Abstract
High-energy narrowband terahertz (THz) pulses, relevant for a plethora of applications, can be created from the interference of two chirped-pulse drive lasers. The presence of third order dispersion, an intrinsic feature of many high-energy drive lasers, however, can significantly reduce the optical-to-THz conversion efficiency and have other undesired effects. Here, we present a detailed description of the effect of third-order dispersion (TOD) in the pump pulse on the generation of THz radiation via phase-matching of broadband highly chirped pulse trains. Although the analysis is general, we focus specifically on parameters typical to a Ti:Sapphire chirped-pulse amplification laser system for quasi-phase-matching in periodically-poled lithium niobate (PPLN) in the range of THz frequencies around 0.5 THz. Our analysis provides the tools to optimize the THz generation process for applications requiring high energy and to control it to produce desired THz waveforms in a variety of scenarios.
Highlights
The last two decades have seen a tremendous surge in development of terahertz (THz) sources of high-energy and high-peak-field for applications ranging from linear and nonlinear spectroscopy [1], to compact electron acceleration [2,3,4,5,6,7] and manipulation [8,9,10,11,12]
We have recently shown compensation for this effect on efficiency via asymmetric addition of group-delay dispersion (GDD) and third-order dispersion (TOD) to the pump pulses, producing mJ-level pulses with 1 % bandwidth at 361 GHz [19], confirming that the TOD does have a significant effect on THz generation efficency
The first conclusion is that TOD changes the difference frequency content of the total pump IR energy, which is due to a varying difference frequency over time within the overlapped train of pulses
Summary
The last two decades have seen a tremendous surge in development of terahertz (THz) sources of high-energy and high-peak-field for applications ranging from linear and nonlinear spectroscopy [1], to compact electron acceleration [2,3,4,5,6,7] and manipulation [8,9,10,11,12]. When TOD is included in the picture as, the pulses are no longer purely linear, and less of the energy of the pump pulses is within the quasi-phase-matching bandwidth (Fig. 1(d)) This manuscript outlines how principally the higher order spectral phase on the near-infrared (NIR) pump—and the complex train of pulses from the specific experimental setup used in Ahr et al [18]—contribute to these nuances and the decreased efficiency compared to the ideal prediction. This specific effect was compensated for in recent work by our group [19], where we produced 600 μJ of total narrowband THz energy.
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