J. Q. Yao

Propagation Characteristics of Two-Dimensional Photonic Crystals in the Terahertz Range

Based on plane wave expansion method, the band gaps of a two-dimensional terahertz photonic crystal with a square lattice are optimized through varying structural parameters. The electromagnetic field distribution is accurately described for a terahertz photonic crystal splitter by finite difference time domain method.

The physical theory and propagation model of THz atmospheric propagation

Terahertz (THz) radiation is extensively applied in diverse fields, such as space communication, Earth environment observation, atmosphere science, remote sensing and so on. And the research on propagation features of THz wave in the atmosphere becomes more and more important. This paper firstly illuminates the advantages and outlook of THz in space technology. Then it introduces the theoretical framework of THz atmospheric propagation, including some fundamental physical concepts and processes. The attenuation effect (especially the absorption of water vapor), the scattering of aerosol particles and the effect of turbulent flow mainly influence THz atmosphere propagation. Fundamental physical laws are illuminated as well, such as Lamber-beer law, Mie scattering theory and radiative transfer equation. The last part comprises the demonstration and comparison of THz atmosphere propagation models like Moliere(V5), SARTre and AMATERASU. The essential problems are the deep analysis of physical mechanism of this process, the construction of atmospheric propagation model and databases of every kind of material in the atmosphere, and the standardization of measurement procedures.

Pump-tuning optical parametric oscillation and sum-frequency mixing with KTP pumped by a Ti:sapphire laser

Abstract We report the implementation of a KTP optical parametric oscillator pumped by a pulsed Ti:sapphire laser. Including signal and idler, it could be continuously tuned from 1.261 through 2.532 μm by varying the pump wavelength. Two major improvements were achieved, including the connection of the signal and idler tuning ranges and the high output pulse energy through the signal and idler tuning ranges. The first improvement was achieved by discovering two particular sets of phase-matching angles. The second improvement was realized by using five sets of resonator mirrors for oscillating either signal or idler. Theoretical calculations were also conducted for the effective nonlinear coefficient, walk-off angle, phase-matching acceptance angle, and output spectral widths for the concerned phase-matching angles. The second part of this paper presents the experimental and theoretical results of sum-frequency mixing (SFM) of a Ti:sapphire laser and a 1.064 μm Nd:YAG laser. By using two KTP crystals cut at θ=76° and 85° (ϕ=90° in both crystals), respectively, we have experimentally achieved SFM tuning range from 459.3 through 472.9 nm. The energy conversion efficiencies were reasonably high.

High-energy, continuously tunable intracavity terahertz-wave parametric oscillator

We have demonstrated an intracavity THz optical oscillator pumped by a diode-side-pumped Q-switched Nd:YAG laser. Based on a noncollinear phase matching geometry in the nonlinear crystal MgO:LiNbO3, high-energy, low-threshold, coherent tunable Stokes light is obtained by changing the angle between the resonated idler wave and the pump wave, which means that the widely tunable, high-energy, coherent THz radiation is also generated. The tuning range for Stokes wave is 1069.4–1073.4nm, corresponding to the THz frequency range of 1.4–2.5THz. The phenomenon of the coherent tunable second-order Stokes light scattering is also observed.