Terahertz Generation Efficiency Research Articles

Water vapor: An extraordinary terahertz wave source under optical excitation

In modern terahertz (THz) sensing and imaging spectroscopy, water is considered a nemesis to be avoided due to strong absorption in the THz frequency range. Here we report the first experimental demonstration and theoretical implications of using femtosecond laser pulses to generate intense broadband THz emission from water vapor. When we focused an intense laser pulse in water vapor contained in a gas cell or injected from a gas jet nozzle, an extraordinarily strong THz field from optically excited water vapor is observed. Water vapor has more than 50% greater THz generation efficiency than dry nitrogen. It had previously been assumed that the nonlinear generation of THz waves in this manner primarily involves a free-electron plasma, but we show that the molecular structure plays an essential role in the process. In particular, we found that THz wave generation from H 2O vapor is significantly stronger than that from D 2O vapor. Vibronic activities of water cluster ions, occurring naturally in water vapor, may possibly contribute to the observed isotope effect along with rovibrational contributions from the predominant monomers.

Terahertz pulse generation from noble gases

Terahertz pulse generation in the laser-induced plasma from a series of noble gases (He, Ne, Ar, Kr, and Xe) was systematically investigated. Femtosecond laser pulses consisting of both a fundamental and its second-harmonic frequency were used for the terahertz generation. Experimental results reveal that terahertz generation efficiency of these noble gases increases with decreasing ionization potential.

Study of differently doped Zn0.95Cd0.05Te〈110〉single crystals as THz emitters

Properties of differently doped Zn0.95Cd0.05Te〈110〉 crystals as terahertz (THz) wave emitter are studied using THz time-domain spectroscopy. It is observed that the THz generation efficiency increases as the DC resistivity increases when the resistivity of crystals is greater than 102 Ω·cm, but the efficiency saturates and even declines when the resistivity goes beyond 106 Ω·cm. It is revealed that the dispersion properties of crystals play an important role, besides the doping-dependent absorption in THz region.