Enhancement of THz generation in LiNbO3 waveguides via multi-bounce velocity matching

Abstract

To realize the full promise of terahertz polaritonics (waveguide-based terahertz field generation, interaction, and readout) as a viable spectroscopy platform, much stronger terahertz fields are needed to enable nonlinear and even robust linear terahertz measurements. We use a novel geometric approach in which the optical pump is totally internally reflected to increase the distance over which optical rectification occurs. Velocity matching is achieved by tuning the angle of internal reflection. By doing this, we are able to enhance terahertz spectral amplitude by over 10x compared to conventional single-pass terahertz generation. An analysis of the depletion mechanisms reveals that 3-photon absorption and divergence of the pump beam are the primary limiters of further enhancement. This level of enhancement is promising for enabling routine spectroscopic measurements in an integrated fashion and is made more encouraging by the prospect of further enhancement by using longer pump wavelengths.

Enhanced Terahertz Phonon Polariton in Lithium Niobate Chip

“…[ 30 ] Lastly, we propose an experimental layout that combines lateral pumping, tilted pulsefront phase matching, and multi‐bounce technique inspired by the reference. [ 21 ] Please refer to Note S3 (Supporting Information) for more detailed discussion.…”

“…Recently, a new phase‐matching technique was introduced, whereby wedge angles are introduced in the LN waveguide to produce multiple total reflections of the pump light. [ 21 ] However, most of the research employed a vertical pumping scheme. Only a small number of experiments have succeeded in propagating THz pulses laterally in a dispersive medium to achieve a frozen phase by lateral pumping.…”

Cascaded Terahertz Parametric Generation Under Noncollinear Phase-Matching Condition

“…The technique of generating terahertz (THz) waves by wavelength conversion using nonlinear optical effects is promising for obtaining high power and wide tunability because it allows the use of welldeveloped pump sources such as near-infrared lasers [1][2][3]. For those THz-wave sources, wavelength conversion e ciency is important for high output power, but is limited by the Manley-Rowe limit.…”