     Laser element  10  includes a substrate, a nitride-based semiconductor laser layer structure, a p-side electrode, and an n-side electrode (all of them are not illustrated in  FIG.  1   ). 
     The substrate includes a first main face and a second main face. The second main face is a face on the reverse side of the first main face and is disposed back-to-back with the first main face. In the present embodiment, the first main face is a face on the p-side which serves as a front face and the second main face is a face on the n-side which serves as a back face. 
     For example, a semiconductor substrate such as a nitride semiconductor substrate is used as the substrate. In the present embodiment, an n-type GaN substrate having a hexagonal crystal structure is used as the substrate. 
     The nitride-based semiconductor laser layer structure is a nitride semiconductor laminate in which a plurality of nitride semiconductor layers each of which is formed using a nitride-based semiconductor material are laminated. The nitride-based semiconductor laser layer structure is formed above the first main face of the substrate. For example, the nitride-based semiconductor laser layer structure includes an n-type cladding layer, an active layer, a p-type cladding layer, and a p-type contact layer that are laminated in this order on the first main face of the substrate. 
     It should be noted that, in the present embodiment, the n-type cladding layer consists essentially of n-type AlGaN, the active layer consists essentially of undoped InGaN, the p-type cladding layer consists essentially of p-type AlGaN, and the p-type contact layer consists essentially of p-type GaN. 
     It should be noted that, aside from the above-described nitride semiconductor layers, the nitride-based semiconductor laser layer structure may include other nitride semiconductor layers, such as an optical guide layer and an overflow suppressing layer. Additionally, an insulating film that includes an opening at a position corresponding to the p-type contact layer may be formed on the surface of the nitride-based semiconductor laser layer structure. 
     The nitride-based semiconductor laser layer structure includes a plurality of waveguides that are elongated in a direction orthogonal to the one direction which is the direction in which the laser bar is elongated. Each of the plurality of waveguides has functions of a current injection region and an optical waveguide in laser element  10 . These waveguides correspond to light emitters  100  according to the present embodiment. The plurality of waveguides that correspond to the plurality of light emitters  100  are parallel to one another and formed at a predetermined pitch in the one direction. 
     The plurality of waveguides are formed on the p-type cladding layer in the nitride-based semiconductor laser layer structure, for example. As an example, the plurality of waveguides have a ridge-stripe structure and are formed as a plurality of ridges on the p-type cladding layer. In this case, the p-type contact layer may be a plurality of semiconductor layers formed individually on each of the plurality of ridges, or may be a single semiconductor layer which is continuously formed to cover the plurality of ridges. 
     The plurality of light emitters  100  that correspond to the plurality of waveguides each emit a laser beam. Specifically, first light emitter  101  emits first laser beam L 1  and second light emitter  102  emits second laser beam L 2 . Similarly, third light emitter  103  to thirty-eighth light emitter  138  emit third laser beam L 3  to thirty-eighth laser beam L 38 , respectively. Here, laser beams L 100  are described when first laser beam L 1  to thirty-eighth laser beam L 38  do not need to be distinguished. 
     The p-side electrode is formed above and in contact with the nitride-based semiconductor laser layer structure. The p-side electrode includes, for example, Ti, Pt, and Au. The p-side electrode is formed above and in contact with the p-type contact layer of the nitride-based semiconductor laser layer structure, for example. A plurality of p-side electrodes are formed corresponding to the plurality of waveguides (ridges). Specifically, the p-side electrode is formed divided into multiple p-side electrodes. It should be noted that the p-side electrode need not be divided into multiple p-side electrodes. For example, the p-side electrode may be a single electrode shared among the plurality of waveguides. 
     The n-side electrode is formed on the second main face of the substrate. The n-side electrode includes, for example, Ti, Pt, and Au. In the present embodiment, a plurality of n-side electrodes are formed corresponding to the plurality of waveguides (ridges). Specifically, the n-side electrode is formed divided into multiple n-side electrodes. It should be noted that the n-side electrode need not be divided into multiple n-side electrodes. For example, the n-side electrode may be a single electrode shared among the plurality of waveguides. 
     Furthermore, the plurality of light emitters  100  emit the plurality of laser beams L 100  from one end face side of laser element  10  in a transverse direction. Specifically, the one end face is a light emission face. Furthermore, the face on the reverse side of the light emission face, that is, the face disposed back-to-back with the light emission face serves as a back end face of laser element  10 . The back end face is covered with an end face coating film as a reflecting film. 
     Furthermore, although not illustrated in the Drawings, a submount on which laser element  10  is mounted is provided. The submount includes a substrate body and an electrode layer that is laminated on the upper face of the substrate body. 
     The substrate body may be formed using a material with a high thermal conductivity and a small thermal expansion coefficient. For example, an SiC ceramic, an AlN ceramic, a semi-insulating SiC crystal, or a synthetic diamond may be used as the material for substrate body  211 . Furthermore, a metal material, such as a Cu—W alloy or a Cu—Mo alloy, may be used as the substrate body. The electrode layer includes, for example, Ti, Pt, and Au in this order from the substrate body side. 
     Furthermore, laser element  10  is mounted on the submount via a bonding layer. In the present embodiment, laser element  10  is electrically connected with the electrode layer of the submount. Accordingly, a metal bonding material, such as an AuSn solder, is used as the bonding layer, for example. 
     The plurality of laser beams L 100  emitted from the plurality of light emitters  100  of laser element  10  thus configured are incident on optical element  20 . 
     Optical element  20  is an optical component that converges the plurality of laser beams L 100  emitted from the plurality of light emitters  100 . Optical element  20  is, for example, a converging lens made of glass, transparent resin, or the like. A reflection preventive coating film for preventing reflection of the plurality of laser beams L 100  may be provided on the surface of optical element  20 . Optical element  20  is, for example, a plano-convex converging lens in which the face facing the plurality of light emitters  100  is convex and the face facing wavelength dispersing element  30  (described later) is planar. 
     As illustrated in  FIG.  1   , the plurality of laser beams L 100  emitted from the plurality of light emitters  100  are parallel to one another. Since optical element  20  is a plano-convex converging lens, it can receive the plurality of parallel laser beams L 100 , and then transmit the plurality of laser beams L 100  so as to converge the plurality of laser beams L 100  toward wavelength dispersing element  30 . 
     It should be noted that optical element  20  is not limited to this. Optical element  20  may be, for example, a plano-convex converging lens in which the face facing the plurality of light emitters  100  is planar and the face facing wavelength dispersing element  30  is convex. Optical element  20  may be a cylindrical lens elongated in the direction in which laser element  10 , which is a laser bar, is elongated. Furthermore, although single optical element  20  is provided in the present embodiment, a plurality of optical elements of mutually different shapes may be provided. When a plurality of optical elements are to be provided, an optical element that converges the plurality of laser beams L 100  along the fast axis and an optical element that converges the plurality of laser beams L 100  along the slow axis may be provided. Furthermore, optical element  20  may be a beam twister element. When optical element  20  is a beam twister element, optical element  20  has the effect of rotating the fast-axis and the slow-axis of the plurality of laser beams L 100  by 90°. 
     In any case, optical element  20  converges the plurality of laser beams L 100 . The plurality of laser beams L 100  converged by optical element  20  are directed to wavelength dispersing element  30 . 
     Wavelength dispersing element  30  is an optical component that causes the optical axes of the plurality of laser beams L 100  that have exited from optical element  20  and are incident on wavelength dispersing element  30  coincide with one another, and then transmits the plurality of laser beams L 100  toward partially reflecting mirror  40  (described later). In the present embodiment, the plurality of laser beams L 100  converged by optical element  20  are incident on one point on the surface of wavelength dispersing element  30 . Wavelength dispersing element  30  is, for example, a diffraction grating that diffracts each of the plurality of laser beams L 100 . More specifically, wavelength dispersing element  30  according to the present embodiment is a blazed diffraction grating; however, wavelength dispersing element  30  is not limited to this and may be a prism or the like, for example. 
     In the present embodiment, the plurality of laser beams L 100  that have exited from optical element  20  are converged by optical element  20  so as to be incident on one point on the surface of wavelength dispersing element  30 . Here, as illustrated in  FIG.  1   , the plurality of laser beams L 100  are incident on wavelength dispersing element  30  at different incident angles θi. Here, i denotes an integer from 1 to 38, which are numbers corresponding to 38 light emitters  100 . For example, first laser beam L 1  emitted from first light emitter  101  is incident on wavelength dispersing element  30  at incident angle θ 1 . 
     The plurality of laser beams L 100  emitted from the plurality of light emitters  100  are diffracted by wavelength dispersing element  30 , and then transmitted through wavelength dispersing element  30  and directed as diffracted beams to partially reflecting mirror  40 . Specifically, in the present embodiment, wavelength dispersing element  30  is a transmissive diffraction grating. It should be noted that wavelength dispersing element  30  may be a reflective diffraction grating. 
     Furthermore, as illustrated in  FIG.  1   , wavelength dispersing element  30  causes the optical axes of the diffracted beams of the plurality of laser beams L 100  coincide with one another, that is, combines the diffracted beams with one another, and then transmits the diffracted beams toward partially reflecting mirror  40 . 
     Partially reflecting mirror  40  is an optical component that reflects a portion of the plurality of laser beams L 100  that have exited from wavelength dispersing element  30 , and transmits the remaining portion of the plurality of laser beams L 100  that have exited from dispersing element  30 . The reflectance of partially reflecting mirror  40  is wavelength-dependent. For example, the reflectance of partially reflecting mirror  40  is wavelength-dependent for the wavelength range of output beam Lo (i.e., the violet to blue range). In the present embodiment, the reflectance of partially reflecting mirror  40  for the wavelength range of output beam Lo is 5% to 25%. Specifically, partially reflecting mirror  40  is an optical component that reflects a portion of first laser beam L 1  in accordance with the reflectance and transmits the non-reflected portion of first laser beam L 1  (i.e., the remaining portion of first laser beam L 1 ), for example. 
     It should be noted that the reflectance range of partially reflecting mirror  40  is not limited to the above-described range. Furthermore, the wavelength range for which the reflectance of partially reflecting mirror  40  is wavelength-dependent is not limited to the above-described wavelength range. 
     Partially reflecting mirror  40  is composed of a dichroic mirror or the like. More specifically, partially reflecting mirror  40  includes a transparent substrate made of glass, transparent resin, or the like, and a dichroic layer that includes a multilayer film of a dielectric provided on the surface of the transparent substrate. 
     By controlling the configuration of the multilayer film and/or the material of the dielectric included in the dichroic layer, partially reflecting mirror  40  can be made to have a predetermined reflectance for a predetermined wavelength. Accordingly, the reflectance of partially reflecting mirror  40  can be wavelength-dependent for the wavelength range of output beam Lo. 
     Furthermore, as described above, the plurality of laser beams L 100  having optical axes that have been made to coincide with one another are incident on partially reflecting mirror  40 . 
     The remaining portion of the plurality of laser beams L 100  that have exited from partially reflecting mirror  40  is outputted as output beam Lo. On the other hand, the portion of the plurality of laser beams L 100  that has been reflected by partially reflecting mirror  40  is again incident on wavelength dispersing element  30 . The plurality of laser beams L 100  having optical axes that have been made to coincide with one another are separated on a wavelength basis by wavelength dispersing element  30 . Wavelength dispersing element  30  transmits the plurality of laser beams L 100  that have been separated on a wavelength basis toward optical element  20 . Furthermore, optical element  20  transmits the plurality of laser beams L 100  that have been separated on a wavelength basis toward the plurality of light emitters  100 . Specifically, a portion of the plurality of laser beams L 100  emitted from the plurality of light emitters  100  are reflected and returned by partially reflecting mirror  40  to the plurality of light emitters  100 . Furthermore, the plurality of laser beams L 100  that have returned to the plurality of light emitters  100  are reflected by the end face coating film provided on the back end face of laser element  10  and directed toward optical element  20 . 
     As described above, in the present embodiment, an external resonator is configured between the back end face of laser element  10  and partially reflecting mirror  40 . In short, laser element  10  is an external cavity laser diode (ECLD). 
     As described above, in such laser light source device  1 , the plurality of laser beams L 100  emitted from the plurality of light emitters  100  are incident on wavelength dispersing element  30  at different incident angles θi. Since the resonator length of each of the plurality of laser beams L 100  differs in accordance with incident angles θi, the plurality of laser beams L 100  have different oscillation wavelengths. Therefore, in the present embodiment, wavelength dispersing element  30  can be described as an optical component that performs wavelength-multiplexing. It should be noted that, in wavelength dispersing element  30  which is a diffraction grating, the diffraction grating shape, such as blaze angle and pitch of diffraction grooves, is determined so that a sufficiently greater proportion of the diffracted beams that have exited from wavelength dispersing element  30  are directed toward partially reflecting mirror  40  than other direction. 
     (Behavior of Returning Beams) 
     Here, out of the plurality of laser beams L 100  that have been emitted from the plurality of light emitters  100 , laser beams that are reflected and returned by partially reflecting mirror  40  to the plurality of light emitters  100  (hereinafter, referred to as returning beams) will be described with reference to a laser light source device according to a comparative example. 
     The laser light source device according to the comparative example includes the same constituent elements as laser light source device  1  according to the present embodiment, except for one point described below. Specifically, the one point is that the reflectance of a partially reflecting mirror included in the laser light source device according to the comparative example is not wavelength-dependent but a constant value (e.g., 10%) for the wavelength range of output beam Lo. 
     Subsequently, the result of simulation performed for the laser light source device according to the comparative example will be described.  FIG.  2    is a graph showing a simulation result of external optical feedback amplitude and amplified spontaneous emission (ASE) amplitude of the plurality of laser beams of the laser light source device according to the comparative example. It should be noted that, in  FIG.  2   , the horizontal axis represents wavelength of laser beam, the five sharp peaks represent external optical feedback amplitude, and the curved line represents ASE amplitude. 
     The simulation result illustrated in  FIG.  2    is used for predicting the behavior of the plurality of laser beams in the laser light source device according to the comparative example. 
     Here, amplified spontaneous emission (ASE) amplitude in  FIG.  2    is an index that indicates laser gain (i.e., ease of amplification) in the plurality of light emitters. Furthermore, external optical feedback amplitude in  FIG.  2    is a value calculated from ASE amplitude, and is an index that indicates the optical feedback efficiency of each of the plurality of light emitters. It should be noted that the optical feedback efficiency of the light emitter indicates the extent to which returning beam returns to the light emitter. As the optical feedback efficiency of the light emitter becomes higher, more of the laser beam returns to the light emitter as a returning beam. 
     Furthermore, λ 5 , λ 4 , λ 3 , λ 2 , and λ 1  in  FIG.  2    denote the peak wavelength (hereinafter, referred to as oscillation peak wavelength) of the oscillation wavelength of a first laser beam, a tenth laser beam, a twentieth laser beam, a thirtieth laser beam, and a thirty-eighth laser beam, respectively, in the comparative example. 
     The simulation result of external optical feedback amplitude in  FIG.  2    shows that, in the comparative example, the optical feedback efficiency becomes higher in the order of a first light emitter, a tenth light emitter, a twentieth light emitter, a thirtieth light emitter, and a thirty-eighth light emitter. In other words, in the laser light source device according to the comparative example, there is a variation in the optical feedback efficiency among the plurality of light emitters. This variation is caused by the influence of the diffraction efficiency of a wavelength dispersing element and the influence of adjacent laser beams. 
     First, the influence of the diffraction efficiency will be described. 
     Diffraction efficiency is a value that is obtained by dividing the energy of diffracted beams by the energy of incident beams. Specifically, out of the laser beams incident on the wavelength dispersing element, the proportion of the laser beams that exit as diffracted beams from the wavelength dispersing element increases as the diffraction efficiency becomes higher. 
     The diffraction efficiency is a value that varies depending on the incident angles and the oscillation wavelengths of the plurality of laser beams. In the comparative example, since the incident angles and the oscillation wavelengths of the plurality of laser beams are different, the diffraction efficiency varies for the plurality of laser beams. In other words, there is a variation in the diffraction efficiency for the plurality of laser beams. 
     Furthermore, as an example, in the comparative example, out of the laser beams that exit from an optical element and are incident on the wavelength dispersing element, the proportion of laser beams that are multiplexed and directed toward the partially reflecting mirror decreases as the diffraction efficiency becomes lower. In other words, as the diffraction efficiency becomes lower, more of the laser beams exhibit behavior different from the behavior of the plurality of laser beams L 100  indicated by the arrows in  FIG.  1   . The laser beams that exhibit such a different behavior do not return to the plurality of light emitters after being emitted from the plurality of light emitters, and thus the optical feedback efficiency of each of the plurality of light emitters decreases. It should be noted that as the diffraction efficiency becomes higher, a phenomenon that is opposite to the above-described phenomenon occurs to a greater extent. 
     In other words, in the comparative example, since the diffraction efficiency is dependent on the incident angle and the oscillation wavelength, there is a variation in the diffraction efficiency for the plurality of laser beams. Consequently, there is a variation in the optical feedback efficiency among the plurality of light emitters. 
     Next, the influence of adjacent laser beams will be described. 
     The first laser beam that is emitted from the first light emitter and a second laser beam that is emitted from a second light emitter are exemplified as the adjacent laser beams. The first laser beam and the second laser beam influence each other in the optical element. For example, the second laser beam influences the first laser beam when the second laser beam leaks into the optical path of the first laser beam. Similarly, the first laser beam influences the second laser beam when the first laser beam leaks into the optical path of the second laser beam. Due to such influence, the optical feedback efficiency of each of the first light emitter that emits the first laser beam and the second light emitter that emits the second laser beam changes. Accordingly, there is a variation in the optical feedback efficiency among the plurality of light emitters including the first light emitter and the second light emitter. 
     Because there is a variation in the optical feedback efficiency in the laser light source device according to the comparative example, the oscillation stability of the plurality of laser beams decreases, for example. Furthermore, in laser light source device  1  according to the present embodiment, the optical feedback efficiency is similarly influenced by the diffraction efficiency of wavelength dispersing element  30  and the plurality of adjacent laser beams L 100 . 
     However, unlike the partially reflecting mirror according to the comparative example, partially reflecting mirror  40  of laser light source device  1  according to the present embodiment is wavelength-dependent. Hereinafter, an advantageous effect of partially reflecting mirror  40  that is wavelength-dependent will be described. 
       FIG.  3    is a graph showing a reflection spectrum of partially reflecting mirror  40  according to the present embodiment and a reflection spectrum of the partially reflecting mirror according to the comparative example. In  FIG.  3   , the solid line represents the reflectance of partially reflecting mirror  40  according to the present embodiment and the broken line represents the reflectance of the partially reflecting mirror according to the comparative example. 
     As described above, the reflectance of partially reflecting mirror  40  according to the present embodiment is wavelength-dependent and the reflectance of the partially reflecting mirror according to the comparative example is not wavelength-dependent but a constant value (10%). It should be noted that λ 5 , λ 4 , λ 3 , λ 2 , and λ 1  in  FIG.  3    denote the oscillation peak wavelength of the first laser beam, the tenth laser beam, the twentieth laser beam, the thirtieth laser beam, and the thirty-eighth laser beam, respectively, in the present embodiment and the comparative example. 
     Here, since more of laser beam L 100  having an oscillation peak wavelength in a predetermined wavelength range is reflected as the reflectance for the predetermined wavelength range becomes higher, the optical feedback efficiency of light emitter  100  that emits such laser beam L 100  is enhanced. Since the reflectance of partially reflecting mirror  40  is wavelength-dependent, the optical feedback efficiency of each of the plurality of light emitters  100  can be controlled by controlling the reflectance for the predetermined wavelength range. 
     Furthermore, in the present embodiment, the reflectance of partially reflecting mirror  40  has a wavelength-dependency that equalizes the optical feedback efficiency of the plurality of light emitters  100 . For example, the reflectance of partially reflecting mirror  40  is determined based on the optical feedback efficiency of the light emitters under the condition that the reflectance of the partially reflecting mirror is assumed to be constant as in the comparative example. 
     The reflectance of partially reflecting mirror  40  for a wavelength range including the oscillation peak wavelength of the laser beam emitted from a predetermined light emitter is determined so that the reflectance becomes higher as the optical feedback efficiency of the predetermined light emitter under the above-described condition becomes lower. In other words, the optical feedback efficiency of the predetermined light emitter under the above-described condition and the reflectance of partially reflecting mirror  40  for the above-described wavelength range have a negative correlation. 
     Specifically, as illustrated in  FIG.  2   , the optical feedback efficiency of the light emitters under the above-described condition (i.e., in the comparative example) becomes lower in the order of the light emitters that emit laser beams having oscillation peak wavelengths of λ 1 , λ 2 , λ 3 , λ 4 , and λ 5 . Correspondingly, as illustrated in  FIG.  3   , the reflectance of partially reflecting mirror  40  becomes higher in the order of a wavelength range including λ 1 , a wavelength range including λ 2 , a wavelength range including λ 3 , a wavelength range including λ 4 , and a wavelength range including λ 5 . Since the optical feedback efficiency of each of the plurality of light emitters  100  rises in accordance with the rise of the reflectance of partially reflecting mirror  40 , the plurality of light emitters  100  tend to have the same optical feedback efficiency. 
     Specifically, in the present embodiment, since the reflectance of partially reflecting mirror  40  has the above-described characteristics, laser light source device  1  in which the plurality of light emitters  100  have the same optical feedback efficiency compared to the comparative example, for example, is realized. Furthermore, since partially reflecting mirror  40  has the above-described reflectance, it can be said that the optical feedback efficiency of each of the plurality of light emitters  100  is adjusted so that the variation in the optical feedback efficiency among the plurality of light emitters  100  is reduced compared to the comparative example. Consequently, decrease in the oscillation stability of the plurality of laser beams L 100  is suppressed. 
     It should be noted that ‘the same optical feedback efficiency’ does not only mean completely identical optical feedback efficiency. For example, when the optical feedback efficiency of each of the plurality of light emitters  100  falls within the range of 90% to 110% of the average value that is calculated from the optical feedback efficiency of the plurality of light emitters  100 , the plurality of light emitters  100  can be considered to have the same optical feedback efficiency. 
     Furthermore, in the present embodiment, wavelength dispersing element  30  is a diffraction grating. 
     Accordingly, since wavelength dispersing element  30  has higher diffraction efficiency, the optical utilization efficiency of laser light source device  1  can be enhanced. 
     Furthermore, in the present embodiment, laser light source device  1  includes laser element  10  including the plurality of light emitters  100  (e.g., first light emitter  101  and second light emitter  102 ). 
     Accordingly, in laser light source device  1  that includes laser element  10  having a multi-emitter structure, the optical feedback efficiency of the plurality of light emitters  100  can be made the same. 
     It should be noted that the reflectance of partially reflecting mirror  40  is preferably 3% to 50%, and more preferably 5% to 40%, and even more preferably 8% to 30%. As the reflectance becomes higher, the optical feedback efficiency can be further enhanced. Furthermore, since output beam Lo increases as the reflectance becomes lower (i.e., as the transmittance becomes higher), the optical utilization efficiency of laser light source device  1  is enhanced. 
     Here, a laser processing apparatus, which is an application example of laser light source device  1 , will be described with reference to  FIG.  4   . 
       FIG.  4    is a schematic diagram illustrating laser processing apparatus  300  according to the present embodiment. Laser processing apparatus  300  includes laser light source device  1 , optical path  500 , and head  600 . 
     Although the configuration of laser light source device  1  is as described above, optical element  20 , wavelength dispersing element  30 , and partially reflecting mirror  40  are illustrated comprehensively as optical member  400  in  FIG.  4    for the sake of simplicity. 
     Optical path  500  is an optical component that receives output beam Lo outputted from laser light source device  1  and outputs output beam Lo to head  600 . Optical path  500  includes an optical component, such as an optical fiber or a reflecting mirror. 
     Head  600  is an optical component that outputs output beam Lo that has been outputted from laser light source device  1  via optical path  500 , as a processing beam L of laser processing apparatus  300 . It is sufficient that head  600  includes an optical element such as a lens having a light-converging function. 
     Laser processing apparatus  300  that has such a configuration can irradiate an object being processed with the plurality of laser beams L 100  that exit from laser element  10 , directly and with high optical density. Furthermore, since the plurality of laser beams L 100  that exit from laser element  10  can be used directly, the wavelength of a laser beam to be utilized can be easily changed by changing laser element  10 . Accordingly, since the wavelength can be selected according to the light absorbance of the object to be processed, the efficiency of processing, such as welding or cutting, can be enhanced. 
     Embodiment 2 
     Next, a laser light source device according to Embodiment 2 will be described with reference to  FIG.  5   .  FIG.  5    is a perspective view illustrating the configuration of a plurality of laser elements included in the laser light source device according to the present embodiment. 
     The present embodiment differs from Embodiment 1 in that a plurality of laser elements are provided in the present embodiment. 
     Specifically, the laser light source device according to the present embodiment has the same configuration as laser light source device  1  according to Embodiment 1, except that laser element  10   a  and laser element  10   b  are provided as the plurality of laser elements. 
     It should be noted that each of laser element  10   a  and laser element  10   b  has the same configuration as laser element  10  according to Embodiment 1. 
     Laser element  10   a  includes a plurality of light emitters  100   a  that are composed of 38 light emitters  100   a , namely, first light emitter  101   a  to thirty-eighth light emitter  138   a . Furthermore, each of the plurality of light emitters  100   a  emits a laser beam. Here, laser beams emitted from the plurality of light emitters  100   a  are comprehensively referred to as a plurality of laser beams L 100   a.    
     Similarly, laser element  10   b  includes a plurality of light emitters  100   b  that are composed of 38 light emitters  100   b , namely, first light emitter  101   b  to thirty-eighth light emitter  138   b . Furthermore, each of the plurality of light emitters  100   b  emits a laser beam. Here, laser beams emitted from the plurality of light emitters  100   b  are comprehensively referred to as a plurality of laser beams L 100   b.    
     The reflectance of a partially reflecting mirror according to the present embodiment has a wavelength-dependency that equalizes the optical feedback efficiency of the plurality of light emitters  100   a  and of the plurality of light emitters  100   b.    
     In other words, the reflectance of the partially reflecting mirror according to the present embodiment has a wavelength-dependency that equalizes the optical feedback efficiency of the total 76 light emitters of first light emitter  101   a  to thirty-eighth light emitter  138   a  and first light emitter  101   b  to thirty-eighth light emitter  138   b . As an example, the reflectance of the partially reflecting mirror according to the present embodiment has a wavelength-dependency that equalizes the optical feedback efficiency of first light emitter  101   a  and of second light emitter  102   b.    
     In this case as well, a laser light source device in which the plurality of light emitters  100   a  and the plurality of light emitters  100   b  have the same optical feedback efficiency is realized, and decrease in the oscillation stability of the plurality of laser beams L 100   a  and the plurality of laser beams L 100   b  is suppressed. 
     Embodiment 3 
     Next, a laser light source device according to Embodiment 3 will be described with reference to  FIG.  6   .  FIG.  6    is a perspective view illustrating the configuration of a plurality of laser elements  10   c  included in the laser light source device according to the present embodiment. 
     The present embodiment differs from Embodiment 1 and Embodiment 2 in that each of the plurality of laser elements  10   c  includes a single light emitter. 
     Specifically, the laser light source device according to the present embodiment has the same configuration as the laser light source device according to Embodiment 1 and Embodiment 2, except that the plurality of laser elements  10   c  are provided and each of the plurality of laser elements  10   c  includes a single light emitter. 
     In the present embodiment, the plurality of laser elements  10   c  are composed of first laser element  1   c  to thirty-eighth laser element  38   c . First laser element  1   c  to thirty-eighth laser element  38   c  include first light emitter  101   c  to thirty-eighth light emitter  138   c , respectively. Specifically, each of the plurality of laser elements  10   c  according to the present embodiment is a laser chip that has a single-emitter structure. Furthermore, each of the plurality of light emitters (first light emitter  101   c  to thirty-eighth light emitter  138   c ) emits a laser beam. Here, laser beams emitted from the plurality of light emitters are comprehensively referred to as a plurality of laser beams L 100   c.    
     In the present embodiment as well, the reflectance of a partially reflecting mirror has a wavelength-dependency that equalizes the optical feedback efficiency of the plurality of light emitters (i.e., first light emitter  101   c  to thirty-eighth light emitter  138   c ). In this case as well, a laser light source device in which the plurality of light emitters have the same optical feedback efficiency is realized, and decrease in the oscillation stability of the plurality of laser beams L 100   c  is suppressed. 
     Furthermore, in the present embodiment, laser light source device includes the plurality of laser elements  10   c . The plurality of laser elements  10   c  include, for example, first laser element  1   c  including first light emitter  101   c  and second laser element  2   c  including second light emitter  102   c.    
     Accordingly, in the laser light source device that includes the plurality of laser elements  10   c  each having a single-emitter structure, the plurality of light emitters can be made to have the same optical feedback efficiency. 
     OTHER EMBODIMENTS 
     Although the laser light source device and the laser processing apparatus according to the present disclosure have been described thus far based on the above-described embodiments, the present disclosure is not limited to the above-described embodiments. 
     Furthermore, although the waveguide in the laser element has a ridge-stripe structure in the above-described embodiments, the waveguide is not limited to this. For example, the waveguide may have an electrode-stripe structure configured of only a divided electrode without forming a ridge-stripe or may have a current constriction structure using a current-blocking layer. 
     Furthermore, although a case where a nitride-based semiconductor material is used for the laser element according to the above-described embodiments has been exemplified, the material is not limited to this. For example, the present disclosure can also be applied to a case where a semiconductor material other than a nitride-based semiconductor material is used. In such a case, the laser element includes a semiconductor laser layer structure using another semiconductor material instead of a nitride-based semiconductor laser layer structure. 
     Additionally, forms obtained by various modifications to the embodiments conceivable by those skilled in the art as well as forms resulting from arbitrary combinations of constituent elements and functions in the embodiments which do not depart from the essence of the present disclosure are intended to be included within the scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The laser light source device and the laser processing apparatus of the present disclosure are useful as, for example, industrial machinery used for processing such as welding or cutting.