Bessel beam adjustable focusing position method and device

Abstract

The present invention discloses a method and device for adjusting the focus position of a Bessel beam, relating to the field of optical technology. The method comprises: obtaining the radius of the adjustment ring on the amplitude filter; obtaining the focal length of the focusing lens; obtaining the angular difference between the first diffractive optical element and the second diffractive optical element; and adjusting the defocus value of the optical system according to the angular difference. The technical solution of the present invention achieves rapid, high-precision, and continuous dynamic adjustment of the focus position of the Bessel beam by the optical system by adjusting only the first diffractive optical element and the second diffractive optical element. The adjustment process does not change the focal depth of the Bessel beam, and therefore does not affect the longitudinal relative spatial distribution of the beam before and after the adjustment.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a Bessel beam adjustable focus position method and a Bessel beam adjustable focus position device. Background Art

[0002] Bessel beams have been widely used in many fields such as laser processing, optical storage, optical tweezers, and large depth of field imaging due to their characteristics of non-diffraction, long focal depth and high lateral resolution.

[0003] To meet the application requirements of different scenarios, it is crucial to achieve dynamic adjustment of the focus position in the Bessel beam generating device. Currently, the main methods for adjusting the focus position of the Bessel beam include adjusting the spacing of the conical lens group to change the focal depth of the Bessel beam, or adjusting the Bessel beam parameters by loading different phase images through a spatial light modulator (SLM), or using Dammann grating and ring filtering technology, or using a translation stage to adjust the sample position for dynamic focus adjustment. These methods have problems when adjusting the focus position of the Bessel beam, such as complex structure, inability to continuously adjust, high cost, and different spatial energy distribution of the beam before and after adjustment due to adjusting the focal depth, which affects the processing effect. Summary of the Invention

[0004] The main purpose of the present invention is to propose a Bessel beam adjustable focus position method and a Bessel beam adjustable focus position device, aiming to solve the technical problems in the prior art such as complex structure, inability to continuously adjust, high cost, and different spatial energy distribution of the Bessel beam before and after adjustment caused by adjusting the focal depth, which affects the processing effect.

[0005] To achieve the above objectives, the present invention provides a method for adjusting the focus position of a Bessel beam. The method is applied to an optical system, wherein the optical system includes an amplitude filter, a grating, and a focusing lens sequentially arranged along an optical axis, wherein the grating includes a first diffractive optical element and a second diffractive optical element arranged opposite to each other. The method comprises:

[0006] Obtaining the radius of the adjustment ring on the amplitude filter;

[0007] Obtaining the focal length of the focusing lens;

[0008] obtaining an angular difference between the first diffractive optical element and the second diffractive optical element;

[0009] adjusting a defocus value of the optical system according to the angle difference;

[0010] The angle difference, the focal length, the annular radius, and the defocus value satisfy the following relationship:

[0011] ;

[0012] Wherein, Δf is the defocus value, f is the focal length, θ is the angle difference, λ is the wavelength of the laser entering the optical system, D is the radius of the ring, and K is a constant coefficient.

[0013] In one embodiment, the step of adjusting the defocus value of the optical system according to the angle difference includes:

[0014] Obtaining an equivalent grating period according to the angle difference;

[0015] adjusting the defocus value of the optical system according to the equivalent grating period;

[0016] The angle difference and the equivalent grating period satisfy the following relationship:

[0017] ;

[0018] The equivalent grating period and the defocus value satisfy the following relationship:

[0019] ;

[0020] Wherein, Λ is the equivalent grating period.

[0021] In one embodiment, the step of obtaining the equivalent grating period according to the angle difference includes:

[0022] obtaining a first transmittance of the first diffractive optical element;

[0023] obtaining a second transmittance of the second diffractive optical element;

[0024] Obtaining a total transmittance of the grating according to the first transmittance, the second transmittance and the angle difference;

[0025] The equivalent grating period is obtained according to the total transmittance.

[0026] In one embodiment, the first transmittance and the second transmittance satisfy the following relationship:

[0027] ;

[0028] When the angle difference is θ, the total transmittance of the grating satisfies the following relationship:

[0029] ;

[0030] Wherein, i is an imaginary unit, r is a radial coordinate value, T is the total transmittance, T1 is the first transmittance, and T2 is the second transmittance.

[0031] In one embodiment, the step of obtaining the angular difference between the first diffractive optical element and the second diffractive optical element includes:

[0032] Acquiring a first rotation angle of the first diffractive optical element, and acquiring a second rotation angle of the second diffractive optical element;

[0033] An angle difference is calculated based on the first rotation angle and the second rotation angle.

[0034] In one embodiment, after the step of adjusting the defocus value of the optical system according to the angle difference, the method further includes:

[0035] Obtaining the divergence half angle of the amplitude filter and the deflection angle of the grating;

[0036] A focal depth value of the optical system is calculated according to the divergence half angle and the deflection angle.

[0037] In one embodiment, the step of calculating the focal depth of the optical system according to the divergence half angle and the deflection angle includes:

[0038] Calculating the far beam point of the optical system according to the divergence half angle and the deflection angle;

[0039] Calculating the near beam point of the optical system according to the divergence half angle and the deflection angle;

[0040] The focal depth value is calculated according to the high beam point and the low beam point.

[0041] In one embodiment, the high beam point, the divergence half angle, and the deflection angle satisfy the following relationship:

[0042] ;

[0043] The near beam point, the divergence half angle, and the deflection angle satisfy the following relationship:

[0044] ;

[0045] The high beam point, the low beam point and the focal depth value satisfy the following relationship:

[0046] ;

[0047] Among them, Z max is the far beam point, Z min is the near light point, ΔZ is the focal depth, α is the divergence half angle, β is the deflection angle, and d is the width of the adjustment ring.

[0048] The present invention further provides a Bessel beam adjustable focus position device, which is applied to the above-mentioned Bessel beam adjustable focus position method. The Bessel beam adjustable focus position device includes an optical system consisting of a light source, a collimating lens, a grating, an amplitude filter, and a focusing lens, which are sequentially arranged along the optical axis. The amplitude filter has an adjustment ring.

[0049] The adjustment ring and the grating are used to adjust the defocus value of the optical system.

[0050] In one embodiment, the grating includes a first diffractive optical element and a second diffractive optical element that are arranged opposite to each other, and the first diffractive optical element and / or the second diffractive optical element are rotatably arranged with the optical axis as a rotation axis;

[0051] When the first diffractive optical element and / or the second diffractive optical element rotates, the defocus value of the optical system is adjusted.

[0052] The technical solution of the present invention achieves rapid, high-precision, and continuous dynamic adjustment of the focus position of a Bessel beam by adjusting only the first and second diffractive optical elements. Furthermore, the adjustment process does not change the focal depth of the Bessel beam, thus maintaining the relative longitudinal spatial distribution of the beam before and after adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0054] Figure 1 This is a schematic flow chart of a first embodiment of a method for adjusting the focus position of a Bessel beam according to the present invention;

[0055] Figure 2 This is a schematic flow chart of a second embodiment of a method for adjusting the focus position of a Bessel beam according to the present invention;

[0056] Figure 3 This is a schematic flow chart of a third embodiment of a method for adjusting the focus position of a Bessel beam according to the present invention;

[0057] Figure 4 This is a schematic flow chart of a fourth embodiment of a method for adjusting the focus position of a Bessel beam according to the present invention;

[0058] Figure 5 This is a schematic flow chart of a fifth embodiment of a method for adjusting the focus position of a Bessel beam according to the present invention;

[0059] Figure 6 Schematic diagram of the structure of the Bessel beam adjustable focus position device of the present invention;

[0060] Figure 7 Schematic diagram of the optical path of the Bessel beam adjustable focus position device of the present invention;

[0061] Figure 8 Schematic diagram of the structure of the grating in the Bessel beam adjustable focus position device of the present invention;

[0062] Figure 9 Schematic diagram of the overlapping area of ​​the grating in the Bessel beam adjustable focus position device of the present invention;

[0063] Figure 10 Schematic diagram of the grating effect in the Bessel beam adjustable focus position device of the present invention;

[0064] Figure 11 This is a diagram showing the light spot effect of the Bessel beam adjustable focus position device in one embodiment of the present invention;

[0065] Figure 12 This is a diagram showing the light spot effect of the Bessel beam adjustable focus position device in another embodiment of the present invention.

[0066] Description of Figure Numbers:

[0067] 10. Light source; 11. Coupling output optical fiber; 12. Fiber coupling output mirror; 20. Collimating lens; 30. Grating; 31. First diffractive optical element; 32. Second diffractive optical element; 40. Amplitude filter; 41. Adjustment ring; 50. Focusing lens.

[0068] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0069] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0070] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0071] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0072] The present invention provides a method for adjusting the focusing position of a Bessel beam.

[0073] See also Figure 1 , Figure 1 This is a flow chart of a first embodiment of the present invention. The Bessel beam adjustable focus method includes the following steps:

[0074] Step S10: obtaining the radius of the adjustment ring 41 on the amplitude filter 40;

[0075] Step S20: obtaining the focal length of the focusing lens 50;

[0076] Step S30: obtaining an angle difference between the first diffractive optical element 31 and the second diffractive optical element 32;

[0077] Step S40: adjusting the defocus value of the optical system according to the angle difference.

[0078] The Bessel beam adjustable focus position method of the present invention is applied to optical systems, see Figure 6 The optical system specifically includes a light source 10, a collimating lens 20, a grating 30, an amplitude filter 40 and a focusing lens 50 which are sequentially arranged along the optical axis.

[0079] The amplitude filter 40 has an adjustment ring 41 , the center of which is located on the optical axis. The light source 10 can be a fiber-coupled output laser, which transmits laser light toward the collimating lens 20 through the coupled output fiber 11 and the fiber-coupled output mirror 12 .

[0080] After passing through the collimating lens 20, the light beam sequentially passes through the grating 30 and the amplitude filter 40. In this embodiment, the grating 30 can be an adjustable radial grating 30, and the amplitude filter 40 can be an annular structure.

[0081] The grating 30 includes a first diffractive optical element 31 and a second diffractive optical element 32 arranged opposite to each other. Specifically, after being shaped by the grating 30 and the amplitude filter 40, the light beam is emitted from the adjustment ring 41 of the amplitude filter 40. The emitted light beam has a deflection angle, which can be adjusted by rotating the first diffractive optical element 31 and / or the second diffractive optical element 32, thereby adjusting the focus position of the Bessel light beam. Figure 7 , to achieve the adjustment of the defocus value Δf of the Bessel beam.

[0082] The angle difference, the focal length, the annular radius, and the defocus value satisfy equation 1:

[0083] ;

[0084] Wherein, Δf is the defocus value, f is the focal length, θ is the angle difference, λ is the wavelength of the laser entering the optical system, D is the radius of the ring, and K is a constant coefficient.

[0085] The technical solution of the present invention achieves rapid, high-precision, and continuous dynamic adjustment of the Bessel beam's focus position by adjusting only the first and second diffractive optical elements 31, 32. Furthermore, the adjustment process does not alter the Bessel beam's focal depth, thus unaffecting the longitudinal relative spatial distribution of the beam before and after adjustment.

[0086] Further, see Figure 2 , Figure 2 This is a flow chart of the second embodiment of the present invention, where step S40 includes:

[0087] Step S41: obtaining an equivalent grating period according to the angle difference;

[0088] Step S42: adjusting the defocus value of the optical system according to the equivalent grating period.

[0089] Specifically, to facilitate adjustment, in this embodiment, the first diffractive optical element 31 can be kept fixed, and only the second diffractive optical element 32 can be rotated, thereby facilitating calculation of the relative deflection angle, i.e., the angle difference, between the first diffractive optical element 31 and the second diffractive optical element 32. Conversely, the second diffractive optical element 32 can be kept fixed, and only the first diffractive optical element 31 can be rotated.

[0090] See also Figure 8 The first diffractive optical element 31 and the second diffractive optical element 32 both adopt a square structure, and their centers are both located on the optical axis to ensure the accuracy of adjustment. In addition, a circle center can also be used, and the circle center is located on the optical axis.

[0091] The equivalent grating period of the grating 30 is adjusted by adjusting the angle difference between the first diffractive optical element 31 and the second diffractive optical element 32. The angle difference and the equivalent grating period satisfy the relationship 2:

[0092] ;

[0093] Wherein, Λ is the equivalent grating period, K is a constant coefficient, and θ is the angle difference.

[0094] Substituting equation 2 into equation 1, the equivalent grating period and the defocus value satisfy equation 3:

[0095] ;

[0096] Wherein, Λ is the equivalent grating period, D is the radius of the ring, f is the focal length, and λ is the wavelength of the laser entering the optical system.

[0097] Therefore, by adjusting the equivalent grating period of the grating 30 , the defocus value of the Bessel beam can be adjusted, thereby improving the compatibility of adjusting the optical parameters of the grating 30 in the optical system.

[0098] Further, see Figure 3 , Figure 3 This is a flow chart of the third embodiment of the present invention, where step S41 includes:

[0099] Step S411: obtaining a first transmittance of the first diffractive optical element 31;

[0100] Step S412: obtaining a second transmittance of the second diffractive optical element 32;

[0101] Step S413: Obtaining the total transmittance of the grating 30 according to the first transmittance, the second transmittance and the angle difference;

[0102] Step S414: Obtaining the equivalent grating period according to the total transmittance.

[0103] When constructing the first diffractive optical element 31 and the second diffractive optical element 32, their transmittance functions respectively satisfy the following relationships:

[0104] ;

[0105] Where T1 is the first transmittance, and T2 is the second transmittance. K is a constant coefficient. For a diffractive optical element, once its structure is determined, K is fixed. The function floor[f] is a floor function.

[0106] Please refer to Figure 9, when the first diffractive optical element 31 rotates one circle relative to the second diffractive optical element 32 with the optical axis as the rotation axis, there is an overlapping area A. By establishing a coordinate system with the center of the overlapping area A as the origin, it can be calculated: ;

[0107] The phase transmittance functions of the first diffractive optical element 31 and the second diffractive optical element 32 are inverted, so they can use the same phase function, thereby reducing processing costs and errors. When in use, the two identical diffractive optical elements are placed facing each other to achieve the designed effect. Figure 10 , and superimposing them results in a schematic diagram of the radial grating 30 .

[0108] The total transmittance function is calculated using the representation function of the first transmittance and the representation function of the second transmittance. When the first diffractive optical element 31 and / or the second diffractive optical element 32 are rotated so that the angle difference therebetween is θ, the total transmittance function satisfies equation 4:

[0109] ;

[0110] Wherein, i is an imaginary unit, r is a radial coordinate value, and T is the total transmittance.

[0111] r is specifically the radial coordinate value of the pupil of the optical component. It should be noted that the optical component has a pupil. For example, the pupil can be a circular frame of the optical component.

[0112] When performing calculations, a polar coordinate system is established with the center of the overlapping area A as the origin. Figure 9 It can be understood that because the optical system is circularly symmetric, the polar coordinate value of the pupil can be obtained without considering the angle, and the radial coordinate value of the polar coordinate can be taken.

[0113] According to equation 4, the corresponding equivalent grating 30 period can be derived .

[0114] See also Figure 4 , Figure 4 This is a flowchart of the fourth embodiment of the present invention, where step S30 includes:

[0115] Step S31: obtaining a first rotation angle of the first diffractive optical element 31 and obtaining a second rotation angle of the second diffractive optical element 32;

[0116] Step S32: Calculating an angle difference according to the first rotation angle and the second rotation angle.

[0117] In this embodiment, when the first diffractive optical element 31 is kept fixed, the first rotation angle is recorded as 0; when the second diffractive optical element 32 is rotated to a certain angle value, it is recorded as the second rotation angle, and the difference between the first rotation angle and the second rotation angle is recorded as the angle difference.

[0118] Similarly, when the second diffractive optical element 32 is fixed, the second rotation angle is recorded as 0. Therefore, the angle difference can be calculated based on the rotation angle of the first diffractive optical element 31. The angle difference can be recorded as the absolute value of the difference to avoid the influence of the sign difference between the forward and reverse angle values ​​of the second diffractive optical element 32.

[0119] In addition, in this embodiment, the first diffractive optical element 31 and the second diffractive optical element 32 may be rotated simultaneously, and the relative rotation angle difference between them may be calculated according to their rotation directions.

[0120] Further, see Figure 5 , Figure 5 This is a flowchart of the fifth embodiment of the present invention. After step S40, the following steps are further included:

[0121] Step S50: obtaining the divergence half angle of the amplitude filter 40 and the deflection angle of the grating 30;

[0122] Step S60: Calculating the focal depth of the optical system according to the divergence half-angle and the deflection angle.

[0123] See also Figure 6 and Figure 7 After passing through the grating 30 , the light beam has a deflection angle and is incident on the amplitude filter 40 ; after passing through the adjustment ring 41 on the amplitude filter 40 , the light beam has a divergence half angle.

[0124] After optical analysis, the light beam forms a near light point Z on the optical axis close to the amplitude filter 40 after passing through the optical system. min , and a far light point Z far away from the amplitude filter 40 max .

[0125] Specifically, through geometric analysis, we know that

[0126] The far beam point, the divergence half angle and the deflection angle satisfy the relational expression 5:

[0127] ;

[0128] The near beam point, the divergence half angle, and the deflection angle satisfy the relationship 6:

[0129] ;

[0130] The focal depth value ΔZ of the optical system is calculated according to the far light point and the near light point, and the far light point, the near light point and the focal depth value satisfy Relation 7:

[0131] ;

[0132] Among them, Z max is the far beam point, Z min is the near light point, ΔZ is the focal depth, α is the divergence half angle, β is the deflection angle, and d is the width of the adjustment ring 41 .

[0133] It is easy to see from equations 1, 3, 5, 6, and 7 that, when adjusting the focus position, that is, when adjusting the defocus value, in the present invention, only the equivalent grating period Λ of the grating 30 changes, and the focal depth value ΔZ of the Bessel beam is not affected by the equivalent grating period. Therefore, during the entire adjustment process, the focal depth value of the Bessel beam is not affected, and the defocus value Δf changes in direct proportion to the inverse of the equivalent grating period of the grating 30.

[0134] As an example, to achieve high-precision defocus position control, this embodiment assigns values ​​to various parameters, assuming that the laser wavelength is 532nm, the ring radius D of the amplitude filter 40 is 1mm, the width d of the adjustment ring 41 is 0.2mm, the focal length f of the focusing lens 50 is 40mm, and the K value of the grating 30 is 1.745. The focal depth ΔZ of the Bessel beam generated under these conditions is 8.51mm. Figure 11 The first diffractive optical element 31 is kept stationary, and the second diffractive optical element 32 is rotated using a motorized rotary stage. When the rotation angle of the second diffractive optical element 32 is 0°, the defocus value Δf is 0, and the focus center is the focal point of the focusing lens 50. When the rotation angle is 22.5°, the equivalent grating period Λ of the grating 30 is 0.16 mm, and the defocus value Δf is 5.32 mm. When the rotation angle is 45°, the equivalent grating period Λ of the grating 30 is 0.08 mm, and the defocus value Δf is 10.64 mm. The resolution of the motorized rotary stage is 0.02°, so the defocus position adjustment resolution is 82.5 nm. This embodiment can be used for high-precision laser processing.

[0135] As another example, assume that the laser wavelength is 532 nm, the radius D of the ring of the amplitude filter 40 is 1 mm, the width d of the adjustment ring 41 is 0.2 mm, the focal length f of the focusing lens 50 is 250 mm, and the K value of the grating 30 is 3.491. The focal depth ΔZ of the Bessel beam generated under these conditions is 166.25 mm. Figure 12The first diffractive optical element 31 is kept stationary, and the second diffractive element is rotated using a motorized rotary stage. When the second diffractive element is rotated to 0°, the defocus value Δf is 0, and the focal center is the focal point of the lens. When the rotation angle is 22.5°, the equivalent grating period Λ of the grating 30 is 0.08mm, and the defocus value Δf is 415.625mm. When the rotation angle is 45°, the equivalent grating period Λ of the grating 30 is 0.04mm, and the defocus value Δf is 831.25mm. In this embodiment, the motorized rotary stage can adjust the angle from 0° to 45° in less than 0.2 seconds, and the focus position can be adjusted at a speed of up to 2m / s. This embodiment can be used for long-range distance sensing.

[0136] The present invention further provides a Bessel beam adjustable focus position device, and the Bessel beam adjustable focus position method is applied to the above-mentioned Bessel beam adjustable focus position method.

[0137] The Bessel beam adjustable focus position device includes an optical system consisting of a light source 10, a collimating lens 20, a grating 30, an amplitude filter 40 and a focusing lens 50 arranged in sequence along the optical axis. The amplitude filter 40 has an adjustment ring 41; the adjustment ring 41 and the grating 30 are used to adjust the defocus value of the optical system.

[0138] Since the present Bessel beam adjustable focus position method adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0139] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformation made by using the contents of the present invention description and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields, is included in the scope of protection of the present invention.

Claims

1. A method for adjusting the focus position of a Bessel beam, characterized in that: The Bessel beam adjustable focus position method is applied to an optical system, wherein the optical system includes an amplitude filter, a grating, and a focusing lens sequentially arranged along an optical axis, wherein the grating includes a first diffractive optical element and a second diffractive optical element arranged opposite to each other, and the Bessel beam adjustable focus position method includes: Obtaining the radius of the adjustment ring on the amplitude filter; Obtaining the focal length of the focusing lens; obtaining an angular difference between the first diffractive optical element and the second diffractive optical element; adjusting a defocus value of the optical system according to the angle difference; The angle difference, the focal length, the annular radius, and the defocus value satisfy the following relationship: ； Wherein, Δf is the defocus value, f is the focal length, θ is the angle difference, λ is the wavelength of the laser entering the optical system, D is the radius of the ring, and K is a constant coefficient.

2. The Bessel beam adjustable focus method according to claim 1, wherein: The step of adjusting the defocus value of the optical system according to the angle difference comprises: Obtaining an equivalent grating period according to the angle difference; adjusting the defocus value of the optical system according to the equivalent grating period; The angle difference and the equivalent grating period satisfy the following relationship: ； The equivalent grating period and the defocus value satisfy the following relationship: ； Wherein, Λ is the equivalent grating period.

3. The method for adjusting the focus position of a Bessel beam according to claim 2, wherein: The step of obtaining the equivalent grating period according to the angle difference comprises: obtaining a first transmittance of the first diffractive optical element; obtaining a second transmittance of the second diffractive optical element; Obtaining a total transmittance of the grating according to the first transmittance, the second transmittance and the angle difference; The equivalent grating period is obtained according to the total transmittance.

4. The method for adjusting the focus position of a Bessel beam according to claim 3, wherein: The first transmittance and the second transmittance satisfy the following relationship: ； Function floor[f] is a floor function. When the first diffractive optical element rotates one circle relative to the second diffractive optical element about the optical axis, there is an overlapping area A. A coordinate system established with the center of the overlapping area A as the origin can be calculated: ; When the angle difference is θ, the total transmittance of the grating satisfies the following relationship: ； Wherein, i is an imaginary unit, r is a radial coordinate value, T is the total transmittance, T1 is the first transmittance, and T2 is the second transmittance.

5. The method for adjusting the focus position of a Bessel beam according to claim 1, wherein: The step of obtaining the angular difference between the first diffractive optical element and the second diffractive optical element includes: Acquiring a first rotation angle of the first diffractive optical element, and acquiring a second rotation angle of the second diffractive optical element; An angle difference is calculated based on the first rotation angle and the second rotation angle.

6. The method for adjusting the focus position of a Bessel beam according to claim 1, wherein: After the step of adjusting the defocus value of the optical system according to the angle difference, the method further includes: Obtaining the divergence half angle of the amplitude filter and the deflection angle of the grating; A focal depth value of the optical system is calculated according to the divergence half angle and the deflection angle.

7. The method for adjusting the focus position of a Bessel beam according to claim 6, wherein: The step of calculating the focal depth value of the optical system according to the divergence half angle and the deflection angle comprises: Calculating the far beam point of the optical system according to the divergence half angle and the deflection angle; Calculating the near beam point of the optical system according to the divergence half angle and the deflection angle; The focal depth value is calculated according to the high beam point and the low beam point.

8. The Bessel beam adjustable focus method according to claim 7, wherein: The far beam point, the divergence half angle, and the deflection angle satisfy the following relationship: ； The near beam point, the divergence half angle, and the deflection angle satisfy the following relationship: ； The high beam point, the low beam point and the focal depth value satisfy the following relationship: ； Among them, Z max is the far beam point, Z min is the near light point, ΔZ is the focal depth, α is the divergence half angle, β is the deflection angle, and d is the width of the adjustment ring.

9. A Bessel beam adjustable focus position device, characterized in that: The Bessel beam adjustable focus position device is applied to the Bessel beam adjustable focus position method according to any one of claims 1 to 8, the Bessel beam adjustable focus position device comprises an optical system consisting of a light source, a collimating lens, a grating, an amplitude filter, and a focusing lens arranged in sequence along the optical axis, wherein the amplitude filter has an adjustment ring; The adjustment ring and the grating are used to adjust the defocus value of the optical system.

10. The Bessel beam adjustable focus position device according to claim 9, characterized in that: The grating includes a first diffractive optical element and a second diffractive optical element that are arranged opposite to each other, and the first diffractive optical element and / or the second diffractive optical element are rotatably arranged with the optical axis as a rotation axis; When the first diffractive optical element and / or the second diffractive optical element rotates, the defocus value of the optical system is adjusted.

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