Encoding terahertz signatures into laser-induced plasma acoustic waves

The enhancement of acoustic waves from a laser-induced plasma, from audible into the ultrasonic range, is a linear function of the terahertz (THz) intensity incident on the plasma, making THz-enhanced acoustics (TEA) useful for THz detection at a standoff distance. When a femtosecond laser of sufficient peak energy is focused into air, the gas is ionized and acoustic waves are launched through the photoacoustic process. THz field-induced energy transfer through acceleration of free electrons, and the following electron-molecule collisions, results in an enhanced acoustic emission from the plasma. A physical understanding of free electron manipulation inside a dual-color laser filament is used to encode THz spectroscopic information into acoustic waves, making it possible to coherently detect the electric field profile of the THz pulse by simply "listening" to the plasma from a distance. Our most recent results utilizing TEA as method for remote THz detection will be presented.