China
Africa
Explore chapters and articles related to this topic
Filamentation Phenomena and Generation of Supercontinuum in Propagation of Laser Pulses in a Nonlinear Medium
Published in Yu. N. Kulchin, Modern Optics and Photonics of Nano and Microsystems, 2018
The spatial self‐action is related to the Kerr nonlinearity of the medium. In a manner similar to the time profile of the envelope intensity of the laser field I0(t) leading to the modulation of the pulse phase, the inhomogeneity of the intensity of the laser field in the beam I0(r) on the transverse coordinate r forms a nonlinear lens n(r) = n0 + n2I0(r), which, in turn, leads to self‐focusing or self‐defocusing of the beam as a function of the sign of n2. The increase in the intensity of laser radiation in a self‐focusing beam leads to an increase in the efficiency of nonlinear optical interactions. As was shown above, self‐focusing is accompanied by an uncontrolled change in the intensity and phase of the laser pulse and leads to a complex spatial dynamics of the laser beam, one of the interesting manifestations of which is the decay of the laser beam into thin filaments. Due to the high intensity of laser radiation, filaments are sources of broadband optical radiation. However, the control of the properties of such radiation is an intractable task.
Optical Solitons in Nonlinear Fibre Systems
Published in Shyamal Bhadra, Ajoy Ghatak, Guided Wave Optics and Photonic Devices, 2017
Recent years have also shown increased interest from different experimental and theoretical groups in the study of self-guided optical beams that propagate in slab waveguides or bulk nonlinear media without supporting waveguide structures [1–12]. Such beams are commonly referred to as spatial solitons even though they do not possess all the properties of temporal solitons. Unlike a guided mode, a beam propagating in a bulk medium generally experiences spatial broadening due to diffraction. However, if an increase in the light intensity in the beam leads to an increase in the nonlinear refractive index, the so-called self-focusing effect, then the beam will induce a higher refractive index on the axis than at its periphery because of the decrease in the beam intensity away from the axis. As a result, the beam experiences a focusing action due to the guidance provided by the induced index distribution. If the beam intensity is sufficiently large so that the strength of the focusing effect exactly balances diffraction, the beam can then propagate without spreading in the form of a self-guided beam or a spatial optical soliton.
(3) Processes
Published in Peter E. Powers, Joseph W. Haus, Fundamentals of Nonlinear Optics, 2017
Peter E. Powers, Joseph W. Haus
Section 8.2 introduces the nonlinear polarization for χ(3) processes, which are proportional to the cube of the input field. Following this formalism, in Section 8.3, we derive the envelope wave equations for χ(3) interactions, which is similar to that derived for χ(2). The wave equation forms the foundation to describe several χ(3) effects. The first process we discuss in Section 8.4 is the nonlinear index of refraction and associated phenomena of self-focusing and nonlinear absorption. We also show how a χ(3) material can be used in a resonator geometry to make devices that can have two (or more) stable output intensities for the same input intensity; a phenomenon called optical bistability.
Dynamics of quadruple laser beams in collisionless plasmas
Published in Waves in Random and Complex Media, 2019
It is also observed that with increase in the value of for there is increase in the extent of the self-focusing as well as in the focusing length of the laser beam. The increase in the extent of self-focusing is due to the fact that with increase in the value of for the top of the intensity profile of the laser beam becomes flatter. As a result of which the off axial part of the wavefront of the laser beam becomes equally stronger as that of axial part. As a result of this nonlinear refraction due to most of the transverse part of the laser beam opposes the diffraction broadening of the laser beam.
Coupled self-similar-traveling optical wave tunneling induced by an injected light beam
Published in Waves in Random and Complex Media, 2021
The effects of an injected beam in a medium are great interest in the study of nonlinear optical wave phenomena [1–4]. These studies focused on liquid crystals (LCs) which might be classified into fluid or solid (LCs). The first type might be branched to smectic A and C [5–7], and nematic (LCs) [8, 9]. In smectic-A (LCs), the molecules have the same local average direction parallel to the local layer with directors parallel to the normal. While in smectic-C (LCs), this is not the case [10]. Nematic (LCs) provide a high level of tunable optical nonlinearity and has been widely studied in the literature [11–13]. Recent works in this area are interesting (see [14–18]). Based on the Hirota method and Darboux transformation, there have been some studies on lump-soliton and rogue-wave solutions for the nonlinear evolution equations (NLEEs) [19–22]. In a recent work, experimental and theoretical studies were studied for optical wave that were induced by an injected beam [23]. Attention was focused to investigate the behavior of optical waves when a light (or laser) beam is injected in the Kerr medium where a metal plate is located at z = 0. The medium is self-focusing as the wave function of the injected beam is positive. It was found that the molecules are reoriented to produce self-focusing nonlinearity [2], this is due to the increasing of Kerr effect via nonlinear coupling of waves. This beam produces incoherent waves that may lead to weak turbulence. The study of weak turbulence was carried via nonlinear interaction of cubic and quadratic waves in the phase space . In the case of strong wave turbulence, the mean of the solution is evaluated by taking into account the fluctuations about the plasma trajectories that depend on those of the electrostatic or magnetic fields. In [23], the effects of the one-dimensional (1D) optical wave turbulence were studied. It provides different stationary solutions to both long and short waves. It was shown that the long-wave system is governed by 1D nonlinear Schrödinger equation (NLS) which results in molecular rotation that are confined to x−z plane. The wave function was taken to vary along z only [24–32]. It was found that this leads to a final condensate state dominated by a single strong soliton relevant to beam injected. Here, it is observed that the beam acts as a reflector barrier so optical wave tunneling occurs. Also we show that the following result holds, namely, randomization of the optical wave does produce which may be argued to the free potential.
Femtosecond laser inscriptions in Kerr nonlinear transparent media: dynamics in the presence of K-photon absorptions, radiative recombinations and electron diffusions
Published in Journal of Modern Optics, 2021
Emmanuel O. Akeweje, G. Bader, Alain M. Dikandé, P. Kameni Nteutse
Theoretical investigations of femtosecond laser interaction with transparent media have been carried out in some past studies [13–18]. In these studies the optical field propagation in the transparent medium is described by the complex Ginzburg-Landau equation, while time evolution of the plasma density is represented by a Drude-type equation, with specific terms accounting for physical ingredients assumed to contribute to photoionization processes. In principle, these models are intended to give account of the laser self-focusing due to Kerr nonlinearity of the transparent medium, enhanced by multiphoton absorption processses [19,20]. However most of these past studies [13–18] were focused mainly on assessing thermal effects related to material processings using femtosecond lasers, and particularly their impact on the quality (e.g. the degree of fineness and refinement) of processed materials. Nevertheless in relatively more recent works [21,22], attention was paid on dynamical properties of some among the models proposed e.g. in refs. [13–18]. Thus in ref. [21] the laser dynamics, together with time evolution of the plasma density, were investigated considering the model proposed by Petrovic et al. [18], according to which the plasma generation was governed essentially by avalanche ionization and K-photon absorption processes. From the assumption that depending on conditions in the optical medium, the femtosecond laser will operate in one of two distinct regimes i.e. either continuous-wave or soliton regimes, it was established [21] that for this specific model a decrease in K, the number of simultaneously absorbed photons, would stabilize continuous waves in the anomalous dispersion regime. However any continuous wave propagating in the transparent medium in the normal dispersion regime, is expected to be always unstable irrespective of the value of K. The same study [21] also established that large values of the phase shift per laser roundtrip, will favour a stronger stability of continuous-wave operation in the normal dispersion regime for any value of K, whereas in the anomalous dispersion regime only for small values of K continuous waves would be stable. Extending this first study, in ref. [22] the same authors considered the problem but including electron–hole radiative recombination processes [16]. In this second work they found that in steady state, the electron plasma density will strongly depend on the electron–hole radiative recombination coefficient. They obtained that an increase of the electron–hole radiative recombination coefficient causes the laser amplitude to increase in the soliton regime, whereas the electron plasma density is more and more strongly decreased in time as the radiative recombination coefficient is increased.