Continuous operation of a monolithic semiconductor terahertz source at room temperature

Abstract

We demonstrate room temperature continuous wave THz sources based on intracavity difference-frequency generation from mid-infrared quantum cascade lasers. Buried ridge, buried composite distributed-feedback waveguide with Čerenkov phase-matching scheme is used to reduce the waveguide loss and enhance the heat dissipation for continuous wave operation. Continuous emission at 3.6 THz with a side-mode suppression ratio of 20 dB and output power up to 3 μW are achieved, respectively. THz peak power is further scaled up to 1.4 mW in pulsed mode by increasing the mid-infrared power through increasing the active region doping and device area.

Recent Advances in Room Temperature, High-Power Terahertz Quantum Cascade Laser Sources Based on Difference-Frequency Generation

“…Given a threshold gain gth = 5 cm −1 for CW operation, a total nonlinear susceptibility of |χ (2) | = 2.0 × 10 4 is obtained from the present design. This is comparable to the value of 2.6 × 10 4 pm/V from the previous lattice-matched active region design at λ ~ 9 µ m with a higher threshold gain [24].…”

“…The far field testing indicates that the device exhibits a good beam profile with divergence angles of 12.5˝in the vertical direction and 36˝in the lateral direction with a dual-peak distribution. Ideally, the far field pattern of theČerenkov THz emission inside of the QCL waveguide should be a conical shape with the cone angle equal to theČerenkov angle because of the much longer emitting wavelength with respect to the width of the QCL waveguide [24]. This indicates that only part of this radiation cone is able to be coupled out through the polished substrate facet limited by the Brewster's angle θ B «˘16.5˝, which is inferred from θ B = sin´1(n air /n InP ) with n air = 1, and n InP = 3.5.…”

Terahertz Frequency Metrology for Spectroscopic Applications: a Review

“…Monolithic tuning range of 3.44 to 4.02 THz was achieved with a dual-section DFG QCL waveguide design [206], and was further expanded to 2.6 to 4.2 THz with a three-section DFG QCL waveguide design [207]. Very recently, by utilizing a low-loss buried-ridge waveguide design and highly dissipative epi-down mounting scheme, room temperature CW operation at 3.6 THz was demonstrated with a continuous power of 3 μW [208]. However, the relatively high threshold current density and low wall-plug efficiency (WPE) of the demonstrated devices prevented the room temperature CW operation of the monolithic tunable devices, which has been only recently demonstrated [209 and therein refs].…”

Compact All-Quantum-Dot-Based Tunable THz Laser Source

“…However, these lasers are extremely bulky and barely support any tunability. The more recent and widely used sources of CW THz radiation are direct quantum cascade lasers (QCLs) [5] and semiconductor mixers of mid-IR QCLs [6,7]. Within the drawbacks of these technologies, though they offer the highest to date wall-plug efficiency, one can mention the following: 1) the need in cryogenic cooling for efficient operation of direct THz QCLs, 2) the lack of broad tunability, 3) the production complexity, and 4) the limitation on the generated frequencies range that barely goes below 2 THz (the most important spectroscopic region covers 1 -2 THz range).…”