Medium type pulse compression grating with large deviation angle around center wavelength 1053 nm

Abstract

A medium type pulse compression grating with large deviation angle around the center wavelength 1053nm, including metal medium and all medium two configurations, the grating from bottom to top in the longitudinal direction includes metal medium or all medium film stack, high or low or high, low refractive index material matching at least one layer of barrier layer, and the top of the grating layer formed by the partial or complete etching of the low refractive index material transverse period distribution grating; The reflectivity of the two grating configurations before etching reaches 99%. The period of the grating layer grating is 625-1000nm, the etching depth is at least 300nm, the inclination angle is greater than 70°, and the width ratio is 0.2-0.6. The invention can be used under the condition of deviating from the Littrow angle of itself by more than 20°, and the-1 order diffraction efficiency is higher than 99% in the neodymium glass gain bandwidth. It is compatible with various compressor layouts, and has important economic and practical value in the field of high-energy lasers.

Description

Technical Field

[0001] This invention pertains to reflective gratings, and more particularly to a dielectric pulse compression grating with a large offset angle around a center wavelength of 1053 nm. Background Technology

[0002] Inertial confinement fusion, driven by high-power lasers, is at a critical juncture of major breakthroughs. Internationally, efforts are being accelerated to increase laser energy to support larger-scale fusion experiments and energy gains, while prioritizing clean energy and national security. Research institutions worldwide are utilizing chirped pulse amplification (CPA) and optical parameter chirped pulse amplification (OPCPA) techniques to push laser output energy to the kilojoule level, achieving peak power levels of tens of petawatts (PW).

[0003] In both CPA and OPCPA laser amplification technologies, the grating compressor is the core module. The key component of the grating compressor is the grating. Picosecond (ps) high-energy pulse compressors based on neodymium glass gain widely employ high-threshold dielectric gratings, including all-dielectric gratings and hybrid metallic-dielectric gratings.

[0004] Currently, the offset angle of pulse compression gratings with a center wavelength of 1053 nanometers (nm) is limited to no more than 10°, thus restricting the types of gratings that can be selected for compressors, the adjustable dispersion, and the layout size. While metallic gratings can provide a wide spectral width, their design principles, bandwidth, and angular characteristics differ significantly from those of dielectric gratings. To our knowledge, there are no reports on dielectric gratings with large offsets. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide a dielectric pulse compression grating with a large offset angle around a center wavelength of 1053 nm, specifically for pulse compressors with neodymium glass gain. This grating achieves a -1st-order diffraction efficiency greater than 99% within the required bandwidth at incident angles exceeding 20° off-center from its Littrow angle. The applicable period for this grating ranges from 625 to 1000 nm, demonstrating practical value. This large offset angle grating has significant economic and application value in the broadening and compression of high-energy pulses.

[0006] The technical solution of the present invention is as follows:

[0007] A dielectric pulse compression grating with a large offset angle around a center wavelength of 1053 nm, comprising both all-dielectric and metallic dielectric configurations, is characterized by:

[0008] The aforementioned all-dielectric grating configuration comprises, in the longitudinal direction from bottom to top, at least sixteen layers of dielectric film stacked with alternating high and low refractive index materials, at least one barrier layer composed of high or low or high and low refractive index materials, and a grating layer at the top formed by partially or completely etching low refractive index material with transversely periodically distributed grating strips.

[0009] The aforementioned metallic dielectric grating configuration comprises, in the longitudinal direction from bottom to top, a metal layer that provides high reflectivity, a dielectric film stack of at least six layers of alternating high and low refractive index materials, a barrier layer consisting of at least one layer of high or low or high and low refractive index materials, and a grating layer at the top formed by partially or completely etching low refractive index materials with transversely periodically distributed grating stripes.

[0010] The refractive index range of the high refractive index material is 1.8 to 2.1;

[0011] The refractive index range of the low-refractive-index material is 1.3 to 1.5;

[0012] The reflectivity of both grating configurations before etching reaches 99%;

[0013] The grating layer has a period of 625–1000 nm, an etching depth of at least 300 nm, an inclination angle greater than 70°, and an aspect ratio of 0.2–0.6.

[0014] The technical effects of this invention are as follows:

[0015] 1) The grating of the present invention can achieve a -1st order diffraction efficiency of over 99% in the neodymium glass gain bandwidth under incident conditions with an incident angle exceeding 20° from its own Littrow angle.

[0016] 2) The grating period of the present invention can be extended from 625nm to 1000nm.

[0017] 3) The grating of the present invention can be compatible with various compressor layouts, thereby achieving various dispersion adjustments with a fixed grating pair spacing.

[0018] 4) The grating structure of this invention is simple and easy to manufacture. The product aperture can be extended to the meter level, which has important economic and practical value in the field of high-energy lasers. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of embodiment 1 of the present invention, which has a large offset angle around a center wavelength of 1053nm.

[0020] Figure 2 This is a graph showing the relationship between the -1st order diffraction efficiency and the incident angle of the grating at 1053nm in Example 1.

[0021] Figure 3 The diagram shows the relationship between the -1st order diffraction effect and wavelength when the grating of Example 1 is incident at 22.2, 41.3 and 70 Å, respectively.

[0022] Figure 4 This is a layout diagram of a grating compressor with an incident angle smaller than the Littrow angle.

[0023] Figure 5 This is a layout diagram of a grating compressor with an incident angle equal to the Littrow angle.

[0024] Figure 6 This is a layout diagram of a grating compressor with an incident angle greater than the Littrow angle.

[0025] Figure 7 This is a schematic diagram of the structure of embodiment 2 of the present invention, which has a large offset angle around a center wavelength of 1053nm.

[0026] Figure 8 This is a graph showing the relationship between the -1st order diffraction efficiency and the incident angle of the grating at 1053nm in Example 2.

[0027] Figure 9 This is a graph showing the relationship between the -1st order diffraction effect and wavelength when the grating of Example 2 is incident at 29.9 and 77.2 nm, respectively.

[0028] In the picture:

[0029] 1-Substrate, 2-Multilayer module stack, 3-Barrier layer, 4-Grating layer, 5-Low refractive index layer, 6-High refractive index layer, 7-Metal layer, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18-Large offset angle grating, 14-Retrospective mirror, f-Aspect ratio, Λ-Period, d H -Physical thickness of high refractive index layer in multilayer stack, d L -Physical thickness of low refractive index layer in multilayer module 2, d B1 d B2 d B3 -Thickness of each layer in barrier layer 3, d G - The etching depth in grating layer 4, d R - The physical thickness of the remaining film layer after etching in grating layer 4, β - tilt angle. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0031] Please refer to Figure 1 , Figure 1This is a schematic diagram of the structure of Embodiment 1 of the dielectric pulse compression grating with a large offset angle around a center wavelength of 1053nm according to the present invention. As can be seen from the figure, the dielectric pulse compression grating with a large offset angle around a center wavelength of 1053nm is composed of, from bottom to top, a base layer 1, a high-reflectivity metal layer 7, a dielectric film stack 2 consisting of at least six layers of alternating high-refractive-index and low-refractive-index materials, a barrier layer 3 consisting of at least one layer of high-refractive-index and low-refractive-index materials, and a grating layer 4 with transversely periodically distributed grating stripes formed by partial or complete etching of low-refractive-index material.

[0032] See Figure 7 , Figure 7 This is a schematic diagram of the structure of embodiment 2 of the dielectric pulse compression grating with a large offset angle around a center wavelength of 1053nm according to the present invention. As can be seen from the figure, the structure of the all-dielectric dielectric pulse compression grating with a large offset angle around a center wavelength of 1053nm includes, from bottom to top, a base layer 1, a dielectric film stack 2 of at least sixteen layers of alternating high refractive index material and low refractive index material, a barrier layer 3 composed of at least one layer of high refractive index material and low refractive index material, and a grating layer 4 with transversely periodically distributed grating stripes formed by partial or complete etching of low refractive index material.

[0033] The refractive index range of the high refractive index material 6 is selected from 1.8 to 2.1, and the refractive index range of the low refractive index material 5 is selected from 1.3 to 1.5.

[0034] Both grating configurations achieved a reflectivity of 99% before etching. Except for the top grating layer, the physical thickness of each layer in each part was controlled to be below 500 nm.

[0035] The initial setting range for the structural parameters of the grating layer strips is as follows: period in the range of 625–1000 nm, and etching depth d. G At least 300nm, tilt angle β greater than 70-90°, and aspect ratio f 0.2-0.6.

[0036] Example 1:

[0037] Large offset angle metallic dielectric grating, such as Figure 1 As shown. The grating film system is: Sub / Au / (HL). 13 B1B2B3T / Air. Where Au is the gold layer, H, B1, and B3 represent high-refractive-index materials, and L, B2, and T represent low-refractive-index materials, with high and low refractive indices set to 1.90 and 1.45, respectively. The physical thickness of each layer is d. H =193nm, d L =171nm, d B1 =114nm, d B2=453nm, d B3 =183nm, d T =844nm. The structural parameters at the top are Λ=800nm, d R =200nm, d G =644nm, f is 0.31, and β is 85°.

[0038] like Figure 2 As shown, the angular spectrum of the 1053 nm, TE-polarized incident light exhibits three peaks at 22.2°, 41.3°, and 70°, respectively, with a -1st-order diffraction efficiency exceeding 99%. Figure 3 As shown, when the incident light is incident at 22.2°, 41.3° and 70° respectively, the average diffraction efficiency of the first order of the grating is higher than 99% at 1053±3nm.

[0039] Figure 4-6 This demonstrates that this grating is compatible with various compressor layouts. For example... Figure 4 As shown, the compressor has a low incident angle layout, and gratings 1-4 are gratings of this embodiment. Light is incident on grating 8 (number 1) at 22.2°, and then exits after passing through gratings 9, 10, and 11 (numbers 2, 3, and 4) in sequence. If the spacing between gratings 1 and 2, or between gratings 3 and 4, is 1m, then the second-order dispersion provided by the grating pair is -156.628 × 10⁻⁶. 6 fs 2 .like Figure 5 As shown, the compressor has a Littrow incident angle layout. 12 and 13 are gratings in this embodiment, and 14 is a rear-facing mirror. Light is incident on grating 12 at 41.3°, then passes through grating 13, rear-facing mirror 14, grating 12 again, and exits. If the distance between grating 12 and grating 13 is 1m, the second-order dispersion provided by the grating pair is -15.04 × 10⁻⁶. 6 fs 2 .like Figure 6 As shown, the compressor has a high incident angle layout, and gratings 15, 16, 17, and 18 are all gratings in this embodiment. Light is incident on grating 15 at 70°, and then exits after passing through gratings 16, 17, and 18 in one pass. If the spacing between grating 15 and 16, or between grating 17 and 18, is 1m, then the second-order dispersion provided by the grating pair is -8.126 × 10⁻⁶. 6 fs 2 . Figure 4 Low incident angle compressor designs exhibit higher dispersion for a given spacing between gratings. Figure 5The Littrow compressor design requires out-of-plane operation to maximize the use of the grating aperture. Figure 6 The high incident angle compressor design exhibits low overall temporal dispersion for a given line density and spacing, and due to the large projection ratio of light onto the grating, the light intensity on the final grating surface is low, which can generate potentially high pulse energy before laser damage occurs.

[0040] Example 2:

[0041] Large offset angle all-dielectric gratings, such as Figure 7 As shown. The grating film system is: Sub / (LH) 20 T / Air. Here, H represents a high-refractive-index material, and L and T represent low-refractive-index materials, with the high and low refractive indices set to 1.9 and 1.45, respectively. The physical thicknesses of each layer are d... H =258nm, d L =184nm, d T =1058nm. The structural parameters at the top are Λ=714nm, d R =258nm, d G =800nm, f is 0.31, and β is 90°.

[0042] like Figure 8 As shown, the angular spectra of the 1053 nm, TE-polarized incident light exhibit three peaks at 29.9° and 77.2°, respectively, with their -1st-order diffraction efficiencies exceeding 99%. Figure 9 As shown, when the incident light is incident at 29.9° and 77.2° respectively, the average diffraction efficiency of the first order of the grating is higher than 99% at 1053±3nm.

[0043] Figure 4 and 6 This demonstrates that this grating is compatible with various compressor layouts. For example... Figure 4 As shown, the compressor has a low incident angle layout, with gratings 1-4 representing this embodiment. Light is incident on grating 1 at 29.9°, then passes through gratings 2, 3, and 4 before exiting. If the spacing between gratings 1 and 2, or 3 and 4, is 1m, the second-order dispersion provided by the grating pair is -750.192 × 10⁻⁶. 6 fs 2 .like Figure 6 As shown, the compressor has a high incident angle layout, with gratings 1-4 representing this embodiment. Light is incident on grating 1 at 77.2°, then passes through gratings 2, 3, and 4 before exiting. If the spacing between gratings 1 and 2, or 3 and 4, is 1m, the second-order dispersion provided by the grating pair is -12.454 × 10⁻⁶. 6 fs 2 .

[0044] The grating of this invention can achieve a -1st-order diffraction efficiency exceeding 99% within the neodymium glass gain bandwidth under incident conditions exceeding 20° of its Littrow angle. It is also compatible with various compressor layouts, thus enabling diverse dispersion tuning with a fixed grating pair spacing. Its flexible application makes it an ideal diffractive optical device with promising practical applications in high-power lasers.

[0045] The above embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. Those skilled in the art can modify or make equivalent substitutions to the technical solutions of the present invention without departing from the concept of the present invention, and these modifications and substitutions all fall within the protection scope of the present invention. The protection scope of the present invention should be determined by the claims.

Claims

1. A dielectric pulse compression grating with a large offset angle around a center wavelength of 1053 nm, comprising both all-dielectric and metallic dielectric configurations, characterized in that: The aforementioned dielectric pulse compression grating with a large offset angle comprises, in the longitudinal direction from bottom to top, a base layer (1), a dielectric film stack (2) of at least sixteen layers of alternating high refractive index material and low refractive index material, a barrier layer (3) composed of at least one layer of high refractive index material and low refractive index material, and a grating layer (4) with transverse periodic grating strips formed by partial or complete etching of low refractive index material. The dielectric pulse compression grating with a large offset angle of the metal dielectric comprises, in the longitudinal direction from bottom to top, a base layer (1), a high reflectivity metal layer (7), a dielectric film stack (2) of at least six layers made of alternating high refractive index material and low refractive index material, a barrier layer (3) composed of at least one layer of high refractive index material and low refractive index material, and a grating layer (4) with transverse periodic grating strips formed by partial or complete etching of low refractive index material at the top. The grating layer (4) has a grating stripe period of 625~1000nm, an etching depth of at least 300nm, a tilt angle β greater than 70°, and an aspect ratio of 0.2~0.6; the grating has a -1st order diffraction efficiency of more than 99% for TE polarized incident light of 1053 nm wavelength at at least two discrete incident angles that deviate from its own Littrow angle by more than 20°.

2. The dielectric pulse compression grating with a large offset angle around a center wavelength of 1053 nm as described in claim 1, characterized in that: The refractive index range of the high refractive index material is 1.6 to 2.1; the refractive index range of the low refractive index material is 1.3 to 1.

5.

3. The dielectric pulse compression grating with a large offset angle around a center wavelength of 1053 nm as described in claim 1, characterized in that: The period, etching depth, tilt angle and fill factor of the grating layer (4) are determined by the synergistic optimization of the film structure of the dielectric film stack (2) and the barrier layer (3) so that the -1 order diffraction efficiency is higher than 99% at the at least two discrete incident angles.

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