Generation Of Higher Optical Harmonics Research Articles

Relativistic Nonlinear Optical Phenomena in the Field of Subterawatt Laser Pulses

Experiments on the generation of high optical harmonics demonstrating that relativistic regimes of interaction of radiation with matter can be implemented in the field of mid-infrared laser pulses with a peak power of 0.3 TW have been reported. The observation of relativistic phenomena at such extraordinary low peak powers of the laser field becomes possible because of the formation of a high-quality space-time mode of the laser field with an exactly specified polarization state. Such a field structure ensures a high intensity of radiation in the focus of the beam and the effective acceleration of electrons by a low-frequency electromagnetic field of a high-contrast laser pulse with an exactly specified polarization at the extremely sharp vacuum-solid interface.

Optical Properties of Excimers in the Field of Intense Laser Radiation

The specific features of the luminescence of excimer molecules are analyzed within the model of a purely repulsive potential for the ground state in the field of intense laser radiation with due regard for the squeezed vibrational states. It is demonstrated that the luminescence band with the inclusion of the equilibrium phonons can be represented by a broad structureless asymmetric bell-shaped curve. The squeezed vibrational states substantially affect the frequency dependence of the luminescence intensity; more specifically, the luminescence band exhibits two maxima in the case of strong electron-phonon coupling. The stabilization of an excited electronic state in the course of luminescence at the fundamental frequency and generation of higher optical harmonics in the field of intense laser radiation is discussed.

Effect of a polar environment on the resonant generation of higher optical harmonics by dipole molecules

An analysis is made of the effect of fluctuations of a polar environment on the resonant generation of higher optical harmonics by dipole molecules in a strong electromagnetic field. The cases of slow and strong fluctuations of the environment are considered. It is shown that the electric fields produced by fluctuating dipole moments of the medium lead to anomalous temperature dependences of the scattered-radiation intensity. In the case of slow fluctuations and some additional conditions, the harmonic intensity exponentially increases with temperature. In contrast, in the case of rapid fluctuations under exact resonant conditions, the harmonic intensity decreases with increasing temperature. Under nonresonant excitation of molecules, a polar medium has no effect on the generation of higher harmonics.

Collective generation of higher optical harmonics by dipole molecules

An analysis is made of the collective resonant generation of higher harmonics by a spatially extended system of two-level molecules possessing an intrinsic electron dipole moment in the excited state. Frequency and angular dependences of the scattered radiation are studied. It is shown that for moderately small numbers of harmonics their intensity depends comparatively weakly on the number (plateau) and the intensity of the emitted harmonics then falls sharply as the number increases. The angular distribution of the harmonics is strongly anisotropic. It is also shown that collective effects significantly change the time profile of the generated harmonic pulse. In addition, as a result of cooperative effects harmonics of a certain parity are suppressed in the low-frequency part of the radiation spectrum.

Generation of x-ray radiation by atoms in an ultrahigh-intensity laser field

A semiclassical approach is used to describe the generation of high optical harmonics by atoms in an ultrahigh-intensity laser field. Account is taken of the influence of the Coulomb potential and of the relativistic effects on the motion of an electron in a continuum, of the spreading of a wave packet of an electron in a continuum, and also of the depletion of atomic states. A new effect is predicred within a framework of this approach: nonmonotonic behaviour of the intensities of the individual harmonics in a certain range of intensities of the pump field in the form of extremely short laser pulses. It is shown that efficient generation of harmonics with the orders as high as 1000 is feasible.

Photon antibunching in nonlinear optical processes (review)

Recent investigations of photon antibunching are reviewed briefly. The fundamental viewpoints regarding this effect are given. A detailed analysis is made of the processes of generation of higher optical harmonics as a source of anticorrelated photons and also of superchaotic light.

Generation of higher optical harmonics in focused beams

An analysis is made of the influence of focusing on third, fourth, and fifth harmonic generation allowing for both direct and cascade processes taking place due to lower-order nonlinearities. It is found that as the focusing parameter increases under conditions of optimized wave mismatch, the fourth and fifth harmonic powers increase monotonically. It is also shown that in the case of phase-matched cascade processes, the harmonic power is highest for focusing on one of the faces rather than at the center of the nonlinear medium.