Subcycle pulsed focused vector beams

Ultrashort pulses in dynamic processes of crystal plates with ultrahigh temporal and spatial resolution

Currently, the use of ultrashort pulses is one of the main methods for studying the structure and dynamics of ultrafast processes in atomic and molecular systems. In this paper, it is shown that ultrashort pulses can be used to determine the time dynamics of crystal plates with ultrahigh temporal and spatial resolution, the distance between which can be only a few angstroms. As an example, the dynamics of diamond layers with NV centers is considered. The results obtained have prospects for developing the presented theory for more complex structural objects and dynamic processes in matter.

Ultrashort pulses in structural analysis of diamond layers with angstrom resolution

X-ray crystallography is commonly used to determine crystal structures, whether continuous or ultrashort x rays are used. In this paper, it is shown that using only ultrashort pulses, it is possible to determine interplanar spacing in diamond layers, the distance between which can be only a few angstroms. The results obtained can be extended, with further development of the presented theory, to determine 3D objects in the crystal structure, the dimensions of which can be only a few angstroms.

Peculiarities of Scattering of Ultrashort Laser Pulses on DNA and RNA Trinucleotides

Currently, X-ray diffraction analysis (XRD) with high spatial and time resolution (TR-XRD) is based on the known theory of X-ray scattering, where the main parameter of USP-its duration-is not taken into account. In the present work, it is shown that, for scattering of attosecond USPs on DNA and RNA trinucleotides, the pulse length is the most important scattering parameter. The diffraction pattern changes considerably in comparison with the previously known scattering theory. The obtained results are extremely important in TR-XRD when using attosecond pulses to study trinucleotides of DNA and RNA, because with the previously known scattering theory, which does not take into account the duration of USP, one cannot correctly interpret, and therefore "decode", DNA and RNA structures.

Specificity of scattering of ultrashort laser pulses by molecules with polyatomic structure

The theory of scattering of ultrashort laser pulses (USP) is the basis of diffraction analysis of matter using modern USP sources. At present, the peculiarities of interaction of USP with complex structures are not well developed. In general, the research focuses on the features of the interaction of USP with simple systems, these are atoms and simple molecules. Here we present a theory of scattering of ultrashort laser pulses on molecules with a multi-atomic structure, taking into account the specifics of the interaction of USP with such a substance. The simplicity of the obtained expressions allows them to be used in diffraction analysis. As an example, the scattering spectra of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are presented. It is shown that the theory developed here is more general in the scattering theory and passes into the previously known one if we consider the duration of the USP to be sufficiently long.

Acceleration of electrons by tightly focused azimuthally polarized ultrashort pulses in a vacuum

Using the complex sink-source model (CSSM) and the Hertz potential method (HPM), the electromagnetic field expressions of tightly focused ultrashort azimuthally polarized pulses can be obtained. By numerically solving the relativistic Newton-Lorentz equation, the acceleration and confinement of electrons by the sub-cycle and few-cycle azimuthally polarized ultrashort pulses in vacuum are studied. Considering the radiation reaction force, it is found that electrons with an initial kinetic energy of less than 1MeV can be accelerated to hundreds of MeV and can be confined in the range of less than 1 micron for hundreds of femtoseconds in the direction perpendicular to the pulse propagation (transverse direction) by the pulses. With the increase of the beam waist and the intensity of the pulse, the electrons can obtain the exit kinetic energy exceeding 1GeV. When electrons are accelerated by the few-cycle pulses, the confined time of the electrons in the transverse direction is three times longer than that of the sub-cycle pulse. When the initial velocity of the electron points to a point in front of the focus, the electron can obtain the maximum exit kinetic energy. The change of the angular frequency corresponding to the spectral peak of the electromagnetic radiation from the electron acceleration with the electric field amplitude parameter E₀ of the pulse is studied. The phenomena of redshift and blueshift of the spectrum peak frequency of the electron radiation with the E₀ are found. These studies provide the methods to confine the movement of electrons in certain directions and accelerate electrons in the same time.

Scattering of X-ray Ultrashort Pulses by Complex Polyatomic Structures

The scattering of X-ray ultrashort pulses (USPs) is an important aspect of the diffraction analysis of matter using modern USP sources. The theoretical basis, which considers the specifics of the interaction of ultrashort pulses with complex polyatomic structures, is currently not well developed. In general, research is focused on the specifics of the interaction of ultrashort pulses with simple systems—these are atoms and simple molecules. In this work, a theory of scattering of X-ray ultrashort pulses by complex polyatomic structures is developed, considering the specifics of the interaction of ultrashort pulses with such a substance. The obtained expressions have a rather simple analytical form, which allows them to be used in diffraction analysis. As an example, it is shown that the obtained expressions can be used to study the structures of deoxyribonucleic (DNA) and ribonucleic (RNA) acids.

Focusing characteristics of linearly polarized ultrashort pulses at the focal plane

The dynamic focusing characteristics of linearly polarized ultrashort pulses are studied. Both the complex source-sink model (CSSM) and the Richards-Wolf diffraction integral theory (RWT) are used to study the focusing phenomena. For the central focus spot, the descriptions of both the CSSM and the RWT are well consistent. Also, the CSSM can describe the super-resolution focused spot very conveniently, and only the beam waist parameters need to be changed. The dynamic convergence and divergence focusing phenomena of linearly polarized ultrashort pulse are studied by both the CSSM and RWT. The numerical simulation results of both the CSSM and the RWT are not consistent. In the convergent focusing process, there are dynamic focusing phenomena transitions from the halo to two light lobes to the elliptical focus spot. In the divergent defocusing process, the phenomena are the inverse process of the phenomena in the focusing process. The peak power of halos versus the beam convergence angles are studied. The specific angles corresponding to the significantly reduced peak powers of halos are given. These studies may be applied in the field of particle manipulation and acceleration.

X-ray diffraction analysis of matter taking into account the second harmonic in the scattering of powerful ultrashort pulses of an electromagnetic field

It is well known that the scattering of ultrashort pulses (USPs) of an electromagnetic field in the X-ray frequency range can be used in diffraction analysis. When such USPs are scattered by various polyatomic objects, a diffraction pattern appears from which the structure of the object can be determined. Today, there is a technical possibility of creating powerful USP sources and the analysis of the scattering spectra of such pulses is a high-precision instrument for studying the structure of matter. As a rule, such scattering occurs at a frequency close to the carrier frequency of the incident USP. In this work, it is shown that for high-power USPs, where the magnetic component of USPs cannot be neglected, scattering at the second harmonic appears. The scattering of USPs by the second harmonic has a characteristic diffraction pattern which can be used to judge the structure of the scattering object; combining the scattering spectra at the first and second harmonics therefore greatly enhances the diffraction analysis of matter. Scattering spectra at the first and second harmonics are shown for various polyatomic objects: examples considered are 2D and 3D materials such as graphene, carbon nanotubes, and hybrid structures consisting of nanotubes. The theory developed in this work can be applied to various multivolume objects and is quite simple for X-ray structural analysis, because it is based on analytical expressions.

Convergence and divergence focusing phenomena at the focal plane of ultrashort pulses

Using the Richards-Wolf diffraction integral theory and the tightly focused ultrashort pulse vector model, the focusing phenomena at the focal plane of subcycle and few-cycle radially polarized ultrashort pulses are studied. The dynamic focusing is revealed at the focal plane. First, the subcycle or few-cycle ultrashort pulses shrink towards the focus. Then the ultrashort pulses diverge from the focus. So, the convergence and divergence moving halo at the focal plane can be observed. When approaching the focus, the amplitude of the pulse becomes larger. The phenomena can be understood from the Huygens-Fresnel principle and are important for applications of the focused ultrashort pulses.

Observing the Importance of the Phase-Volume Effect for Few-Cycle Light-Matter Interactions

The spatially dependent phase distribution of focused few-cycle pulses, i.e., the focal phase, is much more complex than the well-known Gouy phase of monochromatic beams. As the focal phase is imprinted on the carrier-envelope phase (CEP), for accurate modeling and interpretation of CEP-dependent few-cycle laser-matter interactions, both the coupled spatially dependent phase and intensity distributions must be taken into account. In this Letter, we demonstrate the significance of the focal phase effect via comparison of measurements and simulations of CEP-dependent photoelectron spectra. Moreover, we demonstrate the impact of this effect on few-cycle light-matter interactions as a function of their nonlinear intensity dependence to answer the general question: if, when, and how much should one be concerned about the focal phase?

Electron acceleration driven by sub-cycle and single-cycle focused optical pulse with radially polarized electromagnetic field

The space-time properties of the expressions of sub-cycle and single-cycle focused optical pulses with radially polarized electromagnetic field based on the Sink-Source model are studied. The self-induced blue shift of the center frequency of spectrum in the center of the pulse field is found to have an important impact on the electrons acceleration. When the electrons approach to the center of pulse, the electrons will obtain a large kinetic energy gain in a short time. The effect of radiation-reaction force can't be ignored if the net kinetic energy gain of electrons is more than GeVs. The electrons will deviate from the original acceleration channel and the gain of kinetic energy that electrons may gain will be greatly reduced if the radiation-reaction effect is considered. In contrast to the few-cycle laser pulse accelerating electrons, the gain of kinetic energy obtained by electrons is a few times higher and the corresponding peak optical power is one order of magnitude lower in the case of the sub-cycle laser pulses accelerating electrons. The maximal kinetic energy gain of electrons is robust against the variation of the incident angles.

Tighter focus for ultrashort pulse vector light beams: change of the relative contribution of different field components to the focal spot upon pulse shortening

We investigate the focusing of Poisson-spectrum few cycle pulsed light beams for linear, circular, azimuthal, and radial input polarizations with and without a first-order vortex. It is shown that, for all the considered cases, the focal spot is tighter when compared to long pulses due to the increased blue frequency content in the ultrashort pulses spectrum. More significantly, we show, for what we believe is the first time, that upon pulse shortening different focused beam vector components associated with different Bessel functions J₀ and J₁ undergo a change in the relative weight of their respective contribution to the focal spot size. This effect is caused by the different spectral dependencies of J₀ and J₁ near the focus. This newly discovered property of broadband ultrashort pulses could be exploited in light-matter interactions advantageously.

Quantum Quenching of Radiation Losses in Short Laser Pulses

Accelerated charges radiate, and therefore must lose energy. The impact of this energy loss on particle motion, called radiation reaction, becomes significant in intense-laser matter interactions, where it can reduce collision energies, hinder particle acceleration schemes, and is seemingly unavoidable. Here we show that this common belief breaks down in short laser pulses, and that energy losses and radiation reaction can be controlled and effectively switched off by appropriate tuning of the pulse length. This "quenching" of emission is impossible in classical physics, but becomes possible in QED due to the discrete nature of quantum emissions.

Robust signatures of quantum radiation reaction in focused ultrashort laser pulses

Radiation-reaction effects in the interaction of an electron bunch with a superstrong focused ultrashort laser pulse are investigated in the quantum radiation-dominated regime. The angle-resolved Compton scattering spectra are calculated in laser pulses of variable duration using a semiclassical description for the radiation-dominated dynamics and a full quantum treatment for the emitted radiation. In dependence of the laser-pulse duration we find signatures of quantum radiation reaction in the radiation spectra, which are characteristic for the focused laser beam and visible in the qualitative behavior of both the angular spread and the spectral bandwidth of the radiation spectra. The signatures are robust with respect to the variation of the electron and laser-beam parameters in a large range. Qualitatively, they differ fully from those in the classical radiation-reaction regime and are measurable with presently available laser technology.

Improved beam waist formula for ultrashort, tightly focused linearly, radially, and azimuthally polarized laser pulses in free space

We derive an asymptotically accurate formula for the beam waist of ultrashort, tightly focused fundamental linearly polarized, radially polarized, and azimuthally polarized modes in free space. We compute the exact beam waist via numerical cubature to ascertain the accuracy with which our formula approximates the exact beam waist over a broad range of parameters of practical interest. Based on this, we describe a method of choosing parameters in the model given the beam waist and pulse duration of a laser pulse.

Spatiotemporal focusing dynamics of intense supercontinuum THz pulses

High-field terahertz (THz) single-cycle pulses with 1.5 MV/cm are generated by optical rectification in the stilbazolium salt crystal 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate. We show experimentally that the generated THz transient carrying 5 octaves (0.15 to 5.5 THz) undergoes a complex time-frequency evolution when tightly focused, and we present a model based on three independent oscillating dipoles capable to describe this anomalous field evolution. Finally, we present a method to control the absolute phase of such supercontinuum THz pulses as an essential tool for future field-sensitive investigations.