Effect of the Doppler broadening on the nonlinear amplification of a polarized wave that propagates in a resonant medium without population inversion

The general nonlinear stationary theory of propagation of an elliptically polarized pulse that resonantly interacts with the 1/2-1/2 transition is developed taking into account relaxation processes. It is shown that interference of magnetic sublevels in the field of polarized radiation that optically pumps atoms results in inversionless amplification of radiation. Taking into account the Doppler broadening of spectral lines shows that there exists a certain optimal length of the resonant medium along which the radiation that emerges from the medium is maximally amplified.     

Nonlinear nonstationary theory of light propagation through a resonance medium taking into account optical pumping of atoms

The general nonstationary theory of propagation of an elliptically polarized pulse resonantly interacting with the 1/2–1/2 transition is presented. The theory that takes into account relaxation processes is developed in terms of irreducible tensor operator representation allowing diagonalization of the relaxation matrix and introduction of effective decay times governing relaxation of both population and coherence between magnetic sublevels of the resonant system. It is shown that interference of magnetic sublevels in the field of polarized radiation that optically pumps the atoms can result in inversionless amplification of radiation.     

Amplification of a weak circularly polarized light signal in a multilevel atomic medium

Amplification of a weak circularly polarized light signal in a multilevel atomic medium excited by a strong linearly polarized resonant radiation is studied. A strong optical pumping may lead to the population inversion between magnetic sublevels of hyperfine components of the ground and excited states. Solution to the self-consistent system of density matrix equations and Maxwell equations for propagation of the weak signal allows analyzing optimum conditions of amplification.     

Resonant Processes of Scattering with Allowance for Different Populations of Magnetic Sublevels

The effect of different populations of the magnetic sublevels of the ground state on the propagation of polarized radiation through resonant media is studied theoretically. The nonlinear refractive indices for circularly and linearly polarized waves in media with arbitrary angular momenta j ₁ and j ₂ are found. The influence of the coherence between the magnetic sublevels on multiphoton effects is analyzed. It is shown that, as a result of elastic Rayleigh scattering, energy transfer from one component of the wave polarization to the other takes place. The picture of induced four-photon parametric scattering of a weak wave in the presence of a strong wave also changes.     

Interference phenomena in Doppler broadened quantum transitions: Amplification of intense radiation without population inversion

We study the effect of nonlinear interference processes on quantum transitions in intense resonant electromagnetic fields with allowance for changes in level populations, relaxation processes, incoherent excitation, and Doppler broadening of the transitions, on the absorption, amplification, and refraction of the interacting fields. The theory is generalized to the case of nonlinear interference interaction of two intense fields in open and closed three-level quantum systems. Using the density matrix, we derive general expressions in the case of stationary interaction that make it possible to analyze the optical characteristics for various configurations of the interfering transitions by a simple substitution of parameters. The possibility of amplifying light without saturated population inversion in a resonant transition is discussed. We formulate the conditions for such amplification and use examples to show that under appropriate changes in the initial level populations and the intensity of the auxiliary light, the inversionless amplification coefficient does not decrease with increasing intensity of the amplified radiation. We also show that allowance for these accompanying processes greatly affects the choice of optimal conditions for interference in optical transitions. As an illustration we list the results of a numerical analysis of possible experiments. Zh. éksp. Teor. Fiz. 113, 445–470 (February 1998)     

Effects of inversionless lasing in two-level media from the point of view of specificities of the spatiotemporal propagation dynamics of radiation

We report the results of computer simulation of the emission of radiation by an extended two-level medium in a ring cavity. The cases of using strong external monochromatic, quasi-monochromatic, and biharmonic radiation for pumping the two-level medium are analyzed. It is shown that the emission of radiation with spectral content different from that of the pump radiation, which is interpreted as the inversionless oscillation, is the result of the spatiotemporal dynamics of light propagation in an extended two-level medium imbedded in a cavity. The appearance of this radiation is not related to known resonances of amplification of a weak probe field in a thin layer of the two-level system (the effect of inversionless oscillation) induced by strong resonance monochromatic or biharmonic field, as was thought before.     

Interaction of a three-level atom with an elliptically polarized wave

The interaction of elliptically polarized radiation with a resonant medium consisting of atoms with an excited state split into a doublet was studied theoretically. Interference terms associated with the coherent interaction of the field with the excited sublevels of the doublet were found to appear in the refractive index. The dispersion dependence of the refractive index was studied. It was shown that the decay constants for the multipole moments of the current of a dipole-forbidden atomic transition can be determined by the choice of the wave polarization.     

Cyclotron mechanism of free-electron lasing without inversion

We consider one of the “paradoxical” effects of the theory of radiation and matter interaction: stimulated emission in the absence of inversion. The theory of simultaneous inversionless emission of two high-frequency waves due to their parametric interaction with ensemble of free electrons in magnetic field is developed. The analytical investigation and numerical simulation of the most interesting scheme of this two-photon interaction are presented. New effects are revealed; namely they are self-induced parametric instability of sufficiently strong waves and enhanced parametric instability in sufficiently dense electron medium.     

Direct observation of resonant four-photon parametric mixing conditioned by the difference of atomic multipole relaxation rates

Experimental evidence of previously predicted relaxation induced parametric processes is presented. Parametric interaction of orthogonal linearly polarized waves has been observed in the 2s₂-2p₁ (j = 1 → j = 0) Ne transition under λ = 1.52 μm He-Ne laser pumping. Coherence transfer between Zeeman sublevels eliminates the ban of the parametric interaction of orthogonal linearly polarized waves. This transfer is connected with collisions and photon-trapping processes resulting in the difference between relaxation rates of the electric quadrupole and magnetic dipole moments of the Ne atoms in the 2s₂ level.     

Manipulation of the population of hyperfine sublevels by pulsed resonance electromagnetic fields

A method has been proposed for rapidly and deeply changing the population in the system of unequally populated hyperfine atomic levels, including the ground-state sublevels, due to the impact of mutually coherent pulsed resonance electromagnetic fields. The method can be implemented, e.g., to create new schemes of the amplification or effective absorption of the radiation passing through a medium, to develop the new field of quantum electronics, spintronics, involving the current of polarized electrons, and to create new schemes of quantum computers.     

Study of atomic spectral lines in a magnetic field with use of a nanocell with the thickness <Emphasis Type="Italic">L</Emphasis> = λ

We propose a technique which we call “L = λ Zeeman technique” (LZT) for investigation of the transitions between the Zeeman sublevels of the hfs structure of alkali metal atoms in external magnetic fields. The technique is based on the employment of a nanocell with the thickness of the Rb atom vapor column equal to the wavelength of the laser radiation, 780 nm, resonant with the atomic rubidium D₂ transition. At the laser intensities of about 1 mW/cm² in the transmission spectrum of the nanocell narrow (～ 30 MHz) resonant peaks of reduced absorption appear localized exactly on the atomic transitions. In magnetic fields these peaks are split and their amplitudes and frequency positions depend on the magnetic field strength. The theoretical model well describes the experimental results.     

On the possibility of polarizing atoms and nuclei by pulsed electromagnetic fields without using ultra-low temperatures

A method is proposed for fast and deep polarization of the system of hyperfine sublevels of the ground state of an atom having an optical excited state by means of two-component microwave pulses. The pulse of the bichromatic optical field that induces the transitions between the ground state and excited state of the atom is supposed to provide coherence among the hyperfine sublevels of the atomic ground state via the effect of coherent population trapping. The subsequent resonance microwave pulses create the polarization of equally populated ground state sublevels of the atom. The proposed polarization technique may be used for designing the new schemes of quantum computers, for the pulse transformation in optical experiments when light passes through a resonant medium containing rear-earth ions, as well as for producing polarized nuclear targets.     

Determination of polarization relaxation times of atomic levels

Rotation of polarization plane of a probe signal under influence of a time-advanced intense pulse is investigated taking into account optical pumping of atoms in a resonant medium. A formula is derived for the angle of rotation of polarization plane of the probe signal. It follows from this formula that modification of the polarization plane is caused by two processes: radiative decay of atoms and collision-induced redistribution of atoms over magnetic sublevels. It is shown that this method enables direct measuring long times of atomic collisions on the background of short times of the radiation decay.     

Coherence-controlled transparency and far-from-degenerate parametric gain in a strongly absorbing Doppler-broadened medium

An inversionless gain of anti-Stokes radiation above the oscillation threshold in an optically dense far-from-degenerate double- ? Doppler-broadened medium accompanied by Stokes gain is predicted. The outcomes are illustrated with numerical simulations applied to sodium dimer vapor. Optical switching from absorption to gain via transparency controlled by a small variation of the medium and of the driving radiation parameters, which are at a level of less than one photon per molecule, is shown.     

Dispersion of populations of a multilevel system in a strong field of laser emission and a magnetic field

Using the theory and the calculation method developed previously, numerical experiments on the study of dispersion of populations of a multilevel atomic system in strong fields of laser radiation in resonance with adjacent transitions and in a constant magnetic field are conducted. The effect of the magnetic field strength on the character of coherent population trapping in a multilevel system is studied. It is shown that the effect, depending on the magnetic field strength, may be observed for both and for one of the magnetic sublevels of the level that is doubly degenerate in the magnetic quantum number, for which resonance fluorescence is studied. The possibility of obtaining population inversion for magnetic sublevels in the excited state of a multilevel atom under an appropriate choice of parameters is demonstrated.     

Level mixing induced transparency II. Different transition probabilities of the crossing lines

In one of our previous papers (R.N. Shakhmuratov et al. Appl. Phys. B. 81, 883 (2005)) we presented a new type of spatiotemporal interference of gamma radiation propagating in a resonant medium. The excitation scheme consists of two identical V-schemes, each being formed by one type of the transition: one is induced only by the left circular polarized field and the other by the right circular polarized field. The coupling of these V-schemes through level crossing allows resonant scattering of a photon in the forward direction with a change of its polarization. As a result the radiation field, which is resonant with a transition from the ground state to one of the two sublevels of the excited state, develops in a particular combination of radiation fields with left and right circular polarizations, called a normal mode. This combination is much less absorbed in subsequent layers of the absorber. For identical V-schemes, the structure of the modes is fairly simple. In this paper, we show that a similar reduction of absorption is realized for non-identical V-schemes, differing in transition strengths. The structure of the normal modes is found and they have a more complicated form. This general case is actually realized in a level crossing experiment in gamma optics. PACS 42.50.Gy; 33.45.+x     

Induced resonant transparency of magnetic materials for gamma radiation: Propagation dynamics

The theory of spatiotemporal dynamics of gamma radiation in a resonant medium upon excitation of two-frequency gamma magnetic resonance in magnetic materials is considered. The radiation absorption at the fundamental frequency and the harmonic generation are investigated under conditions when the frequency of gamma radiation is shifted by the half-sum or half-difference of the frequencies of radio-frequency magnetic fields. It is shown that the propagation of gamma radiation through an absorber is characterized by a steady-state gamma intensity (resonant transparency). A consistent radio-frequency spectral analysis demonstrates that the intensities of harmonics drastically change at the transparency region boundaries due to nonlinear interference. The theory of quantum and dynamical beats of synchrotron radiation under conditions of induced resonant transparency is proposed.     

线极化Bell-Bloom测磁系统中抽运光对磁场灵敏度的影响

利用适用于线极化Bell-Bloom测磁系统的布洛赫方程和含有自旋弛豫的速率方程,以铯原子为研究对象,分析了抽运光对磁场灵敏度的影响,并在实验上分别采用与铯原子D1线和D2线共振的线偏光作为抽运光和探测光,用充有缓冲气体的气室进行了实验.实验结果与理论分析一致,均表明只有在一定的光强范围内,增大抽运光光强可以提高磁场灵敏度.且利用这一方法分析了原子的自旋弛豫对磁场灵敏度的影响.这项研究对于深入认识线极化的Bell-Bloom测磁系统,以及如何通过优化系统实现磁场灵敏度的提高具有重要的意义.     

基于超精细结构下的激光光泵铯磁力仪的理论研究

激光光泵碱金属磁力仪具有很高的灵敏度,测量范围可以从地球磁场到生物磁场。给出了铯（Cs）光泵磁力仪的理论分析和系统设计以及磁场梯度测量原理,铯原子能级在I—J耦合时形成超精细结构,在外磁场的作用下超精细结构进一步产生塞曼分裂形成塞曼子能级,利用激光泵浦和射频磁场能够使电子在超精细结构中进行能级跃迁,产生光磁双共振的结果,最终通过共振频率就能够达到精确测量外磁场的目的。     

Efficient and fast optical phase conjugation by use of two-photon-induced gratings in the orientation of angular momentum

Optical phase conjugation (OPC) is of interest for many applications. The generation of squeezed light, phase-conjugate mirrors, optical correlation, and turbulence correction would all benefit from improved OPC performance. Using Zeeman sublevels and cross-circularly polarized light in rubidium vapor, we demonstrate an OPC process that uses very low power (30 mW) but is still very fast (60 ns) and efficient (gain of 20). This process is generic enough to be applicable to almost any resonant medium.