Spectral and intensity control of high energy terahertz radiation from bulk liquids

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High power, broadband terahertz (THz) radiation from liquids, excited by intense, femtosecond 800 nm laser pulses has been demonstrated recently, overturning the long held belief that liquids would not give such emission due to their absorption in the THz region. Given the widespread interest in the use of THz radiation for several applications and the energy and bandwidth limitations of existing sources, liquids are expected to attract great attention in the future. While the emission at tens of microjoules from liquids is very promising, it is important to explore whether control of the THz flux and spectrum is achievable by manipulating the laser or liquid parameters. In this paper we present results on manipulating the spectrum of THz radiation from liquids by chirping the input laser pulse and optimizing the THz output energy by laser chirp as well as optimizing the focal position. We demonstrate tunability by varying the chirp of the laser pulse and show that the THz emission predominantly comes from the region near the end of the liquid path, consistent with the absorption of THz radiation by liquids. This control gives us an opportunity to tune the THz radiation to suit experimental needs. We present simulations that support the results.