All-solid-state continuous wave vacuum ultraviolet laser with intra-cavity cascade frequency conversion

Abstract

The utility model relates to the technical field of lasers, in particular to an intracavity cascade frequency conversion all-solid-state continuous wave vacuum ultraviolet laser, which is characterized in that a first cavity mirror M1, a first laser crystal C1, a fourth cavity mirror M4, a fifth cavity mirror M5 and a sixth cavity mirror M6 form a first laser resonant cavity; the second cavity mirror M2, the second laser crystal C2, the third cavity mirror M3, the fourth cavity mirror M4 and the seventh cavity mirror M7 form a second laser resonant cavity; the first nonlinear optical crystal O1 is arranged between the fifth cavity mirror M5 and the sixth cavity mirror M6, and is used for performing frequency doubling on the 526-nm laser generated by the first resonant cavity into 263-nm frequency-doubled laser; the second nonlinear optical crystal O2 is arranged between the fourth cavity mirror M4 and the fifth cavity mirror M5, frequency sum is carried out on 725nm fundamental frequency laser generated by the second resonant cavity and 263nm frequency doubling laser generated by the first nonlinear optical crystal O1, and 193nm vacuum ultraviolet laser is generated and output through the fourth cavity mirror M4. The utility model has the advantages of simple internal structure, few frequency conversion times, stable output and long service life.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more specifically to an all-solid-state continuous-wave vacuum ultraviolet laser with intracavity cascaded frequency conversion. Background Technology

[0002] Vacuum ultraviolet lasers refer to laser sources with wavelengths in the range of 100–200 nm. Among them, 193 nm is a particularly important wavelength, serving as a crucial tool for research in high-resolution spectroscopy, photochemistry, fiber grating fabrication, integrated circuit etching, and precision laser processing. Especially in the field of semiconductor integrated circuit manufacturing, with the increasing density of chips and the continuous shrinking of lithography dimensions, the wavelengths of the required photolithography sources are becoming increasingly shorter.

[0003] Currently, ArF excimer gas lasers are the only type of laser source capable of directly generating laser output at a wavelength of 193 nm in vacuum ultraviolet light. They typically use a combination of rare and reactive gases under high pressure to generate ultraviolet lasers, offering high output power and occupying a significant market share in photolithography light sources. However, the working medium of ArF excimer lasers contains fluorine gas, which is toxic and corrosive, posing risks to personal safety and environmental pollution. Furthermore, gas lasers have limited pulse repetition frequencies (typically <10 kHz), high peak power, poor beam quality, and poor coherence, limiting their applications in detection.

[0004] Compared to gas lasers, solid-state 193nm laser sources offer advantages such as high repetition rate, good beam quality, good coherence, small size, and adjustable pulse width. The generation process of this type of solid-state source primarily relies on nonlinear optical frequency conversion. Although its output power and efficiency are relatively low, it can still meet the needs of applications such as fiber grating writing, angle-resolved photoelectron spectroscopy experiments, semiconductor chip defect detection, and ArF excimer gas laser seeding.

[0005] For solid-state 193nm laser sources, the selection of the fundamental frequency source and the choice of the nonlinear optical frequency conversion path are crucial, directly determining the efficiency and complexity of the entire laser system. Current solid-state 193nm lasers generally use near-infrared lasers as the fundamental frequency source, and then obtain the 193nm laser output through three or more intracavity or extracavity frequency conversions. For example, the paper "Advanced Photonics Nexus, 3, 026012, 2024" first obtains a 258nm laser through two frequency doublings of a 1030nm source, and then achieves the 193nm output through two summing frequencies with a 1553nm source, undergoing a total of four frequency conversions. In the paper "Optics Letters, 40, 5590-5593, 2015," a 275.5nm laser is first obtained through two frequency doublings of an 1102nm source, then a 234.1nm laser is obtained through a summing frequency with a 1560nm source, and finally a 193.4nm output is achieved through a summing frequency with an 1110nm source, also undergoing four frequency conversions. Three fundamental frequency light sources (1102nm, 1560nm, and 1110nm) were used. In patent document CN118610880 A, a 773.6nm laser from an alexandrite crystal was used as the fundamental frequency light source, and a nonlinear crystal was used for frequency doubling, third harmonicization, and fourth harmonicization (three frequency conversions) to achieve the target wavelength of 193.4nm. In summary, existing solid-state 193nm laser technologies all use three or more nonlinear optical frequency conversions, which have drawbacks such as complex generation processes, severe energy attenuation, low conversion efficiency, high manufacturing costs, and poor reliability.

[0006] Therefore, how to provide a 193nm ultraviolet laser with a simple structure and few frequency conversions has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides an all-solid-state continuous wave vacuum ultraviolet laser with intracavity cascaded frequency conversion, which has a simple internal structure, requires fewer frequency conversions, operates stably and reliably, and has a long lifespan.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] An all-solid-state continuous-wave vacuum ultraviolet laser with intracavity cascaded frequency conversion includes: a first pump source LD1, a first cavity mirror M1, a first laser crystal C1, a second cavity mirror M2, a second laser crystal C2, a third cavity mirror M3, a fourth cavity mirror M4, a fifth cavity mirror M5, a sixth cavity mirror M6, a seventh cavity mirror M7, a first nonlinear optical crystal O1, and a second nonlinear optical crystal O2.

[0010] The first cavity mirror M1, the first laser crystal C1, the fourth cavity mirror M4, the fifth cavity mirror M5, and the sixth cavity mirror M6 constitute the first laser resonant cavity.

[0011] The second cavity mirror M2, the second laser crystal C2, the third cavity mirror M3, the fourth cavity mirror M4, and the seventh cavity mirror M7 constitute the second laser resonant cavity;

[0012] The first nonlinear optical crystal O1 is disposed between the fifth cavity mirror M5 and the sixth cavity mirror M6, and frequency doubles the 526nm laser generated by the first resonant cavity into a 263nm frequency doubled laser.

[0013] The second nonlinear optical crystal O2 is disposed between the fourth cavity mirror M4 and the fifth cavity mirror M5. It combines the 725nm fundamental frequency laser generated by the second resonant cavity with the 263nm frequency-doubled laser generated by the first nonlinear optical crystal O1 to generate a 193nm±2nm vacuum ultraviolet laser, which is then output through the fourth cavity mirror M4.

[0014] Furthermore, a first birefringence filter BRF1 is inserted into the optical cavity formed by the first cavity mirror M1 and the third cavity mirror M3; a second birefringence filter BRF2 is inserted into the optical cavity formed by the second cavity mirror M2 and the third cavity mirror M3.

[0015] Furthermore, both the first birefringent filter BRF1 and the second birefringent filter BRF2 are made of quartz, with a thickness of 0.5 mm, and the optical axis C is parallel to the surface.

[0016] The first birefringent filter BRF1 is inserted into the optical cavity formed by the first cavity mirror M1 and the third cavity mirror M3 at a Brewster angle of 57.28°, adjusting the angle A between the incident surface and the principal plane to 38.1°, and controlling the laser wavelength at 526nm.

[0017] The second birefringent filter BRF2 is inserted into the optical cavity formed by the second cavity mirror M2 and the third cavity mirror M3 at a Brewster angle of 57.15°, adjusting the angle α between the incident surface and the principal plane to 38.8°, and controlling the laser wavelength at 725nm.

[0018] Furthermore, both the first laser crystal C1 and the second laser crystal C2 are Pr 3+ :SRA、Pr 3+ BYF or Pr 3+ YGF; wherein, the two light-transmitting end faces of the first laser crystal C1 are coated with a 526nm anti-reflection film; and the two light-transmitting end faces of the second laser crystal C2 are coated with a 725nm anti-reflection film.

[0019] Furthermore, the first nonlinear optical crystal O1 is a frequency doubling crystal for a 526nm laser, using a β-BBO crystal, a KDP crystal, or an ADP crystal, and its two light-transmitting end faces are coated with anti-reflection films of 725nm, 526nm, and 263nm.

[0020] Furthermore, the second nonlinear optical crystal O2 is a sum-frequency crystal of 725nm laser and 263nm laser, using β-BBO crystal or KBBF crystal, and its two light-transmitting end faces are coated with anti-reflection films of 725nm, 526nm, 263nm and 193nm.

[0021] Furthermore, both the first pump source LD1 and the second pump source LD2 are laser diodes with spatial output or fiber-coupled output, and the laser wavelength they emit is 445nm.

[0022] Furthermore, the first cavity mirror M1 is a plane mirror coated with a dielectric film of 445nm anti-reflection and 526nm high reflectivity, and is positioned close to the first pump source LD1; the second cavity mirror M2 is a plane mirror coated with a dielectric film of 445nm high transmittance and 725nm high reflectivity, and is positioned close to the second pump source LD2.

[0023] The first laser crystal C1 is located between the first cavity mirror M1 and the second cavity mirror M2, and is positioned close to the first cavity mirror M1; the second laser crystal C2 is located between the second cavity mirror M2 and the third cavity mirror M3, and is positioned close to the second cavity mirror M2.

[0024] Furthermore, the third cavity mirror M3 is disposed between the first cavity mirror M1 and the fourth cavity mirror M4, and is placed at an angle of 45 degrees relative to the optical path M1M4;

[0025] The third cavity mirror M3 is a plane mirror coated with a dielectric film with high transmittance of 526nm and high reflectivity of 725nm, used to separate the pump source ends of the first laser resonant cavity and the second laser resonant cavity.

[0026] Furthermore, the fourth cavity mirror M4 is a plano-concave mirror, serving as a common reflecting cavity mirror for the first and second laser resonant cavities, as well as an output mirror for the 193nm laser; the fourth cavity mirror M4 is coated with a dielectric film of 193nm high transmittance, 526nm high reflectance and 725nm high reflectance on the side near the resonant cavity, and coated with a 193nm high transmittance dielectric film on the side away from the resonant cavity.

[0027] The sixth cavity mirror M6 is a plane mirror, serving as the total internal reflection end mirror of the first laser resonant cavity; the sixth cavity mirror M6 is coated with a dielectric film with high reflectivity of 263nm and 526nm and high transmittance of 600-750nm on the side near the resonant cavity.

[0028] The seventh cavity mirror M7 is a plano-concave mirror, serving as the total internal reflection end mirror of the second laser resonant cavity; the seventh cavity mirror M7 is coated with a dielectric film with 725nm high reflectivity and 600-650nm high transmittance on the side near the resonant cavity.

[0029] The fifth cavity mirror M5 is a plano-concave mirror used to separate the total reflection ends of the first laser resonant cavity and the second laser resonant cavity; the side of the fifth cavity mirror M5 closest to the second nonlinear optical crystal O2 is coated with a dielectric film of 263nm and 526nm high reflectivity and 725nm antireflection, and the side away from the second nonlinear optical crystal O2 is coated with a dielectric film of 725nm antireflection.

[0030] The first nonlinear optical crystal O1 is positioned close to the sixth cavity mirror M6; the second nonlinear optical crystal O2 is positioned at the waist of the optical cavity formed by the fourth cavity mirror M4 and the fifth cavity mirror M5.

[0031] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The fundamental frequency light wavelength used in this invention is 526nm and 725nm. Only 2 frequency conversions are needed to obtain 193nm laser output. Compared with the previous 3 to 5 frequency conversions, there are fewer nonlinear optical conversion processes and the overall conversion efficiency is higher.

[0033] 2. The first and second laser resonant cavities of this invention share cavity mirrors M3 and M4, and are separated by cavity mirrors M3 and M5. The two resonant cavities constitute a multi-mirror folded cavity. Four beam waist positions are designed in the two resonant cavities to place laser crystals C1 and C2 and nonlinear optical crystals O1 and O2, respectively, which ensures high power and high efficiency of continuous laser generation and nonlinear frequency conversion output.

[0034] 3. This invention uses birefringent filters to adjust the laser wavelengths of the two resonant cavities, precisely controlling the oscillating laser wavelengths at 526nm and 725nm, with narrow spectral lines and stable output. Simultaneously, the BRF also enables the laser's output wavelength to have a certain degree of tunability around 193nm, meeting various special needs, such as precise alignment with its wavelength when used as a seed source for ArF excimer gas lasers.

[0035] 4. This invention uses cavity mirror M5 to separate the total reflection ends of the two laser resonators at 526nm and 725nm. Since the 725nm wavelength does not pass through optical paths M5 and M6, the thermal load on the first nonlinear optical crystal O1 within the M5 / M6 optical path is relatively small, resulting in more stable frequency doubling from 526nm to 263nm. Furthermore, the coating of cavity mirror M6 does not need to consider the reflection at 725nm, simplifying the manufacturing process, reducing the total power it can withstand, and extending its lifespan. Moreover, the second laser resonator, formed by cavity mirrors M2, M3, M4, and M7, contains only one nonlinear optical crystal O2, resulting in lower intracavity loss and higher circulating power. In summary, the separation of the first and second laser resonators at the total reflection ends brings advantages such as high efficiency, stability, and extended lifespan.

[0036] 5. This invention, through careful screening of rare earth ions and matrix crystals, determines that Pr... 3+ SRA crystal is used as the working medium for generating 193nm solid-state laser. This crystal... 3 P1→ 3 The central wavelength of the H5 radiative transition is 525 nm, with a radiative bandwidth of 9.8 nm. A 526 nm laser can be easily obtained through frequency selection using a BRF (Brightness-Radiation-Reflection) method. 3 P0→ 3 The center wavelength of the F4 radiative transition is 725 nm, with a radiative bandwidth of 4.35 nm. Using a BRF (Browser Resonance Array), the output laser can be easily locked at 725 nm. Therefore, Pr 3+ The high-efficiency emission at 526nm and 725nm by the SRA crystal ensures that a precise 193nm wavelength vacuum ultraviolet laser output can be achieved through further intracavity frequency conversion. Furthermore, its large fluorescence emission bandwidth also gives the laser a certain wavelength tuning capability around 193nm, which can be adjusted according to actual needs, requiring only fine-tuning of the BRF and the nonlinear optical crystal.

[0037] In summary, this invention reduces the frequency conversion steps required to generate 193nm solid-state lasers, improves conversion efficiency, reduces device size, simplifies internal structure, and offers advantages such as tunable wavelength, high reliability, easy maintenance, and low cost. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the structure of the all-solid-state continuous wave vacuum ultraviolet laser with intracavity cascaded frequency conversion provided in Embodiment 1 of the present invention.

[0040] Figure 2 This is a schematic diagram of the optical path of the fundamental frequency laser passing through the birefringent filter in Embodiment 1 of the present invention.

[0041] Figure 3 This is a schematic diagram of the transmission characteristics (α = 38.1°, d = 0.5 mm) of the first birefringent filter BRF1 in Embodiment 1 of the present invention.

[0042] Figure 4 This is a schematic diagram of the transmission characteristics (α = 38.8°, d = 0.5 mm) of the second birefringent filter BRF2 in Embodiment 1 of the present invention.

[0043] Figure 5 This is a schematic diagram of the beam size at various positions within the first laser resonant cavity enclosed by M1-M4-M5-M6 in Embodiment 1 of the present invention.

[0044] Figure 6 This is a schematic diagram of the beam size at various positions within the second laser resonant cavity enclosed by M2-M3-M4-M7 in Embodiment 1 of the present invention. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Example 1: In this example, the vacuum ultraviolet laser outputs a wavelength of 193nm, and its specific structure is as follows. Figure 1 As shown, it includes: a first pump source LD1, a first cavity mirror M1, a first laser crystal C1, a second cavity mirror M2, a second laser crystal C2, a third cavity mirror M3, a fourth cavity mirror M4, a fifth cavity mirror M5, a sixth cavity mirror M6, a seventh cavity mirror M7, a first nonlinear optical crystal O1, and a second nonlinear optical crystal O2.

[0047] Among them, the first cavity mirror M1, the first laser crystal C1, the fourth cavity mirror M4, the fifth cavity mirror M5 and the sixth cavity mirror M6 constitute the first laser resonant cavity;

[0048] The second cavity mirror M2, the second laser crystal C2, the third cavity mirror M3, the fourth cavity mirror M4, and the seventh cavity mirror M7 constitute the second laser resonant cavity;

[0049] A first birefringent filter BRF1 is inserted into the M1M3 optical cavity composed of the first cavity mirror M1 and the third cavity mirror M3; a second birefringent filter BRF2 is inserted into the M2M3 optical cavity composed of the second cavity mirror M2 and the third cavity mirror M3; the two birefringent filters are used to precisely adjust the oscillation wavelength to 526nm and 725nm.

[0050] The first nonlinear optical crystal O1 is placed between the fifth cavity mirror M5 and the sixth cavity mirror M6 to frequency double the 526nm laser generated by the first resonant cavity into a 263nm frequency doubled laser.

[0051] The second nonlinear optical crystal O2 is positioned between the fourth cavity mirror M4 and the fifth cavity mirror M5. It combines the 725nm fundamental frequency laser generated by the second resonant cavity with the 263nm frequency-doubled laser generated by the first nonlinear optical crystal O1 to generate a 193nm vacuum ultraviolet laser, which is then output through the fourth cavity mirror M4.

[0052] To ensure effective focusing of the pump light, a focusing lens F1 is placed between the first pump source LD1 and the first mirror cavity M1, and a focusing lens F2 is placed between the second pump source LD2 and the second mirror cavity M2. The focal lengths of F1 and F2 are both 100mm, and their function is to focus the pump light emitted by LD1 and LD2 onto the laser crystals C1 and C2.

[0053] Specifically, the first birefringent filter BRF1 is made of quartz with a thickness of 0.5 mm, and its optical axis C is parallel to its surface. The first birefringent filter BRF1 is inserted into the M1M3 optical cavity formed by the first cavity mirror M1 and the third cavity mirror M3 at a Brewster angle of 57.28° (corresponding to 526 nm). The angle A between the incident plane (the plane formed by the incident ray and the normal to the birefringent filter plane) and the principal plane (the plane formed by the normal to the birefringent filter plane and the optical axis) is adjusted to 38.1° to precisely control the oscillation wavelength at 526 nm. The optimization process for the above parameters is as follows:

[0054] The first birefringent filter BRF1 is positioned at Brewster angle θ b Inserting a laser resonant cavity, the propagation optical path of the fundamental frequency laser is as follows: Figure 2 As shown. Due to the birefringence effect, the incident o-ray and e-ray will have a certain phase difference after passing through the BRF:

[0055]

[0056] Where λ is the incident wavelength, and n o and n eLet be the refractive indices of the ordinary ray and the extraordinary ray, respectively; d be the thickness of the BRF; and β be the angle between the optical axis and the wave vector of the ordinary ray. The angle between the incident plane (the plane formed by the incident ray and the normal to the birefringent filter plane) and the principal plane (the plane formed by the normal to the birefringent filter plane and the optical axis) is the tuning angle α, and the following geometric relationship applies:

[0057] cosβ=cosαcosθ b (2)

[0058] The o-ray and e-ray emitted by the first birefringent filter BRF1 will interfere upon exiting from the rear surface. The single-pass transmittance of BRF1 can be calculated from the intensity of the interference light. When polarized light is incident at Brewster's angle, the transmittance can be expressed as:

[0059]

[0060] Where φ represents the angle between the electric displacement vectors of the o-ray and the incident ray, and we have:

[0061] sinφ=cotβ·tanθ b (4)

[0062] Based on the above formula, the tuning effect of BRF1 on the laser wavelength after insertion into the resonant cavity can be theoretically simulated. Taking the Brewster angle as 57.28° and the birefringence Δn = n... e -n o Approximately 0.009, taking different thicknesses d and tuning angles α, the following conclusions can be drawn from the calculation results of formula (3): at the same tuning angle α, the larger the thickness of BRF, the narrower its transmittance peak will be. As the thickness of BRF1 increases, the interval between transmittance peaks becomes smaller and smaller, and at this time, multi-wavelength output may occur within the gain range of the laser crystal. In order to minimize the insertion loss of BRF1 while taking into account its mechanical strength, the thickness d of BRF1 is optimized to 0.5mm. When the tuning angle α is around 40°, the minimum transmittance of the wavelength is almost zero, and the linewidth compression effect is the best. The more the tuning angle α deviates from 40°, the higher the minimum transmittance and the worse the linewidth narrowing effect. Through multiple iterations of optimization, the α = 38.1° corresponding to the transmittance of 526nm is obtained under the condition of d = 0.5mm, and its transmittance curve is as follows. Figure 3 As shown.

[0063] Similarly, optimized parameters for the second birefringent filter BRF2 can be obtained. The second birefringent filter BRF2 is inserted into the M2M3 optical cavity, which consists of the second cavity mirror M2 and the third cavity mirror M3, at a Brewster angle of 57.15°. The angle α between the incident plane (the plane formed by the incident ray and the normal to the birefringent filter plane) and the principal plane (the plane formed by the normal to the birefringent filter plane and the optical axis) is adjusted to 38.8°, precisely controlling the oscillating laser wavelength at 725nm. Its transmittance curve is shown in the attached figure. Figure 4 As shown.

[0064] Both the first laser crystal C1 and the second laser crystal C2 are Pr 3+ :SRA(Pr 3+ :SrAl 12 O 19 The doping concentration is 0.5 at.%. The first laser crystal C1 has a 526nm antireflection coating on both optically transparent ends, emitting 526nm laser light under the feedback of a 526nm laser resonator. The second laser crystal C2 has a 725nm antireflection coating on both optically transparent ends, emitting 725nm laser light under the feedback of a 725nm laser resonator.

[0065] The first nonlinear optical crystal, O1, is a frequency-doubled crystal for a 526nm laser. Its two optically transparent ends are coated with anti-reflection films of 725nm, 526nm, and 263nm, respectively. It generates a 263nm frequency-doubled laser through type I phase matching. When O1 is a β-BBO crystal, the processing angle is (θ = 48.5°, φ = 0°). When O1 is a CLBO crystal, the processing angle is (θ = 62.8°, φ = 45°). When C3 is a KDP crystal, the processing angle is (θ = 79.5°, φ = 45°). When O1 is an ADP crystal, the processing angle is (θ = 83.7°, φ = 45°).

[0066] The second nonlinear optical crystal, O2, is a sum-frequency crystal for 725nm and 263nm lasers. It is made of β-BBO or KBBF crystal, with anti-reflection coatings of 725nm, 526nm, 263nm, and 193nm on its two optically transparent ends. A 193nm frequency-doubled laser is generated through type I phase matching. When O2 is a β-BBO crystal, the processing angle is (θ = 74.8°, φ = 0°). When O2 is a KBBF crystal, the processing angle is (θ = 47.1°, φ = 0°).

[0067] The first pump source LD1 and the second pump source LD2 are both space-output or fiber-coupled laser diodes (LDs) with a center wavelength of 445nm, aligned with Pr. 3+ SRA crystal 3 H4→ 3 Absorption peak of P2 level transition.

[0068] The first cavity mirror M1 is a plane mirror coated with a dielectric film of 445nm anti-reflection and 526nm high reflectivity, and is positioned close to the first pump source LD1; the second cavity mirror M2 is a plane mirror coated with a dielectric film of 445nm high transmittance and 725nm high reflectivity, and is positioned close to the second pump source LD2; the first laser crystal C1 is located between the first cavity mirror M1 and the second cavity mirror M2, and is positioned close to the first cavity mirror M1; the second laser crystal C2 is located between the second cavity mirror M2 and the third cavity mirror M3, and is positioned close to the second cavity mirror M2.

[0069] The third cavity mirror M3 is positioned between the first cavity mirror M1 and the fourth cavity mirror M4, and is placed at a 45-degree angle relative to the optical path M1M4.

[0070] The third cavity mirror M3 is a plane mirror coated with a dielectric film with high transmittance of 526nm and high reflectivity of 725nm, used to separate the first laser resonant cavity and the second laser resonant cavity.

[0071] The fourth cavity mirror M4 is a plano-concave mirror, serving as a common reflecting cavity mirror for the first and second laser resonant cavities, as well as an output mirror for the 193nm laser. The side of the fourth cavity mirror M4 closest to the resonant cavity is coated with a dielectric film of 193nm high transmittance, 526nm high reflectance, and 725nm high reflectance, while the side furthest from the resonant cavity is coated with a dielectric film of 193nm high transmittance.

[0072] The sixth cavity mirror M6 is a plane mirror, serving as the total internal reflection end mirror of the first laser resonant cavity; the sixth cavity mirror M6 is coated with a dielectric film with high reflectivity of 263nm and 526nm and high transmittance of 600-750nm on the side near the resonant cavity.

[0073] The seventh cavity mirror M7 is a plano-concave mirror, serving as the total internal reflection end mirror of the second laser resonant cavity; the side of the seventh cavity mirror M7 closest to the resonant cavity is coated with a dielectric film with high reflectivity of 725nm and high transmittance of 600-650nm.

[0074] The fifth cavity mirror M5 is a plano-concave mirror used to separate the total reflection end of the first laser resonant cavity and the second laser resonant cavity. The fifth cavity mirror M5 is coated with a dielectric film with high reflectivity of 263nm and 526nm and antireflection of 725nm on the side close to O2, and a dielectric film with antireflection of 725nm on the side away from O2.

[0075] The first laser crystal C1 is positioned close to the first cavity mirror M1, and the second laser crystal C2 is positioned close to the second cavity mirror M2. The first nonlinear optical crystal O1 is positioned close to the sixth cavity mirror M6; the second nonlinear optical frequency crystal O2 is positioned at the waist of the optical cavity formed by the fourth cavity mirror M4 and the fifth cavity mirror M5.

[0076] In this embodiment, the laser-related components and their geometric dimensions are as follows:

[0077] (1) The total cavity length of the first laser resonator is 179 mm, and the beam size at each position of the resonator is as follows: Figure 5 As shown, the beam size here is the laser spot radius at various positions within the resonant cavity, simulated using the ABCD matrix.

[0078] (2) The total cavity length of the second laser resonator is 152 mm, and the beam size at various positions in the resonator is as follows: Figure 6 As shown, the beam size here is the laser spot radius at various positions within the resonant cavity, simulated using the ABCD matrix.

[0079] (2) Crystal: C1: 2×2×10mm 3 C2: 2×2×10mm 3 C4: 3×3×10mm 3 C3: 3×3×10mm 3

[0080] (3) M1 flat mirror, M2 flat mirror, M3 flat mirror, M4 plano-concave mirror (concave curvature 50mm), M5 plano-concave mirror (concave curvature 50mm), M6 flat mirror, M7 plano-concave mirror (concave curvature 50mm), among which the lens M4 is made of a material with high ultraviolet transmittance, such as JGS1 quartz glass, CaF2, MgF2.

[0081] (4) C1 and C2 are close to M1 and M2 respectively. The distance between M1 and M3 is 20mm, the distance between M2 and M3 is 20mm, the distance between M3 and M4 is 24mm, the distance between M4 and M5 is 90mm, C4 is in the middle of M4 and M5, the distance between M5 and M6 is 45mm, C3 is close to M6, and the distance between M5 and M7 is 18mm.

[0082] (5) In the 526nm laser resonator formed by M1-M4-M5-M6, the beam waist radius at the C1 crystal is 58μm, the beam waist radius at the O2 crystal is 57μm, and the beam waist radius at the O1 crystal is 51μm. In the 725nm laser resonator formed by M2-M3-M4-M7, the beam waist radius at the C2 crystal is 61μm, and the beam waist radius at the O2 crystal is 67μm.

[0083] Example 2: The difference between this example and Example 1 is that the first birefringent filter BRF1 and the second birefringent filter BRF2 are removed, while the remaining components and parameters are exactly the same. Due to the absence of the frequency selection effect of the birefringent filters, Pr... 3+ The SRA crystal will emit the wavelength corresponding to the fluorescence peak. C1 emits a 525nm laser, C2 emits a 725nm laser, and the final laser emitted by M4 has a wavelength of 192.7nm.

[0084] Example 3: Compared with Example 2, this example uses Pr to replace the first laser crystal and the second laser crystal. 3+ Replace SRA with Pr 3+ :BYF(Pr 3+ The crystal (BaY2F8) has all other optical components and parameters identical. 3 P1→ 3 The central wavelength of the H5 radiative transition is 522 nm. 3 P0→ 3 The central wavelength of the F4 radiative transition is 720 nm, and the laser wavelength emitted from M4 after two intracavity frequency conversions is 191.6 nm.

[0085] Example 4: Compared with Example 2, this example uses Pr to replace the first laser crystal and the second laser crystal. 3+ Replace SRA with Pr 3+ :YGF(Pr 3+ :β-Y 0.5 Gd 0.5 F3), the rest of the optical components and parameters are exactly the same. This crystal 3 P1→ 3 The central wavelength of the H5 radiative transition is 523 nm. 3 P0→ 3 The central wavelength of the F4 radiative transition is 724 nm, and the wavelength of the laser emitted from M4 after two intracavity frequency conversions is 192.1 nm.

[0086] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0087] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An intracavity frequency cascaded, all solid state continuous wave vacuum ultraviolet laser, characterized by, The application relates to a 193nm vacuum ultraviolet laser device. The first cavity mirror M1, the first laser crystal C1, the fourth cavity mirror M4, the fifth cavity mirror M5 and the sixth cavity mirror M6 constitute a first laser resonant cavity. The second cavity mirror M2, the second laser crystal C2, the third cavity mirror M3, the fourth cavity mirror M4 and the seventh cavity mirror M7 constitute a second laser resonant cavity. The first nonlinear optical crystal O1 is arranged between the fifth cavity mirror M5 and the sixth cavity mirror M6, and the first laser resonant cavity generates 263nm frequency-doubled laser by frequency doubling 526nm laser. The second nonlinear optical crystal O2 is arranged between the fourth cavity mirror M4 and the fifth cavity mirror M5, and the second laser resonant cavity generates 193nm+ / -2nm vacuum ultraviolet laser by frequency mixing 725nm fundamental frequency laser and 263nm frequency-doubled laser generated by the first nonlinear optical crystal O1, and the vacuum ultraviolet laser is output through the fourth cavity mirror M4. The first birefringent filter BRF1 is inserted into the optical cavity composed of the first cavity mirror M1 and the third cavity mirror M3.

2. The intracavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 1, wherein The first birefringent filter BRF1 and the second birefringent filter BRF2 are both made of quartz with a thickness of 0.5mm and an optical axis C parallel to the surface.

3. The intracavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 2, wherein The first birefringent filter BRF1 is inserted into the optical cavity composed of the first cavity mirror M1 and the third cavity mirror M3 at a Brewster angle of 57.28 degrees, the included angle A between the incident plane and the main plane is adjusted to 38.1 degrees, and the laser wavelength is controlled to be 526nm. The second birefringent filter BRF2 is inserted into the optical cavity composed of the second cavity mirror M2 and the third cavity mirror M3 at a Brewster angle of 57.15 degrees, the included angle alpha between the incident plane and the main plane is adjusted to 38.8 degrees, and the laser wavelength is controlled to be 725nm. The first nonlinear optical crystal O1 is a frequency-doubling crystal of 526nm laser, adopts a beta-BBO crystal, a KDP crystal or an ADP crystal, and the two light transmission end faces are coated with 526nm and 263nm antireflection films.

4. The intracavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 1, wherein The first laser crystal C1 and the second laser crystal C2 are Pr 3+ : SRA, Pr 3+ : BYF or Pr 3+ : YGF; wherein, two light transmission end faces of the first laser crystal C1 are coated with 526nm antireflection film; two light transmission end faces of the second laser crystal C2 are coated with 725nm antireflection film.

5. The intracavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 1, wherein The second nonlinear optical crystal O2 is a sum frequency mixing crystal of 725nm laser and 263nm laser, adopts a beta-BBO crystal or a KBBF crystal, and the two light transmission end faces are coated with 725nm, 526nm, 263nm and 193nm antireflection films.

6. The intracavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 1, wherein The first pump source LD1 and the second pump source LD2 are both spatial output or fiber-coupled output laser diodes, and the emitted laser wavelength is 445nm.

7. The intra-cavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 1, wherein ​ 8. The intracavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 1, wherein, The first cavity mirror M1 is a plane mirror coated with 445 nm antireflection and 526 nm high reflection dielectric films, and is arranged close to the first pump source LD1; the second cavity mirror M2 is a plane mirror coated with 445 nm high transmission and 725 nm high reflection dielectric films, and is arranged close to the second pump source LD2; The first laser crystal C1 is arranged between the first cavity mirror M1 and the second cavity mirror M2, and close to the first cavity mirror M1; the second laser crystal C2 is arranged between the second cavity mirror M2 and the third cavity mirror M3, and close to the second cavity mirror M2.

9. The intracavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 1, wherein, The third cavity mirror M3 is arranged between the first cavity mirror M1 and the fourth cavity mirror M4, and is placed at an angle of 45 degrees relative to the optical path M1M4; The third cavity mirror M3 is a plane mirror coated with 526 nm high transmission and 725 nm high reflection dielectric films, and is used to separate the pump source end of the first laser resonant cavity and the second laser resonant cavity.

10. The intracavity frequency-doubled, all-solid-state continuous-wave vacuum ultraviolet laser according to claim 1, wherein The fourth cavity mirror M4 is a plane-concave mirror, which is a common reflecting cavity mirror of the first laser resonant cavity and the second laser resonant cavity, and is also an output mirror of the 193 nm laser; the fourth cavity mirror M4 is coated with 193 nm high transmission, 526 nm high reflection and 725 nm high reflection dielectric films on the side close to the resonant cavity, and is coated with 193 nm high transmission dielectric film on the side away from the resonant cavity; The sixth cavity mirror M6 is a plane mirror, which is a total reflection end mirror of the first laser resonant cavity; the sixth cavity mirror M6 is coated with 263 nm, 526 nm high reflection and 600-750 nm high transmission dielectric films on the side close to the resonant cavity; The seventh cavity mirror M7 is a plane-concave mirror, which is a total reflection end mirror of the second laser resonant cavity; the seventh cavity mirror M7 is coated with 725 nm high reflection and 600-650 nm high transmission dielectric films on the side close to the resonant cavity; The fifth cavity mirror M5 is a plane-concave mirror, which is used to separate the total reflection end of the first laser resonant cavity and the second laser resonant cavity; the fifth cavity mirror M5 is coated with 263 nm, 526 nm high reflection and 725 nm antireflection dielectric films on the side close to the second nonlinear optical crystal O2, and is coated with 725 nm antireflection dielectric film on the side away from the second nonlinear optical crystal O2; The first nonlinear optical crystal O1 is arranged close to the sixth cavity mirror M6; the second nonlinear optical crystal O2 is arranged at the beam waist of the optical cavity composed of the fourth cavity mirror M4 and the fifth cavity mirror M5.

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