Time sequence beam combining device based on laser nonlinear frequency conversion

Abstract

The invention discloses a time sequence beam combining device based on laser nonlinear frequency conversion. The laser beam combining device comprises N light paths, N is larger than or equal to 2, and the first light path comprises a first nonlinear frequency conversion module used for converting fundamental frequency pulse laser into a first frequency conversion laser beam; each nth light path comprises a first double-color beam combiner and a first nonlinear frequency conversion module which are sequentially arranged along the light path, and the first double-color beam combiner is used for coaxially combining the incident fundamental frequency pulse laser of the light path and the (n-1) th frequency conversion laser beam from the (n-1) th light path; the first nonlinear frequency conversion module performs frequency conversion on the fundamental frequency pulse laser in the coaxial combined beam and obtains an nth frequency conversion laser beam with the repetition frequency of nf through an (n-1) th frequency conversion laser beam, n is greater than or equal to 2 and less than or equal to N, the N beams of fundamental frequency pulse laser have the same repetition frequency f, pulse sequences are not overlapped in time, and the n is greater than or equal to 2 and less than or equal to N; and the laser beam combining device outputs a beam-combined variable-frequency laser beam of which the repetition frequency is Nf and the wavelength is smaller than that of the fundamental frequency pulse laser beam.

Description

Technical Field

[0001] The present application relates to the field of laser beam combining technology, and in particular to a sequential beam combining device based on laser nonlinear frequency conversion. Background Art

[0002] High-power and high-beam-quality lasers have important applications in defense, advanced manufacturing, biomedicine and other fields. The most commonly used solid-state laser wavelength is about 1μm. Nonlinear frequency conversion technology can expand the wavelength range of the laser and obtain lasers with shorter wavelengths such as 532nm to better meet the application needs of technical material processing. Therefore, the research on high-power frequency conversion technology of lasers is of great significance and application value. The main goals of laser development are high power and high beam quality. Therefore, how to obtain a wavelength range that meets the requirements through frequency doubling or sum frequency while ensuring the power and beam quality of the output frequency conversion light is a requirement currently faced by development.

[0003] The extracavity frequency conversion structure has the advantages of good frequency conversion polarization output and stable output power, which can minimize the complexity of the system. However, since the performance of the doubled frequency light or summed frequency light in the current technical solution is heavily dependent on the performance of the fundamental frequency light, if the average power or beam quality of the fundamental frequency light is difficult to reach a high level, then the doubled frequency light or summed frequency light will also be difficult to achieve high-power and high-beam quality output. Therefore, various technical means are often used to improve the average power and beam quality of the fundamental frequency light to achieve higher-power doubled frequency light or summed frequency light output, but the difficulty is increasing, and the power of the frequency conversion light is also difficult to further increase. Summary of the invention

[0004] The purpose of the present application is to provide a laser beam combining device for solving the problem of power limitation of nonlinear frequency conversion of lasers, so as to increase the output power of frequency conversion light when the available single beam fundamental frequency light power is limited.

[0005] The present application provides a laser beam combining device, comprising N optical paths, N ≥ 2, wherein

[0006] The first optical path includes a first nonlinear frequency conversion module, which is used to convert the base frequency pulse laser into a first frequency conversion laser beam;

[0007] Each n-th optical path includes a first two-color beam combining mirror and a first nonlinear frequency conversion module sequentially arranged along the optical path, wherein the first two-color beam combining mirror is used to coaxially combine the incident fundamental frequency pulse laser of the optical path with the n-1th frequency conversion laser from the n-1th optical path, and the first nonlinear frequency conversion module converts the fundamental frequency pulse laser in the coaxial beam combination and obtains the n-th frequency conversion laser beam with a repetition frequency of nf through the n-1th frequency conversion laser, 2≤n≤N,

[0008] Among them, the N beams of fundamental frequency pulse laser have the same repetition frequency f and the pulse sequences do not overlap in time.

[0009] The laser beam combining device outputs a combined frequency-variable laser beam with a repetition frequency of Nf and a wavelength smaller than the wavelength of the fundamental frequency pulse laser beam.

[0010] Preferably, each (n-1)th optical path further comprises a first dichroic beam splitter located behind the first nonlinear frequency conversion module, for filtering out the fundamental frequency pulse laser in the frequency conversion laser beam from the first nonlinear frequency conversion module.

[0011] Preferably, each n-1th optical path also includes a beam shaping element located between the first dichroic beam splitter and the first dichroic beam combiner of the nth optical path, for shaping the frequency-converted laser beam from which the fundamental frequency pulse laser is filtered out into a frequency-converted laser beam that matches the incident fundamental frequency pulse laser beam pattern of the first dichroic beam combiner.

[0012] Preferably, the N fundamental frequency pulse laser beams are respectively fundamental frequency pulse laser beams having a first wavelength, the first nonlinear frequency conversion module includes a first frequency doubling crystal, which is used to frequency double the incident fundamental frequency pulse laser of the first wavelength into a frequency-doubled light having a wavelength of half the first wavelength, and the laser beam combining device outputs a combined frequency-converted laser beam having a wavelength of half the first wavelength.

[0013] Preferably, the N fundamental frequency pulsed laser beams respectively include a combined fundamental frequency pulsed laser beam having a first wavelength and a second wavelength, the first nonlinear frequency conversion module includes a sum frequency crystal, which is used to convert the combined fundamental frequency pulsed laser beam having the first wavelength and the second wavelength into a sum frequency light having a third wavelength, and the laser beam combining device outputs a combined frequency-converted laser beam having a wavelength of the third wavelength.

[0014] Preferably, each of the N optical paths includes a second dichroic beam combining mirror for coaxially combining a fundamental frequency pulse laser with a first wavelength and a fundamental frequency pulse laser with a second wavelength to obtain a combined fundamental frequency pulse laser beam with the first wavelength and the second wavelength.

[0015] Preferably, each of the N optical paths includes a second nonlinear frequency conversion module having a second frequency doubling crystal, which is used to double the frequency of a fundamental frequency pulse laser having a first wavelength, and output a fundamental frequency pulse laser beam having the first wavelength and a frequency doubling pulse laser beam having half the wavelength as the combined fundamental frequency pulse laser beam having the first wavelength and the second wavelength.

[0016] Preferably, the pulse width of each beam of fundamental frequency pulse laser is t, and the pulse time interval is 1 / f; preferably, the pulse time delay between two adjacent beams of the fundamental frequency pulse laser is at least 2 times the pulse width t and at most 1 / Nf.

[0017] Preferably, a dielectric film with high transmittance to fundamental frequency pulse laser and high reflectivity to variable frequency laser is formed on the surface of the first two-color beam combining mirror.

[0018] Preferably, the fundamental frequency pulse laser pulse width includes millisecond, microsecond, nanosecond, picosecond, and femtosecond laser pulses.

[0019] The beneficial effects of the present disclosure are as follows:

[0020] The sequential beam combining device based on laser nonlinear frequency conversion provided by the present application does not require the use of any active control device, solves the problem that the average power is difficult to increase in extracavity frequency conversion, and greatly improves the frequency conversion power. The sequential beam combining device based on laser nonlinear frequency conversion in the present application has no strict requirements on the frequency, phase, polarization, etc. of the fundamental frequency pulse light; the optical elements used to form the beam combining device have a simple structure, do not require a precise control system, and have high stability; the present application does not have the phenomenon of thermal deformation of the dispersion element leading to deterioration of the beam quality, and the number of synthesized sub-laser beams is only limited by the repetition frequency and pulse interval of the fundamental frequency pulse light. The laser sequential beam combining device of the present application can realize the coaxial beam combining of frequency conversion lasers. In theory, the beam quality of the synthesized light is equivalent to the frequency conversion laser obtained by frequency conversion of the nonlinear frequency conversion module, and will not drop sharply due to the increase in the number of lasers that have been frequency converted, thereby achieving the improvement of the frequency conversion laser output power while keeping the beam quality unchanged. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The specific implementation methods of the present disclosure are further described in detail below with reference to the accompanying drawings.

[0022] Figure 1 is a schematic structural diagram of a sequential beam combining device based on laser nonlinear frequency conversion according to the first embodiment of the present application;

[0023] Figure 2 is a schematic structural diagram of a sequential beam combining device based on laser nonlinear frequency conversion according to a second embodiment of the present application;

[0024] Figure 3 is a schematic structural diagram of a sequential beam combining device based on laser nonlinear frequency conversion according to a third embodiment of the present application;

[0025] Figure 4 It is a structural schematic diagram of a sequential beam combining device based on laser nonlinear frequency conversion according to a first specific embodiment of the present application;

[0026] Figure 5 It is a waveform diagram of three fundamental frequency pulsed lasers and a waveform diagram of pulsed lasers after time sequence synthesis in the first specific embodiment of the present application;

[0027] Figure 6 It is a structural schematic diagram of a sequential beam combining device based on laser nonlinear frequency conversion according to a second specific embodiment of the present application;

[0028] Figure 71 is a pulsed laser waveform diagram of Example 2 of the present application, (a) is a waveform diagram of the first frequency-doubled sub-laser pulse, (b) is a waveform diagram of the second frequency-doubled sub-laser pulse, and (c) is a waveform diagram of the laser pulse after the two frequency-doubled laser beams are combined;

[0029] Figure 8 1 is the pulsed laser spot diagram of Example 2 of the present application, (a) is the spot diagram of the first frequency-doubled sub-laser, (b) is the spot diagram of the second frequency-doubled sub-laser, and (c) is the laser spot diagram after the two frequency-doubled laser beams are combined;

[0030] Fig. 9 is a schematic structural diagram of a sequential beam combining device based on laser nonlinear frequency conversion according to a third specific embodiment of the present invention;

[0031] Fig.10 It is a structural schematic diagram of a sequential beam combining device based on laser nonlinear frequency conversion according to a fourth specific embodiment of the present invention. DETAILED DESCRIPTION

[0032] The terms “on”, “formed on” and “disposed on” in the present disclosure may mean that one layer is directly formed or disposed on another layer, or may mean that one layer is indirectly formed or disposed on another layer, i.e., there are other layers between the two layers.

[0033] It should be noted that, although the terms "first", "second", etc. may be used herein to describe various parts, components, elements, regions, layers and / or parts, these parts, components, elements, regions, layers and / or parts should not be limited by these terms. Instead, these terms are used to distinguish one part, component, element, region, layer and / or part from another. Thus, for example, the first part, first member, first element, first region, first layer and / or first part discussed below may be referred to as the second part, second member, second element, second region, second layer and / or second part without departing from the teachings of the present disclosure.

[0034] In the present disclosure, unless otherwise specified, the term "same-layer arrangement" used refers to two layers, parts, components, elements or parts that can be formed by the same preparation process (such as a patterning process, etc.), and the two layers, parts, components, elements or parts are generally formed of the same material. For example, two or more functional layers are arranged in the same layer, which means that these functional layers arranged in the same layer can be formed using the same material layer and the same preparation process, thereby simplifying the preparation process of the display substrate.

[0035] Figure 1 The present application provides a sequential beam combining device based on laser nonlinear frequency conversion, which has N optical paths, N ≥ 2, including N beams of fundamental frequency pulse laser 1101, 1102, ..., 110 N, N first nonlinear frequency conversion modules 1201, 1202, ..., 120 corresponding to the N beams of fundamental frequency pulse lasers N , (In this article, the fundamental frequency pulse laser beam of each optical path is also referred to as fundamental frequency sub-beam, fundamental frequency sub-laser, fundamental frequency pulse sub-beam, etc.), N-1 dichroic beam splitters 1301, 1302, ..., 130 N-1 and N-1 first two-color beam combining mirrors 1401, 1402, ..., 140 N-1 , the pulse repetition frequency f of N fundamental frequency pulse lasers is the same, but the pulse sequences are staggered in time.

[0036] The first optical path includes a first nonlinear frequency conversion module 1201 and a dichroic beam splitter 1301 which are sequentially arranged along the optical path. The first nonlinear frequency conversion module 1201 is used to convert the incident first fundamental frequency sub-beam 1101 into a first frequency-converted sub-beam. The dichroic beam splitter 1301 is used to filter out the fundamental frequency pulse laser transmission in the first frequency-converted sub-beam and transmit the frequency-converted laser beam of the first optical path to the second optical path.

[0037] Each n-th optical path, 2≤n≤N, includes a first two-color beam combiner 140 arranged in sequence along the optical path. n-1 and the first nonlinear frequency conversion module 120 n , the first two-color beam combining mirror 140 n-1 The nth fundamental frequency sub-beam 110 is used to inject the optical path n The first nonlinear frequency conversion module 120 is coaxially combined with the n-1th frequency conversion laser beam from the n-1th optical path. n The nth fundamental frequency sub-beam 110 in the coaxial combined laser beam is n The nth frequency-converted laser beam with a repetition frequency of nf is obtained by frequency conversion and passing through the n-1th frequency-converted laser. Because each fundamental frequency sub-beam has the same repetition frequency f and the pulse sequence does not overlap in time, the nth fundamental frequency sub-beam 110 n The optical pulse of the n-1th frequency conversion laser beam does not exist in the first nonlinear frequency conversion module 120 at the same time. n Therefore, no interaction occurs, and each optical pulse of the n-1th frequency conversion laser beam passes through the nonlinear frequency conversion module 120 n After that, due to its nonlinear frequency conversion module 120 n The phase matching condition for continued frequency conversion and the threshold condition for reverse conversion to the fundamental frequency light are not met in the nth fundamental frequency sub-beam 110. nIt is frequency-converted into the nth frequency-converted sub-beam and is coaxially combined with the n-1th frequency-converted laser beam into one beam, completing the time-sequential beam combining of the frequency-converted lasers. The repetition frequency of the nth frequency-converted laser pulse after combining becomes nf, and so on, until the time-sequential beam combining of all N frequency-converted laser beams is completed, and the Nth combined frequency-converted laser beam with a repetition frequency of Nf after combining and a wavelength less than the wavelength of the fundamental frequency pulse laser beam is obtained.

[0038] The sequential beam combining device based on laser nonlinear frequency conversion in the present application does not use any active control device. It obtains N times the fundamental frequency repetition frequency f by sequential beam combining, which greatly improves the frequency conversion power and solves the problem of low average power in extracavity frequency conversion.

[0039] The timing beam combining device based on laser nonlinear frequency conversion of the present application has no strict requirements on the frequency, phase, polarization, etc. of the fundamental frequency pulse light, does not require a precise control system, has a simple structure, is easy to implement and has high stability. The beam combining device of the present application does not include a dispersion element, and there will be no deterioration of the beam quality due to thermal deformation. The number of sub-laser beams used for beam combining is only limited by the repetition frequency and pulse interval of the fundamental frequency pulse light. The present application combines the frequency-converted lasers coaxially. Ideally, the beam quality of the synthesized light is equivalent to that of the laser beam after frequency conversion by the nonlinear frequency conversion module, and will not drop sharply due to the increase in the number of sub-frequency conversion lasers. The output power of the frequency-converted laser can be increased while maintaining the beam quality.

[0040] As a preferred embodiment, Figure 1 As shown, the n-1th optical path also includes the first nonlinear frequency conversion module 120 n-1 The first dichroic beam splitter 130 at the rear n-1 , used to filter out the fundamental frequency pulse laser in the n-1th frequency conversion laser beam from the first nonlinear frequency conversion module of the optical path, and transmit the n-1th frequency conversion laser beam to the first two-color beam combining mirror 140 of the nth optical path n-1 .

[0041] As a preferred embodiment, Figure 2 As shown, the n-1th optical path also includes a first dichroic beam splitter 130 n-1 and the first dichroic beam combiner 140 of the nth optical path n-1 The beam shaping element 150 between n-1 , used to shape the n-1th frequency conversion laser beam after filtering out the fundamental frequency pulse laser into a frequency conversion laser power density that meets the requirements of efficient frequency conversion and is connected to the nth fundamental frequency sub-beam 110 n Keep beam modes matched when combining beams.

[0042] As a preferred embodiment, the N fundamental frequency sub-beams are fundamental frequency pulse laser beams with a first wavelength λ1, and each first nonlinear frequency conversion module includes a first frequency doubling crystal, which satisfies the phase matching condition of the fundamental frequency pulse laser frequency doubling, and converts the incident fundamental frequency sub-beam with the first wavelength λ1 into a frequency doubling light with a wavelength of λ1 / 2. For the nth optical path, the first nonlinear frequency conversion module 120 n The incident light comes from the first two-color beam combiner 140 n-1 The nth fundamental frequency sub-beam with a wavelength of λ1 and the n-1th frequency-doubled laser with a wavelength of λ1 / 2 and a repetition frequency of (n-1)f from the n-1th optical path are coaxially combined laser beams. The light pulses of the nth fundamental frequency sub-beam and the light pulses of the n-1th frequency-doubled laser do not exist in the nonlinear frequency conversion module 120 at the same time. n Therefore, no interaction occurs, and the energy of the light pulse of the n-1th frequency-doubled laser does not change significantly after passing through the nonlinear frequency conversion module, while the nth fundamental frequency sub-beam generates a frequency-doubled sub-laser, so that the n-1th frequency-doubled laser beam and the nth frequency-doubled sub-laser are coaxially combined into the nth frequency-doubled laser beam, completing the sequential combination of the nth frequency-doubled laser. The repetition frequency of the frequency-converted laser pulse after the combination is nf, and the wavelength is λ1 / 2.

[0043] As a preferred embodiment, N fundamental frequency sub-beams 1101, 1102, ..., 110 N The N fundamental frequency sub-beams have the same pulse repetition frequency f, but the pulse sequences are staggered in time. The first nonlinear frequency conversion module includes a sum frequency crystal, which satisfies the phase matching condition of the fundamental frequency pulse laser sum frequency, and converts the incident combined fundamental frequency sub-beams with the first wavelength λ1 and the second wavelength λ2 with the same repetition frequency and time overlap into a sum frequency light with a third wavelength λ3, where the wavelength λ3 = λ1×λ2 / (λ1+λ2). As a further preferred embodiment, Figure 3 As shown, the n-1th optical path also includes a second dichroic beam combining mirror 160 n-1 , used to transmit the fundamental frequency pulse laser 111 of the first wavelength λ1 having the same repetition frequency and time overlap n-1 and the fundamental frequency pulse laser 112 of the second wavelength λ2 n-1 Coaxial beam combination to obtain the fundamental frequency sub-beam 110 n-1 For the nth optical path, the first nonlinear frequency conversion module 120 n The beam from the first two-color beam combiner 140 n-1 The nth fundamental frequency sub-beam 110 with wavelengths λ1 and λ2 n The n-1th fundamental frequency sub-beam 110 is coaxially combined with the n-1th beam of sum frequency laser light with a wavelength of λ3 and a repetition frequency of (n-1)f from the n-1th optical path. nThe optical pulse of the n-1th sum frequency laser beam does not exist in the nonlinear frequency conversion module 120 at the same time. n Therefore, no interaction occurs, and the energy of the light pulse of the n-1th sum frequency laser does not change significantly after passing through the nonlinear frequency conversion module, while the nth fundamental frequency sub-beam generates a sum frequency sub-laser, so that the n-1th sum frequency laser beam and the nth sum frequency sub-laser are coaxially combined into the nth sum frequency laser beam, completing the temporal combination of the nth sum frequency laser, and the repetition frequency of the frequency conversion laser pulse after the combination is nf, and the wavelength is λ3.

[0044] As a further preferred embodiment, each of the N optical paths includes a second nonlinear frequency conversion module having a second frequency doubling crystal, which is used to double the frequency of a fundamental frequency pulse laser having a first wavelength λ1, and output a fundamental frequency pulse laser beam having the first wavelength λ1 and a frequency doubling pulse laser beam having half the first wavelength λ1 / 2 as the fundamental frequency sub-beam having the first wavelength λ1 and the second wavelength λ1 / 2.

[0045] As a preferred embodiment, the pulse width of each beam of fundamental frequency pulse laser is t, and the pulse time interval is 1 / f; more preferably, the pulse time delay between the fundamental frequency pulse lasers of two adjacent optical paths is at least 2 times the pulse width t and at most 1 / Nf.

[0046] As a preferred embodiment, a dielectric film with high transmittance to baseband pulse laser and high reflection to frequency conversion laser is formed on the surface of the two-color beam combining mirror; or a dielectric film with high reflection to baseband pulse laser and high transmittance to frequency conversion laser is formed on the surface of the two-color beam combining mirror.

[0047] Preferably, the pulse width of each fundamental frequency pulse laser includes millisecond, microsecond, nanosecond, picosecond, and femtosecond laser pulses.

[0048] Preferably, the wavelength of the fundamental frequency pulse laser includes but is not limited to 1064nm, 1319nm, 1030nm, 532nm, and 2100nm.

[0049] Preferably, the nonlinear frequency conversion module includes but is not limited to LBO, KTP, CLBO, PPLN, BBO crystals, and both end faces of the nonlinear frequency conversion module are coated with a dielectric film that increases the transmittance of the fundamental frequency pulse laser and the frequency conversion laser.

[0050] Figure 4It is a schematic structural diagram of a sequential beam combining device 200 based on laser nonlinear frequency conversion of the first specific embodiment of the present application. The sequential beam combining device 200 includes three fundamental frequency sub-beams 2101, 2102, 2103, three nonlinear frequency conversion modules 2201, 2202, 2203, two dichroic beam splitters 2301, 2302, two beam shaping elements 2501, 2502 and two dichroic beam combining mirrors 2401, 2402, constituting a beam combining device including the first, second and third optical paths for realizing the sequential beam combining of three fundamental frequency pulsed lasers. The first optical path includes a nonlinear frequency conversion module 2201, a dichroic beam splitter 2301 and a beam shaping element 2501 arranged in sequence; the second optical path includes a dichroic beam combining mirror 2401, a nonlinear frequency conversion module 2202, a dichroic beam splitter 2302 and a beam shaping element 2502 arranged in sequence; the third optical path includes a dichroic beam combining mirror 2402 and a nonlinear frequency conversion module 2203 arranged in sequence, and outputs a frequency-converted laser beam after the third optical path is combined.

[0051] The three fundamental frequency sub-beams 2101, 2102, 2103 correspond to the three nonlinear frequency conversion modules 2201, 2202, 2203 respectively, and their pulse repetition frequencies are the same but the pulse sequences are staggered in time. As an example, the repetition frequency of each fundamental frequency sub-beam is 100kHz, the pulse width is 10ps, the wavelength is 1064nm, and the pulse delay between the two fundamental frequency pulse lasers of two adjacent optical paths is 1μs.

[0052] The nonlinear frequency conversion module includes a KTP frequency doubling crystal. The size of the KTP crystal is 3mm×3mm×20mm, and the size of the light opening on both sides is 3mm×3mm. The two ends of the KTP crystal are coated with a 1064nm&532nm dual-wavelength anti-reflection film. The KTP crystal is equipped with a crystal temperature control device with an accuracy of 0.1℃ for adjusting the temperature.

[0053] The first optical path and the second optical path include dichroic beam splitters 2301 and 2302 respectively. The dichroic beam splitters are plane mirrors coated with a 532nm 45° total reflection film and a 1064nm anti-reflection film, and are used to filter the 1064nm fundamental frequency light and reflect the 532nm double frequency light to the next optical path.

[0054] The second optical path and the third optical path include two-color beam combiner mirrors 2401 and 2402 respectively. The two-color beam combiner mirrors are plane mirrors coated with a 532nm 45° total reflection film and a 1064nm anti-reflection film, and are used to coaxially combine the 532nm doubled frequency light from the previous optical path with the incident 1064nm fundamental frequency pulse laser 210 of the optical path.

[0055] In this example, the beam shaping elements 2501 and 2502 are coated with a 532nm anti-reflection film, and are used to perform beam shaping on the 532nm doubled frequency light with a repetition frequency of 100kHz in the first optical path and the 532nm doubled frequency light with a repetition frequency of 200kHz in the second optical path, respectively, so that the beam modes are matched when they are combined with the corresponding second fundamental frequency sub-beam 2102 and third fundamental frequency sub-beam 2103. Preferably, the beam shaping element can be a lens for beam shaping, such as a ball lens or a ball lens group.

[0056] In this example, each antireflection film has a transmittance greater than 99.8%, and the total reflection film has a reflectivity greater than 99.8%.

[0057] Specifically, the 1064nm fundamental frequency sub-beam 2101 is injected into the nonlinear frequency conversion module 2201 of the first optical path to generate the first 532nm frequency conversion sub-laser I. After the remaining 1064nm fundamental frequency pulse laser is filtered out by the dichroic beam splitter 2301, the 532nm frequency conversion sub-laser of the first optical path is combined with the 1064nm fundamental frequency sub-beam 2102 through the beam shaping element 2501 to keep the beam mode matching. The 532nm frequency conversion sub-laser of the first optical path then passes through the dichroic beam combining mirror 2401 of the second optical path to coaxially combine with the second 1064nm fundamental frequency sub-beam 2102 and then is injected into the second nonlinear frequency conversion module 2202 together. The optical pulse of the 532nm frequency conversion sub-laser in the first optical path and the optical pulse of the second 1064nm fundamental frequency sub-beam 2102 do not exist in the nonlinear frequency conversion module 2202 at the same time, so there is no interaction between them. When the pulse of the 532nm frequency conversion sub-laser in the first optical path passes through the second nonlinear frequency conversion module 2202, the fundamental frequency light has been filtered out and it is difficult to reversely convert it to the 1064nm wavelength. Therefore, there is no loss of energy in the frequency conversion laser pulse, and the second 1064nm fundamental frequency sub-beam 2102 can generate the second 532nm frequency conversion sub-laser II through the frequency doubling process, so that the 532nm frequency conversion sub-laser I and the 532nm frequency conversion sub-laser II in the first optical path are coaxially combined into the frequency conversion laser beam of the second optical path, completing the time combination of the first frequency conversion laser, and the repetition frequency of the frequency conversion laser pulse after the combination is changed from 100kHz to 200kHz. The 200kHz repetition frequency 532nm frequency conversion laser of the second optical path is filtered out by the dichroic beam splitter 2302 to remove the remaining 1064nm fundamental frequency pulse laser, and then is combined with the third fundamental frequency sub-beam 2103 in the third optical path through the beam shaping element 2502 to maintain beam mode matching. Similarly, the frequency-converted laser of the second optical path is then coaxially combined with the third 1064nm fundamental frequency sub-beam 2103 through the two-color beam combining mirror 2402 of the third optical path, and then injected into the nonlinear frequency conversion module 2203 of the third optical path. The third 1064nm fundamental frequency sub-beam 2103 generates a 532nm frequency-converted sub-laser III through the frequency doubling process, so that the frequency-converted laser of the second optical path and the 532nm frequency-converted sub-laser III are coaxially combined into the frequency-converted laser beam of the third optical path, completing the time-sequential combination of the second frequency-converted laser, thereby combining three fundamental frequency sub-beams with a wavelength of 1064nm and a repetition frequency of 100kHz into a combined frequency-converted laser pulse with a wavelength of 532nm and a repetition frequency of 300kHz. The waveform diagram of the three fundamental frequency pulse lasers in this example and the schematic diagram of the pulse laser waveform after time-sequential synthesis are shown in FIG. Figure 5 shown.

[0058] Figure 6It is a schematic diagram of the structure of a sequential beam combining device 300 based on laser nonlinear frequency conversion in the second specific embodiment of the present invention. The sequential beam combining device 300 includes two beams of fundamental frequency pulsed lasers 3101, 3102, two nonlinear frequency conversion modules 3201, 3202, a dichroic beam splitter 3301, a beam shaping element 3501 and a dichroic beam combining mirror 3401, forming two optical paths including the first and second optical paths for realizing the sequential beam combining of two beams of fundamental frequency pulsed lasers. The first optical path includes a nonlinear frequency conversion module 3201, a dichroic beam splitter 3301 and a beam shaping element 3501 arranged in sequence; the second optical path includes a dichroic beam combining mirror 3401 and a second nonlinear frequency conversion module 3202 arranged in sequence, and outputs the frequency-converted laser beam after the second beam combining.

[0059] The two fundamental frequency sub-beams 3101 and 3102 correspond to two nonlinear frequency conversion modules 3201 and 3202 respectively. They have the same pulse repetition frequency but the pulse sequences are staggered in time.

[0060] As Example 1, the repetition frequency of the fundamental frequency sub-beams 3101 and 3102 is 1 MHz, the pulse width is 500 fs, the wavelength is 1030 nm, and the pulse delay between the fundamental frequency sub-beams 3101 and 3102 is 100 ns.

[0061] Nonlinear frequency conversion modules 3201 and 3202 are both LBO frequency doubling crystals. The size of the LBO crystal is 4mm×4mm×20mm, the size of the light openings on both sides is 4mm×4mm, and the phase matching angle of the LBO crystal is θ=90°, φ=0°. Both ends of the LBO crystal are coated with 1030nm&515nm dual-wavelength anti-reflection film, and the LBO crystal is equipped with a crystal temperature control device with an accuracy of 0.1℃ for adjusting the temperature.

[0062] The dichroic beam splitter 3301 is a plane mirror coated with a 515nm 45° total reflection film and a 1030nm anti-reflection film, and is used to filter the 1030nm fundamental frequency light and reflect the 515nm double frequency light to the second optical path.

[0063] The dichroic beam combiner 3401 is a plane mirror coated with a 515nm 45° total reflection film and a 1030nm anti-reflection film, and is used to coaxially combine the frequency-doubled light generated by the fundamental frequency sub-beam 3101 with the fundamental frequency sub-beam 3102.

[0064] In this example, the beam shaping element 3501 is coated with a 515 nm anti-reflection film and is used to beam shape the doubled frequency light generated by the fundamental frequency sub-beam 3101 so as to maintain beam mode matching when the doubled frequency light is combined with the fundamental frequency sub-beam 3102 .

[0065] In this example, the antireflection film has a transmittance greater than 99.8%, and the total reflection film has a reflectivity greater than 99.8%.

[0066] The 1030nm fundamental frequency sub-beam 3101 is injected into the nonlinear frequency conversion module 3201 to generate the first optical path 515nm frequency conversion sub-laser. After the remaining 1030nm fundamental frequency pulse laser is filtered out by the two-color beam splitter 3301, the first optical path 515nm frequency conversion laser is combined with the 1030nm fundamental frequency sub-beam 3101 through the beam shaping element 3501 to maintain beam mode matching. The first optical path 515nm frequency conversion laser is then coaxially combined with the 1030nm fundamental frequency sub-beam 3102 through the two-color beam combiner 3401 and injected into the nonlinear frequency conversion module 3202. The 1030nm fundamental frequency sub-beam 3102 generates the second 515nm frequency conversion sub-laser, so that the first frequency conversion laser and the second frequency conversion sub-laser are coaxially combined into one beam, completing the time combination of a frequency conversion laser. The pulse repetition frequency of the combined 515nm frequency conversion laser changes from 1MHz to 2MHz.

[0067] As Example 2, the repetition frequency of the fundamental frequency sub-beams 3101 and 3102 is 10 kHz, the pulse width is 350 ps, ​​the wavelength is 1064 nm, and the pulse delay between the fundamental frequency sub-beams 3101 and 3102 is 2.67 ns.

[0068] Nonlinear frequency conversion modules 3201 and 3202 are both LBO frequency doubling crystals. The size of the LBO crystal is 4mm×4mm×20mm, the size of the light openings on both sides is 4mm×4mm, and the phase matching angle of the LBO crystal is θ=90°, φ=0°. Both ends of the LBO crystal are coated with 1064nm&532nm dual-wavelength anti-reflection film, and the LBO crystal is equipped with a crystal temperature control device with an accuracy of 0.1℃ for adjusting the temperature.

[0069] The dichroic beam splitter 3301 is a plane mirror coated with a 532nm 45° total reflection film and a 1064nm anti-reflection film, and is used to filter the 1064nm fundamental frequency light and reflect the 532nm doubled frequency light to the second optical path.

[0070] The dichroic beam combiner 3401 is a plane mirror coated with a 532nm 45° total reflection film and a 1064nm anti-reflection film, and is used to coaxially combine the doubled frequency light generated by the fundamental frequency sub-beam 3101 with the fundamental frequency sub-beam 3102.

[0071] In this example, the beam shaping element 3501 is coated with a 532 nm anti-reflection film and is used to beam shape the doubled frequency light generated by the fundamental frequency sub-beam 3101 so as to maintain beam mode matching when the doubled frequency light is combined with the fundamental frequency sub-beam 3102 .

[0072] In this embodiment, preferably, the antireflection film has a transmittance greater than 99.8%, and preferably, the total reflection film has a reflectivity greater than 99.8%.

[0073] The 1064nm fundamental frequency sub-beam 3101, with a power of 1.95W, is injected into the frequency doubling module 3201 to generate the first optical path 532nm frequency conversion sub-laser I, see Figure 7 A and 8A, after the remaining fundamental frequency pulse laser is filtered out by the two-color beam splitter 3301, the power of the first optical path doubled frequency sub-laser, i.e., the 532nm laser, is 1.13W. The first optical path doubled frequency laser passes through the optical beam shaping element 3501 to keep the beam mode matching when it is combined with the 1064nm fundamental frequency sub-beam 3102. The power of the 1064nm fundamental frequency sub-beam 3102 is 1.51W. The first optical path doubled frequency laser then passes through the two-color beam combiner 3401 and is coaxially combined with the 1064nm fundamental frequency sub-beam 3102 and then injected into the frequency doubling module 3202 together. If the second fundamental frequency laser 3102 is blocked by a baffle, it can be observed that the power of the first optical path doubled frequency laser remains almost unchanged after passing through the frequency doubling module 3202. This is because the LBO crystal cutting angle of the frequency doubling module only meets the phase matching of the 1064nm laser frequency doubling to 532nm, and cannot make the 532nm frequency doubling light continue to double, and the 532nm laser power density is not enough to reversely convert to 1064nm through the optical parametric process. If the first optical path frequency doubling laser is blocked by a baffle, the second fundamental frequency laser 3102 will generate the second frequency doubling sub-laser II through the frequency doubling module 3202, Figure 7 B and 8B, the power of the second doubled frequency sub-laser is 0.863W. At this time, if the baffle is removed, the first doubled frequency laser and the second doubled frequency sub-laser will be coaxially combined into one beam. Figure 7 C and 8C complete the sequential beam combining of the frequency-doubled laser. The pulse repetition frequency of the frequency-doubled laser after beam combining changes from 10kHz to 20kHz. The sum of the power of the two separate frequency-converted pulse lasers before beam combining is 1.993W. After the sequential beam combining of the frequency-doubled laser is completed, the combined power is 1.984W. The sequential beam combining efficiency can reach 99.55%, and the laser beam quality after beam combining is almost the same as the beam quality before beam combining.

[0074] Fig. 9 It is a schematic structural diagram of a sequential beam combining device 400 based on laser nonlinear frequency conversion of the third specific embodiment of the present application. The sequential beam combining device 400 includes three beam-combined fundamental frequency sub-beams 4101, 4102, 4103, three nonlinear frequency conversion modules 4201, 4202, 4203, two dichroic beam splitters 4301, 4302, two beam shaping elements 4501, 4502 and two dichroic beam combining mirrors 4401, 4402, constituting a beam combining device including the first, second and third optical paths for realizing the sequential beam combining of three fundamental frequency pulsed lasers.

[0075] In this embodiment, each combined fundamental frequency sub-beam 4101, 4102, 4103 is synthesized by a fundamental frequency sub-beam with a first wavelength λ1, a fundamental frequency sub-beam with a second wavelength λ2, and a dichroic beam combiner, respectively. The dichroic beam combiner is used to coaxially combine a fundamental frequency sub-beam with a first wavelength λ1 and a fundamental frequency sub-beam with a second wavelength λ2 having the same repetition frequency and overlapping in time sequence to obtain a combined fundamental frequency sub-beam with a first wavelength λ1 and a second wavelength λ2. The nonlinear frequency conversion module includes a sum frequency crystal, which satisfies the phase matching condition of the fundamental frequency pulse laser sum frequency, and converts the combined fundamental frequency sub-beam with a first wavelength λ1 and a second wavelength λ2 having the same repetition frequency and overlapping in time sequence in the incident combined fundamental frequency sub-beam into a sum frequency light with a third wavelength λ3, and the wavelength λ3 = λ1×λ2 / (λ1+λ2).

[0076] For example, the wavelength of the first fundamental frequency pulse laser 4111, 4112, 4113 is 1064nm, the wavelength of the second fundamental frequency pulse laser 4121, 4122, 4123 is 1319nm, the repetition frequency is 1.5kHz, the pulse width is 10μs, and the pulse delay between adjacent combined fundamental frequency sub-beams 4101, 4102, 4103 is 222μs.

[0077] The two-color beam combiner mirrors 4601, 4602, 4603 are plane mirrors coated with a 1319nm 45° total reflection film and a 1064nm anti-reflection film, and are used to combine two fundamental frequency pulses into combined fundamental frequency sub-beams 4101, 4102, 4103.

[0078] For example, nonlinear frequency conversion modules 4201, 4202, and 4203 are all LBO crystals, and the size of the LBO crystal is 4mm×4mm×30mm, and the size of the light openings on both sides is 4mm×4mm. Both ends of the LBO crystal are plated with 1000nm~1400nm&589nm wavelength anti-reflection film, and the LBO crystal is equipped with a crystal temperature control device with an accuracy of 0.1℃ for adjusting the temperature.

[0079] The two-color beam splitters 4301 and 4302 are plane mirrors coated with a 589nm 45° total reflection film and an anti-reflection film for the 1000nm to 1400nm band, and are used to filter fundamental frequency light.

[0080] The two-color beam combining mirrors 4401 and 4402 in the second and third optical paths are plane mirrors coated with a 589nm 45° total reflection film and an anti-reflection film for the 1000nm~1400nm band, and are respectively used to coaxially combine the sum frequency laser generated by the first optical path with the combined fundamental frequency pulse laser 4102 of the second optical path; and to coaxially combine the sum frequency laser generated by the combined second optical path with the combined fundamental frequency pulse laser 4103 of the third optical path.

[0081] In this embodiment, the beam shaping elements 4501 and 4502 are coated with a 589 nm anti-reflection film and are respectively used to perform beam shaping on the first and second sum frequency lights so as to keep beam mode matching when they are combined with the combined fundamental frequency pulse lasers 4102 and 4103. Preferably, the beam shaping elements 4501 and 4502 can be lenses for beam shaping, such as a spherical lens or a spherical lens group.

[0082] In this embodiment, preferably, each antireflection film has a transmittance greater than 99.8%; preferably, each total reflection film has a reflectivity greater than 99.8%.

[0083] The first fundamental frequency pulse laser 4111 and the second fundamental frequency pulse laser 4121 are injected into the first nonlinear frequency conversion module 4201 through the two-color beam splitter 4601 to generate sum frequency sub-laser I through the sum frequency process. After the remaining 1064nm and 1319nm fundamental frequency pulse lasers are filtered out by the first two-color beam splitter 4301, the 589nm frequency conversion laser of the first optical path is combined with the second beam combined pulse laser module 4102 through the first beam shaping element 4501 to keep the beam mode matching. The first optical path frequency conversion laser is then coaxially combined with the second beam combined fundamental frequency sub-laser 4102 through the first two-color beam combining mirror 4401 and then injected into the second nonlinear frequency conversion module 4202. The first optical path frequency conversion laser and the second sum frequency sub-laser II are coaxially combined into the second optical path frequency conversion laser, completing the time combination of the first frequency conversion laser. After the combination, the pulse repetition frequency of the second optical path frequency conversion laser changes from 1.5kHz to 3kHz. The second frequency conversion laser beam combination is completed by analogy, and the repetition frequency of the frequency conversion laser pulse after the third optical path beam combination becomes 4.5kHz.

[0084] Fig.10 It is a schematic diagram of the structure of a sequential beam combining device 500 based on laser nonlinear frequency conversion according to the fourth specific embodiment of the present application. The sequential beam combining device 500 includes two beam-combined fundamental frequency sub-beams 5101, 5102, two sum frequency crystals 5201, 5202, a dichroic beam splitter 5301, a beam shaping element 5501, and a dichroic beam combining mirror 5401, constituting a beam combining device including a first and a second optical path for realizing the sequential beam combining of two fundamental frequency pulsed lasers. The pulse repetition frequencies of the two fundamental frequency sub-beams 5101, 5102 are the same, but the pulse sequences are staggered in time with each other.

[0085] In this embodiment, the two combined fundamental frequency sub-beams 5101 and 5102 are synthesized by frequency doubling fundamental frequency sub-beams 5111 and 5112 respectively by two frequency doubling crystals 5701 and 5702.

[0086] For example, the repetition frequency of the fundamental frequency sub-beams 5111 and 5112 is 50 kHz, the pulse width is 50 ns, the wavelength is 1064 nm, and the pulse delay between the two fundamental frequency sub-beams 511 and 511 is 1 μs.

[0087] Frequency doubling crystals 5701 and 5702 are LBO crystals, using type I non-critical phase matching. The size of the LBO crystal is 3mm×3mm×25mm, and the size of the light openings on both sides is 3mm×3mm. Both ends of the LBO crystal are coated with 1064nm&532nm dual-wavelength anti-reflection film. The LBO crystal is equipped with a crystal temperature control device with an accuracy of 0.1℃ for adjusting the temperature.

[0088] The sum frequency crystals 5201 and 5202 also use LBO crystals, and adopt type II non-critical phase matching. The size of the LBO crystal is 7mm×3mm×20mm, and the size of the light openings on both sides is 7mm×3mm. The two ends of the LBO crystal are coated with 1064nm&532nm&355nm anti-reflection films. The LBO crystal is equipped with a crystal temperature control device with an accuracy of 0.1℃ to adjust the temperature.

[0089] The dichroic beam splitter 5301 is a plane mirror coated with a 355nm 45° total reflection film and a 1064nm & 532nm anti-reflection film, which is used to filter the fundamental frequency light.

[0090] The two-color beam combiner 5401 is a plane mirror coated with a 355nm 45° total reflection film and a 1064nm & 532nm anti-reflection film. It is used to combine the first optical path sum frequency light generated by the fundamental frequency pulse sub-beam 5101 with the second optical path combined fundamental frequency pulse sub-beam formed after the fundamental frequency pulse laser 5102 is frequency doubled by the frequency doubling crystal 5702.

[0091] In this embodiment, the beam shaping element 5501 is coated with a 355nm anti-reflection film and is used to perform beam shaping on the sum frequency light of the first optical path so that the sum frequency light can maintain beam mode matching when combined with the combined fundamental frequency pulse sub-beam of the fundamental frequency pulse laser 5102 after frequency doubling by the frequency doubling crystal 5702. Preferably, the beam shaping element 5 can be a lens for beam shaping, such as a spherical lens or a spherical lens group.

[0092] In this embodiment, preferably, the antireflection film has a transmittance greater than 99.8%; preferably, the total reflection film has a reflectivity greater than 99.8%.

[0093] The first beam of 1064nm fundamental frequency pulse laser 5111 is injected into the first frequency doubling crystal 5701, and the 1064nm laser is partially converted into 532nm laser through the frequency doubling process, thereby obtaining the first beam of combined fundamental frequency pulse sub-beam 5101; the second beam of 1064nm fundamental frequency pulse laser 5112 is injected into the second frequency doubling crystal 5702, and the 1064nm laser is partially converted into 532nm laser through the frequency doubling process, thereby obtaining the second beam of combined fundamental frequency pulse sub-beam 5102.

[0094] The first combined fundamental frequency pulse sub-beam 5101 is injected into the first sum frequency crystal 5201 to generate the first optical path 355nm sum frequency laser. After the first dichroic beam splitter 3 filters out the remaining 1064nm and 532nm fundamental frequency pulse lasers, the first optical path sum frequency laser passes through the first beam shaping element 5501 to keep the beam mode matching when combined with the second combined fundamental frequency pulse sub-beam 5102.

[0095] The 355nm frequency-converted laser of the first optical path is then coaxially combined with the second combined fundamental frequency pulse sub-beam 5102 through the first two-color beam combining mirror 5401 and injected into the second sum frequency crystal 5202 to complete the temporal combination of the sum frequency laser. The repetition frequency of the 355nm sum frequency laser pulse after the second optical path is combined changes from 50kHz to 100kHz.

[0096] Obviously, the above embodiments of the present disclosure are merely examples for clearly illustrating the present disclosure, and are not limitations on the implementation methods of the present disclosure. For ordinary technicians in this field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present disclosure are still within the protection scope of the present disclosure.

Claims

1. A laser beam combining device, characterized in that: The laser beam combining device includes N optical paths, N≥2, The first optical path includes a first nonlinear frequency conversion module, which is used to convert the base frequency pulse laser into a first frequency conversion laser beam; Each n-th optical path includes a first two-color beam combining mirror and a first nonlinear frequency conversion module sequentially arranged along the optical path, wherein the first two-color beam combining mirror is used to coaxially combine the incident fundamental frequency pulse laser of the optical path with the n-1th frequency conversion laser beam from the n-1th optical path, and the first nonlinear frequency conversion module converts the fundamental frequency pulse laser in the coaxial combination and transmits the n-1th frequency conversion laser beam therein to obtain the nth frequency conversion laser beam with a repetition frequency of nf, 2≤n≤N, Among them, the N beams of fundamental frequency pulse laser have the same repetition frequency f and the pulse sequences do not overlap in time. The laser beam combining device outputs a combined frequency-variable laser beam with a repetition frequency of Nf and a wavelength smaller than the wavelength of the fundamental frequency pulse laser beam.

2. The laser beam combining device according to claim 1, characterized in that: Each (n-1)th optical path further includes a dichroic beam splitter located behind the first nonlinear frequency conversion module, which is used to filter out the base frequency pulse laser in the frequency conversion laser beam from the first nonlinear frequency conversion module.

3. The laser beam combining device according to claim 2, characterized in that: Each n-1th optical path also includes a beam shaping element located between the first dichroic beam splitter and the first dichroic beam combiner of the nth optical path, which is used to shape the frequency-converted laser beam from which the fundamental frequency pulse laser is filtered out into a frequency-converted laser beam that matches the incident fundamental frequency pulse laser beam mode of the first dichroic beam combiner.

4. The laser beam combining device according to claim 1, characterized in that: The N fundamental frequency pulse laser beams are respectively fundamental frequency pulse laser beams having a first wavelength. The first nonlinear frequency conversion module includes a first frequency doubling crystal, which is used to frequency double the incident fundamental frequency pulse laser of the first wavelength into a frequency-doubled light having a wavelength of half the first wavelength. The laser beam combining device outputs a combined frequency-converted laser beam having a wavelength of half the first wavelength.

5. The laser beam combining device according to claim 1, characterized in that: The N fundamental frequency pulse laser beams are respectively a combined fundamental frequency pulse laser beam having a first wavelength and a second wavelength. The first nonlinear frequency conversion module comprises a sum frequency crystal for converting the combined fundamental frequency pulse laser beam having the first wavelength and the second wavelength into a sum frequency light having a third wavelength. The laser beam combining device outputs a combined frequency-converted laser beam having a wavelength of the third wavelength.

6. The laser beam combining device according to claim 5, characterized in that: Each of the N optical paths includes a second dichroic beam combining mirror for coaxially combining a fundamental frequency pulse laser with a first wavelength and a fundamental frequency pulse laser with a second wavelength to obtain a combined fundamental frequency pulse laser beam with the first wavelength and the second wavelength.

7. The laser beam combining device according to claim 5, characterized in that: Each of the N optical paths includes a second nonlinear frequency conversion module with a second frequency doubling crystal, which is used to double the frequency of a fundamental frequency pulse laser with a first wavelength, and output a fundamental frequency pulse laser beam with the first wavelength and a frequency doubling pulse laser beam with half the first wavelength as the combined fundamental frequency pulse laser beam with the first wavelength and the second wavelength.

8. The laser beam combining device according to claim 1, characterized in that: The pulse width of each fundamental frequency pulse laser beam is t, and the pulse time interval is 1 / f; preferably, the pulse time delay between two adjacent fundamental frequency pulse laser beams is at least 2 times the pulse width t and at most 1 / Nf.

9. The laser beam combining device according to claim 1, characterized in that: A dielectric film with high transmittance to base frequency pulse laser and high reflection to frequency conversion laser is formed on the surface of the first two-color beam combining mirror, or a dielectric film with high reflection to base frequency pulse laser and high transmittance to frequency conversion laser is formed on the surface of the first two-color beam combining mirror.

10. The laser beam combining device according to claim 1, characterized in that: The fundamental frequency pulse laser pulse width includes millisecond, microsecond, nanosecond, picosecond, and femtosecond laser pulses.

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