System and method for generating spectrum-adjustable attosecond soft X-ray light source

Abstract

The invention discloses a system and a method for generating an attosecond soft X-ray light source with an adjustable spectrum. The system comprises an ultrafast laser light source, an optical focusing system and a slab waveguide which are sequentially arranged along a light path, the ultrafast laser light source generates ultrafast laser which enters the optical focusing system; the optical focusing system focuses the incident ultrafast laser, and ultrafast intense laser filaments with different lengths are obtained by changing the focal length of the optical focusing system; the ultrafast intense laser filaments with different lengths are incident to the slab waveguide, the slab waveguide is filled with a working medium, and the ultrafast intense laser filaments with different lengths and the working medium of the slab waveguide perform molecular interaction to obtain attosecond soft X-rays with different light wave intensities and spectral ranges. The length of the ultrafast strong laser filament is adjusted by changing the focal length of the optical focusing system, so that the spectral wavelength and the light intensity of the attosecond soft X-ray are remarkably adjusted, and frequency selection output of the attosecond soft X-ray is realized.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to a system and method for generating a spectrum-adjustable attosecond soft X-ray light source. Background Art

[0002] Since the invention of the world's first ruby ​​laser by scientist Maiman, laser-related technologies have been constantly improving. Scientists have been working hard day after day to further obtain laser light sources with stronger radiation, shorter wavelengths, and more stable and superior performance. -15 With the maturity of laser technology, scientists can observe the vibration of molecules and the movement of atoms in chemical reactions. However, the time scale of electron movement is attoseconds (1 attosecond = 10 -18 Attosecond radiation refers to extremely short light pulses with a duration of attoseconds, and its wavelength is usually in the extreme ultraviolet (EUV) to soft X-ray band. Attosecond soft X-ray radiation is a core tool in the field of ultrafast science. It can directly observe the ultrafast dynamics of electrons in atoms and molecules, filling the gap in the time scale of electron motion that cannot be covered by femtosecond lasers, and promoting ultrafast science into the era of electron dynamics. To this day, due to its wide and important application value in materials, biology, chemistry, physics, medicine and chip manufacturing and processing, attosecond soft X-ray radiation has become the focus of scientists' research. Attosecond soft X-ray radiation (XUV) refers to electromagnetic radiation with a single photon energy in the range of 124eV to 1240eV (corresponding to a wavelength of 10nm to 1nm) and a very short duration. The wavelength of attosecond soft X-ray radiation is close to the atomic scale, which is suitable for detecting changes in the electronic structure and chemical bonds inside the material. And due to its attosecond duration, it can be used to track ultrafast dynamics of electrons, such as ionization and charge migration.

[0003] At present, the main ways to produce attosecond soft X-ray radiation and X-ray light sources are: gas discharge lamps, synchrotron radiation, free electron lasers, discharge plasma (DPP), laser plasma (LPP) and strong field high-order (second and above) harmonic radiation (HGG). The photons of attosecond soft X-ray radiation generated by gas discharge lamps are limited by the electronic energy levels of the gas atoms themselves, so they cannot be tuned and lack coherence and collimation; the emission wavelength of attosecond soft X-ray radiation generated by discharge plasma and laser plasma is highly dependent on the properties of the target material itself, and is currently mainly used in the field of lithography; although the EUV light sources generated by synchrotron radiation devices and free electron lasers have excellent characteristics, they are both large-scale scientific devices at the national level, so the devices themselves are huge and very expensive, with extremely high operating costs, and are not suitable for large-scale laboratory scientific research; and the high-order harmonics generated by the interaction of ultrafast strong field lasers with different target materials can have a wavelength as short as 2.3 to 4.4nm (the "water window" band). The high-order harmonics generated by this method have excellent properties such as adjustable wavelength and narrow radiation spectrum bandwidth. It is an extremely effective method to obtain attosecond soft X-ray radiation with high temporal coherence, high spatial coherence, and ultra-short pulse width. The attosecond soft X-ray source obtained by strong-field high-harmonic (HHG) radiation has the advantages of simple acquisition, high cost performance, and high temporal and spatial coherence. Moreover, this method is currently the most important way to obtain attosecond coherent pulses, which has attracted great attention and development in scientific research, material detection, and desktop equipment processing.

[0004] High-order harmonics were first discovered in 1987 and quickly became one of the important ways to generate attosecond soft X-rays in the laboratory. However, traditional methods cannot obtain adjustable attosecond soft X-ray radiation, and high-order harmonics have low conversion efficiency. Therefore, obtaining attosecond soft X-rays with adjustable wavelength range and high conversion efficiency has become the focus of many researchers. Many methods have been proposed, such as periodically arranged or alternating planar waveguides, multi-color field and micromotor modulation, reverse transmission of light pulses, etc., but they all have disadvantages such as complex operation and large changes in the vacuum degree in the vacuum chamber. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a system and method for generating a spectrally adjustable attosecond soft X-ray light source, which obtains an attosecond soft X-ray (X-ray) radiation light source with adjustable light wave intensity and spectral range through the interaction between an ultrafast high-field laser and a gas medium. The generated spectrum can be adjusted within the wavelength range of 12nm to 18nm, and its light wave intensity can be adjusted within the range of 10000arb.units to 18000arb.units.

[0006] The invention discloses a generation system of a spectrum-adjustable attosecond soft X-ray light source, comprising an ultrafast laser light source, an optical focusing system and a planar waveguide arranged in sequence along an optical path;

[0007] The ultrafast laser light source generates ultrafast laser light which is incident on the optical focusing system;

[0008] The optical focusing system focuses the incident ultrafast laser, and ultrafast strong laser filaments of different lengths are obtained by changing the focal length of the optical focusing system;

[0009] The ultrafast and intense laser filaments of different lengths are incident on the planar waveguide, which is filled with a working medium. The ultrafast and intense laser filaments of different lengths undergo molecular interaction with the working medium of the planar waveguide to obtain attosecond soft X-rays of different light wave intensities and spectral ranges.

[0010] As a further improvement of the present invention, the ultrafast laser light source is a femtosecond laser light source.

[0011] As a further improvement of the present invention, the optical focusing system includes a reflector group and a focusing mirror arranged in sequence along the optical path of the ultrafast laser, the reflector group is used to adjust the optical path of the ultrafast laser, and the focusing mirror is installed on a mirror frame, and the focusing mirror can be adjusted in height and at a rotation angle around a vertical axis on the mirror frame; through the adjustment of the reflector group and the focusing mirror, the ultrafast laser is incident on the focusing mirror, and at this time, an ultrafast strong laser filament is generated along the optical path direction at the focal position of the focusing mirror; wherein the length of the obtained ultrafast strong laser filament is proportional to the focal length of the focusing mirror.

[0012] As a further improvement of the present invention, the reflector group includes a first reflector and a second reflector which are sequentially arranged along the optical path of the ultrafast laser, and the focusing mirror is a convex lens or a conical lens.

[0013] As a further improvement of the present invention, the center position of the ultrafast intense laser filament in the length direction is located inside the planar waveguide, so as to facilitate full interaction with the working medium molecules.

[0014] As a further improvement of the present invention, the working medium is an inert gas molecule that can be driven by the ultrafast intense laser filament to produce high-order harmonics in the attosecond soft X-ray range, and the working medium includes xenon, argon, helium, krypton or neon.

[0015] As a further improvement of the present invention, it also includes: a working medium supply device;

[0016] The working medium supply device fills the required working medium into the planar waveguide through a hollow capillary, and the working medium supply device can also realize gas flow control.

[0017] As a further improvement of the present invention, it also includes: a filter and an X-ray CCD detector arranged in sequence in the light emitting direction of the attosecond soft X-rays;

[0018] The filter matches the wavelength of the ultrafast laser and is used to separate the ultrafast laser seed light source and the generated attosecond soft X-rays; the X-ray CCD detector is used to detect the attosecond soft X-rays filtered by the filter.

[0019] As a further improvement of the present invention, the generation and detection of the attosecond soft X-ray light source are carried out in a vacuum environment.

[0020] As a further improvement of the present invention, it also includes: a bracket or device required to adjust a number of focusing lenses with different focal lengths, a platform or guide rail system for accurately controlling position movement, and a base or supporting structure for stabilizing and fixing the device or component.

[0021] The present invention also discloses a method for generating a spectrum-adjustable attosecond soft X-ray light source, comprising:

[0022] The ultrafast laser light source generates an ultrafast laser that is incident on the optical focusing system;

[0023] The optical focusing system focuses the incident ultrafast laser, and ultrafast strong laser filaments of different lengths are obtained by changing the focal length of the optical focusing system;

[0024] Ultrafast and intense laser filaments of different lengths are incident on a planar waveguide filled with a working medium, and molecular interactions occur between the ultrafast and intense laser filaments and the working medium to obtain attosecond soft X-rays with different light wave intensities and spectral ranges.

[0025] As a further improvement of the present invention, the generation method specifically includes:

[0026] First, optical focusing systems with different effects are placed on the platform to focus the incident ultrafast laser. It should be noted that the propagation path of the incident light source needs to pass through the focus of the installed optical focusing system and be parallel to the plane of the working platform.

[0027] Secondly, when the ultrafast laser light source is turned on, obvious light filaments will be generated at the focal position of the optical focusing system, that is, the ultrafast and strong laser light filaments generated by the optical focusing system. Optical focusing systems with different focal distances will focus and generate ultrafast and strong laser light filaments of different lengths.

[0028] Next, use the prepared flat waveguide and connect it to the working medium supply device (the working medium described in this scheme includes xenon, argon, helium, krypton, neon, etc.), place the flat waveguide horizontally at the ultrafast and intense laser filament, and make the ultrafast and intense laser filament enter the box from the middle of one side of the flat waveguide and pass through the box horizontally;

[0029] Finally, after the working medium molecules in the planar waveguide are excited by the ultrafast laser filaments, a high-order high harmonic (HHG) is generated through a three-step ionization process, that is, attosecond soft X-rays are obtained. By using optical focusing systems with different focal lengths to complete the above operation steps, attosecond soft X-rays with different light wave intensities and spectral ranges can be obtained. The implementation method of the present invention is simple and easy to implement, which has great value and significance in practical engineering applications and scientific research.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention adjusts the length of the ultrafast intense laser filament by changing the focal length of the optical focusing system, thereby regulating the wavelength and intensity distribution of the generated high-order harmonic emission, thereby significantly adjusting the spectral wavelength and light intensity of the generated attosecond soft X-rays, and realizing the frequency-selective output of attosecond soft X-rays. The implementation method of the present invention is simple and easy to implement, which has great value and significance in practical engineering applications and scientific research work. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the optical path of the generation system of the spectrum-tunable attosecond soft X-ray light source disclosed in the present invention;

[0033] Figure 2 This is a diagram of the 63rd order harmonic intensity corresponding to different relative positions of the optical filament center and the planar waveguide disclosed in the present invention.

[0034] In the figure:

[0035] 1. Femtosecond laser; 2. First reflector; 3. Second reflector; 4. Focusing mirror; 5. Planar waveguide; 6. Ultrafast and intense laser filament; 7. Working medium supply device; 8. X-ray CCD detector; 9. Filter. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0038] like Figure 1 As shown, the present invention provides a generation system of a spectrum-adjustable attosecond soft X-ray light source, comprising a femtosecond laser light source, an optical focusing system, a planar waveguide 5, a filter 9 and an X-ray CCD detector 8 arranged in sequence along an optical path; wherein,

[0039] The femtosecond laser 1 generated by the femtosecond laser light source of the present invention is incident on the optical focusing system, and the optical focusing system includes a first reflector 2, a second reflector 3 and a focusing mirror 4 which are sequentially arranged along the optical path of the ultrafast laser; the first reflector 2 and the second reflector 3 are used to adjust the optical path of the ultrafast laser, and the focusing mirror 4 (convex lens or conical lens) is installed on a mirror frame, and the focusing mirror 4 can be adjusted in height and in rotation angle around a vertical axis on the mirror frame; through the adjustment of the first reflector 2, the second reflector 3 and the focusing mirror 4, the femtosecond laser 1 is incident on the focusing mirror 4, and at this time, an ultrafast strong laser filament 6 is generated at the focal position of the focusing mirror 4 along the optical path direction; wherein the length of the obtained ultrafast strong laser filament 6 is proportional to the focal length of the focusing mirror.

[0040] By changing the focal length of the optical focusing system, ultrafast and intense laser filaments of different lengths are obtained; the ultrafast and intense laser filaments of different lengths are incident on the flat waveguide 5, and the flat waveguide is filled with a working medium, which is an inert gas molecule that can be driven by the ultrafast and intense laser filament to produce high-order harmonics in the attosecond soft X-ray range, and the working medium includes xenon, argon, helium, krypton or neon; the ultrafast and intense laser filaments of different lengths interact with the working medium of the flat waveguide to obtain attosecond soft X-rays of different light wave intensities and spectral ranges. Further, the center position of the ultrafast and intense laser filament in the length direction is located in the flat waveguide, which is convenient for fully interacting with the working medium molecules. Further, the working medium supply device 7 fills the required working medium into the flat waveguide through a hollow capillary, and the working medium supply device can also realize gas flow control.

[0041] The filter 9 of the present invention matches the wavelength of the ultrafast laser and is used to separate the ultrafast laser seed light source and the generated attosecond soft X-rays; the X-ray CCD detector 8 is used to detect the attosecond soft X-rays filtered by the filter.

[0042] The generation and detection of the above-mentioned attosecond soft X-ray light source are carried out in a vacuum environment.

[0043] The present invention provides a method for generating a spectrum-adjustable attosecond soft X-ray light source, comprising:

[0044] S1. Build different optical focusing systems:

[0045] 1) Convex lens focusing: Select and fix the convex lens (take a convex lens with a focal length of 300mm as an example). Select a convex lens with a focal length of 300mm, place it on the lens holder, and fix it; then connect the lens holder with the convex lens with a focal length of 300mm to the connecting shaft, and then connect and fix it to the bracket base through the connecting shaft. Here, you can change the height and angle of the convex lens by adjusting the connection under the lens holder, which is convenient for the subsequent focusing of the incident ultrafast laser light source.

[0046] 2) Conical mirror focusing: Select and fix the conical mirror, place the conical mirror on the lens holder and fix it; then connect the holder carrying the conical mirror to the connecting shaft, and then connect and fix it to the holder base through the connecting shaft. Here, the height and angle of the conical mirror can be changed by adjusting the connection under the lens holder. The plane of the conical lens should face the collimated ultrafast laser light source.

[0047] 3) Dual-path delayed focusing system: A beam splitter is used to split the ultrafast laser light source into two ultrafast laser light sources with the same energy chain. The first ultrafast laser light source can generate the first light filament at the focus of the system by focusing with a convex lens or a conical mirror. The second ultrafast laser light source achieves a time delay with the first light source by calculating the optical path difference of the light path, and can generate the second light filament at the focus of the system by focusing with a convex lens or a conical mirror.

[0048] S2. Focusing produces strong laser filaments. After the optical focusing system is built, adjust the height and angle of the connecting axis so that the incident ultrafast laser light source can be incident into the optical focusing system. At this time, a light filament visible to the naked eye will be generated near the focus of the optical focusing system, with a length of about 3 cm, that is, the ultrafast strong laser filament formed after the ultrafast laser light source is focused by the optical focusing system.

[0049] S3. Fix and place the flat waveguide (take a 1cm long flat waveguide as an example). Make a mark at the formed ultrafast and intense laser filament, then place the fixed base of the flat waveguide at the mark, and use a hollow capillary to connect the flat waveguide to the working medium (take He gas as an example) supply device. Use double-sided tape to place the flat waveguide on the fixed base, and adjust the height and angle of the fixed base so that the ultrafast and intense laser filament can be incident and pass through the flat waveguide. It is worth noting that the center position of the ultrafast and intense laser filament needs to be inside the flat waveguide to facilitate interaction with the working medium molecules; the 63rd order harmonic intensity corresponding to the different relative positions of the filament center and the flat waveguide is as follows Figure 2 shown.

[0050] S4, generate attosecond soft X-rays and detect them. Figure 1 After the layout shown is fixed, the ultrafast strong laser filament will pass through the flat waveguide and then pass through the filter (matching the wavelength of the excitation light source) to separate the generated attosecond soft X-rays from the ultrafast laser seed light source. The attosecond soft X-rays filtered by the filter will be incident on the X-ray CCD detector for detection. It should be emphasized here that after adjusting all the optical paths, the vacuum chamber must be sealed and evacuated to vacuum mode to prevent the molecules in the air from scattering and absorbing the generated attosecond soft X-rays and affecting the subsequent monitoring of the X-ray CCD detector. Therefore, the entire process of generating attosecond soft X-rays and detecting them needs to be carried out in a vacuum environment; and the working medium supply device for filling the flat waveguide with gas and controlling the gas flow is placed in a standard atmospheric environment.

[0051] S5. Replace different optical focusing systems and optical devices in the system to adjust the spectrum range and light wave intensity of the generated attosecond soft X-rays. Through S1 to S4, the attosecond soft X-rays generated by the interaction between the ultrafast and strong laser filaments formed by the optical focusing system and the He gas in the 1cm long flat waveguide can be obtained. After obtaining the corresponding spectrum, the air pressure of the vacuum chamber is restored to atmospheric pressure, and optical focusing systems with different effects are replaced. For example, the 300mm optical focusing system is replaced with 250mm, 200mm and 150mm optical focusing systems. Then, the same method as above can be used to obtain the attosecond soft X-rays generated by the interaction between the ultrafast and strong laser filaments formed by the optical focusing systems with 250mm, 200mm and 150mm focal lengths and the He gas in the 1cm long flat waveguide. By comparison, after replacing the optical focusing system with a shorter focal length, the wavelength of the spectrum of the generated attosecond soft X-rays has been significantly reduced, and the intensity of the spectrum has also decreased to a certain extent. Similarly, when the lens focusing the femtosecond laser light source is replaced with an optical focusing system with a focal length of 400 mm, the wavelength of the attosecond soft X-ray spectrum obtained by the X-ray CCD detector has increased significantly, and the intensity of the spectrum has also increased to a certain extent. Therefore, by replacing the optical focusing system with different effects, the spectrum range and light wave intensity of the attosecond soft X-ray generated can be adjusted.

[0052] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A system for generating a spectrum-tunable attosecond soft X-ray source, characterized in that: It includes an ultrafast laser light source, an optical focusing system and a planar waveguide which are sequentially arranged along an optical path; The ultrafast laser light source generates ultrafast laser light which is incident on the optical focusing system; The optical focusing system focuses the incident ultrafast laser, and ultrafast strong laser filaments of different lengths are obtained by changing the focal length of the optical focusing system; The ultrafast and intense laser filaments of different lengths are incident on the planar waveguide, which is filled with a working medium. The ultrafast and intense laser filaments of different lengths undergo molecular interaction with the working medium of the planar waveguide to obtain attosecond soft X-rays of different light wave intensities and spectral ranges.

2. The system for generating a spectrum-tunable attosecond soft X-ray source according to claim 1, characterized in that: The ultrafast laser light source is a femtosecond laser light source.

3. The system for generating a spectrum-tunable attosecond soft X-ray source according to claim 1, characterized in that: The optical focusing system comprises a reflector group and a focusing mirror which are sequentially arranged along the optical path of the ultrafast laser, wherein the reflector group is used to adjust the optical path of the ultrafast laser, and the focusing mirror is mounted on a mirror frame, and the focusing mirror can be adjusted in height and in rotation angle around a vertical axis on the mirror frame; by adjusting the reflector group and the focusing mirror, the ultrafast laser is incident on the focusing mirror, and at this time, an ultrafast strong laser filament is generated at the focal position of the focusing mirror along the optical path direction; wherein the length of the obtained ultrafast strong laser filament is proportional to the focal length of the focusing mirror.

4. The system for generating a spectrum-tunable attosecond soft X-ray source according to claim 3, characterized in that: The reflector group comprises a first reflector and a second reflector which are sequentially arranged along the optical path of the ultrafast laser, and the focusing mirror is a convex lens or a conical lens.

5. The system for generating a spectrum-tunable attosecond soft X-ray source according to claim 1 or 3, characterized in that: The center position of the ultrafast intense laser filament in the length direction is located inside the planar waveguide.

6. The system for generating a spectrum-tunable attosecond soft X-ray source according to claim 1, characterized in that: The working medium is an inert gas molecule that can be driven by the ultrafast intense laser filament to produce high-order harmonics in the attosecond soft X-ray range, and the working medium includes xenon, argon, helium, krypton or neon.

7. The system for generating a spectrum-tunable attosecond soft X-ray source according to claim 6, characterized in that: Also includes: Working medium supply device; The working medium supply device fills the required working medium into the planar waveguide through a hollow capillary.

8. The system for generating a spectrum-tunable attosecond soft X-ray source according to claim 1, characterized in that: Also includes: The filter and the X-ray CCD detector are arranged in sequence in the direction of the attosecond soft X-ray emission; The filter matches the wavelength of the ultrafast laser and is used to separate the ultrafast laser seed light source and the generated attosecond soft X-rays; the X-ray CCD detector is used to detect the attosecond soft X-rays filtered by the filter.

9. The system for generating a spectrum-tunable attosecond soft X-ray source according to any one of claims 1 to 8, characterized in that: The generation and detection of attosecond soft X-ray sources are carried out in a vacuum environment.

10. A method for generating a spectrum-tunable attosecond soft X-ray source, using the apparatus for generating a spectrum-tunable attosecond soft X-ray source as claimed in any one of claims 1 to 9, characterized in that: include: The ultrafast laser light source generates an ultrafast laser that is incident on the optical focusing system; The optical focusing system focuses the incident ultrafast laser, and ultrafast strong laser filaments of different lengths are obtained by changing the focal length of the optical focusing system; Ultrafast and intense laser filaments of different lengths are incident on a planar waveguide filled with a working medium, and molecular interactions occur between the ultrafast and intense laser filaments and the working medium to obtain attosecond soft X-rays with different light wave intensities and spectral ranges.

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