Free Carrier Auger-Meitner Recombination in Monolayer Transition Metal Dichalcogenides.

Microscopic many-body models based on inputs from first-principles density functional theory are used to calculate the carrier losses due to free carrier Auger-Meitner recombination (AMR) processes in Mo- and W-based monolayer transition metal dichalcogenides as a function of the carrier density, temperature, and dielectric environment. Despite the exceptional strength of Coulomb interaction in the two-dimensional materials, the AMR losses are found to be similar in magnitude to those in conventional III-V-based quantum wells for the same wavelengths. Unlike the case in III-V materials, the losses show nontrivial density dependencies due to the fact that bandgap renormalizations on the order of hundreds of millielectronvolts can bring higher bands into or out of resonance with the optimal energy level for the AMR transition, approximately one bandgap from the lowest band.

Multiharmonic Spanning Nonlinear X-wave: An Asymptotic State of Extreme Long Wave Infrared Dispersive Shock Regularization.

We predict the emergence of novel X-waves emitted as a consequence of extreme dispersive shock regularization of an intense long wave few cycle pulse propagating through a weakly dispersive medium. This robust propagation-invariant solution to Maxwell's equations appears as the asymptotic state in the high harmonic conversion when the pump propagates in a strongly nonlinear weakly dispersive regime, while the weakly nonlinear conical emission is dominated by chromatic dispersion.

Photo Luminescence and Radiative Carrier Losses in Monolayer Transition Metal Dichalcogenides.

The carrier losses due to radiative recombination in monolayer transition metal dichalcogenides are studied using fully microscopic many-body models. The density- and temperature-dependent losses in various Mo- and W-based materials are shown to be dominated by Coulomb correlations beyond the Hartree-Fock level. Despite the much stronger Coulomb interaction in 2D materials, the radiative losses are comparable-if not weaker-than in conventional III-V materials.

Dual-wavelength channel GHz repetition rate mode-locked VECSEL cavities sourced from a common gain medium.

Mode-locked vertical external cavity semiconductor lasers are a unique class of nonlinear dynamical systems driven far from equilibrium. We present a novel, to the best of our knowledge, experimental result, supported by rigorous microscopic simulations, of two coexisting mode-locked V-cavity configurations sourced by a common gain medium and operating as independent channels at angle controlled separated wavelengths. Microscopic simulations support pulses coincident on the common gain chip extracting photons from a nearby pair of coexisting kinetic holes burned in the carrier distributions.

Self-channeling of a multi-Joule 10 µm picosecond pulse train through long distances in air.

In the long-wave infrared (LWIR) range, where, due to wavelength scaling, the critical power of Kerr self-focusing P in air increases to 300-400 GW, we demonstrate that without external focusing a train of picosecond CO laser pulses can propagate in the form of a single several-centimeter diameter channel over hundreds of meters. The train of 10 µm pulses, for which the total energy ≥20 J is distributed over several near-terawatt picosecond pulses with a maximum power ≤2P, is generated naturally during short pulse amplification in a CO laser. It is observed that the high-power 10 µm beam forms a large diameter "hot gas" channel in the ambient air with a ≥ 50 ms lifetime.

Gauge Invariant Formulation of the Semiconductor Bloch Equations.

We derive gauge invariant semiconductor Bloch equations (GI-SBEs) that contain only gauge invariant band structure; shift vectors, and triple phase products. The validity and utility of the GI-SBEs is demonstrated in intense laser driven solids with broken inversion symmetry and nontrivial topology. The GI-SBEs present a useful platform for modeling and interpreting light-matter interactions in solids, in which the gauge freedom of the Bloch basis functions obscures physics and creates numerical obstacles.

High-harmonic generation from a subwavelength dielectric resonator.

Higher-order optical harmonics entered the realm of nanostructured solids being observed recently in optical gratings and metasurfaces with a subwavelength thickness. Structuring materials at the subwavelength scale allows us toresonantly enhance the efficiency of nonlinear processes and reduce the size of high-harmonic sources. We report the observation of up to a seventh harmonic generated from a single subwavelength resonator made of AlGaAs material.

Coulomb enhancement of high harmonic generation in monolayer transition metal dichalcogenides.

High harmonic generation (HHG) in monolayer MoS is studied using fully microscopic many-body models based on the semiconductor Bloch equations and density functional theory. It is shown that Coulomb correlations lead to a dramatic enhancement of HHG. In particular, near the bandgap, enhancements of two orders of magnitude or more are observed for a wide range of excitation wavelengths and intensities.

On the importance of electron-electron and electron-phonon scatterings and energy renormalizations during carrier relaxation in monolayer transition-metal dichalcogenides.

Anbased fully microscopic many-body approach is used to study the carrier relaxation dynamics in monolayer transition-metal dichalcogenides. Bandstructures and wavefunctions as well as phonon energies and coupling matrix elements are calculated using density functional theory. The resulting dipole and Coulomb matrix elements are implemented in the Dirac-Bloch equations to calculate carrier-carrier and carrier-phonon scatterings throughout the whole Brillouin zone (BZ).

Nonlinear localization of high energy long wave laser pulses in fully correlated 3D turbulence.

We study the interplay between three-dimensional (3D) fully correlated optical turbulence and nonlinearity in time and 3D space resolved long-wavelength infrared pulsed beam propagation. Here the average self-trapped beam waist exceeds the inner scale in contrast to near-infrared filaments, and we find that their nonlinear self-channeling remains robust even in the presence of strong turbulence. More surprisingly, our simulation results invite a conjecture that in regimes where diffraction and nonlinearity are roughly balanced, turbulence can result in a tighter localization of the nonlinear beam core.

Applicability of multipole decomposition to plasmonic- and dielectric-lattice resonances.

Periodic nanoparticle arrays have attracted considerable interest recently since the lattice effect can lead to spectrally narrow resonances and tune the resonance position in a broad range. Multipole decomposition is widely used to analyze the role of the multipoles in the resonance excitations, radiation, and scattering of electromagnetic waves. However, previous studies have not addressed the validity and accuracy of the multipole decomposition around the lattice resonance.

Generation of long homogeneous plasma channels with high power long-wave IR pulsed Bessel beams.

Long-wave multi-joule ultrashort laser pulses are predicted to confine highly uniform electromagnetic energy and field intensities while sustaining high density uniform plasmas within nonlinear Bessel zones under extreme driving conditions in contrast to near-IR sources. This opens up novel applications in laser wakefield generation, radiofrequency/microwave guiding, and lightning control.

Subcycle spatiotemporal compression of infrared pulses in semiconductors.

Using a full-field propagator model, we report on the emergence of highly localized, subcycle solitonic structures for few-cycle long-wave-infrared (LWIR) pulses propagating through optical semiconductor materials with efficient quadratic nonlinearities and broad anomalous transmission windows. We briefly discuss the theoretical basis for the observed spatiotemporal carrier-wave dynamics and compare it to simulations of a weakly perturbed pulse's propagation through two currently grown, low-loss IR semiconductor crystals.

VECSEL-based virtually imaged phased array spectrometer for rapid gas phase detection in the mid-infrared.

We present a novel, to the best of our knowledge, system for high-resolution, time-resolved spectroscopy in the mid-wave infrared based on a modelocked vertical external cavity surface emitting laser (VECSEL) frequency comb coupled to a virtually imaged phased array (VIPA) spectrometer. The GHz level repetition rate of VECSEL-based systems coupled to VIPA spectrometers enables comb tooth resolved spectra without the use of additional filter cavities often required to increase comb tooth spacing. We demonstrate absorption spectroscopy on a methane () gas mixture at 2900 (3.

Propagation Induced Dephasing in Semiconductor High-Harmonic Generation.

The influence of propagation on the nonperturbative high-harmonic features in long-wavelength strong pulse excited semiconductors is studied using a fully microscopic approach. For sample lengths exceeding the wavelength of the exciting light, it is shown that the propagation effectively acts as a very strong additional dephasing that reduces the relative height of the emission plateau up to six orders of magnitude. This propagation induced dephasing clarifies the need to use extremely short polarization decay times for the quantitative analysis of experimental observations.

Optical Carrier-Wave Subcycle Structures Associated with Supercritical Collapse of Long-Wavelength Intense Pulses Propagating in Weakly Anomalously Dispersive Media.

We predict the emergence of attosecond-duration structures on an optical carrier wave when intense, long-wavelength pulses propagate through bulk media with weak anomalous dispersion. Under certain conditions, these structures can undergo a new type of carrier-resolved supercritical collapse, forming infinite spatiotemporal gradients in the field. The mathematical conditions for the onset of this singularity are briefly overviewed, and we demonstrate with a full 3D+time (3+1) simulation that such structures persist under realistic conditions for a 10 micron laser pulse propagating in air.

Control of the nonlinear response of bulk GaAs induced by long-wavelength infrared pulses.

The nonlinear optical response of GaAs is studied using extremely nonresonant 10 m laser pulses with peak intensities greater than 2 GW/cm . We observe over an order of magnitude enhancement in the four-wave mixing efficiency by decreasing the CO laser beat-wave frequency. This enhancement is attributed to currents of photoexcited unbound carriers modulated at the beat frequency, confirmed by measurements of nonlinear absorption at this long wavelength as well as a fully microscopic analysis of the excitation dynamics.

Two-stage filamentation of 10 μm pulses as a broadband infrared backlighter in the atmosphere.

We identify a two-stage filamentation regime for high-power 10 μm multipicosecond pulses propagating in the atmosphere. The first low-intensity stage is mainly regularized by ionization through excitation induced dephasing, which can lead to strong pulse shortening downstream. This shortening in turn causes a significant reduction of the many-body induced plasma, which changes the dynamics drastically.

Memory effects in the long-wave infrared avalanche ionization of gases: a review of recent progress.

There are currently intense efforts being directed towards extending the range and energy of long distance nonlinear pulse propagation in the atmosphere by moving to longer infrared wavelengths, with the purpose of mitigating the effects of turbulence. In addition, picosecond and longer pulse durations are being used to increase the pulse energy. While both of these tacks promise improvements in applications, such as remote sensing and directed energy, they open up fundamental issues regarding the standard model used to calculate the nonlinear optical properties of dilute gases.

Offset-free mid-infrared frequency comb based on a mode-locked semiconductor laser.

We demonstrate a carrier-envelope offset-free frequency comb in the mid-wavelength infrared (MWIR) based on a passively mode-locked vertical external cavity surface emitting laser (VECSEL) operating at a 1.6 GHz repetition rate. The 290 mW output spanning 3.

Non-equilibrium dynamics in the dual-wavelength operation of vertical external-cavity surface-emitting lasers.

Microscopic many-body theory coupled with Maxwell's equation is used to study dual-wavelength operation in vertical external-cavity surface-emitting lasers. The intrinsically dynamic nature of coexisting emission wavelengths in semiconductor lasers is associated with characteristic non-equilibrium carrier dynamics, which causes significant deformations of the quasi-equilibrium gain and carrier inversion. Extended numerical simulations are employed to efficiently investigate the parameter space to identify the regime for dual-wavelength operation.

Author Correction: High-temperature operation of electrical injection type-II (GaIn)As/Ga(AsSb)/(GaIn)As "W"-quantum well lasers emitting at 1.3 µm.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

High-temperature operation of electrical injection type-II (GaIn)As/Ga(AsSb)/(GaIn)As "W"-quantum well lasers emitting at 1.3 µm.

Electrical injection lasers emitting in the 1.3 μm wavelength regime based on (GaIn)As/Ga(AsSb)/(GaIn)As type-II double "W"-quantum well heterostructures grown on GaAs substrate are demonstrated. The structure is designed by applying a fully microscopic theory and fabricated using metal organic vapor phase epitaxy.

Multi-terawatt 10 μm pulse atmospheric delivery over multiple Rayleigh ranges.

We predict that long wavelength self-trapped multi-terawatt pulses can be sustained over multiple kilometers in the atmosphere. Unlike filaments, these pulses exhibit low loss propagation and retain most of their launch power at range. A novel mechanism involving an aggregation of weakly linear and nonlinear cumulative optical responses is shown to be responsible and is dominated by an ultrafast dynamical lensing resulting from a field intensity driven many-body Coulomb mediated free electron polarization associated with spatially separated species in the gas.

Self-Channeling of High-Power Long-Wave Infrared Pulses in Atomic Gases.

We simulate and elucidate the self-channeling of high-power 10  μm infrared pulses in atomic gases. The major new result is that the peak intensity can remain remarkably stable over many Rayleigh ranges. This arises from the balance between the self-focusing, diffraction, and defocusing caused by the excitation induced dephasing due to many-body Coulomb effects that enhance the low-intensity plasma densities.