Light amplification by seeded Kerr instability Vampa, G; Hammond, T J; Nesrallah, M ...
Science (American Association for the Advancement of Science),
02/2018, Letnik:
359, Številka:
6376
Journal Article
Recenzirano
Odprti dostop
Amplification of femtosecond laser pulses typically requires a lasing medium or a nonlinear crystal. In either case, the chemical properties of the lasing medium or the momentum conservation in the ...nonlinear crystal constrain the frequency and the bandwidth of the amplified pulses. We demonstrate high gain amplification (greater than 1000) of widely tunable (0.5 to 2.2 micrometers) and short (less than 60 femtosecond) laser pulses, up to intensities of 1 terawatt per square centimeter, by seeding the modulation instability in an Y
Al
O
crystal pumped by femtosecond near-infrared pulses. Our method avoids constraints related to doping and phase matching and therefore can occur in a wider pool of glasses and crystals even at far-infrared frequencies and for single-cycle pulses. Such amplified pulses are ideal to study strong-field processes in solids and highly excited states in gases.
A numerical method is developed by which the tunnel ionization dynamics of bound systems in laser fields can be isolated from the total wave function, as given by the time-dependent Schrödinger ...equation. The analysis of the numerical data for a step function field reveals the following definition for the tunnel time. It is the time it takes the ground state to develop the underbarrier wave function components necessary for reaching the static field ionization rate. This definition is generalized to time varying laser fields. The tunnel time is found to scale with the Keldysh tunnel time. Our Letter establishes the physical meaning of the tunnel time, its relation to the Keldysh tunnel time, and suggests how it can be measured.
In solids, high harmonic radiation arises from the subcycle dynamics of electrons and holes under the action of an intense laser field. The strong-field regime opens new opportunities to understand ...and control carrier dynamics on ultrafast time scales, including the coherent dynamics of quasiparticles such as massless Dirac fermions. Here, we irradiate monolayer and few-layer graphene with intense infrared light to produce nonperturbative harmonics of the fundamental up to the seventh order. We find that the polarization dependence shows surprising agreement with gas-phase harmonics. Using a two-band model, we explore the nonlinear current due to electrons near the Dirac points, and we discuss the interplay between intraband and interband contributions to the harmonic spectrum. This interplay opens new opportunities to access ultrafast and strong-field physics of graphene.
High-harmonic generation (HHG) in bulk crystals exposed to intense mid-infrared lasers with photon energies below the bandgap is investigated theoretically. A three dimensional, two-band model that ...considers both interband and intraband currents is used. It is shown that the interband current is the dominant mechanism for HHG in solids. A physical interpretation of interband HHG – similar to atomic HHG – is provided by saddle point analysis. The effects of dephasing time and driving field wavelength on the harmonic specrum are investigated.
Tunneling time, what is its meaning? McDonald, C R; Orlando, G; Vampa, G ...
Journal of physics. Conference series,
03/2015, Letnik:
594, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The tunnel time ionization dynamics for bound systems in laser fields are investigated. Numerical analysis for a step function switch-on of the field allows for the tunnel time to be defined as the ...time it takes the ground state to develop the under-barrier wavefunction components necessary to achieve the static field ionization rate. A relation between the tunnel time and the Keldysh time is established. The definition of the tunnel time is extended to time varying fields and experimental possibilities for measuring the tunnel time are discussed.
Interferametrically CEP controlled few-cycle IR pulses revealed a strong influence on both, directly ionized and rescattered electrons in xenon for pulse durations from 2 to 5 cycles.
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