Room-temperature, continuous-wave Terahertz generation in free-space with an intersubband mid-infrared photomixer

TL;DR

This paper presents a room-temperature, continuous-wave free-space Terahertz source using a novel mid-infrared photomixer with a dual-antenna design, achieving high efficiency and tunability up to 1 THz.

Contribution

The work introduces a new intersubband photomixer architecture that enables efficient, tunable, continuous-wave Terahertz generation at room temperature using mid-infrared pumping.

Findings

Achieved continuous-wave Terahertz generation up to 1 THz at room temperature.

Demonstrated power efficiency exceeding that of $ ext{chi}^{(2)}$-based devices.

Identified carrier lifetime and RC time constant as limiting factors for high-frequency performance.

Abstract

We demonstrate a Terahertz photomixer pumped by mid-infrared photons at 10$\mu$m wavelength. The device is based on a dual-antenna architecture, in which a two-dimensional array of mid-infrared patch-antenna resonators is connected to the electrodes of a log-spiral Terahertz antenna. By exploiting intersubband absorption inside an AlGaAs-GaAs multi-quantum-well heterostructure, a photocurrent is coherently generated at the difference frequency between two quantum cascade lasers. The photocurrent drives the antenna electrodes allowing tunable, continuous-wave generation in free-space up to 1 Terahertz at room temperature. By experimentally studying the photomixer frequency response and dark impedance, we demonstrate that the observed power roll-off at high-frequency is limited by the combined effect of the photoexcited carrier's intrinsic lifetime and of the device $RC$ time constant. In the spectral range investigated we obtain, in continuous-wave, mid-infrared $\rightarrow$ Terahertz conversion efficiencies exceeding by orders of magnitude those of unipolar devices exploiting $\chi^{(2)}$ processes.