Heriott solid multi-pass cell safety optimization method based on light beam evolution calculation

Abstract

The invention provides a beam evolution calculation-based Heriott solid multi-pass cell safety optimization method. The method comprises the following steps of 1, calculating a transmission matrix of each device of a Heriott solid multi-pass cell; step 2, calculating a light beam evolution process of the light beam in the Herriott solid multi-pass cell; and step 3, optimizing system parameters according to light beam evolution, so that the light beam keeps a stable light beam size when the light beam passes through the solid in the Herriott solid multi-pass cell every time in the Herriott solid multi-pass cell. By adopting the method provided by the invention, the beam evolution process of the Heriott solid multipass cell is quickly and accurately calculated, the beam parameters of the beam at different positions in the multipass cell are effectively predicted and evaluated, devices such as a concave reflector and a solid material in the Heriott solid multipass cell are prevented from being damaged by the focused beam, and the reliability of the Heriott solid multipass cell is improved. The safety of the optical system is optimized, and the stability of the optical system is ensured.

Description

Technical Field

[0001] The invention relates to the field of lasers, and in particular to a Herriot solid multi-pass cell safety optimization method based on beam evolution calculation, which is mainly applicable to ultrafast optics, spectroscopy, atomic and molecular physics and quantum precision measurement. Background Art

[0002] The Herriott solid multi-pass cell can effectively increase the optical path under the condition of constant incident laser energy and ensure the beam quality during transmission. Therefore, it is widely used in ultrafast optics, spectroscopy, atomic and molecular physics, and quantum precision measurement. The Herriott solid multi-pass cell has two coaxial concave mirrors, and the solid material is located in the center of the multi-pass cell. In view of the needs of related optical instruments and systems in physics and optics, it is very important to understand, predict and evaluate the beam evolution process of the Herriott solid multi-pass cell. It has important research value and practical significance for protecting optical components and optical systems, improving the accuracy in quantum precision measurement, enhancing the degree of nonlinear effects in ultrafast optics, and improving the excitation intensity in spectroscopy.

[0003] In 2018, Killian Fritsch et al. reported the work of spectral broadening using a solid multipass cell (Anne-Lise Viotti et al. All-solid-state multipass spectral broadening to sub-20fs, Optics Letters, Vol. 43, No. 19, pp 4643-4646, 2018). The light beam passed through the solid medium in the multipass cell multiple times to enhance the nonlinear effect and effectively broaden the spectrum. The spectral broadening factor reached 22, and the pulse width was successfully compressed to 18fs in post-compression. However, in some reports (Jaismeen Kaur et al. Simultaneous nonlinear spectral broadening and temporal contrast enhancement of ultrashort pulses in a multi-pass cell, Vol. 6, 015001, 2024), the beam waist changes during each transmission of the beam in the Herriott solid multi-pass cell. The focused beam will cause the beam power to exceed the damage threshold of the optical device, causing damage to the optical components, which will hinder the stable transmission of the beam in the Herriott solid multi-pass cell and affect the safety of the Herriott solid multi-pass cell optical system. Summary of the invention

[0004] The purpose of the present invention is to provide a Herriott solid multi-pass cell safety optimization method based on beam evolution calculation, which can optimize the safety of the optical system and ensure the stability of the optical system by quickly and accurately calculating the beam evolution process of the Herriott solid multi-pass cell, effectively predicting and evaluating the beam parameters of the beam at different positions in the multi-pass cell.

[0005] In order to achieve the above purpose, the present invention adopts the following technical scheme:

[0006] A safety optimization method for a Herriott solid multi-pass cell based on beam evolution calculation, wherein the Herriott solid multi-pass cell has two coaxial concave reflectors with the same curvature radius, and the solid is located at the center of the multi-pass cell. The structure of "concave reflector-solid-concave reflector" is paraxially approximated and abstracted as an optical system of a series of "thin convex lens-solid" structures. The method comprises:

[0007] Step 1: Obtain the structure of the multi-pass cell and the parameters of each optical device therein, including the central wavelength λ, the radius of curvature R of the concave mirror, and the cavity length d a , solid thickness d b , solid refractive index n b and the gas refractive index n a ; Calculate the transmission matrix for the cavity structure and each optical device therein; Calculate the corresponding transmission matrix based on the optical components that the light beam passes through when it starts from a known position and transmits any number of times in the Herriot solid multi-pass cell to any position. Through iteration, obtain the transmission matrix of the light beam transmitted from the incident position to any position.

[0008] Step 2: According to the transmission matrix of the light beam transmitted from the initial position to any position, the q parameter of the light beam transmitted to any position is calculated. The real part and imaginary part of the q parameter are used to calculate the corresponding beam radius and the curvature radius of the wavefront, that is, the beam evolution process of the light beam in the Herriot multi-pass cell.

[0009] Step 3: According to the beam evolution process, adjust the parameters of the incident beam and calculate the corresponding beam distribution in the Herriott solid multi-pass cell; according to the required beam size and laser intensity, select the corresponding incident beam so that the beam maintains a stable beam size each time it passes through the solid in the Herriott solid multi-pass cell, and the optical components are not damaged by the smaller beam waist, thereby ensuring the safety of the optical components and the system and improving the stability of the system.

[0010] Preferably, in step 1, for the cavity structure and each optical device therein, calculating the transmission matrix specifically includes:

[0011] Step 11: Calculate the transfer matrix M of the concave reflector cm：Get the radius of curvature R of the concave reflector, then its focal length f = R / 2, abstract the concave reflector as a thin convex lens, the transmission matrix M cm for

[0012]

[0013] Step 12: Calculate the solid transmission matrix M b : Get the solid thickness d b The solid refractive index n b , calculate the time in the solid after d b The transmission matrix M of the distance b

[0014]

[0015] Step 13: Calculate the air transmission matrix M a :Fix the solid at the center of the multi-pass cell and obtain the distance d between the solid and the concave reflector a , calculated at distance d a The transmission matrix M of the air a

[0016]

[0017] Step 14: Set the transmission step length d of the light beam in the air air-step , then the light beam propagates in the air air-step The transfer matrix is

[0018]

[0019] Step 15: Set the transmission step length d of the beam in the solid bulk-step , then the light beam propagates in the air bulk-step The transfer matrix is

[0020]

[0021] Step 16: Get the refractive index n of air a ,but:

[0022] The transmission matrix of the light beam refracted on the air-solid surface is

[0023]

[0024] The transmission matrix of a beam refracted at a solid-air surface is

[0025]

[0026] Preferably, the transmission matrix of the light beam from the incident position to any position in step 1 is calculated as follows:

[0027] Step 17. Based on the number of transmissions of the light beam from a known position in the Herriot solid multi-pass cell and the order of the light beam transmission to any position, as well as the order of the optical components passed through, by combining formula (1), formula (2), formula (3), formula (4), formula (5), formula (6) and formula (7), we regard the components passed by the light beam during the transmission process as an optical system, and obtain the transmission matrix of the optical system as follows:

[0028]

[0029] And there is a constraint relationship

[0030] det M=AD-BC=1 (9)

[0031] Preferably, the step 2 specifically includes:

[0032] Step 21. For a wavelength of λ, the solid refractive index is n b , the incident beam size (radius) is ω input , the wavefront curvature radius is R input A Gaussian beam with a q parameter q input for

[0033]

[0034] Where i is the imaginary unit;

[0035] Step 22: Set q input is the q parameter before the optical system transmission matrix described in step 17, q output is the q parameter after the optical system transmission matrix described in step 17, q input and q output The relationship is

[0036]

[0037] Step 23: According to the relationship between the beam size, wavefront curvature radius and q parameter, the beam size and wavefront curvature radius of the beam transmitted to any position in the multi-pass cell are obtained as follows:

[0038]

[0039] That is the beam evolution process of the beam in the Herriot multi-pass cell.

[0040] Through the above steps, according to the parameters and position of the incident light beam, the parameters of the structure and devices in the Herriott solid multi-pass cell, the calculation step size, and the optical components through which the transmission passes, the transmission matrix of the light beam from the initial position to any position can be obtained through iteration, thereby calculating the q parameter of the light beam transmitted to any position, and using the real and imaginary parts of the q parameter, the corresponding beam radius and the curvature radius of the wavefront are calculated, that is, the beam evolution process of the light beam in the Herriott multi-pass cell.

[0041] Compared with the existing methods, the present invention has the following beneficial effects:

[0042] The method of the present invention can quickly and accurately calculate the beam evolution process of the Herriott solid multi-pass cell, so that research and development designers can understand, predict and evaluate parameters such as the beam size and wavefront curvature radius of the beam transmitted to any position during the transmission process of the Herriott solid multi-pass cell. By optimizing system parameters, the optical devices in the Herriott solid multi-pass cell can be protected from being damaged by smaller beams, the safety of the system can be improved, and the experimental effect and stability can be enhanced. It has important research value and practical significance for improving the accuracy in the field of quantum precision measurement, enhancing the degree of nonlinear effects in the field of ultrafast optics, and improving the excitation intensity in the field of spectroscopy. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic structural diagram of the Herriot solid multi-pass cell of the present invention;

[0044] Figure 2 This is a paraxial approximate schematic diagram;

[0045] Figure 3 This is a schematic diagram of beam transmission after paraxial approximation;

[0046] The transmission process of the light beam is as follows: a air, air-solid surface refraction, distance d b Solid, solid-air surface refraction, distance d a of air, focusing concave mirror, distance d a air, air-solid surface refraction, distance d b Solid, solid-air surface refraction, distance d a1 of air;

[0047] Figure 4 It is the beam evolution of the Herriot solid multi-pass cell of the present invention. The simulation parameters in the figure include: central wavelength 1030nm, concave mirror curvature radius 300mm, cavity length 599mm, solid thickness 20mm, solid refractive index 1.45, gas refractive index 1, where, Figure 4(a) and (b) are the evolution of the beam size and wavefront curvature radius of the incident laser when it is transmitted 1 to 50 times in the multi-pass cell. Figure 4 (c) and (d) are the evolution of beam size and wavefront curvature radius when the incident laser is transmitted 1 to 50 times in the multi-pass cell with a beam size of 0.063 mm and a wavefront curvature radius of positive infinity. DETAILED DESCRIPTION

[0048] The following will refer to the accompanying drawings and preferred embodiments to illustrate the implementation of the technical solution of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific implementations, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0049] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0050] The structure of the Herriot solid multi-pass cell involved in this embodiment can be found in Figure 1 The Herriot solid multi-pass cell has two coaxial concave mirrors CM1 and CM2 with the same radius of curvature, and the solid BM is located at the center of the multi-pass cell.

[0051] See also Figure 2 We make a paraxial approximation of the "concave reflector-solid-concave reflector" structure of the multi-pass cell and abstract it into an optical system with a series of "thin convex lens-solid" structures. Figure 3 Schematic diagram of beam transmission after paraxial approximation. The transmission process of the beam is as follows: a air, air-solid surface refraction, distance d b Solid, solid-air surface refraction, distance d a of air, focusing concave mirror, distance d a air, air-solid surface refraction, distance d b Solid, solid-air surface refraction, distance d a1 of air.

[0052] For the Herriot solid multi-pass cell structure, the beam waist changes during each transmission of the beam in the multi-pass cell. The focused beam will cause the beam power to exceed the damage threshold of the optical device, causing damage to the optical components, which will hinder the stable transmission of the beam in the Herriot solid multi-pass cell and affect the safety of the Herriot solid multi-pass cell optical system. In order to optimize the system safety, this implementation adopts the following optimization method, which specifically includes the following steps:

[0053] Step 1: Obtain the structure of the multi-pass cell and the parameters of each optical device therein, mainly including the central wavelength λ, the radius of curvature R of the concave mirror, and the cavity length d a , solid thickness d b , solid refractive index n b and the gas refractive index n a And other parameters. In addition, the transmission matrix is ​​calculated for the cavity structure and each optical device therein. Further, according to the optical components that the light beam passes through when it starts from a known position and transmits any number of times in the Herriot solid multi-pass cell to any position, the corresponding transmission matrix is ​​calculated. Through iteration, the transmission matrix of the light beam transmitted from the initial position to any position is obtained.

[0054] Step 1 specifically includes:

[0055] Step 11: Determine the curvature radius R of the concave reflector, the focal length f=R / 2, and abstract the concave reflector as a thin convex lens. The transmission matrix is:

[0056]

[0057] Step 12: Determine the solid thickness d b The solid refractive index n b , calculate the time in the solid after d b The transmission matrix of distance is

[0058]

[0059] Step 13: Fix the solid at the center of the multi-pass cell. The distance between the solid and the concave reflector is d. a , at a distance d a The transmission matrix for air is

[0060]

[0061] Step 14: Set the transmission step length d in the air air-step , then the light beam propagates in the air air-step The transfer matrix is

[0062]

[0063] Step 15: Set the transmission step size d in the solid bulk-step , then the light beam propagates in the air bulk-step The transfer matrix is

[0064]

[0065] Step 16. Determine the refractive index n of air a , the transmission matrix for refraction at the air-solid surface is

[0066]

[0067] The transmission matrix for refraction at a solid-air interface is

[0068]

[0069] Step 17: Take the example of a light beam introduced from behind a concave mirror. The central wavelength of the incident light beam is λ, and the refractive index of the solid is n. b The refractive index of air is n a , the incident beam size (radius) is ω input , the wavefront curvature radius is R input Gaussian beam, for example: the transmission process of a beam is as follows: a air, air-solid surface refraction, distance d b Solid, solid-air surface refraction, distance d a of air, focusing concave mirror, distance d a air, air-solid surface refraction, distance d b Solid, solid-air surface refraction, distance d a1 After the air, the transmission matrix is

[0070]

[0071] And there is a constraint relationship

[0072] det M=AD-BC=1 (9)

[0073] Similar to step 17, through iteration, the corresponding transmission matrix can be calculated based on the optical components that the light beam passes through when it starts from a known incident position, transmits any number of times in the Herriot solid multi-pass cell, and transmits to any position in the multi-pass cell.

[0074] Step 2: According to the transmission matrix of the light beam transmitted from the initial position to any position, the q parameter of the light beam transmitted to any position is calculated. The real part and imaginary part of the q parameter are used to calculate the corresponding beam radius and the curvature radius of the wavefront, that is, the beam evolution process of the light beam in the Herriot multi-pass cell.

[0075] Step 2 specifically includes:

[0076] Step 21. For a wavelength of λ, the solid refractive index is n b , the incident beam size (radius) is ω input , the wavefront curvature radius is R input A Gaussian beam with a q parameter q input for

[0077]

[0078] Step 22, q input is the q parameter before the optical system transmission matrix described in step 17, q output is the q parameter after the optical system transmission matrix described in step 17, q input and q output The relationship is

[0079]

[0080] Step 23: According to the relationship between the beam size, wavefront curvature radius and q parameter, the beam size and wavefront curvature radius of the beam transmitted to any position in the multi-pass cell are obtained as follows:

[0081]

[0082] Step 3: According to the beam evolution process, adjust the parameters of the incident beam and calculate the corresponding beam distribution in the Herriott solid multi-pass cell; according to the required beam size and laser intensity, select the corresponding incident beam so that the beam maintains a stable beam size each time it passes through the solid in the Herriott solid multi-pass cell, and the optical components are not damaged by the smaller beam waist, thereby ensuring the safety of the optical components and the system and improving the stability of the system.

[0083] The effect of the present invention is further demonstrated by simulation experiments:

[0084] The beam evolution of the Herriot solid multipass cell is as follows Figure 4 As shown, Figure 4 The simulation parameters in include: central wavelength 1030nm, concave mirror curvature radius 300mm, cavity length 599mm, solid thickness 20mm, solid refractive index 1.45, gas refractive index 1, where, Figure 4 (a) and (b) in the figure are the evolution of the beam size and wavefront curvature radius of the incident laser when it is transmitted 1 to 50 times in the multi-pass cell. Figure 4(c) and (d) are the evolution of beam size and wavefront curvature radius when the incident laser is transmitted 1 to 50 times in the multi-pass cell with a beam size of 0.116 mm and a wavefront curvature radius of positive infinity.

[0085] By using the above method, after determining the central wavelength of the incident light beam, the beam size, the wavefront curvature radius, the cavity length of the Herriott solid multi-pass cell, the curvature radius of the concave reflector, the solid length, the solid refractive index, the air refractive index and other parameters, the parameters of the light beam at any position passing through the Herriott solid multi-pass cell can be calculated, such as Figure 4 Figure 4 shows the evolution of a beam in a Herriot solid multi-pass cell, including the beam size and the radius of curvature of the wavefront. Figure 4 (a) and (b) show the evolution of the beam size and wavefront curvature radius when the laser parameters entering the multi-pass cell are 0.063 mm in beam size and infinite wavefront curvature radius, and the beam is transmitted 50 times in the Herriot solid multi-pass cell. The evolution of the beam size and wavefront curvature radius during each transmission between the two concave mirrors of the multi-pass cell is shown in Figure 1. Figure 4 In (a), the black part is the beam waist with a smaller beam size, which is less than 0.4 mm. The energy of the laser is relatively concentrated, and each transmission has a large change. The distribution of the beam waist is very scattered, which can easily damage the optical components in the system. By traversing, a relatively stable beam distribution is obtained. The parameters of the incident beam are adjusted to a beam size of 0.116 mm and a wavefront curvature radius of positive infinity, such as Figure 4 As shown in (c) and (d), each time the light beam passes through the surface of the concave reflector, the light beam has the largest size, and the radius of curvature of the wavefront is the same as the radius of curvature of the concave reflector; each time the light beam passes through the center of the multi-pass cell, that is, the center of the solid, the light beam has the smallest size, and the wavefront is a plane. After safety optimization, the stable beam distribution can ensure the safety of the system and improve the experimental performance. This fully proves the correctness of the calculation method for the evolution of the light beam in the Herriott solid multi-pass cell of the present invention and the reliability of the system safety optimization method. Through this method, it is possible to fully predict and evaluate the evolution of the size and wavefront curvature radius of a light beam at any position after it is transmitted several times in a Herriott solid multi-pass cell with a known structure, and optimize the safety of the system, which is of great significance for the research of the Herriott solid multi-pass cell in ultrafast optics, spectroscopy, atomic and molecular physics and quantum precision measurement.

[0086] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A safety optimization method for Herriot solid multi-pass cell based on beam evolution calculation, characterized in that: The Herriot solid multi-pass cell has two coaxial concave reflectors with the same curvature radius, and the solid is located at the center of the multi-pass cell. The structure of "concave reflector-solid-concave reflector" is paraxially approximated to be an optical system of a series of "thin convex lenses-solid" structures. The method includes: Step 1: Obtain the structure of the multi-pass cell and the parameters of each optical device therein, including the central wavelength λ, the radius of curvature R of the concave mirror, and the concave mirror spacing, i.e., the cavity length d. a , solid thickness d b , solid refractive index n b and the refractive index of air n a , calculate the transmission matrix for the cavity structure and each optical device therein; calculate the corresponding transmission matrix according to the optical components that the light beam passes through when it starts from a known position and transmits any number of times in the Herriot solid multi-pass cell to any position, and obtain the transmission matrix of the incident light beam from the initial position to any position through iteration; Step 2: According to the transmission matrix of the light beam transmitted from the initial position to any position, the q parameter of the light beam transmitted to any position is calculated, and the corresponding beam radius and wavefront curvature radius are calculated using the real part and imaginary part of the q parameter, that is, the beam evolution process of the light beam in the Herriot multi-pass cell; Step 3: According to the beam evolution process, adjust the parameters of the incident beam and calculate the corresponding beam distribution in the Herriott solid multi-pass cell; according to the required beam size and laser intensity, select the corresponding incident beam so that the beam maintains a stable beam size each time it passes through the solid in the Herriott solid multi-pass cell, and the optical components are not damaged by the smaller beam waist, thereby ensuring the safety of the optical components and the system and improving the stability of the system.

2. The Herriot solid multi-pass cell safety optimization method based on beam evolution calculation according to claim 1 is characterized in that: In step 1, the transmission matrix is ​​calculated for the cavity structure and each optical device therein, specifically including: Step 11: Calculate the transfer matrix M of the concave reflector cm :Get the radius of curvature R of the concave reflector, then its focal length f = R / 2, abstract the concave reflector as a thin convex lens, the transmission matrix M cm for Step 12: Calculate the solid transmission matrix M b : Get the solid thickness d b The refractive index of the solid n b , calculate the time in the solid after d b The transmission matrix M of the distance b Step 13: Calculate the air transmission matrix Ma: Fix the solid at the center of the multi-pass cell and obtain the cavity length d a , calculated at distance d a The transmission matrix of air in Step 14: Set the transmission step length d of the light beam in the air air-step , then the light beam propagates in the air air-step The transfer matrix is Step 15: Set the transmission step length d of the beam in the solid bulk-step , then the light beam propagates in the air bulk-step The transfer matrix is Step 16: Get the refractive index n of air a ,but: The transmission matrix of the light beam refracted on the air-solid surface is The transmission matrix of a beam refracted at a solid-air surface is 3. The Herriot solid multi-pass cell safety optimization method based on beam evolution calculation according to claim 2 is characterized in that: The transmission matrix of the light beam from the initial position to any position in step 1 is calculated as follows: Step 17, according to the number of transmissions of the light beam from a known position in the Herriot solid multi-pass cell and the order of the light beam transmission to any position, as well as the order of the optical components passed through, by combining formula (1), formula (2), formula (3), formula (4), formula (5), formula (6) and formula (7), the components passed by the light beam during the transmission process are regarded as an optical system, and the transmission matrix of the optical system is obtained as follows: And there is a constraint relationship det M=AD-BC=1 (9).

4. The Herriot solid multi-pass cell safety optimization method based on beam evolution calculation according to claim 3 is characterized in that: The step 2 specifically includes According to the q-parameter of the beam transmission in the Herriot solid multipass cell: Step 21. For a wavelength of λ, the solid refractive index is nb, the incident beam size (radius) is ωinput, and the wavefront curvature radius is R input A Gaussian beam with a q parameter q input for Where i is the imaginary unit; Step 22: Set q input is the q parameter before the optical system transmission matrix described in step 17, q output is the q parameter after the optical system transmission matrix described in step 17, q input and q output The relationship is Step 23: According to the relationship between the beam size, wavefront curvature radius and q parameter, the beam size and wavefront curvature radius of the beam transmitted to any position in the multi-pass cell are obtained as follows: That is the beam evolution process of the beam in the Herriot multi-pass cell.

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