A dual-frequency deep ultraviolet laser generator

Abstract

This invention discloses a dual-frequency deep ultraviolet laser generator, comprising a fundamental frequency seed source, a first harmonic conversion optical path, a second harmonic conversion optical path, and an output optical path. The first harmonic conversion optical path has a first beam combiner, a first second harmonic module, a third harmonic module, and a first delay line arranged sequentially along the propagation direction of the light. The second harmonic conversion optical path has a second beam combiner, a harmonic conversion optical path branch, and a second delay line. The harmonic conversion optical path branch and the second delay line are connected in parallel between the second beam combiner and the output optical path. The harmonic conversion optical path branch has a second second harmonic module and a fourth harmonic module arranged sequentially after the second beam combiner along the propagation direction of the light. The output optical path has a seventh harmonic module and an eighth harmonic module. This invention avoids the single-path power bottleneck by using distributed amplification, breaking through the power limitation of the fundamental frequency in traditional sum-frequency generation methods.

Description

Technical Field

[0001] This invention relates to the field of laser generating device technology, and in particular to a dual-frequency deep ultraviolet laser generating device. Background Technology

[0002] The 193nm deep ultraviolet solid-state laser source has advantages such as tunable wavelength, adjustable repetition frequency, good beam quality, good coherence, small size, and adjustable pulse width, and is of great significance in application fields such as fiber grating writing, semiconductor chip defect detection, and excimer gas laser seed injection.

[0003] The generation of 193nm deep ultraviolet solid-state laser sources relies on nonlinear optical frequency conversion technology. Besides directly generating deep ultraviolet lasers using KBBF through frequency doubling, two light sources can be generated through harmonic conversion using nonlinear crystals such as BBO, LBO, and CLBO. KBBF crystals contain highly toxic beryllium and exhibit a pronounced layered growth habit, limiting their high-power output performance. BBO, LBO, and CLBO are relatively more mature and more valuable for industrial applications. In harmonic conversion, one of the two light sources is a short wavelength (205–275nm), and the other is a long wavelength (700–3200nm). Based on different light source acquisition techniques, they are mainly classified into three categories: Sum Frequency Generation (SFG), Optical Parametric Oscillator (OPO), and Difference Frequency Generation (DFG).

[0004] Sum Frequency Generation (SFG) involves the interaction of two laser beams in a nonlinear medium to generate a short-wavelength signal laser beam with a frequency equal to the sum of the two beams. When the frequencies of the two laser beams are the same, it is called Second Harmonic Generation (SHG). In the technical approach to obtaining the 193nm band, one can use SFG to down-multiply the frequency, such as summing the frequency of a third-harmonic laser (1547nm) with its fourth-harmonic laser to obtain a 221nm wavelength. The 221nm wavelength is then summed with the 1547nm wavelength. However, the power limitation of the fundamental frequency source, the sole energy source, results in a relatively low power for the final 193nm band. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the existing methods of generating lasers by sum-frequency are limited by the power of the only energy source, the fundamental frequency source, resulting in relatively low power in the 193nm band.

[0006] To solve the above-mentioned technical problems, the present invention provides a dual-frequency deep ultraviolet laser generator, including a fundamental frequency seed source, a first harmonic conversion optical path, a second harmonic conversion optical path, and an output optical path;

[0007] The fundamental frequency seed source is used to emit nanosecond pulsed lasers in the 1547nm band;

[0008] The first harmonic conversion optical path has a first beam combining structure, a first second harmonic module, a third harmonic module, and a first delay line arranged sequentially along the propagation direction of the light. The first beam combining structure is used to combine the two amplified nanosecond pulse laser beams and perform polarization modulation to generate a first polarized laser. The first polarized laser is a single linearly polarized laser with a wavelength of 1547nm. The first polarized laser generates a first laser with a wavelength of 515.7nm after passing through the first second harmonic module, the third harmonic module, and the first delay line in sequence.

[0009] The second harmonic conversion optical path has a second beam combining structure, a harmonic conversion optical path branch, and a second delay line. The second beam combining structure is used to combine the two amplified nanosecond pulse laser beams and perform polarization modulation to generate a second polarized laser. The second polarized laser is a single linearly polarized laser with a wavelength of 1547nm. The harmonic conversion optical path branch and the second delay line are connected in parallel between the second beam combining structure and the output optical path. The harmonic conversion optical path branch has a second second harmonic module and a fourth harmonic module arranged sequentially after the second beam combining structure along the propagation direction of the light. The second polarized laser generates a second laser with a wavelength of 386.75nm after passing through the second second harmonic module and the fourth harmonic module in sequence.

[0010] The output optical path has a seventh-frequency harmonic module and an eighth-frequency harmonic module. The seventh-frequency harmonic module is used to receive the first laser and the second laser, and sum them to produce a third laser with a wavelength of 221nm. The eighth-frequency harmonic module is used to receive the second polarized laser and the third laser, and sum them to produce a fourth laser with a wavelength of 193.375nm.

[0011] Furthermore, the first beam combining structure is identical to the second beam combining structure. The first beam combining structure includes a first fundamental frequency amplification module, a second fundamental frequency amplification module, a first polarization beam combining module, and a first polarization modulation module. The first fundamental frequency amplification module and the second fundamental frequency amplification module are connected in parallel between the fundamental frequency seed source and the first polarization beam combining module to amplify the nanosecond pulse laser. The first polarization beam combining module is used to polarize and combine the two amplified nanosecond pulse lasers into a single pulse laser. The first polarization modulation module is located between the first polarization beam combining module and the first second harmonic module to polarize and modulate the combined single pulse laser into the first polarized laser.

[0012] Furthermore, the first polarization beam combining module includes a third delay line, a first half-wave plate, a first polarization beam splitter, a second half-wave plate, and a first reflector. Along the direction of light propagation, the first fundamental frequency amplification module, the third delay line, the first half-wave plate, and the first polarization beam splitter are sequentially disposed between the fundamental frequency seed source and the first polarization modulation module. The first half-wave plate is used to adjust the nanosecond pulse laser in this path into horizontally linearly polarized light so that it can pass through the first polarization beam splitter.

[0013] Along the direction of light propagation, the second fundamental frequency amplification module, the second half-wave plate, and the first reflector are arranged in sequence. The second half-wave plate is used to adjust the nanosecond pulse laser in this path into vertically polarized light, and the first reflector is set at a 45° angle so as to reflect the nanosecond pulse laser vertically into the first polarization beam splitter.

[0014] Furthermore, the first polarization modulation module includes a first electro-optic modulator, a first electro-optic driving box, and a second polarization beam splitter. The first electro-optic driving box is electrically connected to the first electro-optic modulator. Along the direction of light propagation, the first electro-optic modulator and the second polarization beam splitter are disposed between the first polarization beam combining module and the first frequency doubling module.

[0015] Furthermore, the first frequency doubling module has the same structure as the second frequency doubling module. The first frequency doubling module includes a third half-wave plate, a third polarizing beam splitter, a first focusing lens, a first frequency doubling component, a first collimating lens, a first dichroic mirror, and a fourth half-wave plate arranged sequentially along the direction of light propagation.

[0016] The third half-wave plate is used to rotate the polarization state of the first polarized laser by a preset angle and then incident it into the third polarization beam splitter. The outgoing light is split into two lasers with mutually perpendicular transmission directions. One of the first polarized lasers, transmitted by the third polarization beam splitter, is directed towards the first focusing lens, and the other of the first polarized lasers, reflected by the third polarization beam splitter, is incident into the third frequency harmonic module.

[0017] The first frequency doubling component is used to convert the first polarized laser passing through the first focusing lens into a second harmonic laser with a wavelength of 773.5nm.

[0018] The two surfaces of the third polarizing beam splitter and the two surfaces of the first focusing lens are respectively coated with an anti-reflection film with a center wavelength of 1547nm;

[0019] Both surfaces of the first frequency doubling component and both surfaces of the first collimating lens are coated with dual-wavelength antireflective films with center wavelengths of 1547nm and 773.5nm;

[0020] The incident surface of the first dichroic mirror is coated with a first dichroic film, and the rear surface of the first dichroic mirror is coated with a dual-wavelength antireflection film with center wavelengths of 1547nm and 773.5nm; the first dichroic film is configured to have high reflectivity to light with a wavelength of 773.5nm and high transmittance to light with a wavelength of 1547nm.

[0021] The fourth half-wave plate is designed with a wavelength of 773.5 nm to adjust the 773.5 nm wavelength laser light into horizontally linearly polarized light that is incident on the third harmonic module.

[0022] Furthermore, the third harmonic module includes a second reflecting mirror, a first beam shrinking mirror, a fifth half-wave plate, a fourth polarizing beam splitter, a second dichroic mirror, a second focusing lens, a third harmonic assembly, a second collimating lens, and a third dichroic mirror arranged sequentially along the direction of light propagation;

[0023] The second reflector is set at 45° and its incident surface is coated with a high-reflectivity film with a center wavelength of 1547nm to reflect another path of the first polarized laser to the first beam shrinker.

[0024] The two surfaces of the lens of the first beam shrinking lens and the two surfaces of the fourth polarizing beam splitter are respectively coated with an anti-reflection film with a center wavelength of 1547nm.

[0025] The design wavelength of the fifth half-wave plate is 1547 nm;

[0026] The fourth polarizing beam splitter is used to allow horizontally linearly polarized light, adjusted by the fifth half-wave plate, to pass through and exit to the second dichroic mirror;

[0027] The incident surface of the second dichroic mirror is used to reflect the horizontally linearly polarized light adjusted by the fourth half-wave plate, and the rear surface of the second dichroic mirror is used to transmit the laser light transmitted by the fourth polarizing beam splitter; wherein, the incident surface of the second dichroic mirror is coated with the first dichroic film, and the rear surface of the first dichroic mirror is coated with a dual-wavelength anti-reflection film with center wavelengths of 1547nm and 773.5nm, so as to combine the laser light of wavelength 773.5nm and the laser light of wavelength 1547nm into a first dual-wavelength laser light;

[0028] The third harmonic generation component is used to convert the first dual-wavelength laser into a 515.7nm wavelength laser by third harmonic generation.

[0029] The incident surface of the third dichroic mirror is coated with an optical thin film, which is configured to be an anti-reflective coating that is highly reflective to light with a wavelength of 515.7 nm and highly transmittable to light with wavelengths of 773.5 nm and 1547 nm. The rear surface of the third dichroic mirror is coated with a three-wavelength anti-reflective coating.

[0030] Furthermore, the fourth harmonic module includes a fourth dichroic mirror, a second beam shrinker, a fourth harmonic component, a fifth dichroic mirror, and a sixth half-wave plate arranged sequentially along the optical path.

[0031] The fourth dichroic mirror is used to reflect the horizontally linearly polarized light adjusted by the second second harmonic module to the second beam shrinker.

[0032] The two surfaces of the lens of the second beam shrinking lens are respectively coated with an anti-reflection coating with a center wavelength of 773.5nm;

[0033] The fourth harmonic generation component is used to convert the laser beam condensed by the second beam shrinker into a laser with a wavelength of 386.75nm by fourth harmonic generation.

[0034] The incident surface of the fifth dichroic mirror is coated with a second dichroic film, and the rear surface of the fifth dichroic mirror is coated with a dual-wavelength anti-reflection film; the second dichroic film is configured to have high reflectivity for light with a wavelength of 386.75nm and high transmittance for light with a wavelength of 773.5nm.

[0035] The design wavelength of the sixth half-wave plate is 386.75 nm.

[0036] Furthermore, the seventh frequency harmonic module includes a third beam shrinking mirror, a seventh half-wave plate, a third reflecting mirror, a sixth dichroic mirror, a first window mirror, a seventh frequency harmonic assembly, a seventh dichroic mirror, an eighth dichroic mirror, and a second window mirror arranged sequentially along the optical path.

[0037] The third beam shrinking mirror is used to receive the first laser emitted from the first delay line and transmit it to the seventh half-wave plate;

[0038] The third reflector is coated with a high-reflectivity film with a center wavelength of 515.7 nm to reflect the laser light passing through the seventh half-wave plate to the rear surface of the sixth dichroic mirror.

[0039] The rear surface of the sixth dichroic mirror is used to transmit the laser reflected by the third reflecting mirror, and the incident surface of the sixth dichroic mirror is used to reflect the laser output by the sixth half-wave plate; wherein, the rear surface of the sixth dichroic mirror is coated with an antireflection film with a center wavelength of 515.7nm, and the incident surface of the sixth dichroic mirror is coated with a third dichroic film, which is configured to highly reflect light with a wavelength of 386.75nm and highly transmit light with a wavelength of 515.7nm, so as to combine the laser with a wavelength of 386.75nm and the laser with a wavelength of 515.7nm into a second dual-wavelength laser;

[0040] The first window is coated with a dual-wavelength antireflection film, and the second window is coated with an antireflection film with a center wavelength of 221nm.

[0041] The seventh frequency harmonic component is used to receive the second dual-wavelength laser transmitted from the first window mirror and convert it into a 221nm wavelength laser output to the seventh dichroic mirror;

[0042] The incident surfaces of the seventh and eighth dichroic mirrors are both coated with a third dichroic film, and the exit surfaces of the seventh and eighth dichroic mirrors are both coated with a three-wavelength antireflective film. The third dichroic film is configured to have high reflectivity for light with a wavelength of 221 nm and high transmittance for light with wavelengths of 386.75 nm and 515.7 nm.

[0043] Furthermore, the eighth-frequency harmonic module includes a fourth beam shrinking mirror, a third window mirror, a ninth dichroic mirror, an eighth-frequency harmonic component, a tenth dichroic mirror, and a fourth window mirror arranged sequentially along the optical path direction;

[0044] The fourth beam shrinking mirror is used to receive the second polarized laser emitted from the second delay line and transmit it to the third window mirror;

[0045] The third window mirror is coated with an antireflective coating with a center wavelength of 1547nm, and the fourth window mirror is used to output the fourth laser after passing through the tenth dichroic mirror. The fourth window mirror is coated with an antireflective coating with a center wavelength of 193.375nm.

[0046] The rear surface of the ninth dichroic mirror is used to transmit laser light passing through the third window mirror, and the incident surface of the ninth dichroic mirror is used to reflect the third laser light passing through the second window mirror; wherein, the rear surface of the ninth dichroic mirror is coated with an antireflection film with a center wavelength of 1547nm; the incident surface of the ninth dichroic mirror is coated with a fourth dichroic film, which is configured to highly reflect light with a wavelength of 221nm and highly transmit light with a wavelength of 1547nm, so as to combine the laser light with a wavelength of 221nm and the laser light with a wavelength of 1547nm into a third dual-wavelength laser;

[0047] The eighth-harmonic generation component is used to receive the third dual-wavelength laser emitted from the ninth dichroic mirror and convert it into a laser with a wavelength of 193.375nm, which is then output to the tenth dichroic mirror.

[0048] The incident surface of the tenth dichroic mirror is coated with a fifth dichroic film, and the exit surface of the tenth dichroic mirror is coated with a three-wavelength antireflective film; wherein, the fifth dichroic film is configured to have high reflectivity for light with a wavelength of 193.375nm and high transmittance for light with wavelengths of 1547nm and 221nm.

[0049] Furthermore, the first delay line includes a fourth reflector and a fifth reflector, the extension line of the fourth reflector and the extension line of the fifth reflector are perpendicular to each other, so as to reflect the laser output by the third harmonic module to the seventh harmonic module in sequence through the fourth reflector and the fifth reflector.

[0050] The second delay line includes a sixth, a seventh, and an eighth reflector arranged along the optical path. The sixth, seventh, and eighth reflectors are all coated with a high-reflectivity film with a center wavelength of 1547 nm. The extension line of the seventh reflector is perpendicular to the extension line of the eighth reflector, so that the second polarized laser output from the second beam combining structure is reflected sequentially through the sixth, seventh, and eighth reflectors to the eighth frequency harmonic module.

[0051] Compared with the prior art, the dual-frequency deep ultraviolet laser generator of this invention has the following advantages:

[0052] In this embodiment of the invention, a single seed source is divided into multiple paths and independently amplified before being combined in pairs to form a single linearly polarized laser. Subsequently, the eighth harmonic conversion is achieved through different harmonic conversion optical paths. This embodiment avoids the single-path power bottleneck by using this distributed amplification method, breaks through the power limitation of the fundamental frequency source in the traditional sum-frequency method, and obtains a high-power output laser with a wavelength of 193.375nm. Attached Figure Description

[0053] The present application will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, those skilled in the art will appreciate that these drawings are drawn only for the purpose of explaining the preferred embodiments and therefore should not be construed as limiting the scope of the present application. Furthermore, unless specifically indicated, the drawings are intended only to conceptually represent the composition or structure of the described objects and may contain exaggerated representations, and the drawings are not necessarily drawn to scale.

[0054] Figure 1 This is a schematic diagram of the modules of the dual-frequency deep ultraviolet laser generator provided in an embodiment of the present invention;

[0055] Figure 2 This is a schematic diagram of the structure of the dual-frequency deep ultraviolet laser generator provided in an embodiment of the present invention;

[0056] In the diagram, 1 represents the fundamental frequency seed source;

[0057] 2. First harmonic conversion optical path; 21. First beam combiner structure; 211. First fundamental frequency amplification module; 212. Second fundamental frequency amplification module; 213. First polarization beam combiner module; 2131. Third delay line; 2132. First half-wave plate; 2133. First polarization beam splitter prism; 2134. Second half-wave plate; 2135. First reflector; 214. First polarization modulation module; 2141. First electro-optic modulator; 2142. First electro-optic driver box; 2143. Second polarization beam splitter prism; 22. First second harmonic generation module; 221. Third half-wave plate; 222. 223. Third polarizing beam splitter; 224. First focusing lens; 225. First frequency-second harmonic assembly; 226. First collimating lens; 227. First dichroic mirror; 228. Fourth half-wave plate; 239. Third frequency-second harmonic assembly; 240. Second collimating lens; 25. Fifth half-wave plate; 26. Fourth polarizing beam splitter; 27. Second dichroic mirror; 28. Second frequency-second harmonic assembly; 29. ​​Third dichroic mirror; 20. First delay line; 21. Fourth reflecting mirror; 222. Fifth reflecting mirror;

[0058] 3. Second harmonic conversion optical path; 31. Second beam combiner structure; 311. Third fundamental frequency amplification module; 312. Fourth fundamental frequency amplification module; 313. Second polarization beam combiner module; 3131. Fourth delay line; 3132. Eighth half-wave plate; 3133. Fifth polarization beam splitter prism; 3134. Ninth half-wave plate; 3135. Ninth reflector; 314. Second polarization modulation module; 3141. Second electro-optic modulator; 3142. Second electro-optic drive box; 3143. Sixth polarization beam splitter prism; 32. Harmonic conversion optical path branch; 33. 331. Second delay line; 332. Sixth reflecting mirror; 333. Seventh reflecting mirror; 333. Eighth reflecting mirror; 34. Second second harmonic generation module; 341. Tenth half-wave plate; 342. Seventh polarizing beam splitter; 343. Third focusing lens; 344. Second second harmonic generation assembly; 345. Third collimating lens; 346. Eleventh dichroic mirror; 347. Eleventh half-wave plate; 35. Fourth harmonic generation module; 351. Fourth dichroic mirror; 352. Second beam shrinker; 353. Fourth harmonic generation assembly; 354. Fifth dichroic mirror; 355. Sixth half-wave plate;

[0059] 4. Output optical path; 41. Seventh harmonic module; 411. Third beam shrinker; 412. Seventh half-wave plate; 413. Third reflector; 414. Sixth dichroic mirror; 415. First window mirror; 416. Seventh harmonic assembly; 417. Seventh dichroic mirror; 418. Eighth dichroic mirror; 419. Second window mirror; 420. Sampling unit; 4201. First sampling mirror; 4202. First power detector; 42. Eighth harmonic module; 421. Fourth beam shrinker; 422. Third window mirror; 423. Ninth dichroic mirror; 424. Eighth harmonic assembly; 425. Tenth dichroic mirror; 426. Fourth window mirror; 427. Spot position detector; 428. Second sampling mirror; 429. Second power detector. Detailed Implementation

[0060] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0061] like Figure 1 and Figure 2 As shown, the present invention provides a dual-frequency deep ultraviolet laser generator, including a fundamental frequency seed source 1, a first harmonic conversion optical path 2, a second harmonic conversion optical path 3, and an output optical path 4; the fundamental frequency seed source 1 is used to emit nanosecond pulse lasers in the 1547nm band as the initial light source of the entire system.

[0062] The first harmonic conversion optical path 2 has a first beam combining structure 21, a first second harmonic harmonic module 22, a third harmonic harmonic module 23, and a first delay line 24 arranged sequentially along the propagation direction of the light. The first beam combining structure 21 is used to combine two amplified nanosecond pulse laser beams and perform polarization modulation to generate a first polarized laser. The first polarized laser is a single linearly polarized laser with a wavelength of 1547nm. The first polarized laser passes through the first second harmonic harmonic module 22, the third harmonic harmonic module 23, and the first delay line 24 in sequence to generate a first laser with a wavelength of 515.7nm. Among them, a part of the first polarized laser enters the first second harmonic harmonic module 22 for second harmonic conversion to obtain a laser with a wavelength of 773.5nm, and the other part of the first polarized laser and the laser with a wavelength of 773.5nm enter the third harmonic harmonic module 23 together for third harmonic conversion to obtain a first laser with a wavelength of 515.7nm. Then, the first laser is delivered to the output optical path 4 through the first delay line 24.

[0063] The second harmonic conversion optical path 3 has a second beam combining structure 31, a harmonic conversion optical path branch 32, and a second delay line 33. The second beam combining structure 31 is used to combine two amplified nanosecond pulse laser beams and perform polarization modulation to form a second polarized laser. The second polarized laser is a single linearly polarized laser with a wavelength of 1547nm. The harmonic conversion optical path branch 32 and the second delay line 33 are connected in parallel between the second beam combining structure 31 and the output optical path 4. The harmonic conversion optical path branch 32 has a second delay line 33 arranged sequentially after the second beam combining structure 31 along the propagation direction of the light. The second polarized laser is generated with a wavelength of 386.75nm after passing through the second second harmonic generation module 34 and the fourth harmonic generation module 35 in sequence. Among them, a part of the second polarized laser enters the second second harmonic generation module 34 for second harmonic conversion to obtain a laser with a wavelength of 773.5nm, and then enters the fourth harmonic generation module 35 for fourth harmonic conversion to obtain a second laser with a wavelength of 386.75nm, which is then sent to the output optical path 4. The other part of the second polarized laser is sent to the output optical path 4 through the second delay line 33.

[0064] The output optical path 4 has a seventh frequency multiplication module 41 and an eighth frequency multiplication module 42. The seventh frequency multiplication module 41 is used to receive the first laser and the second laser, and sum them to produce a third laser with a wavelength of 221nm. The eighth frequency multiplication module 42 is used to receive the second polarized laser and the third laser, and sum them to produce a fourth laser with a wavelength of 193.375nm. At the same time, the optical path is adjusted by the first delay line 24 and the second delay line 33 to ensure that the first laser entering the seventh frequency multiplication module 41 and the second laser entering the eighth frequency multiplication module 42 are synchronized in the time domain.

[0065] In this embodiment, the single seed source is divided into multiple paths and amplified independently before being combined in pairs to form a single linearly polarized laser. Subsequently, the eighth harmonic conversion is achieved through different harmonic conversion optical paths. This embodiment avoids the single-path power bottleneck by using this distributed amplification method, breaks through the power limitation of the fundamental frequency in the traditional sum-frequency method, and obtains a high-power output laser with a wavelength of 193.375nm.

[0066] Understandably, the repetition rate of the nanosecond pulsed laser in this embodiment is below 1 MHz, and the pulse width should be on the order of nanoseconds. In some embodiments, the repetition rate of the nanosecond pulsed laser may also be 1 MHz, and the pulse width may be 1.5-2 ns. Its key parameters such as center wavelength, linewidth, and average power can be selected according to actual needs.

[0067] Furthermore, the first beam combining structure 21 includes a first fundamental frequency amplification module 211, a second fundamental frequency amplification module 212, a first polarization beam combining module 213, and a first polarization modulation module 214. The first fundamental frequency amplification module 211 and the second fundamental frequency amplification module 212 are connected in parallel between the fundamental frequency seed source 1 and the first polarization beam combining module 213. The two nanosecond pulse lasers output from the fundamental frequency seed source 1 are respectively input into the first fundamental frequency amplification module 211 and the second fundamental frequency amplification module 212 to amplify each nanosecond pulse laser individually, so that the average output power of a single nanosecond pulse laser is ≥65W, in order to meet the peak power threshold requirements of subsequent harmonic transformation.

[0068] The first polarization beam combining module 213 is used to polarize and combine the amplified two nanosecond pulse lasers into a single pulse laser. The energy of the single pulse laser after polarization beam combining remains unchanged, the repetition rate is 2MHz, and the timing of the two orthogonally polarized single pulse lasers is interleaved. The first polarization modulation module 214 is disposed between the first polarization beam combining module 213 and the first frequency second harmonic module 22 to polarize and modulate the vertical polarization portion of the input orthogonally polarized pulse (i.e., the combined single pulse laser) into a horizontally linearly polarized pulse (i.e., the first polarized laser). This first polarized laser is a single linearly polarized laser with a wavelength of 1547nm, a repetition rate of 2MHz, and an average power ≥100W.

[0069] Understandably, the first beam combining structure 21 and the second beam combining structure 31 have the same structure, that is, the second beam combining structure 31 includes a third fundamental frequency amplification module 311, a fourth fundamental frequency amplification module 312, a second polarization beam combining module 313, and a second polarization modulation module 314. In this embodiment, the output of the fundamental frequency seed source 1 is split into four paths, which are then input into the first fundamental frequency amplification module 211, the second fundamental frequency amplification module 212, the third fundamental frequency amplification module 311, and the fourth fundamental frequency amplification module 312 for individual amplification. That is, the single fundamental frequency seed source 1 is amplified independently into four paths, and then combined into two paths in pairs to achieve the eighth harmonic conversion in stages. This solves the problem that the existing sum-frequency laser generation method has relatively low power in the 193nm band due to the power limitation of the single energy source, the fundamental frequency source.

[0070] Furthermore, the first polarization beam combining module 213 realizes the polarization combining of two laser beams. It includes a third delay line 2131, a first half-wave plate 2132, a first polarization beam splitter 2133, a second half-wave plate 2134, and a first reflector 2135. Along the direction of light propagation, the first fundamental frequency amplification module 211, the third delay line 2131, the first half-wave plate 2132, and the first polarization beam splitter 2133 are sequentially arranged between the fundamental frequency seed source 1 and the first polarization modulation module 214. The first half-wave plate 2132 is used to adjust the nanosecond pulse laser beam of this path into horizontally linearly polarized light so that it can pass through the first polarization beam splitter 2133.

[0071] Based on the above structure, the first fundamental frequency amplification module 211 performs preliminary amplification on the nanosecond pulse laser emitted from the fundamental frequency seed source 1. The third delay line 2131 applies a half-cycle time-domain delay to the nanosecond pulse laser in this path, so that the repetition frequency after polarization beam combining is doubled from 1MHz to 2MHz, while the single pulse energy remains unchanged, in order to match another nanosecond pulse laser. The first half-wave plate 2132 is rotated and adjusted to adjust this nanosecond pulse laser into horizontally linearly polarized light. Since this path is horizontally linearly polarized light, it will directly pass through the first polarizing beam splitter prism 2133 (PBS).

[0072] Along the direction of light propagation, the second fundamental frequency amplification module 212, the second half-wave plate 2134, and the first reflector 2135 are arranged in sequence. The second half-wave plate 2134 is used to adjust the nanosecond pulse laser in this path into vertically polarized light, and the first reflector 2135 is tilted at 45° to change the direction of the light path so that the nanosecond pulse laser is reflected vertically into the first polarizing beam splitter 2133.

[0073] Based on the above structure, the second fundamental frequency amplification module 212 also performs preliminary amplification on the nanosecond pulse laser emitted from the fundamental frequency seed source 1. The second half-wave plate 2134 adjusts this nanosecond pulse laser into vertically linearly polarized light. The first reflector 2135 is placed at a 45° angle, turning this vertically linearly polarized light 90° so that it is perpendicularly incident on the first polarization beam splitter 2133 and reflected by the first polarization beam splitter 2133. It then coincides with the first transmitted horizontally polarized light in space, forming a composite beam containing two polarization states. This allows the two laser beams to exit along the same path after the first polarization beam splitter 2133. The laser beam after polarization beam combining contains equal proportions of horizontal and vertical components, and the pulses are distributed in alternating polarization states in time sequence to improve the total output power.

[0074] Understandably, the second polarization beam combining module 313 in this embodiment has the same structure as the first polarization beam combining module 213. The second polarization beam combining module 313 includes a fourth delay line 3131, an eighth half-wave plate 3132, a fifth polarization beam splitter prism 3133, a ninth half-wave plate 3134, and a ninth reflector 3135. Therefore, their positions and functions will not be described in detail here.

[0075] In this embodiment, after the outputs of the second and fourth fundamental frequency amplification modules 212 and 312, a half-cycle time-domain delay is performed through the third and fourth delay lines 2131. This ensures, through time-domain control, that the path delay difference between the four fundamental frequency amplification modules 211, 212, 311, and 312 is ≤0.2ns, maintaining pulse timing synchronization. This ensures that the single pulse energy remains unchanged after being polarized and combined by the second and first polarization combining modules 213 and 313, with a repetition frequency of 2MHz. The timing of the two orthogonally polarized pulses is interleaved and superimposed. Preferably, in this embodiment, the third and fourth delay lines 2131 are fiber optic delay lines with a delay of 0.5μs and a delay accuracy on the order of ps.

[0076] Furthermore, the first polarization modulation module 214 includes a first electro-optic modulator 2141, a first electro-optic drive box 2142, and a second polarization beam splitter 2143. The first electro-optic drive box 2142 is electrically connected to the first electro-optic modulator 2141. The first electro-optic drive box 2142 is triggered externally, and the trigger signal is given by the controller of the fundamental frequency seed source 1. By controlling the voltage provided by the first electro-optic drive box 2142, a voltage is applied to the first electro-optic modulator 2141 to rotate the polarization state of the vertically linearly polarized light provided by the second fundamental frequency amplification module 212 in the incident orthogonal polarization pulse sequence by 90°, while the horizontally linearly polarized light provided by the first fundamental frequency amplification module 211 is not modulated. Along the direction of light propagation, the first electro-optic modulator 2141 and the second polarization beam splitter 2143 are disposed between the first polarization beam combining module 213 and the first second harmonic generation module 22.

[0077] The synthesized beam emitted from the first polarization beam splitter 2133 in this embodiment is polarized and modulated by the first electro-optic modulator 2141, and then passes through the second polarization beam splitter 2143 to reach the first frequency doubling module 22. This polarization modulation is achieved based on the first electro-optic modulator 2141 (EOM): after the controller of the fundamental frequency seed source 1 gives an enable signal, it delays for 15-20ns before triggering the nanosecond pulse laser output; the first electro-optic drive box 2142 immediately performs a drive voltage switching operation after receiving the enable signal, so as to effectively avoid the nanosecond pulse laser being in the voltage rising edge region, thereby eliminating polarization state modulation distortion. The first electro-optic driver 2142 is set to a modulation frequency of 1MHz and a duty cycle of 50% (50% on / 50% off time). By applying a half-wave voltage (Vπ, corresponding to phase delay π) to the first electro-optic modulator 2141, the polarization state of the incident light is changed. It only modulates the vertical linear polarization component. The voltage application is consistent with the vertical linear polarization timing, and the voltage de-voltage is consistent with the horizontal linear polarization timing. The input orthogonal polarization pulse can be modulated into a horizontal linear polarization pulse with a repetition frequency of 2MHz. After polarization modulation, a single linear polarization laser with an average power ≥100W and a wavelength of 1547nm is obtained, so that the single linear polarization laser passes through the second polarization beam splitter 2143 and is output to the first frequency doubling module 22.

[0078] Understandably, the second polarizing beam splitter 2143 in this embodiment is coated with an antireflection film on both sides with a center wavelength of 1547 nm for polarization detection, allowing horizontally polarized light to pass through and ensuring the extinction ratio of the output fundamental frequency light. The first electro-optic modulator 2141 in this embodiment can be used as a high repetition rate (1 MHz), high-power BBO electro-optic Q-switch, and can be used for nanosecond pulse modulation. Due to device performance limitations (such as capacitive response hysteresis), there is a nanosecond-level rise time during the voltage application process (15 ns in this example). To ensure modulation stability, the timing of the fundamental frequency seed source 1 and the first electro-optic driver 2142 needs to be adjusted.

[0079] It is also understood that the second polarization modulation module 314 in this embodiment has the same structure as the first polarization modulation module 214. The second polarization modulation module 314 includes a second electro-optic modulator 3141, a second electro-optic drive box 3142 and a sixth polarization beam splitter 3143, so its position and function will not be described in detail here.

[0080] Furthermore, the first second-harmonic generation module 22 includes a third half-wave plate 221, a third polarizing beam splitter 222, a first focusing lens 223, a first second-harmonic generation component 224, a first collimating lens 225, a first dichroic mirror 226, and a fourth half-wave plate 227 arranged sequentially along the direction of light propagation.

[0081] The third half-wave plate 221 is designed with a wavelength of 1547nm. It is used to rotate the polarization state of the first polarized laser by a preset angle before it enters the third polarization beam splitter 222. The outgoing light is split into two laser beams with mutually perpendicular transmission directions. One of the first polarized laser beams, transmitted by the third polarization beam splitter 222, is directed towards the first focusing lens 223. The other of the first polarized laser beams, reflected by the third polarization beam splitter 222, is directed towards the third frequency harmonic module 23. In essence, the combination of the third half-wave plate 221 and the third polarization beam splitter 222 can split the single linearly polarized laser beam transmitted through the second polarization beam splitter 2143 into two laser beams with mutually perpendicular transmission directions. Furthermore, the power ratio of the two beams can be adjusted by rotating the third half-wave plate 221, ensuring that one of the beams remains horizontally polarized.

[0082] The first frequency-doubler component 224 is used to convert the first polarized laser light, after passing through the first focusing lens 223, into a 773.5nm wavelength laser light through second harmonic conversion. The first collimating lens 225 collimates the divergent beam after frequency doubler conversion, making it parallel light. In this embodiment, the first frequency-doubler component 224 includes a nonlinear crystal, a clamp, and a temperature control device. The nonlinear crystal can be an LBO (Low-Bearing Beam), which obtains a 773.5nm harmonic in a phase-matched manner, has a large receiving angle, and the harmonic does not drift, thus achieving very high nonlinear conversion efficiency. It is understood that the structure of the first frequency-doubler component 224 described above is a conventional structure and is not particularly limited here.

[0083] The two surfaces of the third polarizing beam splitter 222 and the two surfaces of the first focusing lens 223 are respectively coated with anti-reflection films with a center wavelength of 1547nm, which reduces the reflection loss of 1547nm laser on these components and improves the transmission efficiency; the function of the first focusing lens 223 is to focus the fundamental frequency spot inside the crystal, thereby obtaining high conversion efficiency by increasing the power density.

[0084] Both surfaces of the first second-harmonic generation component 224 and both surfaces of the first collimating lens 225 are coated with dual-wavelength anti-reflection films with center wavelengths of 1547 nm and 773.5 nm; wherein, the two surfaces of the first second-harmonic generation component 224 refer to the two surfaces of the nonlinear crystal in the first second-harmonic generation component 224. The dual-wavelength anti-reflection film with center wavelengths of 1547 nm and 773.5 nm is used to reduce the reflection loss of the two wavelengths.

[0085] The incident surface of the first dichroic mirror 226 is coated with a first dichroic film, and the rear surface of the first dichroic mirror 226 is coated with a dual-wavelength antireflection film with center wavelengths of 1547nm and 773.5nm to ensure that both wavelengths of light can pass through efficiently. The first dichroic film is configured to have high reflectivity for 773.5nm wavelength light and high transmittance for 1547nm wavelength light, separating the remaining fundamental frequency light of 1547nm (i.e., the first polarized laser) that has not been completely converted from the second harmonic light of 773.5nm to prevent interference.

[0086] The fourth half-wave plate 227 is designed with a wavelength of 773.5nm to adjust the 773.5nm wavelength laser into horizontally linearly polarized light that is incident on the third harmonic module 23.

[0087] Understandably, the first second harmonic module 22 and the second second harmonic module 34 in this embodiment have the same structure. The structure of the second second harmonic module 34 includes a tenth half-wave plate 341, a seventh polarizing beam splitter 342, a third focusing lens 343, a second second harmonic assembly 344, a third collimating lens 345, an eleventh dichroic mirror 346, and an eleventh half-wave plate 347 arranged sequentially along the direction of light propagation. Therefore, their positions and functions will not be described in detail here.

[0088] Furthermore, the third harmonic module 23 includes a second reflecting mirror 231, a first beam shrinking mirror 232, a fifth half-wave plate 233, a fourth polarizing beam splitter prism 234, a second dichroic mirror 235, a second focusing lens 236, a third harmonic assembly 237, a second collimating lens 238, and a third dichroic mirror 239 arranged sequentially along the direction of light propagation.

[0089] The second reflecting mirror 231 is set at 45°, and its incident surface is coated with a high-reflectivity film with a center wavelength of 1547nm to reflect another first polarized laser beam to the first beam shrinking mirror 232. The first beam shrinking mirror 232 consists of a positive lens and a negative lens, with a beam shrinking ratio of approximately 1 / √2, in order to reduce the diameter of the laser beam (beam shrinking) and improve the coupling efficiency or focusing capability of the subsequent optical system. The distance between the positive lens and the negative lens is adjustable, and both surfaces of the positive lens and the negative lens are coated with an anti-reflection film with a center wavelength of 1547nm. It can cooperate with the first collimating lens 225 so that the 1547nm wavelength light and the 773.5nm wavelength light can coincide after being focused by the second focusing lens 236.

[0090] The fifth half-wave plate 233 is designed with a wavelength of 1547nm and is used to change the polarization state of the laser (such as rotating vertically polarized light into horizontally polarized light). It is used in conjunction with the polarizing beam splitter to adjust the laser polarization state to achieve the desired optical path. The two surfaces of the fourth polarizing beam splitter 234 are respectively coated with an anti-reflection film with a center wavelength of 1547nm. It is used to allow the horizontally linearly polarized light adjusted by the fifth half-wave plate 233 to pass through and exit to the second dichroic mirror 235, where it is purified.

[0091] The incident surface of the second dichroic mirror 235 is used to reflect the horizontally linearly polarized light adjusted by the fourth half-wave plate 227, and the rear surface of the second dichroic mirror 235 is used to transmit the laser light transmitted by the fourth polarizing beam splitter 234. The incident surface of the second dichroic mirror 235 is coated with a first dichroic film, and the rear surface of the first dichroic mirror 226 is coated with a dual-wavelength antireflective film with center wavelengths of 1547nm and 773.5nm, so as to combine the laser light of wavelength 773.5nm and wavelength 1547nm into a first dual-wavelength laser light.

[0092] The third harmonic generation assembly 237 includes a nonlinear crystal, a fixture, and a temperature control device. The nonlinear crystal can be an LBO (Low-Browser-Board) and employs a type of phase matching, with optimized cut-off angles to reduce walk-off effects. The assembly relationship between the nonlinear crystal, fixture, and temperature control device is the same as that of a conventional third harmonic generation assembly 237, and will not be described in detail here. The second focusing lens 236 is used to focus the first dual-wavelength laser into the third harmonic generation assembly 237. The focal point falls near the center of the nonlinear crystal in the third harmonic generation assembly 237. The third harmonic generation assembly 237 is used to convert the first dual-wavelength laser into a 515.7nm wavelength laser through third harmonic conversion. This 515.7nm wavelength laser is collimated by the second collimating lens 238 and then directed towards the third dichroic mirror 239 for beam splitting. In this embodiment, by adjusting the focal position matching (spatial overlap) of the first dual-wavelength laser within the nonlinear crystal, the wavefront quality of the beam is optimized, providing a high-quality pump source for subsequent high-order harmonic generation.

[0093] The incident surface of the third dichroic mirror 239 is coated with an optical thin film, which is configured to be an anti-reflective coating that is highly reflective to light with a wavelength of 515.7 nm and highly transmittable to light with wavelengths of 773.5 nm and 1547 nm. The rear surface of the third dichroic mirror 239 is coated with a three-wavelength anti-reflective coating.

[0094] Furthermore, the fourth frequency harmonic module 35 includes a fourth dichroic mirror 351, a second beam shrinking mirror 352, a fourth frequency harmonic component 353, a fifth dichroic mirror 354, and a sixth half-wave plate 355 arranged sequentially along the optical path.

[0095] The fourth dichroic mirror 351 is used to reflect the horizontally linearly polarized light adjusted by the second second harmonic module 34 (i.e., the eleventh half-wave plate 347) to the second beam shrinking mirror 352, and its designed wavelength is 773.5nm.

[0096] The second beam shrinking lens 352 consists of a positive lens and a negative lens. The beam shrinking ratio is determined by design. The purpose is to match the 386.75nm wavelength light converted by the fourth harmonic component 353 with the 515.7nm wavelength mode in the seventh harmonic component 416. The two surfaces of the positive lens and the negative lens are respectively coated with an anti-reflection film with a center wavelength of 773.5nm.

[0097] The fourth harmonic generation module 353 includes a nonlinear crystal, a fixture, and a temperature control device. The nonlinear crystal can be an LBO (Low-Range Bore) crystal, employing high-temperature Class I phase matching. The walk-off effect is reduced by optimizing the cutting angle. The arrangement of the nonlinear crystal, fixture, and temperature control device is the same as that of a conventional fourth harmonic generation module 353, and will not be described in detail here. The fourth harmonic generation module 353 is used to convert the laser beam reduced by the second beam reducer 352 into a 386.75nm wavelength laser beam through fourth harmonic conversion, and output it to the fifth dichroic mirror 354 for dichroic separation. The 386.75nm wavelength laser beam is then reflected into the seventh harmonic generation module 41.

[0098] The incident surface of the fifth dichroic mirror 354 is coated with a second dichroic film, and the rear surface of the fifth dichroic mirror 354 is coated with a dual-wavelength antireflection film; the second dichroic film is configured to have high reflectivity for light with a wavelength of 386.75nm and high transmittance for light with a wavelength of 773.5nm.

[0099] The sixth half-wave plate 355 is designed with a wavelength of 386.75 nm to adjust the polarization direction of the laser.

[0100] Furthermore, the seventh frequency harmonic module 41 includes a third beam shrinking mirror 411, a seventh half-wave plate 412, a third reflecting mirror 413, a sixth dichroic mirror 414, a first window mirror 415, a seventh frequency harmonic assembly 416, a seventh dichroic mirror 417, an eighth dichroic mirror 418, and a second window mirror 419 arranged sequentially along the optical path.

[0101] The third beam shrinker 411 is used to receive the first laser emitted from the first delay line 24 and transmit it to the seventh half-wave plate 412. Understandably, the third beam shrinker 411 can shrink the 515.7nm laser beam, and the shrinkage ratio is adjustable. It works in conjunction with the second beam shrinker 352 to adjust the size of the two wavelengths of light entering the seventh harmonic component 416 to achieve mode matching.

[0102] The seventh half-wave plate 412 is used to adjust the polarization direction, and the third reflector 413 is coated with a high-reflection film with a center wavelength of 515.7nm to reflect the laser passing through the seventh half-wave plate 412 to the rear surface of the sixth dichroic mirror 414.

[0103] The rear surface of the sixth dichroic mirror 414 is used to transmit the laser reflected by the third reflecting mirror 413, and the incident surface of the sixth dichroic mirror 414 is used to reflect the laser output by the sixth half-wave plate 355. The rear surface of the sixth dichroic mirror 414 is coated with an anti-reflection film with a center wavelength of 515.7nm, and the incident surface of the sixth dichroic mirror 414 is coated with a third dichroic film. The third dichroic film is configured to highly reflect light with a wavelength of 386.75nm and highly transmit light with a wavelength of 515.7nm, so as to combine the laser with a wavelength of 386.75nm and the laser with a wavelength of 515.7nm into a second dual-wavelength laser that enters the first window mirror 415.

[0104] The first window mirror 415 is coated with a dual-wavelength antireflection film to serve as an isolation layer; the second window mirror 419 is coated with an antireflection film with a center wavelength of 221nm, which works in conjunction with the first window mirror 415 to isolate and seal the intermediate components separately.

[0105] The seventh frequency multiplier 416 includes a nonlinear crystal and its fixture, which is used to receive the second dual-wavelength laser transmitted from the first window mirror 415 and convert it into a 221nm wavelength laser output to the seventh dichroic mirror 417.

[0106] The incident surfaces of the seventh dichroic mirror 417 and the eighth dichroic mirror 418 are both coated with a third dichroic film, and the exit surfaces of both are coated with a three-wavelength antireflective film. The third dichroic film is configured to highly reflect light at a wavelength of 221 nm and highly transmit light at wavelengths of 386.75 nm and 515.7 nm. The seventh dichroic mirror 417 and the eighth dichroic mirror 418 are used to spatially separate light at a wavelength of 221 nm from the fundamental frequency of the sum.

[0107] It should be noted that, in some embodiments, the seventh frequency multiplication module 41 further includes a sampling unit 420, which includes a first sampling mirror 4201 and a first power detector 4202. The first sampling mirror 4201 is coated with a high-reflectivity film with a reflectivity of approximately 99.5% for light with a wavelength of 221 nm. 0.5% of the transmitted light enters the first power detector 4202, which collects the power signal of the light with a wavelength of 221 nm at a certain sampling frequency and feeds it back to the controller for data determination. The first sampling mirror 4201 is located between the eighth dichroic mirror 418 and the second window mirror 419.

[0108] Furthermore, the eighth-frequency harmonic module 42 includes a fourth beam shrinking mirror 421, a third window mirror 422, a ninth dichroic mirror 423, an eighth-frequency harmonic component 424, a tenth dichroic mirror 425, and a fourth window mirror 426 arranged sequentially along the optical path.

[0109] The fourth beam shrinker 421 is used to receive the second polarized laser emitted from the second delay line 33 and transmit it to the third window mirror 422; it can be understood that the fourth beam shrinker 421 is used to shrink the laser with a wavelength of 1547nm, and the shrinkage ratio is adjustable, with the aim of matching the 221nm wavelength mode emitted from the seventh harmonic module 41.

[0110] The third window mirror 422 is coated with an antireflective film with a center wavelength of 1547nm, which serves as an isolation and sealing function; the fourth window mirror 426 is used to output the fourth laser after passing through the tenth dichroic mirror 425. The fourth window mirror 426 is coated with an antireflective film with a center wavelength of 193.375nm. Its function is to work together with the third window mirror 422 to isolate and seal the eighth harmonic part separately.

[0111] The rear surface of the ninth dichroic mirror 423 is used to transmit the laser light passing through the third window mirror 422, and the incident surface of the ninth dichroic mirror 423 is used to reflect the third laser light passing through the second window mirror 419. The rear surface of the ninth dichroic mirror 423 is coated with an anti-reflection film with a center wavelength of 1547nm. The incident surface of the ninth dichroic mirror 423 is coated with a fourth dichroic film, which is configured to highly reflect light with a wavelength of 221nm and highly transmit light with a wavelength of 1547nm, so as to combine the laser light with a wavelength of 221nm and the laser light with a wavelength of 1547nm into a third dual-wavelength laser light and enter the eighth frequency-multiplied component 424.

[0112] The eighth frequency harmonic component 424 contains a nonlinear crystal and its fixture, which is used to receive the third dual-wavelength laser emitted from the ninth dichroic mirror 423 and convert it into a laser with a wavelength of 193.375nm and output it to the tenth dichroic mirror 425.

[0113] The incident surface of the tenth dichroic mirror 425 is coated with a fifth dichroic film, and the exit surface of the tenth dichroic mirror 425 is coated with a three-wavelength antireflective film; wherein, the fifth dichroic film is configured to highly reflect light with a wavelength of 193.375nm and highly transmit light with wavelengths of 1547nm and 221nm, so as to spatially separate the light with a wavelength of 193.375nm from the fundamental frequency of the sum frequency.

[0114] It should be noted that, in some embodiments, the eighth-harmonic generation module 42 further includes a spot position detector 427, a second sampling mirror 428, and a second power detector 429. The spot position detector 427 is located on one side of the rear surface of the ninth dichroic mirror 423. It collects the coordinates of the energy center of the 221nm wavelength laser spot at a certain sampling frequency and feeds them back to the control program. The program issues instructions to the corresponding devices to adjust and correct the input optical path of the eighth-harmonic generation. The second sampling mirror 428 is coated with a high-reflectivity film with a reflectivity of about 99.5% for light with a wavelength of 193.375nm. The 0.5% of transmitted light enters the second power detector 429, which collects the power signal of the 193.375nm wavelength light at a certain sampling frequency and feeds it back to the controller for data judgment.

[0115] Furthermore, the first delay line 24 includes a fourth reflector 241 and a fifth reflector 242. The extension line of the fourth reflector 241 is perpendicular to the extension line of the fifth reflector 242. It can be moved back and forth along the y-axis to compensate for the optical path, so that the laser output by the third frequency harmonic module 23 is reflected sequentially through the fourth reflector 241 and the fifth reflector 242 to the third beam shrinking mirror 411 of the seventh frequency harmonic module 41, thereby achieving time-domain matching of the two wavelengths of light, 515.7nm and 386.75nm, in the seventh frequency harmonic module 41.

[0116] The second delay line 33 is used to compensate for the optical path and fold the optical path. It includes a sixth reflector 331, a seventh reflector 332, and an eighth reflector 333 arranged along the optical path. The sixth reflector 331, the seventh reflector 332, and the eighth reflector 333 are all coated with a high-reflection film with a center wavelength of 1547nm. The extension line of the seventh reflector 332 is perpendicular to the extension line of the eighth reflector 333. It can be moved back and forth along the x-axis to compensate for the optical path, so that the second polarized laser output from the second beam combining structure 31 is reflected sequentially through the sixth reflector 331, the seventh reflector 332, and the eighth reflector 333 to the eighth frequency doubling module 42, realizing the time-domain matching of the two wavelengths of light, 1547nm and 221nm, in the eighth frequency doubling component 424. It can be understood that the second polarized laser output from the second beam combining structure 31 is reflected by the seventh polarization beam splitter prism 342 of the second second frequency doubling module 34 and then output to the sixth reflector 331.

[0117] The specific implementation is as follows: A single fundamental frequency seed source 1 with a repetition rate of 1MHz generates four independent lasers through a beam splitter, which are injected into the first fundamental frequency amplification module 211, the second fundamental frequency amplification module 212, the third fundamental frequency amplification module 311, and the fourth fundamental frequency amplification module 312 respectively to achieve power enhancement (single-channel power ≥ 65W); after amplification, a half-cycle delay is applied to the two optical paths containing the first fundamental frequency amplification module 211 and the third fundamental frequency amplification module 311, and then the two lasers of the first fundamental frequency amplification module 211 and the second fundamental frequency amplification module 212, and the third fundamental frequency amplification module 311 and the fourth fundamental frequency amplification module 312 are combined into two orthogonally polarized pulse fundamental frequency beams with a repetition rate of 2MHz through polarization beam combining technology; after polarization modulation, electro-optic Q-switching is used with a modulation frequency of 1MHz to rotate the polarization state of the vertically linearly polarized light component provided in the incident orthogonally polarized pulse sequence by 90°, and outputting a single linearly polarized pulse laser with a repetition rate of 2MHz. To ensure modulation stability, after the controller of the fundamental frequency seed source 1 gives the enable signal, it delays for 15ns before emitting light into the amplification system. After receiving the enable signal, the electro-optic driver performs voltage increase and decrease operations, which can effectively avoid the optical pulse being in the voltage rise edge region, thereby eliminating polarization modulation distortion. The polarization beam combining and polarization-modulated two fundamental frequencies have a single-channel power ≥100W.

[0118] The first and second polarized lasers, after polarization modulation, undergo harmonic conversion: the first polarized laser enters the first second harmonic conversion optical path 2, where it undergoes second harmonic conversion in the first second harmonic conversion module 2 to obtain a laser with a wavelength of 773.5 nm. The 773.5 nm laser and the remaining 1547 nm laser then enter the third harmonic conversion module 23 to undergo third harmonic conversion, obtaining a first laser with a wavelength of 515.7 nm.

[0119] The second polarized laser is split into two paths. The first path enters the second delay line 33 of the second harmonic conversion optical path 3, and the second path enters the second second harmonic conversion module 34 of the second harmonic conversion optical path 3 for second harmonic conversion, obtaining a laser with a wavelength of 773.5nm. The 773.5nm laser enters the fourth harmonic conversion module 35 for fourth harmonic conversion, obtaining a second laser with a wavelength of 386.75nm. The first and second lasers are combined in the seventh harmonic conversion module 41 of the output optical path 4 to obtain a third laser with a wavelength of 221nm.

[0120] The third laser and the second polarized laser are summed in the eighth-harmonic generation module 42 to obtain a fourth laser with a wavelength of 193.375 nm, which is then finally output. In the time domain, taking the optical path of the harmonic conversion optical path branch 32 where the fourth-harmonic generation module 35 is located as the timing reference, a first delay line 24 and a second delay line 33 are respectively set on the branch path directly entering the eighth-harmonic generation module 42 after the third-harmonic generation module 23 and the second polarization modulation module 314 to ensure that the two laser beams entering the seventh-harmonic generation module 41 and the eighth-harmonic generation module 42 are synchronized in the time domain.

[0121] In summary, this invention provides a dual-frequency deep ultraviolet laser generator. Its single seed source is divided into multiple paths and independently amplified before being combined in pairs to form a single linearly polarized laser. Subsequently, it achieves eighth harmonic conversion output through different harmonic conversion optical paths. This embodiment avoids the single-path power bottleneck by using this distributed amplification method, breaks through the power limitation of the fundamental frequency in the traditional sum-frequency method, and obtains a high-power output laser with a wavelength of 193.375nm.

[0122] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A dual-frequency deep ultraviolet laser generator, characterized in that, This includes a fundamental frequency seed source, a first harmonic conversion optical path, a second harmonic conversion optical path, and an output optical path; The fundamental frequency seed source is used to emit nanosecond pulsed lasers in the 1547nm band; The first harmonic conversion optical path has a first beam combining structure, a first second harmonic module, a third harmonic module, and a first delay line arranged sequentially along the propagation direction of the light. The first beam combining structure is used to combine the two amplified nanosecond pulse laser beams and perform polarization modulation to generate a first polarized laser. The first polarized laser is a single linearly polarized laser with a wavelength of 1547nm. The first polarized laser generates a first laser with a wavelength of 515.7nm after passing through the first second harmonic module, the third harmonic module, and the first delay line in sequence. The second harmonic conversion optical path has a second beam combining structure, a harmonic conversion optical path branch, and a second delay line. The second beam combining structure is used to combine the two amplified nanosecond pulse laser beams and perform polarization modulation to generate a second polarized laser. The second polarized laser is a single linearly polarized laser with a wavelength of 1547nm. The harmonic conversion optical path branch and the second delay line are connected in parallel between the second beam combining structure and the output optical path. The harmonic conversion optical path branch has a second second harmonic module and a fourth harmonic module arranged sequentially after the second beam combining structure along the propagation direction of the light. The second polarized laser generates a second laser with a wavelength of 386.75nm after passing through the second second harmonic module and the fourth harmonic module in sequence. The output optical path has a seventh-frequency harmonic module and an eighth-frequency harmonic module. The seventh-frequency harmonic module is used to receive the first laser and the second laser, and sum them to produce a third laser with a wavelength of 221nm. The eighth-frequency harmonic module is used to receive the second polarized laser and the third laser, and sum them to produce a fourth laser with a wavelength of 193.375nm.

2. The dual-frequency deep ultraviolet laser generator according to claim 1, characterized in that, The first beam combining structure is identical to the second beam combining structure. The first beam combining structure includes a first fundamental frequency amplification module, a second fundamental frequency amplification module, a first polarization beam combining module, and a first polarization modulation module. The first fundamental frequency amplification module and the second fundamental frequency amplification module are connected in parallel between the fundamental frequency seed source and the first polarization beam combining module to amplify the nanosecond pulse laser. The first polarization beam combining module is used to polarize and combine the two amplified nanosecond pulse lasers into a single pulse laser. The first polarization modulation module is located between the first polarization beam combining module and the first second harmonic module to polarize and modulate the combined single pulse laser into the first polarized laser.

3. The dual-frequency deep ultraviolet laser generator according to claim 2, characterized in that, The first polarization beam combining module includes a third delay line, a first half-wave plate, a first polarization beam splitter, a second half-wave plate, and a first reflector. Along the direction of light propagation, the first fundamental frequency amplification module, the third delay line, the first half-wave plate, and the first polarization beam splitter are sequentially disposed between the fundamental frequency seed source and the first polarization modulation module. The first half-wave plate is used to adjust the nanosecond pulse laser in this path into horizontally linearly polarized light so that it can pass through the first polarization beam splitter. Along the direction of light propagation, the second fundamental frequency amplification module, the second half-wave plate, and the first reflector are arranged in sequence. The second half-wave plate is used to adjust the nanosecond pulse laser in this path into vertically polarized light, and the first reflector is set at a 45° angle so as to reflect the nanosecond pulse laser vertically into the first polarization beam splitter.

4. The dual-frequency deep ultraviolet laser generator according to claim 2, characterized in that, The first polarization modulation module includes a first electro-optic modulator, a first electro-optic drive box, and a second polarization beam splitter. The first electro-optic drive box is electrically connected to the first electro-optic modulator. Along the direction of light propagation, the first electro-optic modulator and the second polarization beam splitter are disposed between the first polarization beam combining module and the first frequency doubling module.

5. The dual-frequency deep ultraviolet laser generator according to claim 1, characterized in that, The first frequency doubling module has the same structure as the second frequency doubling module. The first frequency doubling module includes a third half-wave plate, a third polarizing beam splitter, a first focusing lens, a first frequency doubling component, a first collimating lens, a first dichroic mirror, and a fourth half-wave plate arranged sequentially along the direction of light propagation. The third half-wave plate is used to rotate the polarization state of the first polarized laser by a preset angle and then incident it into the third polarization beam splitter. The outgoing light is split into two lasers with mutually perpendicular transmission directions. One of the first polarized lasers, transmitted by the third polarization beam splitter, is directed towards the first focusing lens, and the other of the first polarized lasers, reflected by the third polarization beam splitter, is incident into the third frequency harmonic module. The first frequency doubling component is used to convert the first polarized laser passing through the first focusing lens into a second harmonic laser with a wavelength of 773.5nm. The two surfaces of the third polarizing beam splitter and the two surfaces of the first focusing lens are respectively coated with an anti-reflection film with a center wavelength of 1547nm; Both surfaces of the first frequency doubling component and both surfaces of the first collimating lens are coated with dual-wavelength antireflective films with center wavelengths of 1547nm and 773.5nm; The incident surface of the first dichroic mirror is coated with a first dichroic film, and the rear surface of the first dichroic mirror is coated with a dual-wavelength antireflection film with center wavelengths of 1547nm and 773.5nm; the first dichroic film is configured to have high reflectivity to light with a wavelength of 773.5nm and high transmittance to light with a wavelength of 1547nm. The fourth half-wave plate is designed with a wavelength of 773.5 nm to adjust the 773.5 nm wavelength laser light into horizontally linearly polarized light that is incident on the third harmonic module.

6. The dual-frequency deep ultraviolet laser generator according to claim 5, characterized in that, The third harmonic module includes a second reflecting mirror, a first beam shrinking mirror, a fifth half-wave plate, a fourth polarizing beam splitter, a second dichroic mirror, a second focusing lens, a third harmonic assembly, a second collimating lens, and a third dichroic mirror arranged sequentially along the direction of light propagation. The second reflector is set at 45° and its incident surface is coated with a high-reflectivity film with a center wavelength of 1547nm to reflect another path of the first polarized laser to the first beam shrinker. The two surfaces of the lens of the first beam shrinking lens and the two surfaces of the fourth polarizing beam splitter are respectively coated with an anti-reflection film with a center wavelength of 1547nm. The design wavelength of the fifth half-wave plate is 1547 nm; The fourth polarizing beam splitter is used to allow horizontally linearly polarized light, adjusted by the fifth half-wave plate, to pass through and exit to the second dichroic mirror; The incident surface of the second dichroic mirror is used to reflect the horizontally linearly polarized light adjusted by the fourth half-wave plate, and the rear surface of the second dichroic mirror is used to transmit the laser light transmitted by the fourth polarizing beam splitter; wherein, the incident surface of the second dichroic mirror is coated with the first dichroic film, and the rear surface of the first dichroic mirror is coated with a dual-wavelength anti-reflection film with center wavelengths of 1547nm and 773.5nm, so as to combine the laser light of wavelength 773.5nm and the laser light of wavelength 1547nm into a first dual-wavelength laser light; The third harmonic generation component is used to convert the first dual-wavelength laser into a 515.7nm wavelength laser by third harmonic generation. The incident surface of the third dichroic mirror is coated with an optical thin film, which is configured to be an anti-reflective coating that is highly reflective to light with a wavelength of 515.7 nm and highly transmittable to light with wavelengths of 773.5 nm and 1547 nm. The rear surface of the third dichroic mirror is coated with a three-wavelength anti-reflective coating.

7. The dual-frequency deep ultraviolet laser generator according to claim 1, characterized in that, The fourth frequency harmonic module includes a fourth dichroic mirror, a second beam shrinker, a fourth frequency harmonic component, a fifth dichroic mirror, and a sixth half-wave plate arranged sequentially along the optical path. The fourth dichroic mirror is used to reflect the horizontally linearly polarized light adjusted by the second second harmonic module to the second beam shrinker. The two surfaces of the lens of the second beam shrinking lens are respectively coated with an anti-reflection coating with a center wavelength of 773.5nm; The fourth harmonic generation component is used to convert the laser beam condensed by the second beam shrinker into a laser with a wavelength of 386.75nm by fourth harmonic generation. The incident surface of the fifth dichroic mirror is coated with a second dichroic film, and the rear surface of the fifth dichroic mirror is coated with a dual-wavelength anti-reflection film; the second dichroic film is configured to have high reflectivity for light with a wavelength of 386.75nm and high transmittance for light with a wavelength of 773.5nm. The design wavelength of the sixth half-wave plate is 386.75 nm.

8. The dual-frequency deep ultraviolet laser generator according to claim 7, characterized in that, The seventh frequency multiplication module includes a third beam shrinker, a seventh half-wave plate, a third reflector, a sixth dichroic mirror, a first window mirror, a seventh frequency multiplication component, a seventh dichroic mirror, an eighth dichroic mirror, and a second window mirror arranged sequentially along the optical path. The third beam shrinking mirror is used to receive the first laser emitted from the first delay line and transmit it to the seventh half-wave plate; The third reflector is coated with a high-reflectivity film with a center wavelength of 515.7 nm to reflect the laser light passing through the seventh half-wave plate to the rear surface of the sixth dichroic mirror. The rear surface of the sixth dichroic mirror is used to transmit the laser reflected by the third reflecting mirror, and the incident surface of the sixth dichroic mirror is used to reflect the laser output by the sixth half-wave plate; wherein, the rear surface of the sixth dichroic mirror is coated with an antireflection film with a center wavelength of 515.7nm, and the incident surface of the sixth dichroic mirror is coated with a third dichroic film, which is configured to highly reflect light with a wavelength of 386.75nm and highly transmit light with a wavelength of 515.7nm, so as to combine the laser with a wavelength of 386.75nm and the laser with a wavelength of 515.7nm into a second dual-wavelength laser; The first window is coated with a dual-wavelength antireflection film, and the second window is coated with an antireflection film with a center wavelength of 221nm. The seventh frequency harmonic component is used to receive the second dual-wavelength laser transmitted from the first window mirror and convert it into a 221nm wavelength laser output to the seventh dichroic mirror; The incident surfaces of the seventh and eighth dichroic mirrors are both coated with a third dichroic film, and the exit surfaces of the seventh and eighth dichroic mirrors are both coated with a three-wavelength antireflective film. The third dichroic film is configured to have high reflectivity for light with a wavelength of 221 nm and high transmittance for light with wavelengths of 386.75 nm and 515.7 nm.

9. The dual-frequency deep ultraviolet laser generator according to claim 8, characterized in that, The eighth frequency multiplication module includes a fourth beam shrinking mirror, a third window mirror, a ninth dichroic mirror, an eighth frequency multiplication component, a tenth dichroic mirror, and a fourth window mirror arranged sequentially along the optical path. The fourth beam shrinking mirror is used to receive the second polarized laser emitted from the second delay line and transmit it to the third window mirror; The third window mirror is coated with an antireflective coating with a center wavelength of 1547nm, and the fourth window mirror is used to output the fourth laser after passing through the tenth dichroic mirror. The fourth window mirror is coated with an antireflective coating with a center wavelength of 193.375nm. The rear surface of the ninth dichroic mirror is used to transmit laser light passing through the third window mirror, and the incident surface of the ninth dichroic mirror is used to reflect the third laser light passing through the second window mirror; wherein, the rear surface of the ninth dichroic mirror is coated with an antireflection film with a center wavelength of 1547nm; the incident surface of the ninth dichroic mirror is coated with a fourth dichroic film, which is configured to highly reflect light with a wavelength of 221nm and highly transmit light with a wavelength of 1547nm, so as to combine the laser light with a wavelength of 221nm and the laser light with a wavelength of 1547nm into a third dual-wavelength laser; The eighth-harmonic generation component is used to receive the third dual-wavelength laser emitted from the ninth dichroic mirror and convert it into a laser with a wavelength of 193.375nm, which is then output to the tenth dichroic mirror. The incident surface of the tenth dichroic mirror is coated with a fifth dichroic film, and the exit surface of the tenth dichroic mirror is coated with a three-wavelength antireflective film; wherein, the fifth dichroic film is configured to have high reflectivity for light with a wavelength of 193.375nm and high transmittance for light with wavelengths of 1547nm and 221nm.

10. The dual-frequency deep ultraviolet laser generator according to claim 1, characterized in that, The first delay line includes a fourth reflector and a fifth reflector. The extension line of the fourth reflector and the extension line of the fifth reflector are perpendicular to each other, so that the laser output by the third harmonic module is reflected sequentially through the fourth reflector and the fifth reflector to the seventh harmonic module. The second delay line includes a sixth, a seventh, and an eighth reflector arranged along the optical path. The sixth, seventh, and eighth reflectors are all coated with a high-reflectivity film with a center wavelength of 1547 nm. The extension line of the seventh reflector is perpendicular to the extension line of the eighth reflector, so that the second polarized laser output from the second beam combining structure is reflected sequentially through the sixth, seventh, and eighth reflectors to the eighth frequency harmonic module.

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