Laser Ablation of Metals by Low-Density Picosecond Pulses

Thresholds of laser ablation ofmetals for the picosecond range of laser pulse duration are determined. Within the two-temperature metal model, the space-time dependences of the electron and lattice temperature are obtained. It is shown that ablation parameters become dependent on the pulse duration at the pulse duration τ _p ≥ τ _ie , where τ _ie is the cooling time of the electron gas. For noble metals, such pulse durations are τ _p ≈ 3 ? 10 ps.     

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。     

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.     

Super-Resolution with a Photochromic Mask Layer in an Optical Memory

The possibility of a super-resolution optical memory using a photochromic mask layer was theoretically discussed. An equation which estimates the transmittance change of the mask layer was derived. The numerical simulation based on the equation showed that the reflectance increase of the layer by photo-irradiation is nonlinear when the optical density of the layer is high. The nonlinear response decreased the crosstalk in adjacent recording tracks and improved the MTF (modulation transfer function) characteristics, resulting in a higher recording density.     

单模光纤中线偏振皮秒脉冲光的光致多脉冲现象的新解释

结合单模光纤的本征线性双折射与非线性双折射效应，利用二偏振分量的耦合方程对单模光纤中线偏振皮秒脉冲光的光致多脉冲现象作出了解释，得到的计算结果与实验符合得很好。     

激光导致水击穿和等离子体形成过程的物理分析

对短脉冲激光作用水介质中引起光学击穿的机制进行了分析,通过自由电子密度速率方程的数值解确定激光的击穿阈值.将数值计算结果与波长在可见光和近红外波段,脉宽为ns、ps和fs的激光脉冲在纯净水和含有杂质的水中的实验测量的击穿阈值作了比较.还计算了等离子体中自由电子密度的演化、等离子体吸收系数和能量密度.通过解自由电子密度速率方程得到结果与实验测量的值符合得很好.     

皮秒脉冲在色散缓变光纤中的孤子效应压缩

本文给出了描述皮秒脉冲在色散缓变单模光纤中孤子效应压缩过程的数学模型。通过数值求解，首次对该孤子效应压缩进行了全面的计算和分析。结果表明，与常规光纤相比，采用色散缓变程度合适的光纤压缩皮秒脉冲，不仅能显著地提高压缩后脉冲的峰值功率和脉冲压缩比，而且能有效地消除压缩后脉冲的次峰和脉座。对于确定的脉冲输入，发现，当光纤的色散缓变程度取某一最佳值时，能获得最佳的压缩效果。进一步研究表明，色散的这一最佳变     

Spot Shape on Super-Resolution Optical Disks with a Photon-Mode Mask Layer

The spot shape on super-resolution optical disks with a photon-mode mask layer was theoretically analyzed. The spot shape was found to depend on the lifetime of the bleached state of the dyes, the light power, and the disk rotation speed. When the lifetime is short, the super-resolution spot shape is not produced at high disk speeds. On the other hand, a dye mask layer with long lifetime, such as a photochromic mask, can produce a sharp spot shape in the higher disk speed region, and therefore is suitable for obtaining a super-resolution disk with a high data transfer rate.     

Spectrally Adjustable Picosecond Dye Laser Pulses Generated with Nanosecond Nitrogen Lasers

ＳｐｅｃｔｒａｌｌｙＡｄｊｕｓｔａｂｌｅＰｉｃｏｓｅｃｏｎｄＤｙｅＬａｓｅｒＰｕｌｓｅｓＧｅｎｅｒａｔｅｄｗｉｔｈＮａｎｏｓｅｃｏｎｄＮｉｔｒｏｇｅｎＬａｓｅｒｓＮｇｕｙｅｎＤａｉＨｕｎｇ；ＰｈａｍＬｏｎｇ；ＤｉｎｈＶａｎＴｒｕｎｇ；ＮｇｕｙｅｎＶａ...     

Direct Generation of Tunable UV Picosecond Laser Pulses Using Spectrotemporal Selection

ＤｉｒｅｃｔＧｅｎｅｒａｔｉｏｎｏｆＴｕｎａｂｌｅＵＶＰｉｃｏｓｅｃｏｎｄＬａｓｅｒＰｕｌｓｅｓＵｓｉｎｇＳｐｅｃｔｒｏｔｅｍｐｏｒａｌＳｅｌｅｃｔｉｏｎＮｇｕｙｅｎＤａｉＨｕｎｇ１）ＹｕｓａｂｕｒｏＳｅｇａｗａ（ＰｈｏｔｏｄｙｎａｍｉｃＲｅｓｅａ...     

Laser Mode-Dependent Size of Plasma Zones Induced by Femtosecond Laser Pulses in Fused Silica

We carry out the numerical simulations of femtosecond laser propagation with TEMoo mode, TEM10 mode and a beam combining both the modes in fused silica. It is found that the transverse size of plasma zones induced by laser pulses with the TEM10 mode is smaller than that induced by the TEM00 mode, while the longitudinal size is almost the same, and the saturated plasma density is higher. The transverse size, the longitudinal size and the ratio of the longitudinal to transverse size, for the beam combining both the modes, all could be reduced at the same time in comparison with the TEM00 mode under the same focusing conditions.     

Super-Resolution Recording by an Organic Photochromic Mask Layer

By using the super-resolution near-field structure （super-RENS） method, the super-resolution recording marks are obtained practically by an organic photochromic diarylethene mask layer, under much lower recording laser power of 0.45roW. The size of recording marks is decreased by 60% （from 1.6μm to 0.7μm） for a diarylethene （photo-mode） recording layer by the optical detection method （limited by optical diffraction）, or decreased by 97% （from 160Onto to 5Onto） for a heptaoxyl copper phthalocyanine （thermo-optical） recording layer, the latter is much smaller than the limitation of optical diffraction. In order to obtain a desirable result, a proper extent of photochemistry reaction in the mask layer is needed. Thus, the super-resolution recording marks can be obtained by adjusting the concentration of diarylethene in the mask layer, the recording laser power, and the moving speed of the sample disc.     

Broadband Optical Active Waveguides Written by Femtosecond Laser Pulses in Lithium Fluoride

Broadband waveguiding through light-emitting strips directly written in a blank lithium fluoride crystal with a femtosecond laser is reported. Light guiding was observed at several optical wavelengths, from blue, 458 nm, to near-infrared, at 155nm. Visible photoluminescence spectra of the optically active F2 and F33 color centers produced by the fs laser writing process were measured. The wavelength-dependent refractive index increase was estimated to be in the order of 10-3-10-4 in the visible and near-infrared spectral intervals, which is consistent with the stable formation of point defects in LiF.     

Wavelength Switching of a Fabry-Perot Semiconductor Laser by Optical Input Pulses

Wavelength switchings of a Fabry-Perot semiconductor laser are experimentally demonstrated by applying externally optical input pulses detuned from a cavity-resonant wavelength of the semiconductor laser with a constant injection current. The wavelength region of optical switching ranges from less than 0.1 nm to several nm over gain spectrum, being locked to the wavelength of optical inputs. These behaviors are based on multistability and multi-split branches in the optical output versus detuned optical input characteristics, caused by the carrier-induced refractive index change accompanied by optical injections. The experimental results are believed to be useful for wavelength division multiplexing and exchange in optical communication.     

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.     

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.     

Theoretical Analysis of Super-Resolution Optical Disk Mastering Using a Photoreactive Dye Mask Layer

The super-resolution mastering of read-only optical disks using a photoreactive bleachable dye mask layer was theoretically analyzed. Equations have been derived which describe the photoreactions of the resist layer and mask layer. A numerical simulation based on these equations showed that the transmittance of the mask directly affects the quality of the formed pit shape. A high-quality pit shape is obtained by using a low transmittance mask.     

Estimation of the Refractive Index Change in Glass Induced by Femtosecond Laser Pulses

It is known that local refractive index change occurs when femtosecond laser pulses with extremely high peak power are launched into glass. We focused 130-femtosecond laser pulses of 800 nm into the bulk of glass and examined the shape of the induced refractive index change. We found that the length of the spot of the refractive index change along the optical axis reached about 30 μm despite the diameter being about 2 μm. To estimate the distribution of induced refractive index change, we fabricated Bragg grating by scanning the focused spot and calculated the amount of the change by applying Kogelnik’s coupled mode theory to the measured diffraction efficiencies of the higher order diffracted beams.     

调Q双红外脉冲激光皮下消脂初探

人体过多的脂肪严重影响形体美和健康。为了提高消脂效率可选择高吸收系数的激光,但其不易穿透表皮和真皮到达脂肪表面进行消脂。基于消融性微小光热解效应和选择性光热解效应的基本原理,采用聚焦、调Q的2.75 mm波长中红外脉冲激光消融皮肤表皮和真皮,形成微小的通道,便于后续聚焦、调Q的2.3 mm波长红外脉冲激光能量无损地穿过通道选择性光热解脂肪组织,光热解产物通过新陈代谢排出体外,微小消融区在周围正常组织作用下快速愈合,实现消脂治疗安全性和有效性的和谐统一。该研究可为皮肤科手术治疗提供一种新方法。