Resonant Scattering of Picosecond Laser Pulses by Atoms in Alkali Metal Vapors

Resonant scattering of ultrashort laser pulses (ULPs) in the vicinity of spectral doublets in monatomic lithium and sodium vapors is studied theoretically. The scattering probability over the entire time of pulse action is calculated as a function of various parameters of the problem (carrier frequency and ULP duration, as well as vapor pressure and temperature). It is shown that the dependence of the total scattering probability on the pulse duration is generally nonlinear by nature.     

Dependence of the Two-Photon Absorption Coefficient of Steel on the Pulse Duration During Its Ablation by Femto- and Picosecond Laser Pulses

JETP Letters - The dependences of the depth of single-pulse ablation of the steel surface on the energy density of ultrashort laser pulses (0.3–12 ps) with a wavelength of 515 nm have the...     

Optical Switch Formation in Antimony Super-Resolution Mask Layers Induced by Picosecond Laser Pulses

Sb is a classic material of a super-resolution near field structure （super-RENS） mask layer in which the optical switch formation is often realized by nanosecond laser pulse stimulation. We achieve fast and repeatable optical switching driven by picosecond laser pulses in a proper fluence range on Sb thin films. The optical properties of Sb thin films before and after switching are studied by surface-sensitive micro-area ellipsometry. The change of optical constants after switching is less than 2% in the whole visible range. The Sb mask layer is shown to be very promising for ultrafast super-resolution optical storage applications.     

Direct Generation of Tunable UV Picosecond Laser Pulses Using Spectrotemporal Selection

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Spectrally Adjustable Picosecond Dye Laser Pulses Generated with Nanosecond Nitrogen Lasers

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A Hydrodynamic Model of the Interaction of Picosecond Laser Pulses with Condensed Targets

We consider a physical model of the interaction of highpower laser pulses with plasma created upon irradiation of condensed targets. The model is based on the equations of singlefluid, twotemperature hydrodynamics taking into account the ponderomotive force, and the Maxwell equations for laser radiation at oblique incidence in the cases of s and ppolarizations. The model takes into account the generation of fast electrons in the conditions of plasma resonance at the critical surface, and their transport with consideration for the friction force, caused by the ionization losses. Heating of ions in the plasma due to beats of the ponderomotive potential is considered. The results of numerical modeling of the interaction of a picosecond laser pulse, containing a prepulse, with a deuterium target at power densities of 10¹⁶–10¹⁷ W/cm² are presented. It is shown that the neutron yield of the DDreaction decreases with increase in prepulse energy, because the plasma created inhibits heating of the dense region of the target where a high rate of the reactions can be realized. It is also shown that the laser radiation losses caused by the stimulated scattering increase with increase in prepulse energy.     

Silicon Ablation by Single Ultrashort Laser Pulses of Variable Width in Air and Water

The ablation of silicon by single laser pulses of variable width (0.3–9.5 ps) with a wavelength of 515 nm has been comparatively studied in air and water. A nonmonotonic behavior of ablation thresholds with a minimum at 1.6 ps, which is due to achieving the thermalization time of the electron and ion subsystems in silicon, has been revealed. It has been shown that, with an increase in the pulse width in the considered width range, the efficiency of the ablation of silicon decreases by a factor of 2.5 in air and increases by a factor of 2 in water. This behavior of ablation in air is attributed to a partial transition from phase explosion to surface evaporation, which is suppressed in water.     

不同烧蚀条件下飞秒激光脉冲诱导ZnO纳米结构研究

烧蚀条件对飞秒激光脉冲诱导氧化锌纳米结构有重要影响.研究了800 nm,150 fs,250 kHz的飞秒激光脉冲分别在空气中,去离子水中以及无水乙醇中垂直聚焦于氧化锌晶体表面,诱导形成不同形态的纳米结构.实验结果表明,在空气中利用飞秒激光脉冲辐照样品表面,形成了周期为180 nm的纳米线;在去离子水中辐照诱导形成了由氧化锌纳米线聚集而成的"纳米球";在无水乙醇中形成出现分叉结构的纳米线.拉曼光谱分析辐照前后晶体晶相结果表明,形成的纳米结构相对于辐照前特征峰437 cm-1强度有所下降,在570 cm-1处的峰值则显著增强.分析了在各种烧蚀条件下诱导形成纳米结构的演化过程以及物理机理.     

High Repetition Rate Fiber Laser Coupled to a Linear Cavity Generating Picosecond Pulses

An experimental investigation is presented for obtaining picosecond (ps) pulses at a repetition rate of 11 GHz using a fiber laser coupled to an external cavity. Without applying active mode locking and without a nonlinear element in the coupled cavity, pulses of about 15 ps with an average power of 20 mW have been generated using a (cw) diode pump laser. The pulse duration decreases with increasing repetition rate.     

Nanoparticles by Laser Ablation

This review concerns nanoparticles collected in the form of nanopowder or a colloidal solution by laser ablating a solid target that lies in a gaseous or a liquid environment. The paper discusses the advantages of the method as compared with other methods for nanoparticle synthesis, outlines the factors on which the properties of the produced nanoparticles depend, explains the mechanisms and models involved in the generation of nanoparticles by laser ablation, clarifies the differences between nanoparticle generation in gaseous and liquid environments, presents some experimental desigins and equipment used by the several groups for nanoparticle generation by laser ablation, describes the techniques used for “tuning” the width of the nanoparticles size distribution, and finally presents a few interesting examples of nanoparticles generated by laser ablation.     

铒激光脉冲消融泌尿结石和胆结石比较研究

利用光学弱相干显微成像系统对脉冲激光消融硬生物组织后形成的凹坑二维和三维形貌进行了扫描,分析了Erbium∶YAG激光脉冲消融生物硬组织特性.结果表明：相同激光参量条件下,消融胆结石比消融泌尿结石具有更高的消融效率|消融胆结石或消融泌尿结石时,脉冲能量越大,消融效率越高|消融效率提高主要体现在凹坑表面直径更宽、高度更深、体积更大|光学弱相干显微成像技术比光学弱相干光层析成像技术测量准确度提高约一个量级,更适合于测量脉冲激光消融生物硬组织后形成的凹坑形貌.     

Focusing Waveguide Structure for High-Gradient Electron Acceleration by Picosecond Terahertz Pulses

Radiophysics and Quantum Electronics - We propose an ultra-wideband metal–dielectric structure for high-gradient acceleration of electrons by the field of an ultrashort terahertz pulse. The...     

Obtaining Single Picosecond Pulses in a Short-Cavity Dye Laser with Switching of Lasing to the Saturable Absorber

A new method of lasing of single picosecond pulses in a short-cavity dye laser with spatial separation of the lasing medium and the saturable absorber in the case of pumping by nanosecond pulses with energies much higher than the oscillation threshold has been developed and experimentally realized. The method is based on the use of a high-Q, external cavity tuned to the amplification wavelength of the saturable absorber. The first picosecond pulse is lased at a lasing-medium wavelength and the subsequent pulses are lased at a saturable-absorber amplification wavelength.     

Phase Conjugation with Picosecond Pulses in BaTi03

The self-pumped phase conjugate signal of picosecond laser pulses is observed. The width of the incident laser pulses is about 1.5 ps and their repetition rate is 82 MHz. The wavelength of the pulses can be tuned in the range from 710 nm to 850 nm. The pulse character of the conjugate signal is determined by an autocorrelator. The quality of the conjugate pulses is found to be good by the well-known phase distorter method.     

Nanoparticle Formation by Laser Ablation

The properties of nanoparticle aerosols of size ranging from 4.9nm to 13nm, generated by laser ablation of solid surfaces are described. The experimental system consisted of a pulsed excimer laser, which irradiated a rotating target mounted in a cylindrical chamber 4cm in diameter and 18-cm long. Aerosols of oxides of aluminum, titanium, iron, niobium, tungsten and silicon were generated in an oxygen carrier gas as a result of a reactive laser ablation process. Gold and carbon aerosols were generated in nitrogen by non-reactive laser ablation. The aerosols were produced in the form of aggregates of primary particles in the nanometer size range. The aggregates were characterized using a differential mobility analyzer and electron microscopy. Aggregate mass and number concentration, electrical mobility size distribution, primary particle size distribution and fractal dimension were measured. System operating parameters including laser power (100mJ/pulse) and frequency (2Hz), and carrier gas flow rate (1l/min) were held constant.A striking result was the similarity in the properties of the aerosols. Primary particle size ranged between 4.9 and 13nm for the eight substances studied. The previous studies with flame reactors produced a wider spread in primary particle size, but the order of increasing primary particle size follows the same trend. While the solid-state diffusion coefficient probably influences the size of the aerosol in flame reactors, its effect is reduced for aerosols generated by laser ablation. It is hypothesized that the reduced effect can be explained by the collision-coalescence mechanism and the very fast quenching of the laser generated aerosol.     

梳状色散光纤中皮秒脉冲压缩特性研究

利用数值法解非线性薛定谔方程,分析了光脉冲在梳状色散光纤中的传输特性,比较了光脉冲在几种不同的色散变化趋势的梳状色散光纤中的脉冲压缩比及脉冲质量,提出了高阶孤子压缩加梳状色散光纤压缩的方法,并初步讨论了梳状色散光纤对增益开关激光器输出脉冲进行压缩的效果。     

Ablation of (111) and (001) Crystal Plates by Ultrashort Laser Pulses with Rotated Linear Polarization

JETP Letters - The dependence of the threshold fluence for surface ablation of such crystalline materials as silicon and diamond (with orientations (001) and (111)) on the direction of linear...     

On a New Method of Acoustic Monitoring of the Nanosecond Laser Ablation of Metals

The possibility of the formation of lattices of magnetic skyrmions in thickness-modulated films with perpendicular magnetic anisotropy has been studied experimentally. The samples constitute a regular rectangular lattice (300 nm in period) of cylindrical bulges (150 nm in diameter) formed in a Co/Pt multilayer film by electron lithography. The spatial symmetry of a magnetic force microscopy signal indicates the formation of magnetic skyrmions in the process of remagnetization of the system. Formed skyrmions remain stable in the absence of an external magnetic field. The experimental data are in good agreement with the numerical micromagnetic simulation of the system.