Abstract
We explore the dynamics of a system where input spectra in the optical domain with very disparate center frequencies are strongly coupled via highly phase-matched, cascaded second-order nonlinear processes driven by terahertz radiation. The only requirement is that one of the input spectra contain sufficient bandwidth to generate the phase-matched terahertz-frequency driver. The frequency separation between the input spectra (or pump and seed spectra) can be more than ten times larger than the phase-matched terahertz frequency. This is in contrast to our previous work on cascaded parametric amplification, where the frequency separation between the pump and seed is required to be equal to the phase-matched terahertz frequency. A practical application of such a system where the cascading of a narrowband pump line centered at 1064 nm induced by a group of weaker seed lines centered about 1030 nm and separated by the phase-matched terahertz frequency is introduced. This approach is predicted to generate terahertz radiation with percent-level conversion efficiencies and millijoule-level pulse energies in cryogenically-cooled periodically poled lithium niobate. A model that solves for the nonlinear coupled interaction of terahertz and optical waves is employed. The calculations account for second and third-order nonlinearities, dispersion in the optical and terahertz domains as well as terahertz absorption. Ramifications of pulse formats on laser-induced damage are estimated by tracking the generated free-electron density. Strategies to mitigate laser-induced damage are outlined.
Highlights
Nonlinear optical interactions which give rise to further coupled nonlinear interactions in a cascade of processes maybe broadly referred to as cascaded optical nonlinearities
Very interesting spectral dynamics are observed in such systems
The reasons for this are apparent by inspecting the schematic in Fig. 1, which describes the spectral dynamics of a terahertz generation system with optical parametric amplifier (OPA)-like initial conditions
Summary
Nonlinear optical interactions which give rise to further coupled nonlinear interactions in a cascade of processes maybe broadly referred to as cascaded optical nonlinearities. It was theoretically shown that even for ≈ 0% optical-to-terahertz energy conversion efficiency, such configurations can only be reasonably described by considering cascading effects, i.e. the simultaneous evolution of a large number of coupled three-wave mixing processes [16] The reasons for this are apparent by inspecting the schematic, which describes the spectral dynamics of a terahertz generation system with OPA-like initial conditions. The wave of highest intensity could be present at a lower frequency (ω−1) to produce terahertz amplification, which is disallowed in conventional parametric amplifiers This is because the input optical spectrum is rapidly washed out due to the simultaneous evolution of many strongly coupled phase-matched processes and becomes inconsequential.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
