Generation of squeezed light upon frequency self-doubling in active nonlinear crystals with regular domain structure

A quantum theory of self-convers of the lasing frequency in active nonlinear crystals placed in a cavity is developed. The generation of nonclassical (quadrature squeezed) light upon self-doubling of the laser radiation frequency is studied in detail, with no limitations on the relations between the relaxation times of the inverse population and the polarization of the medium and the lifetime of a photon in the cavity. The fluctuation spectra of the quadrature components of the fields of the laser radiation and its second harmonic are studied in dependence on the pumping parameters and the parameters of the cavity. Numerical calculations are performed for a Nd:Mg:LiNbO₃ crystal with a regular domain structure.     

Effect of thermal blooming in second-harmonic generation in nonlinear crystals with a regular domain structure

Analytical expressions are obtained for the power of the second harmonic in nonlinear crystals having a regular domain structure with allowance for thermal blooming for a Gaussian beam of basic radiation in the quasi-stationary plane-wave approximation. Calculations were carried out in both the approximation of an assigned field of basic radiation and a substantially nonlinear regime of exhaustion of basic radiation. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp,. 257–260, March–April, 2000.     

On the theory of the second optical harmonic in nonlinear crystals with a regular domain structure

The theory of the second-harmonic generation in crystals with a regular domain structure (RDS) is developed in the approximation of the fixed intensity of the fundamental radiation. An analytical expression for the second-harmonic intensity is derived. The results are compared with the data obtained in the fixed-field approximation and the numerical solution. The maximum number of layers n _max at which the theory remains valid is determined. Numerical estimates of n _max are presented for the frequency doubling of an ultrashort light pulse in the LiNbO₃ RDS crystal.     

Localization of a nonlinear switching wave in an active bistable medium with an isolated inhomogeneity

An analysis is made of the one-dimensional propagation of a switching wave in an active medium when one of the parameters of the medium is a function of the coordinate over a certain region and remains constant outside this region. The possibility of localization (stopping) of the wave at this type of inhomogeneity is investigated. An analytical expression is obtained for the wave shift in the case of a small-amplitude inhomogeneity. Constraints on the amplitude and length of the inhomogeneity at which localization takes place are obtained for an inhomogeneity of finite dimensions. Zh. Tekh. Fiz. 67, 14–20 (August 1997)     

Extremely short dissipative solitons in an active nonlinear medium with quantum dots

A medium consisting of quartz with embedded active (amplifying) or passive (absorbing) impurities, i.e., quantum dots, is proposed for producing extremely short dissipative solitons on the basis of the effect of enhanced self-induced transparency. The calculations show that, in such a medium, the initial standard femtosecond pulses can be transformed into extremely short dissipative solitons with a peak intensity of ～10¹¹ W/sm², with a duration corresponding to the inverse frequency of transitions in impurities, and with the coherent spectral supercontinuum covering almost the entire transmission region of quartz.     

Self-organization of two-dimensional waves in an active dispersive-dissipative nonlinear medium

We consider the pattern-formation dynamics of a two-dimensional (2D) nonlinear evolution equation that includes the effects of instability, dissipation, and dispersion. We construct 2D stationary solitary pulse solutions of this equation, and we develop a coherent structures theory that describes the weak interaction of these pulses. We show that in the strongly dispersive case, 2D pulses organize themselves into V shapes. Our theoretical findings are in good agreement with time-dependent computations of the fully nonlinear system.     

Cone-type light beam structure in a nonlinear medium

The formation is predicted of a cone-type structure in an intense light beam propagating in an amplifying medium exhibiting the Kerr nonlinearity and a multiphoton absorption.     

Second optical harmonic generation in nonlinear crystals with a disordered domain structure

A theory describing the second harmonic generation in nonlinear-optical crystals with random domains is developed. The theory takes into account the fluctuations of both the phase mismatch and the nonlinear coupling coefficient of the interacting waves. It is shown that, in such crystals, the maximal efficiency of fundamental-to-second harmonic conversion is low, and the dependence of the average intensity of the second harmonic on the fundamental intensity differs considerably from a square law.     

Investigating RF and microwave nonlinear magnetoelastic interactions in a three-layer structure

The problem of hypersound excitation in a structure consisting of three magnetic layers is considered. Motion equations and boundary conditions for the components of magnetization and elastic displacement when there is an arbitrary angle of magnetization vector precession are obtained. The development of oscillations over time in an alternating field is considered.     

用激活性非线性介质Nd：MgO：LiNbO3产生二次谐波

以Nd:MgO:LiNbO_3同时兼作激活介质和非线性光学材料,研究自倍频激光器。用小型氙灯泵浦,在室温下获得二次谐波激光(0.547μm) 阈值小于4.8'J,最大输出400μJ/shot,工作温度范围大于20℃～45℃,无光损伤。     

Allowance for angular divergence in the generation of the second harmonic in crystals with a regular domain structure

We obtained basic analytical expressions for the efficiency of the second harmonic in nonlinear crystals with a regular domain structure; in these expressions we took into account the angular divergence of the laser beam. The calculation was done in the geometric-optics approximation of the given field of laser radiation. We show that the expressions obtained are similar to the corresponding expressions for homogeneous nonlinear crystals. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 134–138, January–February, 2000.     

Two-body propagators with dynamic effective interactions in a many-fermion medium: I. General structure

Excitations of the many-body medium cause dynamic effective interactions between fermions. In actual calculations these interactions are almost always replaced by static approximations. In this paper a Green function approach is outlined which preserves the dynamic structure of the interactions. The central quantity is the four-vertex or two-fermion scattering amplitude Γ in the medium, which depends on three energy variables s, t, and u. Integral equations connect Γ to irreducible effective interactions in the three channels. With static interactions the s- and t-channels correspond to particle-particle and particle-hole configurations, respectively. Dynamic interactions mix these configurations. They also introduce poles in the crossed channels: the exchange of a phonon is a t-pole in the s-channel while pairons induce s-poles in the t-channel. Poles of the one-body propagator G(ω) and the two-body propagators K(s) and K(t) correspond to states of the A ± 1, A ± 2 and A-particle systems. The dynamic coupling between channels results in an intricate connection between various aspects of the many-fermion problem.     

Stimulated gamma emission in an active medium with hidden inversion

This paper reviews some features of the nuclear electromagnetic transitions accompanied by recoil from the momentum of absorbed or emitted photons. We have presented, based on rigorous quantum mechanical calculations, the cross sections for nuclear anti-Stokes and Rayleigh scattering with recoil. The impact of recoil is critical to the establishing the hidden inversion of nuclear state populations and amplification of stimulated gamma radiation.