Abstract
AbstractQuantum cascade lasers (QCLs) represent a fascinating accomplishment of quantum engineering and enable the direct generation of terahertz (THz) frequency radiation from an electrically biased semiconductor heterostructure. Their large spectral bandwidth, high output powers, and quantum‐limited linewidths have facilitated the realization of THz pulses by active mode‐locking and passive generation of optical frequency combs (FCs) through intracavity four‐wave‐mixing, albeit over a restricted operational regime. Here, an integrated architecture is conceived for the generation of high power (5.5–8.0 mW) THz FCs comprising an ultrafast THz polaritonic reflector, exploiting intersubband (ISB) cavity polaritons, and a broad bandwidth (2.3–3.8 THz) heterogenous THz QCL. By tuning the group‐delay‐dispersion in an integrated geometry, through the exploitation of light‐induced bleaching of the ISB‐based THz polaritons, spectral reshaping of the QCL emission and stable FC operation over an operational range up to 38%, characterized by a single and narrow (down to 700 Hz) intermode beatnote are demonstrated. This concept provides design guidelines for a new generation of compact, cost‐effective, electrically driven chip‐scale FC sources based on ultrafast polariton dynamics, paving the way toward the generation of mode‐locked THz microlasers that can strongly impact a broad range of applications in ultrafast sciences, data storage, high‐speed communication, and spectroscopy.
Highlights
The generation of stable frequency comb (FC) synthesizers with large optical powers per comb tooth [1], at terahertz (THz) frequencies, is fundamental for the investigation of light-matter interaction phenomena at the nanoscale, for quantum metrology [2], for communications [3], and for multiplexed analysis of gas samples requiring narrow-linewidth and a tight control of frequency jitter [4]
Our concept provides design guidelines for a new generation of compact, cost-effective, electrically driven chip-scale FC sources based on ultrafast polariton dynamics, paving the way towards the generation of mode locked THz micro-lasers that will strongly impact a broad range of applications in ultrafast sciences, data storage, high-speed communication and spectroscopy
When radiation polarized orthogonal to the grating lines (p-polarization) impinges at normal incidence, a fringe electric field is localized within the MQW heterostructure at the metallic edges of the grating
Summary
The generation of stable frequency comb (FC) synthesizers with large optical powers per comb tooth [1], at terahertz (THz) frequencies (wavelength 300–30 μm), is fundamental for the investigation of light-matter interaction phenomena at the nanoscale, for quantum metrology [2], for communications [3], and for multiplexed analysis of gas samples requiring narrow-linewidth and a tight control of frequency jitter [4]. The most common technique to generate an FC in a solid-state laser is through mode-locking [5, 6]: the longitudinal modes of the laser cavity are locked in phase by means of an external (active) or internal (self- or passive) modulation mechanism, giving rise to a train of equidistant and intense pulses with a repetition rate equal to the inverse cavity round-trip time. There is a fundamental obstacle preventing mode-locking with passive generation of ultrashort pulses in the semiconductor gain medium of a THz QCL: owing to the intersubband (ISB) architecture, the carrier relaxation is extremely fast (5-10 ps) [11]. The gain recovery time is shorter than the cavity round-trip time (∼70 ps for a 3 mm cavity) [12], complicating the generation of stable “ultrafast” laser pulses
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
