Chirp-free nanosecond laser amplifier for precision spectroscopy

We describe a simple method for greatly reducing optical phase perturbations in a nanosecond pulsed dye amplifier. The laser dye mix is tailored to produce a susceptibility near zero at the operating wavelength. Frequency shifts are reduced to less than 3 MHz, and frequency chirping to less than 10 MHz, without significant loss of amplified power. This technique has been used to improve the accuracy of precision far-UV wavelength measurements in H(2) to ~7 parts in 10(9).     

Time-resolved spectroscopy measurements of a titanium plasma induced by nanosecond and femtosecond lasers

We have studied the plasma induced at the surface of a titanium target following irradiation with femtosecond and nanosecond laser pulses. Time-resolved imaging and spectroscopic measurements allowed us to evidence some features specific to the femtosecond-laser-induced plasma. In this ultrashort interaction regime, we could discriminate between three different velocity populations in the plasma expansion. Coulomb explosion firstly creates highly energetic Ti⁺ ions, which are followed by atomic neutral titanium and lastly by nanoscale titanium oxide clusters. Received: 28 September 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +33-1/6931-9996, E-mail: albert@ensta.fr     

纳秒激光诱导等离子体发射光谱中的自吸收效应

为了减小激光诱导等离子体发射光谱中光谱线的自吸收效应,提高激光光谱分析技术对物质中高含量元素的检测水平,实验采用了一种平面反射镜装置约束等离子体,比较了有或无平面反射镜装置时光谱线的线型变化。实验表明,在无平面反射镜装置时,样品元素Al,Mg和Mn的光谱线半高全宽度分别为0.16,0.24,0.058nm,而采用由四块平面反射镜组成的装置在空间上约束激光等离子体时分别为0.11,0.13,0.047nm。结果表明,光谱线的自吸收明显减小,谱线线型变得比较锐且强度显著提高。通过观测等离子体照片,测量等离子体温度和电子密度,分析讨论了激光光谱自吸收效应降低的原因。     

纳秒激光诱导等离子体发射光谱中的自吸收效应

为了减小激光诱导等离子体发射光谱中光谱线的自吸收效应,提高激光光谱分析技术对物质中高含量元素的检测水平,实验采用了一种平面反射镜装置约束等离子体,比较了有或无平面反射镜装置时光谱线的线型变化。实验表明,在无平面反射镜装置时,样品元素Al,Mg和Mn的光谱线半高全宽度分别为0.16,0.24,0.058 nm,而采用由四块平面反射镜组成的装置在空间上约束激光等离子体时分别为0.11,0.13,0.047 nm。结果表明,光谱线的自吸收明显减小,谱线线型变得比较锐且强度显著提高。通过观测等离子体照片,测量等离子体温度和电子密度,分析讨论了激光光谱自吸收效应降低的原因。     

纳秒脉冲激光诱导空气等离子体的近红外辐射特性

开展纳秒激光诱导空气等离子体近红外辐射特性的实验研究,对波长为532 nm的脉冲ns激光诱导产生的空气等离子体的近红外光谱进行测量.结果表明:空气等离子体的近红外辐射在光谱范围为1100-2400 nm内由连续谱和线状谱组成,光谱指认表明线谱主要来源于N,O原子的中性原子谱和氮分子的振动光谱.通过对连续谱的分析得知,黑体辐射是连续辐射的主要来源.空气中波长1128 nm附近的辐射,可能是N和O中性原子谱的贡献.保持真空腔内气压不变,改变腔内氮气和氧气气体组分含量,分析测得的红外光谱数据,可知混合气体中氧气和氮气含量变化只对波长为1128 nm附近的辐射有影响.利用二元线性回归分析对数据进行分析后得知,氧气对波长为1128 nm附近的辐射贡献较大.最后从电离难易的角度分析造成这一结果的原因.     

Reflectivity measurements from a nanosecond CO2 laser produced plasma

The back-scattered light from a laser produced plasma has been studied using a nanosecond gigawatt CO₂ laser. The spectral shift and width of the reflected light have been determined as a function of the incident laser energy.     

X-ray emission from plasma generated by nanosecond laser irradiating tantalum

A continuum spectrum of X-rays, originating from the interaction of a moderate intensity nanosecond Nd:Yag laser (1064 nm, 9 ns, 30 Hz, 900 mJ, 10¹¹ W/cm²) with metal targets producing plasma, is investigated. The photon emission intensity is particularly high when the plasma expands in a low-pressure gas. The photon energy is measured through selective thin absorber films employed in front of the solid state detector. The temperature of the hot electrons generated from the plasma, responsible for the continuum spectrum emission, is calculated from the fit of the X-ray spectrum with a Maxwellian distribution, and it is about 1–2 keV.     

Spectroscopic studies of sodium nitrate plasma produced by nanosecond laser ablation

We present the optical emission characteristics of the sodium plasma produced at the surface of sodium nitrate (NaNO₃) also known as Chile saltpeter. We used a Q-switched Nd:YAG (Quantel Brilliant) pulsed laser having a pulse duration of 5?ns and 10?Hz repetition rate which is capable of delivering 400?mJ at 1064?nm and 200?mJ at 532?nm. The target material was placed in front of laser beam in air (atmospheric pressure). The experimentally observed line profiles of neutral sodium have been used to extract the electron temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying the distance from the target surface along the line of propagation of the plasma plume and also by varying the laser irradiance. Besides, we have studied the variation of number density as a function of laser irradiance as well as its variation with the distance from the target surface. It is observed that electron temperature and electron number density increase as the laser irradiance is increased.     

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.     

Investigation of a near-surface laser plasma by the method of intraresonator laser spectroscopy

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 6, pp. 919–927, December, 1990.     

Energy balance measurements on a nanosecond CO2 laser created plasma

Interaction of nanosecond CO₂ laser radiation with a solid deuterium target has been investigated with incident laser fluxes up to several times 10¹²W/cm². Reflection, X-ray and ion measurements were performed at different angles in the relevant half-space around the target. The energy balance deduced from reflection and ion time-of-flight measurements led to a total integrated reflectivity of 60 to 80%. Fast D⁺ ions with kinetic energies as high as 40 keV were detected and identified. Hard X-rays were observed in the range of 1 to 10 keV. A discussion of these results is presented.     

Ionization effect to plasma expansion study during nanosecond pulsed laser deposition

The dynamic characteristic and effects of plasma play an important role in film growth process of pulsed laser deposition (PLD). Based on numerical hydrodynamic modeling, supposed the laser radiation and partial ionization of the plasma as a dynamic source, we deduce a set of new plasma expansion dynamics equations. Based on which, as an example of carbon target, using finite difference method, the plasma flow dynamics evolvement in vacuum is investigated. Our results show the dynamic partial ionization increases the expansion in all directions, which changes into a new dynamic source for plasma expansion. In the axial direction, because of the collisional interactions between particles, the plume density peak is in the vicinity of the target surface and the acceleration of plasma occurs mainly near the target surface too. In the transverse direction, the plume peak is not near the target, but at the surface. The space expansion distance is far less than the axial direction because there is no high initial velocity component in this direction. The predictions of the plasma expansion action based on the proposed dynamics source assumption are found to be in agreement with the experimental observation.     

等离子体削波纳秒激光脉冲波形测量

实验上采用比对方法测试了激光不经过固体与经过固体介质产生等离子体削波的脉冲波形信号,获得等离子体削波效应产生的脉冲削波倍数。实验结果表明,在波长1.064 m,脉宽1 ns,聚焦透镜焦距100 mm,薄石英片厚度100 m,约束等离子体的小孔直径80 m情况下,等离子体效应产生的脉冲削波倍数为12~14;分别改变石英片厚度和约束等离子体小孔直径,等离子体脉冲削波倍数不变;增加入射激光能量,脉冲削波倍数增加,且经过等离子体后的激光脉冲波形的后沿逐渐出现很陡的下降沿。在产生脉冲削波的截断点位置进行图形拼接重构得到激光脉冲波形信息。     

等离子体削波纳秒激光脉冲波形测量

实验上采用比对方法测试了激光不经过固体与经过固体介质产生等离子体削波的脉冲波形信号,获得等离子体削波效应产生的脉冲削波倍数。实验结果表明,在波长1.064 m,脉宽1 ns,聚焦透镜焦距100 mm,薄石英片厚度100 m,约束等离子体的小孔直径80 m情况下,等离子体效应产生的脉冲削波倍数为12~14;分别改变石英片厚度和约束等离子体小孔直径,等离子体脉冲削波倍数不变;增加入射激光能量,脉冲削波倍数增加,且经过等离子体后的激光脉冲波形的后沿逐渐出现很陡的下降沿。在产生脉冲削波的截断点位置进行图形拼接重构得到激光脉冲波形信息。     

Development of a nanosecond oscillator–four pass amplifier XeCl laser system

This paper describes the development of a nanosecond oscillator–four pass amplifier XeCl laser system. A two times increase of the pulse peak power of the free running amplifier module has been experimentally demonstrated. The comparison with numerical results issued from a code describing the amplification of the oscillator beam in the active amplifier medium suggests further experimental improvements to optimize the energy extraction from the amplifier.     

Laser plasma propulsion generation in nanosecond pulse laser interaction with polyimide film

The plasma propulsion generated in nanosecond pulse laser interaction with polyimide film is investigated. A comparison of coupling coefficient and specific impulse with glass layer and water layer confinement is given. It shows that polyimide has a higher efficiency in water confinement ablation. Through doped carbon black in polyimide film, a higher coupling coefficient is obtained. In ablated surface images, less re-deposited products on polyimide surface have been observed compared with other polymers at the same laser intensity.     

Role of laser-induced plasma in ultradeep drilling of materials by nanosecond laser pulses

Radiative effects of the laser-induced ablative plasma on the heating and ablation dynamics of materials irradiated by nanosecond laser pulses are studied by the example of graphite ablation. On the basis of combined thermal and gas dynamic modeling, the laser-induced plasma plume is shown to be a controlling factor responsible for ultradeep laser drilling due to plasma radiation, both bremsstrahlung and recombinative. We demonstrate that plasma radiative heating of the target considerably deepens the molten layer, thus explaining the observed crater depths.