Method and device for separating attosecond pulses in soft X-ray water window wave band

Abstract

The invention belongs to the field of attosecond pulses, and particularly relates to a dispersion compensation and separation method and device for soft X-ray water window wave band attosecond pulses. The dispersion compensation device comprises a vacuum cavity and a liquid film generation mechanism, the working end of the liquid film generation mechanism is arranged in the vacuum cavity and used for outputting a working medium to generate a liquid film with the uniform and adjustable thickness. The separation device comprises a vacuum cavity and a liquid film generation mechanism, the working end of the liquid film generation mechanism is arranged in the vacuum cavity and used for outputting a working medium to generate a liquid film which is non-uniform and adjustable in thickness. The dispersion compensation and separation device comprises a vacuum cavity and two liquid film generation mechanisms, and the working ends of the two liquid film generation mechanisms are respectively arranged in the vacuum cavity and are used for respectively outputting working media to generate liquid films with non-uniform and adjustable thicknesses. Dispersion compensation or separation of attosecond pulses can be independently achieved through the liquid film, and dispersion compensation and separation can also be achieved at the same time.

Description

[0001] This application is a divisional application. The parent application was filed on August 27, 2024, with application number 2024111828724, and is entitled "Method and Apparatus for Dispersion Compensation and Separation of Attosecond Pulses in the Water Window Band of Soft X-rays". Technical Field

[0002] This invention relates to a dispersion compensation and separation device for soft X-rays, specifically to a dispersion compensation and separation method and device for attosecond pulses in the water window band of soft X-rays. Background Technology

[0003] A Miao (10) -18 Attosecond pulses, invented in the early 21st century, are the fastest pulses currently known to humankind. Over the past two decades, they have propelled significant progress and breakthroughs in attosecond science research, providing new research tools and important innovative opportunities for fields such as physics, chemistry, biology, materials science, and information science. Compared to traditional extreme ultraviolet (EUV) attosecond pulses, soft X-ray attosecond pulses have higher photon energies, thus achieving higher spatial resolution. They can be used for inner-shell electron dynamics studies, support shorter pulse widths, and are also more suitable for studying biological samples, especially in the soft X-ray water window band.

[0004] Currently, soft X-ray attosecond sources face two problems: 1. Dispersion compensation for attosecond pulses.

[0005] In attosecond pulse generation methods based on higher harmonic generation technology, according to the three-step model of higher harmonics, for commonly used short orbits, the kinetic energy gained by electrons increases with the recombination time. Attosecond pulses exhibit positive chirp, requiring negative dispersion to compress their width. Currently, the main method for compensating attosecond pulse dispersion is the use of metallic films. In the soft X-ray band, the group delay dispersion (GDD) of commonly used metallic films is... Figure 1 As shown, the transmittance of commonly used metal films is as follows: Figure 2 As shown, the horizontal axis in the figure represents photon energy. The main problems with metal film for dispersion compensation are: (1) Considering the reasonable transmittance of attosecond pulses, the thickness of the metal film is generally controlled at 100-200 nm. However, under this thickness condition, the negative dispersion provided by the metal film is limited, and the dispersion compensation effect is not ideal; (2) The thickness of the metal film is fixed, and the inability to adjust the thickness means that the amount of dispersion cannot be precisely adjusted; (3) The damage threshold of the metal film is low; (4) The fixed mesh structure of the metal film will affect the spatial profile of the attosecond pulse; (5) The oxidation of the metal film will lead to a decrease in the transmittance of the attosecond pulse.

[0006] 2. Separation of attosecond pulses and driving laser.

[0007] Currently, femtosecond laser-driven gas high-harmonic processes are the most common method for obtaining attosecond pulses. In this method, after the driving laser interacts with the gas target to generate an attosecond pulse, a portion of the driving laser remains and propagates collinearly with the generated attosecond pulse. Since this residual driving laser can adversely affect the application of attosecond pulses, it is necessary to separate this portion of the residual driving laser from the attosecond pulse. However, separating attosecond pulses in the soft X-ray band is quite difficult, and traditional methods have many limitations.

[0008] Currently, there are three commonly used methods: (1) using a metal film for separation. Driving lasers (mid-infrared band) generally have low photon energy and are difficult to penetrate the metal film, while attosecond pulses are generally in the extreme ultraviolet or soft X-ray bands, which have relatively high transmittance, such as... Figure 2 As shown. Considering the transmittance of attosecond pulses, the thickness of the metal film is generally controlled at 100-200nm. The main problems with metal film for attosecond pulse separation are: 1) Low damage threshold. In high-performance attosecond light sources, the residual driving laser still has high power or energy, and the metal film is very easy to be damaged; 2) The mesh structure of fixing the metal film will affect the spatial profile of the attosecond pulse; 3) Oxidation of the metal film will lead to a decrease in the transmittance of the attosecond pulse. (2) Use a beam splitter to separate attosecond pulses. When the light pulse is incident at the Brewster angle corresponding to the wavelength of the driving laser, the reflectivity of the driving light is low. Since the Brewster angles corresponding to different wavelengths of light are different, the extreme ultraviolet light is not incident at the Brewster angle, so it has a higher reflectivity. However, this method is mainly used in the extreme ultraviolet band. There are no suitable materials in the soft X-ray band, and the reflectivity is very low. (3) Use a ring driving light. Utilize the spatial distribution of the driving light. Since most of the energy of the driving pulse is distributed in the central region, this method will result in a large amount of driving light energy loss. Summary of the Invention

[0009] The purpose of this invention is to address the problem that traditional solutions such as metal films and beam splitters in soft X-ray attosecond light sources cannot effectively solve the dispersion compensation and separation problem of attosecond pulses in the soft X-ray water window band. By comprehensively calculating and analyzing the dispersion, transmittance, refractive index of water in the soft X-ray water window band, as well as the characteristics of attosecond pulses in the soft X-ray water window band, this invention provides a method and apparatus for dispersion compensation and separation of attosecond pulses in the soft X-ray water window band.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A dispersion compensation method for attosecond pulses in the soft X-ray water window band, characterized by the following features: A uniform and adjustable liquid film was used to compensate for the dispersion of attosecond pulses in the soft X-ray water window band.

[0011] A dispersion compensation device for attosecond pulses in the soft X-ray water window band, used to implement the aforementioned dispersion compensation method for attosecond pulses in the soft X-ray water window band, is characterized by: Includes a vacuum chamber and a liquid thin film generation mechanism; The working end of the liquid thin film generation mechanism is placed inside the vacuum chamber to output the working medium to generate a liquid thin film with uniform and adjustable thickness. An inlet and an outlet are respectively provided on two opposite side walls of the vacuum chamber, and the inlet and outlet are located on both sides of the liquid film. The attosecond pulse of soft X-ray water window band to be dispersion compensated is incident on the liquid film through the inlet. After dispersion compensation by the liquid film, it is led out of the vacuum chamber through the outlet.

[0012] This invention also provides a method for separating attosecond pulses in the soft X-ray water window band, which is characterized by: Attosecond pulses in the soft X-ray water window band are separated using a non-uniform and adjustable liquid film.

[0013] This invention also provides a device for separating attosecond pulses in the soft X-ray water window band, used to realize the aforementioned method for separating attosecond pulses in the X-ray water window band, characterized in that: Includes a vacuum chamber and a liquid thin film generation mechanism; The working end of the liquid thin film generation mechanism is placed inside the vacuum chamber, and is used to output the working medium to generate a liquid thin film with non-uniform and adjustable thickness. An inlet and an outlet are respectively provided on two opposite side walls of the vacuum chamber, and the inlet and outlet are located on both sides of the liquid film. The collinearly transmitted attosecond pulses of soft X-rays in the water window band and the residual infrared-driven laser are incident on the liquid film through the inlet. After the residual infrared-driven laser is separated by the liquid film, the soft X-ray attosecond pulses in the water window band are exported to the outside of the vacuum cavity through the outlet.

[0014] Furthermore, the cross-section of the liquid film along the thickness direction is an isosceles trapezoid, with the included angle between its two inclined sides ranging from 1 mrad to 10 mrad.

[0015] Furthermore, it also includes a baffle or reflector disposed within the vacuum cavity; the baffle or reflector is disposed in the optical path of the residual infrared-driven laser that has been separated by the liquid film; the baffle is used to block the residual infrared-driven laser. Alternatively, an outlet is provided on the side wall of the vacuum cavity located on the reflector's optical path. The reflector is used to reflect the residual infrared-driven laser and then export it outside the vacuum cavity through the outlet.

[0016] This invention also provides a method for dispersion compensation and separation of attosecond pulses in the soft X-ray water window band, which is characterized by: Two non-uniform and adjustable liquid films were used to separate and compensate for attosecond pulses in the soft X-ray water window band.

[0017] This invention also provides a dispersion compensation and separation device for attosecond pulses in the soft X-ray water window band, used to realize the aforementioned dispersion compensation and separation method for attosecond pulses in the soft X-ray water window band, characterized in that: Includes a vacuum chamber and two liquid thin film generation mechanisms; The working ends of the two liquid thin film generation mechanisms are respectively placed inside the vacuum chamber, and are used to output working medium to generate liquid thin films with non-uniform and adjustable thickness. Two liquid films are spaced apart along the length of the vacuum cavity. The two liquid films are of the same size. The sides of the two films that are close to each other are arranged in parallel, and the sides that are far from each other are arranged in parallel. The center lines of the two films in the height direction coincide. An inlet and an outlet are respectively provided on two opposite side walls of the vacuum chamber, and the inlet and outlet are located on the two liquid films that are far apart from each other. The liquid film near the inlet is defined as the first liquid film, and the liquid film near the outlet is defined as the second liquid film. The collinearly transmitted attosecond pulses of soft X-ray water window band and the residual infrared-driven laser, which are to be dispersion compensated and separated, are incident on the first liquid film through the inlet. The residual infrared-driven laser and dispersion compensation are separated by the first liquid film. After the second liquid film performs dispersion compensation on the attosecond pulses of soft X-ray water window band, they are led out of the vacuum cavity through the outlet.

[0018] Furthermore, the cross-section of the first liquid film along the thickness direction is a regular isosceles trapezoid, and the cross-section of the second liquid film along the thickness direction is an inverted isosceles trapezoid. The included angle between the two inclined sides of the first liquid film is 1 mrad to 10 mrad, and the included angle between the two inclined sides of the second liquid film is -10 mrad to -1 mrad. Alternatively, the cross-section of the first liquid film along the thickness direction is an inverted isosceles trapezoid, and the cross-section of the second liquid film along the thickness direction is a regular isosceles trapezoid. The included angle between the two inclined sides of the first liquid film is -10 mrad to -1 mrad, and the included angle between the two inclined sides of the second liquid film is 1 mrad to 10 mrad.

[0019] Furthermore, it also includes a baffle or reflector disposed within the vacuum cavity; the baffle or reflector is located in the optical path of the residual infrared-driven laser that has undergone spatial separation via a liquid thin film; the baffle is used to block the residual infrared-driven laser. Alternatively, an outlet is provided on the side wall of the vacuum cavity located on the reflector's optical path. The reflector is used to reflect the residual infrared-driven laser and then export it outside the vacuum cavity through the outlet.

[0020] The beneficial effects of this invention are: 1. This invention uses a uniformly thick liquid film for dispersion compensation, allowing for thicknesses tens of times greater than metal films to provide greater negative dispersion. Furthermore, the thickness of the liquid film can be adjusted according to actual needs, making dispersion compensation more precise. Simultaneously, it does not affect the spatial profile of the attosecond pulse, avoiding the problem of reduced attosecond pulse transmittance due to metal film oxidation. This is significant for achieving shorter pulse widths of attosecond pulses and thus obtaining higher time resolution. Compared to traditional metal film methods, the method proposed in this invention, under the same transmittance conditions, provides a greater amount of negative dispersion with flexible and tunable dispersion, and also has a higher damage threshold.

[0021] 2. This invention achieves spatial separation of attosecond pulses and infrared-driven lasers in the collinear propagation soft X-ray water window band using a non-uniform thickness liquid film. At the same time, since the infrared-driven laser has low transmittance in the liquid film, the liquid film itself can also absorb a certain amount of the infrared-driven laser, which helps with separation. Furthermore, since the liquid film is fluid, it can still work under high-power / high-energy laser driving conditions without damage.

[0022] 3. By employing two non-uniformly thick liquid films, this invention can simultaneously achieve the separation and dispersion compensation of attosecond pulses in the soft X-ray water window band.

[0023] 4. The present invention can guide the separated infrared-driven laser to outside the vacuum cavity through the set reflector, so as to realize the secondary utilization of the infrared-driven laser.

[0024] 5. This invention has low transmission loss for attosecond pulses in the soft X-ray water window band. Attached Figure Description

[0025] Figure 1 It is the dispersion diagram of a commonly used metal film (100nm thickness) in the existing soft X-ray band; Figure 2 This is a transmittance diagram of commonly used metal films (100nm thickness) in the existing soft X-ray band; Figure 3 It is a dispersion map of water and different metal films in the soft X-ray band of 200-530 eV; Figure 4 This is a transmittance diagram of attosecond pulses in the soft X-ray water window band of this invention at liquid water films of different thicknesses. Figure 5This is a schematic diagram of an embodiment of the dispersion compensation device for attosecond pulses in the soft X-ray water window band of the present invention; Figure 6 This is a schematic diagram of the separation principle of an embodiment of a separation device for attosecond pulses in the soft X-ray water window band of the present invention. a is a schematic diagram of the separation optical path, and b is a schematic diagram of the principle. Figure 7 This is a schematic diagram of an embodiment of a separation device for attosecond pulses in the soft X-ray water window band according to the present invention. a is a schematic diagram of the structure when the baffle is set, and b is a schematic diagram of the structure when the reflector is set. Figure 8 This is a schematic diagram of the dispersion compensation and separation device for attosecond pulses in the soft X-ray water window band according to the present invention. a is a schematic diagram of the structure with the baffle set, and b is a schematic diagram of the structure with the reflector set.

[0026] In the figure: 1-vacuum cavity, 2-liquid thin film generation mechanism, 3-liquid thin film, 4-baffle, 5-reflector. Detailed Implementation

[0027] To make the objectives, advantages, and features of the present invention clearer, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a method and apparatus for dispersion compensation and separation of attosecond pulses in the soft X-ray water window band. The advantages and features of the present invention will become clearer according to the following specific embodiments. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the objectives of the embodiments of the present invention; furthermore, the structures shown in the drawings are often part of the actual structures.

[0028] Example 1 Dispersion compensation methods and scheme design There is no publicly available data on the group delay dispersion of water (H2O) in the soft X-ray band. The dispersion of water in this range is calculated based on the refractive index parameter of water in the soft X-ray band of 200-530 eV. Figure 3 The GDD of 100 nm thick water and different metals in the soft X-ray band 200-530 eV was calculated. The green curve represents the GDD of 100 nm thick H₂O (as 2 Water exhibits negative dispersion in the 200-530 eV range, which can compensate for the inherent positive dispersion of attosecond pulses. At 250 eV, the GDD is approximately -6.32 as. 2 At 300 eV, GDD is approximately -3.67 as. 2 At 350 eV, GDD is approximately -2.44 as. 2 At 400 eV, GDD is approximately -1.81 as. 2 At 450 eV, GDD is approximately -1.60 as.2 At 500 eV, GDD is approximately -2.07 as. 2 .according to Figure 3 The calculated dispersion curves of commonly used metallic materials in the soft X-ray band show that, within this band, the negative dispersion provided by a water film of the same thickness is lower than but close to that provided by a metal film, and has a wider negative dispersion range compared to Ag, Ti, and Sn.

[0029] Transmittance of liquid water of different thicknesses within the water window band of 282-533 eV is as follows: Figure 4 As shown, at a thickness of 100 nm, water has a transmittance of over 95%, far exceeding that of metal films. Even at a thickness of 5 µm, it still maintains an overall transmittance of approximately 30%.

[0030] Based on the calculation and analysis of the dispersion coefficient and transmittance of attosecond pulses in the soft X-ray water window band in water, water has a higher transmittance, allowing for thicknesses tens of times greater than those of metal films, thus providing greater negative dispersion. Considering both transmittance and dispersion, the thickness of the liquid water film can be reasonably set between several hundred nanometers and several micrometers to provide an appropriate amount of negative dispersion; for example, with a thickness of 5µm, the GDD at 250eV is approximately -316as. 2 At 300 eV, GDD is approximately -183.5 as. 2 At 350 eV, GDD is approximately -122 as. 2 At 400 eV, GDD is approximately -90.5 as. 2 At 450 eV, GDD is approximately -80 as. 2 At 500 eV, GDD is approximately -103.5 as. 2 It can compensate for the positive dispersion of attosecond pulses in the soft X-ray water window band, thus achieving a shorter attosecond pulse width.

[0031] Equally important, unlike metal films which have a fixed thickness (typically 100nm, 150nm, 200nm, or 250nm), the thickness of liquid water films can be adjusted in real time with high precision. Therefore, real-time dispersion compensation management can be performed based on the attosecond pulse characteristics, resulting in more accurate dispersion compensation. Consequently, using liquid water films can effectively compensate for dispersion in attosecond pulses within the soft X-ray water window band, playing a crucial role in achieving shorter pulse widths for attosecond pulses.

[0032] The design of a scheme for attosecond pulse dispersion compensation in the water window band of soft X-rays using liquid water films is as follows: Figure 5As shown. The dispersion compensation device mainly includes a vacuum chamber 1 and a liquid film generation mechanism 2. The liquid film generation mechanism 2 uses a liquid working medium, specifically water in this embodiment. Its working end is placed inside the vacuum chamber 1 to output the working medium to generate a liquid film 3 of uniform thickness. In this embodiment, the liquid film is a liquid water film. An inlet and an outlet (not shown in the figure) are respectively provided on two opposite side walls of the vacuum chamber 1, and the inlet and outlet are located on both sides of the liquid water film. The attosecond pulse of the soft X-ray water window band to be dispersion compensated is incident on the liquid water film through the inlet. The liquid water film is used to perform dispersion compensation on the attosecond pulse of the soft X-ray water window band that passes through it. The dispersion-compensated attosecond pulse of the soft X-ray water window band is led out of the vacuum chamber 1 through the outlet.

[0033] To balance transmittance and dispersion compensation, the thickness of the liquid water film is ideally set between several hundred nanometers and several micrometers. Mature solutions exist for generating liquid water films within this thickness range. One approach involves two liquid nozzles spraying the film together [Christopher J. Crissman, et al. Sub-micron thick liquidsheets produced by isotropically etchedglass nozzles. Lab on a Chip, 2022,22.7: 1365-1373], while another approach uses a specially designed single nozzle fabricated by 3D printing or etching [Maria Ekimova, et al. A liquid flatjet system for solution phase soft-x-ray spectroscopy. Structural Dynamics, 2015,2.5]. The thickness of the liquid water film can be adjusted based on the angle between the two nozzles or the liquid flow rate to achieve thicknesses from several hundred nanometers to several micrometers. The surface size of the liquid water film can also be adjusted by changing the flow rate to match the spot size. Under this adapted flow rate, liquid recycling in a vacuum is also a mature solution.

[0034] When used solely for dispersion compensation, attosecond pulses should be transmitted from a region of relatively uniform thickness in the liquid water film.

[0035] In addition to water, alcoholic liquids such as methanol, ethanol, and propanol can also be used.

[0036] Example 2 Separation methods and scheme design Based on the analysis of the refractive index of liquid water in different wavelength bands and the spatial size of the liquid water thin film, a separation scheme was designed.

[0037] Attosecond pulses in the soft X-ray water window band are typically generated using a mid-infrared driving laser. In the mid-infrared band, the refractive index of water is around 1.3, while in the soft X-ray water window band, the refractive index is around 1. The difference between this embodiment and Embodiment 1 is that a non-uniform thickness liquid water film is used; the rest of the structure is the same as in Embodiment 1.

[0038] Non-uniform thickness liquid water films specifically include: (1) The thickness decreases from top to bottom (equivalent isosceles trapezoid). Soft X-ray water window band attosecond pulses have almost no effect on the beam direction after passing through the liquid water film, while mid-infrared driven lasers will be oriented upwards due to refraction in the liquid water. Figure 6 As shown, after a certain transmission distance, it separates spatially from the attosecond pulse.

[0039] (2) The thickness increases from top to bottom (inverted isosceles trapezoid). The attosecond pulse of soft X-ray water window band hardly affects the beam direction after passing through the liquid water film, while the mid-infrared driven laser will be oriented downward due to refraction in the liquid water.

[0040] A non-uniform thickness liquid water film approximates an isosceles trapezoid, and the included angle between its two sides determines the deflection angle of the infrared light. In the infrared band, taking a refractive index of 1.3 as an example, when the included angle between the two sides of the liquid water film is 1 mrad, the deflection angle is 0.3 mrad; when the included angle is 5 mrad, the deflection angle is 1.5 mrad; and when the included angle is 10 mrad, the deflection angle is 3 mrad. At this point, after transmitting a distance of 1 m, the center of the infrared-driven laser deviates from the center of the attosecond pulse by 3 mm.

[0041] Considering the divergence angle of the infrared-driven laser, and taking a practical example from a soft X-ray attosecond source, the infrared-driven laser divergence angle is 5 mrad, and the soft X-ray attosecond pulse divergence angle is 0.5 mrad. To completely separate the two beams spatially, the deflection angle needs to reach 2.75 mrad, and the included angle between the two sides of the liquid water film needs to be approximately 9.167 mrad. When the distance between the attosecond generation location and the liquid water film is 0.5 m, the diameter of the infrared-driven laser spot is approximately 2.5 mm, and the diameter of the attosecond pulse spot is approximately 0.25 mm. At a deflection angle of 2.75 mrad, after passing through the liquid water film, the two beams need to propagate for 0.5 m to completely separate spatially. In this case, the included angle between the two sides of the liquid water film needs to be approximately 9.167 mrad. For an attosecond pulse with a diameter of 0.25 mm, the thickness change of the liquid water film through which the attosecond pulse passes is 2.29 µm (from the top to the bottom of the spot).

[0042] The design of a scheme for attosecond pulse separation in the water window band of soft X-rays using liquid water thin films is as follows: Figure 7As shown. The liquid water film needs to be placed inside vacuum chamber 1, and can be recycled to ensure efficiency. The collinear propagating residual infrared-driven laser and attosecond pulse propagation are spatially separated by the liquid water film.

[0043] The residual infrared-driven laser that has undergone spatial separation via a liquid water film can be blocked by baffle 4. Figure 7 (a) or using a reflector 5 ( Figure 7 In section (b), the residual laser is reflected and placed at an outlet (not shown in the figure) on the vacuum chamber 1, so that it can be exported and reused.

[0044] Because mid-infrared driven lasers have low transmittance in water, the liquid water film itself can absorb a certain amount of the mid-infrared driven laser, which aids in separation. Furthermore, since the liquid water film is fluid, it can still function well under high-power / high-energy driven laser conditions without causing damage.

[0045] Example 3 Simultaneous Dispersion Compensation and Separation Methods and Schemes Design In Example 1, the liquid water film has a uniform thickness and cannot spatially separate the infrared-driven laser and the attosecond pulse, making it suitable for cases where only attosecond pulse dispersion compensation is considered.

[0046] In Example 2, the liquid water film has a non-uniform thickness. Since the attosecond pulse spot passes through liquid water films of different thicknesses at different positions, it means that there are different dispersion compensation amounts, which is disadvantageous under normal circumstances. It is suitable for situations where only attosecond pulse separation is considered.

[0047] If attosecond pulse separation and dispersion compensation are performed simultaneously, the scheme is as follows: Figure 8 As shown. Combining the solutions of Embodiment 1 and Embodiment 2, this embodiment uses two liquid water films. The cross-section of the first liquid water film along the thickness direction is a regular isosceles trapezoid, that is, the thickness decreases from top to bottom. The cross-section of the second liquid water film along the thickness direction is an inverted isosceles trapezoid, that is, the thickness increases from top to bottom. The included angle between the two inclined sides of the first liquid water film is 1 mrad to 10 mrad, and the included angle between the two inclined sides of the second liquid water film is -10 mrad to -1 mrad; or, the cross-section of the first liquid water film along the thickness direction is an inverted isosceles trapezoid, that is, the thickness increases from top to bottom, and the cross-section of the second liquid water film along the thickness direction is a regular isosceles trapezoid, that is, the thickness decreases from top to bottom. The included angle between the two inclined sides of the first liquid water film is -10 mrad to -1 mrad, and the included angle between the two inclined sides of the second liquid water film is 1 mrad to 10 mrad.

[0048] The first liquid water film separates the attosecond pulse and the infrared-driven laser, and provides some dispersion compensation. The second liquid water film is placed at a certain distance, which spatially separates the infrared-driven laser spot from the attosecond pulse spot, and further compensates for the dispersion of the attosecond pulse through the second liquid water film. After passing through the two liquid water films, the attosecond pulse passes through liquid water films of equal thickness at different positions on the spot.

[0049] Considering a practical example of an attosecond source in the soft X-ray water window band, the infrared-driven laser divergence angle is 5 mrad, the soft X-ray water window band attosecond pulse divergence angle is 0.5 mrad, and the included angle between the two sides of the liquid water film is approximately 9.167 mrad. When the refractive index of the infrared-driven laser in water is 1.3, the deflection angle reaches 2.75 mrad, which meets the minimum deflection angle required for complete separation of the two beams. When the distance between the attosecond generation location and the liquid water film is 0.5 m, the diameter of the infrared-driven laser spot is approximately 2.5 mm, and the diameter of the attosecond pulse spot is approximately 0.25 mm. The attosecond pulse passes through the first liquid water film with a thickness change of 2.29 µm (from the top to the bottom of the spot), and after propagating for 0.5 m, the two beams can be completely separated in space. After this propagation distance, the thickness change of the second liquid water film is opposite to that of the first liquid water film. The attosecond pulse passes through the second liquid water film with a thickness change of 2.29 µm (from the top to the bottom of the spot), but the thicknesses at the top and bottom are opposite. After passing through the second liquid water film, different positions on the attosecond pulse spot pass through liquid water films of equal thickness. For an attosecond pulse, the equivalent thickness of the two liquid water films is approximately 2.29 µm, at which point the overall transmittance is greater than 50%, and the provided dispersion is: GDD at 250 eV is approximately -144.73 as. 2 At 300 eV, GDD is approximately -84.04 as. 2 At 350 eV, GDD is approximately -55.876 as. 2 At 400 eV, GDD is approximately -41.45 as. 2 At 450 eV, GDD is approximately -36.64 as. 2 At 500 eV, GDD is approximately -47.4 as. 2 .

[0050] This method offers flexible and precisely adjustable dispersion, high efficiency, and the ability to withstand high power / energy. It is well-suited for soft X-ray water window band attosecond sources and is of great significance for achieving shorter pulse widths of attosecond pulses to obtain higher time resolution.

[0051] This embodiment is the same as Embodiment 2, and a baffle 4 or a reflector 5 can also be set in the vacuum cavity 1; the difference is that the baffle 4 or reflector 5 in this embodiment needs to be set in the optical path of the residual infrared driving laser that has been separated by the first liquid film.

Claims

1. A method for separating attosecond pulses in the soft X-ray water window band, characterized in that: Attosecond pulses in the soft X-ray water window band are separated using a non-uniform and adjustable liquid film.

2. A device for separating attosecond pulses in the soft X-ray water window band, used to implement the method for separating attosecond pulses in the soft X-ray water window band as described in claim 1, characterized in that: It includes a vacuum chamber (1) and a liquid thin film generation mechanism (2); The working end of the liquid film generation mechanism (2) is placed inside the vacuum chamber (1) and is used to output the working medium to generate a liquid film (3) with non-uniform and adjustable thickness; the working medium is water or alcohol liquid; The vacuum cavity (1) has an inlet and an outlet on its two opposite side walls, and the inlet and outlet are located on both sides of the liquid film (3). The collinearly transmitted attosecond pulses of soft X-ray water window band and the residual infrared driving laser are incident on the liquid film (3) through the inlet. After the residual infrared driving laser is separated by the liquid film (3), the soft X-ray water window band attosecond pulses are exported to the outside of the vacuum cavity (1) through the outlet.

3. The attosecond pulse separation device in the soft X-ray water window band according to claim 2, characterized in that: The liquid film (3) has an isosceles trapezoidal cross section along the thickness direction, with the included angle between its two inclined sides being 1 mrad to 10 mrad.

4. The separation device for attosecond pulses in the soft X-ray water window band according to claim 2 or 3, characterized in that: It also includes a baffle (4) or a reflector (5) disposed in the vacuum cavity (1); The baffle (4) or reflector (5) is disposed on the optical path of the residual infrared-driven laser that is separated by the liquid film (3); The baffle (4) is used to block the residual infrared-driven laser; Alternatively, the vacuum cavity (1) may have an outlet on the side wall of the reflector (5) reflecting the light path, and the reflector (5) may be used to reflect the residual infrared driving laser and then export it to the outside of the vacuum cavity (1) through the outlet.

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