Optical oscillator, optical oscillator design method, and laser device

Abstract

One embodiment of the optical oscillator includes: a first reflector that reflects light of a first wavelength; a laser medium that is excited by excitation light of a second wavelength different from the first wavelength to emit light of the first wavelength; a second reflector that, together with the first reflector, forms an unstable resonator that outputs a ring-shaped laser of the first wavelength; and a saturable absorber disposed between the laser medium and the second reflector, whose transmittance increases with the absorption of the first wavelength light, wherein the power of the excitation light is set to P. p (kw), let the inner diameter of the ring laser be d i Set the outer diameter to d o , will d o / d i When the magnification is set to m, the magnification m satisfies a0 + a1Log(P) p )≤m≤b0+b1P p +b2P p 2 Where a0 = 1.421, a1 = 0.10678, b0 = 2.8698, b1 = 0.79408, b2 = -0.022536.

Description

Technical Field

[0001] This invention relates to optical oscillators, methods for designing optical oscillators, and laser devices. Background Technology

[0002] In this technical field, the technologies described in Non-Patent Documents 1 to 3 are known. The optical oscillator described in Non-Patent Documents 1 to 3 is a passive Q-switched microchip laser having a pair of plane mirrors constituting a resonator, and a ceramic laser medium and a ceramic Q-switching element disposed between the pair of plane mirrors.

[0003] Existing technical documents

[0004] Non-patent literature

[0005] Non-patent literature 1: Pingdeng Tuofan, “High-power laser materials based on micro-domain control”, Applied Physics, 2016, Vol. 85, No. 10, pp. 863-869

[0006] Non-patent literature 2: Masaki Tsunekane, et al., 'High Peak Power, Passively Q-switched Microlaser for Ignition of Engines', IEEE JOURNAL OF QUANTUMELCTRONICS, February 2010, Vol. 46, No. 2, pp. 277-284

[0007] Non-patent literature 3: Masaki Tsunekane, et al., 'High Peak Power, Passively Q-switched Yb:YAG / Cr:YAG Micro-Lasers', IEEE JOURNALOF QUANTUM ELCTRONICS, May 2013, VOL.49, NO.5, pp.454-461 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] There are cases where a laser beam is focused using a focusing optical system (e.g., a lens), utilizing high energy at the focusing point. In this case, it is desirable to have high energy (hereinafter referred to as "effective energy") within the Airy disk of the laser beam at the focusing point. The energy of the laser beam depends on the energy of the excitation light.

[0010] Therefore, the object of the present invention is to provide a technology that, when laser light is focused, can achieve an effective energy at the focusing position that is higher than the energy of the excitation light.

[0011] Technical means to solve the problem

[0012] The optical oscillator of one side of the present invention includes: a first reflective portion that reflects light having a first wavelength; a laser medium that is excited by excitation light of a second wavelength different from the first wavelength to emit light of the first wavelength; a second reflective portion disposed opposite to the laser medium on the opposite side of the first reflective portion, forming an unstable resonator together with the first reflective portion to output a ring-shaped laser having the first wavelength; and a saturable absorber disposed opposite to the laser medium on the opposite side of the first reflective portion, the transmittance of which increases with the absorption of light having the first wavelength, and the power of the excitation light of the second wavelength is set to P. p (kW), let the inner diameter of the above-mentioned ring laser be d. i (mm), set the outer diameter as d o (mm), d o / d i When the magnification is set to m, the magnification m satisfies the following equation (A):

[0013] a0+a1Log(P p )≤m≤b0+b1P p +b2P p 2 ···(A)

[0014] in,

[0015] a0 = 1.421

[0016] a1 = 0.10678

[0017] b0 = 2.8698

[0018] b1 = 0.79408

[0019] b2 = -0.022536.

[0020] In the above structure, due to the presence of an unstable resonator, a pulsed annular laser can be output. When the annular laser is focused using a focusing optical system, the energy of the Airy disk (central part) of the annular laser at the focusing position is called the effective energy. The amplification m of the above optical oscillator satisfies equation (A). Therefore, a high effective energy relative to the excitation light energy can be achieved.

[0021] Alternatively, when viewed from the first reflective part, the size of the second reflective part may be smaller than the size of the first reflective part.

[0022] Another aspect of the laser device of the present invention includes the aforementioned optical oscillator and excitation light supply unit, which outputs the excitation light supplied to the aforementioned laser medium. In the above structure, due to the presence of an unstable resonator, it is possible to output the aforementioned pulsed annular laser. The amplification m of the aforementioned optical oscillator satisfies equation (A). Therefore, it is possible to achieve an effective energy that is high relative to the energy of the excitation light.

[0023] It may also include a focusing optical system that focuses the aforementioned annular laser output from the aforementioned unstable resonator.

[0024] It may also include: a nonlinear optical system that transforms the aforementioned annular laser output from the aforementioned unstable resonator.

[0025] The design method of an optical oscillator according to another aspect of the present invention includes: a first reflector that reflects light having a first wavelength; a laser medium that is excited by excitation light of a second wavelength different from the first wavelength to release light of the first wavelength; a second reflector disposed opposite to the first reflector relative to the laser medium, forming an unstable resonator together with the first reflector to output a ring laser having the first wavelength; and a saturable absorber disposed opposite to the first reflector relative to the laser medium, whose transmittance increases with the absorption of light having the first wavelength. In the optical oscillator design method, when the ring laser output from the unstable resonator is focused by supplying the excitation light to the laser medium, the energy conversion efficiency of the Airy disk of the ring laser relative to the energy of the excitation light is defined as the effective energy conversion efficiency η. eff (%), let the inner diameter of the above-mentioned annular laser be d. i (mm), set the outer diameter as d o (mm), d o / d i When the amplification factor is set to m, the conversion efficiency distribution is obtained. The above conversion efficiency distribution is the above effective energy conversion efficiency η. eff Relative to the aforementioned distribution of magnification m, a magnification m is set such that the aforementioned effective energy conversion efficiency η is achieved. eff The standardized effective energy conversion efficiency, obtained by standardizing the maximum effective energy conversion efficiency in the above conversion efficiency distribution, is above 50%.

[0026] The amplification m set by the above design method can satisfy the above equation (A). Therefore, when the ring laser output from the optical oscillator designed as described above is focused, a high effective energy relative to the energy of the excitation light can be achieved at the focusing position.

[0027] Other examples of the optical oscillator of the present invention include: a first reflector that reflects light having a first wavelength; a laser medium that is excited by excitation light of a second wavelength different from the first wavelength to emit light of the first wavelength; a second reflector disposed opposite to the first reflector relative to the laser medium, forming together with the first reflector an unstable resonator that outputs a ring-shaped laser having the first wavelength; and a saturable absorber disposed opposite to the first reflector relative to the laser medium, whose transmittance increases with the absorption of light having the first wavelength, wherein the inner diameter of the ring-shaped laser is set as d. i (mm), set the outer diameter as d o (mm), d o / d i When the magnification is set to m, the magnification m is greater than 2. 1 / 2 .

[0028] In the above structure, due to the presence of an unstable resonator, it is possible to output pulsed, ring-shaped laser light. The amplification m of the above optical oscillator is greater than 2. 1 / 2 Therefore, it is possible to achieve an effective energy that is high relative to the energy of the excitation light.

[0029] Other examples of the laser device of the present invention include: an optical oscillator as one of the other examples described above; and an excitation light supply unit that outputs the excitation light supplied to the laser medium, wherein the amplification factor m is 1.44 to 4.01 when the power of the excitation light is 1.5 kW or more and 12 kW or less, the amplification factor m is 1.47 to 5.1 when the power of the excitation light is 3 kW or more and 12 kW or less, or the amplification factor m is 1.50 to 6.82 when the power of the excitation light is 6 kW or more and 12 kW or less.

[0030] The effects of the invention

[0031] According to the present invention, it is possible to provide laser devices and optical oscillators that can achieve high effective energy. Attached Figure Description

[0032] Figure 1 This is a diagram showing a schematic structure of a laser device according to one embodiment.

[0033] Figure 2 It means from Figure 1 A schematic diagram of an example of pulsed laser output from the laser device shown.

[0034] Figure 3 This is a graph showing the measurement results of the beam diameter in the reference experimental example.

[0035] Figure 4It is a coordinate graph plotted by the beam radius of the ring beam (pulsed laser) near the focal point in the reference experimental example and the radius of the Airy disk of the ring beam.

[0036] Figure 5 It is an image of the beam pattern at the focal point in the reference experimental example.

[0037] Figure 6 It means to Figure 5 The white line shown is a graph of the intensity distribution along the y-axis when the white line represents the y-axis.

[0038] Figure 7 This is a schematic diagram representing a model of an optical oscillator used in numerical calculations.

[0039] Figure 8 It represents the energy conversion efficiency η and the effective energy rate E. eff A coordinate graph showing the magnification dependence.

[0040] Figure 9 It represents the effective energy conversion efficiency η. eff A coordinate graph showing the magnification dependence.

[0041] Figure 10 It represents the standardized effective energy conversion efficiency η. eff A coordinate graph showing the magnification dependence.

[0042] Figure 11 This is a schematic diagram of the first application example of a laser device.

[0043] Figure 12 This is a schematic diagram of the second application example of the laser device.

[0044] Figure 13 This is a schematic diagram of the third application example of the laser device.

[0045] Figure 14 This is a schematic diagram of the fourth application example of the laser device.

[0046] Figure 15 This is a schematic diagram of the fifth application example of the laser device.

[0047] Figure 16 This is a schematic diagram of the sixth application example of the laser device.

[0048] Figure 17 This is a schematic diagram of the seventh application example of the laser device.

[0049] Figure 18 This is a schematic diagram representing the first modified example of an optical oscillator.

[0050] Figure 19 This is a schematic diagram representing the second modified example of an optical oscillator.

[0051] Figure 20 This is a schematic diagram representing the third variation of an optical oscillator.

[0052] Figure 21 This is a schematic diagram representing the fourth variant of an optical oscillator.

[0053] Figure 22 This is a diagram used to illustrate the relationship between the radius of curvature and magnification when the first and second reflectors are bent. Detailed Implementation

[0054] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are referred to by the same symbols, and repeated descriptions are omitted. The scale of the drawings is not necessarily consistent with the described structure.

[0055] like Figure 1 As shown, a laser device 1A according to one embodiment includes an excitation light supply unit 2, an optical oscillator 3A, and a focusing optical system 4. The laser device 1A outputs a pulsed laser L2 by incidenting excitation light L1 supplied from the excitation light supply unit 2 onto the optical oscillator 3A. The laser device 1A of this embodiment is a passive Q-switched laser device. In the laser device 1A, the pulsed laser L2 is further focused by the focusing optical system 4. The laser device 1A is suitable for laser ignition, laser-induced breakdown beam splitting, various laser processing for ablation purposes, or laser-based surgery. In this embodiment, the pulsed laser L2 has a first wavelength, and the excitation light L1 has a second wavelength.

[0056] The second wavelength mentioned above, for example, if the laser medium 31 of the optical oscillator 3A is Nd:YAG, then the wavelength is 808 nm or 885 nm; if the laser medium 31 is Yb:YAG, then the wavelength is 940 nm or 968 nm. The first wavelength mentioned above, for example, if the laser medium 31 is Nd:YAG, then the wavelength is 1064 nm; if the laser medium 31 is Yb:YAG, then the wavelength is 1030 nm.

[0057] The excitation light supply unit 2 has a structure capable of supplying excitation light L1 to the optical oscillator 3A. The excitation light supply unit 2 may include, for example, an optical fiber 21, a laser diode (LD) 22, and an incident optical system 23. The excitation light supply unit 2 may also have a bundle of multiple optical fibers 21. Alternatively, the excitation light supply unit 2 may have a structure without optical fibers 21, i.e., a structure in which excitation light L1 is supplied to the optical oscillator 3A from the LD 22 via the incident optical system 23.

[0058] LD22 outputs excitation light L1. The power of excitation light L1 is, for example, 0.8 kW or higher. LD22 can be oscillated by continuous wave or quasi-continuous wave. The input end of optical fiber 21 is coupled to LD22. Optical fiber 21 outputs the excitation light L1 from LD22 to incident optical system 23. Incident optical system 23 focuses the excitation light L1 output from optical fiber 21 and directs it onto optical oscillator 3A. Incident optical system 23 is, for example, as follows: Figure 1 As illustrated, it has lenses 23a and 23b. The excitation light L1 can also be incident on the first reflector 33 as parallel light or a gently focused light that is substantially parallel light.

[0059] The optical oscillator 3A includes a laser medium 31, a Q-switching element (saturable absorber) 32, a first reflector 33, a support 34, and a second reflector 35. The first reflector 33, the second reflector 35, the laser medium 31, and the Q-switching element 32 are arranged along the Z-axis in the order of first reflector 33, laser medium 31, Q-switching element 32, and second reflector 35. This Z-axis corresponds to the optical axis of the optical oscillator 3A.

[0060] [Laser medium]

[0061] In the excited state, the laser medium 31 forms an inverted distribution with an amplification exceeding absorption, and the light is amplified by inductive release. The laser medium 31 is also called a gain medium. As long as the laser medium 31 can release light with a first wavelength by being supplied with excitation light L1 with a second wavelength, various known laser media can be used.

[0062] Examples of materials for the laser medium 31 include light-gain materials formed from oxides containing rare-earth ions that serve as light-emitting centers, light-gain materials formed from oxides containing transition metal ions that serve as light-emitting centers, and light-gain materials formed from oxides that serve as color centers.

[0063] Examples of rare earth ions include Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. Examples of transition metal ions include Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. Examples of parent materials include garnet-based materials such as YAG, YSAG, YGAG, YSGG, GGG, GSGG, and LuAG; fluoride-based materials such as YLF, LiSAF, LiCAF, MgF2, and CaF2; vanadate-based materials such as YVO4, GdVO4, and LuVO4; apatite-based materials such as FAP, sFAP, VAP, and sVAP; alumina-based materials such as Al2O3 and BeAl2O3; dioxide and trioxide-based materials such as Y2O3, Sc2O3, and Lu2O3; and tungstate-based materials such as KGW and KYW. Parent materials can be single-crystal or polycrystalline ceramic materials. Parent materials can also be amorphous glasses.

[0064] Examples of the shape of the laser medium 31 include plate-like and columnar shapes. Figure 1 In the illustrated embodiment, the central axis of the laser medium 31 is aligned with the Z-axis. The laser medium 31 has a first end face 31a and a second end face 31b (the face opposite to the first end face 31a in the Z-axis direction). The first end face 31a and the second end face 31b are orthogonal to the Z-axis. An example of the length of the laser medium 31 along the Z-axis direction is 0.2 mm to 26 mm.

[0065] Examples of the shape (top view) of the laser medium 31 viewed from the Z-axis include circles, rectangles, squares, and polygons. When the top view of the laser medium 31 is circular, the diameter is typically 1.4 mm to 100 mm. When the top view of the laser medium 31 is rectangular or square, the approximate diagonal length is typically 1.9 mm to 140 mm.

[0066] Hereinafter, the shape of an element when viewed from the Z-axis direction, as described above, will be referred to as the "top view shape".

[0067] The Q-switching element 32 is a saturable absorber, characterized by its absorption capacity saturating as the intensity of light of the first wavelength incident on the Q-switching element 32 increases. The transmittance of the Q-switching element 32 increases with the absorption of light of the second wavelength. The Q-switching element 32 can be coaxially configured with the laser medium 31. The Q-switching element 32 can also be coupled to the second end face 31b.

[0068] When viewed along the Z-axis, the size of the Q-switching element 32 is, for example, smaller if it is Cr:YAG and the laser medium 31 is Nd:YAG. When the laser medium 31 is Nd:YVO4 or Yb:YAG, its length along the Z-axis is shorter than that of the Q-switching element 32. Examples of the shape of the Q-switching element 32 include plate-like and columnar shapes. The Q-switching element 32 has a first end face 32a and a second end face 32b on the side of the laser medium 31 (the face opposite to the first end face 32a in the Z-axis direction). The first end face 32a is orthogonal to the Z-axis. Examples of the length of the Q-switching element 32 along the Z-axis are 0.1 to 10 mm.

[0069] When both the laser medium 31 and the Q-switching element 32 are made of ceramic, they can be sintered together, but surface-activated bonding is preferred. Surface-activated bonding is a method in which the oxide film or surface deposits on the bonding surfaces of materials bonded in a vacuum are removed by irradiation with an ion beam or FAB (neutral atom beam), so that the exposed bonding surfaces of the constituent atoms are bonded together flatly. The above bonding is a direct bonding using intermolecular bonding. If it is surface-activated bonding, the laser medium is not limited to ceramic; bonding between single crystals or their mixtures can be achieved, as well as bonding after excitation light reflection coating, etc. When a bonded body is formed by bonding the laser medium 31 and the Q-switching element 32, the length of the bonding direction (corresponding to the length in the Z-axis direction) of the laser medium 31 and the Q-switching element 32 in the bonded body is, for example, less than 10 mm.

[0070] At least one of the second end face 31b of the laser medium 31 and the first end face 32a of the Q-switching element 32 may be provided with a coating layer that adjusts the reflection characteristics (e.g., the reflection characteristics of light of the second wavelength) in the second end face 31b and the first end face 32a. When such a coating layer is provided on at least one of the second end face 31b and the first end face 32a, for example, the laser medium 31 and the Q-switching element 32 can be bonded via the coating layer as described above. At least one of the first end face 32a and the second end face 32b of the Q-switching element 32 may also be provided with a coating layer that functions as an HR coating relative to the excitation light L1 of the second wavelength and as an AR coating relative to light of the first wavelength. In the case of constituting a composite resonator, the coating layer may also be a coating layer that partially reflects light relative to the first wavelength. Such a coating layer may also be part of a saturable absorber. That is, the saturable absorber, in addition to the saturable absorber (… Figure 1 In addition to the Q-switching element 32), the above-mentioned coating layer may be provided. When the coating layer is provided on the end face of the saturable absorber, the end face of the coating layer is equivalent to the end face of the saturable absorber.

[0071] [First Reflector]

[0072] A first reflective portion 33 is disposed on the first end face 31a of the laser medium 31. The first reflective portion 33 transmits excitation light L1 of the second wavelength and reflects light of the first wavelength. The transmittance of the first reflective portion 33 relative to the excitation light L1 of the second wavelength is 80% or more (preferably 95% or more), and the reflectance of the first reflective portion 33 relative to light of the first wavelength is 90% or more (preferably 99% or more). The first reflective portion 33 is, for example, a dielectric multilayer film. The first reflective portion 33 functions as an AR coating relative to the excitation light L1 of the second wavelength and as an HR coating relative to light of the first wavelength. When the first reflective portion 33 is a dielectric multilayer film, the first reflective portion 33 can be formed on the first end face 31a by a thin film forming technique.

[0073] The first reflecting portion 33 has a first surface 33a and a second surface 33b. The first surface 33a is the surface into which the excitation light L1 is incident. The second surface 33b is the surface opposite to the first surface 33a in the Z-axis direction. The first surface 33a and the second surface 33b are planes orthogonal to the Z-axis. Therefore, the first reflecting portion 33 is a plane mirror having the aforementioned transmission and reflection characteristics. However, the first reflecting portion 33 may also be a mirror with curvature (a curved mirror), for example, it may be a concave mirror.

[0074] [Support]

[0075] The support 34 is disposed separately from the Q-switching element 32. The support 34 supports the second reflector 35. The support 34 transmits light of the first wavelength (pulsed laser L2). The transmittance of the support 34 relative to the first wavelength of light is 90% or more. Examples of materials for the support 34 include glass. In this embodiment, the central axis of the support 34 is aligned with the Z-axis.

[0076] The first surface 34a (the surface on the side of the Q-switching element 32) of the support 34 is curved toward the Q-switching element 32. The radius of curvature of the first surface 34a is, for example, the same as the radius of curvature of the second reflector 35. The second surface 34b (the surface on the opposite side of the Q-switching element 32) of the support 34 is, for example, a plane. An example of the support 34 is a plano-convex lens. An AR coating relative to a first wavelength of light may also be applied to the first surface 34a. Such an AR coating may also be part of the support 34. The second reflector 35 is provided on the first surface 34a.

[0077] [Second Reflector]

[0078] The second reflective portion 35 reflects light of the first wavelength formed on the first surface 34a. The second reflective portion 35 is, for example, a dielectric multilayer film. The optical axis of the second reflective portion 35 is aligned with the Z-axis. The reflectivity of the second reflective portion 35 relative to light of the first wavelength is 80% or more (preferably 99% or more). The second reflective portion 35 is, for example, a dielectric multilayer film that functions as an HR coating relative to light of the first wavelength. When the second reflective portion 35 is a dielectric multilayer film, it can be formed on the first surface 34a using a thin film forming technique.

[0079] Optical oscillator 3A, such as Figure 1 The image shown may also have lens 36. Lens 36 is a lens that parallelizes the pulsed laser L2.

[0080] [Concentrating Optical System]

[0081] The focusing optical system 4 is an optical system that focuses the pulsed laser L2 output from the optical oscillator 3A. Figure 1 In the configuration shown, the focusing optical system 4 is a lens. Examples of focal distances for the focusing optical system 4 are 5mm to 500mm.

[0082] The laser device 1A may also include a housing 5. The housing 5 is, for example, a casing. The housing 5 houses the irradiation optical system 23, the optical oscillator 3A, and the focusing optical system 4. In this case, for example, the output end of the optical fiber 21 is mounted on the first end wall 5a of the housing 5 (one of a pair of walls orthogonal to the Z-axis). An opening 5c ​​is formed on the second end wall 5b of the housing 5 (the end wall opposite to the first end wall 5a along the Z-axis). The opening 5c ​​is closed by a window member 6. The window member 6 is a member that is transparent to the pulsed laser L2.

[0083] Further explanation of optical oscillator 3A.

[0084] The first reflector 33 and the second reflector 35 of the optical oscillator 3A constitute an unstable resonator UR. Figure 1 In the embodiment shown, the optical axis of the unstable resonator UR formed by the first reflector 33 and the second reflector 35 is aligned with the Z-axis.

[0085] When viewed along the Z-axis, the size of the second reflective portion 35 is smaller than the size of the first reflective portion 33. Furthermore, the second reflective portion 35 is curved towards the first reflective portion 33. The second reflective portion 35 is curved in the same way as the first surface 34a. Because the second reflective portion 35 is curved as described above, it causes light of the second wavelength to diverge. Therefore, the first reflective portion 33 and the second reflective portion 35 form a magnifying optical system.

[0086] When viewed from the Z-axis, the second reflective part 35 is circular or polygonal, with an example diameter or diagonal length of 1 mm to 20 mm. The diameter or diagonal length of the second reflective part 35 can also be 1 mm to 3 mm. An example of the radius of curvature of the second reflective part 35 is 10 mm to 2 m. An example of the radius of curvature of the second reflective part 35 can also be 10 mm to 100 mm.

[0087] The distance between the portion of the second reflector 35 closest to the first reflector 33 (the top of the second reflector 35) and the second surface 33b of the first reflector 33 (hereinafter referred to as "resonator length Lc") is approximately 4 mm to 50 mm. The resonator length Lc may also be less than 15 mm.

[0088] The first reflector 33 and the second reflector 35 constitute an unstable resonator UR. Therefore, from the optical oscillator 3A with the Q-switching element 32, such as... Figure 2 As shown, the output is a ring-shaped (doughnut) pulsed laser L2 (ring laser). This will be explained in detail.

[0089] When excitation light L1 from excitation light supply unit 2 is incident on the first surface 33a of the first reflector 33, excitation light L1 is supplied to the laser medium 31 through the first reflector 33. As a result, the laser medium 31 is excited, and light of the first wavelength is released. The light of the first wavelength released from the laser medium 31 is reflected by the second reflector 35 towards the first reflector 33. The first reflector 33 reflects the light of the first wavelength. Thus, the light of the first wavelength passes through the laser medium 31 multiple times. Due to the induced release when the light of the first wavelength passes through the laser medium 31, the light of the first wavelength is amplified, and through the action of the Q-switching element 32, it is output as a pulsed laser L2.

[0090] Because the second reflector 35 bends towards the first reflector 33, the second wavelength of light reflected by the second reflector 35 diverges. Therefore, when viewed from the Z-axis direction, pulsed laser L2 is output from the outside of the second reflector 35. As a result, the shape (intensity distribution) of the pulsed laser L2 is as follows: Figure 2 The ring shape shown is indicated. That is, the laser device 1A is capable of outputting a ring-shaped pulsed laser L2.

[0091] Let the inner diameter of the pulsed laser L2 be d. i Let the outer diameter of the pulsed laser L2 be d. o , magnification m is expressed as d o / d i definition.

[0092] In the aforementioned laser device 1A, when excitation light L1 is input to the optical oscillator 3A, a ring-shaped pulsed laser L2 is output. The laser device 1A has a focusing optical system 4. Therefore, the pulsed laser L2 is focused by the focusing optical system 4.

[0093] Here, with reference to the reference experimental example, the characteristics of a laser device with an unstable resonator will be explained. In the following explanation of the reference experimental example, the ring-shaped pulsed laser will be referred to as a doughnut beam.

[0094] In the reference experimental example, apart from the absence of the storage section 5 and the window component 6, it is used with... Figure 1 The laser device shown is the same as the laser device 1A shown.

[0095] In the reference experimental example, an LD 22 coupled with fiber 21 was used, and the excitation light L1 was incident on the first reflector 33 using the incident optical system 23. The incident optical system 23 is a telescope using lenses 23a and 23b. The excitation method of the LD 22, the wavelength of the excitation light L1, and the output power are described below.

[0096] • Excitation method: Quasi-continuous wave excitation

[0097] • Wavelength of excitation light L1: 808nm

[0098] • Output power of excitation light L1: 700W

[0099] In laser medium 31, Nd:YAG ceramic (Nd 3+ The amount added: 1.1 at.%). In the Q-switch element 32, Cr is used. 4+ YAG ceramic. The initial transmittance of the Q-switching element 32 is 30%. The laser medium 31 and the Q-switching element 32 are bonded. The length of the bonded body in the Z-axis direction of the laser medium 31 and the Q-switching element 32 is 7 mm, and the volume of the bonded body is 6×6×7 mm. 3 AR coatings for light with wavelengths of 1064 nm and 808 nm are applied to both ends of the junction of the laser medium 31 and the Q-switching element 32 (i.e., the first end face 31a of the laser medium 31 and the second end face 32b of the Q-switching element 32).

[0100] The first reflector 33 is a plane mirror that reflects light with a wavelength of 1064 nm and transmits light with a wavelength of 808 nm. The support 34 uses a plano-convex lens with a radius of curvature of 52 mm on its first surface 34a. At the center of the first surface 34a of the support 34, as the second reflector 35, a dielectric multilayer film that functions as an HR coating relative to light with a wavelength of 1064 nm is partially coated. An AR coating is applied to the area of ​​the first surface 34a other than the second reflector 35. When viewed from the Z-axis direction, the second reflector 35 is a circle with a diameter of 2 mm. The resonator length Lc is 10 mm.

[0101] In the above structure, the amplification m in the unstable resonator is equivalent to 2. 1 / 2 .

[0102] A convex lens is used as lens 36 to parallelize the ring beam (pulsed laser L2). A lens (focal distance: 300mm) is used as the focusing optical system 4.

[0103] In the reference experimental example, the pulse energy and pulse width of the pulsed laser L2 were measured. The pulse energy was measured using a pyroelectric energy sensor (manufactured by Ophir Optronics Solutions Ltd.). The pulse width was measured using a photodetector with a rise time of 30 ps and a 13 GHz oscilloscope. Both pulse energy and pulse width were measured without using the focusing optical system 4. The measured pulse energy was 13.2 mJ at a repetition frequency of 10 Hz, and the pulse width was 476 ps at half maximum width.

[0104] In the reference experimental example, the beam quality (M) near the focusing position of the focusing optical system 4 was measured. 2 In measuring beam quality, a beam quality measuring instrument (beam quality M) according to ISO 11146 is used. 2 tool (made by Cinogy Technologies) and parsing software (RayCi).

[0105] Beam quality (M 2 The beam diameter was obtained as follows. The beam diameter was measured at multiple locations before and after the focusing position along the propagation direction of the annular beam. Based on these measurements, M was calculated. 2 The measurement results of the beam diameter are as follows: Figure 3 As shown. Figure 3 The horizontal axis represents the measured position (mm) of the beam diameter, and the vertical axis represents the radius of the annular beam. Figure 3The diagram shows the radii of the annular beam in the X-axis and Y-axis directions relative to the three-dimensional coordinate system defined by the Z-axis. Figure 3 The square markings represent the radius of the beam along the X-axis, and the black circles represent the radius along the Y-axis. The ring beam is theoretically a perfect circle, but in reality, it has a slightly elliptical shape. The X-axis corresponds to the major axis of the ellipse, and the Y-axis corresponds to the minor axis. Figure 3 The beam patterns at each measurement location are also shown. For example... Figure 3 As shown, the far-field patterns at the focal position are Airy disks and Airy patterns.

[0106] according to Figure 3 Calculated M 2 The value is 6.8 relative to the X-axis and 5.3 relative to the Y-axis. Refer to M in the experimental example. 2 The values ​​are based on the beam diameter of the second moment. Furthermore, M, representing 86.5% of the beam diameter based on photoelectric force, was also calculated. 2 PC M in the X-axis and Y-axis directions 2 PC The values ​​are 6.5 and 5.2 respectively. Here, M in the X-axis and Y-axis directions is defined using the following formulas. 2 The average M 2 ave .

[0107] [Number 1]

[0108]

[0109] In this case, M is calculated relative to the X-axis and Y-axis directions. 2 The average M 2 ave The value is 6. Similarly, M is calculated relative to the X-axis and Y-axis directions. 2 pc The average M 2 ave It is 5.8.

[0110] Figure 4 This is a coordinate graph plotting the beam radius of the annular beam near the focal point and the radius of the Airy disk of the annular beam. The beam radius of the annular beam is... Figure 3 The average value of the radii in the X-axis and Y-axis directions shown. Figure 4 Curve α1 in the figure represents the fitted curve of the measurement results relative to the beam radius of the annular beam. Figure 4 Curve α2 in the figure represents the fitted curve relative to the measured Airy disk radius. Furthermore, Figure 4 The curve α3 in the figure represents the Gaussian beam radius when the Gaussian beam is focused using the same lens.

[0111] according to Figure 4 The results show that the radius of the Airy disk is approximately 0.2 times the beam radius of the ring beam. Here, the width of the Airy disk and the beam quality are set as w. Airy and M 2 Airy Set the width and beam quality of the ring beam to w. d and M 2 d In this case, the following relationship holds true.

[0112] [Number 2]

[0113]

[0114] As mentioned above, M 2 d It is 6, w Airy / w d It is approximately 0.2. Therefore, the overall beam quality M of the ring beam is... 2 On the other hand, in the Airy disk, a beam quality of approximately 1.2 is obtained. In other words, in the Airy disk, a beam quality close to that of the Gaussian mode is obtained.

[0115] Furthermore, according to Figure 4 When focusing on the region of the Airy disk, which is equivalent to a ring beam, a long Rayleigh length can be achieved (in Figure 4 (In the middle, it is about 4 times that of a Gaussian beam).

[0116] Figure 5 It is an image of the beam pattern at the focal point. According to... Figure 5 It is also understandable that Airy spots and Airy patterns are formed at the focal point.

[0117] Figure 6 It means to Figure 5 The white line shown (in) Figure 6 The graph shows the intensity distribution along the y-axis when the white line extending longitudinally (in the middle) represents the y-axis. Figure 6 middle, Figure 5 The intensity (experimental results) of the cross-section along the y-axis at the center of the image is plotted using a white circle. The horizontal axis in the figure represents the position along the y-axis, and the vertical axis represents the normalized intensity. The second-moment beam diameter (2w) of the Airy disk and Airy pattern is also shown. y The value is 0.29 mm. Figure 6 In the diagram, solid lines represent Gaussian distributions with the same beam diameter (0.29 mm), and dashed lines represent beams with a diameter of 0.2 mm. y The Gaussian distribution. Furthermore, the width w y It is the width relative to the region where position 0 is positive (or negative). Figure 6The length da shown is equivalent to the diameter of the Airy disk.

[0118] When a plane wave passes through a circular aperture lens, an Airy disk pattern is generated due to diffraction. Therefore, the intensity distribution of the annular beam was fitted using Equation (1) which represents the intensity distribution at the focal point (focus position) when the plane wave is focused by the circular aperture lens (for example, see B. Lu, et al., “The beam quality of annular lasers and related problems,” J. Mod. Opt. 48, 1171 (2001)).

[0119] [Number 3]

[0120]

[0121] In equation (1), m is b / a. In equation (1), b is defined as the outer radius of the circular aperture lens, and a is the inner radius of the circular aperture. F is the focal distance of the circular aperture lens. r is the radial position of the Airy disk at the focal point. I(0, f) is the peak intensity in the focal plane. I(0, f) is determined by S... 2 / (λ 2 f 2 S is represented by πa. S is the area of ​​the circular aperture lens. 2 (m 2 -1) represents J1, which is a first-order Bessel function. k (=2π / λ) is the wave number.

[0122] exist Figure 6 In the fitted curve shown, m, 2b, and f are as described below.

[0123] m = 1.48

[0124] 2b = 7.5mm

[0125] f = 315mm

[0126] The amplification m of the unstable resonator in the reference experiment is 2. 1 / 2 Therefore, compared to the fitting result based on the above equation (1), we can consider m in equation (1) as the amplification factor of the unstable resonator (in other words, as d). i =2a,d o =2b), thus the intensity distribution of the Airy disk at the focal position of the ring beam (pulsed laser L2) can be calculated based on equation (1).

[0127] return Figure 1 The laser device 1A will be further explained.

[0128] In this embodiment, the power of the excitation light L1 (hereinafter referred to as "excitation power") is set as P. p When the amplification factor m is (kW), the following equation (2a) is satisfied. In other words, the unstable resonator UR (specifically, the first reflector 33 and the second reflector 35) is designed such that the amplification factor m satisfies equation (2a).

[0129] a0+a1Log(P p )≤m≤b0+b1P p +b2P p 2 ···(2a)

[0130] In equation (2a), a0, a1, b0, b1 and b2 are as follows.

[0131] a0 = 1.421

[0132] a1 = 0.10678

[0133] b0 = 2.8698

[0134] b1 = 0.79408

[0135] b2 = -0.022536

[0136] The magnification m can also satisfy the following equation (2b). In other words, the unstable resonator UR (specifically, the first reflector 33 and the second reflector 35) can also be designed with the magnification m satisfying equation (2b).

[0137] a0+a1Log(P p )≤m≤b0+b1P p +b2P p 2 ···(2b)

[0138] In equation (2b), a0, a1, b0, b1 and b2 are as follows.

[0139] a0 = 1.613

[0140] a1 = 0.16827

[0141] b0 = 2.6961

[0142] b1 = 0.71522

[0143] b2 = -0.023234

[0144] The magnification m can also satisfy the following equation (2c). In other words, the unstable resonator UR (specifically, the first reflector 33 and the second reflector 35) can also be designed with the magnification m satisfying equation (2c).

[0145] a0+a1Log(P p )≤m≤b0+b1P p +b2P p 2 ···(2c)

[0146] In equation (2c), a0, a1, b0, and b1 are as follows.

[0147] a0 = 1.886

[0148] a1 = 0.28888

[0149] b0 = 2.6771

[0150] b1 = 0.51375

[0151] b2 = -0.021411

[0152] The magnification m can also satisfy the following equation (2d). In other words, the unstable resonator UR (specifically, the first reflector 33 and the second reflector 35) can also be designed with the magnification m satisfying equation (2d).

[0153] a0+a1Log(P p )≤m≤b0+b1Log(P p )···(2d)

[0154] In equation (2d), a0, a1, b0, and b1 are as follows.

[0155] a0 = 1.9308

[0156] a1 = 0.37083

[0157] b0 = 2.9116

[0158] b1 = 2.3422

[0159] Specifically, the magnification m is greater than 2 1 / 2 Large. Magnification m is, for example, below 10. Magnification can be below 7, or below 6, 5, or 4.

[0160] [Excitation power P] p This applies to applications with power ratings between 1.5kW and 12kW (or, between 3kW and 6kW, especially the 1.5kW case).

[0161] The magnification m can be above 1.44 or below 4.01.

[0162] The magnification m can be above 1.64 or below 3.72.

[0163] The magnification m can be above 1.93 or below 3.40.

[0164] The magnification m can be above 1.99 or below 3.32.

[0165] [Excitation power P] p This applies to cases between 3kW and 12kW (or below 6kW) (especially the 3kW case).

[0166] The magnification m can be above 1.47 or below 5.1.

[0167] The magnification m can be above 1.69 or below 4.64.

[0168] The magnification m can be above 2.02 or below 4.03.

[0169] The magnification m can be above 2.10 or below 4.03.

[0170] [Excitation power P] p This applies to cases between 6kW and 12kW (especially 6kW).

[0171] The magnification m can be above 1.50 or below 6.82.

[0172] The magnification m can be above 1.74 or below 6.20.

[0173] The magnification m can be above 2.11 or below 4.99.

[0174] The magnification m can be above 2.22 or below 4.74.

[0175] [Excitation power P] P [For the 12kW case]

[0176] The magnification m can be above 1.53 or below 9.16.

[0177] The magnification m can be above 1.79 or below 7.94.

[0178] The magnification m can be above 2.19 or below 5.76.

[0179] The magnification m can be above 2.33 or below 5.44.

[0180] In the aforementioned laser device 1A, when excitation light L1 is input to the optical oscillator 3A, a ring-shaped pulsed laser L2 is output. The laser device 1A has a focusing optical system 4. Therefore, the pulsed laser L2 is focused by the focusing optical system 4.

[0181] The energy contained in the center of the pulsed laser L2 at the focusing position (focal position) of the focusing optical system 4, which is the Airy disk, is called the "effective energy". In the laser device 1A described above, the amplification m satisfies equation (2). Therefore, it is possible to achieve an effective energy that is higher than the energy of the excitation light L1. Therefore, in the field of laser applications that use laser focusing, laser device 1A and optical oscillator 3A are effective.

[0182] The Airy disk is smaller than the pulsed laser L2. Because high effective energy can be achieved within this Airy disk area, it enables applications such as micro-machining and surgery in small areas. At the focal point, the energy of the pulsed laser L2 is largely contained within the Airy disk, and because the focal depth, equivalent to the Rayleigh length, is also longer, stable breakdown can be expected.

[0183] Next, referring to the numerical calculation results, we will explain the situation where a higher effective energy than the excitation light L1 can be achieved.

[0184] Figure 7 This is a schematic diagram representing a model of an optical oscillator used in numerical calculations. For example... Figure 7 As shown, the optical oscillator used as the numerical calculation model has a first reflector 33, a laser medium 31, a Q-switching element 32, and a second reflector 35. In the numerical calculation, it is assumed that the excitation light L1 is input to the optical oscillator, and the output amplification m(=d) o / d i The case of pulsed laser L2.

[0185] The shape and size of the excitation light L1, the diameter of the second reflector 35, and the reflectivity are assumed as follows.

[0186] • Shape of excitation light L1 (shape viewed from the Z-axis): Circular

[0187] • Size (diameter) of excitation beam L1: Set as the diameter d of the output pulsed laser L2. o .

[0188] • The diameter d of the second reflector 35 i 1mm

[0189] • Reflectivity (or coupling efficiency) of the second reflector 35: 1 / m 2

[0190] Furthermore, the effective mode area (A) of the laser medium 31 g ) and the effective mode area (A) of Q-switching element 32 SA Set to the same.

[0191] In the numerical calculation, the effective energy E was calculated with the output pulsed laser L2 focused by a lens. Airy disk The energy E relative to the excitation light L1 pump The ratio (hereinafter referred to as "effective energy conversion efficiency η") eff Effective energy E Airy disk The above describes the energy within the Airy disk at the focusing position of the pulsed laser L2.

[0192] The following equations (3) and (4) (for example, refer to references 1-3 below) are used for the above calculations. E is expressed by equation (4). pulse It is the energy of the pulsed laser L2.

[0193] [Number 4]

[0194]

[0195] [Number 5]

[0196]

[0197] In equations (3) and (4), n gi Equation (5) represents the initial population inversion density of the gain medium 31.

[0198] [Number 6]

[0199]

[0200] The parameters in equations (3) to (5) are as follows.

[0201] T0: Initial transmittance of the Q-switching element

[0202] R: Reflectivity equivalent to the diffraction loss of the second reflector 35

[0203] L: Round-trip loss in the unstable resonator UR

[0204] σ g (m 2 ): Induction release cross-sectional area

[0205] l g(mm): Length of laser medium 31

[0206] A g (=π(d o / 2) 2 ): Mode area in laser medium 31

[0207] γ g Inversion distribution reduction factor of laser medium 31

[0208] n gf The final inversion distribution of laser medium 31

[0209] P p Peak power of excitation light L1

[0210] τ g (ms): Upper-level lifetime

[0211] W p : activation rate

[0212] Reference 1: N.Pavel, J.Saikawa, S.Kurimura, and T.Taira, "High average power diode end-pumped composite Nd:YAG laserpassively Q-switched by Cr4+:YAGsaturable absorber," Jpn.J.Appl.Phys.40 (Part 1, No.3A), 1253-1259 (2001).

[0213] Reference 2: H Sakai, H Kan, T Taira, “1MW peak powersingle-mode high-brightness passively Q-switched Nd 3+ :YAG microchiplaser Optics Express; Vol.16, Issue 24, pp.19891-19899, ​​(2008).

[0214] Reference 3: A.Kausas and T.Taira, "Giant-pulse Nd:YVO4microchiplaserwithMW-level peak power by emission cross-sectional control," Opt.Express24(4),3137-3149(2016).

[0215] In numerical calculations, T0, R, L, σ g l g (mm), γ g τ g Set it to the following value.

[0216] T0 = ​​0.3

[0217] R = 0.5

[0218] L = 0.06

[0219] σ g =2.63×10 ―23 (m 2 )

[0220] l g =4mm,

[0221] γ g =2

[0222] τ g =0.23ms

[0223] During the numerical calculation process, n was calculated sequentially. gf In addition, W p It is determined by the excitation power Pp and the excitation area.

[0224] In addition, based on the intensity distribution calculated according to equation (1), the energy E within the Airy disk was calculated. Airy disk When using equation (1), m in equation (1) is set to the magnification m. Specifically, a in equation (1) is set to d. i / 2, let b in equation (1) be d o / 2.

[0225] The energy E of pulsed laser L2 pulse The energy E relative to the excitation light L1 PUMP The ratio is called the energy conversion efficiency η.

[0226] The energy E of pulsed laser L2 pulse Effective energy E in Airy disk The ratio is called the effective energy rate E. eff .

[0227] The energy E of pulsed laser L2 pulse The energy E relative to the excitation light L1 PUMP The ratio is called the effective energy conversion efficiency η. eff .

[0228] Energy conversion efficiency η, effective energy rate E effand effective energy conversion efficiency η eff They are represented by the following formulas respectively.

[0229] [Number 7]

[0230]

[0231]

[0232]

[0233] For excitation powers Pp of 1.5kW, 3kW, 6kW, and 12kW, the energy conversion efficiency η and effective energy rate E were calculated for various amplification ratios m. eff and effective energy conversion efficiency η eff The magnification m is obtained by fixing d. i (Equivalent to the inner diameter of pulsed laser L2) and make d o The adjustment was made by varying the outer diameter (equivalent to the outer diameter of pulsed laser L2). The calculation results are as follows: Figure 8 and Figure 9 .

[0234] Figure 8 It represents the energy conversion efficiency η and the effective energy rate E. eff A coordinate graph showing the magnification dependence. Figure 8 The horizontal axis represents the magnification. Figure 8 The vertical axis on the right represents the energy conversion efficiency η, and the vertical axis on the left represents the energy conversion efficiency η. Figure 9 It represents the effective energy conversion efficiency η. eff A coordinate graph of the amplification dependence (conversion efficiency distribution). Figure 9 The horizontal axis represents the magnification. Figure 9 The vertical axis represents the effective energy conversion efficiency η. eff . Figure 9 As understood according to equation (6c), it is Figure 8 The effective energy rate E shown eff The product of the energy conversion efficiency η.

[0235] In addition, the calculation was performed on Figure 9 The effective energy conversion efficiency η shown eff Amplification dependence according to effective energy conversion efficiency η eff The maximum effective energy conversion efficiency (maximum value) has been standardized to η. n_eff The excitation power P relative to each excitation beam L1 p Effective energy conversion efficiency η eff The amplification dependence was used to calculate the normalized effective energy conversion efficiency η. n_eff The result is as follows: Figure 10 As shown. Figure 10 The horizontal axis represents the magnification m, and the vertical axis represents the normalized effective energy conversion efficiency η. n_ef .

[0236] Figure 10 The shaded area in the figure represents the normalized effective energy conversion efficiency η. n_eff The area is over 50%. The magnification m relative to this shaded region is related to the excitation power P. p The relationship is represented by equation (2a).

[0237] Therefore, when the amplification factor m satisfies equation (2a), a normalized effective energy conversion efficiency η of over 50% can be obtained. n_eff That is, it can efficiently convert the energy of the excitation light L1 into effective energy. As a result, high effective energy can be achieved.

[0238] The standardized effective energy conversion efficiency η represents the efficiency of energy conversion. n_eff Equation (2b) defines the region with an efficiency of 63.21% or higher. Therefore, when the amplification factor m satisfies equation (2b), a normalized effective energy conversion efficiency η of 63.21% or higher can be obtained. n_eff That is, it can more efficiently convert the energy of the excitation light L1 into effective energy. As a result, higher effective energy can be achieved.

[0239] The standardized effective energy conversion efficiency η represents the efficiency of energy conversion. n_eff Equation (2c) defines the region with an efficiency of 86.47% or higher. Therefore, when the amplification factor m satisfies equation (2c), a normalized effective energy conversion efficiency η of 86.47% or higher can be obtained. n_eff That is, it can more efficiently convert the energy of the excitation light L1 into effective energy. As a result, higher effective energy can be achieved.

[0240] The standardized effective energy conversion efficiency η represents the efficiency of energy conversion. n_eff The equation for the region exceeding 90% is equation (2d). Therefore, when the amplification m satisfies equation (2d), a normalized effective energy conversion efficiency η exceeding 90% can be obtained. n_eff That is, it can more efficiently convert the energy of the excitation light L1 into effective energy. As a result, higher effective energy can be achieved.

[0241] according to Figure 10 You can also understand the following points.

[0242] [Excitation power P] p This applies to applications with power ratings between 1.5kW and 12kW (or, between 3kW and 6kW, especially the 1.5kW case).

[0243] When the magnification m is above 1.44 and below 4.01, a standardized effective energy conversion efficiency η of over 50% can be achieved. n_eff .

[0244] When the magnification m is above 1.64 and below 3.72, a standardized effective energy conversion efficiency η of over 63.21% can be achieved. n_eff .

[0245] When the magnification m is above 1.93 and below 3.40, a standardized effective energy conversion efficiency η of over 86.47% can be achieved. n_eff .

[0246] When the magnification m is above 1.99 and below 3.32, a standardized effective energy conversion efficiency η of over 90% can be achieved. n_eff .

[0247] according to Figure 10 You can also understand the following points.

[0248] [Excitation power P] p This applies to cases between 3kW and 12kW (or below 6kW) (especially the 3kW case).

[0249] When the magnification m is above 1.47 and below 5.1, a standardized effective energy conversion efficiency η of over 50% can be achieved. n_eff .

[0250] When the magnification m is above 1.69 and below 4.64, a standardized effective energy conversion efficiency η of over 63.21% can be achieved. n_eff .

[0251] When the amplification factor m is between 2.02 and 4.03, a standardized effective energy conversion efficiency η of over 86.47% can be achieved. n_eff .

[0252] When the magnification m is above 2.10 and below 4.03, a standardized effective energy conversion efficiency η of over 90% can be achieved. n_eff .

[0253] according to Figure 10 You can also understand the following points.

[0254] [Excitation power P] p This applies to cases between 6kW and 12kW (especially 6kW).

[0255] When the magnification m is above 1.50 and below 6.82, a standardized effective energy conversion efficiency η of over 50% can be achieved. n_eff .

[0256] When the magnification m is above 1.74 and below 6.20, a standardized effective energy conversion efficiency η of over 63.21% can be achieved. n_eff .

[0257] When the magnification m is between 2.11 and 4.99, a standardized effective energy conversion efficiency η of over 86.47% can be achieved. n_eff .

[0258] When the magnification m is above 2.22 and below 4.74, a standardized effective energy conversion efficiency η of over 90% can be achieved. n_eff .

[0259] according to Figure 10 You can also understand the following points.

[0260] [Excitation power P] P [For the 12kW case]

[0261] When the magnification m is above 1.53 and below 9.16, a standardized effective energy conversion efficiency η of over 50% can be achieved. n_eff .

[0262] When the magnification m is above 1.79 and below 7.94, a standardized effective energy conversion efficiency η of over 63.21% can be achieved. n_eff .

[0263] When the magnification m is above 2.19 and below 5.76, a standardized effective energy conversion efficiency η of over 86.47% can be achieved. n_eff .

[0264] When the magnification m is above 2.33 and below 5.44, a standardized effective energy conversion efficiency η of over 90% can be achieved. n_eff .

[0265] When designing the optical oscillator 3A of the laser device 1A, for example, the following design method is possible.

[0266] First, the normalized effective energy conversion efficiency η is calculated using the same method as the numerical calculations described above. n_eff The amplification factor *m* is set to achieve a standardized effective energy conversion efficiency of 50% or higher. The shapes and sizes of the first and second reflective parts are determined to achieve this amplification factor *m*. Therefore, an optical oscillator 3A capable of realizing a laser device 1A can be designed, resulting in the ability to design a device with a standardized effective energy conversion efficiency *η* of 50% or higher. n_eff Laser device 1A.

[0267] Next, various application examples of using the laser device disclosed in this embodiment will be described.

[0268] Figure 11 This is a schematic diagram of the first application example of a laser device. Figure 11 This is an example of using laser device 1A for laser ignition of an internal combustion engine 100 in an automobile, waste heat power generation, or similar application. In this case, laser device 1A is installed in the internal combustion engine such that the focusing position of the pulsed laser L2 output from laser device 1A is within the combustion chamber 101 of the internal combustion engine 100. As described above, laser device 1A has high effective energy, thus enabling efficient laser ignition.

[0269] Figure 12 This is a schematic diagram of the second application example of the laser device. Figure 12 This is an example of using laser device 1A for laser ignition in a jet engine 200. In this case, laser device 1A is installed in the jet engine 200 such that the focusing position of the pulsed laser L2 output from laser device 1A is within the combustion chamber 201 of the jet engine 200. As described above, laser device 1A has high effective energy, thus enabling efficient laser ignition.

[0270] Figure 13 This is a schematic diagram of the third application example of the laser device. Figure 13 The image shows the use of laser device 1A in laser processing such as marking and micro-machining. Figure 13 In the example shown, the laser device 1A (specifically, the storage unit 5) is mounted on the robotic arm 300. By operating the robotic arm 300, a pulsed laser L2 is irradiated onto the processing position of the workpiece 301. Therefore, laser processing such as marking and micro-machining described above can be performed. The laser device 1A has an effective energy that is higher than the energy of the excitation light L1, thus enabling efficient laser processing. Furthermore, the effective energy is the energy found in an Airy disk, thus also enabling micro-machining.

[0271] Figure 14 This is a schematic diagram of the fourth application example. Figure 14 The image shows laser processing, such as laser shot peening and laser forming, applied to the workpiece 302. Figure 11 The example shown is essentially the same as the one where the liquid jetting part 303 used in laser shot peening and laser forming processes is mounted in the receiving part 5, except that it is mounted in the receiving part 5. Figure 13 The third application example shown is the same. In Figure 14In the example shown, while supplying liquid 304 (e.g., water) from the liquid jetting unit 303 to the processing position of the workpiece 302, a pulsed laser L2 is irradiated onto the processing position, thereby performing the aforementioned laser peening and laser forming processes. The laser device 1A has effective energy higher than the energy of the excitation light L1, thus enabling efficient laser peening and laser forming processes. Furthermore, since the effective energy is the same as that found in Airy disks, it also allows for micro-machining.

[0272] Figure 15 This is a schematic diagram of application example 5. In Figure 15 In this example, laser device 1B, a modified example of a laser device, is used. Figure 15 The image shows an example of applying laser device 1B to laser-induced breakdown (LIBS) spectrophotometry on sample 400. The light emitted from the laser device 1B onto sample 400 is called inspection light L3.

[0273] Laser device 1B includes an excitation light supply unit 2, an optical oscillator 3A, and a focusing optical system 4. The excitation light supply unit 2, optical oscillator 3A, and focusing optical system 4 are the same as in laser device 1A, and therefore their description is omitted. In the fifth application example, the focusing optical system 4 is, for example, a lens. Laser device 1B includes the excitation light supply unit 2, optical oscillator 3A, and focusing optical system 4, and therefore, like laser device 1A, it can output pulsed laser L2. Laser device 1A is configured relative to sample 400 such that the focusing position of the pulsed laser L2 is located in the inspection area of ​​sample 400.

[0274] To analyze the light (hereinafter referred to as "inspection light") generated from the sample 400 by the irradiation of the pulsed laser L2, a beam splitter 401 is mounted on the laser device 1B via an optical fiber 402. The laser device 1B also includes an optical branch filter 7, a reflector 8, and a receiving unit 5B.

[0275] An optical branch filter 7 is disposed between lens 36 and condenser optical system 4. The optical branch filter 7 transmits pulsed laser L2 and reflects inspection light L3 from sample 400, i.e., the inspection light L3 focused by condenser optical system 4. The optical branch filter 7 is, for example, a wavelength selective filter.

[0276] The reflector 8 reflects the light reflected by the light branch filter 7 so that it is incident on one end of the optical fiber 402 installed in the housing 5B.

[0277] The receiving section 5B houses the incident optical system 23, optical oscillator 3A, focusing optical system 4, optical branch filter 7, and reflector 8 of the excitation light supply section 2. An optical fiber 21 is mounted on the first end wall 5a of the receiving section 5B, and an optical fiber 402 is mounted on the third end wall 5d. Furthermore, an opening 5c ​​for outputting pulsed laser L2 is formed on the second end wall 5b of the receiving section 5B. The opening 5c ​​is closed by the focusing optical system 4. Thus, similar to the case of the laser device 1A, pulsed laser L2 can be output from the receiving section 5B.

[0278] The pulsed laser L2 output from the laser device 1B is irradiated onto the inspection area positioned at the focal point of the pulsed laser L2. This causes laser-induced breakdown in the inspection area, resulting in plasma emission. The inspection light L3 generated by the plasma emission is then incident again on the focusing optical system 4 and reflected by the optical branch filter 7 towards the reflector 8. The reflected inspection light L3 is then reflected by the reflector 8 and incident on the optical fiber 21. The optical fiber 21 is connected to the beam splitter 401, thus enabling the beam splitter 401 to split the inspection light L3.

[0279] Laser device 1B can output the same pulsed laser L2 as laser device 1A. The pulsed laser L2 at the focusing position has a higher effective energy than the excitation light L1. Therefore, laser-induced breakdown can be generated efficiently.

[0280] Figure 16 This is a schematic diagram of application example 6. Figure 16 In this example, laser device 1C is used as a modification of the laser device. The structure of laser device 1C is identical to that of laser device 1A, except that it lacks the window component 6 and the opening 5c ​​is closed by the focusing optical system 4. Therefore, laser device 1C outputs the same pulsed laser L2 as laser device 1A.

[0281] exist Figure 16 The image shows an example of applying the laser device 1C to photoacoustic imaging. Specifically, the laser device 1C is used to irradiate an object 500, such as a biological tissue. In this case, the laser device 1C is configured relative to the object 500 in such a way that it focuses the pulsed laser L2 within the examination area of ​​the object 500.

[0282] When the area to be inspected is irradiated with pulsed laser L2, the area expands thermally. This thermal expansion generates ultrasonic waves US. These ultrasonic waves US are detected using detector 501 (e.g., a high-sensitivity micro-vibration detector).

[0283] The pulsed laser L2 at the focusing position has a higher effective energy than the excitation light L1. Therefore, it can efficiently generate thermal expansion and the resulting ultrasonic waves US.

[0284] Figure 17 This is a schematic diagram of application example number 7. In Figure 17 In this example, a laser device 1D, a variation of laser device 1A, is used. The main structural difference between laser device 1D and laser device 1A is that it also includes a laser operation unit 10. Laser device 1D will be described focusing on this difference. Figure 17 The image shows an example of applying a laser device 1D to eye surgery (such as glaucoma, cataract surgery, etc.).

[0285] The laser device 1D includes an excitation light supply unit 2, an optical oscillator 3A, a focusing optical system 4, a storage unit 5, and a laser operation unit 10. The excitation light supply unit 2, the optical oscillator 3A, and the focusing optical system 4 are the same as those in the laser device 1A, so their description is omitted.

[0286] The housing 5 houses the incident optical system 23 and the optical oscillator 3A of the excitation light supply unit. The housing 5 is identical to the housing in the sixth application example, except that it does not house the focusing optical system 4. The opening 5c ​​of the housing 5 is closed by the lens 36.

[0287] The laser operating unit 10 includes a light propagation optical system 11, a scanning unit 12, and a focusing optical system 4. The light propagation optical system 11 is an optical system that propagates the pulsed laser L2 toward the eye 600, which is the object of treatment. The light propagation optical system 11 can be composed of, for example, multiple lenses, mirrors, etc. The scanning unit 12 and a portion of the focusing optical system 4 also function as part of the light propagation optical system. The scanning unit 12 is the part that scans the pulsed laser L2 for treatment; for example, it includes a drive unit with a mirror and a scanning mirror. The focusing optical system 4, similar to that in the laser device 1A, focuses the pulsed laser L2.

[0288] Laser device 1D includes an optical oscillator 3A. Therefore, it outputs a pulsed laser L2 identical to that of the optical oscillator 3A in laser device 1A. Laser operation unit 10 includes a focusing optical system 4 to focus the pulsed laser L2. Therefore, laser device 1D has the same effect as laser device 1A. Therefore, the pulsed laser L2 at the focusing position has a higher effective energy relative to the excitation light L1. Therefore, it can efficiently treat the eye 600.

[0289] The various embodiments described above are illustrative of the present invention. The present invention is not limited to the illustrative embodiments, and is intended to encompass all modifications within the scope and meaning of the claims.

[0290] Figure 18 This is a schematic diagram illustrating the first modified example of an optical oscillator. For example... Figure 18As shown in the optical oscillator 3B, the first reflective portion 33 can also be separated from the laser medium 31. In this case, for example, the first reflective portion 33 can be supported by a support 37A that is transparent to the excitation light L1.

[0291] Figure 19 This is a schematic diagram illustrating a second modified example of an optical oscillator. For example... Figure 19 As shown in the optical oscillator 3C, at the point where the first reflector 33 bends, with Figure 18 The optical oscillator 3A shown is different. In this case, for example, the first reflector 33 can be supported by a support 37B that is transparent relative to the excitation light L1 and whose support surface is curved. If a ring-shaped pulsed laser L2 is obtained, the curvature direction of the first reflector 33 can also be... Figure 19 The opposite side of the direction shown.

[0292] Figure 20 This is a schematic diagram illustrating the third variation of an optical oscillator. (For example...) Figure 20 As shown in the optical oscillator 3D, the second reflector 35 can also be provided on the second end face 32b of the Q-switching element 32. In this case, the second end face 32b can be bent in such a way that the second reflector 35 is bent into the desired shape.

[0293] Figure 21 This is a schematic diagram representing the fourth variant of an optical oscillator. Figure 21 The optical oscillator 3E shown is at the point where the first reflector 33 bends, with Figure 20 The optical oscillator 3D shown is different. In this case, the first end face 31a of the laser medium 31 can be bent in the desired shape by bending the first reflective portion 33. If a ring-shaped pulsed laser L2 is obtained, the bending direction of the first reflective portion 33 can also be... Figure 21 The opposite side of the direction shown.

[0294] like Figure 22 As shown, when the first reflective portion 33 and the second reflective portion 35 are bent, the first reflective portion 33 and the second reflective portion 35 can also be reflective portions having R1 and R2 that can be expressed by the following formula. R1 is the radius of curvature of the first reflective portion 33, and R2 is the radius of curvature of the second reflective portion 35.

[0295] R1 = -2Lc / (m-1)

[0296] R2 = 2 mLc / (m-1)

[0297] In the above equations R1 and R2, m is used Figure 2 The magnification m (=d) is explained o / d i Lc is using Figure 1The resonator length Lc is specified.

[0298] d in magnification m i Corresponding to the size (diameter, etc.) of the second reflector 35, d o This corresponds to the diameter of the output pulsed laser (ring beam). Therefore, the laser device can be designed using the above formulas R1 and R2 to obtain a pulsed laser with a ring shape and the desired amplification m.

[0299] The saturable absorber, exemplified as a Q-switching element, can also be separated from the laser medium. When viewed from the optical axis of the optical oscillator, the size of the saturable absorber can be larger than the second reflector but smaller than the laser medium.

[0300] The laser device also includes a birefringent phase matching (BPM), a quasi-phase matching (QPM), or a combination of both nonlinear optical systems (e.g., nonlinear optical elements) for transforming the annular laser output from the unstable resonator (e.g., the annular beam-shaped pulsed laser L2 described in the above embodiment). In this case, for example, transformations from a fundamental wavelength of 1 μm (the laser oscillation wavelength depends on the added element that becomes the emission center) to short wavelengths in the visible region, ultraviolet region, etc., obtained by combinations of high frequencies or sum frequencies, further including parameterization processes or difference frequencies, and transformations from the mid-infrared region to terahertz waves in combinations of parameterization processes or difference frequencies, further including high frequencies or sum frequencies, can also be performed efficiently, thus being effective for processing and measurement. Furthermore, the aforementioned nonlinear optical systems (e.g., nonlinear optical elements) are also useful for pulse shaping that includes compression and elongation of pulses utilizing spectral chirps.

[0301] The various embodiments and modifications described above can be appropriately combined without departing from the spirit of the present invention.

[0302] Explanation of symbols

[0303] 1A, 1B, 1C, 1D… Laser device, 2… Excitation light supply unit, 3A, 3B, 3C, 3D, 3E… Optical oscillator, 4… Focusing optical system, 31… Laser medium, 32… Q-switch element, 33… First reflector, 34… Support, 35… Second reflector, 36… Lens, L1… Excitation light, L2… Pulsed laser (ring laser), UR… Unstable resonator.

Claims

1. An optical oscillator, in, include: The first reflector reflects light with a first wavelength; A laser medium that is excited by excitation light of a second wavelength, which is different from the first wavelength, and emits light of the first wavelength; A second reflector, disposed opposite to the first reflector relative to the laser medium, together with the first reflector forms an unstable resonator that outputs a ring-shaped laser having the first wavelength; and A saturable absorber, disposed on the opposite side of the first reflective portion relative to the laser medium, exhibits increased transmittance with the absorption of light having the first wavelength. Set the power of the excitation light to P. p Let the inner diameter of the ring laser be d. i Set the outer diameter to d o , will d o / d i When the magnification is set to m, the magnification m satisfies the following equation (1): a0+a1Log(P p )≤m≤b0+b1P p +b2P p 2 ···(1) in, a0＝1.421 a1＝0.10678 b0＝2.8698 b1＝0.79408 b2＝－0.022536， P p The unit is kW, d i The unit is mm, d o The unit is mm. When viewed from the first reflective portion, the size of the second reflective portion is smaller than the size of the first reflective portion.

2. A laser device, in, include: The optical oscillator according to claim 1; and An excitation light supply unit outputs the excitation light supplied to the laser medium.

3. The laser device according to claim 2, wherein, Also includes: A focusing optical system that focuses the ring laser output from the unstable resonator.

4. The laser device according to claim 2, wherein, Also includes: A nonlinear optical system for transforming the ring-shaped laser output from the unstable resonator.

5. A design method for an optical oscillator, wherein, The optical oscillator includes: a first reflector that reflects light having a first wavelength; a laser medium that is excited by excitation light of a second wavelength different from the first wavelength to emit light of the first wavelength; a second reflector disposed opposite to the laser medium on the opposite side of the first reflector, forming together with the first reflector an unstable resonator that outputs a ring-shaped laser having the first wavelength; and a saturable absorber disposed opposite to the laser medium on the opposite side of the first reflector, whose transmittance increases with the absorption of light having the first wavelength. The optical oscillator design method, in which the annular laser output from the unstable resonator is focused by supplying the excitation light to the laser medium, defines the energy conversion efficiency of the Airy disk of the annular laser relative to the energy of the excitation light as the effective energy conversion efficiency η. eff Let the inner diameter of the ring laser be d. i Set the outer diameter to d o , will d o / d i When the magnification is set to m, Obtain the transformation efficiency distribution, where the transformation efficiency distribution is the effective energy transformation efficiency η. eff Relative to the distribution of the magnification m, Set the amplification factor m such that the effective energy conversion efficiency η is achieved. eff The standardized effective energy conversion efficiency, obtained by standardizing the maximum effective energy conversion efficiency in the aforementioned conversion efficiency distribution, is above 50%. Viewed from the first reflective portion, the size of the second reflective portion is smaller than the size of the first reflective portion. Where, η eff The unit is %, d i The unit is mm, d o The unit is mm.

6. A laser device, in, include: An optical oscillator includes: a first reflector that reflects light having a first wavelength; a laser medium that is excited by excitation light of a second wavelength different from the first wavelength to emit light of the first wavelength; a second reflector disposed opposite to the laser medium on the opposite side of the first reflector, forming, together with the first reflector, an unstable resonator that outputs a ring-shaped laser having the first wavelength; and a saturable absorber disposed opposite to the laser medium on the opposite side of the first reflector, whose transmittance increases with absorption of light having the first wavelength; and An excitation light supply unit outputs the excitation light supplied to the laser medium. Let the inner diameter of the ring laser be d. i Set the outer diameter to d o , will d o / d i When the magnification is set to m, the magnification m is greater than 2. 1 / 2 , where d i The unit is mm, d o The unit is mm. Viewed from the first reflective portion, the size of the second reflective portion is smaller than the size of the first reflective portion. When the power of the excitation light is 1.5 kW or more and 12 kW or less, the amplification m is 1.44 or more and 4.01 or less. When the power of the excitation light is 3kW or more and 12kW or less, the amplification m is 1.47 or more and 5.1 or less, or, When the power of the excitation light is 6kW or more and 12kW or less, the amplification m is 1.50 or more and 6.82 or less.

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