Hybrid tilted-pulse-front excitation scheme for efficient generation of high-energy terahertz pulses

Abstract

Conception of a hybrid type tilted-pulse-front pumping scheme for the generation of high-energy terahertz pulses is presented. The proposed setup is the combination of the conventional setup containing imaging optics and the contact grating. The solution was developed for nonlinear materials requiring large pulse-front-tilt angle, like LiNbO₃. Due to the creation of the pulse-front-tilt in two steps the limitations of imaging errors can be significantly reduced. Furthermore the necessary grating constant of the contact grating can be larger compared to the simple contact grating scheme making possible the fabrication of the grating profile with significantly higher precision. A detailed optimization procedure with respect to the diffraction efficiency on the contact grating is given for LiNbO₃. Instructions are also given how to construct the geometry of the setup in order to minimize imaging errors. Examples are given for LiNbO₃ based practically realizable, optimized schemes with reduced imaging errors and high diffraction efficiency on the contact grating.

1.4‐mJ High Energy Terahertz Radiation from Lithium Niobates

“…[ 51,63 ] The second is that the narrowing of the spectrum reduces the chromatic aberration caused by wide spectral and imaging error caused by the large divergence angle by the angular dispersion. [ 64 ] The third is the asymmetry of the spectrum, which is discussed in detail in the numerical simulation section.…”

Laser‐Driven Strong‐Field Terahertz Sources

“…Recently, the combination of a conventional TPFP setup using imaging and a CG was proposed, [69] in which imaging distortions can be significantly reduced and less stringent requirements on the grating profile have to be fulfilled. Even though in such hybrid setups, a prism-shaped LN crystal needs to be used with ≈30° wedge angle, this angle is sufficiently small to significantly reduce transverse nonuniformity across beams as large as 1 cm.…”

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

“…Hybrid-type setups which tilt the pulse front in two stages have also been proposed to combine the advantages of different techniques. The concept of combining transmission and contact gratings was initially proposed to lower the requirement for high-groove contact grating and maintain the advantage of reducing imaging errors [78]. In addition, as shown in Figure 6a, since the THz radiation needs to leave the surface perpendicularly, the wedge angle δ follows the relation δ = γ − θ d2 , where γ is the tilt angle for phase matching and θ d2 is the diffracted angle by contact grating.…”

“…A smaller wedge angle is good to accommodate larger pump spot size and improve the THz beam profile [79], since different edges of the THz beam undergo different generation and absorption processes in the prism. We note that it is possible to reduce the wedge angle further by combining the continuous and discrete techniques to generate a TPF [78][79][80]. As in Figure 6b, a transmission grating and lens are used to pre-tilt the pulse front in air to be parallel with the pump entrance surface.…”