为了实现激光/红外双模导引头成像系统的小型化，简化光学系统结构，设计了四次反射的双模共光路环形孔径超薄成像系统，研究了该系统的分光路设计原理，给出了遮拦比与视场角的关系，实现了仅有单一光学元件的长波红外7.7~9.5 μm和激光1.064 μm双模导引头成像系统。双模环形孔径系统在长波红外波段的焦距为70 mm、等效F数为1.3、全视场为8°、空间频率为41.7 lp/mm时各视场MTF值均大于0.136。双模环形孔径系统在激光波长的焦距为53.8 mm、等效F数为1、全视场为10°、全视场范围内的光斑分布均匀。在环境温度范围为−40~80 ℃时，长波红外波段各视场MTF值均大于0.13，激光波长的弥散斑形状和能量分布基本不变，实现了光学被动无热化。通过公差分析可知双模环形孔径系统具备可加工性。

Two-dimensional (2D) transition metal dichalcogenides alloys are potential materials in the application of photodetectors over a wide spectral range due to their composition-dependent bandgaps. The study of bandgap engineering is important for the application of 2D materials in devices. Here, we grow the Mo_1-xW_xSe₂ alloys on mica, sapphire and SiO₂/Si substrates by chemical vapor deposition (CVD) method. Mo_1-xW_xSe₂ alloys are grown on the mica substrates by CVD method for the first time. Photoluminescence (PL) spectroscopy is used to investigate the effects of substrates and interlayer coupling force on the optical bandgaps of as-grown Mo_1-xW_xSe₂ alloys. We find that the substrates used in this work have an ignorable effect on the optical bandgaps of as-grown Mo_1-xW_xSe₂. The interlayer coupling effect on the optical bandgaps of as-grown Mo_1-xW_xSe₂ is larger than the substrates effect. These findings provide a new way for the future study of the growth and physical properties of 2D alloy materials.

Mechanical exfoliation (ME) and chemical vapor deposition (CVD) MoS₂ monolayers have been extensively studied, but the large differences of nonlinear optical performance between them have never been clarified. Here, we prepared MoS₂ monolayers using ME and CVD methods and investigated the two-photon absorption (TPA) response and its saturation. We found that the TPA coefficient of the ME monolayer was about (1.88 ± 0.21) × 10³ cm/GW, nearly two times that of the CVD one at (1.04 ± 0.15) × 10³ cm/GW. Furthermore, we simulated and compared the TPA-induced optical pulse modulation in multilayer cascaded structures, which is instructive and meaningful for the design of optical devices such as a beam shaper and optical limiter.

Questions hovering over the modulation of bandgap size and excitonic effect on nonlinear absorption in two-dimensional transition metal dichalcogenides (TMDCs) have restricted their application in micro/nano optical modulator, optical switching, and beam shaping devices. Here, degenerate two-photon absorption (TPA) in the near-infrared region was studied experimentally in mechanically exfoliated MoS2 from single layer to multilayer. The layer-dependent TPA coefficients were significantly modulated by the detuning of the excitonic dark state (2p). The shift of the quasiparticle bandgap and the decreasing of exciton binding energy with layers were deduced, combined with the non-hydrogen model of excitons in TMDCs and the scaling rule of semiconductors. Our work clearly demonstrates the layer modulation of nonlinear absorption in TMDCs and provides support for layer-dependent nonlinear optical devices, such as optical limiters and optical switches.