29 research outputs found
Coherent multi-mode dynamics in a Quantum Cascade Laser: Amplitude and Frequency-modulated Optical Frequency Combs
We cast a theoretical model based on Effective Semiconductor Maxwell-Bloch
Equations and study the dynamics of a multi-mode mid-Infrared Quantum Cascade
Laser in Fabry Perot with the aim to investigate the spontaneous generation of
optical frequency combs. This model encompasses the key features of a
semiconductor active medium such as asymmetric,frequency-dependent gain and
refractive index as well as the phase-amplitude coupling of the field dynamics
provided by the linewidth enhancement factor. Our numerical simulations are in
excellent agreement with recent experimental results, showing broad ranges of
comb formationin locked regimes, separated by chaotic dynamics when the field
modes unlock. In the former case, we identify self-confined structures
travelling along the cavity, while the instantaneous frequency is characterized
by a linear chirp behaviour. In such regimes we show that OFC are characterized
by concomitant and relevant amplitude and frequency modulation
Extrinsic electromagnetic chirality in all-photodesigned one-dimensional THz metamaterials
We suggest that all-photodesigned metamaterials, sub-wavelength custom
patterns of photo-excited carriers on a semiconductor, can display an exotic
extrinsic electromagnetic chirality in terahertz (THz) frequency range. We
consider a photo-induced pattern exhibiting 1D geometrical chirality, i.e. its
mirror image can not be superposed onto itself by translations without
rotations and, in the long wavelength limit, we evaluate its bianisotropic
response. The photo-induced extrinsic chirality turns out to be fully
reconfigurable by recasting the optical illumination which supports the
photo-excited carriers. The all-photodesigning technique represents a feasible,
easy and powerful method for achieving effective matter functionalization and,
combined with the chiral asymmetry, it could be the platform for a new
generation of reconfigurable devices for THz wave polarization manipulation.Comment: 11 page
Terahertz optically tunable dielectric metamaterials without microfabrication
We theoretically investigate the terahertz dielectric response of a
semiconductor slab hosting an infrared photoinduced grating. The periodic
structure is due to the charge carries photo-excited by the interference of two
tilted infrared plane waves so that the grating depth and period can be tuned
by modifying the beam intensities and incidence angles, respectively. In the
case where the grating period is much smaller than the terahertz wavelength, we
numerically evaluate the ordinary and extraordinary component of the effective
permittivity tensor by resorting to electromagnetic full-wave simulation
coupled to the dynamics of charge carries excited by infrared radiation. We
show that the photoinduced metamaterial optical response can be tailored by
varying the grating and it ranges from birefringent to hyperbolic to
anisotropic negative dielectric without resorting to microfabrication.Comment: 3 pages, 2 figure
Retrieval of the Dielectric Properties of a Resonant Material in the Terahertz Region via Self-Detection Near Field Optical Microscopy
We present a numerical and analytical study of the self-detection scattering type near field optical microscopy (SD s-SNOM), a recently demonstrated technique based on a combination of self-mixing interferometry and scattering near-field microscopy. This scheme, which exploits a terahertz (THz) quantum cascade laser as both a laser source and detector, allows to investigate the optical properties of resonant materials in the THz range with resolution far beyond the diffraction limit. Our study, developed by using a modified version of the Lang-Kobayashi model, is focused on the weak feedback regime (Acket parameter C approximate to 10(-1)), where we derive an approximated method for the retrieval of the scattering coefficient of the SD s-SNOM configuration applied to a sample of Cesium Bromide (CsBr). These results were used in turn to derive the dielectric permittivity of the sample, reporting a good accuracy in the estimation of its phonon resonances
Dissipative phase solitons in semiconductor lasers
We experimentally demonstrate the existence of non dispersive solitary waves
associated with a 2 phase rotation in a strongly multimode ring
semiconductor laser with coherent forcing. Similarly to Bloch domain walls,
such structures host a chiral charge. The numerical simulations based on a set
of effective Maxwell-Bloch equations support the experimental evidence that
only one sign of chiral charge is stable, which strongly affects the motion of
the phase solitons. Furthermore, the reduction of the model to a modified
Ginzburg Landau equation with forcing demonstrates the generality of these
phenomena and exposes the impact of the lack of parity symmetry in propagative
optical systems.Comment: 5 pages, 5 figure
Dynamics of Optical Frequency Combs in Ring and Fabry-Perot Quantum Cascade Lasers
Since the demonstration that multimode Quantum Cascade Lasers (QCLs) can operate as sources of Optical Frequency Combs (OFC) [1] , an extended class of theoretical models, based on standard two or three level Maxwell-Bloch equations, has been proposed to interpret such phenomenology
Versatile Multimodality Imaging System Based on Detectorless and Scanless Optical Feedback Interferometry-A Retrospective Overview for A Prospective Vision
In this retrospective compendium, we attempt to draw a "fil rouge" along fifteen years of our research in the field of optical feedback interferometry aimed at guiding the readers to the verge of new developments in the field. The general reader will be moved at appreciating the versatility and the still largely uncovered potential of the optical feedback interferometry, for both sensing and imaging applications. By discovering the broad range of available wavelengths (0.4-120 ÎĽm), the different types of suitable semiconductor lasers (Fabry-Perot, distributed feedback, vertical-cavity, quantum-cascade), and a number of unconventional tenders in multi-axis displacement, ablation front progression, self-referenced measurements, multispectral, structured light feedback imaging and compressive sensing, the specialist also could find inspirational suggestions to expand his field of research
Terahertz near-field nanoscopy based on detectorless laser feedback interferometry under different feedback regimes
Near-field imaging techniques, at terahertz frequencies (1–10 THz), conventionally rely on bulky laser sources and detectors. Here, we employ a semiconductor heterostructure laser as a THz source and, simultaneously, as a phase-sensitive detector, exploiting optical feedback interferometry combined with scattering near-field nanoscopy. We analyze the amplitude and phase sensitivity of the proposed technique as a function of the laser driving current and of the feedback attenuation, discussing the operational conditions ideal to optimize the nano-imaging contrast and the phase sensitivity. As a targeted nanomaterial, we exploit a thin (39 nm) flake of Bi2Te2.2Se0.8, a topological insulator having infrared active optical phonon modes. The self-mixing interference fringes are analyzed within the Lang–Kobayashi formalism to rationalize the observed variations as a function of Acket's parameter C in the full range of weak feedback (C < 1)
Cavity Light Bullets: 3D Localized Structures in a Nonlinear Optical Resonator
We consider the paraxial model for a nonlinear resonator with a saturable
absorber beyond the mean-field limit and develop a method to study the
modulational instabilities leading to pattern formation in all three spatial
dimensions. For achievable parametric domains we observe total radiation
confinement and the formation of 3D localised bright structures. At difference
from freely propagating light bullets, here the self-organization proceeds from
the resonator feedback, combined with diffraction and nonlinearity. Such
"cavity" light bullets can be independently excited and erased by appropriate
pulses, and once created, they endlessly travel the cavity roundtrip. Also, the
pulses can shift in the transverse direction, following external field
gradients.Comment: 4 pages, 3 figures, simulations files available at
http://www.ba.infn.it/~maggipin/PRLmovies.htm, submitted to Physical Review
Letters on 24 March 200