To obtain high efficiency and high bandwidth grating based on large dispersion, we propose a 2-layer transmission grating with a high-line-density in this paper. A unitary fused-silica grating and a 2- layer grating combined with high and low refractive index dielectric material are designed respectively and their performance are compared briefly. The groove density of the grating is 1624 line/mm. By optimizing the grating parameters, the -1st diffraction efficiencies of the 2-layer transmission grating are both greater than 80% for TE and TM polarized incident lights in a wavelength range from 850nm to 1050nm and it can reach an efficiency of more than 97% for both polarizations at a central wavelength of 900nm when the light is incident from the front of grating. Moreover, we found that when the incident mode is in backside incidence mode, i.e. the light is incident from the back of grating, the -1st diffraction efficiency can reach to the maximum value of 97.9%.
Laser beam combining technology currently plays an important role in optical systems. The combined beam grating is the most important realization component inside, so it is necessary to study the beam grating. Conventional metal gratings have high absorbance, and the damage threshold of metal gratings is usually not high. Multilayer dielectric film gratings are necessary for research because they have almost no absorption and high damage thresholds at the same time as high diffraction efficiency. Based on the theory of rigorous coupled wave (RCWA), a multilayer dielectric film grating model is established and a multilayer dielectric film grating with a center wavelength of 1053 nm is designed in the paper After a series of optimal design, the following results are obtained. Ta2O5 and SiO2 are selected as multi-layer material, and the multi-layer structure is S(HL)^12HTA .The groove density is 1480 lines/mm. The profile of grating grooves is rectangular .The duty cycle of surface relief structure is between 0.3-0.4, the groove depth is between 750-850nm, the sum of residual thickness and groove depth is between 930-1030nm.The -1st diffraction average efficiency of the grating is over 95% at the Littrow angle (51.2 degrees).Wavelength bandwidth greater than 40nm.The diffraction efficiency is the same as that of a metal grating .At the same time, the laser induced damage threshold can be improved.
A antireflection film with adjustable refractive index from 1.17 to 1.41 was prepared at room temperature via a template-free sol–gel method, using tetraethylorthosilicate(TEOS) as co-precursor. In this study, the regulation of the refractive index is achieved by mixing different volumes of acid-catalyzed silica sol having a refractive index of 1.41 with a base-catalyzed silica sol having a refractive index of 1.17. The silica coating, with a refractive index of 1.2332, prepared by this base/acid two step catalysis sol-gel process can increase the transmittance of K9 glass by about 3.5%.
Crossed-grating, as the standard element for metrology in two-dimensional precision positioning system, has been widely used in precision machine tools, highly sophisticated manufacturing and machining system. The technical indicators of crossed-grating, such as its diffraction efficiency and the efficiency equilibrium of the TE or TM polarized light are relevant to the microstructure of crossed-grating. While the structure of crossed-grating is determined by the microstructure of holographic photoresist grating. For exploring the evolution of microstructure of crossed holographic photoresist grating. In this paper, a new method for obtaining the variation curve of groove depth with exposure volume （the contrast curve of photoresist）is proposed, this method does not need a series of repeated experiments and is easy to operate compared with previous step experiments. The contrast curve of photoresist under different developing conditions (such as developer concentration and developing time) are analyzed. In addition, the top-view groove profile of crossed holographic photoresist grating under different process conditions are revealed too. The above research results provides a theoretical basis for the process parameters in holographic recording and developing of crossed holographic photoresist grating.