The influence of laser wavelength and fluence on palladium nanoparticles produced by pulsed laser ablation in deionized water

Homogeneous spherical palladium (Pd) nanoparticles were synthesized by pulsed laser ablation of a solid Pd foil target submerged in deionized water, without the addition of any external chemical surfactant. The influence of laser wavelength (355, 532, and 1064 nm) and fluence (8.92, 12.74, and 19.90 J/cm²) on nucleation, growth, and aggregation of Pd nanoparticles were systematically studied. Microstructural and optical properties of the obtained nanoparticles were studied by field emission transmission electron microscopy (FETEM), energy dispersive X-ray spectroscopy, and UV–vis spectroscopy. FETEM micrographs indicate that the average nanocrystallite sizes are relatively low (3–6 nm) and homogeneous for the particles synthesized at the laser wavelengths of 355 and 532 nm. However, at a laser wavelength of 1064 nm, the average nanocrystallite size is relatively large and inhomogeneous in nature. Moreover, we observe that the mean diameter and production rate of particles increases with an increase in laser fluence. The selected area electron diffraction patterns obtained from isolated Pd nanoparticles show the characteristic diffused electron diffraction rings of polycrystalline materials with a face-centered cubic structure. Absorbance spectrum of the synthesized nanoparticle solution shows a broad absorption band, which corresponds to a typical inter-band transition of a metallic system, indicating the production of pure palladium nanoparticles. The present work provides new insights into the effect of laser wavelength and fluence on the control of size and aggregation of palladium nanoparticles in the liquid medium.     

Influence of wavelength,irradiance, and the buffer gas pressure on high irradiance laser ablation and ionization source coupled with an orthogonal Time of Flight Mass Spectrometer

Influence of laser wavelength, laser irradiance and the buffer gas pressure were studied in high irradiance laser ablation and ionization source coupled with an orthogonal time-of-flight mass spectrometer. Collisional cooling effects of energetic plasma ions were proved to vary significantly with the elemental mass number. Effective dissociation of interferential polyatomic ions in the ion source, resulting from collision and from high laser irradiance, was verified. Investigation of relative sensitivity coefficients (RSC) of different elements performed on a steel standard GBW01396, which was ablated at 1064 nm, 532 nm, 355 nm, and 266 nm, has demonstrated that the thermal ablation mechanism could play a critical role with the first three wavelengths, while 266 nm induces non-thermal ablation principally. Experimental results also indicated that there is no evident discrepancy for most metal elements on RSCs and LODs among four wavelengths at high irradiance, except that high boiling point elements like Nb, Mo, and W have higher RSCs at higher irradiance regions of 1064 nm, 532 nm, and 355 nm due to thermal ablation. A geological standard and a garnet stone were also used in the experiment subsequently, and their RSCs and LODs for metal elements show nonsignificant dependence on wavelength at designated irradiances. All results reveal that relatively uniform sensitivity can be achieved at any wavelength for metal elements in the solids used in our experiments at an appropriate irradiance for the low pressure high irradiance laser ablation and ionization source.     

Laser ablation inductively coupled plasma atomic emission spectrometry of a uranium-zirconium alloy: ablation properties and analytical behavior

The ablation properties and analytical behavior of a uranium-zirconium alloy have been examined using tandem laser ablation/pneumatic nebulization sample introduction in conjunction with inductively coupled atomic emission spectrometry (LA-ICP-AES). An apparent change in composition of the laser ablation aerosol (1–15 GW cm⁻² Zr deficient, 40–250 GW cm⁻² Zr rich) is observed. This phenomenon is independent of laser wavelength. After collection and bulk chemical analysis of the ablation product, this phenomenon is attributed to an atomization interference in the ICP.

Two distinct modes of laser ablation have been observed which depend upon the wavelength of the ablating laser (visible or near infrared). These two modes result in characteristic ablation crater types and analyte emission behavior. Ablation yields at 1064 nm are dependent upon laser power density only, whilst yields at 532 nm are dependent upon both laser power density and illumination area. The latter is considered to be symptomatic of direct interaction of the laser light with the surface, and the former, of indirect coupling of laser energy, via a micro-plasma, into the surface.     

Multiphoton ionization versus dissociation of diatomic molecules irradiated by an intense 40 ps laser pulse

The production of molecular and atomic ions has been measured for CO, N₂ and O₂ with 1064 and 532 nm 40 ps pulses in the 10¹²-10¹⁴ W cm^?2 intensity range. A simultaneous ionization-dissociation process occurs at lower intensities, while a sequential process appears in oxygen at higher intensities.     

Experimental determination of laser induced breakdown thresholds of metals under nanosecond Q-switched laser operation

Laser-induced breakdown thresholds for several pure metals were determined using a nanosecond laser. A Q-switched pulsed Nd:YAG laser operating at infrared (1064 nm), visible (532 nm) and ultraviolet (266 nm) wavelengths has been used. The plasma was generated by focusing the Nd:YAG laser on the target in air at atmospheric pressure. The dispersed plasma light was detected using a two-dimensional intensified charge-coupled device (CCD) detector. The studied elements were chosen according to their different thermal and physical properties, particularly boiling point, melting point and thermal conductivity. The effect of wavelength on the plasma threshold has been discussed. Laser fluence thresholds in the ultraviolet were larger than those obtained using visible and infrared radiation, while the energy threshold is larger using infrared radiation. Correlations between the plasma threshold of metal targets and the melting point and boiling point at 266, 532 and 1064 nm have been established. The results indicate that thermal effects have an important influence on the ablation behavior of metals at the three wavelengths used.     

Multiphoton-ionization of hydrogen atoms in intense laserfields

The interaction of hydrogen atoms with strong laser fields at intensities up to some 10¹³ W cm^?2 was studied experimentally at the wavelengths λ=355 nm, 532 nm and 1064 nm. The ion yield, the energy spectrum of the photoelectrons and their angular distributions were measured. The angular distributions at λ=355 nm and λ=532 nm provide a sensitive test for theoretical calculations. Comparison with the calculations available shows that perturbation theory with proper inclusion of atomic structure yields results which agree with experiment. Intensity dependent changes of angular distributions at λ=532 nm are observed, which indicate that at 10¹³ W cm^?2 higher order processes become noticable. At λ=1064 nm the situation is more complicated, experimentally as well as theoretically. Intensities of some 10¹³ W cm^?2 are necessary to observe ionization. Strong distortions of the atomic structure can be expected. Presently only qualitative aspects of the angular distributions can be discussed.     

Wavelength dependence of polyyne preparation by liquid-phase laser ablation using pellet targets

The amount of polyynes produced by Nd:YAG laser (355, 532, and 1064 nm) ablation of fullerene and graphite pellet targets was the largest for 1064 nm ablation, contrary to the powder target in the previous report. This result is believed to come from the difference in the main polyyne-production area in liquids in the optical cell, depending on the pellet and powder targets.     

Quantification of the intensity enhancements for the double-pulse laser-induced breakdown spectroscopy in the orthogonal beam geometry

Simple- and double-pulse laser-induced breakdown spectroscopy was studied on aluminum samples at atmospheric pressure in air. The double-pulse experiments were carried out in the orthogonal beam geometry in two different ways: the reheating scheme and the pre-ablation spark dual-pulse scheme. An ablation laser emitting at 532 nm was combined with a second laser operating at 1064 nm according to the orthogonal geometry. For both schemes, the influence of the delay between the two laser pulses was investigated. In particular, different optima of interpulse delays were determined, underlying the differences of physical mechanisms involved in both processes. The estimation of the plasma temperatures provided explanations on the signal increases for both schemes. Whatever the configuration developed in the orthogonal geometry, a correlation between the increases in emission lines intensities and their excitation energy levels was established in the double-pulse approach. Besides, the effect of laser energy for both pulses was studied so as to make comparisons of the different configurations at the same total laser energy.     

Multiphoton ionization of magnesium and calcium atoms by short and intense laser pulses

Single and double ionization of magnesium and calcium atoms following Nd: YAG laser multiphoton excitation at 1064 and 532 nm have been studied by employing pulses of 35 ps and 200 ps duration at intensities of the order of 10¹⁰–2×10¹³ W/cm². The dependence of ion formation on the laser intensity has been measured and the slopes of the linear parts of the log-log plots and the ratios of saturation intensities for two pulse durations have been compared with the predictions of the scaling law. No evidence for a pure direct double ionization process has been obtained.     

Characterization and surface-enhanced Raman spectral probing of silver hydrosols prepared by two-wavelength laser ablation and fragmentation

A four step Ag foil laser ablation-Ag nanoparticle fragmentation procedure in ultrapure water was carried out both under argon and in air. Pulses of a high power Nd/YAG laser were used for laser ablation (1064 nm) and for the three step Ag hydrosol treatment in the absence of Ag foil in the sequence 1064-532-1064 nm. Transmission electron microscopy (TEM) and surface plasmon (SP) extinction spectra provide evidence of Ag nanoparticle fragmentation in the second and third step of the procedure carried out under argon. While polydispersity of Ag hydrosol increases in the second step, both the polydispersity and the mean size of the nanoparticles are reduced in the third step. Qualitative and quantitative surface-enhanced Raman scattering (SERS)/surface-enhanced resonance Raman scattering (SERRS) spectral probing of systems with Ag hydrosols and the selected adsorbates at 514.5 nm excitation shows that Ag hydrosols obtained in the second step of the preparation procedure carried out in air are the most suitable substrates for SERS/SERRS experiments performed at this excitation wavelength.     

Coulomb explosion of ammonia clusters induced by intense nanosecond laser at 532 and 1064 nm: wavelength dependence of the multicharged nitrogen ions

The Coulomb explosion of ammonia clusters induced by nanosecond laser field with intensity in the range of 10(10)-10(12) W cm(-2) and wavelength of 532 and 1064 nm has been studied. N2+ and N3+ ions are the main multicharged ions at 532 nm, while He-like N5+ ion is the domain multicharged ion at 1064 nm.     

基于大气压下介质阻挡放电抑制LA-ICP-MS分析中元素分馏效应研究

采用自制的大气压下介质阻挡放电装置串联在激光剥蚀池与ICP炬管之间, 对激光剥蚀产生的气溶胶进行预电离. 结果表明, 元素瞬时信号轮廓的平滑度得以改善, 元素分析信号精密度(RSD, n=3)可提高2.55％. 在ArF准分子激光(193 nm)和Nd∶YAG 固体激光(213 nm)两种不同波长的激光剥蚀系统中, 元素分馏因子均比常规模式下更接近于1, 表明采用介质阻挡放电对气溶胶预电离后元素分馏效应得以有效抑制. 相比两种不同波长的激光剥蚀系统, 介质阻挡放电对213 nm固体激光的元素分馏效应改善作用明显.     

Diagnostic study of laser ablated YBa2Cu3Oy plumes

Post-ablation ionisation in conjunction with a reflectron time-of-flight mass spectrometer has been used to investigate a number of species in the ablation plume from a YBa₂Cu₃O_y target. The experiments were carried out using a Q-switched Nd:YAG laser with typical intensities of ≈ 10⁸ W cm⁻² characteristic of the fluences (1 J cm⁻²) required for the pulsed laser deposition of thin superconducting films. By varying the delay between the ablation and the ionisation laser, the velocity distributions of several of the species from the target have been measured simultaneously. It has been observed that, although some of the atoms and molecules (i.e. Cu, Ba and BaO) have similar velocities, the atoms and oxides of Y (Y and YO) have very different velocities. The yttrium atoms and oxides were observed to be slower than the barium atoms and oxides at both ablation wavelengths examined (355 and 532 nm) and at two different distances from the target surface (2 and 3 mm). It is suggested that Ba, Cu and their oxides are ablated directly from the surface as neutrals, whereas Y and YO form clusters in the ablation plume. These clusters are then fragmented by the post-ionisation laser to produce Y and YO ions.     

Two- and three-wavelength laser multiphoton ionization for highly sensitive detection in solution

Novel two- and three-wavelength laser multiphoton ionization techniques for highly sensitive detection in solution have been established. The photocurrent signal obtained for benzo[a]pyrene by irradiation at 355 nm in n-heptane was effectively enhanced by additional simultaneous irradiation at 532 and/or 1064 nm. The additional irradiation at 532 nm (5 mJ) doubled the signal-to-noise ratio, while that at 1064 nm (30 mJ) increased it 5.5-fold relative to that obtained when only the 355 nm radiation was used. The simultaneous action of 355, 532 (5 mJ) and 1064 (25 mJ) nm radiation further improved the S/N ratio; the detection limit was as low as 1.9 x 10(-10)M. The 532 nm radiation enhanced the photocurrent signal more effectively than did the 1064 nm radiation.     

1,3-二硫杂环戊烯-2-硫酮-4,5-二巯基类复合物在不同波长下的三阶非线性光学性质

合成了两种新的金属双噻吩类复合物:(苄基三乙基铵)双(1,3-二硫杂环戊烯-2-硫酮-4,5-二巯基)-金(BTEAADT)和(苄基三乙基铵)双(1,3-二硫杂环戊烯-2-硫酮-4,5-二巯基)-镍(BTEANDT).采用Z扫描方法,在皮秒脉冲下,分别测试了两种材料的乙腈溶液在532和1064nm的三阶非线性光学特性.Z扫描的结果表明,BTEAADT的乙腈溶液在532nm具有反饱和吸收效应,在1064nm非线性吸收效应可以忽略且在两种波长都有自散焦效应,三阶非线性折射率为负值.BTEANDT的乙腈溶液在532nm非线性吸收效应可以忽略,在1064nm具有饱和吸收效应且在两种波长都有自聚焦效应,三阶非线性折射率为正值.分析了造成这种差异的原因.经过计算得到了两种材料在532和1064nm的三阶非线性折射率,三阶非线性吸收系数,三阶非线性极化率和超极化率.BETAADT的非线性折射率在532nm为-1.685×10-18m2·W-1,在1064nm为-1.459×10-18m2·W-1;BTEANDT的非线性折射率在532nm为1.452×10-18m2·W-1,在1064nm为7.311×10-18m2·W-1.两种材料的三阶非线性吸收系数,三阶非线性极化率和超极化率的数量级分别是10-11m·W-1,10-13esu和10-31esu.结果表明这两种材料在非线性光学领域有潜在的应用价值.     

Gold nanoparticles fabricated by pulsed laser ablation in supercritical CO2

Nanosecond pulsed laser ablation (PLA) of gold plate with an excitation wavelength of 532?nm was carried out in supercritical CO₂ (scCO₂) to fabricate gold nanoparticles. Surface morphology of the gold plate after irradiation and the crater depth after PLA were observed by scanning electron microscopy and laser scanning microscopy, while extinction spectra of gold nanoparticles collected in the glass slide was measured by UV?CVis spectrophotometer. The gold plate was ablated at various scCO₂ densities and irradiation times at constant temperature of 40??C. The ablation was also conducted at atmospheric condition with air to evaluate the environmental dependence of ablation. Both surface morphology of the irradiated gold plate and crater depth formation were significantly affected by the changes in scCO₂ density, the surrounding environment, and irradiation time. As expected, the increasing scCO₂ density resulted in a deeper ablation crater, however, the deepest crater was obtained at a density of 0.63?g/cm³ or pressure of 10?MPa. Gold nanoparticles generated by PLA in scCO₂ have been confirmed at the spectra band near 530?nm.     

Sol-Gel Processing of Zirconia Coating for HR Mirrors with High Laser Damage Threshold

High laser-damage resistant coatings are very important in high power laser systems. In this study ZrO₂ thin films are prepared by sol-gel spin-coating technology from suitable zirconia aqueous colloidal suspensions containing nano-crystalline ZrO₂ at room temperature synthesized by a hydrothermal process from an inorganic precursor (ZrOCl₂·8H₂O). By adding a soluble organic binder PVP to the suspension prior to application, it is possible to substantially increase the coating refractive index and the abrasion-resistance as well as the laser damage threshold. The features of the coatings and the colloidal suspensions are investigated. Multilayer highly reflective dielectric coatings are also elaborated by applying quarterwave-thick alternating coatings of the binder-aided zirconia and silica, which is prepared with the sol-gel process from TEOS. To achieve 99% reflectivity, 19–21 layers are required. Single shot laser damage tests are carried out using a high power laser at 1064 nm wavelength with a pulse duration of 2.5 ns. The laser damage thresholds of 18 and 15 J/cm² are achieved for single ZrO₂-PVP coating and ZrO₂-PVP/SiO₂ multilayers respectively.     

Desorption of Physisorbed Molecules from the Sapphire Surface by Yttrium–Aluminum Garnet Laser Second-Harmonic Radiation

Energy fluence dependences for the laser-enhanced desorption of physisorbed NO, SO₂, CO₂, NH₃, and C₆H₆molecules from the sapphire surface by second-harmonic radiation of a pulse neodymium-doped yttrium–aluminum garnet (YAG) laser were experimentally studied. It was shown that the one-photon absorption of radiation at the second-harmonic wavelength ( = 532 nm) by adsorbed NO molecules was so low that their desorption was accomplished via two-photon absorption. Nonlinear energy fluence dependence with a nonlinearity index of greater than 4 was observed for polyatomic molecules. The desorption of these molecules did not occur at the YAG laser emission wavelength ( =1064 nm), thus suggesting that the long-wavelength edge of their one-photon absorption lies within the range 1064–532 nm.     

Recent trends and developments in laser ablation-ICP-mass spectrometry

The increased interest in laser technology (e.g. for micro-machining, for medical applications, light shows, CD-players) is a tremendous driving force for the development of new laser types and optical set-ups. This directly influences their use in analytical chemistry. For direct analysis of the elemental composition of solids, mostly solid state lasers, such as Nd:YAG laser systems operating at 1064 nm (fundamental wavelength), 266 nm (frequency quadrupled) and even 213 nm (frequency quintupled) have been investigated in combination with all available inductively coupled plasma mass spectrometers. The trend towards shorter wavelengths (1064 nm– 157 nm) was initiated by access to high quality optical materials which led to the incorporation of UV gas lasers, such as excimer lasers (XeCl 308 nm, KrF 248 nm, ArF 193 nm, and F₂ 157 nm) into laser ablation set-ups. The flexibility in laser wavelengths, output energy, repetition rate, and spatial resolution allows qualitative and quantitative local and bulk elemental analysis as well as the determination of isotope ratios. However, the ablation process and the ablation behavior of various solid samples are different and no laser wavelength was found suitable for all types of solid samples. This article highlights some of the successfully applied systems in LA-ICP-MS. The current fields of applications are explained on selected examples using 266 nm and 193 nm laser ablation systems.     

Study of laser ablation of brass materials using inductively coupled plasma atomic emission spectrometric detection

A XeCl laser and a Q-switched Nd:YAG laser operating at 1064, 532, 355 and 266 nm were used to ablate brass materials with varying concentrations of Zn and Cu. The ablated material was transported to an inductively coupled plasma for further atomization, excitation and ionization with an atomic emission spectrometric detection. A Zn enhancement was observed, which could be suppressed by using a Nd:YAG laser working at 266 nm with fluences higher than 400 J cm⁻² (equivalent to 80 GW cm⁻²). In contrast, a lack of linearity was observed for Cu as a function of the concentration, regardless of the wavelength and the fluence. The Cu problem seemed to occur during the ablation and was related to the structure of the brass material. Lack of linearity was also observed for Zn and other contained elements when samples from different origins were used.