Heriott gas multi-pass cell adjusting method and system based on light beam distribution calculation

Abstract

The invention discloses a Heriott gas multi-pass cell adjusting method based on light beam distribution calculation, and belongs to the technical field of laser. The adjusting method comprises the following steps: S1, calculating a transmission matrix of a concave reflector and a transmission matrix of each step length in gas according to the refractive index of the Heriott gas multi-pass cell gas, the transmission step length, the curvature radius of the concave reflector and the spacing; s2, determining a q parameter of an incident beam, and calculating the q parameter of each position of the multi-pass pool according to the transmission step length and the transmission matrix; s3, calculating the beam size and wavefront radius of the beam transmitted to each position in the multi-pass cell according to the q parameter of each position, and obtaining the beam distribution of each position of the multi-pass cell; and S4, optimizing and adjusting the parameters of the incident light beam, and enabling the light beam to achieve stable light beam distribution required by the system in each time of transmission in the multi-pass pool. The beam distribution of the Herriott gas multi-pass cell can be quickly and accurately calculated, the incident beam of the multi-pass cell is optimized, and the transmission stability of the beam in the multi-pass cell is improved.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to a Herriott gas multi-pass cell adjustment method and device based on beam distribution calculation. Background Art

[0002] The Herriott gas multi-pass cell can effectively increase the optical path and ensure the quality of the laser beam before and after passing through the multi-pass cell. Therefore, it is widely used in quantum precision measurement, atomic and molecular physics, ultrafast optics, spectroscopy, laser interferometer systems and other fields. The Herriott gas multi-pass cell has two coaxially placed concave mirrors, and gas is filled into the multi-pass cell. Such a symmetrical multi-pass cell system is similar to the structure of a resonant cavity. However, since the multi-pass cell is not a vacuum after being filled with gas, the refractive index changes. How to accurately calculate the beam distribution in the multi-pass cell has important research value and practical significance for protecting optical devices, improving measurement accuracy in quantum precision measurement, improving nonlinear effects in ultrafast optics, and improving spectral excitation intensity in spectroscopy.

[0003] In 2022, Christoph M Heyl et al. reported related work on spectral broadening and pulse compression using multi-pass cells (Christoph M Heyl et al. High-energy bow tie multi-pass cells for nonlinear spectral broadening applications, Journal of Physics: Photonics, Vol. 4, 014002, 2022). The beam parameter calculation of the Herriott gas multi-pass cell used the traditional calculation formula of the resonant cavity eigenmode. However, compared with the air medium, the refractive index after filling with gas is different, and there will be errors in calculating the beam distribution of the Herriott gas multi-pass cell using the calculation formula of the resonant cavity. And in many research reports, such as (RuifengWang et al.Double-enhanced multipass cell-based wavelength modulation spectroscopy CH4 sensor for ecological applications,OpticsExpress,Vol.31,No.2,pp3237,2023) and (Christopher R.Webster et al.Herriott cellspot imaging increases the performance oftunable laser spectrometers,Vol.60,No.7,pp1958,2021), it can be observed that the beam size changes in each transmission of the beam in the Herriott gas multipass cell, and there is a smaller focused spot on the optical device. If the damage threshold of the device is exceeded, it will cause damage to the device and affect the stable transmission of the beam in the Herriott gas multipass cell. Therefore, for the Herriott gas multipass cell, it is urgent to explore and develop an accurate beam distribution calculation method and an optimization method to improve the stability of beam transmission. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the above-mentioned related art at least to a certain extent.

[0005] To this end, the object of the present invention is to provide a Herriott gas multi-pass cell adjustment method and device based on beam distribution calculation, which can quickly and accurately calculate the beam distribution of the Herriott gas multi-pass cell and optimize the stability of the beam transmission in the Herriott gas multi-pass cell.

[0006] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0007] The embodiment of the present invention provides a Herriott gas multi-pass cell adjustment method based on beam distribution calculation, wherein the Herriott gas multi-pass cell includes two concave reflectors and a gas filled between two adjacent concave reflectors; the calculation method includes the following steps:

[0008] S1. Calculate the transmission matrix of the concave reflector and the transmission matrix of each step in the gas according to the gas refractive index, transmission step length, curvature radius and spacing parameters of the Herriott gas multi-pass cell;

[0009] The transmission matrix is ​​expressed as:

[0010] Wherein, A, B, C, and D represent elements in the transmission matrix; the determinant value of the transmission matrix is ​​1;

[0011] S2, determining the q parameter of the incident light beam, and calculating the q parameter of each position in the Herriott gas multi-pass cell according to the transmission step length and the transmission matrix of step S1;

[0012] S3, according to the q parameter calculated in step S2, the beam size and wavefront curvature radius of the light beam transmitted to any position in the Herriott gas multi-pass cell are calculated, and the distribution of the light beam in the Herriott gas multi-pass cell is obtained by iterative calculation;

[0013] S4. Repeat the method of steps S2 and S3 to calculate the beam distribution of incident light beams with different parameters when transmitted in the Herriot gas multi-pass cell, optimize and adjust the incident light beam parameters according to the calculation results, and obtain the required incident light beam and its corresponding light field and light intensity.

[0014] In addition, the Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to the present invention may also have the following additional technical features:

[0015] In some of the embodiments, the transmission matrix M is obtained by multiplying one or more transmission matrices of the light beam in the concave reflector and the transmission matrix of the light beam in the gas.

[0016] In some of the embodiments, the transmission matrix of the light beam in the concave reflecting mirror is obtained according to the radius of curvature of the concave reflecting mirror.

[0017] In some of the embodiments, the transmission matrix of the light beam in the gas is determined according to the transmission distance of the light beam in the gas and the refractive index of the gas.

[0018] In some of the embodiments, the transmission distance of the light beam in the gas is determined according to the distance between two adjacent concave reflectors and the number of steps of the light beam in the air.

[0019] In some embodiments, the q parameter before passing through the optical system in the Herriott gas multi-pass cell is recorded as q1, and the q parameter after passing through the optical system in the Herriott gas multi-pass cell is recorded as q2; the relationship between q1 and q2 is:

[0020]

[0021] In some of the embodiments, the beam radius of the light beam at any position transmitted to the Herriott gas multi-pass cell is determined according to the wavelength of the light beam, the gas refractive index, and the q parameter of the light beam after passing through the optical system in the Herriott gas multi-pass cell;

[0022] The wavefront curvature radius of the light beam when it is transmitted to any position in the Herriott gas multi-pass cell is determined according to the q parameter of the light beam after it passes through the optical system in the Herriott gas multi-pass cell.

[0023] In some embodiments, when the beam is transmitted to any position in the Herriott gas multi-pass cell, the beam radius and wavefront curvature radius are calculated as follows:

[0024]

[0025] In the formula, ω new is the beam radius, R new is the wavefront curvature radius, n a is the gas refractive index, and λ is the wavelength of the light beam.

[0026] In some of the embodiments, the transmission matrix of the light beam in the concave reflector is:

[0027] Where R is the radius of curvature of the concave reflector;

[0028] The transmission matrix of the light beam in the gas is:

[0029] Where, d step is the distance that the light beam travels in each step in the gas, where the number of transmission steps in the gas is d a / d step , d a is the distance between the two concave reflectors, n a is the gas refractive index.

[0030] An embodiment of the present invention also provides a Herriott gas multi-pass cell adjustment device based on beam distribution calculation, comprising a memory and a processor, wherein a program is stored on the memory, and when the processor runs the program on the memory, it can implement the calculation process of the Herriott gas multi-pass cell adjustment method based on beam distribution calculation as described in any one of the above items.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] In the embodiments of the present invention, the Herriott gas multi-pass cell adjustment method based on beam distribution calculation can quickly and accurately calculate the beam distribution of the light beam in the Herriott gas multi-pass cell, so that researchers can clearly understand the beam parameters and state of the light beam at any position in the multi-pass cell, and can protect optical devices from being damaged by smaller focused beams. It is of great significance to improve measurement accuracy in quantum precision measurement, improve nonlinear effects in ultrafast optics, and improve spectral excitation intensity in spectroscopy.

[0033] The Herriott gas multi-pass cell adjustment device based on beam distribution calculation of the present invention is used to implement the Herriott gas multi-pass cell adjustment method based on beam distribution calculation, and thus at least has all the features and advantages of the Herriott gas multi-pass cell adjustment method based on beam distribution calculation, which will not be repeated here. Additional aspects and advantages of the present invention will be partially given in the following description, and partially become obvious from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the structure of a Herriott gas multi-pass cell disclosed in one embodiment of the present invention;

[0035] Figure 2 The beam distribution during 100 transmissions of a Herriott gas multi-pass cell disclosed in one embodiment of the present invention, the cavity length is 590 mm, the radius of curvature of the concave reflector is 300 mm, the gas refractive index is 1, the step length is 1 mm, the horizontal axis is different positions in the multi-pass cell, and the vertical axis is the number of transmissions, Figure 2 (a) and (b) are the beam distribution and wavefront curvature radius distribution of a beam with an incident beam size of 0.120 mm and a wavefront curvature radius of positive infinity in 100 transmissions, respectively. Figure 2 (c) and (d) are the beam distribution and wavefront curvature radius distribution of a beam with an incident beam size of 0.114 mm and a wavefront curvature radius of positive infinity in 100 transmissions, respectively. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 embodiments of the present invention are described in detail below through specific embodiments and application scenarios in conjunction with the accompanying drawings.

[0038] An embodiment of the present invention provides a Herriott gas multi-pass cell adjustment method based on beam distribution calculation, wherein the Herriott gas multi-pass cell includes two concave reflectors and a gas filled between two adjacent concave reflectors; the calculation method includes the following steps:

[0039] S1. Calculate the transmission matrix of the concave reflector and the transmission matrix of each step in the gas according to the gas refractive index, transmission step length, curvature radius and spacing parameters of the Herriott gas multi-pass cell;

[0040] The transmission matrix is ​​expressed as:

[0041] Wherein, A, B, C, and D represent elements in the transmission matrix; the determinant value of the transmission matrix is ​​1;

[0042] S2, determining the q parameter of the incident light beam, and calculating the q parameter of each position in the Herriott gas multi-pass cell according to the transmission step length and the transmission matrix of step S1;

[0043] S3, according to the q parameter calculated in step S2, the beam size and wavefront curvature radius of the light beam transmitted to any position in the Herriott gas multi-pass cell are calculated, and the distribution of the light beam in the Herriott gas multi-pass cell is obtained by iterative calculation;

[0044] S4. Repeat the method of steps S2 and S3 to calculate the beam distribution of incident light beams with different parameters when transmitted in the Herriot gas multi-pass cell, optimize and adjust the incident light beam parameters according to the calculation results, and obtain the required incident light beam and its corresponding light field and light intensity.

[0045] The transmission matrix M is obtained by multiplying one or more transmission matrices of the light beam in the concave reflector and the transmission matrix of the light beam in the gas. The transmission matrix of the light beam in the concave reflector is obtained according to the curvature radius of the concave reflector. In some embodiments, the transmission matrix of the light beam in the gas is determined according to the transmission distance of the light beam in the gas and the refractive index of the gas. The transmission distance of the light beam in the gas is determined according to the distance between two adjacent concave reflectors and the number of steps of the light beam in the air. The beam radius of the light beam transmitted to any position in the Herriott gas multi-pass cell is determined according to the wavelength of the light beam, the refractive index of the gas, and the q parameter of the light beam after passing through the optical system in the Herriott gas multi-pass cell; the wavefront curvature radius of the light beam transmitted to any position in the Herriott gas multi-pass cell is determined according to the q parameter of the light beam after passing through the optical system in the Herriott gas multi-pass cell.

[0046] See also Figure 1As shown, in some embodiments of the present invention, a Herriott gas multi-pass cell system adjustment method based on beam distribution calculation is provided, and the steps of the calculation method include:

[0047] Step 1: The Herriott gas multi-pass cell has two concave reflectors with the same radius of curvature, placed face to face, and the centers of the two concave reflectors are located on the same optical axis. Fill the multi-pass cell with gas and let it stand to allow the gas to be evenly distributed. The "concave reflector-gas-concave reflector" structure of the Herriott gas multi-pass cell is paraxially approximated and abstracted as an optical system with a series of "thin convex lens-gas" structures. The transmission matrix is ​​calculated for the cavity structure and each optical device therein, which specifically includes the following steps:

[0048] Step 11: Determine the radius of curvature R of the two concave reflectors, the focal length f=R / 2, and the transmission matrix of each concave reflector (thin convex lens) is:

[0049]

[0050] Step 12: Determine the distance d between the two concave mirrors a , d a The step length d of the transmission in the gas step , the relationship between the number of steps N is d a =N*d step , and the gas refractive index n a , calculate the time in the gas after d step The transmission matrix of distance is:

[0051]

[0052] Step 2: Determine the q parameter q1 of the initial beam, and iterate the calculation according to the transmission matrix [A, B; C, D] of formula (1) and formula (4) to obtain the q parameter q(z) of the beam transmitted to any position of the Herriott gas multi-pass cell:

[0053]

[0054] Step 3: According to the q parameter q(z) at each position, calculate the beam radius ω(z) and wavefront curvature radius R(z) at each position:

[0055]

[0056] Where i is the imaginary unit, λ is the wavelength of the beam, and n a is the gas refractive index.

[0057] Through these three steps, the parameters of the Herriott gas multi-pass cell, which are the central wavelength of 1064nm, the cavity length of the Herriott gas multi-pass cell of 590mm, the curvature radius of the concave reflector of 300mm, the gas refractive index of 1, and the transmission step of 1mm, can be obtained. In step 4, calculations are performed for two incident beams with different parameters, and their parameters are: (1) the beam size is 0.120mm, and the wavefront curvature radius is positive infinity; (2) the beam size is 0.114mm, and the wavefront curvature radius is positive infinity. Using these parameters as input, the beam parameters such as the beam size and wavefront curvature radius of the beam transmitted to any position in the Herriott gas multi-pass cell can be calculated, as shown in FIG. Figure 2 shown. Figure 2 (a)-(d) The horizontal axis is the direction of the optical axis of the Herriott gas multi-pass cell, the range is the spacing of the concave reflectors, the vertical axis is the number of transmissions of the light beam in the Herriott gas multi-pass cell, and the origin is one of the concave reflectors. Figure 2 Each data point (x1, y1, z1) in (a) and (c) is the beam size z1 at a distance x1 from the origin in the Herriott gas multi-pass cell when the beam is transmitted for the y1th time in the multi-pass cell. Figure 2 Each data point (x2, y2, z2) in (b) and (d) is the wavefront curvature radius z2 of the beam transmitted through the Herriot gas multi-pass cell for the y2th time and transmitted to the multi-pass cell at a distance x2 from the origin. It can be observed that Figure 2 In (a), an incident beam with a beam size of 0.120 mm is transmitted 100 times in a Herriott gas multi-pass cell. The beam size shows a very obvious periodic change. Figure 2 The wavefront curvature radius in (b) is also very unstable, and the distribution range of the beam focus in the gas multi-pass cell is very large, which can easily damage the components of the multi-pass cell. After optimization, the incident beam size was optimized and adjusted to 0.114 mm. Figure 2 (c) and (d) are the distribution of the light beam size and wavefront curvature radius in 100 transmissions. Each time the light beam passes through the Herriott gas multi-pass cell, the distribution of the light beam is stable and consistent, and the error of the incident light beam is only 0.006 mm. However, after multiple transmissions, the distribution of the light beam in the Herriott gas multi-pass cell is far apart, indicating that the method proposed in the present invention is very necessary and effective in improving device safety and system stability in the structural design of the Herriott gas multi-pass cell.

[0058] The method proposed in the present invention can accurately calculate the beam distribution in the Herriott gas multi-pass cell and optimize the system stability. Researchers can clearly predict and evaluate the beam parameters and state of the beam at any position in the multi-pass cell, and optimize the incident beam. It can protect optical devices from being damaged by smaller focused beams and improve system stability. It is of great significance to improve measurement accuracy in quantum precision measurement, improve nonlinear effects in ultrafast optics, and improve spectral excitation intensity in spectroscopy.

[0059] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0060] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A Herriott gas multi-pass cell adjustment method based on beam distribution calculation, characterized in that: The Herriott gas multi-pass cell includes two concave reflectors and a gas filled between two adjacent concave reflectors; the calculation method includes the following steps: S1. Calculate the transmission matrix of the concave reflector and the transmission matrix of each step in the gas according to the gas refractive index, transmission step length, curvature radius and spacing parameters of the Herriott gas multi-pass cell; The transmission matrix is ​​expressed as: Wherein, A, B, C, and D represent elements in the transmission matrix; the determinant value of the transmission matrix is ​​1; S2, determining the q parameter of the incident light beam, and calculating the q parameter of each position in the Herriott gas multi-pass cell according to the transmission step length and the transmission matrix of step S1; S3, according to the q parameter calculated in step S2, the beam size and wavefront curvature radius of the light beam transmitted to any position in the Herriott gas multi-pass cell are calculated, and the distribution of the light beam in the Herriott gas multi-pass cell is obtained by iterative calculation; S4. Repeat the method of steps S2 and S3 to calculate the beam distribution of incident light beams with different parameters when transmitted in the Herriot gas multi-pass cell, optimize and adjust the incident light beam parameters according to the calculation results, and obtain the required incident light beam and its corresponding light field and light intensity. The optical system refers to a structure for light transmission including a concave reflector and a gas of a certain thickness.

2. The Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to claim 1, characterized in that: The transmission matrix M is obtained by multiplying one or more transmission matrices of the light beam in the concave reflector and the transmission matrix of the light beam in the gas.

3. The Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to claim 2, characterized in that: The transmission matrix of the light beam in the concave reflecting mirror is obtained according to the curvature radius of the concave reflecting mirror.

4. The Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to claim 2, characterized in that: The transmission matrix of the light beam in the gas is determined according to the transmission distance of the light beam in the gas and the refractive index of the gas.

5. The Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to claim 4, characterized in that: The transmission distance of the light beam in the gas is determined according to the distance between two adjacent concave reflectors and the number of steps of the light beam in the air.

6. The Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to any one of claims 1 to 5, characterized in that: The q parameter before passing through the optical system in the Herriott gas multi-pass cell is recorded as q1, and the q parameter after passing through the optical system in the Herriott gas multi-pass cell is recorded as q2; the relationship between q1 and q2 is:

7. The Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to claim 6, characterized in that: The beam radius at the point where the light beam is transmitted to any position in the Herriott gas multipass cell is determined according to the wavelength of the light beam, the gas refractive index, and the q parameter of the light beam after it passes through the optical system in the Herriott gas multipass cell; The wavefront curvature radius of the light beam when it is transmitted to any position in the Herriott gas multi-pass cell is determined according to the q parameter of the light beam after it passes through the optical system in the Herriott gas multi-pass cell.

8. The Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to claim 7, characterized in that: When the beam is transmitted to any position in the Herriott gas multi-pass cell, the beam radius and wavefront curvature radius are calculated as follows: In the formula, ω new is the beam radius, R new is the wavefront curvature radius, n a is the gas refractive index, and λ is the wavelength of the light beam.

9. The Herriott gas multi-pass cell adjustment method based on beam distribution calculation according to claim 2, characterized in that: The transmission matrix of the light beam in the concave reflector is: Where R is the radius of curvature of the concave reflector; The transmission matrix of the light beam in the gas is: Where, d step is the distance that the light beam travels in each step in the gas, where the number of transmission steps in the gas is d a / d step , d a is the distance between the two concave reflectors, n a is the gas refractive index.

10. A Herriott gas multi-pass cell adjustment device based on beam distribution calculation, comprising a memory and a processor, wherein a program is stored in the memory, characterized in that: When the processor runs the program on the memory, it can implement the calculation process of the Herriott gas multi-pass cell adjustment method based on beam distribution calculation as described in any one of claims 1 to 9.

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