The polarization modulation of Cherenkov diffraction radiation facilitates intriguing potentials to explore material properties and advanced technologies such as free-electron lasers; however, it is still challenging to achieve polarization modulation. Here, we propose versatile on-chip silicon-patterned silicon-nitride photonic integrated waveguides to produce a direction-dependent polarization modulator for Cherenkov diffraction radiation. The radiation angle can be manipulated arbitrarily by arranging the period of the grating and the propagation direction of the electron beam. Furthermore, the polarization and the number of output directions of the radiation can be controlled by the gradient metasurfaces. In particular, the linear, left-, and right-handed circular polarized Cherenkov diffraction radiation could be generated in separate radiation directions. Our results pave the way to modulate the polarization of free-electron radiation and further promote the development of on-chip light sources.
The brightness and height of the sodium laser guide star of adaptive optics could vary significantly due to the temporal dynamics of sodium column density and the mean height of the sodium layer. To measure these dynamics, an independent sodium Lidar is a necessity. Without such an instrument, it is almost impossible to discern the cause of the brightness variation of the laser guide star from the sodium layer's dynamics or other factors from the laser itself. For applications such as characterizing the performance of sodium laser for sodium laser guide star generation, minutes scale short term statistics of the sodium layers' abundance and height is extremely helpful for estimating the contribution of sodium layer's variation to the variation of laser guide star's brightness. In this paper, we analyzed our previous measurement of sodium layer dynamics that has been gathered in two winters, and presented the temporal variation statistics of sodium column density and mean height within a minute timescale based on our measurements.
In the past few years, Chinese astronomical community is actively testing astronomical sites for several new optical/infrared ground-based telescopes. These site testing campaigns conducted were mainly focused on fundamental performances of the sites, such as cloud coverage, seeing, temperature, etc. With increasing interests in sodium laser guide star adaptive optics for these new telescopes in the Chinese astronomical community, it is interesting to investigate the performance of the laser guide star at these sites, especially considering that the sodium laser guide star’s on-sky performance is significantly influenced by sites’ local performances, such as geomagnetic field, sodium layer dynamics, density of air molecule, etc. In this paper, we studied sodium laser guide star’s performance of a 20W class Quasi Continuous Wave (QCW) pulsed laser developed by TIPC with numerical simulation for five selected sites in China.
Transverse scattering is a special directional scattering perpendicular to the propagation direction, which has attracted great interest due to its potential applications from directional antennas, optical metrology to optical sensing. Here we reveal annular transverse scattering and unidirectional transverse scattering by magnetoelectric coupling of Omega particle. The annular transverse scattering can be achieved by the longitudinal dipole mode of the Omega particle. Furthermore, we demonstrate the highly asymmetric unidirectional transverse scattering by adjusting the transverse electric dipole (ED) and longitudinal magnetic dipole (MD) modes. Meanwhile, the forward scattering and backward scattering are suppressed by the interference of transverse ED and longitudinal MD modes. In particular, the lateral force exerted on the particle is accompanied by the transverse scattering. Our results provide a useful toolset for manipulating light scattered by the particle and broaden the application range of the particle with magnetoelectric coupling.
In this paper, we investigated the impact of the linewidth of a QCW pulsed sodium laser on the brightness performance of a generating sodium laser guide star by using the numerical simulation tool PRS. We compared the field test results with the simulation results for two TIPC’s 30W class sodium guide star lasers and found the results are in good agreement which proves the tool can be used for prediction. Then, we used the tool to study the influence of D2b repumping and different linewidths from 10MHz to 1GHz on the coupling efficiency and the photon return flux. For the TIPC’s QCW pulsed solid-state laser, when the on-sky power density is 1 W/m2, the coupling efficiency is 79.6 (photons/s/W/(atoms/m2)) without D2b repumping, however, the value is up to 213.3 (photons/s/W/(atoms/m2)) with 15% D2b enabled and is increased by 168% than the value without D2b; when the power density reaches 10 W/m2, the coupling efficiencies without D2b and with 15% D2b are 66.6 and 233.6 (photons/s/W/(atoms/m2)), respectively. The results show that for the QCW pulsed laser, D2b repumping is necessary. With D2b enabled, if the spectral linewidth is too wide or too narrow, the photon return flux will be adversely affected. The return flux of 60MHz is 52.5% higher than that of 1GHz, while the return flux of 300MHz is 37.8% higher than that of 10 MHz when the laser power is 100W.
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