Methane (CH₄) is one of the major greenhouse gases in the atmosphere, second only to carbon dioxide (CO₂) in atmospheric content, but its contribution to the greenhouse effect per unit concentration is about 25 times that of CO₂. With the development of human civilization, the total amount of CH₄ has been increasing, which has an important impact on the Earth's climate change. By monitoring the concentration of CH₄, the trend of earth's climate change can be more accurately assessed, and by identifying the main sources of CH₄ emissions, corresponding measures can be taken to reduce emissions. Imaging spectrometers, which uniquely combine the advantages of imaging and spectral detection, have been widely used for remote sensing monitoring of the atmosphere and environment. The prism grating is an important dispersive element of the satellite-borne methane imaging spectrometer. Unlike the traditional grating, the prism grating structure is submerged in the high refractive index medium, which improves the dispersion and resolution of the grating by a factor of n, where n is the refractive index of the high refractive index medium. Therefore, compared with the traditional grating, the prism grating with the same spectral resolution can reduce the size of the grating to achieve more compact optomechanical structures. Therefore, the development of the prism grating is of great significance.According to the needs of methane detection, and in order to further improve the compactness of the system, a high refractive index material, TiO₂ dielectric film was introduced into the quartz prism grating. The diffraction characteristics of the prism grating were analyzed by the Finite-Difference Time-Domain (FDTD). In order to achieve a the first-order diffraction efficiency greater than 70% in the 2.275-2.325 μm band, for the rectangular groove shape, the duty cycle is in the range of 0.3-0.45, TiO₂ film thickness between 165-170 nm, and slot depth between 800-950 nm. Experimentally, holographic lithography-ion beam etching combined with atomic layer deposition technique was used to fabricate prism gratings. Firstly, a layer of photoresist of appropriate thickness was uniformly coated onto the prism substrate. Second, holographic exposure and development were performed with a krypton ion laser (wavelength of 413.1 nm) to form a photoresist grating mask, and the slot shape of the photoresist grating mask was effectively controlled by adjusting the exposure and development time. Then, the prism substrate was etched by ion beam etching under the mask of photoresist, and the photoresist grating pattern was transferred to the prism substrate. The TiO₂ film layer was then deposited using Atomic Layer Deposition (ALD) technique. Finally, vacuum coating was applied to create a reflective silver film.Experimentally, a prism grating with a period of 1020 nm and an effective grating area larger than 110 mm×275 mm was fabricated using holographic lithography-ion beam etching combined with atomic layer deposition technology (Fig.5). The grating groove shape is trapezoidal, the groove depth is 872 nm, the central duty cycle is 0.42, and the thickness of the TiO₂ film layer is 166 nm (Fig.4). The prism grating diffraction efficiency measurement adopts a dual optical path test method to eliminate the influence of the fluctuation of the light source and ensure the accuracy of the test. Figure 6 shows the experimental setup for measuring the diffraction efficiency. In the test, the beam splitter divides the light beam into two paths, one to monitor the stability of the light source, and the other for the measurement of the optical path. The experimental test shows that the first-order diffraction efficiency is greater than 70% in the 2.275-2.325 μm band.The diffraction characteristics of prism gratings for methane imaging spectrometers are analyzed in detail. In order to further improve the compactness of the system, a high refractive index material TiO₂ dielectric film has been introduced into the quartz prism gratings, and for the rectangular groove shape, when the duty cycle is in the range of 0.3-0.45, when the thickness of the TiO₂ film layer is between 165-170 nm, and when the groove depth is between 800-950 nm, the grating's diffraction efficiency is higher than 70%. The diffraction efficiency is higher than 80% when the TiO₂ film layer thickness is 165 nm and the slot depth is between 870-930 nm. High-quality photoresist grating masks were fabricated using holographic lithography in the experiments. The combination of Ar ion-beam etching and CHF₃ reactive ion-beam etching was optimized during the etching process, and a quartz prism grating with a duty cycle of 0.42 in the middle, a slot depth of 872 nm, and trapezoidal bottom angles of 85.5° and 82° on both sides was fabricated, and then a 166 nm TiO₂ film layer was deposited by using the Atomic Layer Deposition (ALD) technique, and finally a reflective silver film was vacuum-plated. In order to eliminate the influence of light source fluctuation, the dual-optical path test method was adopted for the diffraction efficiency measurement, and the first-order diffraction efficiency was greater than 70% in the band of 2.275-2.325 μm, which was successfully applied to the satellite-mounted methane imaging spectrometer.