Abstract
Terahertz radiation has unique potential for applications to material diagnostics including semiconductors, chemical compounds, biomolecules and biotissues, imaging for medical and security applications, remote atmospheric sensing and monitoring, astronomy, etc. The search for efficient, high-power, inexpensive, portable and room temperature suitable methods of generation of THz radiation is one of the main topics in modern optoelectronics and photonics. Specifically, coherent solid-state compact efficient THz sources are desirable. Recently we suggested a new approach to the problem of generation of short coherent THz pulses in molecular gases taking advantage of the dramatic enhancement of a nonlinear response of a medium via quantum coherence. Stimulated Raman adiabatic passage (STIRAP) technique was proposed for preparation of maximal molecular coherence by two optical pump fields, which is further used to efficiently scatter off an IR probe beam and generate a Stokes THz field in a double Λ scheme. The central idea of the crystal-based technique is to generate THz radiation by resonantly inducing coherence at the corresponding transition by coherent optical fields. Electronic levels of the THz transition are coupled by a pair of optical fields to a common ground state forming a V scheme of energy levels. Coherence induced by the optical fields at the THz transition gives rise to polarization provided that the corresponding dipole moment is not zero, which will radiate out a THz pulse. We show that coherently driven molecular (such as methanol, H2F2, CH3Cl, etc.) and solid-state (ruby, alexandrite) media can potentially produce strong, controllable, short pulses of THz radiation. The pulses have energies ranging from hundreds pJ to J and time durations from several fs to ns at room temperature.
© 2006 Optical Society of America
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