A family of methods has been developed recently for generation, control, and visualization of terahertz (THz) phonon-polaritons in polar crystals<sup>1</sup>. Phonon-Polaritons (below simply "polaritons") are admixture of polar lattice vibration and electromagnetic modes of similar frequency and wave vector. In this paper, we discuss the possible application of phonon-polariton spectroscopic imaging to the chemical sensing. Advantages of the polariton imaging for the use of sensor application include (1) No need for THz optics, (2) Compactness of the cell, and (3) Quick acquisition of time domain signal. In this paper, we present experimental results of solid and liquid samples, and show simultaneous measurement of multiple samples.
We report the first systematic study of broadband THz wave generation by using the focused femtosecond laser beams in ambient air. Generations of pulsed THz waves using air as the nonlinear media have been previously demonstrated by Cook <i>et al.</i> and Hartmut <i>et al.</i> We measured dependence of generated THz wave on the polarization, amplitude and phase of the individually controlled fundamental and second harmonic beams. Our results confirms that four-wave-mixing rectification is the major mechanism of THz wave generation with mixing the fundamental and the SH beams in air. This work is significant by providing the feasibility of standoff distance detection greater than 50 meters.
Impulsive stimulated scattering (ISS) has been used to obtain the orientation dependence of the velocity of the surface acoustic waves (SAW) on single crystal metal and semiconductor surfaces. The ISS data is presented for mechanically polished (001) plane of nickel and germanium, and (111) of aluminum at ambient pressure. The orientationally dependent ISS results for Ni (100) are compared with the results of Brillouin scattering measurement as well as calculation results. Finally, the results of high pressure ISS experiments are presented for the SAW on polycrystalline aluminum.