Laser Pulse Of Finite Duration Research Articles

Unveiling the interplay of Mollow physics and perturbed free induction decay by nonlinear optical signals of a dynamically driven two-level system

Nonlinear optical signals in optically driven quantum systems can reveal coherences and thereby open up the possibility for manipulation of quantum states. While the limiting cases of ultrafast and continuous-wave excitation have been extensively studied, the time dynamics of finite pulses bear interesting phenomena. In this paper, we explore the nonlinear optical probe signals of a two-level system excited with a laser pulse of finite duration. In addition to the prominent Mollow peaks, the probe spectra feature several smaller peaks for certain time delays. Similar features have been recently observed for resonance fluorescence signals [K. Boos , ]. We discuss that the emergent phenomena can be explained by a combination of Mollow triplet physics and perturbed free induction decay effects, providing an insightful understanding of the underlying physics. Published by the American Physical Society 2024

The errors when determining the thermophysical characteristics of liquids by the laser flash method

The analysis of errors in determining the thermophysical characteristics of typical organic liquids, specified by conductive-radiative heat transfer of ultrathin heated up to high temperature sample layer, under conditions consistent with the implementation of the laser pulse method, when exposed to the surface of the collimated laser pulse of finite duration was made. The influence to the error of the radiation absorption process was discovered.

Effect of Laser Pulse Duration on the Error in Determining the Thermal Characteristics of Construction Materials

The errors in determining the thermal characteristics of materials with a finite duration laser pulse method are estimated. Handbook values of the characteristics of materials are compared with numerical solutions of the two-dimensional problem of heat conduction in a sample during exposure to a heat pulse of short duration under experimental conditions.

Influence Pulse Duration Methodical Error of Determination of Thermal Translucent Materials Laser Flash Method

The analysis of errors in the determination of thermal diffusivity of a typical semiconductor material - Germany, due to radiative energy transfer in the heated layer of material, under conditions consistent with the implementation of the method under the influence of the laser pulse on the surface of the collimated laser pulse of finite duration.

Third-order nonlinearity of graphene: Effects of phenomenological relaxation and finite temperature

We investigate the effect of phenomenological relaxation parameters on the third order optical nonlinearity of doped graphene by perturbatively solving the semiconductor Bloch equation around the Dirac points. An analytic expression for the nonlinear conductivity at zero temperature is obtained under the linear dispersion approximation. With this analytic formula as starting point, we construct the conductivity at finite temperature and study the optical response to a laser pulse of finite duration. We illustrate the dependence of several nonlinear optical effects, such as third harmonic generation, Kerr effects and two photon absorption, parametric frequency conversion, and two color coherent current injection, on the relaxation parameters, temperature, and pulse duration. In the special case where one of the electric fields is taken as a dc field, we investigate the dc-current and dc-field induced second order nonlinearities, including dc-current induced second harmonic generation and difference frequency generation.

Choice of the sizes of samples in case of determination of heat diffusivity of optical quartz glass by method of laser pulse

The analysis of errors in the determination of thermal diffusivity of optical quartz glass, caused by radiative energy transfer in the heated layer of material in the corresponding implementation of the method of the laser pulse when exposed to the surface of the collimated laser pulse of finite duration. Influence on value of this error of the geometrical sizes of a sample and process of absorption of radiation is set.

Effect of polarization and focusing on laser pulse driven auto-resonant particle acceleration

The effect of laser polarization and focusing is theoretically studied on the final energy gain of a particle in the Auto-resonant acceleration scheme using a finite duration laser pulse with Gaussian shaped temporal envelope. The exact expressions for dynamical variables viz. position, momentum, and energy are obtained by analytically solving the relativistic equation of motion describing particle dynamics in the combined field of an elliptically polarized finite duration pulse and homogeneous static axial magnetic field. From the solutions, it is shown that for a given set of laser parameters viz. intensity and pulse length along with static magnetic field, the energy gain by a positively charged particle is maximum for a right circularly polarized laser pulse. Further, a new scheme is proposed for particle acceleration by subjecting it to the combined field of a focused finite duration laser pulse and static axial magnetic field. In this scheme, the particle is initially accelerated by the focused laser field, which drives the non-resonant particle to second stage of acceleration by cyclotron Auto-resonance. The new scheme is found to be efficient over two individual schemes, i.e., auto-resonant acceleration and direct acceleration by focused laser field, as significant particle acceleration can be achieved at one order lesser values of static axial magnetic field and laser intensity.

Spin effects in nonlinear Compton scattering in ultrashort linearly-polarized laser pulses

AbstractThe nonlinear Compton scattering by a linearly polarized laser pulse of finite duration is analyzed, with a focus on the spin effects of target electrons. We show that, although the Compton scattering accompanied by the electron no-spin flip is dominant, for some energy regions of Compton photons their emission is dominated by the process leading to the electron spin flip. This feature is observed for different pulse durations, and can be treated as a signature of quantum behavior. Similar conclusions are reached when analyzing the scattered electron energy spectra. This time, the sensitivity of spin effects to the carrier-envelope phase of the driving pulse is demonstrated. The possibility of electron acceleration by means of Compton scattering is also discussed.

Adiabatic formulation of charged particle dynamics in an inhomogeneous electro-magnetic field

AbstractThe relativistic motion of a charged particle is studied in an inhomogeneous field of finite duration laser pulse. An inhomogeneity in a laser field is due to the spatial variation of laser intensity. Such a variation in laser intensity is characteristic of focused and de-focused laser beams. In the presence of an inhomogeneity, the problem becomes non-integrable and hence particle dynamics can not be derived exactly. In the present work considering a slow variation in the laser intensity, it is shown that the particle dynamics is associated with an adiabatic invariant. It is further found that the adiabatic invariant itself evolves and in a typical example changes such that the adiabaticity parameter attains a value of order unity. Thus higher orders of invariance are required for specifying the particle dynamics in terms of an adiabatic invariant. An adiabatic formalism is derived using the Lie transform perturbation method for calculating the higher orders of invariance and to obtain the evolution of the adiabatic invariant. The estimates of energy gained by a particle considering focused laser field are obtained by solving the equation of motion numerically. On comparing the results of a numerical experiment with theoretical predictions, it is found that the energy estimates improve on taking into account higher orders of invariance predicted by the present theory.

The errors in determining the thermal characteristics of semitransparent materials by a pulse method

The errors in determining the thermal characteristics of a semitransparent material by a pulsed method are determined by comparing the results of a numerical solution of the problem of the steady temperature field of a sample when a collimated laser pulse of finite duration acts on its surface with the true values of the thermal diffusivity, thermal conductivity, and specific heat capacity.

Exact analysis of particle dynamics in combined field of finite duration laser pulse and static axial magnetic field

Dynamics of a charged particle is studied in the field of a relativistically intense linearly polarized finite duration laser pulse in the presence of a static axial magnetic field. For a finite duration laser pulse whose temporal shape is defined by Gaussian profile, exact analytical expressions are derived for the particle trajectory, momentum, and energy as function of laser phase. From the solutions, it is shown that, unlike for the monochromatic plane wave case, resonant phase locking time between the particle and laser pulse is finite. The net energy transferred to the particle does not increase monotonically but tends to saturate. It is further shown that appropriate tuning of cyclotron frequency of the particle with the characteristic frequency in the pulse spectrum can lead to the generation of accelerated particles with variable energies in MeV-TeV range.

The effect of excitation pulse carrier frequency on ultrafast charge recombination dynamics of excited donor–acceptor complexes

The excitation of a charge transfer band by a laser pulse of finite duration and the ensuing charge recombination are calculated in the framework of the perturbation theory. The influence of the spectral characteristics of the laser pulse on the charge recombination dynamics is investigated for models including several nuclear modes that differ greatly in their timescales. It is shown that, in the area of applicability of the perturbation theory, the variation of the pulse carrier frequency inside the absorption band can significantly change the effective charge recombination rate constant.

Scattering of relativistic electrons by a focused laser pulse

The problem of the motion of a classical relativistic electron in a focused high-intensity laser pulse is solved. A new three-dimensional model of the electromagnetic field, which is an exact solution of Maxwell’s equations, is proposed to describe a stationary laser beam. An extension of the model is proposed. This extension describes a laser pulse of finite duration and is an approximate solution of Maxwell’s equations. The equations for the average motion of an electron in the field of a laser pulse, described by our model, are derived assuming weak spatial and temporal nonuniformities of the field. It is shown that, to a first approximation in the parameters of the nonuniformities, the average (ponderomotive) force acting on a particle is described by the gradient of the ponderomotive potential, but it loses its potential character even in second order. It is found that the three-dimensional ponderomotive potential is asymmetric. The trajectories of relativistic electrons moving in a laser field are obtained and the cross sections for scattering of electrons by a stationary laser beam are calculated. It is shown that reflection of electrons from the laser pulse and the surfing effect are present in the model studied. It is found that for certain impact parameters of the incident electrons the asymmetic ponderomotive potential can manifest itself effectively as an attractive potential. It is also shown that even in the case of a symmetric potential the scattering cross section contains singularities, known as rainbow scattering. The results are applicable for fields characterized by large (compared to 1) values of the dimensionless parameter η2 = e2〈E2〉/m2ω2 and arbitrary electron energies.

Coherent pulse-duration control of electron quantum beats in tunnel-coupled quantum wells

The temporal evolution of electrons in asymmetric double quantum well structure is analysed, when the carriers are photoexcited by finite duration laser pulse. Because of interference between switch-on and switch-off contributions to the interwell charge oscillations, the quantum beats can be controlled by varying the pulse duration. Calculations take into account the influence of relaxation as well as the dependence on splitting of tunnel-coupled levels and on detuning between pumping and effective bandgap frequencies. The results show that the coherent dynamical response is transformed from the oscillatory regime to nonvanishing time average of dipole moment when varying the exciting pulse shape from rectangular to Gaussian-like.