Terahertz wave emission from a liquid water film under the excitation of asymmetric optical fields

Liquid water excited by intense two-color laser pulses radiates electromagnetic waves at terahertz frequencies. Compared with one-color excitation, two-orders of magnitude enhanced terahertz energy are observed by using asymmetric optical excitation with the same total excitation pulse energy and focusing geometry. Modulation of the terahertz field is achieved via the coherent control approach. We find that modulated and unmodulated terahertz energies have, respectively, quadratic and linear dependence on the laser pulse energy. This work, as part of terahertz aqueous photonics, paves an alternative way of studying laser-liquid interactions and developing intense terahertz sources.