Search Results for « Subcycle pulses »

Structured light is essential in various fields such as imaging, communications, computing, laser microprocessing, and ultrafast and nonlinear optics. The structuring of light can occur in terms of space, amplitude, phase, polarization, time, frequency, and duration. One of the intriguing properties that can be obtained is resistance to the diffractive spread and dispersive broadening of the pulsed beams. This happens when temporal properties such as frequency are coupled with spatial properties like angles of propagation of plane-wave components. In this case, pulsed light beams exhibit characteristics similar to optical bullets, resisting both diffraction and material dispersion. This study questions whether free-space optical bullets that possess nondiffracting and nondispersive properties are possible with subcycle durations. We report on the possibility to create nondiffracting and nondispersing localized subcycle pulsed beams and their complex polarization topologies when controlling the group velocity of these light structures.

A simple but exact treatment of spatiotemporal behavior of ultrawideband pulses under an arbitrarily tight focusing is developed. The model makes use of the oblate spheroidal coordinate system to represent free scalar field as if generated by a point-like source-and-sink pair placed at a complex location. The results, illustrated by animated 3D plots, demonstrate characteristic temporal reshaping of the pulses in the course of propagation through the focus, which is a spectacular manifestation of the Gouy phase shift. It is shown that the salient features of the reshaping, which were recently established for the paraxial limit, remain valid beyond it. The treatment is particularly applicable to an ultrawideband isodiffracting ultrashort terahertz-domain or light pulses in high-aperture resonators, such as microcavities, and it is usable in femto- and attosecond optics in general.

We solve the problem of ultrashort pulse propagation in a two-level medium beyond the rotating-wave (RWA) and slowly varying-envelope approximations. The method of solution is based on the Maxwell-Bloch equations represented in the form that allows one to switch between RWA and general (non-RWA) cases in the framework of a single numerical algorithm. Using this method, the effect of a subcycle pulse (containing less than a single period of field oscillations) on the two-level medium was analyzed. It is shown that for such short pulses, the clear breakdown of the area theorem occurs for the pulses of large enough area. Moreover, deviations from the area theorem appear to be strongly dependent on the pulse shape that cannot be observed for longer few-cycle pulses.

Abstract Compression of optical pulses to ultrashort pulse widths using methods of nonlinear optics is a well-established technology of modern laser science. Extending these methods to pulses with high peak powers, which become available due to the rapid progress of laser technologies, is, however, limited by the universal physical principles. With the ratio P/Pcr of the peak power of an ultrashort laser pulse, P, to the critical power of self-focusing, Pcr, playing the role of the fundamental number-of-particles integral of motion of the nonlinear Schrödinger equation, keeping this ratio constant is a key principle for the power scaling of laser-induced filamentation. Here, we show, however, that, despite all the complexity of the underlying nonlinear physics, filamentation-assisted self-compression of ultrashort laser pulses in the regime of anomalous dispersion can be scaled within a broad range of peak powers against the principle of constant P/Pcr. We identify filamentation self-compression scaling strategies whereby subcycle field waveforms with almost constant pulse widths can be generated without a dramatic degradation of beam quality within a broad range of peak powers, varying from just a few to hundreds of Pcr.

We demonstrate the possibility of inducing, erasing and extra rapidly controlling population difference gratings resulting from coherent interaction of unipolar subcycle pulses with a resonant medium. Gratings can be produced without overlap of pulses in the medium, which is an important distinction of the proposed approach from the traditional one, in which gratings are produced using interference of two or more overlapping quasi-monochromatic light beams. The use of unipolar subcycle pulses ensures faster control over gratings in comparison with bipolar pulses studied by us previously.

We propose a novel scheme for frequency-tunable subcycle electromagnetic pulse generation. To this end a pump electron beam is injected into an electromagnetic seed pulse as the latter is reflected by a mirror. The electron beam is shown to be able to amplify the field of the seed pulse while upshifting its central frequency and reducing its number of cycles. We demonstrate the amplification by means of 1D and 2D particle-in-cell simulations. In order to explain and optimize the process, a model based on fluid theory is proposed. We estimate that using currently available electron beams and terahertz pulse sources, our scheme is able to produce millijoule-strong midinfrared subcycle pulses.

We investigate the influence of subcycle laser pulses on holographic and nonholographic intracycle interferences by analyzing the photoelectron momentum distributions of helium using time-dependent Schrödinger equation simulations supported by classical-trajectory calculations. The results show that the forward-scattering holographic (FSH), backward-scattering holographic (BSH), and time double-slit (TDS) interference structures are found to be highly sensitive to the pulse duration, carrier-envelope phase (CEP), and temporal envelope in the subcycle regime. Subcycle pulses with CEP values of 0 ∘ and 90 ∘ selectively enhance or suppress distinct features, isolating holographic patterns and enhancing BSH fringes. Classical analysis reveals that the intrinsic chirp inherent to subcycle fields shortens the recollision time for scattering trajectories, thereby increasing the fringe spacing in FSH and BSH patterns, while simultaneously enlarging the above-threshold ionization peak spacing associated with TDS interference. Pulse envelope variations, even at fixed FWHM duration, further reshape the fringe spacings by modifying the instantaneous frequency and vector potential slope near ionization times. These results demonstrate that subcycle pulses enable precise temporal control of holographic interference, offering opportunities for probing and manipulating attosecond electron dynamics.

Sources of intense, ultrashort electromagnetic pulses enable applications such as attosecond pulse generation, control of electron motion in solids, and the observation of reaction dynamics at the electronic level. For such applications, both high intensity and carrier-envelope-phase (CEP) tunability are beneficial, yet hard to obtain with current methods. In this Letter, we present a new scheme for generation of isolated CEP tunable intense subcycle pulses with central frequencies that range from the midinfrared to the ultraviolet. It utilizes an intense laser pulse that drives a wake in a plasma, copropagating with a long-wavelength seed pulse. The moving electron density spike of the wake amplifies the seed and forms a subcycle pulse. Controlling the CEP of the seed pulse or the delay between driver and seed leads to CEP tunability, while frequency tunability can be achieved by adjusting the laser and plasma parameters. Our 2D and 3D particle-in-cell simulations predict laser-to-subcycle-pulse conversion efficiencies up to 1%, resulting in relativistically intense subcycle pulses.

The validity issues of some approximations widely used to describe subcycle pulse propagation in various non-magnetic media are addressed. As the validity criteria we apply the fundamental electric area conservation rule, which directly follows from Maxwell’s equations in the 1D case. The general relations are derived for the possible values of the electric area in different media. It is shown that several theoretical models do not in general comply with the electric area conservation rule, which implies their limited applicability to correctly describe the subcycle pulse interaction with media. Therefore, any results obtained using such models cannot be taken as scientifically valid and meaningful.

Owning to their high controllability, laser pulses have contributed greatly to our understanding of strongly correlated electron systems. However, typical multicycle pulses do not control the symmetry of systems, which plays an important role in the emergence of novel quantum phases. Here, we demonstrate that subcycle pulses whose oscillation is less than one period within a pulse envelope can control inversion and time-reversal symmetries in the electronic states of the one-dimensional extended Hubbard model. Using an ultrashort subcycle pulse, one can generate a steady electric current (SEC) in a photoexcited state due to an Aharonov-Bohm flux instantaneously introduced through the phase of an electric field. Consequently, time-reversal symmetry is broken. In contrast, a broad subcycle pulse does not induce SEC but instead generates electric polarization, thus breaking inversion symmetry. Both symmetry breakings in a photoexcited state can be monitored by second-harmonic generation. These findings provide a new methodology for designing the symmetries of electronic states and open up a new field of subcycle-pulse engineering.