A high power high harmonic generation device

Abstract

The application provides a high-power high-harmonic generation device, and relates to the field of extreme ultraviolet light sources.The application comprises a femtosecond laser emitter for emitting femtosecond laser light, and further comprises a first compression module, a frequency doubling module, a second compression module and a high-harmonic generation and detection mechanism arranged in sequence in the femtosecond laser light path; the first compression module is used for compressing the pulse width of the femtosecond laser light; the frequency doubling module is used for generating frequency-doubled light; the second compression module is used for compressing the pulse width of the frequency-doubled light; and the high-harmonic generation and detection mechanism is used for generating high-harmonic light.The application can realize high-power high-harmonic generation: when Ar is used as the HHG medium, high-harmonic light with a total power of up to 159.3 muW can be generated, wherein the average power of the 11th order (26.5 eV) is up to 92.4 muW, and relatively high-power coherent EUV output is realized.

Description

Technical Field

[0001] This invention relates to the field of extreme ultraviolet light sources, and in particular to a high-power high-order harmonic generation device. Background Technology

[0002] Coherent extreme ultraviolet (EUV) radiation generated by high-harmonic generation (HHG) has shown significant application potential in transient absorption spectroscopy, high spatial resolution imaging, and as a substitute source for synchrotron radiation. However, significant technical bottlenecks remain in achieving a synergistic improvement in high average power, high photon energy, and excellent spatial coherence. The energy scale and temporal characteristics of the driving pulse directly limit the conversion efficiency of HHG. Although hollow-core fiber (HCF) and gas multi-cavity (MPC) are currently the main methods for broadening the spectrum, thermally induced device damage and output instability under high power loads severely restrict their application limits. Furthermore, reflection loss in dispersion management and absorption attenuation during harmonic separation and metal thin-film filtering further reduce the output efficiency of the final EUV.

[0003] To address the aforementioned challenges, exploring an integrated front-end technology architecture with high power handling capacity, efficient spectral broadening, and low transmission loss is of significant strategic importance for developing stable, high-performance, and cost-effective EUV coherent light sources. Summary of the Invention

[0004] To address the aforementioned problems, the first aspect of this invention provides a high-power high-order harmonic generation device capable of generating high-power high-order harmonics.

[0005] The first aspect of this invention provides a high-power high-harmonic generation device, including a femtosecond laser emitter for emitting femtosecond laser light. The device is characterized by further comprising: a primary compression module, a frequency doubling module, a secondary compression module, and a high-harmonic generation and detection mechanism, sequentially located in the femtosecond laser optical path. The primary compression module includes a multi-pass cavity and a first chirped mirror group, the first chirped mirror group comprising a plurality of sequentially arranged chirped mirrors, the first chirped mirror group being located in the output optical path of the multi-pass cavity, and the output light from the first chirped mirror group being incident on the frequency doubling module. The frequency doubling module includes a frequency doubling crystal and a dichroic mirror, the frequency doubling crystal being used to double the frequency of the femtosecond laser to obtain... Frequency-doubled light is obtained; the dichroic mirror is disposed in the output optical path of the frequency-doubled crystal to separate the femtosecond laser and the frequency-doubled light; the frequency-doubled light separated by the dichroic mirror is incident on a secondary compression module; the secondary compression module includes a hollow-core optical fiber and a second chirped mirror group, the second chirped mirror group includes multiple chirped mirrors arranged in sequence, the second chirped mirror group is located in the output optical path of the hollow-core optical fiber, and the output light of the second chirped mirror group is incident on a high-order harmonic generation and detection mechanism; the high-order harmonic generation and detection mechanism includes a vacuum cavity and a gas box located inside the vacuum cavity, the gas box is filled with gas, and the gas can act on the frequency-doubled light to generate high-order harmonics.

[0006] In one feasible embodiment, the primary compression module further includes a plurality of first reflectors, which are respectively located in the incident optical path and the outgoing optical path of the multi-channel cavity; the secondary compression module further includes a plurality of second reflectors, which are respectively located in the incident optical path of the hollow optical fiber, the outgoing optical path of the hollow optical fiber, and the outgoing optical path of the second chirped mirror group.

[0007] In one feasible embodiment, in the second chirped mirror group, the chirped mirrors are defined in order of contact with the frequency-doubled light. For example, the first chirped mirror to contact the frequency-doubled light is the first chirped mirror. A second reflector is provided between the first and second chirped mirrors to reflect the light from the first chirped mirror to the second chirped mirror. For the other chirped mirrors in the second chirped mirror group, a third chirped mirror is used to reflect the light from the second chirped mirror, and so on.

[0008] In one feasible embodiment, the secondary compression module further includes an optical fiber loading component, which has a groove in which the hollow optical fiber is disposed; the hollow optical fiber includes an optical fiber body and a window disposed at the incident end of the optical fiber body, and the interior of the optical fiber body is filled with gas.

[0009] In one feasible embodiment, the optical fiber loading component is made of copper, the window is made of fused silica, and the angle between the window and the optical fiber body is Brewster's angle; the frequency doubling crystal is made of barium borate.

[0010] In one feasible embodiment, the high-order harmonic generation and detection mechanism further includes: an aperture and a focusing lens disposed outside the vacuum cavity, wherein the frequency-doubled light is incident on the gas box after passing through the aperture and the focusing lens; a quartz glass plate, an aluminum film, a flat focal field grating, a silver mirror, and a camera disposed inside the vacuum cavity and sequentially located in the high-order harmonic optical path generated by the gas box; wherein the quartz glass plate is coated with an Nb2O5 thin film.

[0011] In one feasible embodiment, the higher harmonic generation and detection mechanism further includes a photodiode, which is movable into the optical path of the higher harmonics to measure the harmonic power after passing through the aluminum film.

[0012] In one feasible embodiment, the high-order harmonic generation and detection mechanism further includes: a chopper disposed outside the vacuum cavity and a test aluminum film disposed inside the vacuum cavity, wherein the frequency-doubled light is incident on the aperture after passing through the chopper; the test aluminum film can be moved into the optical path of the high-order harmonic, and when the test aluminum film moves into the optical path of the high-order harmonic, it is located between the quartz glass plate and the flat focal field grating.

[0013] In one feasible embodiment, the high-order harmonic generation and detection mechanism further includes a first attitude adjustment stage, a second attitude adjustment stage, and a third attitude adjustment stage. The photodiode is disposed on the first attitude adjustment stage, the flat focal field grating is disposed on the second attitude adjustment stage, and the silver mirror is disposed on the third attitude adjustment stage.

[0014] A second aspect of the present invention also provides a method for generating high-power high-order harmonics, employing a high-power high-order harmonic generating apparatus as provided in the first aspect of the present invention, comprising:

[0015] The femtosecond laser emitter emits a femtosecond laser, which undergoes multiple reflections within the multi-pass cavity. The accumulated self-phase modulation effect with air achieves spectral broadening, and then it is incident on the first chirped mirror group to compensate for the dispersion.

[0016] A femtosecond laser is incident on a frequency-doubled crystal and generates frequency-doubled light. A dichroic mirror separates the femtosecond laser and the frequency-doubled light.

[0017] Frequency-doubled light is incident on a hollow fiber to broaden its spectrum, and then incident on a second chirped mirror group to compensate for dispersion.

[0018] The frequency-doubled light is incident on the gas box and comes into contact with the gas loaded in the gas box, generating higher harmonics.

[0019] In one feasible implementation, it further includes:

[0020] 1) The femtosecond laser emitted by the femtosecond laser emitter has a center wavelength of 1030 nm, a single pulse energy of 260 μJ, a repetition frequency of 100 kHz, an average power of 26 W, and a pulse width of 600 fs.

[0021] 2) After passing through the first-stage compression module, the femtosecond laser has an average power of 24.5 W and a pulse width of 130 fs;

[0022] 3) The frequency-doubled light emitted by the frequency-doubled module is green light, with an output power of 15.7 W and a pulse width of 130 fs;

[0023] 4) After passing through the secondary compression module, the output power of the frequency-doubled light is 9.5 W, and the pulse width is 15 fs;

[0024] 5) The power of higher harmonics is 159.3 μW; of which, the average power of the 11th harmonic is 92.4 μW.

[0025] The high-power high-order harmonic generation device provided by this invention has the following beneficial effects:

[0026] 1) This invention can achieve high-power high-order harmonic generation: when Ar is used as the HHG medium, high-order harmonics with a total power of up to 159.3 μW can be generated, of which the 11th order (26.5 eV) average power can reach 92.4 μW, realizing relatively high-power coherent EUV output.

[0027] 2) Furthermore, the present invention can reduce transmission loss: by using a glass plate coated with Nb2O5 thin film in the separation section to attenuate the driving light, the loss of harmonics during transmission can be reduced.

[0028] 3) Furthermore, the present invention can improve system stability: the hollow fiber optic tube copper groove heat dissipation structure is conducive to long-term stable operation. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of Embodiment 1 of the present invention.

[0030] Figure 2 This is the high-order harmonic spectrum obtained in Embodiment 1 of the present invention.

[0031] Figure 3 This is a schematic diagram of the newly added structure in Embodiment 2 of the present invention. Detailed Implementation

[0032] 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. In the description of the present invention, it should be noted that the terms "left side", "right side", "upper side", "lower side", "above", "below", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0035] This invention provides a high-power high-order harmonic generation device, such as... Figure 1 As shown, the device includes a femtosecond laser emitter for emitting femtosecond laser light, and further includes: a primary compression module, a frequency doubling module, a secondary compression module, and a high-order harmonic generation and detection mechanism, sequentially located in the femtosecond laser optical path. Specifically, the primary compression module is used to compress the pulse width of the femtosecond laser, the frequency doubling module is used to generate frequency-doubled light from the femtosecond laser, the secondary compression module is used to compress the frequency-doubled light, and the high-order harmonic generation and detection mechanism is used to generate high-order harmonics.

[0036] Specifically, the first-stage compression module includes a multi-pass cavity and a first chirped mirror group. The first chirped mirror group comprises multiple chirped mirrors arranged sequentially and is located in the outgoing optical path of the multi-pass cavity. The outgoing light from the first chirped mirror group is incident on the frequency doubling module. The multi-pass cavity is typically filled with gas (e.g., air or inert gas). After the femtosecond laser is incident, the femtosecond laser and the gas undergo self-phase modulation, resulting in spectral broadening due to the accumulation of femtosecond laser light, creating a prerequisite for compressing the pulse width of the femtosecond laser. The chirped mirrors are used to precisely compensate for the dispersion of the femtosecond laser, thereby compressing the pulse width of the femtosecond laser and ensuring the peak power of the femtosecond laser pulse.

[0037] Specifically, the frequency doubling module includes a frequency doubling crystal and a dichroic mirror. The frequency doubling crystal is used to double the frequency of the femtosecond laser to obtain frequency-doubled light. For example, when the femtosecond laser is near-infrared light, the frequency doubling crystal can double the frequency of the near-infrared light to green light. Frequency doubling means that the frequency of the laser is doubled, and the wavelength is correspondingly halved, which is a typical nonlinear optical phenomenon. The dichroic mirror is disposed in the output optical path of the frequency doubling crystal to separate the femtosecond laser and the frequency-doubled light. The frequency-doubled light separated by the dichroic mirror is incident on the secondary compression module. The dichroic mirror can determine whether to reflect or allow the light to pass through based on the wavelength of the light. The frequency-doubled light separated by the dichroic mirror is incident on the secondary compression module.

[0038] Furthermore, common frequency doubling crystals include lithium triborate, barium metaborate, potassium dihydrogen phosphate / potassium dideuterium phosphate, etc.

[0039] Specifically, the secondary compression module includes a hollow-core optical fiber and a second chirped mirror group. The second chirped mirror group comprises multiple chirped mirrors arranged sequentially and is located in the outgoing optical path of the hollow-core optical fiber. The outgoing light from the second chirped mirror group is incident on the high-order harmonic generation and detection mechanism. The hollow-core optical fiber is filled with gas, such as Kr gas at a pressure of 1.3 bar. The femtosecond laser interacts with the gas to generate further spectral broadening. The chirped mirrors are used to precisely compensate for the dispersion of green light, thereby compressing the pulse width of the green light and ensuring the peak power of the green light pulse.

[0040] Specifically, the higher harmonic generation and detection mechanism includes a vacuum cavity and a gas box located inside the vacuum cavity. The gas box is filled with gas, which can act on frequency-doubled light to generate higher harmonics. The principle of higher harmonic generation is as follows: the gas box is filled with inert gas. When an ultra-intense femtosecond laser pulse is focused into it, the laser electric field first tunnels and ionizes electrons, which then accelerate in the laser field to gain high kinetic energy. Finally, when the electric field reverses, the electrons are pulled back and collide with the parent ions, radiating high-energy extreme ultraviolet photons, thereby generating higher harmonics.

[0041] Furthermore, such as Figure 1 As shown, the primary compression module further includes multiple first reflectors, which are located in the incident and exit optical paths of the multi-pass cavity, respectively. The reflectors located in the incident optical path of the multi-pass cavity are typically focusing reflectors, used to focus the femtosecond laser beam spot to ensure that the beam size and divergence angle of the femtosecond laser are consistent with the eigenmode of the multi-pass cavity. The secondary compression module further includes multiple second reflectors, which are located in the incident optical path of the hollow-core fiber, the exit optical path of the hollow-core fiber, and the exit optical path of the second chirped mirror group, respectively. The reflectors located in the incident optical path of the hollow-core fiber are typically focusing reflectors, used to focus the frequency-doubled light beam spot to ensure that the beam size and divergence angle of the frequency-doubled light are matched with the aperture of the hollow-core fiber.

[0042] Furthermore, such as Figure 1 As shown, in the second chirped mirror group, these chirped mirrors are defined in the order they come into contact with the frequency-doubled light. For example, the first chirped mirror to come into contact with the frequency-doubled light is the first chirped mirror. A second reflecting mirror is provided between the first and second chirped mirrors to reflect the light from the first chirped mirror to the second chirped mirror. For the other chirped mirrors in the second chirped mirror group, the third chirped mirror is used to reflect the light from the second chirped mirror, and so on. For illustration, the second reflecting mirror provided between the first and second chirped mirrors can be a reflecting focusing mirror with a focal length of 1m. Its function is to collimate the diverging light beam. The focal length of the reflecting focusing mirror determines the size of the collimated spot, and the diameter of the collimated spot is approximately 10mm. Because the 1m focal length reflecting focusing mirror must be placed 1m from the back end of the hollow fiber, it was positioned between the first and second chirped mirrors after careful consideration of space constraints. The spot diameter and the focal length of the lens used in subsequent high-order harmonic generation jointly determine the focusing intensity, which is crucial for efficient high-order harmonic generation.

[0043] Furthermore, such as Figure 1As shown, the secondary compression module further includes an optical fiber loading component. The optical fiber loading component has a groove, and the hollow optical fiber is disposed in the groove. The optical fiber loading component is preferably made of copper to improve heat dissipation. The hollow optical fiber includes an optical fiber body and a window disposed at the incident end of the optical fiber body. The interior of the optical fiber body is filled with gas. The optical fiber body and the window are preferably positioned to form a Brewster angle, that is, the plane of the window is rotated to a specific angle relative to the incident light path, rather than passing perpendicularly to the light path. For light with a polarization direction parallel to the incident plane (P-polarized light), its reflectivity will drop to exactly zero.

[0044] Furthermore, in higher harmonic generation and detection mechanisms, such as Figure 1 As shown, the higher harmonic generation and detection mechanism further includes: an aperture and a focusing lens disposed outside the vacuum cavity, wherein the frequency-doubled light is incident on the gas box after passing through the aperture and focusing lens; a quartz glass plate, an aluminum film, a flat focal field grating, a silver mirror, and a camera disposed inside the vacuum cavity and sequentially located in the higher harmonic optical path generated by the gas box; wherein, the quartz glass plate is coated with an Nb2O5 thin film to attenuate the driving light to prevent damage to the aluminum film, the aluminum film is used to transmit higher harmonics and completely filter out the driving light, the flat focal field grating is used to spatially separate the generated higher harmonics according to frequency, the silver mirror is used to deflect the separated higher harmonics to hit the camera, and the camera is used to image the higher harmonics. Furthermore, as... Figure 1 As shown, the higher harmonic generation and detection mechanism further includes a photodiode, which is movable into the optical path of the higher harmonics and used to measure the harmonic power after passing through the aluminum film.

[0045] In one example embodiment, the high-order harmonic generation and detection mechanism further includes a first attitude adjustment stage, a second attitude adjustment stage, and a third attitude adjustment stage. The photodiode is disposed on the first attitude adjustment stage, the flat focal field grating is disposed on the second attitude adjustment stage, and the silver mirror is disposed on the third attitude adjustment stage. The first and second attitude adjustment stages can be Lianyi XM50-50-V-35ZYDJ linear translation stages; the third attitude adjustment stage can be an RM1R60H-O-60-V-35ZYDJ rotary stage.

[0046] The present invention also provides a method for generating high-power high-order harmonics, employing the high-power high-order harmonic generating apparatus provided by the present invention, comprising:

[0047] Step 1) The femtosecond laser emitter emits a femtosecond laser. The femtosecond laser undergoes multiple reflections in the multi-pass cavity, accumulating a self-phase modulation effect with the air to achieve spectral broadening, and then is incident on the first chirped mirror group to compensate for the dispersion.

[0048] Step 2) The femtosecond laser is incident on the frequency doubling crystal and generates frequency-doubled light. The dichroic mirror separates the femtosecond laser and the frequency-doubled light.

[0049] Step 3) The frequency-doubled light is incident on the hollow fiber to broaden the spectrum, and then incident on the second chirped mirror group to compensate for the dispersion.

[0050] Step 4) The frequency-doubled light is incident on the gas box and comes into contact with the gas loaded in the gas box, generating higher harmonics.

[0051] Example 1

[0052] like Figure 1 As shown, in this embodiment, the parameters of the femtosecond laser emitted from femtosecond laser emitter 1 are as follows: center wavelength of 1030 nm, single pulse energy of 260 μJ, repetition frequency of 100 kHz, average power of 26 W, and a near-infrared pulse width of 600 fs. Specific parameters of the components used in this embodiment are shown in [reference needed].

[0053] like Figure 1 As shown, the primary compression module includes: a reflector 2, a reflector 3, and a multi-channel cavity (…). Figure 1 The multi-channel cavity is represented by the multi-channel mirror 4 and multi-channel mirror 5, the reflector 6, the chirped mirror 7, the chirped mirror 8 and the reflector 9 arranged opposite to each other. For specific parameters, please refer to Table 1 for the relevant parameters of mirror working elements and Table 2 for the relevant parameters of non-mirror elements.

[0054] As an explanation, reflectors 2 and 3 ensure that the spot size and divergence angle of the femtosecond laser are consistent with the eigenmode of the multi-pass cavity, thus coupling the femtosecond laser into the cavity. Inside the cavity, after 36 reflections by the opposing multi-pass mirrors 4 and 5, the femtosecond laser achieves spectral broadening through accumulated self-phase modulation with air. After exiting the cavity, the femtosecond laser sequentially strikes reflectors 6, 7, 8, and 9. Each reflection by chirped mirrors 7 and 8 compensates for a dispersion of -1 × 10⁻⁶. 4 fs 2 Finally, after being compressed by the first-stage compression module, the femtosecond laser outputs 24.5 W of short-pulse near-infrared light with a pulse width of 130 fs.

[0055] like Figure 1 As shown, the frequency doubling module includes: a frequency doubling crystal 10, a dichroic mirror 11, a dichroic mirror 12, and a light block 13.

[0056] For illustration, the frequency doubling crystal 10 is mounted on a manually operated translation stage to maximize its conversion efficiency by adjusting its orientation. The thickness of the frequency doubling crystal 10 is configured to 500 µm to match the pulse width and achieve optimal frequency doubling efficiency. Dichroic mirrors 11 and 12 are incident at a 45-degree angle to separate the frequency-doubled green light from the femtosecond laser. Finally, after passing through the frequency doubling module, the femtosecond laser is converted into green light with an output power of 15.7 W and a pulse width of 130 fs.

[0057] like Figure 1 As shown, the secondary compression module includes: mirror 14, mirror 15, hollow optical fiber 16, mirror 17, mirror 18, chirped mirror 19, mirror 20, chirped mirrors 21 to 28, mirror 29 and mirror 30.

[0058] As an illustration, the frequency-doubled light passes through mirrors 14 and 15 to ensure the focused spot size matches the fiber optic aperture. The fiber optic conduit of the hollow fiber 16 uses a 1 mm thick fused silica sheet as a window, positioned at a Brewster angle to improve transmission efficiency. Simultaneously, a copper groove supports the fiber optic conduit, whose excellent thermal conductivity helps improve the stability of the output laser. The fiber optic conduit uses a 250 μm inner diameter fiber and selects Kr gas, which exhibits strong nonlinear effects, to broaden the green light spectrum. Mirrors 17 and 18 are used to adjust the optical path of the frequency-doubled light emitted from the hollow fiber 16. The broadened spectrum is collimated using mirror 20 at a distance of 1 m from the fiber's output end, followed by dispersion compensation using chirped mirrors 21-28. The dispersion compensation for each reflection is -100 fs. 2 After nine reflections, the original positive dispersion of the pulse is compensated, and the positive dispersion introduced by the subsequent incident window and focusing lens is pre-compensated. Reflectors 29 and 30 are used to adjust the optical path of the frequency-doubled light reflected by the chirped mirror 28. Finally, after passing through the two-stage compression module, the frequency-doubled light outputs a 9.5 W, 15 fs pulse-width, few-period femtosecond pulse.

[0059] like Figure 1 As shown, the high-order harmonic generation and detection mechanism includes: aperture 31, focusing lens 32, gas box 33, two ultraviolet fused silica glass plates 34-35 coated with Nb2O5, light block 36, aluminum film 37, photodiode 38, flat focal field grating 39, silver mirror 40, and XUV camera 41.

[0060] After passing through aperture 31, the frequency-doubled light is focused by focusing lens 32 and enters gas box 33 to generate higher harmonics. A capillary glass tube is used as gas box 33, which can be easily penetrated by the focused laser and can withstand the thermal effects of high-power laser focusing. Different inner diameter gas boxes 33 or nozzles and different gases such as He, Ne, Ar, and Kr can be selected according to the actual experimental results. Gas box 33 is mounted on a three-dimensional displacement stage for precise position adjustment. The generated higher harmonics are attenuated by two quartz glass plates 34-35 coated with Nb2O5 thin films to prevent damage to the aluminum film. Its transmission efficiency for p-polarized higher harmonics is approximately 10%. Optical block 36 blocks the transmitted driving light, while aluminum film 37 allows the higher harmonics to pass through and completely filters out the driving light. Photodiode 38 measures the harmonic power after passing through aluminum film 37 and is mounted on the displacement stage, allowing for fine-tuning of its position and insertion / extraction in the optical path. The flat-field grating 39 is used to spatially separate the generated higher harmonics according to frequency. It is mounted on a vacuum motorized mirror mount, and its attitude can be adjusted during experiments to obtain better imaging results. The silver mirror 40 is used to deflect the separated higher harmonics so that they can be directed onto the XUV camera 41 for detection. The silver mirror 40 is mounted on a rotating displacement stage, and its angle can be adjusted to detect different orders of harmonics, thereby indirectly increasing the detection range of the CCD.

[0061] Figure 2 shows the higher harmonic spectrum obtained in this embodiment. Based on the experimentally measured higher harmonic power, the transmittance of the aluminum film, and the transmission efficiency of the Nb₂O₅-coated glass plate, the initial total power of the generated higher harmonics can be accurately calculated. Further power allocation is performed by combining the intensity proportions of each order of higher harmonics in the higher harmonic spectrum. The results show that the total power of the generated higher harmonics is 159.3 μW; among which, the average power of the 11th order higher harmonic is 92.4 μW.

[0062] Table 1. Relevant parameters of working elements of mirrors

[0063] Mirror 2 Reflective focusing mirror 1030 nm 1.5 m Mirror 3 Reflective focusing mirror 1030 nm 1.5 m Mirror 6 Reflective focusing mirror 1030 nm 1.5 m Chirping Mirror 7 / 1030 nm / Chirping Mirror 8 / / / Mirror 9 Reflective focusing mirror / 2 m Dichroic mirror 11 / / / Dichroic mirror 12 / / / Mirror 14 Reflective focusing mirror 515 nm 1 m Mirror 15 Reflective focusing mirror 515 nm 40 cm Mirror 17 High Reflectivity 515 nm 1 m Mirror 18 High Reflectivity 515 nm 1 m Chirping Mirror 19 / 515 nm / Mirror 20 Reflective focusing mirror / 1 m Chirping Mirror 21~28 / 515 nm / Mirror 29 High Reflectivity 515 nm / Mirror 30 High Reflectivity 515 nm / Focusing lens 32 / / /

[0064] Table 2 Parameters of Non-Mirror Related Components

[0065] Multi-channel laparoscopy 4, 5 / Frequency doubling crystal 10 Thickness: 500 µm; Cutting angle: 23.4° Light block 13 / Hollow fiber 16 Inner diameter: 250 µm; Length: 1 m Aperture 31 / Gas Box 33 Inner diameter: 0.6 mm <![CDATA[Ultraviolet fused silica glass plate coated with Nb2O5 34~35]]> Dimensions: 50x70 mm Light block 36 Black, high temperature resistant Aluminum film 37 Thickness: 500 nm Photodiode 38 Model: AXUV100G 39 flat focal field gratings / Silver Mirror 40 / XUV camera 41 Model: Dhyana XF95

[0066] Example 2

[0067] To accurately calculate the generated high-order harmonic power, this embodiment introduces a dedicated in-situ transmission efficiency measurement optical path based on the device in Embodiment 1, which is used to accurately calibrate the actual transmittance of each optical element.

[0068] like Figure 3As shown, the newly added measurement optical path components in this embodiment include a mechanical chopper 42, ultraviolet fused silica glass plates 43 and 44 coated with Nb2O5 that are exactly the same in specifications as the Nb2O5-coated ultraviolet fused silica glass plates 34 and 35, and an aluminum film to be tested 45 for calibration.

[0069] In the specific experimental measurement procedure:

[0070] First, the transmittance of the aluminum film 45 to be tested is calibrated. The movement of the aluminum film 45 to be tested is controlled by a displacement stage. The aluminum film 45 is inserted into and removed from the optical path in sequence. The photocurrent values ​​under the two states are measured by photodiode 38, and the true transmittance of the aluminum film 45 can be obtained by comparing the two values.

[0071] Subsequently, the transmission efficiency of the Nb2O5-coated ultraviolet fused silica glass plates 34, 35, 43, and 44 was measured. In this step, the mechanical chopper 42 must first be activated to reduce the average power of the driving light to 10% of its rated power. Because the driving laser in the system has an extremely high power load, without using a chopper for pre-stage energy attenuation, the high-power driving light would directly strike the aluminum film 37 at the rear, causing irreversible thermal damage and complete destruction of the aluminum film 37. After the energy is safely reduced by the chopper 42, the photocurrent value is recorded. Then, the Nb2O5-coated ultraviolet fused silica glass plates 34, 35, 43, and 44, along with the light block 36, are moved away using a displacement stage. Keeping the optical path structure unchanged, the beam is allowed to directly strike the photodiode 38 along the original path, and the new current value is recorded. By comparing the two current values, the transmission efficiency of the Nb2O5-coated ultraviolet fused silica glass plates 34, 35, 43, and 44 can be accurately obtained.

[0072] The innovations and technical advantages of this embodiment are mainly reflected in the following two aspects:

[0073] Avoiding thermal damage to components: An innovative mechanical chopper is used to control the duty cycle of a high-power laser in the time dimension, forcibly cutting off most of the light energy. This allows the fragile aluminum film at the back end to withstand direct irradiation by the driving light without the need for glass plate attenuation, fundamentally solving the industry problem that aluminum films are easily damaged by high-power lasers during calibration.

[0074] Ensuring the Authenticity of the Measurement Environment: Given the extremely high nonlinear sensitivity of the three-stage compression link (multi-cavity + frequency doubling + hollow fiber) used in this invention, its output beam parameters (such as spot shape, divergence angle, and pulse characteristics) are highly dependent on the input energy. This device abandons the conventional method of reducing energy by adjusting the laser repetition frequency, instead employing a mechanical chopping method. This allows for precise measurement of transmission efficiency while ensuring that the output beam parameters are completely consistent with the actual experimental conditions, thus ensuring that the measurement results have substantial reference value.

[0075] 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.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention. For those skilled in the art, any equivalent improvements or substitutions made without departing from the core principles of the present invention should be covered within the protection scope of the present invention.

Claims

1. A high-power high-order harmonic generation device, comprising a femtosecond laser emitter, wherein the femtosecond laser emitter is used to emit femtosecond laser light, characterized in that, Also includes: The first-stage compression module, frequency doubling module, second-stage compression module, and high-order harmonic generation and detection mechanism are located sequentially in the femtosecond laser optical path. The first-level compression module includes a multi-pass cavity and a first chirped mirror group. The first chirped mirror group includes a plurality of chirped mirrors arranged in sequence. The first chirped mirror group is located in the outgoing optical path of the multi-pass cavity, and the outgoing light of the first chirped mirror group is incident on the frequency doubling module. The frequency doubling module includes a frequency doubling crystal and a dichroic mirror. The frequency doubling crystal is used to double the frequency of the femtosecond laser to obtain frequency-doubled light. The dichroic mirror is disposed in the output optical path of the frequency doubling crystal to separate the femtosecond laser and the frequency-doubled light. The frequency-doubled light separated by the dichroic mirror is incident on the secondary compression module. The secondary compression module includes a hollow optical fiber and a second chirped mirror group. The second chirped mirror group includes multiple chirped mirrors arranged in sequence. The second chirped mirror group is located in the outgoing optical path of the hollow optical fiber. The outgoing light of the second chirped mirror group is incident on the high-order harmonic generation and detection mechanism. The high-order harmonic generation and detection mechanism includes a vacuum cavity and a gas box located inside the vacuum cavity. The gas box is filled with gas, which can act on the frequency-doubled light to generate high-order harmonics.

2. The high-power high-order harmonic generation device according to claim 1, characterized in that: The primary compression module further includes multiple first reflectors, which are respectively located in the incident optical path and the outgoing optical path of the multi-channel cavity; the secondary compression module further includes multiple second reflectors, which are respectively located in the incident optical path of the hollow fiber, the outgoing optical path of the hollow fiber, and the outgoing optical path of the second chirped mirror group.

3. The high-power high-order harmonic generation device according to claim 2, characterized in that, In the second chirped mirror group, the chirped mirrors are defined in the order in which they come into contact with the frequency-doubled light. For example, the first chirped mirror to come into contact with the frequency-doubled light is the first chirped mirror. A second reflecting mirror is provided between the first and second chirped mirrors to reflect the light from the first chirped mirror to the second chirped mirror. For the other chirped mirrors in the second chirped mirror group, the third chirped mirror is used to reflect the light from the second chirped mirror, and so on.

4. The high-power high-order harmonic generation device according to claim 1, characterized in that: The secondary compression module also includes an optical fiber loading component, which has a groove in which the hollow optical fiber is disposed; the hollow optical fiber includes an optical fiber body and a window disposed at the incident end of the optical fiber body, and the interior of the optical fiber body is filled with gas.

5. The high-power high-order harmonic generation device according to claim 4, characterized in that: The optical fiber loading component is made of copper, the window is made of fused silica, and the angle between the window and the optical fiber body is Brewster's angle; the frequency doubling crystal is made of barium borate.

6. The high-power high-order harmonic generation device according to claim 1, characterized in that: The high-order harmonic generation and detection mechanism further includes: an aperture and a focusing lens disposed outside the vacuum cavity, wherein the frequency-doubled light is incident on the gas box after passing through the aperture and the focusing lens; a quartz glass plate, an aluminum film, a flat focal field grating, a silver mirror, and a camera disposed inside the vacuum cavity and sequentially located in the high-order harmonic optical path generated by the gas box; wherein the quartz glass plate is coated with an Nb2O5 thin film.

7. The high-power high-order harmonic generation device according to claim 6, characterized in that: The higher harmonic generation and detection mechanism further includes a photodiode, which is movable into the optical path of the higher harmonics and used to measure the harmonic power after passing through the aluminum film.

8. The high-power high-order harmonic generating device according to claim 7, characterized in that: The higher harmonic generation and detection mechanism further includes: a chopper located outside the vacuum cavity and a test aluminum film located inside the vacuum cavity; the frequency-doubled light is incident on the aperture after passing through the chopper; the test aluminum film can be moved into the optical path of the higher harmonic, and when the test aluminum film moves into the optical path of the higher harmonic, it is located between the quartz glass plate and the flat focal field grating; and / or, the higher harmonic generation and detection mechanism further includes: a first attitude adjustment stage, a second attitude adjustment stage and a third attitude adjustment stage; the photodiode is located on the first attitude adjustment stage, the flat focal field grating is located on the second attitude adjustment stage, and the silver mirror is located on the third attitude adjustment stage.

9. A method for generating high-power high-order harmonics, characterized in that, The high-power high-order harmonic generation device according to any one of claims 1 to 8 comprises: The femtosecond laser emitter emits a femtosecond laser, which undergoes multiple reflections within the multi-pass cavity. The accumulated self-phase modulation effect with air achieves spectral broadening, and then it is incident on the first chirped mirror group to compensate for the dispersion. A femtosecond laser is incident on a frequency-doubled crystal and generates frequency-doubled light. A dichroic mirror separates the femtosecond laser and the frequency-doubled light. Frequency-doubled light is incident on a hollow fiber to broaden its spectrum, and then incident on a second chirped mirror group to compensate for dispersion. The frequency-doubled light is incident on the gas box and comes into contact with the gas loaded in the gas box, generating higher harmonics.

10. The method according to claim 9, characterized in that, It also includes any of the following: 1) The femtosecond laser emitted by the femtosecond laser emitter has a center wavelength of 1030 nm, a single pulse energy of 260 μJ, a repetition frequency of 100 kHz, an average power of 26 W, and a pulse width of 600 fs. 2) After passing through the first-stage compression module, the femtosecond laser has an average power of 24.5 W and a pulse width of 130 fs; 3) The frequency-doubled light emitted by the frequency-doubled module is green light, with an output power of 15.7 W and a pulse width of 130 fs; 4) After passing through the secondary compression module, the output power of the frequency-doubled light is 9.5 W, and the pulse width is 15 fs; 5) The power of higher harmonics is 159.3 μW; of which, the average power of the 11th harmonic is 92.4 μW.

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