Method and apparatus for dispersion compensation and separation of soft x-ray water window attosecond pulses

Abstract

The application belongs to the field of attosecond pulse, and particularly relates to a dispersion compensation and separation method and device for soft X-ray water window band attosecond pulse. The dispersion compensation device comprises a vacuum cavity and a liquid film generating mechanism; the working end of the liquid film generating mechanism is arranged in the vacuum cavity, and is used for outputting a liquid film with uniform and adjustable thickness generated by a working medium. The separation device comprises a vacuum cavity and a liquid film generating mechanism; the working end of the liquid film generating mechanism is arranged in the vacuum cavity, and is used for outputting a liquid film with non-uniform and adjustable thickness generated by a working medium. The dispersion compensation and separation device comprises a vacuum cavity and two liquid film generating mechanisms; the working ends of the two liquid film generating mechanisms are respectively arranged in the vacuum cavity, and are used for respectively outputting liquid films with non-uniform and adjustable thickness generated by a working medium. The application can realize dispersion compensation or separation of attosecond pulse by a liquid film alone, and can also realize dispersion compensation and separation simultaneously.

Description

TECHNICAL FIELD

[0001] The present application relates to a soft X-ray dispersion compensation and separation device, in particular to a soft X-ray water window band attosecond pulse dispersion compensation and separation method and device. BACKGROUND

[0002] Attosecond (10 -18 s) pulses were born in the early 21st century, and are currently the fastest pulses mastered by humans. In the past 20 years, attosecond science research has made significant progress and breakthroughs, providing new research methods and important innovation opportunities for the development of physics, chemistry, biology, materials, information, and other fields. Compared with traditional extreme ultraviolet band attosecond pulses, soft X-ray band attosecond pulses have higher photon energy, so higher spatial resolution can be obtained, and they can be used for inner-shell electron dynamics research and can support shorter pulse widths. Soft X-ray water window band attosecond pulses are also more suitable for biological sample research.

[0003] Currently, soft X-ray attosecond light sources face two problems:

[0004] 1. Dispersion compensation of attosecond pulses.

[0005] In the attosecond pulse generation method based on high harmonic technology, according to the three-step model of high harmonic, for the commonly used short track, the kinetic energy of the electron increases with the increase of the recombination time, and the attosecond pulse has positive chirp, which requires negative dispersion to compress the width of the attosecond pulse. Currently, the main method for compensating the dispersion of attosecond pulses is to use metal films. In the soft X-ray band, the group delay dispersion (GDD) of the commonly used metal film is as shown in Figure 1 , and the transmission of the commonly used metal film is as shown in Figure 2 , and the horizontal coordinates in the figures are photon energy. The main problems of metal film dispersion compensation are: (1) considering the reasonable transmission rate of attosecond pulses, the thickness of the metal film is generally controlled at 100-200 nm, but 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 dispersion amount cannot be accurately 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) oxidation of the metal film will cause a decrease in the transmission rate 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 metal films for separation. Driving lasers (mid-infrared band) generally have low photon energy and are difficult to penetrate metal films, while attosecond pulses are generally in the extreme ultraviolet or soft X-ray bands and 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 lead to 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:

[0011] A dispersion compensation method for attosecond pulses in the soft X-ray water window band, characterized by the following features:

[0012] A uniform and adjustable liquid film was used to compensate for the dispersion of attosecond pulses in the soft X-ray water window band.

[0013] A dispersion compensation device for soft X-ray water window band attosecond pulses, for implementing the dispersion compensation method for soft X-ray water window band attosecond pulses described above, is characterized in that:

[0014] It comprises a vacuum cavity and a liquid film generating mechanism.

[0015] The working end of the liquid film generating mechanism is placed inside the vacuum cavity, and is used to output a working medium to generate a liquid film with uniform and adjustable thickness.

[0016] The two opposite side walls of the vacuum cavity are respectively provided with an entrance and an exit, and the entrance and the exit are respectively located on the two sides of the liquid film.

[0017] The soft X-ray water window band attosecond pulses to be dispersion compensated enter the liquid film through the entrance, are dispersion compensated by the liquid film, and are then guided out of the vacuum cavity through the exit.

[0018] The application also provides a separation method for soft X-ray water window band attosecond pulses, which is characterized in that:

[0019] A liquid film with non-uniform and adjustable thickness is used to separate the soft X-ray water window band attosecond pulses.

[0020] The application also provides a separation device for soft X-ray water window band attosecond pulses, for implementing the separation method for X-ray water window band attosecond pulses described above, which is characterized in that:

[0021] It comprises a vacuum cavity and a liquid film generating mechanism.

[0022] The working end of the liquid film generating mechanism is placed inside the vacuum cavity, and is used to output a working medium to generate a liquid film with non-uniform and adjustable thickness.

[0023] The two opposite side walls of the vacuum cavity are respectively provided with an entrance and an exit, and the entrance and the exit are respectively located on the two sides of the liquid film.

[0024] The collinearly transmitted soft X-ray water window band attosecond pulses and residual infrared driving laser to be separated enter the liquid film through the entrance, and the residual infrared driving laser is separated by the liquid film, and then the soft X-ray water window band attosecond pulses are guided out of the vacuum cavity through the exit.

[0025] Further, the cross section of the liquid film along the thickness direction is an isosceles trapezoid, and the included angle of the two inclined sides is 1 mrad to 10 mrad.

[0026] Further, a baffle or a mirror is arranged in the vacuum cavity; the baffle or the mirror is arranged on the light path of the residual infrared drive laser separated by the liquid film; the baffle is used to shield the residual infrared drive laser.

[0027] Alternatively, the vacuum cavity is provided with an outlet on the side wall of the light path of the mirror; the mirror is used to reflect the residual infrared drive laser and then guide the residual infrared drive laser out of the vacuum cavity through the outlet.

[0028] The application further provides a dispersion compensation and separation method of soft X-ray water window band attosecond pulses, which is characterized in that:

[0029] The two liquid films with non-uniform and adjustable thicknesses are used to separate and dispersion compensate the soft X-ray water window band attosecond pulses.

[0030] The application further provides a dispersion compensation and separation device of soft X-ray water window band attosecond pulses, which is used to realize the dispersion compensation and separation method of the soft X-ray water window band attosecond pulses, and is characterized in that:

[0031] The dispersion compensation and separation device comprises a vacuum cavity and two liquid film generating mechanisms.

[0032] The working ends of the two liquid film generating mechanisms are arranged in the vacuum cavity, respectively, and are used to output working medium to generate liquid films with non-uniform and adjustable thicknesses.

[0033] The two liquid films are provided with a spacing along the length direction of the vacuum cavity, have the same specifications, are arranged in parallel on the side close to each other, are arranged in parallel on the side away from each other, and the midlines in the height direction of the two liquid films coincide.

[0034] The vacuum cavity is provided with an entrance and an exit on the two opposite side walls, respectively, and the entrance and the exit are located on the sides away from each other of the two liquid films.

[0035] The liquid film close to the entrance is defined as the first liquid film, and the liquid film close to the exit is defined as the second liquid film.

[0036] The collinearly transmitted soft X-ray water window band attosecond pulses and the residual infrared drive laser to be dispersion compensated and separated are incident on the first liquid film through the entrance, the residual infrared drive laser is separated by the first liquid film, and the dispersion compensation is performed; the soft X-ray water window band attosecond pulses are dispersion compensated by the second liquid film, and then are guided out of the vacuum cavity through the exit.

[0037] Further, the cross section of the first liquid film along the thickness direction is a positive isosceles trapezoid, the cross section of the second liquid film along the thickness direction is an inverse isosceles trapezoid, the included angle of the two inclined sides of the first liquid film is 1 mrad to 10 mrad, and the included angle of the two inclined sides of the second liquid film is -10 mrad to -1 mrad.

[0038] Alternatively, the cross section of the first liquid film along the thickness direction is an inverse isosceles trapezoid, the cross section of the second liquid film along the thickness direction is a positive isosceles trapezoid, the included angle of the two inclined sides of the first liquid film is -10 mrad to -1 mrad, and the included angle of the two inclined sides of the second liquid film is 1 mrad to 10 mrad.

[0039] Further, the vacuum cavity is provided with a baffle or a mirror, the baffle or the mirror is located on the light path of the residual infrared drive laser that is spatially separated by the liquid film, and the baffle is used for shielding the residual infrared drive laser.

[0040] Alternatively, the vacuum cavity is provided with a guide outlet on the side wall of the light path of the mirror, and the mirror is used for reflecting the residual infrared drive laser and guiding the residual infrared drive laser out of the vacuum cavity through the guide outlet.

[0041] The beneficial effects of the present application are:

[0042] 1. The present application can provide greater negative dispersion by using a liquid film with uniform thickness, and the thickness of the liquid film can be adjusted according to actual needs, so that the dispersion compensation is more accurate, and the spatial profile of the attosecond pulse is not affected, thereby avoiding the problem of reduced transmittance of the attosecond pulse due to oxidation of the metal film, and having important significance for realizing shorter pulse width of the attosecond pulse and obtaining higher time resolution. Compared with the traditional metal film method, the method provided by the present application can provide greater negative dispersion and flexible and tunable dispersion under the same transmittance condition, and has a higher damage threshold.

[0043] 2. The present application can separate the collinearly transmitted soft X-ray water window waveband attosecond pulse and the infrared drive laser in space by using a liquid film with non-uniform thickness, and the liquid film itself can also absorb a certain amount of infrared drive laser due to the low transmittance of the infrared drive laser in the liquid film, which is helpful for separation. Moreover, the liquid film is flowable, and can still work under the working condition of high-power / high-energy drive laser without damage.

[0044] 3. The present application can simultaneously realize separation and dispersion compensation of the soft X-ray water window waveband attosecond pulse by using two liquid films with non-uniform thickness.

[0045] 4、The reflector of the present application can guide the separated infrared driving laser out of the vacuum cavity, realizing the secondary use of the infrared driving laser.

[0046] 5、The present application has low loss for the transmission of soft X-ray water window band attosecond pulse. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is the dispersion diagram of the existing commonly used metal film (100nm thickness) in the soft X-ray band;

[0048] Figure 2 is the transmittance diagram of the existing commonly used metal film (100nm thickness) in the soft X-ray band;

[0049] Figure 3 is the dispersion diagram of water and different metal films in the soft X-ray band 200-530eV range;

[0050] Figure 4 is the transmittance diagram of the soft X-ray water window band attosecond pulse in the different thickness liquid water thin film in the embodiment of the present application;

[0051] Figure 5 is the structural schematic diagram of the dispersion compensation device for the soft X-ray water window band attosecond pulse;

[0052] Figure 6 is the separation principle schematic diagram of the separation device for the soft X-ray water window band attosecond pulse, a is the separation light path schematic diagram, and b is the principle schematic diagram;

[0053] Figure 7 is the structural schematic diagram of the separation device for the soft X-ray water window band attosecond pulse, a is the structural schematic diagram when the baffle is arranged, and b is the structural schematic diagram when the reflector is arranged;

[0054] Figure 8 is the structural schematic diagram of the dispersion compensation and separation device for the soft X-ray water window band attosecond pulse, a is the structural schematic diagram when the baffle is arranged, and b is the structural schematic diagram when the reflector is arranged.

[0055] In the figure: 1-vacuum cavity, 2-liquid thin film generating mechanism, 3-liquid thin film, 4-baffle, 5-reflector. DETAILED DESCRIPTION

[0056] In order to make the purposes, advantages and features of the present application clearer, a soft X-ray water window band attosecond pulse dispersion compensation and separation method and device are further described in detail below in combination with the drawings and specific embodiments. The advantages and features of the present application will be clearer according to the following specific embodiments. It should be noted that: the drawings are very simplified and use non-precise proportions, only to facilitate and clarify the purpose of assisting the description of the embodiments of the present application; secondly, the structures shown in the drawings are often part of the actual structure.

[0057] Embodiment one

[0058] Dispersion compensation method and scheme design

[0059] There is no public data on the group delay dispersion of water (H2O) in the soft X-ray band range. According to the refractive index parameters of water in the soft X-ray band 200-530eV range, the dispersion of water in this range is calculated. Figure 3 To calculate the GDD of water and different metals in the soft X-ray band 200-530eV range at a thickness of 100nm. The green curve is the GDD of 100nm thick H2O (as 2 ). Water has negative dispersion characteristics in the range of 200-530eV, which can compensate for the inherent positive dispersion of attosecond pulses. At 250eV, the GDD is about -6.32as 2 ; at 300eV, the GDD is about -3.67as 2 ; at 350eV, the GDD is about -2.44as 2 ; at 400eV, the GDD is about -1.81as 2 ; at 450eV, the GDD is about -1.60as 2 ; at 500eV, the GDD is about -2.07as 2 . Figure 3 The dispersion curves of commonly used metal materials in the soft X-ray band are calculated. In this band range, the negative dispersion provided by the water film of the same thickness is lower but close to the negative dispersion provided by the metal film, and has a wider negative dispersion range than Ag, Ti and Sn.

[0060] The transmittance of liquid water of different thicknesses in the water window band 282-533eV range is shown in Figure 4 . When the thickness is 100nm, water has a transmittance of more than 95%, which is much higher than that of a metal film. When the thickness is 5μm, it still has a transmittance of about 30% as a whole.

[0061] ​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 5 μm, the GDD at 250 eV is approximately -316 as. 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.

[0062] 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 the dispersion of attosecond pulses in the soft X-ray water window band, playing a crucial role in achieving shorter pulse widths for attosecond pulses.

[0063] 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 5 As 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.

[0064] The thickness of the liquid water thin film is reasonably set between hundreds of nanometers and several microns, taking into account the transmittance and dispersion compensation. The liquid water thin film generating mechanism that meets this thickness range has mature solutions. The liquid water thin film can be formed by two liquid nozzles [Christopher J. Crissman, et al. Sub-micron thick liquid sheets produced by isotropically etched glass nozzles. Lab on a Chip, 2022, 22.7: 1365-1373], or a special design single nozzle made 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 thin film can be adjusted according to the angle or liquid flow rate of the two nozzles, achieving a thickness of hundreds of nanometers to several microns. The surface size of the liquid water thin film can also be adjusted by adjusting the flow rate to adapt to the spot size. Under this adaptive flow rate, the liquid recovery and recycling in vacuum is also a mature solution.

[0065] When used only as a dispersion compensation function, the attosecond pulse should be transmitted from the relatively uniform thickness area of the liquid water thin film.

[0066] In addition to using water, alcohol liquids such as methanol, ethanol, and propanol can also be used.

[0067] Embodiment two

[0068] Separation method and scheme design

[0069] Through the analysis of the refractive index of liquid water in different wave bands and the spatial size of the liquid water thin film, a separation scheme is designed.

[0070] The soft X-ray water window waveband attosecond pulse is usually generated by using a mid-infrared waveband driving laser. The refractive index of water in the mid-infrared waveband is around 1.3, while the refractive index of water in the soft X-ray water window waveband is around 1. This embodiment is different from embodiment one in that a liquid water thin film with non-uniform thickness is used, and the rest of the structure is the same as embodiment one.

[0071] The liquid water thin film with non-uniform thickness specifically includes:

[0072] (1) The thickness decreases from top to bottom (positive isosceles trapezoid), and the soft X-ray water window waveband attosecond pulse almost does not affect the beam pointing after passing through the liquid water thin film, while the mid-infrared driving laser will be deflected upward due to the refractive index of liquid water, as shown inFigure 6 As shown, the soft X-ray attosecond pulse is separated from the attosecond pulse in space after a certain transmission distance.

[0073] (2) The thickness increases from top to bottom (reverse isosceles trapezoid), and the soft X-ray water window band attosecond pulse has little effect on the beam pointing after passing through the liquid water film, while the mid-infrared driving laser will be deflected downward due to the refractive index of liquid water.

[0074] The liquid water film with non-uniform thickness is approximately isosceles trapezoidal, and the angle between the two sides determines the deflection angle of the infrared light. In the infrared band, taking the refractive index of 1.3 as an example, when the angle between the two sides of the liquid water film is 1 mrad, the deflection angle is 0.3 mrad; when the angle between the two sides of the liquid water film is 5 mrad, the deflection angle is 1.5 mrad; when the angle between the two sides of the liquid water film is 10 mrad, the deflection angle is 3 mrad. At this time, after transmitting 1 m, the center of the infrared driving laser and the center of the attosecond pulse deviate by 3 mm.

[0075] Considering the divergence angle of the infrared driving laser, considering the example of the actual situation in the soft X-ray attosecond light source, the divergence angle of the infrared driving laser is 5 mrad, and the divergence angle of the soft X-ray attosecond pulse is 0.5 mrad. In order to completely separate the two beams in space, the deflection angle needs to reach 2.75 mrad, and the angle between the two sides of the liquid water film needs to be about 9.167 mrad. When the distance between the attosecond generation position and the liquid water film is 0.5 m, the infrared driving laser spot diameter is about 2.5 mm, and the attosecond pulse spot diameter is about 0.25 mm. When the deflection angle is 2.75 mrad, after passing through the liquid water film, it needs to propagate 0.5 m to completely separate the two beams in space. In this case, the angle between the two sides of the liquid water film needs to be about 9.167 mrad. For the 0.25 mm diameter attosecond pulse, the thickness of the liquid water film through which the attosecond pulse passes changes to 2.29 μm (the uppermost end to the lowermost end of the spot).

[0076] The design of the scheme for separating the soft X-ray water window band attosecond pulse by using the liquid water film is as shown in Figure 7 The liquid water film needs to be placed in the vacuum cavity 1, and recycling can be performed to ensure the use efficiency. The residual infrared driving laser and the attosecond pulse transmitted in the same line are transmitted through the liquid water film to achieve spatial separation.

[0077] The residual infrared driving laser separated by the liquid water film can be blocked by the baffle 4 Figure 7 (a) or reflected by the reflecting mirror 5 Figure 7 (b), and the residual laser is reflected and discharged from the outlet (not shown in the figure) of the vacuum cavity 1, and then reused.

[0078] Since the transmittance of mid-infrared driving laser in water is low, the liquid water film itself can also absorb a certain mid-infrared driving laser, which is helpful for separation. At the same time, since the liquid water film is flowing, it can still work well under the condition of high-power / high-energy driving laser and will not be damaged.

[0079] Embodiment three

[0080] Method and scheme design for simultaneously performing dispersion compensation and separation

[0081] In embodiment one, the liquid water film is of uniform thickness, which cannot separate the infrared driving laser and the attosecond pulse in space, and is suitable for the case of only considering dispersion compensation of the attosecond pulse.

[0082] In embodiment two, the liquid water film is of non-uniform thickness, since the attosecond pulse spot passes through the liquid water film of different thicknesses at different positions, which means that it has different dispersion compensation amounts, which is generally not conducive, and is suitable for the case of only considering separation of the attosecond pulse.

[0083] If the separation and dispersion compensation of the attosecond pulse are simultaneously performed, the scheme is as shown in Figure 8 In combination with the schemes of embodiment one and embodiment two, this embodiment adopts two liquid water films, the cross section of the first liquid water film along the thickness direction is a right 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 of the two inclined sides of the first liquid water film is 1 mrad to 10 mrad, and the included angle of 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, the cross section of the second liquid water film along the thickness direction is a right isosceles trapezoid, that is, the thickness decreases from top to bottom, the included angle of the two inclined sides of the first liquid water film is -10 mrad to -1 mrad, and the included angle of the two inclined sides of the second liquid water film is 1 mrad to 10 mrad.

[0084] The first liquid water film realizes the separation of the attosecond pulse and the infrared driving laser and a certain dispersion compensation, and the second liquid water film is placed at a certain distance, which makes the infrared driving laser spot separate from the attosecond pulse spot in space, and realizes the dispersion compensation of the attosecond pulse again through the second liquid water film. After passing through the two liquid water films, the attosecond pulse passes through the liquid water films of the same thickness at different positions on the spot.

[0085] Considering the example of the actual situation in the soft X-ray water window attosecond light source, the divergence angle of the infrared driving laser is 5 mrad, the divergence angle of the soft X-ray water window attosecond pulse is 0.5 mrad, the angle between the two sides of the liquid water film is about 9.167 mrad, and the deflection angle of the infrared driving laser in water with a refractive index of 1.3 is 2.75 mrad, which meets the minimum deflection angle for completely separating the two beams of light. When the distance between the attosecond generation position and the liquid water film is 0.5 m, the infrared driving laser spot diameter is about 2.5 mm, the attosecond pulse spot diameter is about 0.25 mm, and the attosecond pulse passes through the first liquid water film with a thickness variation of 2.29 μm (the uppermost end to the lowermost end of the spot), and the two beams of light can be completely spatially separated after propagating 0.5 m. After this propagation distance, the second liquid water film is placed with a thickness variation opposite to that of the first liquid water film, and the attosecond pulse passes through the second liquid water film with a thickness variation of 2.29 μm (the uppermost end to the lowermost end of the spot) but with opposite thicknesses at the upper and lower ends. In this way, after passing through the second liquid water film, the attosecond pulse spot at different positions passes through liquid water films with the same thickness. For the attosecond pulse, the equivalent thickness of the two liquid water films is about 2.29 μm, at which time the overall transmittance is greater than 50%, and the provided dispersion is: at 250 eV, the GDD is about -144.73 as 2 ; at 300 eV, the GDD is about -84.04 as 2 ; at 350 eV, the GDD is about -55.876 as 2 ; at 400 eV, the GDD is about -41.45 as 2 ; at 450 eV, the GDD is about -36.64 as 2 ; at 500 eV, the GDD is about -47.4 as 2 .

[0086] This method can provide flexible and precise adjustment of the dispersion amount, has high efficiency, can withstand high power / high energy, and is very suitable for soft X-ray water window attosecond light sources, and is of great significance for realizing shorter pulse width attosecond pulses to obtain higher time resolution.

[0087] The embodiment is the same as embodiment two, and the baffle 4 or the mirror 5 can also be arranged in the vacuum cavity 1; the difference is that the baffle 4 or the mirror 5 of the embodiment needs to be arranged on the light path of the residual infrared driving laser after being separated by the first liquid film.

Claims

1.A method for dispersion compensation and separation of soft X-ray water window attosecond pulses, characterized in that: two liquid films with non-uniform and adjustable thickness are used to separate and dispersion compensate the soft X-ray water window attosecond pulses; the thickness of the liquid films ranges from 100 nm to 5 μm. 2.An apparatus for dispersion compensation and separation of soft X-ray water window attosecond pulses, used to implement the method for dispersion compensation and separation of soft X-ray water window attosecond pulses according to claim 1, characterized in that: it comprises a vacuum cavity (1) and two liquid film generating mechanisms (2); the working ends of the two liquid film generating mechanisms (2) are respectively arranged inside the vacuum cavity (1) to output working medium generated liquid films (3) with non-uniform and adjustable thickness; the working medium is water or alcohol liquid; a gap is provided between the two liquid films (3) along the length direction of the vacuum cavity (1); the two liquid films (3) have the same specification, and are arranged in parallel on the side close to each other and on the side far away from each other, and the midlines in the height direction of the two liquid films coincide; an entrance and an exit are respectively arranged on the two opposite side walls of the vacuum cavity (1), and the entrance and the exit are respectively located on the side far away from each other of the two liquid films (3); the liquid film (3) close to the entrance is defined as the first liquid film, and the liquid film (3) close to the exit is defined as the second liquid film; the collinearly transmitted soft X-ray water window attosecond pulses and residual infrared driving laser to be dispersion compensated and separated are incident to the first liquid film through the entrance, the residual infrared driving laser is separated and dispersion compensated by the first liquid film, the soft X-ray water window attosecond pulses are dispersion compensated by the second liquid film, and then are guided out of the vacuum cavity (1) through the exit. 3.The apparatus for dispersion compensation and separation of soft X-ray water window attosecond pulses according to claim 2, characterized in that: the cross section of the first liquid film along the thickness direction is a right isosceles trapezoid, the cross section of the second liquid film along the thickness direction is an inverted isosceles trapezoid, the included angle of the two inclined sides of the first liquid film is 1 mrad to 10 mrad, and the included angle of 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, the cross section of the second liquid film along the thickness direction is a right isosceles trapezoid, the included angle of the two inclined sides of the first liquid film is -10 mrad to -1 mrad, and the included angle of the two inclined sides of the second liquid film is 1 mrad to 10 mrad. 4.The apparatus for dispersion compensation and separation of soft X-ray water window attosecond pulses according to claim 2 or 3, characterized in that: it further comprises a baffle (4) or a mirror (5) arranged in the vacuum cavity (1); the baffle (4) or the mirror (5) is located on the light path of the residual infrared driving laser separated by the first liquid film; the baffle (4) is used to shield the residual infrared driving laser. Or, the vacuum cavity (1) is located on the side wall of the light path of the mirror (5) and is provided with an outlet, and the mirror (5) is used for reflecting the residual infrared driving laser and guiding the residual infrared driving laser out of the vacuum cavity (1) through the outlet.

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