Analysis of terahertz generation by beamlet superposition

Abstract

A theory of terahertz generation using a superposition of beamlets is developed. It is shown how such an arrangement produces a distortion-free tilted pulse front. We analytically show how a superposition of beamlets produces terahertz radiation with greater efficiency and spatial homogeneity compared to tilted pulse fronts generated by diffraction gratings. The advantages are particularly notable for large pump bandwidths and beam sizes, suggesting better performance in the presence of cascading effects and for high energy pumping. Closed-form expressions for terahertz spectra and transients in three spatial dimensions are derived. Conditions for obtaining performance better than conventional tilted pulse fronts and bounds for optimal pump parameters are furnished. arXiv:1810.09118v3 [physics.optics]

High Field Single- to Few-Cycle THz Generation with Lithium Niobate

“…Ideally, a mJ THz pulse with tight focus would achieve a greater-than 10 MV/cm peak field, but the current peak field record remains at 6.3 MV/cm from a more than 1 mJ THz pulse [31]. In addition, the discrete TPF method shows great potential to achieve higher conversion efficiency, although the experimental results stay far below those of the theoretical calculation [75]. More complex theoretical models including the cascading effect will be helpful to understand the current discrepancy and limitations.…”

“…However, this large angular dispersion limits the effective interaction length for optical-THz conversion, distorts the image for short pulses with large spectral bandwidth, and deteriorates the THz beam profile, inhibiting THz generation and its tight focusing. Recently, methods free of angular dispersion have been proposed to minimize these issues [75]. As shown in Figure 5c, a reflective stair-step echelon splits the pump beam into a superposition of beamlets [76].…”

Performance comparison of lithium-niobate-based extremely high-field single-cycle terahertz sources [Invited]

“…These phase differences can result in less constructive interference between the wavelets, causing a drop in the THz generation efficiency. On the other hand, the segmented parts of the beam can be considered in the model as independent beamlets [31,44] . These beamlets are diffracted during the propagation.…”

Simultaneous generation and compression of broadband terahertz pulses in aperiodically poled crystals

“…This is because, at high conversion efficiencies, cascading effects produce large spectral and angular broadening of the pump. This issue may be alleviated using a superposition of beamlets [31][32][33] and variants thereof [34,35]. Alternatively, attempts to eliminate the drawbacks of tilted pulse fronts in lithium niobate by utilizing smaller pulse-front tilt angles are being pursued [36,37].…”