A second-order autocorrelator for single-shot measurement of femtosecond laser pulse durations

A second-order autocorrelator for single-shot measurement of ultrashort laser pulse durations has been set up. It is based on recording the spatial profile of non-collinear phase-matched second harmonic generation in a KDP crystal using a CCD camera-framegrabber combination. Performance of the system is described from measurement of 250 femtosecond transform-limited laser pulses from a passively mode-locked, diode pumped Nd:glass laser. It can also be used for measurement of picosecond laser pulses in the multi-shot scanning mode.     

激光熔融键合在新型室温红外探测器的应用

运用Nd：YAG激光在功率300W、光束运动速度为0．05m／s、光束直径为700μm的条件下能得到键合强度平均为9．3MPa的硅／玻璃熔融键合效果。该键合方法能进行选择区域键合,完全避免了由于键合过程中电场给超薄敏感可动微结构带来的畸变甚至失效,为新型室温红外探测器的研制奠定了良好的工艺基础。     

Electrical diagnostics of laser ablated platinum plasma

The most significant parameters of laser-induced plasma are investigated here experimentally. Pure platinum targets of 4 N were irradiated both in air and under vacuum (∼10⁻³ Torr) by Q-switched Nd: YAG laser (1064 nm, 10 mJ, 9-14 ns, 1.1 MW). A self fabricated Langmuir probe was used as an electric diagnostic tool. Varying voltages were applied to the probe and the corresponding values of currents were recorded to draw current-voltage (I-V) characteristics curves. The electronic signals were recorded on 500 MHz DL1740, YOKOGAWA four channels digital storage oscilloscope. Different plasma characteristics like electron temperature, electron density, Debye's length, plasma frequency and numbers of particles in the “Debye's Sphere” were calculated both in air and under vacuum.     

Characterization of plasma propulsion by Nd:YAG laser

Significant propulsion parameters, specific impulse and coupling coefficient for the different metallic pendulums are presented. 4 N (99.99%) pure, solid targets are in the form of foils of aluminium, copper and gold. The targets are irradiated by Q-switched pulsed Nd:YAG laser (1064 nm, 10 mJ, 1.1 MW, 9-14 ns) under standard conditions of temperature and pressure. Plasma plume of these targets is also observed by employing CCD (BOSCH LTC0510, monochrome camera) based, computer controlled image capturing system and it was seen that expansion of plasma plume for oscillating targets is anisotropic in air. The results reveal that not only very high exhaust velocity of propellant 10⁶ m/s is achieved but also very specific impulse values of Al, Cu and Au targets (3.14 × 10⁶ s, 1.37 × 10⁷ s, 7.16 × 10⁵ s respectively) are obtained. Coupling coefficients are for Al, Cu and Au were 1.54 × 10³ (N-s/J), 1.88 × 10³ (N-s/J), and 1.08 × 10³ (N-s/J) respectively.     

钕玻璃脉冲激光材料表面改性处理及其应用

本文论述了激光材料表面改性处理的发展概况及钕玻璃脉冲激光用于材料表面改性处理的特点。给出了MG-1型钕玻璃脉冲激光热处理的性能及其应用结果。     

Measurement of the characteristics of a point source of x-rays using a picosecond laser plasma

The emissive properties of silicon and aluminum plasmas, produced by 40 psec laser pulses with a peak intensity of greater than 10¹⁴ W/cm², are investigated. The x-ray line spectra of H- and He-like ions, measured with high resolution, are analyzed to determine the plasma parameters. The form of the resonance lines and their intensity with respect to the corresponding dielectronic satellites and the intercombination line are compared with model calculations.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 50–55, January, 2005.     

长脉冲Nd:YAG激光器驱动电源与控制技术

改进了适合于长脉冲激光器泵浦氪灯的驱动电源和控制技术,特别是在脉冲式预燃方式、放电脉冲时间的精确控制以及大幅度减小电源发热量(近一个数量级)等方面.完成的装置具有工作稳定、可靠、效率高、智能操作、控制方便等优点,可广泛应用于YAG型激光医疗设备和工业加工设备.     

High speed plasma diagnostics for laser plasma interaction and fusion studies

Laser plasma interaction and fusion studies involve many high speed plasma diagnostics to determine the various parameters for explaining the physical processes taking place in plasma. Detection and analysis of short-term or transient radiations (X-ray and visible) are the bases for diagnosing the physical processes occurring during laser-plasma interaction or similar radiation-emitting processes. This paper reviews the development of various high speed plasma diagnostics which are not only applicable in determining the temporal, spatial and spectral properties of X-rays for this purpose but also have wide use in various other fields of research.     

MF2(M=Mg,Ca,Zn,Sr,Ba)对掺Yb3+磷酸盐玻璃性质的影响

熔制了60P2O5.6Al2O3@(33-x)BaO.xBaF2.1Yb2O3(x=0,3,6,9)和60P2O5.6Al2O3.27BaO@6MF2.1Yb2O3(M=Mg、Ca、Sr、Zn、Ba)(分子分数)玻璃,测试了其折射率、密度、转变温度、析晶温度、熔点温度、红外光谱和紫外吸收光谱,讨论了二价氟化物MF2(M=Mg、Ca、Sr、Zn、Ba)对磷酸盐玻璃热稳定性及内部结构的影响,测试了Yb3+离子的吸收光谱、荧光光谱、荧光寿命,计算了光谱参数,讨论了MF2对Yb3+磷酸盐玻璃光谱性质的影响.结果表明二价金属氟化物是作为网络外体进入到磷酸盐玻璃结构中,并没有改变磷酸盐玻璃内部的[PO4]链状结构,二价金属氟化物还有助于提高Yb3+离子的受激发射截面,和自发辐射几率,荧光半高宽.     

MF2(M=Mg,Ca,Zn,Sr,Ba)对掺Yb3+磷酸盐玻璃性质的影响

熔制了60P₂O₅·6Al₂O₃·(33-x)BaO·xBaF₂·1Yb₂O₃(x=0,3,6,9)和60P₂O₅·6Al₂O₃·27BaO·6MF₂·1Yb₂O₃(M=Mg、Ca、Sr、Zn、Ba)(分子分数)玻璃,测试了其折射率、密度、转变温度、析晶温度、熔点温度、红外光谱和紫外吸收光谱,讨论了二价氟化物MF₂(M=Mg、Ca、Sr、Zn、Ba)对磷酸盐玻璃热稳定性及内部结构的影响,测试了Yb³⁺离子的吸收光谱、荧光光谱、荧光寿命,计算了光谱参数,讨论了MF₂对Yb³⁺磷酸盐玻璃光谱性质的影响,结果表明二价金属氟化物是作为网络外体进入到磷酸盐玻璃结构中,并没有改变磷酸盐玻璃内部的[PO₄]链状结构,二价金属氟化物还有助于提高Yb³⁺离子的受激发射截面,和自发辐射几率,荧光半高宽。     

Effect of laser welding parameters on fusion zone morphological,mechanical and microstructural characteristics of AISI 304 stainless steel

Nowadays, the Nd:YAG laser has been a promising key tool for joining thin components. In this research, mechanical and microstructural properties of laser welded thin austenitic stainless steel sheets were investigated with experimental investigations, as a function of laser welding parameters. Butt welded joints were made using a Nd:YAG laser in the pulsed wave mode. The appropriate laser welding parameters were found in order to obtain quality and strong weld seam. The pulsed laser seam welding process is controlled by a variety of parameters. We focus on the effects of the several processing parameters on mechanical and microstructural characteristics of joint and weld quality. The aim of this research was to evaluate the influence of these processing parameters on joint strength and microstructure. And also we examined the weldability of stainless steels in butt joint configuration by a pulsed Nd:YAG laser beam.     

新型激光防护材料的研究

随着激光技术广泛应用，激光所造成的意外伤害也不断的增加，传统的激光防护器材由于只能防护特定波长的激光以及具有可见光透过率低等特点，已经满足了不了现代激光的防护要求。研制了具有多波长防护和可见光透过度高的新型激光防护功能材料。测试结果表明，玻璃在0.53μm处T0.53μm为0．015，在1.06μm处，T1.06μm为0．055，白光透过率大于60％。     

Development of iridium TES by pulsed laser deposition with a Nd:YAG laser

The use of cryogenics micro calorimeters with Transition Edge Sensors for high-resolution spectroscopy for space applications puts several constraints on the detector's performances. Among several requirements, the long term stability of TES from a chemical and physical point of view is one of the most important. Iridium is a very interesting material for TES fabrication due to its excellent chemical stability and low transition temperature. Starting from the promising results we had with a cryogenic microcalorimeter with TES made of an Ir single crystal, we are developing a procedure to produce patterned Ir thin films by means of the Pulsed Laser Deposition (PLD). PLD with an infrared laser, in UHV, allows very clean evaporation process, good efficiency (about 4 nm/shot) and low dissipated power in the vacuum chamber (about 1 W). We have applied a lift-off mask technique that allows to heat the substrate during the deposition, which improves the adhesion and the thermal conductivity and circumvents the needs of very aggressive etchant solutions.     

Sensitivity enhancement of laser absorption spectroscopy for atomic oxygen measurement in microwave air plasma

A high sensitive laser absorption spectroscopy system has been developed for the detection of atomic oxygen in a microwave plasma. Firstly, the sensitivity of this system was evaluated by ring-down time measurement. The effective absorbing pass length was extended up to 640 times as long as that of the conventional laser absorption spectroscopy. Then, the system was applied to the air plasma diagnostics. As a result, the absorption signal from the meta-stable atomic oxygen at 777.19 nm could be observed at the input enthalpy range from 0.93 MJ/kg to 467 MJ/kg. The detected minimum number density was 1.6 × 10¹¹ m⁻³ with temperature of 388 K, which correspond to the center fractional absorption of 1.4 × 10⁻²% in the LAS.     

Morphological and structural analysis of nano-structured gold thin film on silicon by pulsed laser deposition technique

Structural and morphological investigations on optimized nano-structured gold thin film (under vacuum ∼10⁻³ Torr) are reported. The Au optimized thin film was deposited on 4 N polished and analytic grade p-type single crystal (111) Silicon wafer by pulsed laser deposition (PLD) technique, under a vacuum of about 10⁻³ Torr at room temperature. The space resolved dynamics of the plume is studied by analyzing CCD images of plume. Average size of deposited nanoparticles is along the preferred (111) orientation is ∼ 20 nm using PLD technique. The deposited film is non-uniform with particle size within the range of 6.19 nm-19.62 nm. There is decrease in the value of dislocation line density. XRD and SEM investigations support each other.     

Angular distribution of ions produced by laser ablation of magnesium with special reference to sublimation energy

A 99.99% pure Mg target was irradiated with 100 shots of a Q-switched pulsed Nd:YAG laser (1.064 μm, 9 ns, 1.1 MW) in a vacuum ∼10⁻³ mbar to generate ions from laser-produced plasma (LPP). CR-39 detectors were positioned at 0°, 30°, 60° and 90° with respect to the normal of the target surface. The LPP Mg ions made tracks on the detectors, which were then etched in 6 N NaOH solution for 8 h at 70 ± 1 °C. The etched detectors were then analyzed using computer controlled Motic DMB series optical microscope. It is found that the Mg ions with maximum energy and maximum flux were obtained at an angle 0° with respect to the normal of the target surface, whereas both energy and flux of the ions decrease with the increase in angle. The angular distribution of Mg ions is encompassed by a cosine power-law in which the exponent n of the cosⁿ θ distribution is found to be 0.24. This together with the wealth of data (n = 3-24) obtained by Konomi et al. (2009) for 11 different metals has been shown to follow a linear relationship between the exponent n and the sublimation energy of target metals.     

Measurement of laser-produced plasma impulses on molten metals for thermophysical property determination

A high-power pulsed laser excitation of a material surface generates a well-separated sequence of plasma, fluid flow, and acoustic events. When the movement of the surface due to evaporation by laser heating is kept in pace with the thermal diffusion front, the ablative mass loss from a solid surface becomes strongly correlated with the thermal diffusivity of the target matter. The other thermophysiocal properties which figure in this correlation are the mass density, heat of formation, and molecular weight. The functional relationship, which is given in this text for the first time, can be exploited to measure the thertnophysical properties. We have now extended such an approach to measurement of the thermal diffusivity of molten specimens by developing a new instrumentation for determining the ablative mass loss due to a single laser pulse. This has been accomplished by combining a facility for controlled generation of a molten specimen and a novel transducer for real-time measurement of the impulse imparted to the molten target by a laser-produced plasma plume, The transducer design, calibration, signal recovery, and method of extracting the mass loss per laser excitation are detailed by comparing the results for metallic specimens in the solid and molten state.Paper presented at the Twelfth Symposium on Tile rmophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Studies on fatigue life enhancement of pre-fatigued spring steel specimens using laser shock peening

SAE 9260 spring steel specimens after enduring 50% of their mean fatigue life were subjected to laser shock peening using an in-house developed 2.5 J/7 ns pulsed Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser for studying their fatigue life enhancement. In the investigated range of process parameters, laser shock peening resulted in the extension of fatigue life of these partly fatigue damaged specimens by more than 15 times. Contributing factors for the enhanced fatigue life of laser peened specimens are: about 400 μm thick compressed surface layer with magnitude of surface stress in the range of −600 to −700 MPa, about 20% increase in surface hardness and unaltered surface finish. For laser peening of ground steel surface, an adhesive-backed black polyvinyl chloride (PVC) tape has been found to be a superior sacrificial coating than conventionally used black paint. The effect of repeated laser peening treatment was studied to repair locally surface melted regions and the treatment has been found to be effective in re-establishing desired compressive stress pattern on the erstwhile tensile-stressed surface.     

Design and performance studies of an MCP based pinhole camera for laser-produced plasma diagnostics

An X-ray pinhole camera system has been developed and tested to obtain spatially resolved time-integrated X-ray images of laser-produced plasmas (Nd: YAG laser of 75mJ energy in 35 picoseconds) using a single stage micro channel plate (MCP) detector coupled to a CCD camera-frame grabber system instead of X-ray film. Thick slab targets of aluminium, copper and gold were used to produce plasmas with different X-ray yields at laser intensities ranging from 8 × 10¹¹ to 8 × 10¹² W/cm². MCP gain was increased with the help of biasing voltages to record low intensity X-ray images, which have been analysed using an image processing software “PROMISE” developed in-house. The experimental results are presented.     

Spectroscopic analysis of a novel Nd3+-activated barium borate glass for broadband laser amplification

Spectroscopic parameters of a novel Nd³⁺-activated barium borate (BBONd) glass have been analyzed for broadband laser amplification. The Judd–Ofelt (JO) intensity parameters were determined through a systematic analysis of the absorption spectrum of Nd³⁺ ions in the BBONd glass. High values of the JO intensity parameters reveal a great centro-symmetrical loss of the Nd³⁺ sites and high covalency degree of the ligand field. The very high Ω₆ intensity parameter value makes evident both a great structural distortion of the Nd³⁺ sites and a strong electron–phonon coupling between Nd³⁺ and free OH⁻ ions, which is consistent with the phonon energy maximum (3442.1 cm⁻¹) recorded by Raman spectroscopy. This strong electron–phonon coupling favors high effective bandwidth and gain bandwidth values of the laser emission (⁴F_3/2 → ⁴I_11/2) of Nd³⁺ ions. The electric-dipole oscillator strengths of all the Nd³⁺ absorption transitions, and in particular that of the hypersensitive transition (⁴I_9/2 → ⁴G_5/2), are enhanced by this great structural distortion of the host. Broadband laser amplification of the ⁴F_3/2 → ⁴I_11/2 emission (1062 nm) of Nd³⁺ ions in the BBONd glass pumped at 805 nm (⁴I_9/2 → ⁴F_5/2 + ²H_9/2) is evaluated through the main fluorescent parameters in competition with non-radiative processes. In general, the BBONd glass exhibits spectroscopic parameters comparable with those reported in the literature for broadband laser amplification into the IR region.