2,270 research outputs found
Spectral control of high harmonics from relativistic plasmas using bicircular fields
We introduce two-color counterrotating circularly polarized laser fields as a
new way to spectrally control high harmonic generation (HHG) from relativistic
plasma mirrors. Through particle-in-cell simulations, we show that only a
selected group of harmonic orders can appear owing to the symmetry of the laser
fields and the related conservation laws. By adjusting the intensity ratio of
the two driving field components, we demonstrate the overall HHG efficiency,
the relative intensity of allowed neighboring harmonic orders, and the
polarization state of the harmonic source can be tuned. The HHG efficiency of
this scheme can be as high as that driven by a linearly polarized laser field.Comment: 6 pages, 4 figure
Bright high-order harmonic generation with controllable polarization from a relativistic plasma mirror
Ultrafast extreme ultraviolet (XUV) sources with a controllable polarization
state are powerful tools for investigating the structural and electronic as
well as the magnetic properties of materials. However, such light sources are
still limited to only a few free-electron laser facilities and, very recently,
to high-order harmonic generation from noble gases. Here we propose and
numerically demonstrate a laser-plasma scheme to generate bright XUV pulses
with fully controlled polarization. In this scheme, an elliptically-polarized
laser pulse is obliquely incident on a plasma surface, and the reflected
radiation contains pulse trains and isolated circularly- or
highly-elliptically-polarized attosecond XUV pulses. The harmonic polarization
state is fully controlled by the laser-plasma parameters. The mechanism can be
explained within the relativistically oscillating mirror model. This scheme
opens a practical and promising route to generate bright attosecond XUV pulses
with desirable ellipticities in a straightforward and efficient way for a
number of applications.Comment: 10 pages, 5 figure
Strain-controlled high harmonic generation with Dirac fermions in silicene
Two-dimensional (2D) materials with zero band gap exhibit remarkable
electronic properties with wide tunability. High harmonic generation (HHG) in
such materials offers unique platforms to develop novel optoelectronic devices
at nanoscale, as well as to investigate strong-field and ultrafast nonlinear
behaviour of massless Dirac fermions. However, control of HHG by modulating
electronic structure of materials remains largerly unexplored to date. Here we
report controllable HHG by tuning the electronic structures via mechanical
engineering. Using an \textit{ab initio} approach based on time-dependent
density-functional theory (TDDFT), we show that the HHG process is sensitive to
the modulation of band structures of monolayer silicene while preserving the
Dirac cones under biaxial and uniaxial strains, which can lead to significant
enhancement of harmonic intensity up to an order of magnitude. With the
additional advantage of silicene in compatibility and integration into the
current silicon-based electronic industry, this study may open a new avenue to
develop efficient solid-state optoelectronic nano-devices, and provide a
valuable tool to understand the strong-field and mechanically induced ultrafast
nonlinear response of Dirac carriers in 2D materials.Comment: 24pages, 7 figure
Circularly polarized extreme ultraviolet high harmonic generation in graphene
Circularly polarized extreme ultraviolet (XUV) radiation is highly
interesting for investigation of chirality-sensitive light-matter interactions.
Recent breakthroughs have enabled generation of such light sources via high
harmonic generation (HHG) from rare gases. There is a growing interest in
extending HHG medium from gases to solids, especially to 2D materials, as they
hold great promise to develop ultra-compact solid-state photonic devices and
provide insights into electronic properties of the materials themselves.
However, HHG in graphene driven by terahertz to mid-infrared fields reported so
far only generate low harmonic orders, and furthermore no harmonics driven by
circularly polarized lasers. Here, using first-principles simulations within a
time-dependent density-functional theory framework, we show that it is possible
to generate HHG extending to the XUV spectral region in monolayer extended
graphene excited by near-infrared lasers. Moreover, we demonstrate that a
single circularly polarized driver is enough to ensure HHG in graphene with
circular polarization. The corresponding spectra reflect the six-fold
rotational symmetry of the graphene crystal. Extending HHG in graphene to the
XUV spectral regime and realizing circular polarization represent an important
step towards the development of novel nanoscale attosecond photonic devices and
numerous applications such as spectroscopic investigation and nanoscale imaging
of ultrafast chiral and spin dynamics in graphene and other 2D materials.Comment: 5 figure
Strong-field nonlinear optical properties of monolayer black phosphorus
Within the past few years, atomically thin black phosphorus (BP) has been
demonstrated as a fascinating new 2D material that is promising for novel
nanoelectronics and nanophotonics applications, due to its many unique
properties such as direct and widely tunable bandgap, high carrier mobility and
remarkable intrinsic in-plane anisotropy. However, its important extreme
nonlinear behavior and ultrafast dynamics of carriers under strong-field
excitation have yet to be revealed to date. Herein, we report nonperturbative
high harmonic generation (HHG) in monolayer BP by first-principles simulations.
We show that BP exhibits extraordinary HHG properties, with clear advantages
over three major types of 2D materials under intensive study, i.e.,
semimetallic graphene, semiconducting MoS, and insulating hexagonal boron
nitride, in terms of HHG cutoff energy and spectral intensity. This study
advances the scope of current research activities of BP into a new regime,
suggesting its promising future in applications of extreme-ultraviolet and
attosecond nanophotonics, and also opening doors to investigate the
strong-field and ultrafast carrier dynamics of this emerging material.Comment: 24 pages, 5 figure
Wavebreaking-associated transmitted emission of attosecond extreme-ultraviolet pulses from laser-driven overdense plasmas
We present a new mechanism of attosecond extreme-ultraviolet (XUV) pulses
generation from a relativistic laser-driven overdense plasma surfaces in the
wavebreaking regime. Through particle-in-cell simulations and analysis, we
demonstrate that the observed ultrashort XUV emission for the parameters we
considered is predominantly due to a strong plasma-density oscillation
subsequent to wavebreaking. The coupling of the strong density variation and
the transverse fields in the front surface layer gives rise to the transmitted
emission with frequencies mainly around the local plasma frequency. This
mechanism provides new insights into the scenarios of XUV generation from solid
surfaces and the dynamics of laser-plasma interactions.Comment: 19 pages, 10 figure
Enabling the self-contained refrigerator to work beyond its limits by filtering the reservoir
In this paper, we study the quantum self-contained refrigerator [N. Linden,
S. Popescu and P. Skrzypczyk, Phys. Rev. Lett. \textbf{105}, 130401 (2010)] in
the strong internal coupling regime with engineered reservoirs. We find that if
some modes of the three thermal reservoirs can be properly filtered out, the
efficiency and the working domain of the refrigerator can be improved in
contrast to the those in the weak internal coupling regime, which indicates one
advantage of the strong internal coupling. In addition, we find that the
background natural vacuum reservoir could cause the filtered refrigerator to
stop working and the background natural thermal reservoir could greatly reduce
the cooling efficiency.Comment: 11 pages, 5 figure
Intense isolated few-cycle attosecond XUV pulses from overdense plasmas driven by tailored laser pulses
A method to generate an intense isolated few-cycle attosecond XUV pulse is
demonstrated using particle-in-cell simulations. When a tailored laser pulse
with a sharp edge irradiates a foil target, a strong transverse net current can
be excited, which emits a few-cycle XUV pulse from the target rear side. The
isolated pulse is ultrashort in the time domain with a duration of several
hundred attoseconds. It also has a narrow bandwidth in the spectral domain
compared to other XUV sources of high-order harmonics. It has most energy
confined around the plasma frequency and no low-harmonic orders below the
plasma frequency. It is also shown that XUV pulse of peak field strength up to
V can be produced. Without the need for
pulse selecting and spectral filtering, such an intense few-cycle XUV pulse is
better suited to a number of applications.Comment: 9 pages,5 figures; Published in Optics Expres
Probing structural chirality of crystals using high harmonic generation in solids
Structural chirality plays an important role in solid state physics and leads
to a variety of novel physics. The feasibility of probing structural chirality
of crystals using high harmonic generation in solids is explored in this work.
Through first-principles calculations based on the time-dependent density
functional theory framework, we demonstrate that evident circular dichroism
(CD) effects can be induced in the high harmonic spectra from a chiral crystal
-- bulk tellurium. The CD signal reverses for crystals with opposite structural
chirality. Besides, the high harmonic spectroscopy also provides an all-optical
method for probing lattice symmetry properties and determining orientation of
the tellurium crystal.Comment: 7 pages, 5 figure
Intense high harmonic vector beams from relativistic plasma mirrors
Vector beam, with a spatial nonuniform polarization distribution, is
important for many applications due to its unique field characteristics and
novel effects when interacting with matter. Here through three-dimensional
particle-in-cell simulations, we demonstrate that intense vector beams in the
extreme-ultraviolet to x-ray spectral region can be generated by means of high
harmonic generation (HHG) in the relativistic regime. The vector features of
the fundamental laser beam can be transferred to the higher frequency emission
coherently during the extreme nonlinear HHG dynamics from relativistic plasma
mirrors. The vector harmonic beams can be synthesized into attosecond vector
beams. It is also possible to generate vector harmonic beam carrying orbital
angular momentum. Such bright vortices and vector light sources present new
opportunities in various applications such as imaging with high spatial and
temporal resolution, ultrafast magnetic spectroscopy, and particle
manipulation.Comment: 17 pages, 6 figure
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