Intense Narrowband THz Generation from Organic NLO Crystal BNA Fused to Sapphire

Terahertz frequencies (0.1 to 10 THz) can be generated from optical rectification of ultrafast laser pulses and have a wide range of applications, from studying phonon modes to noninvasive hyperspectral imaging. There are several applications that become possible with multi-cycle tunable narrowband THz generation, such as selective excitation of phonon modes. In a chirp-and-delay scheme, the beam is linearly chirped, split, and recombined to interfere with a time-delay such that there is a single frequency present in the multiple oscillations of the modulated pulse. Optical rectification of these modulated pulses generates narrowband THz, whose frequency is tunable depending on the time delay and chirp. The frequency ranges of these chirp-and-delay setups have previously been restricted to 0.1 to 1.5 THz, or have used special, custom laser technologies to achieve tunability up to 6 THz. We propose a simple setup that generates narrowband THz from 0.1 to 5 THz using the output of an 800-nm Ti:Sapphire laser to pump organic nonlinear optical crystal BNA fused to high thermal conductivity sapphire. We generate narrowband THz with higher spectral amplitude than a traditional optical rectification approach.