Strong-field ionization of heteronuclear diatomic molecules in circularly polarized laser fields

Abstract

We theoretically investigate the strong-field ionization of heteronuclear diatomic molecules, CO and NO, by calculating the photoelectron angular distribution and the photoelectron momentum distribution in circularly polarized fields. We find that the photoelectron angular distribution and the photoelectron momentum distribution of CO are inversion asymmetric, but symmetric about the molecular axis, most of the photoelectrons are ejected from the neighborhood of the C core. In contrast, for NO the photoelectron angular distribution and photoelectron momentum distribution are nearly fourfold symmetric about the molecular axis and its vertical axis, which means that the photoelectrons are equally ejected from the neighborhood of the N and O cores. By our results, the photoelectron angular distribution and photoelectron momentum distribution can be used to imprint the molecular orbitals.     

Generation of multifrequency laser emission quasi equally spaced throughout the entire visible region

A circularly polarized, monochromatic laser beam is focused into a Raman cell, which contains hydrogen to generate rotational stimulated Raman emission. After linear polarization, this two-color (separated by 587 cm(-1)) laser beam is focused several times into a second Raman cell that is filled with hydrogen to generate a multifrequency laser emission. Many rotational and vibrational lines are generated efficiently by this multipass effect. Eighteen colors that are quasi equally spaced with a rather flat intensity distribution are generated throughout the entire visible region. The present multifrequency laser emission may be advantageously used for illumination in a higher-grade display, such as a laser light show.     

Magnetic and Electric Control of Circularly Polarized Emission through Tuning Chirality‐Generated Orbital Angular Momentum in Organic Helical Polymeric Nanofibers

Circularly polarized light emission promotes the development of smart photonic materials for advanced applications in chiral sensing and information storage. The orbital angular momentum is a unique property for organic chiral helical materials. In this work, a type of organic chiral polymeric nanowires is designed with strong chirality induced orbital angular momentum. Under the stimulus of an external magnetic field of 600 mT, circularly polarized emission from the chiral polymeric nanowire becomes more pronounced, where the g factor increases from 0.21 to 0.3. The observed phenomena mainly originate from the chirality‐dependent orbital angular momentum. Moreover, the orbital angular momentum in helical chiral nanowire structures can be suppressed by inhibiting electron transport in a helical way to diminish circularly polarized light emission at room temperature.     

Pulse-duration dependent sequential double ionization by elliptically polarized laser pulses

Using a fully classical model, we have studied sequential double ionization of argon driven by elliptically polarized laser pulses at intensities well in the over-barrier ionization region. The results show that the joint electron momentum distributions in the minor elliptical direction depend strongly on the pulse duration. From pulse number N = 4 to 10, the clustering regions of the joint electron momentum increase with the pulse duration. For even larger pulse durations, the clustering region does not increase further but the population of the joint electron momentum in these regions changes with the pulse duration. Back analysis of double ionization trajectories shows the phenomenon of multiple ionization bursts and the pulse duration-dependent multiple ionization bursts of the second electron is responsible for the evolution of the joint electron momentum distribution with the pulse duration.     

Controlling the red boundary of the tunneling photoeffect in nanodimensional carbon structures in a broad (UV-IR) wavelength range

The tunneling photoeffect (PE) has been studied in a microdiode with an electrostatic field localized at an emitter based on a nanodimensional carbon structure. It is established that, when the carbon nanoemitter is exposed to laser and LED radiation photons of low energy (below work function) in the spectral range from near-UV (380 nm) to near-IR (1150 nm) at micro- and milliwatt optical power, a tunneling photocurrent can be initiated by controlling the electric field strength in the emitter-anode gap. The observed phenomenon can be adequately interpreted using a modified Fowler-Nordheim equation for non-equilibrium photoelectrons. Specific features of the construction and operation of photodetectors based on the tunneling PE with a controlled long-wavelength threshold (red boundary) of photoelectron emission are considered. The bandwidth of photoelectron emitters is evaluated, and the possibility of their operation in the wavelength range from UV up to far-IR is predicted.     

Electrogyration in CHBrClF chromophores stimulated by circularly polarized light

We have found that the CHBrClF chiral-like racemic molecule incorporated into oligoetheracrylate photopolymer matrices demonstrates considerable photoinduced linear electrogyration (EG) caused by circularly polarized bicolour coherent light. The maximally achieved value of the EG, described by the third-order axial tensor for the circularly polarized light of the probe at a wavelength of 633?nm, was equal to about 12°mm^?1 at an applied electric field strength equal to 250?V?cm^?1. We have established that the maximal EG coefficient is achieved for 5.10?wt% of CHBrClF chromophores. The investigated composites possess a long-lived screw-like helicoidal EG decreasing less than 18% after laser treatment for 100?min by the circularly polarized coherent frequencies of an ND-doped yattric aluminium garnet laser. Application of non-circular pump light leads to a decrease in the observed EG.     

Theoretical study and 2D computational modeling of middle-infrared radiation generation in the field of few-cycle laser pulse propagating in GaSe slab waveguide

We have performed the theoretical study and 2D finite-difference time-domain-based computational modeling of middle-infrared radiation generation in the field of few-cycle laser pulse propagating in GaSe slab waveguide. The interaction of linearly polarized pulse with 1.98 um central wavelength, 22.44 fs duration, and electric field amplitudes 100 MV/m, propagated along the [010] crystalline direction of GaSe crystal with polarization aligned along [100] is considered. The crystal length chosen is equal to 21.78 um. Symmetric GaSe slab waveguides with 6.336 um, 7.92 um, 11.88 um, and 15.84 um thicknesses excited by the Gaussian pump beams with 3.96 um, 5.94 um, 8.91 um, and 11.88 um diameters, respectively, are considered. The 2D distributions of the electric fields are obtained by numerical integration of Maxwell’s equations’ systems. The spatially spectral normalized distributions of the electric fields are obtained. The efficiency of generated infrared (IR) radiation vs. spatial transverse coordinate is obtained.     

Control of spin angular momentum in quasi-phase-matched material

A method to control spin angular momentum (SAM), based on mutual effects of a electro-optic effect and a quasi-phase-matched (QPM) technique in QPM material, is proposed. By controlling the external electric field or operating wavelength, the transfer between left- and right-handed circularly polarized photons is achieved, thus the total SAM is manipulated. The external electric field needed in this method for the complete modulation of the total SAM per photon from 0 to ? is as low as 0.44 kV/cm. This method will see its applications in micromanipulation by light.     

Electron photodetachment by short laser pulse

Expressions are derived for calculations of the total probabilities and electron spectra for the photodetachment of electrons from negative ions with filled valence s shells by ultrashort laser pulses. Particular calculations have been performed for two negative ions (H⁻ and Li⁻) and titanium-sapphire laser pulses with a carrier wavelength of 0.8 μm and a duration of 4 fs. It is shown that measurements of the electron energy spectra allow either the emission spectrum to be determines for the known cross-section of photodetachment or a dispersion curve of the electron photodetachment cross section to be constructed for the given spectrum of laser pulses. In addition, these measurements provide a tool for the exact determination of electron binding energies.     

Control of the molecular alignment inside liquid-crystal droplets by use of laser tweezers

Here, we demonstrate how the light-induced birefringence due to the dipole molecular realignment and anisotropic polarizability of a nematic liquid crystal inside a droplet changes the droplet's radial (and thus optically isotropic) structure into a birefringent one. This intensity-dependent change of birefringence can be understood in terms of the anisotropic polarizability and orientational optical nonlinear effect. Birefringence induced by laser tweezers changes the momentum of the passing light. In turn, for the circularly polarized tweezers, this change generates an angular momentum change large enough to spin micrometer-sized droplets. For the linearly polarized tweezers, the molecular ordering generates momentum, which laterally displaces the droplet. It is shown that the optical nonlinearity can be "large" enough to have mechanical (ponderomotive) implications, that is, it allows control of the movement and position of micro-objects with submicrometer resolution. The optically induced molecular alignment controlled by the polarization and power of the laser tweezers allows one to actuate, rotate, and translate objects which are up to 10(3)-10(4) times larger than the constituent molecules themselves.     

Highly convergent focusing of light based on rotating dipole polarization

Focusing properties of transverse circular polarization modes that bring light to a small focal spot are investigated. Two particular illumination polarization distributions are discussed. Rotating electric dipole polarization results in a central lobe diameter 8% smaller than for the circularly polarized aplanatic case at a NA of 0.95 in air and is also smaller than for radial polarization at NAs less than 0.90. Azimuthal polarization with a phase singularity of charge unity results in a small central lobe width that is smaller than that produced by focusing radially polarized light, having a width that is 17% smaller than for circularly polarized illumination at a NA of 0.95.     

Propagation modes and regimes of intense laser beam in magnetized plasma

This paper presents an analytical and numerical investigation of a circularly polarized beam propagating along the static magnetic field parallel to oscillating magnetic field in plasma at relativistic intensities. In the high intensity regime, such a magnetic field is created by the pulse itself. The authors have identified three regimes of propagation taking into account the relativistic mass correction. Based on WKB and paraxial ray theory, an appropriate expression for a dielectric tensor has been evaluated in the presence of an externally applied magnetic field. The natural electromagnetic modes are circularly polarized. Consequently, extraordinary and ordinary modes propagate, which are significantly affected due to the relativistic mechanism. The regimes are characterized by dimensionless power and beamwidth, characterizing the nature of propagation as steady divergence, oscillatory divergence and self-focusing. Numerical computations are presented and discussed for typical parameters of laser plasma interaction; defined through critical parameters, namely cyclotron-to-beam frequency (Ω _c ), plasma-to-beam frequency (Ω _p ) and beam power for arbitrary large intensities.     

Plasmonic near-electric field enhancement effects in ultrafast photoelectron emission: correlated spatial and laser polarization microscopy studies of individual ag nanocubes

Electron emission from single, supported Ag nanocubes excited with ultrafast laser pulses (λ = 800 nm) is studied via spatial and polarization correlated (i) dark field scattering microscopy (DFM), (ii) scanning photoionization microscopy (SPIM), and (iii) high-resolution transmission electron microscopy (HRTEM). Laser-induced electron emission is found to peak for laser polarization aligned with cube diagonals, suggesting the critical influence of plasmonic near-field enhancement of the incident electric field on the overall electron yield. For laser pulses with photon energy below the metal work function, coherent multiphoton photoelectron emission (MPPE) is identified as the most probable mechanism responsible for electron emission from Ag nanocubes and likely metal nanoparticles/surfaces in general.     

Extremely narrowed spontaneous emission spectrum induced by elliptically polarized light

Abstract

We demonstrate the control of spontaneous emission from a five-level atom embedded in a modified reservoir under the action of a single control beam with elliptical polarization. For different initial-state preparations, we take into account the influence of the phase difference between the two circularly polarized components of the control beam on the behavior of spontaneous emission. For the ground initial states, the spontaneous emission spectrum usually shows ultranarrow central lines which are greatly enhanced. In contrast, for the excited initial states, these enhanced ultranarrow lines are significantly suppressed due to the destructive quantum interference. Furthermore, our numerical simulations indicate that the multipeak structure appears in the presence of the elliptically polarized control beam and external magnetic field. Such a scheme for controlling spontaneous emission may find applications in high-precision spectroscopy.     

Selective excitation of individual plasmonic hotspots at the tips of single gold nanostars

Plasmonic hotspots in single gold nanostars are located at the tips and can be excited selectively by laser light as evidenced by photoelectron emission microscopy. Selectivity is achieved through wavelength and polarization of the excitation light. Comparing photoelectron emission intensity and dark-field scattering spectra of the same individual nanostars reveals differences in terms of observable plasmon resonance wavelengths and field enhancements. Differences are explained with the underlying near- and far-field processes of the two techniques.     

Optimal control of high harmonics for the generation of double attosecond pulses by using a chirped laser pulse

An efficient scheme for the optimization of ultrashort femtosecond pulse shapes interacting with an atom to control high harmonics spectrum and double attosecond pulse generation is presented. The time-dependent Schrödinger equation of one-dimensional hydrogen atom is solved numerically to obtain electric field emission. The genetic algorithm optimization method is used to control the phase and amplitude of ultrashort excitation laser pulses to generate the desired attosecond-shaped pulses. An appropriate cost function is introduced for genetic algorithm optimization of double attosecond pulse generation. It is shown that the relative intensity of two generated pulses, their delay time and duration can be controlled in this approach. Finally, the parameters of the optimized emitted attosecond pulse are compared with those of desired pulses, and the underlying physical mechanisms are discussed in detail.     

Emergent Nonreciprocal Circularly Polarized Emission from an Organic Thin Film

Controlling circularly polarized (CP) emission is key for both fundamental understanding and applications in the field of chiral photonics and electronics. Here, a completely new way to achieve this goal is presented. A luminescent thin film, made from a chiral conjugated phenylene bis-thiophenylpropynone able to self-assemble into ordered structures, emits highly circularly polarized light with opposite handedness from its two opposite faces. Such emergent nonreciprocal behavior in CP emission, so far unprecedented, represents a fundamental advance, opening new opportunities in design, preparation, and applications of CP emitting materials.     

Adiabatic description of superfocusing of femtosecond plasmon polaritons

A surface plasmon polariton is a collective oscillation of free electrons at a metal–dielectric interface. As wave phenomena, surface plasmon polaritons can be focused with the use of an appropriate excitation geometry of metal structures. In the adiabatic approximation, we demonstrate a possibility to control nanoscale short pulse superfocusing based on generation of a radially polarized surface plasmon polariton mode of a conical metal needle in view of wave reflection. The results of numerical simulations of femtosecond pulse propagation along a nanoneedle are discussed. The space–time evolution of a pulse for the near field strongly depends on a linear chirp of an initial laser pulse, which can partially compensate wave dispersion. The field distribution is calculated for different metals, chirp parameters, cone opening angles and propagation distances. The electric field near a sharp tip is described as a field of a fictitious time-dependent electric dipole located at the tip apex.     

Non-sequential double ionization of argon by elliptically polarized laser pulses

With a classical ensemble model, we investigated non-sequential double ionization (NSDI) of argon by elliptically polarized laser pulses. The results show that the correlation behaviors of two electrons depend strongly on the laser intensity. At relatively high laser intensity, the momentum spectra of two electrons along the long axis of the laser polarization plane are mainly distributed in the first and third quadrants and display V-like structures. However, at relatively low laser intensity, the momentum spectra of two electrons are mainly distributed in the second and fourth quadrants. By back analyzing the classical trajectories of NSDI, we find that all of the successful NSDI events still come from recollision in the cases of elliptically polarized laser pulses, and the final-state electron repulsion plays a decisive role for the V-like structure along the long axis of the laser polarization plane. In addition, we find that the initial velocity of the first electron at ionization along the short axis of the laser polarization plane are essential for the recollision, and the time delay between the first ionization and recollision depends on the ellipticity strongly.     

Effect of self-generated axial magnetic field and on propagation of intense laser radiation in plasmas

The present paper deals with an analytical study of a self-generated axial magnetic field (SGAMF) through the inverse Faraday effect (IFE) and its influence on the propagation of circularly polarized light wave for relativistic intensities. As a first step, the non-linear dielectric constant incorporating a magnetic field in the relativistic factor within the framework of WKB (for Wentzel, Kramers, and Brillouin) and a paraxial ray theory is formulated. It is noticed that for intensities (>10¹⁸ W cm^?2), circularly polarized radiation can propagate in electron plasma whose density is greater than the critical density as well as a strong flow of relativistic electrons, axially co-moving with the pulse rise. The above generates a magnetic field up to 100 MG and strongly influences the light propagation. Two modes of propagation exist, namely, extraordinary and ordinary, and critical power for focusing is different for the two modes. The non-linear dielectric tensor, propagation equation, and the self-trapped radius are evaluated incorporating an induced magnetic field. The focusing conditions strongly depend on the power of the beam, strength of the magnetic field as well as on the density of the medium. Numerical calculations are made for a typical set of relativistic laser plasma interaction processes.