Self-induced transparency and electromagnetic pulse compression in a plasma or an electron beam under cyclotron resonance conditions

Based on analogy to the well-known process of the self-induced transparency of an optical pulse propagating through a passive two-level medium we describe similar effects for a microwave pulse interacting with a cold plasma or rectilinear electron beam under cyclotron resonance condition. It is shown that with increasing amplitude and duration of an incident pulse the linear cyclotron absorption is replaced by the self-induced transparency when the pulse propagates without damping. In fact, the initial pulse decomposes to one or several solitons with amplitude and duration defined by its velocity. In a certain parameter range, the single soliton formation is accompanied by significant compression of the initial electromagnetic pulse. We suggest using the effect of self-compression for producing multigigawatt picosecond microwave pulses.     

Soliton-induced transparency of inhomogeneously broadened three-level atoms

The effect of soliton-induced transparency (SOIT) that arises for a weak pulse that interacts with one of allowed transitions of inhomogeneously broadened three-level atoms with the V configuration of the levels under the action of a self-induced transparency soliton that simultaneously interacts with the adjacent transition is studied theoretically. The effect is explained by phasing of the ensemble of dipoles oscillating with different frequencies in the soliton field. The weak pulse is locked by the soliton, so that both pulses propagate with the same velocity independently of the ratio of the propagation constants. If the latter are equal, the weak pulse loses no energy; when they are different, the rate of energy loss is considerably slower than it follows from Beer’s law.     

Carrier-envelope phase dependence of the duration of generated solitons for few-cycle rectangular laser pulses propagation

We investigate the nonlinear propagation of few-cycle rectangular laser pulses on resonant intersubband transitions in semiconductor quantum wells using an iterative predictor–corrector finite-difference time-domain method. An initial 2π rectangular pulse will split into Sommerfeld–Brillouin precursors and a self-induced transparency soliton during the course of propagation. The duration of generated soliton depends on the carrier-envelope phase of the incident pulse. In our case, not only the near-resonant frequency components but also the low frequency components could contribute to the generation of the soliton pulse when the condition of multi-photon resonance is satisfied. The phase-sensitive property of the solitons results from the phase-dependent distribution of high and low frequency sidebands of few-cycle rectangular pulses.     

Propagation dynamics of nonlinear chirped optical laser pulses in a two-level medium

We investigate the propagation dynamics of nonlinear chirped optical laser pulses in a two-level medium. For certain chirp strength and chirp width, an incident 2π nonlinear chirped pulse will split into optical precursors and a stable self-induced transparency soliton. This is caused by the particular Fourier spectrum that includes not only central resonant frequency components but also high-frequency and low-frequency sidebands. Moreover, the effects of chirp parameters on the evolution of nonlinear chirped pulses are also discussed.     

Self-induced transparency in a resonance medium with the dipole-dipole interaction

Propagation of a pulse of self-induced transparency in a resonance medium is discussed for the case when it is necessary to take into account the direct electric dipole-dipole interaction between atoms. An equation for the envelope of a wave packet—the sine-Gordon equation—is obtained for the case of durations short compared to ω ₀ ^?1 (ω₀ is the transition frequency). The dependence of the velocity and the amplitude of the soliton on the magnitude of the dipole-dipole interaction of atoms is examined in the adiabatic approximation.     

Passive mode locking and formation of dissipative solitons in electron oscillators with a bleaching absorber in the feedback loop

The mechanisms of passive mode locking and formation of ultrashort pulses in microwave electron oscillators with a bleaching absorber in the feedback loop have been analyzed. It is shown that in the group synchronism regime in which the translational velocity of particles coincides with the group velocity of the electromagnetic wave, the pulse formation can be described by the equations known in the theory of dissipative solitons. At the same time, the regimes in which the translational velocity of electrons differs from the group velocity and the soliton being formed and moving along the electron beam consecutively (cumulatively) receives energy from various electron fractions are optimal for generating pulses with the maximal peak amplitudes.     

Self-induced transparency of hydrogen-containing ferroelectrics for extremely short pulses in the vicinity of the curie temperature

Nonlinear propagation of extremely short (carrierless) electromagnetic pulses in a KDP-type ferroelectric is investigated at temperatures close to the phase transition point. It is demonstrated that, although weak monochromatic signals undegro a sharp attenuation at these temperatures, an extremely short high-power pulse can propagate in the self-induced transparency regime and the associated soliton is stable to transverse perturbations.     

Photoluminescence Properties of Thin-Film Nanohybrid Material Based on Quantum Dots and Gold Nanorods

The dynamics of coherent propagation of a unipolar subcycle pulse of a large electric-field area (the integral of the electric-field strength with respect to time) in a nonlinear two-level resonant medium is studied theoretically. The propagating pulse is shown to be capable of splitting into a pair of individual components, each of which behaves like a pulse of self-induced transparency. This phenomenon is similar to the well-known phenomenon of splitting of a 4π or 6π pulse into a pair of 2π pulses of self-induced transparency, which occurs in the case of propagation of long pulses, when the notion of the pulse area is applicable and the area theorem holds.     

Soliton formation processes in optically dense media

Numerical methods are used to investigate the characteristics of soliton formation when optical pulses of arbitrary shape and duration propagate in resonantly absorbing media of large optical thickness. It is shown that a regime of soliton propagation in a resonant medium, characterized by a nonlinear Schrödinger equation model, changes to a self-induced transparency regime. Incoherent steady-state interaction conditions are then replaced by coherent interaction. This effect can be utilized to compress laser pulses.V. D. Kuznetsov Siberian Physicotechnical Institute at the State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 95–99, October, 1994.     

Resonant transparency effects in an anisotropic medium with a permanent dipole moment

The propagation of a two-component laser pulse in an optically uniaxial medium is investigated under the conditions of the Zakharov-Benney resonance (viz., resonance of long and short waves). The short-wave ordinary component of the pulse, which is in resonance with the atomic subsystem, effectively generates a video pulse of the extraordinary wave (long-wave component). The latter dynamically detunes the ordinary pulse from the resonance and causes its phase modulation due to nonzero diagonal matrix elements of the dipole moment. An approximate operator approach is proposed for solving constitutive equations for the density matrix, which is equivalent to the asymptotic WKB method and makes it possible to reduce the analysis to solving a system of nonlinear wave equations for both components of the pulse. The possibility an extraordinary wave video pulse being generated with the help of a quasimonochromatic ordinary pulse with a longer wave-length. It is shown that, when the ordinary component dominates, the self-induced transparency mode is realized; in the opposite limit, the effect known as extraordinary transparency takes place. Solitary pulses corresponding to the latter case experience a decrease in the velocity of propagation, which is similar to that observed for self-induced transparency and practically do not change the population of quantum levels. Physical situations reducing the initial system of constituent and wave equations to familiar integrable models are analyzed.     

Unidirectional optical solitons in a two-level medium

Self-induced transparency is analyzed for optical pulses interacting with a two-level system by solving an integrable system of evolution equations without using the slowly varying envelope approximation. A suitable modification of the inverse scattering method is developed to find soliton solutions. The characteristics of linearly and circularly polarized optical solitons (including those created in a laser) are compared. To assess the scope of the two-level model, the effects due to additional levels are analyzed in the adiabatic approximation. It is shown that these effects violate the integrability of the model and lead to loss of self-induced transparency for pulses with duration comparable to oscillation period. However, self-induced transparency is recovered in the quasi-monochromatic limit. Applications of the results are discussed.     

Temporal characteristics of few-cycle pulse on- and non-resonance propagating in a ladder-type atomic medium

Time evolution characteristic of few-cycle pulse propagating in a ladder-type atomic medium is investigated. It is shown that, time evolution of few-cycle pulse has significant difference in the both cases on- and non-resonance. In the non-resonant case, if the pulse central frequency is twice as large as medium atomic transition frequency, the pulse form (including carry-envelope phase, pulse duration, oscillation amplitude and frequency) remains unchanging or remains unchanging basically (only carry-envelope phase has some variation) in the propagation process, which means that self-induced transparency (SIT) or approximate transparency phenomenon appears. However, in the resonant case, the pulse form changes obviously in the propagation process. In addition, there is evident difference in the propagating velocity for on- and non-resonance when the pulse area is smaller.     

Propagation of a self-induced transparency pulse in a spatially dispersive medium

Propagation of a self-induced transparency pulse in spatially dispersive media is analyzed. A generalized model of two-level systems allowing for excitonic energy transfer is proposed. Periodic and soliton solutions to the governing equations are found. Estimates show that the spatial dispersion of a pulse propagating in a slow-light medium can be substantially enhanced and become important in the case of resonant transition and sufficiently long pulse duration.     

具有超辐射特性的回旋器件模拟研究

 在详细分析快波结构中的束波互作用基础上,采用2.5维PIC粒子模拟软件设计了一种回旋器件。该器件采用摇摆器形成回旋电子束,并采用强耦合方式和优化的互作用段长度,在束压250 kV、束流200 A、脉宽1 ns的电子束驱动下,模拟获得了峰值功率7 MW、频率38.5 GHz的微波短脉冲输出,峰值功率转换效率达到14%。其峰值输出功率与束脉宽之间的平方关系符合超辐射效应的特征。     

在反常色散区艾里脉冲与光孤子相互作用规律的研究

本文采用分步傅里叶法,研究了在反常色散区孤子和艾里脉冲相互作用的规律,并且对相互作用后的孤子和艾里脉冲各自的强度、时域和时移进行了MATLAB仿真.通过仿真发现光孤子和艾里脉冲在光纤中相互重叠时,交叉相位调制(XPM)就会建立并且这种调制会影响孤子和艾里脉冲的性质.在相互作用过程中,孤子的形状保持不变,但是受到艾里脉冲自加速特性的影响孤子会发生偏移.艾里脉冲受XPM的影响会转化为孤子,传播方向也会发生偏移.可见,XPM使得艾里脉冲和孤子各自的性质都相互影响着对方.艾里脉冲和孤子的时域也会受到XPM的影响,使得原本不相同的脉冲形状都转变为含有一个主峰和一个次峰的相似结构,并且主峰和次峰的位置和脉冲宽度也大致相同,这也是艾里脉冲能够转换为孤子的一个依据.另外本文还模拟了不同输入强度r下的孤子和艾里脉冲的变化情况,模拟发现不管是艾里脉冲还是孤子时移都随着输入强度r的增大而增大,并且它们的变化趋势都是一样的,同时模拟还发现在相同的的r值下,时移也会随着a值的增大而增大.     

High-power relativistic microwave sources based on the backward wave oscillator with a modulating resonant reflector

Results of theoretical and experimental investigations into a relativistic backward wave oscillator with a modulating resonant reflector are generalized. The modulating resonant reflector is used to reflect a counter propagating wave and guide it toward an electron collector. It is shown that premodulation of the electron beam near the reflector may have a significant effect on the starting conditions of oscillation; selective properties of the oscillator; and its efficiency, which may reach 40% when a high-current beam is transported by a strong magnetic field. In the reduced magnetic fields that were employed in the pulsed-periodic regime and were 1.5–2.0 times lower than those at which cyclotron resonance with the counter propagating wave is observed, the oscillator efficiency (30–35% at a wavelength of 8 mm) is limited by position and velocity spreads of particles. Mechanical pulsewise frequency tuning within about 10% at a repetition rate of 1–50 Hz and a multigigawatt microwave power, as well as a rise in the power and energy of microwave pulses via an increase in the cross-sectional dimensions of the slow-wave structure, are demonstrated to be feasible.     

Vector solitons in semiconductor quantum dots

A theory of an optical vector soliton of self-induced transparency in an ensemble of semiconductor quantum dots is considered. By using the perturbative reduction method, the system of the Maxwell–Liouville equations is reduced to the two-component coupled nonlinear Schrödinger equations. It is shown that a distribution of transition dipole moments of the quantum dots and phase modulation changes significantly the pulse parameters. The shape of the optical two-component vector soliton with the sum and difference of the frequencies in the region of the carrier frequency is presented. The vector soliton can be reduced to the breather solution of self-induced transparency with a different profile. Explicit analytical expressions in the presence of single-excitonic and biexcitonic transitions for the optical vector soliton are obtained with realistic parameters which can be reached in current experiments.     

Resonant electromagnetic soliton in a dense plasma

A study is made of the propagation of an electromagnetic wave along a constant magnetic field B₀ in a high-density plasma under cyclotron resonance conditions when the interaction between the electrons and the wave is strongly nonlinear. It is found that the relativistic reduction in the electron gyrofrequency in the field of the electromagnetic pulse stabilizes the wave. A solution is obtained in the form of an envelope soliton and it is shown that its group velocity is considerably reduced.State University, Rostov-on-Don. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 3–7, January, 1994.