Acousto-optic deflector dispersion compensation method based on dispersion prism group

Abstract

The invention belongs to the technical field related to laser, and particularly relates to an acousto-optic deflector dispersion compensation method based on a dispersion prism group, which comprises the following steps: configuring the dispersion prism group; with the light spot of the monochromatic laser beam emitted from the prism group as a circle as a constraint, the incident angle of the laser incident to the first dispersion prism and the second dispersion prism when the negative space dispersion generated by the prism group and the positive space dispersion of the to-be-compensated acousto-optic deflector are equal and opposite in size is calculated; the relative spatial position between the two prisms is determined and adjusted by taking the incident angle of a laser beam incident to the first dispersion prism and the second dispersion prism and the vertical incidence of laser emitted from the prism group to the receiving surface of the acousto-optic deflector as constraints, so that spatial dispersion compensation is realized; and the distance between the central position of the dispersion prism group and the central position of the acousto-optic deflector is calculated and adjusted when the negative time dispersion generated by the prism group is equal to and opposite to the positive time dispersion of the acousto-optic deflector, so that time dispersion compensation is realized. The method is wide in application range of space-time dispersion to be compensated.

Description

Technical Field

[0001] The present invention belongs to the field of laser-related technologies, and more specifically, relates to a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group. Background Art

[0002] Acousto-optic deflector (AOD), as a device with no inertia and high-speed scanning, can achieve high-precision beam control with high accuracy, high speed and flexible scanning mode when combined with femtosecond laser, which plays an important role in precision processing, microscopic imaging, semiconductor defect detection and other fields. However, since femtosecond laser has a certain bandwidth in the spectrum, the inherent material dispersion and diffraction deflection beam of AOD will produce spatiotemporal dispersion of the scanned femtosecond laser, resulting in the broadening of laser pulses in the time domain and the reduction of beam quality in the spatial domain. Therefore, it is necessary to effectively compensate for the spatiotemporal dispersion introduced by it.

[0003] At present, the compensation schemes for AOD spatiotemporal dispersion mainly include the monochromatic prism method, the grating method and the acousto-optic modulator (AOM) method.

[0004] The monochromatic dispersion prism method fixes the monochromatic dispersion prism in front of the AOD to provide spatial dispersion pre-compensation. At the same time, the monochromatic dispersion prism and the AOD form a pulse compressor to provide temporal dispersion pre-compensation. The advantage of the monochromatic dispersion prism method is that it has high light transmission efficiency and lower cost than other solutions. The disadvantage is that the structure of the dispersion prism itself will cause the light spot to be spatially distorted, and the output light spot may be an elliptical light spot. The elliptical light spot will change the shape of the laser processing and reduce the laser processing accuracy. Even if a mirror group is introduced or a customized dispersion prism is used to suppress the spatial distortion of the light spot, it will still face the problem of limited scope of application and increased cost.

[0005] The grating method fixes the grating in front of the AOD to provide spatial dispersion pre-compensation. At the same time, the grating and AOD form a pulse compressor to provide temporal dispersion pre-compensation. The advantage of the grating method is that there is no spatial distortion effect, but the disadvantage is that the grating is expensive and needs to be customized. Even if a mirror group is introduced to adjust the dispersion provided by the grating, it still faces the problems of limited scope of application and high cost.

[0006] The AOM method places the AOM and AOD in reverse, placing it in front of the AOD to provide spatial dispersion pre-compensation. At the same time, the AOM and AOD form a pulse compressor to provide temporal dispersion pre-compensation. The advantage of the AOM method is that the AOM itself is easy to operate, but the disadvantage is that the scope of application is limited, and in order to compensate for the positive temporal dispersion introduced by the AOM, the distance between the AOM and the AOD is long, the space occupied is large, and the optical path adjustment is difficult.

[0007] In summary, the monochromatic prism method, grating method and AOM method currently used for AOD dispersion compensation all have certain defects. Therefore, it is necessary to overcome the many technical difficulties in the existing compensation technology and study more convenient and more applicable compensation technology. Summary of the invention

[0008] In view of the above defects or improvement needs of the prior art, the present invention provides a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, which aims to solve the problems of limited application range and high customization cost of the dispersion compensation device.

[0009] To achieve the above object, according to one aspect of the present invention, a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group is provided, comprising:

[0010] A dispersion prism group and a rotating stage group are configured; the rotating stage group includes a first rotating stage and a second rotating stage; the dispersion prism group includes a first dispersion prism arranged on the first rotating stage and a second dispersion prism arranged on the second rotating stage; the second dispersion prism is located on the vertical incident path of the laser beam of the acousto-optic deflector to be compensated; the laser beam first passes through the first dispersion prism and then passes through the second dispersion prism;

[0011] Taking the circular spot of the monochromatic laser beam emitted from the dispersion prism group as a constraint, calculate the incident angle of the laser beam incident on the first dispersion prism and the second dispersion prism when the negative spatial dispersion generated by the dispersion prism group is equal to and opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; taking the incident angle of the laser beam incident on the first dispersion prism and the second dispersion prism and the vertical incidence of the laser beam emitted from the dispersion prism group on the receiving surface of the acousto-optic deflector to be compensated as constraints, determine and adjust the relative spatial position between the two prisms; control the laser beam to be incident on the dispersion prism group parallel to the table surface of the first rotating table, and rotate the rotating table group to fine-tune the incident angle of the first dispersion prism and the second dispersion prism to the calculated incident angle, so as to achieve spatial dispersion compensation;

[0012] The spatial positions of the two prisms are adjusted so that the laser beam is transmitted near the edge area of ​​each dispersion prism; the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated when the negative time dispersion generated by the dispersion prism group is equal to or opposite to the positive time dispersion of the acousto-optic deflector to be compensated is calculated and adjusted to achieve time dispersion compensation.

[0013] Furthermore, when performing temporal dispersion compensation, the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is also fine-tuned to achieve compensation for the temporal dispersion additionally introduced by the dispersion prism group.

[0014] Further, the configuration is implemented as follows:

[0015] The first rotating table is placed vertically, that is, its table normal is parallel to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table of the first rotating table; the second rotating table is placed horizontally, that is, its table normal is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table.

[0016] Furthermore, the constraint that the spot of the monochromatic laser beam emitted from the dispersion prism group is circular is specifically:

[0017] The incident angle of the laser beam incident on the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

[0018] Furthermore, the negative spatial dispersion generated by the dispersion prism group is:

[0019]

[0020] In the formula, represents the negative spatial dispersion, whose value is equal to or opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; Represents the spatial dispersion produced by a single dispersive prism;

[0021] By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass The incident angle of the laser beam incident on the dispersion prism group is obtained, that is, the incident angle of the laser beam incident on the first dispersion prism.

[0022] Furthermore, the acousto-optic deflector to be compensated is composed of two acousto-optic deflector units placed orthogonally, and the dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor, and the negative time dispersion GDD generated by the pulse compressor is:

[0023]

[0024] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the acoustic field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and its value is the opposite of the positive spatial dispersion of the acousto-optic deflector to be compensated.

[0025] Further, the configuration is as follows:

[0026] The first rotating table is placed horizontally, that is, the normal line of the table surface is perpendicular to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table surface of the first rotating table; the second rotating table is placed horizontally, that is, the normal line of the table surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table;

[0027] The entire rotating stage assembly is rotated upward by 45° with the central axis of the laser beam vertically incident from the second dispersion prism to the acousto-optic deflector as the rotation axis.

[0028] Furthermore, the constraint that the spot of the monochromatic laser beam emitted from the dispersion prism group is circular is specifically:

[0029] The exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

[0030] Furthermore, the negative spatial dispersion generated by the dispersion prism group is:

[0031]

[0032] In the formula, represents the negative spatial dispersion, whose value is equal to or opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; represents the spatial dispersion produced by a single dispersion prism, subscripts 1 and 2 represent the first dispersion prism and the second dispersion prism respectively; M represents the magnification of the first dispersion prism;

[0033] By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass Obtaining an incident angle of the laser beam incident on the second dispersion prism;

[0034] According to the fact that the exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism, based on The incident angle value of the laser beam incident on the second dispersion prism is obtained, and the incident angle value of the laser beam incident on the first dispersion prism is calculated.

[0035] Furthermore, the acousto-optic deflector to be compensated is composed of two acousto-optic deflector units placed orthogonally, and the dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor, and the negative time dispersion GDD generated by the pulse compressor is:

[0036]

[0037] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the acoustic field frequency of the AOD scanned in the vertical direction, fx is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and its value is the opposite of the positive spatial dispersion of the acousto-optic deflector to be compensated.

[0038] In general, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

[0039] 1. The present invention proposes a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, which uses a double prism to compensate for the spatiotemporal dispersion of the acousto-optic deflector. The price of prisms is lower than other dispersion compensation devices, which controls the system cost. The incident angle of the light beam is adjusted by rotating the dispersion prism group. While ensuring that the output light beam of the acousto-optic deflector is parallel, the spatial dispersion of the acousto-optic deflector is compensated. There is no need to customize prisms of specific materials and angles, which controls the system cost. In addition, since the present scheme adopts a prism group scheme, the spatial dispersion compensation amount can be continuously adjusted while the light spot does not undergo spatial distortion due to the prism, and the adjustment is flexible and has a wide range of applications. By changing the spacing between the prism group and the acousto-optic deflector, the temporal dispersion of the acousto-optic deflector is compensated. Therefore, the present invention solves the problems of limited application range and high customization cost of the dispersion compensation device.

[0040] 2. When performing temporal dispersion compensation, the present invention also fine-tunes the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated, so as to achieve compensation for the temporal dispersion additionally introduced by the dispersion prism group. Because the prism group will introduce a small amount of additional temporal dispersion, by fine-tuning the above distance, the temporal dispersion of the acousto-optic deflector itself and the additional temporal dispersion introduced by the prism group are compensated at the same time, thereby solving the problems of limited application range and high customization cost of the dispersion compensation device and ensuring the compensation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flowchart of a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group provided by an embodiment of the present invention;

[0042] Figure 2 Schematic diagram of the principle of compensating the dispersion of the acousto-optic deflector by the prism group provided in an embodiment of the present invention;

[0043] Figure 3 is a schematic diagram of the orthogonal prism group and the cascade prism group provided in the embodiment of the present invention respectively shaping monochromatic light;

[0044] Figure 4 is a schematic diagram of a prism structure provided by an embodiment of the present invention;

[0045] Figure 5is a schematic diagram of spatial dispersion of a single prism provided by an embodiment of the present invention;

[0046] Figure 6 is a schematic diagram of spatial dispersion introduced by an acousto-optic medium in a single acousto-optic deflector unit provided by an embodiment of the present invention;

[0047] Figure 7 is a schematic diagram of time dispersion introduced by an acousto-optic medium in a single acousto-optic deflector unit provided by an embodiment of the present invention;

[0048] Figure 8 Schematic diagram of an orthogonal prism group provided by an embodiment of the present invention compensating for the spatiotemporal dispersion of an acousto-optic deflector;

[0049] Fig. 9 is a graph showing the relationship between the spatial dispersion of the orthogonal prism set provided by an embodiment of the present invention and the incident angle of the femtosecond laser relative to the first dispersion prism;

[0050] Fig.10 is a schematic diagram of a cascaded prism group provided by an embodiment of the present invention for compensating for the spatiotemporal dispersion of an acousto-optic deflector;

[0051] Fig.11 4 is a graph showing the relationship between the spatial dispersion of the cascaded prism group provided by an embodiment of the present invention and the incident angle of the femtosecond laser relative to the second dispersion prism.

[0052] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0053] 1 is a prism group, 1.1 is a first dispersion prism, 1.2 is a second dispersion prism, 2 is an acousto-optic deflector, 2.1 and 2.2 are two acousto-optic deflector units, 3 is a rotating stage group, 3.1 is a first rotating stage, and 3.2 is a second rotating stage; 4 is a femtosecond laser spot, 4.1 is a femtosecond laser spot before passing through the prism group, 4.2 is a femtosecond laser spot after passing through the first dispersion prism, and 4.3 is a femtosecond laser spot after passing through the second dispersion prism; 5.1 is a component with a smaller wavelength in the femtosecond laser beam, and 5.2 is a component with a larger wavelength in the femtosecond laser beam; 6 is an elliptical spot obtained due to spatial dispersion after the femtosecond laser passes through the acousto-optic medium in the acousto-optic deflector unit; 7.1 is an input pulse of the acousto-optic deflector, and 7.2 is an output pulse of the acousto-optic deflector; 8 is a horizontal plane; 9.1 is an acousto-optic medium. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0055] Embodiment 1

[0056] A dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, such as Figure 1 As shown, including:

[0057] A dispersion prism group and a rotating stage group are configured; the rotating stage group includes a first rotating stage and a second rotating stage; the dispersion prism group includes a first dispersion prism arranged on the first rotating stage and a second dispersion prism arranged on the second rotating stage; the second dispersion prism is located on the vertical incident path of the laser beam of the acousto-optic deflector to be compensated; the laser beam first passes through the first dispersion prism and then passes through the second dispersion prism;

[0058] Taking the circular spot of the monochromatic laser beam emitted from the dispersion prism group as a constraint, calculate the incident angle of the laser beam incident on the first dispersion prism and the second dispersion prism when the negative spatial dispersion generated by the dispersion prism group is equal to and opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; taking the incident angle of the laser beam incident on the first dispersion prism and the second dispersion prism and the vertical incidence of the laser beam emitted from the dispersion prism group on the receiving surface of the acousto-optic deflector to be compensated as constraints, determine and adjust the relative spatial position between the two prisms; control the laser beam to be incident on the dispersion prism group parallel to the table surface of the first rotating table, and rotate the rotating table group to fine-tune the incident angle of the first dispersion prism and the second dispersion prism to the calculated incident angle, so as to achieve spatial dispersion compensation;

[0059] The spatial positions of the two prisms are adjusted so that the laser beam is transmitted near the edge area of ​​each dispersion prism; the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated when the negative time dispersion generated by the dispersion prism group is equal to or opposite to the positive time dispersion of the acousto-optic deflector to be compensated is calculated and adjusted to achieve time dispersion compensation.

[0060] The present embodiment proposes a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, which uses a double prism to compensate for the spatiotemporal dispersion of the acousto-optic deflector. The prism is relatively cheap compared to other dispersion compensation devices. By rotating the dispersion prism group to adjust the incident angle of the light beam, the spatial dispersion of the acousto-optic deflector is compensated while ensuring that the output light beam of the acousto-optic deflector is parallel, and there is no need to customize a prism of a specific material and angle, thereby controlling the system cost. Therefore, the present invention solves the problem of high customization cost of the dispersion compensation device.

[0061] In addition, this embodiment adopts a prism group solution, and adjusts the spatial dispersion compensation amount by changing the incident angle of the incident light relative to the prism, so that the spatial dispersion compensation amount is continuously adjustable, and the light spot does not suffer from spatial distortion due to the prism. The temporal dispersion compensation amount is adjusted by changing the spacing between the prism group and the acousto-optic deflector, and the dispersion compensation amount is flexibly adjustable. Therefore, the method of this embodiment solves the problem of limited application range of the dispersion compensation device.

[0062] like Figure 2 As shown, the principle diagram corresponding to the method of this embodiment includes: a prism group 1, an acousto-optic deflector 2 composed of two orthogonal acousto-optic deflector units, and a one-dimensional rotating stage group 3;

[0063] The prism group is composed of a first dispersion prism 1.1 and a second dispersion prism 1.2. Figure 3 As shown in the upper and lower sub-figures in the figure, it is used to provide spatial dispersion pre-compensation, and form a pulse compressor with the acousto-optic deflector 2 to provide temporal dispersion pre-compensation, and ensure that the light spot does not undergo spatial distortion due to the prism structure. It should be noted that when the incident angles of the first dispersion prism and the second dispersion prism are fine-tuned to the calculated incident angle by rotating the rotating stage group to achieve spatial dispersion compensation, the light beam emitted from the acousto-optic deflector is a group of parallel light, and the parallel light is focused into a circular light spot after passing through the focusing lens. By observing that the light spot on the focusing plane after the parallel light passes through the focusing lens is circular, it can be easily judged that the spatial dispersion compensation has been achieved.

[0064] The acousto-optic deflector to be compensated is composed of two orthogonal acousto-optic deflector units 2.1 and 2.2, which are used for scanning femtosecond laser.

[0065] The one-dimensional rotating stage set is composed of a one-dimensional first rotating stage 3.1 and a second rotating stage 3.2, and is used for carrying and rotating the dispersion prism assembly.

[0066] In this embodiment, the first dispersion prism 1.1 and the second dispersion prism 1.2 are both standard prisms, and the materials and shapes of the two prisms are the same. Figure 4 Taking the first dispersion prism 1.1 as an example, the prism has a deflection effect on the incident light, as shown in Figure 5 As shown, the light beam has an incident angle I 11 Entering the prism, the outgoing light has a deflection angle θ relative to the incident light p , the spatial dispersion of the first dispersion prism 1.1 It is expressed as:

[0067]

[0068] Among them, I 11 is the incident angle of the laser relative to the first dispersion prism 1.1, α is the prism vertex angle, n is the prism refractive index, λ is the central wavelength of the incident light, is the first-order dispersion rate of the prism material.

[0069] Similarly, the spatial dispersion of the second dispersion prism 1.2 It is expressed as:

[0070]

[0071] Among them, I21 is the incident angle of the laser relative to the second dispersion prism 1.2, α is the prism vertex angle, n is the prism refractive index, λ is the central wavelength of the incident light, is the first-order dispersion rate of the prism material.

[0072] In this embodiment, the acousto-optic deflector 2 generates spatial dispersion when scanning the femtosecond laser. Figure 6 As shown, taking the acousto-optic deflector unit 2.1 as an example, there is an acousto-optic medium 9.1 in the acousto-optic deflector unit 2.1, and the light is deflected by an angle θ after being incident on the acousto-optic medium 9.1. A , which can be expressed as:

[0073]

[0074] Among them, f s is the acoustic field frequency of the acousto-optic deflector, v s is the speed of sound and λ is the wavelength.

[0075] Since femtosecond laser has a certain bandwidth in the spectrum, the deflection angle of each spectral component is different, such as Figure 6 , the component with a larger wavelength 5.2 in the beam has a difference angle Δθ relative to the component with a smaller wavelength 5.1 in the beam, which can be expressed as:

[0076]

[0077] Here, Δλ is the wavelength difference between the diffracted light 5.2 and the diffracted light 5.1.

[0078] Therefore, the spatial dispersion of the AOD 2 can be expressed as:

[0079]

[0080] Due to the different deflection angles of the diffracted light and the different heights on the receiving surface, after the femtosecond laser passes through the acousto-optic medium 9.1, an elliptical spot 6 is obtained on the receiving surface, and the elliptical spot will change the laser processing shape and reduce the laser processing accuracy. Therefore, the spatial dispersion of the acousto-optic deflector is compensated, so that the output light beam of the acousto-optic deflector is parallel light, and the output light beam is a circular spot under the focus of the focusing mirror.

[0081] like Figure 7 After the femtosecond laser pulse passes through the acousto-optic medium 9.1 in the acousto-optic deflector unit 2.1, group velocity dispersion is introduced due to the different propagation speeds of each spectral component in the acousto-optic medium 9.1, resulting in the input pulse 7.1 being broadened to the output pulse 7.2.

[0082] Group velocity dispersion GVD A It can be expressed as:

[0083]

[0084] Where λ is the central wavelength of the incident light, c is the speed of light, and n A is the refractive index of the acousto-optic crystal.

[0085] Temporal dispersion GDD of the acousto-optic deflector unit 2.1 A It can be expressed as the product of group velocity dispersion and the thickness of the acousto-optic crystal:

[0086]

[0087] Where l is the thickness of the acousto-optic crystal.

[0088] The stretched pulse τ out It can be expressed as:

[0089]

[0090] Among them, τ in The input pulse width is 7.1, τ out The output pulse width is 7.2.

[0091] The temporal dispersion of the AOD causes pulse broadening, which results in a decrease in the pulse peak power.

[0092] As a preferred implementation, when performing temporal dispersion compensation, the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is also fine-tuned to achieve compensation for the temporal dispersion additionally introduced by the dispersion prism group.

[0093] As an effective implementation method, the above configuration can be implemented as follows:

[0094] The first rotating table is placed vertically, that is, its table normal is parallel to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table of the first rotating table; the second rotating table is placed horizontally, that is, its table normal is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table.

[0095] Further preferably, the constraint that the spot of the monochromatic laser beam emitted from the dispersion prism group is circular is specifically:

[0096] The incident angle of the laser beam incident on the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

[0097] As a further preferred embodiment, the negative spatial dispersion generated by the dispersion prism group is:

[0098]

[0099] In the formula, represents the negative spatial dispersion, whose value is equal to or opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; Represents the spatial dispersion produced by a single dispersive prism;

[0100] By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass The incident angle of the laser beam incident on the dispersion prism group is obtained, that is, the incident angle of the laser beam incident on the first dispersion prism.

[0101] Further preferably, the acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units, the dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor, and the negative time dispersion GDD generated by the pulse compressor is:

[0102]

[0103] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the acoustic field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and its value is the opposite of the positive spatial dispersion of the acousto-optic deflector to be compensated.

[0104] In this embodiment, Figure 8 As shown, a schematic diagram of the dispersion compensation principle of an acousto-optic deflector based on an orthogonal prism group.

[0105] like Figure 8 As shown, the first rotating table 3.1 is perpendicular to the horizontal plane 8, and the second rotating table 3.2 is parallel to the horizontal plane 8. The first dispersion prism 1.1 is placed on the first rotating table 3.1 and rotates with L1 as the axis; the second dispersion prism 1.2 is placed on the second rotating table 3.2 and rotates with L2 as the axis. The femtosecond laser is incident parallel to the first rotating table near the top angle of the dispersion prism, and the incident angle of the femtosecond laser relative to the first dispersion prism 1.1 is equal to the incident angle of the femtosecond laser relative to the second dispersion prism 1.2. Finally, the output light of the acousto-optic deflector 2 is a group of parallel light, in which the component with a larger wavelength is 5.2 and the component with a smaller wavelength is 5.1.

[0106] The orthogonal prism group 1 is used to provide spatial dispersion pre-compensation, and together with the acousto-optic deflector 2, forms a pulse compressor to provide temporal dispersion pre-compensation and ensure that the light spot does not suffer from spatial distortion due to the prism structure;

[0107] The acousto-optic deflector 2 is used to scan the femtosecond laser.

[0108] The orthogonal one-dimensional rotating stage group 3 is used to carry and rotate the orthogonal prism group;

[0109] like Figure 3 In the figure above, when monochromatic light is incident, first, one axis of the light spot 4.1 is reduced (enlarged) by the dispersion prism 1.1 to obtain the light spot 4.2; then, the dispersion prism 1.2 reduces (enlarges) the other axis of the light spot 4.2 to obtain the light spot 4.3. The magnification of the first dispersion prism 1.1 and the second dispersion prism 1.2 is the same, both M, so the light spot does not suffer from spatial distortion due to the prism structure. The relationship corresponding to the magnification M is:

[0110]

[0111] Among them, I 11 is the incident angle of the femtosecond laser relative to the first dispersion prism 1.1, α is the prism vertex angle, and n is the prism refractive index.

[0112] The incident angle I of the femtosecond laser relative to the first dispersion prism 1.1 11 The incident angle I of the femtosecond laser relative to the dispersion prism 1.2 21 The laser beam is controlled to be incident on the dispersion prism group parallel to the first rotating table surface, and the incident angles of the first dispersion prism and the second dispersion prism are fine-tuned to the calculated incident angles by rotating the rotating table group to achieve spatial dispersion compensation.

[0113] The first dispersion prism 1.1 and the second dispersion prism 1.2 provide equal spatial dispersion in orthogonal directions, that is,

[0114]

[0115] in Represents the spatial dispersion produced by a single dispersion prism, and the subscripts 1 and 2 represent the first dispersion prism and the second dispersion prism, respectively.

[0116] The spatial dispersion provided by the orthogonal prism set 1 can be expressed as:

[0117]

[0118] in, is the spatial dispersion of orthogonal prism set 1.

[0119] When the spatial dispersion of the prism set 1 is equal to and opposite to the spatial dispersion of the AOD 2, the spatial dispersion of the AOD 2 is compensated.

[0120] The prism group 1 and the acousto-optic deflector 2 form a pulse compressor. The negative time dispersion GDD provided by the pulse compressor can be expressed as:

[0121]

[0122] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the acoustic field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the spatial dispersion of orthogonal prism set 1.

[0123] When the temporal dispersion of the pulse compressor is equal to and opposite to the temporal dispersion of the AOD 2, the temporal dispersion of the AOD 2 is compensated.

[0124] If a femtosecond laser with a wavelength of 1030 nm is used, an orthogonal equilateral dispersion prism set with a vertex angle of 60° and a material of N-SF11 is used to compensate for the spatiotemporal dispersion of the orthogonal acousto-optic deflector.

[0125] The refractive index of the prism made of N-SF11 is:

[0126]

[0127] in

[0128] B1=1.73759695

[0129] B2=0.313747346

[0130] B3=1.89878101

[0131] C1=0.013188707

[0132] C2=0.0623068142

[0133] C3=155.23629

[0134] When the wavelength is 1030nm, the refractive index of the dispersion prism 1.1 and the dispersion prism 1.2 is n = 1.7549, and the first-order dispersion rate is The relationship between the spatial dispersion of the orthogonal prism set 1 and the incident angle of the femtosecond laser relative to the dispersion prism 1.1 is calculated, as shown in FIG. Fig. 9 shown.

[0135] At this time, in order to compensate for the TeO2 acousto-optic deflector with a center frequency of 80 MHz, a sound velocity of 670 m / s, and an acousto-optic crystal length of 20 mm, the incident angle of the first dispersion prism 1.1 is I 11 =51.61°, the incident angle of the second dispersion prism 1.2 is also I 21 =51.61°, and the distance between the orthogonal prism group and the acousto-optic deflector is about 272.15mm.

[0136] As a preferred implementation, the above configuration is as follows:

[0137] The first rotating table is placed horizontally, that is, the normal line of the table surface is perpendicular to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table surface of the first rotating table; the second rotating table is placed horizontally, that is, the normal line of the table surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table;

[0138] The entire rotating stage assembly is rotated upward by 45° with the central axis of the laser beam vertically incident from the second dispersion prism to the acousto-optic deflector as the rotation axis.

[0139] On this basis, it is further preferred that the constraint that the spot of the monochromatic laser beam emitted from the dispersion prism group is circular is specifically:

[0140] The exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

[0141] On this basis, it is further preferred that the negative spatial dispersion generated by the dispersion prism group is:

[0142]

[0143] In the formula, represents the negative spatial dispersion, whose value is equal to or opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; represents the spatial dispersion produced by a single dispersion prism, subscripts 1 and 2 represent the first dispersion prism and the second dispersion prism respectively; M represents the magnification of the first dispersion prism;

[0144] By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass Obtaining an incident angle of the laser beam incident on the second dispersion prism;

[0145] According to the fact that the exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism, based on The incident angle value of the laser beam incident on the second dispersion prism is obtained, and the incident angle value of the laser beam incident on the first dispersion prism is calculated.

[0146] On this basis, it is further preferred that the acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units, and the dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor, and the negative time dispersion GDD generated by the pulse compressor is:

[0147]

[0148] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the acoustic field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and its value is the opposite of the positive spatial dispersion of the acousto-optic deflector to be compensated.

[0149] In this embodiment, Fig.10 As shown, a dispersion compensation principle diagram of an acousto-optic deflector based on a cascaded prism group. The cascaded one-dimensional rotating stage group 3 is placed at a 45° angle to the horizontal plane 8. The first dispersion prism 1.1 is placed on the first rotating stage 3.1 and rotates with L1 as the axis; the second dispersion prism 1.2 is placed on the second rotating stage 3.2 and rotates with L2 as the axis. The femtosecond laser is close to the prism vertex and is incident parallel to the first rotating stage surface. The exit angle of the femtosecond laser relative to the first dispersion prism 1.1 is equal to the incident angle of the femtosecond laser relative to the second dispersion prism 1.2. Finally, the output light of the acousto-optic deflector 2 is a group of parallel light, in which the component with a larger wavelength is 5.2 and the component with a smaller wavelength is 5.1.

[0150] The prism group 1 is used to provide spatial dispersion pre-compensation and form a pulse compressor with the acousto-optic deflector 2 to provide temporal dispersion pre-compensation and ensure that the light spot does not suffer from spatial distortion due to the prism structure; the acousto-optic deflector 2 is used to scan the femtosecond laser. The cascaded one-dimensional rotating stage group 3 is used to carry and rotate the cascaded prism group;

[0151] like Figure 3 In the figure below, when monochromatic light is incident, first, one axis of the light spot 4.1 is reduced (enlarged) by the dispersion prism 1.1 to obtain the light spot 4.2; then, the same axis of the light spot 4.2 is enlarged (reduced) by the dispersion prism 1.2 to obtain the light spot 4.3. Among them, the magnification of the first dispersion prism 1.1 is M, and the magnification of the second dispersion prism 1.2 is 1 / M, so the light spot does not suffer from spatial distortion due to the prism structure. The relationship corresponding to the magnification M of the first dispersion prism 1.1 is:

[0152]

[0153] Among them, I 11 is the incident angle of the femtosecond laser relative to the first dispersion prism 1.1, α is the prism vertex angle, and n is the prism refractive index.

[0154] The emission angle I of the femtosecond laser relative to the first dispersion prism 1.1 12 The incident angle I of the femtosecond laser relative to the second dispersion prism 1.2 21 Equal, can be expressed as:

[0155]

[0156] Among them, I 11 is the incident angle of the femtosecond laser relative to the first dispersion prism 1.1, I 12 is the exit angle of the femtosecond laser relative to the first dispersion prism 1.1, I 21 is the incident angle of the femtosecond laser relative to the second dispersion prism 1.2, α is the prism vertex angle, and n is the prism refractive index.

[0157] The laser beam is controlled to be incident on the dispersion prism group parallel to the first rotating table surface, and the incident angles of the first dispersion prism and the second dispersion prism are fine-tuned to the calculated incident angles by rotating the rotating table group to achieve spatial dispersion compensation.

[0158] The first dispersion prism 1.1 provides negative spatial dispersion, and the second dispersion prism 1.2 amplifies (reduces) the dispersion amount, and also provides a spatial dispersion itself. Therefore, the spatial dispersion amount provided by the cascaded prism group can be expressed as:

[0159]

[0160] in, is the spatial dispersion of prism group 1, M is the magnification of the first dispersion prism 1.1, Represents the spatial dispersion produced by a single dispersion prism, and the subscripts 1 and 2 represent the first dispersion prism and the second dispersion prism, respectively.

[0161] Since the exit angle of the first dispersion prism 1.1 is equal to the incident angle of the second dispersion prism 1.2, it can be deduced that:

[0162]

[0163] Therefore, the amount of spatial dispersion provided by the cascaded prism set can be expressed as:

[0164]

[0165] When the spatial dispersion of the prism set 1 is equal to and opposite to the spatial dispersion of the AOD 2, the spatial dispersion of the AOD 2 is compensated.

[0166] The cascaded prism group 1 and the acousto-optic deflector 2 form a pulse compressor. The negative time dispersion GDD provided by the pulse compressor can be expressed as:

[0167]

[0168] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f yis the acoustic field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the spatial dispersion of cascaded prism group 1.

[0169] When the temporal dispersion of the pulse compressor is equal to and opposite to the temporal dispersion of the AOD 2, the temporal dispersion of the AOD 2 is compensated.

[0170] Compared with the orthogonal prism group solution, the incident light spot and the exit light spot of the cascade prism group are equal in size, no additional beam expansion is required before the dispersion prism 1.1, and the dispersion prism 1.1 and the dispersion prism 1.2 are in the same plane, which is easier to operate.

[0171] If a femtosecond laser with a wavelength of 1030nm is used, and a cascaded equilateral dispersion prism set with a vertex angle of 60° and a material of N-SF11 is used to compensate for the spatiotemporal dispersion of the orthogonal acousto-optic deflector, then the refractive index n of the dispersion prism 1.1 and the dispersion prism 1.2 is n=1.7549, and the first-order dispersion rate The relationship between the spatial dispersion of the cascade prism group 1 and the incident angle of the femtosecond laser relative to the dispersion prism 1.2 is calculated, as shown in FIG. Fig.11 shown.

[0172] At this time, in order to compensate for the central frequency of 80MHz, the sound speed of 670m / s, the acousto-optic crystal length of 20mm, the TeO2 orthogonal acousto-optic deflector 2, the incident angle I of the dispersion prism 1.1 11 =68.88°, the incident angle I of the dispersion prism 1.2 21 =55.17°, and the distance between the cascaded prism group and the acousto-optic deflector is about 272.15 mm.

[0173] In general, the present invention uses a double prism to compensate for the spatiotemporal dispersion of the acousto-optic deflector. The price of the prism is lower than that of other dispersion compensation devices, which controls the system cost. By rotating the dispersion prism group to adjust the incident angle of the light beam, the spatial dispersion of the acousto-optic deflector is compensated while ensuring that the light spot does not undergo spatial distortion due to the prism. There is no need to customize prisms of specific materials and angles, which controls the system cost. In addition, since the present solution uses a prism group to avoid the spatial distortion of the light spot, the spatial dispersion compensation amount is continuously adjustable while the output light spot does not undergo spatial distortion due to the prism. The adjustment is flexible and has a wide range of applications. The temporal dispersion of the acousto-optic deflector is compensated by changing the spacing between the prism group and the acousto-optic deflector. Regarding the compensation of temporal dispersion, it should be noted that because the prism group will introduce a small amount of additional temporal dispersion, by fine-tuning the spacing, the temporal dispersion of the acousto-optic deflector itself and the additional temporal dispersion introduced by the prism group are compensated at the same time.

[0174] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, characterized in that: include: A dispersion prism group and a rotating stage group are configured; the rotating stage group includes a first rotating stage and a second rotating stage; the dispersion prism group includes a first dispersion prism arranged on the first rotating stage and a second dispersion prism arranged on the second rotating stage; the second dispersion prism is located on the vertical incident path of the laser beam of the acousto-optic deflector to be compensated; the laser beam first passes through the first dispersion prism and then passes through the second dispersion prism; Taking the circular spot of the monochromatic laser beam emitted from the dispersion prism group as a constraint, calculate the incident angle of the laser beam incident on the first dispersion prism and the second dispersion prism when the negative spatial dispersion generated by the dispersion prism group is equal to and opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; taking the incident angle of the laser beam incident on the first dispersion prism and the second dispersion prism and the vertical incidence of the laser beam emitted from the dispersion prism group on the receiving surface of the acousto-optic deflector to be compensated as constraints, determine and adjust the relative spatial position between the two prisms; control the laser beam to be incident on the dispersion prism group parallel to the table surface of the first rotating table, and rotate the rotating table group to fine-tune the incident angle of the first dispersion prism and the second dispersion prism to the calculated incident angle, so as to achieve spatial dispersion compensation; Adjust the spatial positions of the two prisms so that the laser beam is transmitted near the edge region of each dispersion prism; When the negative time dispersion generated by the dispersion prism group is equal to or opposite to the positive time dispersion of the acousto-optic deflector to be compensated, the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is calculated and adjusted to achieve time dispersion compensation.

2. The method for compensating dispersion of an acousto-optic deflector according to claim 1, characterized in that: When performing temporal dispersion compensation, the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is also fine-tuned to achieve compensation for the temporal dispersion additionally introduced by the dispersion prism group.

3. The method for compensating dispersion of an acousto-optic deflector according to claim 1, characterized in that: The configuration is implemented as follows: The first rotating table is placed vertically, that is, its table normal is parallel to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table of the first rotating table; the second rotating table is placed horizontally, that is, its table normal is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table.

4. The method for compensating dispersion of an acousto-optic deflector according to claim 3, characterized in that: The constraints for the monochromatic laser beam spot emitted from the dispersion prism group to be circular are as follows: The incident angle of the laser beam incident on the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

5. The method for compensating dispersion of an acousto-optic deflector according to claim 3, characterized in that: The negative spatial dispersion produced by the dispersion prism group is: In the formula, represents the negative spatial dispersion, whose value is equal to or opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; Represents the spatial dispersion produced by a single dispersive prism; By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass The incident angle of the laser beam incident on the dispersion prism group is obtained, that is, the incident angle of the laser beam incident on the first dispersion prism.

6. The method for compensating dispersion of an acousto-optic deflector according to claim 3, characterized in that: The acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units. The dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor. The negative time dispersion GDD generated by the pulse compressor is: in, λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, f y is the acoustic field frequency of the AOD scanned in the vertical direction, f x is the acoustic field frequency of the AOD scanned in the horizontal direction, υ s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and its value is the opposite of the positive spatial dispersion of the acousto-optic deflector to be compensated.

7. The method for compensating dispersion of an acousto-optic deflector according to claim 1, characterized in that: The configuration method is: The first rotating table is placed horizontally, that is, the normal line of the table surface is perpendicular to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table surface of the first rotating table; the second rotating table is placed horizontally, that is, the normal line of the table surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table; The entire rotating stage assembly is rotated upward by 45° with the central axis of the laser beam vertically incident from the second dispersion prism to the acousto-optic deflector as the rotation axis.

8. The method for compensating dispersion of an acousto-optic deflector according to claim 7, characterized in that: The constraints for the monochromatic laser beam spot emitted from the dispersion prism group to be circular are as follows: The exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

9. The method for compensating dispersion of an acousto-optic deflector according to claim 7, characterized in that: The negative spatial dispersion produced by the dispersion prism group is: In the formula, represents the negative spatial dispersion, whose value is equal to or opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; represents the spatial dispersion produced by a single dispersion prism, subscripts 1 and 2 represent the first dispersion prism and the second dispersion prism respectively; M represents the magnification of the first dispersion prism; By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass Obtaining an incident angle of the laser beam incident on the second dispersion prism; According to the fact that the exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism, based on The incident angle value of the laser beam incident on the second dispersion prism is obtained, and the incident angle value of the laser beam incident on the first dispersion prism is calculated.

10. The method for compensating dispersion of an acousto-optic deflector according to claim 7, characterized in that: The acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units. The dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor. The negative time dispersion GDD generated by the pulse compressor is: Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the acoustic field frequency of the AOD scanned in the vertical direction, f x is the acoustic field frequency of the AOD scanned in the horizontal direction, υ s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and its value is the opposite of the positive spatial dispersion of the acousto-optic deflector to be compensated.

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