Electromagnetic Energy Transfer in the Atmosphere Ionized by Laser Radiation

Russian Physics Journal - The physical processes occurring in the atmosphere, when weak ionization channels are formed by laser radiation, are discussed. An electromagnetic energy transmission...     

Sound Generation by Breakdown Plasma Formations Initiated by Solid Aerosol Particles upon Exposure to Laser Radiation

The results of experimental investigations into the characteristics of acoustic signals generated by breakdown plasma formations initiated by a solid aerosol particle or an ensemble of monodisperse aerosol particles upon exposure to laser radiation with a wavelength of 1.06 m are presented as functions of the materials and sizes of particles and of the acting laser energy density. It is demonstrated that the acoustic signal amplitude and duration depend linearly on the effective sizes of particles initiating plasma formations with the proportionality coefficient depending on the particle material. The coefficient of laser energy conversion into the acoustic energy is estimated. The acoustic pulse shape is satisfactorily approximated by a blast N-wave for particles of micron sizes. A comparison of the obtained results with the data available from the literature indicates their good agreement.     

Adaptive Correction of a High-Power Titanium-Sapphire Laser Radiation

An adaptive optical closed-loop feedback system based on a phase-conjugation algorithm has been developed and investigated. It includes a deformable bimorph mirror and a Shack-Hartmann wavefront sensor. This system was used to improve the radiation focusing in an ultrashort-pulse laser designed for basic research in the field of high-energy physics. With the indicated system, the power density of 10-TW radiation pulses in the focal plane of a Ti:Al₂O₃ laser reached 4 ⋅ 10¹⁹ W/cm². Report at the Fifth International Scientific and Technical Conference “Quantum Electronics,” November 22–25, 2004, Minsk, Belarus. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 678–683, September–October, 2005.     

超短强激光脉冲在大气传播中的自聚焦行为

通过建立涉及克尔效应和多光子电离效应的非线性数学模型,利用数值方法研究了超短激光脉冲在大气传播中的聚焦行为。结果表明由自聚焦导致的成丝现象具有间断,而不是一种稳态的模式。每次轴上的成丝都会由于光场损耗减弱,但同时由于克尔效应会使离轴区域的能量间断地补充到光轴上。     

Generation of THz Radiation by Laser Plasma Interaction

This paper presents the three wave parametric decay process to generate the Terahertz (THz) radiations in magnetized plasma. The pump wave (Laser beam) is considered in the extraordinary mode (x‐mode), propagating perpendicular to the background magnetic field. This pump wave decays into an upper hybrid wave and a THz wave which is in magnetosonic mode. The appropriate expressions for the coupling coefficients of the threewave interaction and THz wave amplitude have been derived. Subsequently, the growth rate of this decay instability is also calculated. Various laser and plasma parameters were optimized and we report efficiency of the order of ～1.4 × 10^–2 for current scheme. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Emission of Concentrated Solutions of Organic Compounds Excited with High-Power Laser Radiation

Specific features of emission of concentrated (C 1.2·10¹⁹ cm^–3) solutions of organic molecules (rhodamine 6G, rhodamine C, phenalemine 512, and substituted paraterphenyl (LOC-1)) are investigated as functions of the exciting photon energy (at _exc = 308 and 532 nm) and power density of exciting radiation (up to 1 GW/cm²). One of the observed emission types – band emission – is studied. The intensity of band emission (its short- and long-wavelength maxima) is investigated versus the exciting radiation power density, and its time and polarization characteristics are also analyzed. The results obtained together with the specific features of the emission spectrum of concentrated rhodamine-C solution, measured after passage of sounding radiation with maximum at the wavelength equal to that of the short-wavelength maximum of band emission, demonstrate that the band emission is simply superfluorescence.     

Generation of Continuum Extreme-Ultraviolet Radiation by Carrier-Envelope-Phase-Stabilized 5-fs Laser Pulses

Coherent extreme-ultraviolet （XUV） radiation is studied by interaction of carrier-envelope （CE） phase stabilized high energy 5-fs infrared （800 nm） laser pulses with neon gas at a repetition rate of 1 kHz. A broadband continuum XUV spectrum in the cut-off region is demonstrated when the CE phase is shifted to about zero, rather than modulated spectral harmonics when setting of CE phase is nonzero. The results show the generation of isolated attosecond XUV pulses.     

基于超辐射机理产生X波段高功率亚纳秒脉冲研究

设计了一种基于超辐射机理的X波段相对论返波管结构, 利用全电磁2.5维粒子模拟程序对返波管中的超辐射机理进行了粒子模拟研究. 模拟表明: 在束430kV、束流4kA, 脉宽3.1ns的电子束驱动下,实现了峰值功率1.5GW、频率10GHz、脉宽500ps的亚纳秒微波脉冲输出, 峰值功率转换效率达到87.2%;在超辐射机理作用下, 微波峰值功率与电子束脉宽在一定的范围内成平方关系.     

Analysis of Inner-Scale Effect on Atmosphere Scintillation for Infrared Laser Beam Propagating on Earth-Space Paths

On Earth-space paths, based on ITU-R C_n² (h) model, by means of a modification of the Rytov method that incorporates an amplitude spatial frequency filter function under strong fluctuation conditions, considering atmospheric turbulence inner-scale, an expression is developed for the scintillation index of a visible or a near and middle infrared laser beam wave that is valid under moderate to strong irradiance fluctuations. The quantitative analyses of scintillation index are done by this analytic model for laser Gaussian collimated beam wave at visible or near and middle infrared wave band. The results agree with theoretic analysis scintillation. This scintillation model can be converted into a Gaussian beam wave model with finite inner-scale on horizontal sight paths of invariable C_n².     

On the Effective Metric for an Electromagnetic Wave Propagating in the Field of an Intense Laser Radiation

It is shown that in the nonlinear electrodynamics of vacuum, which is a corollary of quantum electrodynamics, a weak electromagnetic wave propagates in the field of an intense laser radiation as if this took place in some effective space-time whose metric tensor depends on the electric field of the laser radiation. The components of the metric vector of the effective space-time along the geodesic lines of which the rays of the weak electromagnetic wave propagate in the given case have been found. It is pointed out that this property may serve as a basis for observing the manifestations of the nonlinearity of the electrodynamics of vacuum.     

Investigation of Heating of Optical Elements During Formation of High-Power CW Fiber Laser Radiation

Russian Physics Journal - The problem of heating of optical components during the formation of the high-power continuous-wave fiber laser radiation is considered. The results of experimental...     

Calculation of Momentum Coupled by a High-Power Laser Beam

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Generation of High-Power Ultrashort Optical Pulses Using a Semiconductor Laser with Controlled Current Pumping

Technical Physics - Fiber-coupled semiconductor lasers are studied under pumping with high-power short current pulses. Appropriate parameters of the current pumping make it possible to...     

Radio Emission of Rydberg Atoms in the Upper Atmosphere Modified by High-Power HF Radio Waves

Radiophysics and Quantum Electronics - We report on the results of studying the radio emission of the Rydberg states of atoms and molecules in the Earth’s upper atmosphere at ionospheric...     

1150 nm High-Power Fiber Laser Oscillator Pumped by 976 nm Laser Diode

We present an all-fiber 1150 nm Yb-doped fiber laser oscillator pumped by a 976 nm laser diode. To suppress amplified spontaneous emission and avoid parasitic laser oscillation, we propose a long-length gain fiber and a high-reflectivity output fiber Bragg grating in the fiber laser oscillator. The 1150 nm band single-mode fiber laser with output power of 20.5 W is demonstrated at room temperature. The optical-to-optical conversion efficiency ranges up to 51.6% at the maximum output. The central wavelength of the fiber laser oscillator is 1150.35 nm, and its 3 dB spectral width is 0.72 nm. No evidence of amplified spontaneous emission, residual pump light, or parasitic laser oscillation were observed in the experiments. The high-power 1150 nm fiber laser oscillator can be used as a pump source in the development of a 3 μm Ho-doped fiber laser.     

Generation of THz Radiation from Laser Beam Filamentation in a Magnetized Plasma

The terahertz (THz) frequency radiation production as a result of nonlinear interaction of high intense laser beam with low density ripple in a magnetized plasma has been studied. If the appropriate phase matching conditions are satisfied and the frequency of the ripple is appropriate then this difference frequency can be brought in the THz range. Self focusing (filamentation) of a circularly polarized beam propagating along the direction of static magnetic field in plasma is first investigated within extended‐paraxial ray approximation. The beam gets focused when the initial power of the laser beam is greater than its critical power. Resulting localized beam couples with the pre‐existing density ripple to produce a nonlinear current driving the THz radiation. By changing the strength of the magnetic field, one can enhance or suppress the THz emission. The expressions for the laser beam width parameter, the electric field vector of the THz wave have been obtained. For typical laser beam and plasma parameters with the incident laser intensity ≈ 10¹⁴ W/cm², laser beam radius (r₀) = 50 μm, laser frequency (ω₀) = 1.8848 × 10¹⁴rad/s, electron plasma (low density rippled) wave frequency (ω₀) = 1.2848 × 10¹⁴ rad/s, plasma density (n₀) = 5.025 × 10¹⁷cm^–3, normalized ripple density amplitude (μ)=0.1, the produced THz emission can be at the level of Giga watt (GW) in power (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Efficient High-Power Ho:YAG Laser Pumped by Dual-End-Diode-Pumped Tm:YLF Laser

We report a Ho:YAG (Ho-doped yttrium aluminum garnet) laser pumped by a dual-end-diode-pumped Tm:YLF (Tm-doped yttrium lithium fluoride) laser to obtain an efficient experimental device with high output-power characteristics. We study the influence of the specific values of the output coupling mirror transmittance, the resonant cavity length, and the radius of curvature of the output coupling mirror on the Ho:YAG laser output characteristics. Under optimum experimental conditions, under which the output coupling mirror transmittance was 30%, the resonant cavity length was 25 mm and the output coupling mirror radius of curvature was 300 mm, and the maximum pumping power of the dual-end-diode-pumped Tm:YLF laser was 15.2 W. We obtain an efficient high-power 2.122-μm laser output of 7.98 W from the Ho:YAG laser. The optical-to-optical conversion efficiency is 52.5%, and the beam quality factor figures are M _x ² ?=?2.89 and M _y ² ?=?2.97.     

Dependence of Doubly Charged Ion Formation by the Two-Electron Mechanism on the intensity of Laser Radiation

Experimental dependences of the doubly charged ion yield N ²⁺ on the laser radiation intensity F are analyzed for the case of ion formation by the two-electron mechanism. It is shown that the region where the dependence N ²⁺(F) is characterized by the degree of nonlinearity K≈2.5 corresponds to the saturation of the process of doubly charged ion formation. This region is described well by theoretical calculations performed for Gaussian laser beams.