Interaction of molecular nitrogen with Free-Electron-Laser radiation

Nonlinear absorption of ultrapower laser radiation by relativistic underdense plasma

The nonlinear absorption of laser radiation of relativistic intensities in the underdense plasma by a mechanism of stimulated bremsstrahlung of electrons on the ions/nuclei is investigated in the low frequency approximation. Coefficient of nonlinear inverse-bremsstrahlung absorption is studied for relativistic Maxwellian plasma at asymptotically large values of laser fields and high temperatures of electrons.

Theory of femtosecond strong field ion excitation and subsequent lasing in N$_2^+$

Delayed cavity-free forward lasing at the wavelengths of 391 and 428 nm was observed in recent experiments in air or pure nitrogen pumped with an intense femtosecond laser pulse at wavelength of 800~nm. The mechanism responsible for the lasing is highly controversial. In this article we explain the delayed emission by the presence of long-lived polarizations coupling simultaneously ground state X$^2Σ_g^+$ to states A$^2Π_u$ and B$^2Σ_u^+$ of singly ionized nitrogen molecules N$_2^+$. Ionization of neutral nitrogen molecules in a strong laser field and subsequent ion excitation are described by…

Coherent control of superradiance from nitrogen ions pumped with femtosecond pulses

Singly ionized nitrogen molecules in ambient air pumped by near-infrared femtosecond laser give rise to superradiant emission. Here we demonstrate coherent control of this superradiance by injecting a pair of resonant seeding pulses inside the nitrogen gas plasma. Strong modulation of the 391.4 nm superradiance with a period of 1.3 fs is observed when the delay between the two seeding pulses are finely tuned, pinpointing the essential role of macroscopic coherence in this lasing process. Based on this time-resolved method, the complex temporal evolution of the macroscopic coherence between two…

在氮离子激光中对携带轨道角动量（OAM）的光脉冲进行放大

Amplification of light pulses with orbital angular momentum (OAM) in nitrogen ions lasing

本研究证明在氮等离子体中可显著放大携带轨道角动量（OAM）的种子光脉冲，并利用空间错位实现高斯与OAM模式切换的光开关。

Harmonics generation and intense terahertz radiation from polar molecules at multiphoton resonant excitation in laser fields

The coherent radiation spectrum of two-level polar molecules with UV transition is studied at the multiphoton resonant excitation by a moderately strong laser field. The spectrum corresponding to harmonic generation and low-frequency radiation is investigated both analytically and numerically. Specifically, a mechanism for generation of intense smoothly tunable terahertz radiation by two-level molecular configurations (with dynamic Stark shifts) possessing permanent dipole moments, is considered.

沟道辐射与激光辐射源的地位

On the status of channeling radiation and laser based radiation sources

本文用两个洛伦兹不变量统一描述定向晶体沟道辐射与激光辐射源，揭示二者关键差异，并指出定向晶体可研究强非均匀场中的QED过程。

Formation and stimulated photodissociation of metastable molecules with emission of photon at the collision of two atoms in a laser radiation field

The Formation of metastable molecules (Feshbach resonances) at the collision of two atoms and subsequent stimulated transition to a lower unbound electronic molecular state, with emission of a photon of the laser radiation has been investigated. This can develop, in particular, for $Rb_2$ molecules due to resonance scattering of two $Rb$ atoms. The considered process is a basis for the creation of excimer lasers. Expressions for the cross sections of elastic and inelastic resonance scattering and the intensity of the stimulated emission of the photons have been obtained.