A device and method for improving the utilization of a free electron laser beam line

Abstract

This invention belongs to the field of optical engineering technology, and specifically relates to a device and method for improving the utilization rate of a free electron laser beamline. The device includes a dispersive optical element and a reflective optical element. The dispersive optical element is disposed within a vacuum unit and is used to decompose the incident light path I into a reflected light path II and a dispersive light path III. The vacuum unit provides a vacuum environment for the dispersive optical element. The reflective optical element is disposed within a vacuum unit and is used to reflect the dispersive light path III, thereby changing the direction of the dispersive light path III. The vacuum unit provides a vacuum environment for the reflective optical element. This invention, through the combination of dispersive and reflective optical elements, provides users with low-intensity diffracted light of varying intensities, meeting the needs of weak-light experiments while ensuring that strong-light experiments are not affected. This doubles the experimental time and effectively improves the utilization rate of the free electron laser beamline.

Description

Technical Field

[0001] This invention belongs to the field of optical engineering technology, and specifically relates to a device and method for improving the utilization rate of free electron laser beamlines. Background Technology

[0002] As a fourth-generation light source, free-electron lasers (LEX) possess advantages such as a wide and continuously tunable wavelength range, high and tunable peak and average power, high temporal and spatial coherence, tunable polarization, and controllable temporal structure for picosecond and femtosecond pulses. They are widely used to provide users with high-quality lasers for experimental applications. Experiments involving the detection of electron information, such as X-ray photoelectron spectroscopy (XPS) and angle-resolved photoelectron spectroscopy (ARPES), require low electron yields per pulse to prevent excessive electron space charge forces. Therefore, weak-light experiments are necessary, necessitating attenuation of the LEX. Direct attenuation is wasteful; saturated output results in multi-order-of-magnitude attenuation, which is technically very challenging in high-repetition-rate LEX. Unsaturated output leads to multi-order-of-magnitude reductions, causing instability in light intensity. Therefore, a method of beam splitting can be used to generate weak light, doubling the weak-light operation time without affecting the main optical path, enabling long-term operation of such experiments. Traditional beam splitting methods involve passing the laser along an edge through a mirror to split it into two beams for individual use. However, this method suffers from drawbacks such as weak adjustment capability for low-light conditions, narrow adjustment range, and strong diffraction effects when splitting low-light beams, failing to adequately meet the needs of low-light experiments. Therefore, a novel beam splitting method is urgently needed to effectively improve the utilization rate of free-electron laser beamlines while meeting the requirements of low-light experiments. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a device and method for improving the utilization rate of free electron laser beamlines, thereby meeting the needs of weak light experiments while effectively improving the utilization rate of free electron laser beamlines.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] An embodiment of the present invention provides a device for improving the utilization rate of free electron laser beamlines, comprising:

[0006] A dispersive optical element is disposed within a dispersive optical element vacuum unit. The dispersive optical element is used to decompose the incident light path into a reflected light path and a dispersive light path. The dispersive optical element vacuum unit provides a vacuum environment for the dispersive optical element.

[0007] The reflective optical element is housed within the vacuum unit of the reflective optical element. The reflective optical element is used to reflect the dispersive light path, thereby changing the direction of the dispersive light path; the vacuum unit of the reflective optical element provides a vacuum environment for the reflective optical element.

[0008] The dispersive optical element has a beam splitting point, and the incident light path is incident on the beam splitting point.

[0009] The dispersive optical element is a planar equidistant grating with a central scribe line and surrounding mirrors. The beam splitting point is the center of the planar equidistant grating.

[0010] The device for improving the utilization rate of free electron laser beamlines further includes a motion unit disposed within the vacuum unit of the reflective optical element. The reflective optical element is disposed on the motion unit, and the motion unit is used to adjust the spatial position of the reflective optical element so that the dispersion light emission direction remains the same.

[0011] The motion unit includes a translation mechanism and a rotation mechanism, wherein the translation mechanism has a degree of freedom to move along the reflection direction; the rotation mechanism is disposed on the translation mechanism, and the reflective optical element is disposed on the rotation mechanism, which has a degree of freedom to rotate circumferentially.

[0012] The reflective optical element is a plane mirror, and the center of the plane mirror is the reflection point; the dispersive light path is incident on the reflection point.

[0013] Both the dispersive optical element vacuum unit and the reflective optical element vacuum unit are evacuated by a molecular pump assembly.

[0014] Another embodiment of the present invention provides a method for improving the utilization rate of a free electron laser beamline, including the apparatus for improving the utilization rate of a free electron laser beamline as described above, the method comprising the following steps:

[0015] Step S1: Place the device for improving the utilization rate of the free electron laser beamline in the free electron laser beamline;

[0016] Step S2: Turn on the vacuum unit of the dispersive optical element and the vacuum unit of the reflective optical element to maintain the vacuum level of the dispersive optical element and the reflective optical element and ensure the laser transmission efficiency.

[0017] Step S3: Adjust the motion unit according to the wavelength of the free electron laser to change the spatial position of the reflective optical element and thus collimate the optical path.

[0018] Step S4: The free electron laser is used as the incident light and is incident on the dispersion point of the dispersive optical element along the incident light path. The free electron laser is split by the dispersive optical element. The reflected light is emitted along the reflected light path. The dispersive light is incident on the reflection point of the reflective optical element and then emitted along the dispersive light path.

[0019] Step S5: Provide the reflected light path and the dispersive light path to different users.

[0020] The spatial position of the reflective optical element ensures that the direction of the dispersed light emission remains the same.

[0021] The motion unit includes a translation mechanism and a rotation mechanism mounted on the translation mechanism. The translation mechanism adjusts the position of the reflective optical element along the reflection direction, and the rotation mechanism adjusts the rotation angle of the reflective optical element.

[0022] The advantages and beneficial effects of this invention are: by combining a grating and a mirror, the diffraction order of the grating can be adjusted and selected, providing low-intensity diffracted light of different intensities to the user, which can meet the user's weak light experiment needs, while strong light experiments are not affected, doubling the experimental time and effectively improving the utilization rate of the free electron laser beamline. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a device for improving the utilization rate of a free electron laser beamline in an embodiment of the present invention;

[0024] Figure 2 This is a graph showing the relationship between the first-order diffraction angle of a planar equidistant grating and the wavelength of light in an embodiment of the present invention for a device to improve the utilization of free electron laser beamlines.

[0025] Figure 3 This is a graph showing the relationship between the incident angle of a plane mirror and the wavelength of light in a device for improving the utilization of free electron laser beamlines according to an embodiment of the present invention.

[0026] Figure 4 This is a graph showing the relationship between the total transmission efficiency of first-order diffraction light and the wavelength of light in a device for improving the utilization of free electron laser beamlines according to an embodiment of the present invention.

[0027] In the diagram: 1. Dispersive optical element; 2. Reflective optical element; 3. Vacuum unit of dispersive optical element; 4. Vacuum unit of reflective optical element; 5. Translation mechanism; 6. Rotation mechanism; A. Splitting point; B. Reflection point; Ⅰ. Incident light path; Ⅱ. Reflected light path; Ⅲ. Dispersive light path. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1As shown, an embodiment of the present invention provides a device for improving the utilization rate of a free electron laser beamline, including a dispersive optical element 1, a reflective optical element 2, a dispersive optical element vacuum unit 3, and a reflective optical element vacuum unit 4. The dispersive optical element 1 is disposed within the dispersive optical element vacuum unit 3 and is used to decompose the incident light path I into a reflective light path II and a dispersive light path III. The dispersive optical element vacuum unit 3 provides a vacuum environment for the dispersive optical element 1. The reflective optical element 2 is disposed within the reflective optical element vacuum unit 4 and is used to reflect the dispersive light path III, thereby changing the direction of the dispersive light path III. The reflective optical element vacuum unit 4 provides a vacuum environment for the reflective optical element 2.

[0030] In an embodiment of the present invention, the dispersive optical element 1 has a beam splitting point A, and the incident light path I is incident on the beam splitting point A.

[0031] Specifically, the dispersive optical element 1 is a planar equidistant grating with a central grating and mirrors around it. The beam splitting point A is the center of the planar equidistant grating.

[0032] Furthermore, the device for improving the utilization rate of free electron laser beamlines provided by the present invention also includes a motion unit disposed within the vacuum unit 4 of the reflective optical element. The reflective optical element 2 is disposed on the motion unit, and the motion unit is used to adjust the spatial position of the reflective optical element 2 so that the dispersion light emission direction remains the same.

[0033] In an embodiment of the present invention, the motion unit includes a translation mechanism 5 and a rotation mechanism 6, wherein the translation mechanism 5 has a degree of freedom to move along the reflection direction; the rotation mechanism 6 is disposed on the translation mechanism 5, the reflective optical element 2 is disposed on the rotation mechanism 6, and the rotation mechanism 6 has a degree of freedom to rotate in the circumferential direction.

[0034] Specifically, the reflective optical element 2 is a plane mirror, and the center of the plane mirror is the reflection point B; the dispersive light path III is incident on the reflection point B.

[0035] In embodiments of the present invention, both the dispersive optical element vacuum unit 3 and the reflective optical element vacuum unit 4 are evacuated by a molecular pump assembly.

[0036] In operation, the device of this invention is placed within a free-electron laser beamline. The free-electron laser is incident into the device along incident light path I. After reflection and dispersive beam splitting by the planar equidistant grating, the reflected light exits along reflection light path II, and the diffracted light exits through dispersive light path III. Since the efficiency of the reflected light is only related to the reflection efficiency of the planar equidistant grating, it is relatively high. The intensity of the diffracted light, however, is related to the diffraction efficiency of the planar equidistant grating and the reflection efficiency of the planar mirror. Furthermore, the diffraction order can be selected to choose different grating diffraction efficiencies, resulting in lower but adjustable efficiency, which can meet the user's needs for weak-light experiments. In addition, both reflected and diffracted light can be provided to the user simultaneously, improving the utilization rate of the free-electron laser beamline.

[0037] Example

[0038] like Figure 1 As shown, an embodiment of the present invention provides a device for improving the utilization rate of a free electron laser beamline, comprising a laser dispersion unit, a laser reflection unit, a vacuum unit, and a motion unit, which can be applied to 30-180nm extreme ultraviolet free electron laser devices.

[0039] The laser dispersion unit comprises a dispersive optical element 1 and a beam splitter A. The dispersive optical element 1 is a planar equidistant grating with a substrate of single-crystal silicon and a gold film with a thickness of 50 nm. The planar equidistant grating has a surface size of 250 mm × 30 mm, with etched lines at the center at a linear density of 600 l / mm. The etched area is 30 mm × 10 mm in size and surrounded by mirrors. The beam splitter A is located at the center of the planar equidistant grating. A free-electron laser beam is incident at beam splitter A at an angle of 87° along incident light path I. Part of the beam is diffracted by the grating etched area and exits along dispersive light path III, while the other part is reflected by the grating reflection area and exits along reflection light path II, thus achieving beam splitting.

[0040] The laser reflection unit has a dispersive optical element 2 and a reflection point B. The reflective optical element 2 is a plane mirror with a size of 250mm × 30mm. The substrate is single-crystal silicon with a gold film deposited on the surface. The gold film thickness is 50nm. The reflection point B is the center of the plane mirror. The free electron laser beam diffracted by the plane equidistant grating is incident on the reflection point B, reflected by the plane mirror, and exits along the dispersive light path III.

[0041] The vacuum unit has a dispersive optical element vacuum unit 3 and a reflective optical element vacuum unit 4, both of which are molecular pump groups used to maintain the vacuum level of the optical elements and ensure laser transmission efficiency.

[0042] The motion unit comprises a translation mechanism 5 and a rotation mechanism 6. The translation mechanism 5 is a slide rail, enabling one-dimensional translational motion with a translation range of 300 mm and a translation accuracy of ≤10 μm. The rotation mechanism 6 is a rotary table, enabling rotational motion around an axis with a rotation range of 7.88° and a rotation accuracy of ≤1″. The motion unit is used to adjust the spatial position of the plane mirror to maintain the same direction of diffracted light emission.

[0043] One embodiment of the present invention provides a device for improving the beamline utilization of a free-electron laser, applied in a 30-180nm extreme ultraviolet free-electron laser device. The incident angle of the beam on a planar equidistant grating is constant at 87°, and the diffraction angle can be given by the grating equation.

[0044] sinα - sinβ = nmλ

[0045] Where α is the incident angle, β is the diffraction angle, n is the grating line density, m is the diffraction order, and λ is the wavelength. By selecting the first-order diffraction, the first-order diffraction angle corresponding to 30-180nm can be calculated from the grating equation.

[0046] Figure 2 This is a graph showing the relationship between the first-order diffraction angle of a planar equidistant grating and the wavelength of light, representing a device for improving the utilization of free-electron laser beamlines according to an embodiment of the present invention. Figure 2 As shown, the difference in first-order diffraction angle between the maximum and minimum wavelengths is 15.85°. Therefore, a sliding rail is needed to drive the plane mirror to translate. The sliding rail translation range is 300mm. To ensure that the output direction of the first-order diffracted light is fixed, the distance between the plane equidistant grating and the plane mirror also changes with the wavelength. It is 771.09mm at 30nm and 951.46mm at 180nm. At the same time, the reflection angle of the plane mirror also changes with the wavelength. It is 30° at 30nm and 22.12° at 180nm. The above geometric relationships are obtained by trigonometric function calculations.

[0047] Figure 3 This is a graph showing the relationship between the incident angle of a plane mirror and the wavelength of light in a device for improving the utilization of a free electron laser beamline according to an embodiment of the present invention. Figure 3 As shown, extreme ultraviolet light in the 30-180nm wavelength range experiences a loss in reflection efficiency after passing through a plane mirror. After passing through a plane variable-spacing grating, the diffraction efficiency depends on the diffraction order. For first-order diffracted light, the total transmission efficiency in this device is the product of the first-order diffraction efficiency and the reflection efficiency.

[0048] Figure 4 This is a graph showing the relationship between the total transmission efficiency of first-order diffracted light and the wavelength of light in a device for improving the utilization of free-electron laser beamlines according to an embodiment of the present invention. Figure 4As shown, the overall transmission efficiency of the first-order diffracted light is between 0.002 and 0.02, which is equivalent to a light intensity attenuation of 2 to 3 orders of magnitude, meeting the requirements of weak light experiments. Furthermore, according to the technical concept and features of this invention, diffracted light of other orders can be selected, realizing the ability to adjust the intensity of weak light. While using the diffracted light, the reflected light from the planar equidistant grating also propagates along the reflected light path, unaffected by strong light experiments. Both reflected and diffracted light can be provided to the user simultaneously, effectively doubling the user's working time and significantly improving the utilization rate of the free electron laser beamline.

[0049] Based on the above design concept, another embodiment of the present invention provides a method for improving the utilization rate of a free electron laser beamline, including the device for improving the utilization rate of a free electron laser beamline in any of the above embodiments. The method includes the following steps:

[0050] Step S1: Place the device for improving the utilization rate of the free electron laser beamline in the free electron laser beamline;

[0051] Step S2: Turn on the vacuum unit 3 of the dispersive optical element and the vacuum unit 4 of the reflective optical element to maintain the vacuum level of the dispersive optical element 1 and the reflective optical element 2, and ensure the laser transmission efficiency.

[0052] Step S3: Based on the wavelength of the free electron laser, the diffraction angle and reflection angle are calculated using the grating equation and geometric relationship. The motion unit is adjusted to change the spatial position of the reflecting optical element 2 in order to accurately reflect the scattered light and play the role of collimating the optical path.

[0053] Step S4: The free electron laser is used as the incident light and is incident on the dispersion point A of the dispersive optical element 1 along the incident light path I. The free electron laser is split by the dispersive optical element 1. The reflected light is emitted along the reflection light path II. The dispersive light is incident on the reflection point B of the reflection optical element 2 and then emitted along the dispersive light path III.

[0054] Step S5: Provide the reflected light path II and the dispersive light path III to different users.

[0055] In embodiments of the present invention, the spatial position of the reflective optical element 2 ensures that the direction of dispersion light emission remains the same. Specifically, the motion unit includes a translation mechanism 5 and a rotation mechanism 6 disposed on the translation mechanism 5. The translation mechanism 5 adjusts the position of the reflective optical element 2 along the reflection direction; the rotation mechanism 6 adjusts the rotation angle of the reflective optical element 2.

[0056] This invention provides a device and method for improving the utilization rate of free-electron laser beamlines, applicable to extreme ultraviolet (VUV) and soft X-ray to hard X-ray free-electron lasers. By fixing the incident angle of the grating, rotating the reflector, selecting the diffraction order of the grating, and adjusting the diffraction path, diffracted light is provided to the user. Since the intensity of the diffracted light is related to the diffraction order, it can meet the needs of weak-light experiments and has strong intensity regulation capabilities. Because both the reflected light and the diffracted light from the grating are provided to the user simultaneously, the utilization rate of the free-electron laser is effectively improved.

[0057] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, extensions, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A device for improving the utilization of a free electron laser beam line, characterized in that, include: A dispersive optical element (1) is disposed in a dispersive optical element vacuum unit (3). The dispersive optical element (1) is used to decompose the incident light path (Ⅰ) into a reflected light path (Ⅱ) and a dispersive light path (Ⅲ). The dispersive optical element vacuum unit (3) provides a vacuum environment for the dispersive optical element (1). The reflective optical element (2) is disposed in the vacuum unit (4) of the reflective optical element. The reflective optical element (2) is used to reflect the dispersive light path (III), thereby changing the direction of the dispersive light path (III). The vacuum unit (4) of the reflective optical element provides a vacuum environment for the reflective optical element (2).

2. The apparatus of claim 1, wherein, The dispersive optical element (1) has a beam splitting point (A), and the incident light path (Ⅰ) is incident on the beam splitting point (A).

3. The apparatus of claim 2, wherein, The dispersive optical element (1) is a planar equidistant grating with a central grating and a surrounding mirror. The beam splitting point (A) is the center of the planar equidistant grating.

4. The apparatus of claim 1, wherein, It also includes a motion unit disposed within the vacuum unit (4) of the reflective optical element, wherein the reflective optical element (2) is disposed on the motion unit, and the motion unit is used to adjust the spatial position of the reflective optical element (2) so that the dispersion light emission direction remains the same.

5. The apparatus of claim 4, wherein, The motion unit includes a translation mechanism (5) and a rotation mechanism (6), wherein the translation mechanism (5) has a degree of freedom to move along the reflection direction; the rotation mechanism (6) is disposed on the translation mechanism (5), and the reflective optical element (2) is disposed on the rotation mechanism (6), and the rotation mechanism (6) has a degree of freedom to rotate in the circumferential direction.

6. The apparatus of claim 4, wherein, The reflective optical element (2) is a plane mirror, and the center of the plane mirror is the reflection point (B); the dispersive optical path (Ⅲ) is incident on the reflection point (B).

7. The device for improving the utilization rate of free electron laser beamlines according to claim 1, characterized in that, Both the dispersive optical element vacuum unit (3) and the reflective optical element vacuum unit (4) are evacuated by a molecular pump assembly.

8. A method of improving the utilization of a free electron laser beamline, characterized in that, The method comprising the apparatus for improving the utilization of free electron laser beamlines according to any one of claims 1-7, the method comprising the following steps: Step S1: Place the device for improving the utilization rate of the free electron laser beamline in the free electron laser beamline; Step S2: Turn on the vacuum unit (3) of the dispersive optical element and the vacuum unit (4) of the reflective optical element to maintain the vacuum level of the dispersive optical element (1) and the reflective optical element (2) and ensure the laser transmission efficiency. Step S3: Adjust the motion unit according to the free electron laser wavelength to change the spatial position of the reflective optical element (2) and play the role of collimating the optical path; Step S4: The free electron laser is used as the incident light and is incident on the dispersion point (A) of the dispersive optical element (1) along the incident light path (Ⅰ). The free electron laser is split by the dispersive optical element (1), and the reflected light is emitted along the reflection light path (Ⅱ). The dispersive light is incident on the reflection point (B) of the reflection optical element (2) and then emitted along the dispersive light path (Ⅲ). Step S5: Provide the reflected light path (II) and the dispersive light path (III) to different users.

9. The method for improving the utilization of a free electron laser beamline according to claim 8, wherein, The spatial position of the reflective optical element (2) ensures that the direction of the dispersed light emission remains the same.

10. The method for improving the utilization of a free electron laser beamline according to claim 8, wherein, The motion unit includes a translation mechanism (5) and a rotation mechanism (6) disposed on the translation mechanism (5). The translation mechanism (5) is used to adjust the position of the reflective optical element (2) along the reflection direction; the rotation mechanism (6) is used to adjust the rotation angle of the reflective optical element (2).

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