Intense Pump Beam Research Articles

Effects of ion trapping and fluctuations of electron temperature and plasma flow on cross-beam energy transfer

The influences of ion trapping and fluctuations of electron temperature and plasma flow on cross-beam energy transfer (CBET) are examined using two- and three-dimensional particle-in-cell simulations in parameter regimes relevant to recent CBET experiments at the OMEGA laser facility. In mid-Z plasma irradiated by an intense pump beam and weaker probe beam, ion trapping, collisional de-trapping, and plasma flow induced by thermal effects are shown to affect the CBET gain. Ion trapping can enhance or detune the CBET resonance [Nguyen et al., Phys. Plasmas 28, 082705 (2021)]. Collisional de-trapping can affect the CBET gain at low seed beam intensity near the onset threshold for ion trapping. Thermal-effects-induced flow can also detune the CBET resonance at a level comparable to that from trapping at low seed beam intensity. As a consequence, the CBET gain is sensitive to collisions and dimensionality at low seed beam intensity where ion trapping is weak but is insensitive to collisions and dimensionality at high seed beam intensity where ion trapping is strong.

Hot carrier effects on Brillouin amplification in AIIIBV and AIIBVI semiconductors

A theoretical formulation followed by numerical analysis is carried out to study the hot carrier effects (HCEs) on Brillouin amplification in AIIIBV and AIIBVI semiconductors. The threshold condition for the onset of Brillouin amplification and the parameters characterizing Brillouin amplification of the Brillouin cell are estimated. Numerical analysis is made for three different Brillouin cells at illuminated by a pulsed CO2 laser. HCEs of intense pump beam modifies the momentum transfer collision frequency of carriers and consequently the nonlinearity of the Brillouin medium, which in turn (i) lowers the threshold intensity, (ii) enhances the parameters characterizing Brillouin amplification, (iii) shifts the enhanced Brillouin gain spectrum towards smaller values of magnetic field, and (iv) widens the range of magnetic field at which peak of Brillouin gain spectrum (around resonance) occurs. The incorporation of HCEs in the analysis validate the selection of appropriate Brillouin medium for the fabrication of efficient Brillouin amplifiers.

Directly extracting the authentic basis of cylindrical vector beams by a pump-probe technique in an atomic vapor

The projective measurement of light polarization is usually employed by using a combination of a quarter-waveplate, half-waveplate, and polarizing beam splitter. This configuration is also widely used for exploring quantum states. However, this kind of measurement destroys the real polarization state of the target. Here, an effective measurement configuration to extract the “authentic basis” of cylindrical vector beams with arbitrary polarization distribution in an atomic vapor is presented. An intense pump beam induces a distribution of atoms at different Zeeman sublevels, which allows for the extraction of the special polarization state of a counter propagated weak probe beam. The extracted part still maintains the original polarization and the vortex phase. Different orders of cylindrical vector beams are tested in this configuration, and the authentic basis of cylindrical vector beams is extracted as predicted. This work has potential applications in atomic physics and polarization optics. Furthermore, it provides a reference for the quantum projective measurement based on atom-optical devices.

Nonlinearity-induced PT-symmetry without material gain

Parity-time symmetry has raised a great deal of attention in optics in recent years, yet its application has been so far hindered by the stringent requirements on coherent gain balanced with loss. In this paper, we show that the conditions to enable parity and time symmetry can be simultaneously satisfied for a pair of modes with mixed frequencies interacting in a nonlinear medium, without requiring the presence of material gain. First, we consider a guided wave structure with second order nonlinearity and we derive the PT-symmetric Hamiltonian that governs the interaction of two waves of mixed frequencies when accompanied by a high intensity pump beam at the sum frequency. We also extend the results to an array of coupled nonlinear waveguide channels. It is shown that the evolution dynamics of the low-frequency waves is associated with a periodic PT-symmetric lattice while the phase of the pump beams can be utilized as a control parameter to modify the gain and loss distribution, thus realizing different PT lattices by design. Our results suggest that nonlinear wave mixing processes can form a rich platform to realize PT-symmetric Hamiltonians of arbitrary dimensions in optical systems, without requiring material gain.

Design and Analysis of XOR Logic Gate Based on Two-Photon Absorption

Two-photon absorption with high intensity pump beam occurs in a SOA depends on fast phase change of a weak probe signal. This work analysed optical XOR logic function using two-photon absorption induced fast phase change. A rate equation for SOA and both input data signals A and B with high intensity, configured in the form of MZI has also been proved. The model shows that XOR operation at 10 Gb/s with good signal to noise ratio is obtained with high input intensities. The result on the generation of XOR indicates that operations on 10 Gb/s with a high signal to noise ratio can easily be implemented. The average input power into the SOA is 20 dbm corresponding to the peak power of 5.5 dBm at 10 Gb/s when the width of the input pulse 3.6 ps. The short narrow pulse width is utilised in the study for stronger effect of two-photon absorption.

Necklace beam generation in nonlinear colloidal engineered media.

Modulational instability is a phenomenon that reveals itself as the exponential growth of weak perturbations in the presence of an intense pump beam propagating in a nonlinear medium. It plays a key role in such nonlinear optical processes as supercontinuum generation, light filamentation, rogue waves, and ring (or necklace) beam formation. To date, a majority of studies of these phenomena have focused on light-matter interactions in self-focusing Kerr media existing in nature. However, a large and tunable nonlinear response of a colloidal suspension can be tailored at will by judiciously engineering the optical polarizability. Here, we analytically and numerically show the possibility of necklace beam generation originating from spatial modulational instability of vortex beams in engineered soft-matter nonlinear media with different types of exponential nonlinearity.

Theoretical analysis of mid-infrared molecular spectral line profiles with transversal relaxation in an intense optical field

Nonlinear effects by intense optical field on mid-infrared spectral lines (∼3  μm) are discussed. Recent development of intense mid-infrared coherent radiation makes nonlinear mid-infrared spectroscopy possible. In the mid-infrared region, the transversal relaxation process is important compared to the visible or near-infrared region. In the analysis, a two-energy-state system is discussed. The intense pump beam scattering spectral lines (Mollow triplet) and the absorption spectral lines of the probe beam with the intense pump beam are calculated.

A plateau in the sensitivity of a compact optically pumped atomic magnetometer

In a compact optically pumped atomic magnetometer (OPAM), there is a plateau in the sensitivity where the dependence of the sensitivity on pumping power is small compared with that predicted by the uniform polarization model. The mechanism that generates this plateau was explained by numerical analysis. The distribution of spin polarization in the alkali metal cell of an OPAM was modeled using the Bloch equation incorporating a diffusion term and an equation for the attenuation of the pump beam. The model was well-fitted to the experimental results for a module with a cubic cell with 20 mm sides and pump and probe beams with 8 mm diameter. On the plateau, strong magnetic response was generated at the regions that were not illuminated directly by the intense pump beam, while at the same time spin polarization as large as 0.5 was maintained due to diffusion of the spin-polarized atoms. Thus, the sensitivity of the magnetometer monitored with a probe beam decreases only slightly with increasing pump beam intensity because the spin polarization under an intense pump beam is saturated. This plateau, which is characteristic of this type of magnetometer using a narrow pump and probe beams, can be used in arrays of magnetometers because it enables stable operation with little sensitivity fluctuation from changes in pump beam power.

An accurate optical technique for measuring the nuclear polarisation of 3He gas

In the metastability exchange optical pumping cells of our on-site production unit and of our other experimental set-ups, we use a light absorption technique to measure the 3He nuclear polarisation. It involves weak probe beams at 1083 nm, that are either perpendicular or parallel to the magnetic field and cell axis, with suitable light polarisations. When metastability exchange collisions control the populations of the sublevels in the 23S state, absolute values of the 3He ground state nuclear polarisation are directly inferred from the ratio of the absorption rates measured for these probe beams. Our report focuses on the transverse detection scheme for which this ratio, measured at low magnetic field for σ and π light polarisations, hardly depends on gas pressure or the presence of an intense pump beam. This technique has been systematically tested both in pure 3He and isotopic mixtures and it is routinely used for accurate control of the optical pumping efficiency as well as for calibration of the NMR system.

Nonlinear birefringence due to non-resonant, higher-order Kerr effect in isotropic media

The recent interpretation of experiments on the nonlinear non-resonant birefringence induced in a weak probe beam by a high intensity pump beam in air and its constituents has stimulated interest in the non-resonant birefringence due to higher-order Kerr nonlinearities. Here a simple formalism is invoked to determine the non-resonant birefringence for higher-order Kerr coefficients. Some general relations between nonlinear coefficients with arbitrary frequency inputs are also derived for isotropic media. It is shown that the previous linear extrapolations for higher-order birefringence (based on literature values of n2 and n4) are not strictly valid, although the errors introduced in the values of the reported higher- order Kerr coefficients are a few percent.

Competition between the modulation instability and stimulated Brillouin scattering in abroadband slow light device

We observe competition between the modulation instability (MI) and stimulated Brillouinscattering (SBS) in a 9.2 GHz broadband SBS slow light device, in which a standard 20 kmlong single-mode LEAF fibre is used as the SBS medium. We find that MI is dominantand depletes most of the pump power when we use an intense pump beam at ∼ 1.55 µm, where the LEAF fibre is anomalously dispersive. The dominance of the MI in theLEAF-fibre-based system suppresses the SBS gain, degrading the SBS slow light delay andlimiting the SBS gain-bandwidth to 125 dB GHz. In a dispersion-shifted highly nonlinearfibre, the SBS slow light delay is improved due to the suppression of the MI, resulting in again-bandwidth product of 344 dB GHz, limited by our available pump power of 0.82 W.

Observation of Broadband Time-Dependent Rabi Shifting in Microplasmas

Coherent broadband radiation in the form of Rabi sidebands is observed when a ps probe laser propagates through a weakly ionized, electronically excited microplasma generated in the focus of an intense pump beam. The sidebands arise from the interaction of the probe beam with pairs of excited states of a constituent neutral atom via the probe-induced Rabi oscillation. Sideband shifting of >90 meV from the probe carrier frequency results in an effective bandwidth of 200 meV. The sidebands are controlled by the intensity and temporal profile of the probe pulse; with amplitude and shift in agreement with the predictions of a time-dependent generalized Rabi cycling model.

Nonlinear inter-core coupling in triple-core photonic crystal fibers

We have developed a coupled-mode theory to describe light propagation in triple-core photonic crystal fibers (PCFs) in the nonlinear regime. The propagation equations including nonlinearities have been solved analytically. The nonlinear coupling for symmetric and asymmetric fibers is modeled for different coupling and nonlinear parameters. We investigate nonlinear inter-core coupling experimentally with a single high intensity pump beam. Optical switching of a signal beam in the presence of a control pump beam at a different wavelength is also demonstrated. The self-phase modulation (SPM) parameter gamma in the triple-core PCF studied is determined.

All-optical logic gates based on two-photon absorption in semiconductor optical amplifiers

When the two-photon absorption of a high intensity pump beam takes place in a semiconductor optical amplifier there is an associated fast phase change of a weak probe signal. A scheme to realize fast all-optical XOR logic function using two-photon absorption induced phase change has been analyzed. Rate equations for semiconductor optical amplifiers, for input data signals with high intensity, configured in the form of a Mach–Zehnder interferometer has been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The model shows that both XOR operation and pseudo-random binary sequence generation at 250 Gb/s with good signal to noise ratio is feasible.

Broadband four-wave optical parametric amplification in bulk isotropic media in the ultraviolet

We report on four-wave optical parametric amplification of the ultrashort ultraviolet light pulses in bulk fused silica and CaF 2 . Exact phase-matching in these isotropic media is achieved by means of non-collinear interaction with cylindrical beam focusing. Four-wave optical parametric amplifier efficiently operates in the UV spectral range with 1-ps laser pulses, delivering amplified signal energy exceeding 50 μJ using millijoule pump pulses in the visible (527 nm). Results of scanning of the parametric gain profile suggest that broad amplification bandwidth as wide as ∼20 nm (at FWHM) under these experimental settings is achieved, which might support amplification of sub-10-fs ultraviolet pulses with central wavelength around 330 nm. It is also shown experimentally and verified theoretically that the parametric gain profile exposes a distinct inhomogeneity and its bandwidth notably broadens due to effects of self- and cross-phase modulation imposed by the intense pump beam.

Coupled-mode analysis of Bragg-reflection filters based on asymmetric nonlinear dual-core fibers

We demonstrate a Bragg-reflection grating coupler using a nonlinear dual-core fiber with a long-period grating (LPG) and a fiber Bragg grating (FBG) inscribed in different cores. The LPG couples light from the primary core to the cladding, while the FBG operating in reflection acts to drop the channel from the secondary core. The coupler is nonreflective along the launching core. Theoretical analysis of this structure demonstrates a design for obtaining a flat-top bandpass filter with high reflectivity, steep band transitions, and negligible sidelobes. By launching an intense pump beam into the individual cores, a switchable and a wavelength tunable passband can be achieved. The results demonstrate the usefulness of the device as a grating-based all-optical element.

自散焦介质中的光开关现象

A spatial optical switch phenomenon caused by the induced focusing of a weak probe beam occurring in self-defocusing nonlinear media is discussed theoretically. A weak beam is induced to focus when it copropagates with an intense pump beam under the conditions that the probe and pump beams peak at different positions and propagate in different directions. Due to the effect of cross-phase modulation, the weak beam can not only be focused but also be deflected. The phenomenon is discussed by numerically solving the coupled amplitude equations.

Optical parametric amplification beyond the slowly varying amplitude approximation

The coupled-wave equations describing optical parametric amplification (OPA) are usually solved in the slowly varying amplitude (SVA) approximation regime, in which the second-order derivatives of the signal and idler amplitudes are ignored and in fact the electromagnetic effects due to exit face of the medium is not involved. Here, an analytical plane-wave solution of these coupled-wave equations in a non-absorbing medium is presented. The solutions are derived beyond the SVA approximation up to order of κ/k (coupling constant over the wave number). The intensity distributions of the signal and the idler waves show a periodic behavior about their corresponding distributions of SVA-adapted solution. This behavior can be explained by the interference of the forward propagating signal (idler) wave and the corresponding backward one resulted from the reflection by the end face of the medium. Furthermore, this interference pattern in the medium can in turn serve as a periodic source for the next generations of the signal and idler waves. Therefore, the superposition of the waves, generated from different points of this periodic source, at the exit face of the medium shows an oscillatory behavior of the transmitted signal (idler) wave in terms of normalized coupling constant, κL. This study also shows that this effect is more considerable for high intensity pump beam, high relative refractive index and short length of the nonlinear medium.

Steady-state and transient Brillouin gain in magnetoactive narrow band gap semiconductors

Using electromagnetic treatment, a detailed analytical investigation is made to investigate both the steady-state and transient gains of Brillouin Stokes mode in magnetoactive piezoelectric III–V semiconductors. The Brillouin Stokes mode arises from the nonlinear interaction of an intense pump beam with the internally generated acoustic phonon mode and magnetoacoustic phonon mode in the finiteness of piezoelectricity and electrostriction. Following a coupled-mode approach, the third-order (Brillouin) susceptibility and steady-state and transient regime Brillouin gain of the backward Stokes mode are obtained in the presence and absence of an external static magnetic field. The dependence of the piezoelectricity, an external static magnetic field and pump pulse duration on growth rate of the backward Stokes mode has been analysed. The piezoelectricity and an externally applied static magnetic field substantially enhance both the steady-state and transient gain coefficients in a moderately doped III–V semiconductor. The enhanced transient gain coefficient can be greatly used in the compression of the backward scattered Stokes pulse.

SIMPLIFIED MODELING OF STEADY-STATE AND TRANSIENT BRILLOUIN GAIN IN MAGNETOACTIVE NON-CENTROSYMMETRIC SEMICONDUCTORS

With the aid of a hydrodynamic model of semiconductor-plasmas, a detailed analytical investigation is made to study both the steady-state and the transient Brillouin gain in magnetized non-centrosymmetric III-V semiconductors arising from the nonlinear interaction of an intense pump beam with the internally-generated acoustic wave, due to piezoelectric and electrostrictive properties of the crystal. Using the fact that the origin of coherent Brillouin scattering (CBS) lies in the third-order (Brillouin) susceptibility of the medium, we obtained an expression of the gain coefficient of backward Stokes mode in steady-state and transient regimes and studied the dependence of piezoelectricity, magnetic field and pump pulse duration on its growth rate. The threshold-pump intensity and optimum pulse duration for the onset of transient CBS are estimated. The piezoelectricity and externally-applied magnetic field substantially enhances the transient CBS gain coefficient in III-V semiconductors which can be of great use in the compression of scattered pulses.