Polarization resolved laser induced breakdown spectroscopy by single shot nanosecond pulsed Nd:YAG laser

Single shot nanosecond polarization resolved laser induced breakdown spectroscopy is introduced to spectrally analyse solid sample, e.g. copper. It is shown that continuum background emission of plasma generated by such laser pulse is much strongly polarized than discrete line radiation. By using the PRLIBS technique, continuum background emission is effectively suppressed. Furthermore, it is illustrated that polarization state of continuum emission in copper sample is mostly in vertical direction and, also, does not depend on laser beam polarization.     

Polarization switching in a quasi-isotropic microchip Nd:YAG laser induced by optical feedback

This paper demonstrates the influence of external optical feedback on the polarization state of longitudinal modes in quasi-isotropic microchip Nd:YAG lasers. Under optical feedback, the polarization state of longitudinal modes in quasi-isotropic lasers relies strongly on the intracavity anisotropy loss and mode competition. When the intracavity anisotropy loss is small, external optical feedback can cause polarization switching and strong mode competition between two orthogonal linearly polarized eigenstates of one laser longitudinal mode, which leads to the distortion of laser intensity modulation waveform. The polarization switching is independent of the initial external cavity length. By increasing the intracavity anisotropy loss, one polarization eigenstate can be suppressed and the laser works in single-polarization state. A theoretical analysis based on the compound cavity model is presented, which is in good agreement with the experimental results. The results offer guidance to the development of laser feedback interferometers.     

Time dependence of the optical emission of laser induced breakdown in gases

A detailed study of the decay of the emission intensity of the laser spark in air, Ar, Xe, Cl₂, Br₂, I₂, ICl, NO₂ and NO reveals an exponential component with one or two time constants and a non-exponential long-time component extending to 100 μsec. The emission volume at the beginning of the spark is shown to be considerably greater than the plasma core.     

Spectral and energy characteristics of acoustic emission in the laser radiation breakdown of water

Results from experimental investigations of acoustic emission from the optical breakdown zone in liquid formed by laser radiation at a wavelength of 532 nm are presented. The linear dependence of the acoustic pressure on the laser pulse energy is revealed. It is shown that the effect of an additional source of sound at a frequency of 37 kHz enhances the acoustic emission from the optical breakdown zone.     

Generation of terahertz radiation by the optical breakdown induced by a bichromatic laser pulse

Experimental results are presented on generation of terahertz radiation by the air breakdown induced by a high-intensity laser pulse having not only a fundamental component, but also a second-harmonic one. A theoretical explanation of the experimental data is proposed, based on a model of field ionization of a gas by a bichromatic laser.     

Frequency conversion of Nd:YAG laser radiation in RDA

Frequency doubling and tripling of a Nd:YAG laser has been studied in a rubidium dihydrogen arsenate (RDA) crystal. An overall power conversion efficiency of 34% and 12% has been obtained for doubling and tripling, respectively. Some comparison with rubidium dihydrogen phosphate (RDP) crystal is reported for the generation of the third-harmonic radiation at 3547 Å.     

Laser-induced breakdown of soda-lime glass microspheres using Nd:YAG laser

The Nd:YAG laser-induced breakdown of 20 μm glass microspheres was investigated using time-resolved optical shadow and Schlieren images. Time-resolved imaging showed the location of the initial breakdown and the shockwave motion over its first 400 μm of expansion. Measured shockwave velocities were in the range of 1–10 km/s and showed a linear dependency on laser fluence within 30 ns.     

用腔倒空Nd：YAG激光器对fs超短脉冲的同步放大

实现了用腔倒空Nd:YGA激光器对fs超短脉冲放大器的同步泵浦。由碰撞锁模环形染料激光器产生的80fs脉冲经二级染料放大后,实现放大倍数6.2×10~4,输出超短脉冲峰值功率～2×10~7W。     

Nd:YAG纳秒激光诱导硅表面微结构的演化

利用Nd:YAG纳秒激光(波长为532和355 nm)对单晶硅在真空中进行了累积脉冲辐照,研究了表面微结构的演化情况.在激光辐照的初始阶段,532和355 nm激光脉冲均在硅表面诱导出了波纹结构,后者辐照硅表面后形成了近似同心但稍显混乱的环形波纹结构.随着脉冲数的增加,波纹结构逐渐演化为一种类似珠形的凹凸结构,最后形成准规则排列的微米量级锥形结构,该微结构的生长依赖于表面张力波和结构自组织.分析发现,形成的交叉环形结构主要是在355 nm激光辐照硅的过程中,表面张力波导致波纹结构部分叠加的结果.     

Approximate model for laser trepanning with microsecond Nd:YAG laser radiation

Trepanning of 200 m cooling holes in 2–4 mm thick CMSX-4 turbine material is done by a lamp-pumped Nd:YAG slab laser with pulse durations of 100–500 s and pulse energies up to 1 J determining the material removal mainly by melt expulsion. The high removal velocities achieved enable us to describe the motion of the melt front – the phase boundary of solid/liquid material – approximately. Compared to the complete solution including heat conduction and phase transition (Stefan problem) the approximate model is asymptotically accurate and its errors are controllable. The simulation is compared with experimental results of cross sections of trepanning kerfs, assuming that the melt is removed instantaneously by being expelled by a coaxial gas stream during trepanning. The assumption of temperature-independent material parameters is discussed. First results with an assumed Gaussian beam profile (M²=2) are compared with a refined simulation considering the measured spatial beam profile. PACS 42.60.Jf; 42.62.Cf; 44.05.+e; 46.15.Cc     

Mode hopping in single-mode microchip Nd：YAG lasers induced by optical feedback

The mode hopping phenomenon induced by optical feedback in single-mode microchip Nd：YAG lasers is presented. With optical feedback, mode hopping strongly depends on two factors： the ratio of external cavity length to intra-cavity length, and initial gains of the two hopping modes, When external cavity length equals an integral multiple of intracavity length, there is almost no mode hopping. However, if the external cavity length does not equal an integral multiple of intra-cavity length, mode hopping occurs. The ratio of external cavity length to intra-cavity length determines the position of two-mode hopping, The initial gains of the two hopping modes determine the corresponding peak values and oscillating periods of them in the intensity modulation curves.     

Nd：YAG激光治疗机计算机光反馈控制技术

本文讨论了Ｎｄ；ＹＡＧ激光治疗机的计算机光反馈技术以及可控要素的确定。提高了激光输出的稳定性。预置功率误差３％，激光输出功率不稳定度±２％。     

Mixing of XeCl laser and mode-Locked Nd:YAG laser radiation in KDP crystal

This paper reports the first direct application of an excimer laser in phase matched mixing experiments. The sum and difference frequency of the radiation of a XeCl excimer laser and a mode-locked Nd:YAG laser were generated in KDP crystals. The energy of the obtained single subnanosecond pulses at 239 nm and 434 nm were almost 50% and 25%, respectively of the excimer laser energy taking part in the nonlinear interaction.     

Intracavity optical parametric oscillator pumped by an actively Q-switched Nd:YAG laser

A non-critically phase-matched KTiOPO₄ optical parametric oscillator (OPO) intracavity pumped by a laser diode end-pumped acousto-optically Q-switchedNd:YAG laser is experimentally demonstrated. The highest average power is obtained at the pulse repetition rate (PRR) of around 15 kHz, which is different from the widely reported Nd:YVO₄ laser pumped OPO in which the highest average power is obtained at a very high PRR, e.g. 80 kHz. With an incident laser diode power of 6.93 W and a pulse repetition rate of 15 kHz, an average signal power of 0.72 W is obtained with a peak power of 7.7 kW and an optical-to-optical conversion efficiency of 10.4%. PACS 42.65.Yj; 42.60.Gd; 42.55.Xi     

Analysis of laser drilled deep holes in stainless steel by superposed pulsed Nd:YAG laser radiation

Deep drilling of through holes in stainless steel (1.4301, sample thicknesses 5, 8 and 10 mm) has been performed with the superposed radiation of two pulsed Nd:YAG lasers with pulse duration of 0.5 ms superposed by 17 ns pulses. The drilling efficiency is improved by the spatially and temporally superposed radiation of the two lasers. The enhanced drilling speed and the larger reproducibility of the drilling time are explained by a modified formation of closures in the hole during percussion drilling which are recorded by high-speed photography. The metallographic hole analysis exhibits high-temperature oxidation marks. The development of these marks is described by a ray tracing of the incident beam within the hole and the resulting intensity distribution at the hole wall.     

Thermal unbalance by an amplified spontaneous emission absorber in an Nd:YAG thin-disk laser

We investigate heat generation in a Nd:YAG thin-disk laser composite with an undoped anti-amplified spontaneous emission (ASE) cap and a side ASE absorber under lasing and nonlasing conditions. The heat load unbalance in three different regions induces a large transverse temperature inhomogeneity under the nonlasing condition. The additional heat fraction generated by the concentration quenching is observed.     

Autocorrelation coefficient of the radiation output of a frequency-doubled Nd:YAG laser

The autocorrelation coefficient of a frequency-doubled Nd:YAG laser output has been extracted for various operating conditions from the pulse form measured by a streak camera and from the enhancement of the nonresonant CARS intensity for correlated as against uncorrelated pump beams. The measured values are compared with values in the normalized Gaussian model.     

Generation and characterization of Nd-Fe-B-C nanoparticles by pulsed Nd:YAG laser ablation in liquid

We have generated Nd-Fe-B-C nanoparticles by Nd:YAG (1064 nm) laser irradiation in distilled water. Exposure times were 1, 5, and 10 min. Characterization of such nanoparticles in terms of their size distribution, shape, and chemical composition was carried out by transmission electron microscopy, energy-dispersive X-rays, and Fourier transform infrared spectroscopy. To investigate the nanoparticle stability, the size distribution of nanoparticles was measured two weeks after the nanoparticle generation, using dynamic light scattering. Investigations with the help of the atomic force microscope and magnetic force microscope showed other aspects of the generated nanoparticles.