The Lorentz local field in nonlinear dielectrics (original) (raw)

Polarization fluctuations in a dipolar medium in an electrostatic field

Radiophysics and Quantum Electronics, 1989

Dispersion parameters are examined for a dipolar medium in an electrostatic field E0. The kinetic equation is solved with a self-consistent field to derive the tensor for the complex dielectric constant, which is examined for branches involving longitudinal and transverse oscillations in the polarization vector.

Noninstantaneous polarization dynamics in dielectric media

Third-order optical nonlinearities play a vital role for generation 1,2 and characterization 3-5 of some of the shortest optical pulses to date, for optical switching applications 6,7 , and for spectroscopy 8,9. In many cases, nonlinear optical effects are used far off resonance, and then an instantaneous temporal response is expected. Here, we show for the first time resonant frequency-resolved optical gating measurements 10-12 that indicate substantial nonlinear polarization relaxation times up to 6.5 fs in dielectric media, i.e., significantly beyond the shortest pulses directly available from commercial lasers. These effects are among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schrödinger equation 13,14 are in excellent agreement with experimental observations. The simulations indicate that pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect. Moreover, our approach opens an avenue for application of frequency-resolved optical gating as a highly selective spectroscopic probe in high-field physics.

Frequency dependence of the nonlinear dielectric effect in diluted dipolar solutions

Physics Letters A, 1999

The nonlinear dielectric relaxation in dilute solutions of strongly polar molecules (4,4'-n-hexylcyanobiphenyl) in nonpolar medium (benzene) has been investigated. The nonlinear dielectric increment, induced by a d.c. electric field of high intensity (Eo = lo7 V/m), was detected with an a.c. field of small intensity and variable frequency ( 1 MHz-3 GHz). The relaxational behavior of the increment is discussed in the framework of the theory proposed by Coffey et al. [Proc. R. Ir. Acad. 78 (1978) 171.

Steady state response of the nonlinear dielectric relaxation and birefringence in strong superimposed ac and dc bias electric fields: Polar and polarizable molecules

The Journal of Chemical Physics, 2000

Both nonlinear dielectric relaxation and dynamic Kerr effect responses of an assembly of polar and anisotropically polarizable molecules acted on by strong superimposed external dc E 0 and ac E 1 (t)ϭE 1 cos t electric fields are evaluated in the context of the rotational diffusion model in the noninertial limit. The relaxation functions f n (t) ͑the expectation value of the Legendre polynomials P n ͒, which are appropriate to describe these nonlinear relaxation phenomena, are calculated by expanding them as a Fourier series in the time domain. An infinite hierarchy of recurrence relations for these Fourier amplitudes of f n (t) is obtained, the solution of which is expressed in terms of an infinite matrix continued fraction, so allowing us to evaluate the dynamic characteristics of the electric polarization and birefringence. For a weak ac field, the results predicted by the theory are in complete agreement with previous solutions obtained by perturbation methods. The solutions for the particular cases, where only either permanent or induced dipole moments are taken into account, can easily be extracted from the general solution. Diagrams of the frequency behavior of the in-phase and out-of-phase components of the electric birefringence and polarization are presented showing pronounced nonlinear effects due to the high ac field.

Polaritons of dispersive dielectric media

Vacuum, 2005

We quantize the electromagnetic field in a polar medium starting with the fundamental equations of motion. In our model the medium is described by a Lorenz-type dielectric function ðr; oÞ appropriate e.g. for ionic crystals, metals and inert dielectrics. There are no restrictions on the spatial behavior of the dielectric function, i.e. there can be many different polar media with arbitrary shapes. We assume no losses in our system so the dielectric function for the whole space is assumed as real. The quantization procedure is based on an expansion of the total field (transverse and longitudinal) in terms of the coupled (polariton) eigenmodes, so our theory gives the Hamiltonian of polaritons of dispersive dielectric media. We pay particular attention to the derivation of the fundamental (equal-time) commutation relations between the conjugate field operators. As an example, we apply our theory to the quasi-two-dimensional Wigner crystal, formed by electrons at very low temperature. We discuss the influence of the quantized electromagnetic field on the dynamics of Wigner electrons, i.e., on the dispersion relation of Wigner phonons. We expect a significant influence in the case when frequencies of (surface) polaritons and Wigner phonons coincide, and we discuss the energy spectrum of such a system.

Calculation of nonlinear optical susceptibilities of pure liquids within the Polarizable Continuum Model: the effect of the macroscopic nonlinear polarization at the output frequency

Journal of Molecular Structure-theochem, 2003

We present an extension of the Polarizable Continuum Model to compute nonlinear optical (NLO) macroscopic susceptibilities of pure liquids. The procedure is based on the interpretation of the molar property (i.e. the macroscopic susceptibilities) in terms of effective molecular dipoles and (hyper)polarizabilities for a system immersed in the surrounding medium, represented by a continuum dielectric. The effective quantities are obtained through an ab initio description of the molecule under scrutiny interacting with the macroscopic field at the fundamental frequency and with the nonlinear macroscopic polarization at the output frequency. q (J. Tomasi). measured response becomes [5,6]:

On the theory of dielectric polarization for fluids of ellipsoidal dipoles

Chemical Physics Letters, 1986

For fluids of dipolar hard ellipsoids the long-range contribution of the direct correlation function to the dielectric polarization is evaluated employing spherical tensor methods and the depolarization tensor known from classical electrostatics. The result is independent of molecular size, but depends on the ratio of the axes and the direction of the dipole moment in respect to the molecular axes. For molecules with an axis of revolution the corresponding contribution to the dielectric virial expansion differs in sign and magnitude if the dipole moment points in the direction of the axis of revolution or perpendicular to it.