Circularly Polarized Photodetectors Based on Chiral Materials: A Review

Circularly polarized light (CPL) plays an important role in many photonic techniques, including tomographic scanning based on circular polarization ellipsometry, optical communication and information of spin, and quantum-based optical calculation and information processing. To fully exploit the functions of CPL in these fields, integrated photoelectric sensors capable of detecting CPL are essential. Photodetectors based on chiral materials can directly detect CPL due to their intrinsic optical activity, without the need to be coupled with polarizers and quarter-wave plates as in conventional photodetectors. This review summarizes the recent research progress in CPL photodetectors based on chiral materials. We first briefly introduce the CPL photodetectors based on different types of chiral materials and their working principles. Finally, current challenges and future opportunities in the development of CPL photodetectors are prospected.

Electronic and optical properties of Janus Monolayers MoXB2(X=S,Se): First-principles prediction

By means of comprehensive first-principles calculations, we studied the geometric structure, the stability and electronic properties of the new two-dimensional(2D) Janus MoXB2(X=S, Se) monolayers. Our calculations demonstrated that the predicted Janus MoXB2 monolayers are all stable semiconductors with direct band gap. In this paper, we focus on impacts upon the electronic and optical properties of the MoXB2 monolayers under the different biaxial strains. With the compressive stress increases, the MoXB2 monolayers would become indirect band gap semiconductors, and then behave as semimetal. While under tensile strain, MoXB2 still maintain direct band gap. In addition, the optical calculation shows that biaxial strain leads to blue shifts in the optical absorption and reflectivity. The result indicates that MoXB2 may be promised nano candidate materials in optoelectronic devices.

Tracing the evolution of morphology and mixing state of soot particles along with the movement of an Asian dust storm

Tracing the aging progress of soot particles during transport is highly challenging. An Asian dust event could provide an ideal opportunity to trace the continuous aging progress of long-range transported soot particles. Here, we collected individual aerosol particles at an inland urban site (T1) and a coastal urban site (T2) in China and a coastal site (T3) in southwestern Japan during an Asian dust event. Microscopic analysis showed that the number fraction of soot-bearing particles increased from 19 % to 22 % from T1 to T2 in China but surprisingly increased to 56 % at T3 in Japan. The dominant fresh soot (71 %) at T1 became partially embedded (70 %) at T2 and fully embedded (84 %) at T3. These results indicated that the soot particles had lower deposition than other aerosol types and became more aged from T1 to T3. The fractal dimension of the soot particles slightly changed from 1.74 at T1 and 1.78 at T2 but significantly became 1.91 at T3. We found that the soot morphology compressed depending on secondary coating thickness and relative humidity. Moreover, we observed a unique mixing structure at T3 that tiny soot particles were seemly broken from large ones cross the East China Sea and distributed in organic coatings instead of sulfate core in particles. Our study provide important constraints of the morphological effects to better understand changes of microscopic structures of soot. These new findings will be helpful to improve optical calculation and modeling of soot particles and their regional climate effects in the atmosphere.

Multiple Reflections Modeling for Multi-Layered Optical Structures

Fresnel equations and transfer matrix approach are usually employed to solve for exact solution to Maxwell’s equations for multi-layered optical structures. In this paper, we demonstrate that the Fresnel equations and transfer matrix approach can be expanded using Geometric series. This geometric series give an insight to how the light is trapped and behaves in multi-layered optical structures. It also allows us to calculate multiple reflections and count the number of round-trip inside the structure. One main issue in optical calculation is that layers are usually treated as an infinitely large layer. This is, of course, not practical in term of device fabrication. We also demonstrate how this simple geometric calculation will enable us to calculate a smallest practical size that can accommodate a required optical resonant effect.

Wave Optical Calculation of Probe Size in Low Energy Scanning Electron Microscope

A wave optical calculation of the probe size of a low energy scanning electron microscope is presented. The resolution for the optimal aperture was computed and compared with results of standard approaches. The effect of deflection aberrations is also considered, and it was found to be critical for the landing energies below 5eV and fields of view larger than 100 x 100 μm2.