Method for relieving laser near-field modulation caused by splicing of spliced gratings

Abstract

The invention relates to a method for relieving laser near-field modulation caused by splicing of a spliced grating by using a light beam soft edge of a nested inverted super Gaussian function, which comprises the following steps of: shaping light beam spatial distribution at the front end of a kilojoule picosecond laser system by using amplitude modulators such as a soft edge diaphragm or a spatial light modulator; according to the optical grating compressor, the embedded inverted super Gaussian soft edge distribution is arranged at the corresponding position of the optical grating abutted seam, the inner layer is an inverted high-order super Gaussian function, and the outer layer is an inverted low-order super Gaussian function, so that when a light beam is transmitted to the first optical grating of the optical grating compressor, the optical grating abutted seam is shielded by the soft edge; therefore, near-field energy flow modulation at the last grating of the compressor and a subsequent optical element caused by the splicing seams of the gratings is smoothed, and the risk of laser damage is reduced. The method has the advantages of being low in energy loss and convenient to implement, the problem that extra energy flow modulation occurs after a single super Gaussian soft edge is subjected to spatial filtering and diffraction transmission in the compressor is solved, and the damage risk of downstream optical elements is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of high-power laser near-field modulation mitigation technology, specifically to a method for mitigating output near-field energy flow modulation caused by the splicing seams of the splicing grating in the compressor of a kilojoule picosecond petawatt laser system. Background Technology

[0002] Chirped pulse amplification (CPA) is an indispensable enabling technology for generating high-energy short-pulse lasers, involving the broadening, amplification, and compression of laser pulses. To achieve kilojoule-level pulse energy, the beam aperture reaches hundreds of millimeters after amplification, requiring meter-level dimensions in the dispersion direction of the pulse compression grating. Grating splicing is one of the main technical routes for manufacturing meter-scale gratings. Mature grating splicing techniques include mechanical splicing and exposure splicing, both of which produce spliced ​​gratings with seams. In high-energy picosecond laser systems, the diffraction effect of the upstream splicing grating seams, leading to near-field modulation of the laser, can easily cause laser damage to downstream optical components, especially the last grating of the compressor, severely limiting the output capability of the laser device and threatening the safe operation of the system.

[0003] To alleviate the near-field modulation of the laser caused by the seam, the solution of a typical high-energy picosecond laser system in the prior art [1] (J. Bromage, SWIBAhk, D. Irwin, et al. A focal-spot diagnostic for on-shot characterization of high-energy petawatt lasers[J]. Optics Express, 2008, 16(21): 16561-16572.) is to split the beam into two sub-beams at the front end so that when the beam is transmitted to the compressor, there is no light field in the area corresponding to the seam. This method avoids the influence of the mechanical splicing grating seam, but it will cause a large energy loss. For the exposure splicing grating, the prior art [2] (Chen Xinrong, Method and grating for suppressing the straight edge diffraction effect of splicing grating seam, CN118377075A) proposes a mitigation method by symmetrically setting grating teeth of different groove depths on both sides of the seam so that the corresponding area of ​​the grating has a gradually changing diffraction efficiency to suppress the straight edge diffraction effect of the seam. However, this method requires precise control of the exposure stitching process, which is difficult to implement. In addition, in the existing high-power laser damage point shielding technology [3] (SWBahk, JDZuegel, JRFienup, et al. Spot-shadowing optimization to mitigate damage growth in a high-energy-laser amplifier chain[J]. Applied Optics, 2008, 47(35): 6586-6593.), the method of using near-field beam shaping to shield the stitching seam has been pointed out. However, a single near-field shaping device cannot simultaneously modulate the amplitude and phase of the beam. To reduce system complexity, the existing technology [4] (YinBoZheng,RongSheng Ba,XinDa Zhou,et al.Spot-shadowing deployment for mitigating damage-growth of optics in high-power lasers based on a programmable spatialbeam-shaping system[J].Optics&Laser Technology,2018,108:602-608.) uses an inverted super-Gaussian amplitude soft edge to shield damage points to alleviate damage growth. When the other parameters are determined, the higher the order of the super-Gaussian function, the better the shielding effect on damage points.However, due to the low damage threshold of near-field shaping devices, beam shaping can only be performed at the front end of high-energy picosecond systems. After the beam passes through the spatial filter in the amplification link and is transmitted inside the compressor, the high-order inverted super-Gaussian soft edge distribution will generate additional energy flow modulation. Summary of the Invention

[0004] This invention proposes a method to alleviate laser near-field modulation caused by the seams of spliced ​​gratings by using the soft edge of the beam with a nested inverted super-Gaussian function. The aim is to overcome the problems of high energy loss, high implementation difficulty, or additional energy flow modulation caused by existing solutions.

[0005] The technical solution of this invention is as follows:

[0006] A method for mitigating near-field modulation of laser beams caused by seams in splicing gratings is characterized by using an amplitude modulator at the front end of a kilojoule picosecond laser system to modulate the beam distribution along the grating dispersion direction into a nested inverted super-Gaussian function soft edge. This modulated beam is then transmitted through a laser amplification link to a splicing grating compressor to shield the grating seams. The inner layer of this nested inverted super-Gaussian soft edge is a high-order super-Gaussian function, which provides better shielding against seams. Since the Gaussian soft edge is significantly affected by spatial filtering in the laser amplification link, the outer layer is set to a low-order super-Gaussian function to smooth out the additional energy flux modulation generated by the high-order super-Gaussian soft edge of the inner layer after spatial filtering and diffraction transmission within the compressor.

[0007] The transmittance function of the nested inverted super-Gaussian soft edge follows the formula below:

[0008]

[0009] Where A(x) is the normalized amplitude transmittance distribution along the x-direction of the soft edge, the x-direction refers to the dispersion direction of the splicing grating, i.e., perpendicular to the splicing seam direction, x0 is the x-axis position corresponding to the splicing seam, and x0 = 0 when the splicing seam is located in the center of the grating, exp represents the exponential function with the natural constant e as the base; R1 and R2 are the transparency parameters of the outer and inner super-Gaussian functions, respectively, used to adjust the transmittance of the soft edge region, and 0 <R1≤1,0<R2≤1;σ x1 ,σ x2 e is the corresponding supergaussian function -2 The half-width at the intensity, where e is the inner supergaussian function. -2 Half-width σ x2 The value range corresponds to the projection width of the seam onto the incident beam surface, and varies depending on the width of the grating seam projected onto the incident beam surface that needs to be shielded. For exposure splicing gratings, the width of the grating seam projected onto the incident beam surface is approximately 1–1.6 mm. Dividing this by the beam expansion factor yields σ. x2The reference range for the value of ; the e of the outer supergaussian function -2 Half-width σ x1 The spatial filter cutoff frequency for matching the laser amplification link can be σ. x2 Several times, but should not be greater than σ. x2 To avoid excessive energy loss, 10 times the amount, i.e., σ x2 <σ x1 ≤10σ x2 D is the half-width at 1% of the maximum value of the inner super-Gaussian distribution, and is related to σ. x2 The relationship is: 2N1 and 2N2 are the orders of the inner and outer super-Gaussian functions. The higher the order, the steeper the function shape and the closer it is to a step function, and 2N1≤N2. The range of 2N2 is considered to be 2≤2N2≤12. The higher the order, the lower the energy loss, but the manufacturing difficulty of the amplitude modulation device will also increase. The lower the order of the outer super-Gaussian function 2N1, the better, so as to avoid additional energy flow modulation caused by diffraction.

[0010] By using the seam of the first splicing grating in this nested inverted super-Gaussian soft-edge shielded grating compressor, the near-field energy flow modulation caused by the seam diffraction effect can be smoothed, and the additional energy flow modulation generated by a single inverted super-Gaussian soft edge after spatial filtering and diffraction transmission inside the grating compressor can be suppressed.

[0011] The amplitude modulation device is a spatial light modulator, a soft-edge aperture, or other beam shaping device.

[0012] The grating compressor is a single-pass dual-grating pair compressor or a dual-pass single-grating pair compressor, and the near field refers to the near field distribution at the last grating of the grating compressor.

[0013] This invention only shields the seam of the first splicing grating in the grating compressor. This is because the angular dispersion of the second and third gratings causes a linear shift in the spatial position of the seam with wavelength, thus smoothing the near-field energy flux modulation caused by the seam. Furthermore, unlike damage point shielding techniques, since the position of the grating seam is constant, a static beam near-field shaping module can be used to shield the seam. Therefore, this solution is based on static optical design and essentially eliminates the need for complex real-time feedback control.

[0014] Beneficial technical effects of the present invention:

[0015] A seam shielding method with lower energy loss, easier implementation, and no additional energy flux modulation is achieved through the soft edges of nested inverted super-Gaussian functions. The nested super-Gaussian soft edges lose approximately 3% of energy, reducing the modulation increase at the near-field of the fourth grating caused by the diffraction effect of the 5mm wide first grating seam from 1.7 to 1.13. For the 3mm wide first grating seam, the near-field modulation of the fourth grating caused by its diffraction is reduced from 1.53 to 1.16.

[0016] Furthermore, compared to schemes requiring dynamic wavefront modulation, this invention employs static optical shaping, eliminating the need for a complex real-time feedback control system. This significantly reduces system complexity and cost, while improving long-term stability and reliability. The specific innovation lies in using nested inverted super-Gaussian soft edges as the transmittance function of the near-field beam shaping element. The additional modulation generated after the high-order super-Gaussian distribution of the smooth inner layer passes through the spatial filter and compressor's internal near-field transmission is eliminated without feedback control, resulting in low system complexity. Attached Figure Description

[0017] Figure 1 This is a schematic diagram showing the relative positions of the beam amplitude shaping device and the splicing grating compressor described in this invention in a kilojoule picosecond petawatt laser system.

[0018] Figure 2 (a) is a schematic diagram of the distribution of the diffraction beam at the center frequency when the seam width of the first grating is 5 mm. Figure 2 (b) is the near-field energy flow modulation pattern of the fourth grating caused by the diffraction of the 5mm wide seam of the first grating. Figure 2 (c) is a schematic diagram of the distribution of the diffraction beam at the center frequency when the seam width of the first grating is 3mm. Figure 2 (d) is the near-field energy flow modulation pattern of the fourth grating caused by the diffraction of the 3mm wide seam of the first grating.

[0019] Figure 3 (a) is a schematic diagram of Example 1, which uses only the inner layer inverted super-Gaussian soft edge. Figure 3 (b) is Figure 3 (a) Energy flux distribution at the image transfer surface after passing through a spatial filter with a 30x diffraction-limited (DL) aperture. Figure 3 (c) is a schematic diagram of the shielding of the seam of the first grating. Figure 3 (d) is the near-field energy flow modulation diagram of the fourth grating after shielding.

[0020] Figure 4 (a) is a schematic diagram of Example 1, which uses only the outer inverted super-Gaussian soft edge. Figure 4 (b) is Figure 4 (a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 4(c) is a schematic diagram of the shielding of the seam of the first grating. Figure 4 (d) is the near-field energy flow modulation diagram of the fourth grating after shielding.

[0021] Figure 5 (a) is a schematic diagram of the nested inverted super-Gaussian soft edge in Example 1. Figure 5 (b) is Figure 5 (a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 5 (c) is a schematic diagram of the shielding of the seam of the first grating. Figure 5 (d) is the near-field energy flow modulation diagram of the fourth grating after shielding.

[0022] Figure 6 (a) is a schematic diagram of the nested inverted super-Gaussian soft edge in Example 2. Figure 6 (b) is Figure 6 (a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 6 (c) is a schematic diagram of the shielding of the seam of the first grating. Figure 6 (d) is the near-field energy flow modulation diagram of the fourth grating after shielding.

[0023] Figure 7 This is a schematic diagram of the nested inverted super-Gaussian soft edge in Example 3. Figure 7 (b) is Figure 7 (a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 7 (c) is a schematic diagram of the shielding of the seam of the first grating. Figure 7 (d) is the near-field energy flow modulation diagram of the fourth grating after shielding. Detailed Implementation

[0024] Figure 1 This diagram illustrates the relative positions of the near-field beam shaping device and the Treacy structure single-pass dual-grating compressor in a kilojoule picosecond petawatt laser system. After being modulated by the amplitude shaping device 2 in the front-end injection system 1, the beam passes through the first-stage spatial filter 3, the main amplification system 4, and the final-stage spatial filter 5 before being transmitted to the grating compressor 6. The main amplification system 4 includes multiple stages of rod and sheet amplifiers with different apertures and a built-in spatial filter. The beam transmission within the main amplification system is achieved through spatial filtering, image transmission, and aperture amplification via the built-in spatial filter. The amplitude shaping device 2 is assumed to directly transmit the image to the surface of the first grating in the grating compressor 6 via the spatial filter in the amplification link. Since the primary concern is the modulation growth caused by grating seam diffraction, the amplifier is assumed to uniformly amplify the laser. When the beam reaches the grating compressor 6, it is incident on the first grating at a 71° angle, and the width of the exposed grating seam is typically 3–5 mm. Figure 2 (a) is a schematic diagram showing the distribution of the 5mm wide seam of the first grating on the diffraction beam surface at the center frequency. The zero-intensity aperture of the incident beam is 320×320mm. 2 . Figure 2 (b) is the near-field energy flow modulation pattern of the fourth grating caused by the seam of the first grating. The 5mm wide grating seam caused a modulation increase of 1.7 times. Figure 2 (c) is a schematic diagram of the distribution of the 3mm wide seam of the first grating on the diffraction beam surface at the center frequency. Figure 2 (d) is the near-field energy flow modulation diagram of the fourth grating caused by the seam of the first grating. The 3mm wide grating seam caused a modulation increase of 1.53 times.

[0025] The 5mm wide grating seam corresponds to an incident beam width of only about 1.6mm, and the diffracted beam width to the center frequency is about 2.3mm. Therefore, in Example 1, to reduce energy loss and achieve good seam shielding, under the conditions of a kilojoule picosecond petawatt laser system, the transparency R1 of the outer super-Gaussian soft edge is set to 0.2. -2 Half-width σ x1 The width is set to correspond to the cutoff frequency of the filter aperture, and its order 2N1 is set to the lowest order, 4th. The e of the inner soft edge... -2 Half-width σ x2 The width of the seam projection onto the compressor's incident beam surface is taken as the reference point. Based on experience with damage point shielding techniques, Example 1 employs a nested inverted super-Gaussian soft-edge distribution with an outer layer of inverted fourth-order super-Gaussian functions and an inner layer of inverted tenth-order super-Gaussian functions. The transparency R2 is set to 1 to mitigate laser near-field modulation caused by the 5mm wide grating seam. Specifically, the parameters of the inner super-Gaussian function are set as follows:

[0026] R2=1,σ x2 =1.6 / R D mm, 2N2=10

[0027] Where R D The beam expansion factor of the spatial filter is used to expand the beam of each stage of the spatial filter in the kilojoule picosecond laser system to 30×30mm. 2 The beam expansion is 320×320mm 2 Among the various levels of spatial filters, the spatial filter with the smallest aperture constrains the transmission properties of the entire amplification link. Based on the actual operation of the system, the transmission process is equivalent to a spatial filter with a 30x diffraction-limited (DL) aperture. Figure 3 (a) is a schematic diagram of the soft edge of the inner inverted super-Gaussian beam used only in Example 1, and its energy ratio with that of the case without soft edge is 98.8%. Figure 3 (b) is Figure 3(a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 3 (c) is a schematic diagram of the shielding of the first grating seam by the inner soft edge in Embodiment 1. Figure 3 (d) shows the near-field energy flux modulation at the fourth grating after inner soft-edge shielding. The modulation index decreases from 1.7 to 1.32, meaning that when only the inner soft-edge is used for shielding, an additional 1.3 times energy flux modulation occurs at the edge of the soft edge, while the beam modulation caused by the seam is shielded. Based on calculations of the transmission properties of a 30x DL aperture microaperture spatial filter, the parameters of the outer super-Gaussian function are set as follows:

[0028] R1=0.2,σ x1 =8 / R D mm, 2N1 = 4

[0029] Figure 4 (a) is a schematic diagram of the soft edge of the outer inverted super-Gaussian beam used only in Example 1, and its energy ratio with that of the case without the soft edge is 98%. Figure 4 (b) is Figure 4 (a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 4 (c) is a schematic diagram of the shielding of the first grating seam by the outer soft edge in Embodiment 1. Figure 4 (d) is the near-field energy flux modulation diagram at the fourth grating after the inner soft edge shielding. The modulation degree decreased from 1.7 to 1.21, that is, when only the outer soft edge is used for shielding, the transparency is not enough and it cannot completely shield the energy flux modulation caused by the splice. A 1.2-fold energy flux modulation appeared at both the splice edge and the soft edge edge. Moreover, the soft edge edge position is affected by the splice diffraction sidelobe and has multiple peaks.

[0030] Figure 5 (a) is a schematic diagram of the soft edge in Example 1, which shows that the energy ratio of the nested inverted super-Gaussian soft edge beam distribution to the case without a beam soft edge is 97.2%, which is only about 3% lower than the energy. Figure 5 (b) is Figure 5 (a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 5 (c) is a schematic diagram of the shielding of the seam of the first grating. Figure 5 (d) shows the near-field energy flow modulation pattern of the fourth grating after shielding, with a modulation index of 1.13. Clearly, the nested inverted super-Gaussian soft-edge distribution provides better seam shielding than using only the inner or outer layer inverted super-Gaussian soft-edge distribution.

[0031] To account for the influence of the order of the inner super-Gaussian function while keeping other parameters constant, the nested super-Gaussian soft-edge parameters used in Example 2 are as follows:

[0032] R1=0.2,σ x1 =8 / R D mm, 2N1 = 4

[0033] R2=1,σ x2 =1 / R D mm, 2N2=4

[0034] Figure 6 (a) is a schematic diagram of the soft edge in Example 2, which shows that the ratio of the energy of the nested inverted super-Gaussian soft edge beam distribution to that of the case without a beam soft edge is 97%. Figure 6 (b) is Figure 6 (a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 6 (c) is a schematic diagram of the shielding of the seam of the first grating. Figure 6 (d) shows the near-field energy flow modulation diagram of the fourth grating after shielding, with a modulation index of 1.13. It can be seen that the results of Example 2 are not significantly different from those of Example 1. Theoretical calculations show that the results using inverted inner super-Gaussian soft edges of orders 6, 8, and 12 are also similar. This indicates that, with appropriate outer super-Gaussian function parameters, the control requirements for the order of the inner super-Gaussian function are not strict, making this invention more flexible.

[0035] Example 3 employs a nested super-Gaussian soft edge to mitigate laser near-field modulation caused by a 3mm wide seam. The seam corresponds to an incident beam width of approximately 1mm and a diffracted beam width of approximately 1.4mm at the center frequency. The parameters of the nested super-Gaussian function used are:

[0036] R1=0.2,σ x1 =8 / R D mm, 2N1 = 4

[0037] R2=1,σ x2 =1 / R D mm, 2N2=10

[0038] Figure 7 (a) is a schematic diagram of the soft edge in Example 3, which shows that the ratio of the energy of the nested inverted super-Gaussian soft edge beam distribution to that of the soft edge without beam is 97.5%. Figure 7 (b) is Figure 7 (a) Energy flux distribution on the image transfer surface after passing through a spatial filter with a 30x DL aperture. Figure 7 (c) is a schematic diagram of the shielding of the seam of the first grating. Figure 5 (d) shows the near-field energy flow modulation pattern of the fourth grating after shielding, with a modulation index of 1.17, slightly larger than the result with a 5mm seam. Figure 1 It can be seen that because the energy flow modulation of the narrow slit diffraction side lobes is stronger, it has a stronger effect on the soft edge.

[0039] As can be seen, in each embodiment, under the condition of losing less input energy, the laser near-field modulation caused by the seam is greatly smoothed, which effectively reduces the risk of laser damage and is of great significance to ensuring the safe operation of the system.

Claims

1. A method for mitigating laser near-field modulation caused by the seams of spliced ​​gratings, characterized in that, In the front-end system of a kilojoule picosecond laser system, an amplitude modulation device is used to modulate the distribution of the light beam in the grating dispersion direction into a nested inverted super-Gaussian function light beam soft edge, so that the modulated light beam passes through a laser amplification link and is transmitted to a spliced grating compressor to shield the grating seams, and the transmittance function of the nested inverted super-Gaussian soft edge satisfies: wherein, n is the order of the super-Gaussian function, and σ is the width of the super-Gaussian function. where A(x) is the normalized amplitude transmittance distribution of the soft edge in x direction, x direction refers to the dispersion direction of the tiled gratings, i.e. perpendicular to the tile seam direction, x0 is the x axis position corresponding to the tile seam, x0=0 when the tile seam is located at the center of the grating, exp represents the exponential function with the natural constant e as the base; R1, R2 are the transparency parameters of the outer super-Gaussian function and the inner super-Gaussian function respectively, used to adjust the transmittance of the soft edge region, and 0 x1 ,σ x2 is the e -2 half width at the corresponding super-Gaussian function, wherein the e -2 half width σ x2 of the inner super-Gaussian function corresponds to the projected width of the tile seam on the incident light beam plane, the e -2 half width σ x1 of the outer super-Gaussian function matches the spatial filtering cutoff frequency of the laser amplification link, and σ x2 <σ x1 ≤10σ x2 ; D is the half width at 1% of the maximum value of the inner super-Gaussian distribution, and the relationship with σ x2 is: 2N1,2N2 are the orders of the corresponding super-Gaussian functions, the higher the order, the closer the soft edge to the step function, and 2N1≤N2; By shielding the seams of the first spliced grating in the grating compressor with the nested inverted super-Gaussian soft edge, the near-field energy flow modulation caused by the uniform sliding of the seams can be smoothed, and the additional energy flow modulation caused by the transmission of a single inverted super-Gaussian soft edge through spatial filtering and internal diffraction of the grating compressor can be suppressed.

2. The method for mitigating laser near-field modulation caused by the seams of spliced ​​gratings according to claim 1, characterized in that, The order of the inner super-Gaussian function is 2N2, and the value range of 2N2 is: 2≤2N2≤12.

3. The method for mitigating laser near-field modulation caused by the seams of spliced ​​gratings according to claim 1, characterized in that, The order 2N1 of the outer super-Gaussian function is set to 4th order, its e -2 Half-width σ x1 The spatial filter cutoff frequency of the matching laser amplifier link; the order 2N2 of the inner super-Gaussian function is set to 10th order, its e -2 Half-width σ x2 Corresponding to the width of the joint projected to the compressor incident beam surface; the transmittance parameter R1 of the outer super-Gaussian function is 0.2, and the transmittance parameter R2 of the inner super-Gaussian function is 1.

4. The method for mitigating laser near-field modulation caused by the seams of spliced ​​gratings according to claim 1, characterized in that, The order 2N1 of the outer super-Gaussian function is set to 4th order, and its e -2 Half-width σ x1 The spatial filter cutoff frequency of the matching laser amplifier link; the order 2N2 of the inner super-Gaussian function is set to 4th order, and its e -2 Half-width σ x2 Corresponding to the width of the joint projected to the compressor incident beam surface; the transmittance parameter R1 of the outer super-Gaussian function is 0.2, and the transmittance parameter R2 of the inner super-Gaussian function is 1.

5. The method of mitigating laser near-field modulation due to the aperture of a tiled grating according to any of claims 1-4, wherein, The amplitude modulation device is a spatial light modulator, a soft edge diaphragm or other beam shaping device.

6. The method of mitigating laser near-field modulation due to the aperture of a tiled grating according to any of claims 1-4, wherein, The grating compressor is a single-pass double-grating pair compressor or a double-pass single-grating pair compressor, and the near field refers to the near field distribution at the last grating of the grating compressor.

7. The method of mitigating laser near-field modulation due to the aperture of a tiled grating according to any of claims 1-4, wherein, After the laser pulse is injected from the front end, it is transmitted to the grating compressor in turn through the first-stage spatial filter, the main amplification system and the final-stage spatial filter; the main amplification system includes multiple laser amplifiers and built-in spatial filters, and when the light beam is transmitted in the main amplification system, spatial filtering, image transfer and aperture amplification are realized through the built-in spatial filters.

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