Broadly tunable terahertz generation in mid-infrared quantum cascade lasers

Abstract

Room temperature, broadly tunable, electrically pumped semiconductor sources in the terahertz spectral range, similar in operation simplicity to diode lasers, are highly desired for applications. An emerging technology in this area are sources based on intracavity difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers. Here we report terahertz quantum cascade laser sources based on an optimized non-collinear Cherenkov difference-frequency generation scheme that demonstrates dramatic improvements in performance. Devices emitting at 4 THz display a mid-infrared-to-terahertz conversion efficiency in excess of 0.6 mW W À 2 and provide nearly 0.12 mW of peak power output. Devices emitting at 2 and 3 THz fabricated on the same chip display 0.09 and 0.4 mW W À 2 conversion efficiencies at room temperature, respectively. High terahertzgeneration efficiency and relaxed phase-matching conditions offered by the Cherenkov scheme allowed us to demonstrate, for the first time, an external-cavity terahertz quantum cascade laser source tunable between 1.70 and 5.25 THz.

Quantum Čerenkov Radiation: Spectral Cutoffs and the Role of Spin and Orbital Angular Momentum

“…Namely, it can also occur for classical charge distributions having a well-defined spread angle θ i , as well as in analogs of the Čerenkov effect in other areas of physics (for example, see Refs. [13,14]; similar conditions could be designed in other systems analogous to ČR [8][9][10][11][12][13][14][15][16][17][18][19]21,22]). In either case, the cone splitting we show here is uniquely tied to the shape of the incoming electron wave packet (or the charge distribution in a classical electron beam), and it is independent of material properties that can cause other kinds of cone splittings [50].…”

“…Since its discovery, the Čerenkov effect has become a fundamental part of many fields [2]: Devices like the ring-imaging Čerenkov detector are used for cosmic radiation measurements [3,4], while other implications also suggest novel acceleration methods [5], and even an unusual imaging tool in biology [6,7]. Because of the fundamental nature of ČR, it is found in many different physical systems, such as in nonlinear optics [8][9][10][11], it is used in the design of quantum cascade lasers [12], and it is predicted to yield the generation of entangled photon pairs [13,14]. Other kinds of ČR were found in photonic crystals [15,16], tunable light sources [17], coherently driven ultracold atomic gas [18], and recently even in active gain medium [19].…”

Transformation optics beyond the manipulation of light trajectories

“…Experimentally, this radiation was discovered by Pavel Cherenkov [39] and, theoretically, it was formalized by Frank & Tamm [40]. Nowadays, this effect is well understood and has been proved useful in a wide range of applications in applied and experimental physics [41], including high-energy particle physics, detection of cosmic rays in astrophysical measurements [42], development of novel electromagnetic sources [43][44][45], localized sensing in biological systems [46], spectroscopy of complex nanostructures [47]. In recent years, there has been significant interest in the manipulation of Cherenkov radiation inside or in the vicinity of electromagnetic structured media [48][49][50][51][52][53][54][55][56][57][58][59][60][61].…”

Room-temperature two-color lasing by current injection into a GaAs/AlGaAs coupled multilayer cavity fabricated by wafer bonding

“…Recently, intracavity difference-frequency generation (DFG) in dual-wavelength mid-infrared QCLs has been demonstrated as a THz source. 13,14) We have proposed a GaAs=AlAs coupled multilayer cavity structure for compact and room-temperature operable THz emitting devices. 15) The structure is composed of two equivalent cavity layers and three distributed Bragg reflector (DBR) multilayers.…”