1.4‐mJ High Energy Terahertz Radiation from Lithium Niobates

Abstract

Free‐space super‐strong terahertz (THz) electromagnetic fields offer multifaceted capabilities for reaching extreme nonlinear THz optics. However, the lack of powerful solid‐state THz sources with single pulse energy >1 mJ is impeding the proliferation of extreme THz applications. The fundamental challenge lies in hard to achieve high efficiency due to high intensity pumping caused crystal damage, linear absorption, and nonlinear distortion induced short effective interaction length, and so on. Here, through cryogenically cooling the crystals, tailoring the pump laser spectra, chirping the pump pulses, and magnifying the laser energies, 1.4‐mJ THz pulses are successfully realized in lithium niobates under the excitation of 214‐mJ femtosecond laser pulses via tilted pulse front technique. The 800 nm‐to‐THz energy conversion efficiency reaches 0.7%, and a free‐space THz peak electric and magnetic field reaches 6.3 MV cm−1 and 2.1 Tesla. Numerical simulations reproduce the experimental optimization processes. To show the capability of this super‐strong THz source, nonlinear absorption in high conductive silicon induced by strong THz electric field is demonstrated. Such a high‐energy THz source with a relatively low peak frequency is very appropriate not only for electron acceleration toward table‐top X‐ray sources but also for extreme THz science and nonlinear applications.

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

“…The focusing of high-energy THz pulses to the diffraction limit is still lacking. 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].…”

“…Under a very high pump fluence of more than 50 mJ/cm 2 , the system needs delicate design, such as choosing a pump with the appropriate spectrum, pulse duration, group delay, and LN crystal under cooling, to suppress the saturation effects and prevent an efficiency decrease. With that in mind, a 1.4 mJ THz pulse has been demonstrated using a 214 mJ 800 nm pump pulse [31]. For a 1030 nm pump, the record-high efficiency reaches 3.8% at 150 K and 1.7% at room temperature [28,40] and the highest pulse energy reaches 0.4 mJ with a 0.77% energy conversion efficiency [30].…”

“…Currently, the conversion efficiency can reach as high as 3.8% using a 1.03 µm pump and a cryogenically cooled crystal to reduce absorption [28]. The peak field record was established at 1.2 MV/cm with a kHz system [29], while the output THz pulse energy can reach mJ levels using 10 Hz laser system [30,31]. In the following, we focus on single-to few-cycle THz generation from LN, i.e., single-to few-periods of the generated field at the central frequency.…”

“…The peak field records and typical outputted spectrum are listed for different conventional methods. Dual-color laser air plasma: 100 MV/cm [23] for 1-20 THz; organic crystal: 83 MV/cm[21] for 1-10 THz; GaSe: 12 MV/cm[32] for 10-40 THz; spintronic emitter: 300 kV/cm[33] for 1-30 THz; LAPCA: 330 kV/cm for 0.1-3 THz; ZnTe: 570 kV/cm for 0.1-3 THz[20]; LN: 6.3 MV/cm[31] for 0.1-3 THz. (b) Development of THz generation from LN with TPF techniques over the years[27,[29][30][31][34][35][36][37][38][39][40].…”

Deep learning enhanced terahertz imaging of silkworm eggs development

“…However, most THz imaging techniques based on scanning method are still suffering the time-consuming disadvantage, greatly hindering the widespread applications of THz technology (Cocker et al, 2013;Watts et al, 2014). Along with the accelerated advances of high-power THz sources (Chen et al, 2019;Khalatpour et al, 2021;Samizadeh Nikoo et al, 2020;Zhang et al, 2021;Zhao et al, 2020) and various high-sensitivity THz detectors (Gayduchenko et al, 2021;Guo et al, 2020;Ma et al, 2019;Peng et al, 2020), THz spectral imaging technology turns out to be feasible. Among these devices, high-power THz quantum cascaded laser (QCL) light sources are facing the dawn of moving from the laboratory research stage to practical applications (Khalatpour et al, 2021;Stantchey et al, 2020), and THz video imaging technique is expected to usher in rapid development (Zhou et al, 2018).…”