The effect of spherical aberration on temperature distribution inside glass by irradiation of a high repetition rate femtosecond pulse laser

In this paper, we study the effect of spherical aberrations on the light intensity and the temperature distribution in the focal region in a 250-kHz femtosecond laser irradiated Ag⁺-doped borosilicate glass. When a focused beam goes through an interface between air and glass, spherical aberration will result in the separation of the focal point and then cause a clear change of the light intensity distribution along the incident direction. That phenomenon will further influence the longitudinal cross-section temperature distribution in glass. Here we use Ag nanoparticle formation as a marker for establishing temperature distribution and we find that the formation of nanoparticle shows a strong dependence on the temperature field and the detailed precipitation process is also discussed.     

Efficiency factors of scattering,absorption, and backscattering of a femtosecond laser pulse train by a transparent spherical particle

Analytical expressions are derived for integral optical characteristics (the scattering, absorption, and backscattering efficiency factors) of aerosol particles irradiated by a femtosecond laser pulse train. The behavior of these integral characteristics attendant to variations of the particle size and pulse period-to-pulse duration ratio is investigated based on the results of numerical calculations. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 33–36, March, 2008.     

分子的飞秒强光电离

文章以一个实验者的角度,介绍了分子的飞秒强光电离的研究现状.文章从对比飞秒激光电离质谱与纳秒激光电离质谱开始,接着介绍分子在激光场作用下的可能电离机理,着重描述了几个处理分子场致电离的理论模型和实验验证,最后对飞秒激光导致的分子在激光脉冲作用后取向研究进行了简单介绍.     

分子的飞秒强光电离

文章以一个实验者的角度，介绍了分子的飞秒强光电离的研究现状。文章从对比飞秒激光电离质谱与纳秒激光电离质谱开始，接着介绍分子在激光场作用下的可能电离机理，着重描述了几个处理分子场致电离的理论模型和实验验证，最后对飞秒激光导致的分子在激光脉冲作用后取向研究进行了简单介绍。     

High-order optical vortex harmonics generated by relativistic femtosecond laser pulse

Harmonics generated by an intense femtosecond Gaussian laser pulse normally incident on a spiral-shaped thin foil target were studied.By using two-dimensional(2D) particle-in-cell(PIC) simulation,we observed evident odd harmonics signals in the reflection direction and found that the reflected field has a helical structure determined by the target shape.This method provides a new way to generate an intense ultraviolet vortex with high-order topological charge by use of ultrahigh intense laser-driven harmonics.     

Controllable photoinduced optical attenuation in a single-mode optical fiber by irradiation of a femtosecond pulse laser

Novel optical attenuation fibers were fabricated by the irradiation of a focused infrared femtosecond pulsed laser onto the core of a silica glass single-mode optical fiber. Optical attenuation at a wavelength of 1.55 microm proportionally increased with increasing numbers of irradiation points and was controllable under laser irradiation conditions. The single-mode property of the waveguide and the mode-field diameter of the optical fiber were maintained after irradiation of the femtosecond laser. It is suggested that the attenuation results from optical scattering at photoinduced spots formed inside the fiber core.     

Light field characteristics of reflective thin-films irradiated by femtosecond laser pulses

The formation of interference field in optical thin-films is a process of unsteady state when irradiated by femtosecond pulses. Based on the methods of plane-wave decomposition and the using of thin-film characteristic matrix, the model is presented focusing on the issues of mirror reflectance and internal light field in femtosecond timescale. The numerical results reveal that with the decrease of the pulse width a reduction of reflection performance occurs. In addition, the traditional approach that simplifies the incident femtosecond pulse to monochromatic continuous wave cannot get the exact value of the light field magnitude and the temporal profile of ultrashort laser pulse should be taken into account to reach more accurate results.     

飞秒激光场中原子所受光学偶极力研究

通过求解全波矢布洛赫方程研究了两能级原子与飞秒超快激光脉冲的相互作用过程,计算了不同拉比频率取值下原子所受光学偶极力和粒子数布居随时间的演化情况,分析了光场失谐量对光学势分布情况的影响.研究发现:由飞秒激光场产生的横向光力的时间平均值并不等于零,而是随着拉比频率的增加呈现振荡的增大趋势;纵向光力的时间平均作用也并非是拉比频率的单调函数,而是随着拉比频率的增加呈现周期性的振荡分布特性;光学势的分布对光场的失谐量具有明显的依赖性,随着失谐量的变化,光学势的性质也随之发生了改变.     

Thermal behavior of thin metal films irradiated by shaped femtosecond pulse sequences laser

A numerical solution of the two-temperature model has been performed up to the shaped femtosecond pulse sequences heated metal target. The two-temperature model is used to analyze the shaped femtosecond pulse sequences with the following major conclusions. We confirm the distinctly different results on the different shaped femtosecond pulse sequences. As the number of shaped femtosecond pulses increases, the nonequilibrium state between electrons and phonons gradually disappears, the highest transient electron temperature is lowered and the thermolization time is prolonged, the electron heat conductivity remains higher because of the effect of incubation on the electron temperature, which preserves the advantages of ultrashort lasers. The shaped femtosecond pulse sequences can increase the efficiency in ablation and micromachining.     

New mechanism of the formation of the nanorelief on a surface irradiated by a femtosecond laser pulse

The kinetics of fast processes induced by an ultrashort laser pulse is considered. The reliefs remaining after the action of a series of ultrashort laser pulses {S. A. Akhmanov, V. I. Emelyanov, N. I. Koroteev, et al., Usp. Fiz. Nauk 147, 675 (1985) [Sov. Phys. Usp. 28, 1084 (1985)]; F. Costache, S. Kouteva-Arguirova, and J. Reif, Appl. Phys. A 79, 1429 (2004)} have been studied. A new mechanism of perturbing the surface of the initially ideal crystal face is described. First, the formation of a relief is induced by a single pulse. Second, the relief scale along the target surface is about the heating depth d _T ～ 10–100 nm rather than the pump-pulse wavelength λ_pump ～ 1 μm. Third, the formation of the relief is not attributed to the modulation of the electromagnetic field near the surface due to the interference of the incident light wave with the electromagnetic surface waves on the initial perturbations of the boundary. These three conditions are satisfied for a known instability induced by the interference of the incident and surface waves (see the works cited above [1]). In our case, the nanorelief is formed due to the deformation of the spalled layer by cavitation bubbles owing to the inhomogeneity of the drag force in the target plane. Cavitation is caused by the tension of the substance in the process of the expansion of a heated target. It is similar to the known phenomenon of the cavitation “spallation” in a liquid despite the large difference between the space-time scales of the usual spallation facility and the femtosecond heating. Owing to this difference, usual cavitation does not leave any morphological trace on the outer free surface of the spalled layer.     

Dynamics of a spherical particle in an intense optical field

The evaporation rate of a spherical particle in an intense, isotropic optical field is calculated.     

Scattering of a light pulse by a spherical particle

In this work the scattering of a brief light pulse by a homogeneous spherical particle is studied within the framework of linear electrodynamics. Convenient formulas are obtained for the scattered fields of the pulse. As a concrete example the Rayleigh scattering of a light pulse is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 80–84, August, 1972.     

Superluminal pulse reflection from a weakly absorbing dielectric slab

Group delay for a reflected light pulse from a weakly absorbing dielectric slab is theoretically investigated, and large negative group delay is found for weak absorption near a resonance of the slab [Re(kd)=mpi]. The group delay for both the reflected and transmitted pulses will be saturated with an increase of the absorption.     

Generating optical vortex with computer-generated hologram fabricated inside glass by femtosecond laser pulses

We introduce a novel method to generate the optical vortex with computer-generated hologram (CGH) fabricated inside glass by femtosecond laser pulses. The CGH was directly written inside glass by femtosecond laser pulses induced microexplosion without any pre- or post-treatment of the material. We also realized the restructured optical vortex beams of both the transmission and reflection pattern with high fidelity using a collimated He-Ne laser beam. The total diffractive efficiency of both the transmission and reflection pattern is about 4.79%.     

Formation of nanocavities in the surface layer of an aluminum target irradiated by a femtosecond laser pulse

It has been revealed experimentally that nanocavities remain inside a surface layer of aluminum after action of a femtosecond laser pulse. This result is in agreement with numerical simulation. A detailed picture of melting, formation of expansion and compression waves, and bubble nucleation in the stretched melt has been reconstructed through atomistic simulation. It has been shown that the bubbles do not fully collapse but remain as frozen disk-shaped nanocavities upon recrystallization of the melt. The formation of a porous metal with small voids is very important for understanding the physics of laser exposure and may have significant applications.     

Three-dimensional simulation on explosions of hydrogen atomic clusters irradiated by an intense femtosecond laser pulse

Using classic particle dynamics simulations, the interaction process between an intense femtosecond laser pulse and icosahedral hydrogen atomic clusters H_{13}, H_{55} and H_{147} has been studied. It is revealed that with increasing number of atoms in the cluster, the kinetic energy of ions generated in the Coulomb explosion of the ionized hydrogen clusters increases. The expansion process of the clusters after laser irradiation has also been examined, showing that the expansion scale decreases with increasing cluster size.     

Large negative refractive index modification induced by irradiation of femtosecond laser inside optical glasses

We report on the refractive index modification (Δn) and its cross sectional profile of the created lines inside the different types of optical glasses, containing BaO, TiO₂, or La₂O₃ as a metal oxide. The lines were fabricated by scanning a stage and focusing the femtosecond laser pulses, 800 nm wavelength, a 250 kHz repetition rate and 200 fs pulse duration, from the Ti:sapphire regenerative amplifier system. The Δn measurements were performed with the qualitative phase microscopy technique. As a result, it was found that the Δn and its sign are different depending on glass types. For example, in the glasses containing TiO₂, the Δn became smaller in the modified region and some of them showed relatively large decrease of the Δn, Δn < −0.01, with about 10 μm width. Such a glass material could be useful for the compact optics and optical devices.     

Intensity of electromagnetic energy radiation by a quiescent ferromagnetic spherical particle placed in a permanent magnetic field

Technical Physics - The classical problem of calculating the energy of electromagnetic energy radiated from a ferromagnetic particle is solved for the case when the vector of spontaneous...