A High-Power Broadband Terahertz Source Enabled by Three-Dimensional Light Confinement in a Plasmonic Nanocavity

Abstract

The scope and potential uses of time-domain terahertz imaging and spectroscopy are mainly limited by the low optical-to-terahertz conversion efficiency of photoconductive terahertz sources. State-of-the-art photoconductive sources utilize short-carrier-lifetime semiconductors to recombine carriers that cannot contribute to efficient terahertz generation and cause additional thermal dissipation. Here, we present a novel photoconductive terahertz source that offers a significantly higher efficiency compared with terahertz sources fabricated on short-carrier-lifetime substrates. The key innovative feature of this source is the tight three-dimensional confinement of the optical pump beam around the terahertz nanoantennas that are used as radiating elements. This is achieved by means of a nanocavity formed by plasmonic structures and a distributed Bragg reflector. Consequently, almost all of the photo-generated carriers can be routed to the terahertz nanoantennas within a sub-picosecond time-scale. This results in a very strong, ultrafast current that drives the nanoantennas to produce broadband terahertz radiation. We experimentally demonstrate that this terahertz source can generate 4 mW pulsed terahertz radiation under an optical pump power of 720 mW over the 0.1–4 THz frequency range. This is the highest reported power level for terahertz radiation from a photoconductive terahertz source, representing more than an order of magnitude of enhancement in the optical-to-terahertz conversion efficiency compared with state-of-the-art photoconductive terahertz sources fabricated on short-carrier-lifetime substrates.

Metallic and dielectric metasurfaces in photoconductive terahertz devices: a review

“…[133][134][135][136] In this case, the THz generation occurs due to nonlinear optical processes 134 as well as the heat redistribution inside metal due to electron heating by an optical excitation. 137,138 However, the emitted THz power of the standalone metal metasurface is relatively low compared with the plasmonic PCA 69 and even to the surface photo-Dember THz emitter 136 and amounts, on average, to 0.15 mW, corresponding to an optical-to-THz conversion efficiency of up to 0.01% at 5.8 THz. 135 Furthermore, both metallic and dielectric metasurface configurations can be designed to effectively interact with THz radiation and thus can be used in ultrasensitive THz sensors, THz absorbers, highly selective THz detectors, tunable THz field modulators, [139][140][141][142] and THz mirrors, 143 as well as to control a wavefront at THz frequency, 144 etc.…”

“…In this case, the photocarriers are generated in very close proximity to the nanoantennas, and if a bias voltage is simultaneously applied, almost all of them can reach the nanoantennas and contribute to the THz emission. Yardimci et al 69 70 They demonstrated an SNR of 100 dB when operating with an optical pump power of 5 mW. However, as an optical power exceeds 5 mW, the sensitivity of the detector starts saturating, whereas the LT-GaAs-based PCA-detector exhibits higher responsivities working with the same optical pump.…”

“…3(b), adapted from Ref. 69]. In this case, the photocarriers are generated in very close proximity to the nanoantennas, and if a bias voltage is simultaneously applied, almost all of them can reach the nanoantennas and contribute to the THz emission.…”

Comparative Efficiency and Power Assessment of Optical Photoconductive Material-Based Terahertz Sources for Wireless Communication Systems

“…Using distributed Bragg re°ector-based nanocavity, authors have achieved strong con¯nement of the optical beam and 4-mW terahertz power is reported in Ref. 68. In order to see the di®erences clearly, reported results of recent OPM studies are summarized in Table 5 and plotted in Fig.…”

Prediction of leaf water potential and relative water content using terahertz radiation spectroscopy

“…Terahertz time‐domain spectroscopy (THz‐TDS) employs short pulses of electromagnetic radiation, which have a broad terahertz frequency range (Skoog, Holler, & Crouch, ). The transmitted and reflected pulses through and from the sample are detected to extract the time‐ and frequency‐domain responses (Yardimci, Cakmakyapan, Hemmati, & Jarrahi, ; Yardimci & Jarrahi, ). Because of these specifications, there has been great interest in predicting plant water status using THz‐TDS systems (Table ; Hu & Nuss, ; Hadjiloucas, Karatzas, & Bowen, ; Jördens, Scheller, Breitenstein, Selmar, & Koch, ; Castro‐Camus, Palomar, & Covarrubias, ; Gente et al, ; Born et al, ; Gente, Rehn, & Koch, ; Santesteban et al, ; Baldacci et al, ; Gente et al, ).…”