arXiv subjects

Valentino Pistore

Publications and source records attributed to Valentino Pistore.

4 recordsLinked to original sources

arXiv2026

GHz control of THz QCL band structure and gain by standing acoustic strain

Active frequency comb generation and waveform control are central challenges in the terahertz (THz) domain. In THz quantum cascade lasers (QCLs), these functions have typically been achieved through active bias modulation, which alters the operating point of the device and imposes severe limitations on its flexibility. To address these challenges, we propose an approach based on the direct modulation of the QCL bandstructure using GHz-frequency standing bulk acoustic waves (BAWs), promising direct and localized control of the optical gain and chromatic dispersion. To this end, we fabricated a bulk acoustic transducer on top of a THz QCL in order to excite GHz standing BAWs within its active region. We demonstrate that radio-frequency driving of the transducer leads to the tunable generation of standing BAWs in 5-12 GHz frequency range with wavelengths commensurate to the QCL period length. The effect of the BAW on the QCL bandstructure is revealed by measuring photoluminescence (PL) of the active region, where the BAW strain leads to a considerable modulation of the PL energy up to a few meV around its non-modulated value. We also develop a model and perform bandstructure simulations to predict the effect of the BAW on the QCL subband structure and gain. These results mark the first demonstration of dynamic bandstructure modulation in a THz QCL using GHz acoustic strain, introducing a fundamentally new paradigm that establishes a powerful synergy between QCLs and BAWs towards coherent control and frequency comb engineering in the THz domain.

physics.optics↗

arXiv2023

Sculpting harmonic comb states in terahertz quantum cascade lasers by controlled engineering

Optical frequency combs (FCs), that establish a rigid phase-coherent link between the microwave and optical domains of the electromagnetic spectrum, are emerging as a key high-precision tools for the development of quantum technology platforms. These include potential applications for communication, computation, information, sensing and metrology, and can extend from the near-infrared with micro-resonator combs, up to the technologically attractive terahertz (THz) frequency range, with powerful and miniaturized quantum cascade laser (QCL) FCs. The recently discovered ability of the QCLs to produce a harmonic frequency comb (HFC), a FC with large intermodal spacings, has attracted new interest in these devices for both applications and fundamental physics, particularly for the generation of THz tones of high spectral purity for high data rate wireless communication networks, for radiofrequency arbitrary waveform synthesis, and for the development of quantum key distributions. The controlled generation of harmonic states of a specific order remains, however, elusive in THz QCLs. Here we devise a strategy to obtain broadband HFC emission of a pre-defined order in QCL, by design. By patterning n regularly spaced defects on the top-surface of a double-metal Fabry-Perot QCL, we demonstrate harmonic comb emission with modes spaced by (n+1) free spectral range and with a record optical power/mode of ~270 $μW$.

physics.optics↗

arXiv2022

Ultrashort pulse generation from a graphene-coupled passively mode-locked terahertz laser

The generation of stable trains of ultra-short (fs-ps), terahertz (THz)-frequency radiation pulses, with large instantaneous intensities, is an underpinning requirement for the investigation of light-matter interactions, for metrology and for ultra-high-speed communications. In solid-state electrically-pumped lasers, the primary route for generating short pulses is through passive mode-locking. However, this has not yet been achieved in the THz range, defining one of the longest standing goals over the last two decades. In fact, the realization of passive mode-locking has long been assumed to be inherently hindered by the fast recovery times associated with the intersubband gain of THz lasers. Here, we demonstrate a self-starting miniaturized ultra-short pulse THz laser, exploiting an original device architecture that includes the surface patterning of multilayer-graphene saturable absorbers distributed along the entire cavity of a double-metal semiconductor 2.30-3.55 THz wire laser. Self-starting pulsed emission with 4.0-ps-long pulses in a compact, all-electronic, all-passive and inexpensive configuration is demonstrated.

physics.optics↗

arXiv2021

Chip-scale terahertz frequency combs through integrated intersubband polariton bleaching

Quantum 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, we conceive an integrated architecture for the generation of high power (10 mW) THz FCs comprising an ultrafast THz polaritonic reflector, exploiting intersubband cavity polaritons, and a broad bandwidth (2.3-3.8 THz) heterogeneous THz QCL. Quantum 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. By tuning the group delay dispersion in an integrated geometry, through the exploitation of light induced bleaching of the intersubband-based THz polaritons, we demonstrate spectral reshaping of the QCL emission and stable FC operation over an operational dynamic range of up to 38%, characterized by a single and narrow (down to 700 Hz) intermode beatnote. 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.

physics.optics↗