Laser annealing of dielectrics with metal nanoparticles

The effect of nanosecond excimer laser pulses on a composite layer of sodium-calcium silicate glass with silver nanoparticles has been investigated. Nanoparticles were synthesized by ion implantation. Based on measuring the optical absorption and reflection spectra of the composite layers, it is found that an increase in the number of laser pulses leads to a monotonic decrease in the size of silver nanoparticles. However, laser irradiation with a longer duration leads to the growth of nanoparticles with their subsequent destruction. The effects observed are discussed in terms of heating a glass composite layer as a result of the effective absorption of laser radiation.     

Excimer laser-assisted annealing of silicate glass with ion-synthesized silver nanoparticles

The effect of KrF excimer laser radiation on a composite layer consisting of sodium-potassium silicate glass with silver nanoparticles is studied as a function of the number of laser nanosecond pulses. The silver nanoparticles are synthesized by ion implantation. The measured optical absorption of the composite layer demonstrates that the silver nanoparticle size decreases monotonically as the number of laser pulses increases. Rutherford backscattering shows that laser annealing is accompanied by silver diffusion into the bulk of the glass and partial metal evaporation from the sample surface. The detected decrease in the silver nanoparticle size is discussed in terms of simultaneous melting of silver nanoparticles and the glass matrix due to the absorption of laser radiation.     

Intensity-driven,laser induced transformation of Ag nanospheres to anisotropic shapes

The shapes of initially spherical Ag nanoparticles in soda-lime glass are persistently changed using fs laser irradiation. With linearly polarized pulses, this shape transformation of the nanoparticles causes optical dichroism of the material. The intensity dependence of this effect is studied comprehensively, addressing the whole intensity range of permanent modifications as well as the influence of the number of laser pulses applied to one spot on the sample. The results are used as basis to develop a complete scenario of the possible mechanisms leading to the laser-induced shape transformation of metallic nanoparticles in glass.     

飞秒激光作用下金掺杂硅酸盐玻璃的光致晶化研究

研究了金掺杂硅酸盐玻璃在飞秒激光辐照和热处理作用下的光致晶化行为，分析探讨了其机理和激光辐照条件的影响.吸收光谱测试表明玻璃内部析出金纳米颗粒. 金纳米颗粒掺杂玻璃在近共振纳秒脉冲作用下显示了强的光限幅效应, 且改变飞秒激光诱导参数可改变该复合玻璃的光学非线性. 关键词： 光致晶化 飞秒激光 金纳米颗粒 硅酸盐玻璃 光限幅     

飞秒激光在6H SiC晶体表面制备纳米微结构

激光诱导周期性纳米微结构在多种材料包括电介质、半导体、金属和聚合物中观察到。研究了800nm和400nm飞秒激光垂直聚焦于6H SiC晶体表面制备纳米微结构。实验观察到800nm和400nm线偏光照射样品表面分别得到周期为150nm和80nm的干涉条纹,800nm圆偏振激光单独照射样品表面得到粒径约100nm的纳米颗粒。偏振相互垂直的800nm和400nm激光同时照射晶体得到粒径约100nm的纳米颗粒阵列,该纳米阵列的方向随400nm激光强度增加而向400nm偏振方向偏转。利用二次谐波的观点对以上纳米结构的形成给出了解释。     

Ion synthesis of copper nanoparticles in sapphire and their modification by high-power excimer laser pulses: A review

Composite layers made in sapphire by implantation of 40-keV Cu⁺ ions at a dose of 1 × 10¹⁷ cm⁻² and an ion beam current density varying from 2.5 to 10 μA/cm² are studied. It is shown that ion implantation makes it possible to synthesize a composite layer containing copper nanoparticles at the surface of the insulator. However, the nanoparticle size distribution in this layer is nonuniform. The composite layer is exposed to high-power excimer laser radiation with the aim of modifying the size and size distribution of the metal nanoparticles in it. The resulting structures are examined by Rutherford backscattering, optical reflection spectroscopy, and atomic force microscopy. It is found that the laser irradiation diminishes copper nanoparticles in the composite layer. Experimental data on laser modification may be explained by photofragmentation and/or melting of the nanoparticles in the sapphire matrix under the action of nanosecond laser pulses.     

Laser Fabrication of Nanostructures on a Pure Aluminum Surface in Air

We report on the fabrication of surface nanoparticles and micro/nanograting structures on bulk pure aluminum in air using a 150 fs, 775 nm femtosecond laser. We investigate the size of the generated surface nanoparticles under irradiation with different femtosecond laser pulses. Smaller nanoparticles can be induced by a larger number of laser pulses and a lower laser fluence. In addition, we observe the formation of micro/nanogratings when the laser focus is scanned across a pure aluminum surface in air. We obtain micro- and nano-grating composite structures on a pure aluminum surface by adjusting the laser fluence and scan velocity. Femtosecond laser surface ablation of bulk pure aluminum in air is potentially a promising technique for efficient fabrication of surface nanostructures.     

Activation of color centers in bismuth glass by femtosecond laser radiation

The activation of color centers in the bismuth aluminum-boron-phosphate glass by high-intensity femtosecond laser radiation is experimentally studied. The dynamics of the laser-induced emitting centers in the bulk of sample is characterized. The photoactivation of bismuth glasses is possibly related to the recharging of structural precursors, which serve as effective electron traps and whose possible configuration is discusses. The effect of the femtosecond irradiation involves the initiation of the nonlinear ionization of the glass matrix and the generation of plasma with the concentration of carriers that is sufficiently high to provide almost complete recharging of precursors over several laser pulses.     

Optical three-dimensional shape analysis of metallic nanoparticles after laser-induced deformation

The 3D shape of Ag nanoparticles in glass irradiated by fs laser pulses is investigated by optical spectroscopy. It is shown that in general spheroids are produced with their symmetry axis oriented along the direction of the linear laser polarization. Depending on the actual irradiation conditions, oblate or prolate spheroids are obtained. The halo of small Ag clusters and Ag ions around the reshaped particles causes a redshift of the surface plasmon resonances via refractive index increase.     

Interaction of high-power laser pulses with glasses containing implanted metallic nanoparticles

Sodium calcium silicate glasses with Ag⁺ implanted ions are studied. The ion implantation conditions are as follows: the energy is 60 keV, the dose is 7×10¹⁶ cm⁻², and the ion current density is 10 μA/cm². Ion implantation provides the formation of a composite layer that incorporates silver nanoparticles in the surface region of glass. The size distribution of nanoparticles over the depth in the composite layer is strongly nonuniform. The effect of a high-power pulsed excimer laser on the composite layer is investigated. It is found that, under laser irradiation, the size of silver nanoparticles in the implanted layer decreases but the size distribution of nanoparticles over the depth remains nonuniform, even though it becomes slightly narrower compared to that observed prior to irradiation. The experimental results are interpreted in terms of the effects of the melting of glass and metallic particles on a nanosecond scale. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 11, 2001, pp. 2100–2106. Original Russian Text Copyright ? 2001 by Stepanov, Popok, Hole, Bukharaev.     

Nonlinear properties of composites based on dielectric layers containing copper and silver nanoparticles

Nonlinear optical characteristics of copper and silver nanoparticles in glass host matrices are studied by the Z-scan method at the wavelength of a Nd:YAG laser (λ=1064 nm) in a field of picosecond pulses. It is found that the third-order nonlinear susceptibility is more pronounced in glasses with copper nanoparticles than in glasses with silver nanoparticles. On the basis of experimental data obtained for samples with copper nanoparticles synthesized by ion implantation, it is shown for the first time that the nonlinear absorption of laser radiation with a wavelength lying out of the plasmon resonance region can be caused by a two-photon effect in metal particles. The character of the optical limiting process in the samples with copper nanoparticles when two-photon absorption is involved is discussed.     

Deposition of nanoparticles during laser ablation of nanoparticle-containing targets

We analyze the morphology of ablated nanoparticles after their laser-induced deposition on various substrates. We show that, at moderate laser intensity of the 210 ps pulses on the surface of nanoparticle-containing materials (<5×10⁹ W?cm^?2), the deposited material remains approximately the same as the initial nanoparticles. We compare these deposited nanoparticles with the debris obtained by the laser ablation of bulk material of the same origin as nanoparticles at different intensities of laser radiation. The presence of nanoparticles in laser plumes allowed for analyzing high-order nonlinear optical properties of nanoparticles. The efficient high-order harmonic generation was achieved during propagation of femtosecond pulses through such plasmas.     

A novel femtosecond-laser formation of CdS nanocrystallites in zirconia matrices

A novel method for direct laser writing of two-dimensional cadmium sulfide (CdS) semiconductor nanoparticle microstructures is reported. A two photon or a higher-order multiphoton absorption process, originating from femtosecond laser pulses, was used to decompose CdS precursors dispersed in a zirconia thin film previously dip-coated on a glass substrate. The kinetics of nanoparticle formation as a function of laser power were monitored in situ by photoluminescence spectroscopy. Raman spectroscopy was also performed to characterize the structural changes of the zirconia matrix under irradiation and to verify the formation of CdS nanoparticles. Results show that CdS nanoparticles were formed by two-photon absorption (TPA) with or without the help of an additional carbazole photoinitiator.     

Nanoparticles size modifications during femtosecond laser ablation of nickel in vacuum

Nanoparticles were synthesized by irradiating a nickel target with femtosecond laser pulses in high vacuum, and subsequently analyzed. The proof-of-principle experiments aim to modify the size characteristics of the produced nanoparticles. For nickel it is found that: (i) ultraviolet laser pulses lead to a remarkable change in the nanoparticles size distribution with respect to visible laser pulses; (ii) irradiation of the femtosecond pulses induced ablation plume with a second, delayed ultraviolet laser pulse can change the size characteristics of the produced nanoparticles.     

基于Fokker-Planck方程的电介质材料短脉冲激光破坏机制分析

基于Pokker-Planck方程,建立一个描述短脉冲激光作用下电介质材料中导带电子能量分布随时间变化的模型,用数值方法计算电子能量分布与电子数密度随时间的演化过程,根据临界等离子体密度准则得到了不同激光脉冲宽度和波长下电介质材料(以SiO<,2>为例)的破坏阈值.结果发现,尽管激光波长通过3种途径对材料破坏阈值的确定...     

Investigation of plumes produced by material ablation with two time-delayed femtosecond laser pulses

We experimentally investigated and herewith reported the results of laser ablation of copper and gold with two time-delayed femtosecond laser pulses at 800 nm in vacuum. The ablation plume dynamic was monitored by fast plume imaging and time- and space-resolved optical emission spectroscopy. Optical microscopy was used to follow the ablation depth as a function of the delay between the two laser pulses. Nanoparticles deposition on mica substrates was analysed by atomic force microscopy.We estimate roughly the plume's atomization degree - that is the mass fraction of atomized material over the total ablated mass - from the relative intensities of radiation emitted from atoms and nanoparticles. It is shown that the atomization degree depends critically on the time delay between both laser pulses and on the characteristic time of electron-lattice relaxation. The increase of the atomization degree is accompanied by the decrease of the ablation depth. Atomic force microscopy measurements confirm the partial atomization of nanoparticles, as the analyses of particle deposition on mica substrates show a large decrease of the number of nanoparticles for large delay between the two pulses.     

Coloration of a metal surface under pulsed laser irradiation

The regimes of irradiation using nanosecond laser pulses for creation of color images on stainless-steel and titanium surfaces upon laser engraving are studied. Parameters of radiation that correspond to the spectrum of resulting colors on the sample surface are experimentally determined. The spectral analysis of the irradiated area is performed and probe microscopy is used to study the surface relief. Complicated surface relief that results from irradiation indicates the contribution of several optical effects responsible for the surface color under laser engraving.     

Formation of Si structure in glass with a femtosecond laser

Mixing metallic Al into the starting material for silicate glass is proposed as a means of forming Si structures in glass. We confirmed that Si nanocrystals are space-selectively deposited in silicate glass via a thermite reaction triggered by femtosecond laser pulses. Small Si particles were transformed into larger, but still micrometer sized, Si particles by laser irradiation. These structures grew to micro-size particles due to the thermite reaction promoted by heat treatment. We discuss what effect the irradiation of the focused laser pulse had on the Si deposition process in the laser-irradiated region. Localized high temperatures and pressures and generation of shock waves appear to be very important in forming Si-rich structures that contribute to the growth of Si particles. The diffusion of calcium ions by the generation of shock waves and the presence of Al-rich structures is important for forming Si-rich structures such as Si clusters, which is achieved by continuously breaking Si–O bonds using localized high temperatures.     

Space-selective co-precipitation of silver and gold nanoparticles in femtosecond laser pulses irradiated Ag, Au co-doped silicate glass

We report on space-selective co-precipitation of silver and gold nanoparticles in Ag⁺, Au³⁺ co-doped silicate glasses by irradiation of femtosecond laser pulses and subsequent annealing at high temperatures. The color of the irradiated area in the glass sample changed from yellow to red with the increase of the annealing temperature. The effects of average laser power and annealing temperature on precipitation of the nanoparticles were investigated. A reasonable mechanism was proposed to explain the observed phenomena.     

Local phase-structure modification inside of lithium silicate glass by combined double-wavelength laser action

The process of local structure modification inside of lithium silicate glass under the combined laser action of two different wavelengths is considered. The first step is laser irradiation of ultrashort laser pulses with 532 nm wavelength, which is used to create of nucleation centers inside of the optically transparent glass. The crystallization of the structural modification areas was carried out by a photothermal action of CO₂ laser radiation with a 10.6 μm wavelength. The range of crystallization temperatures was defined and the kinetics of the phase transformations of the modified regions inside of the glass were studied. Duration of crystallization was about 10 min with a slow heating and 25 s at the fast heating to crystallization temperature.