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We studied the applicability of Pulsed Laser Deposition (PLD) as a particle engineering method in the field of drug preformulation. Improving the dissolution and thereby the bioavailability of poorly water-soluble compounds is still a challenging task in pharmaceutical formulation. It was shown earlier that particle size reduction or the development of stable amorphous forms may both facilitate drug absorption. Using ibuprofen as a model drug, we studied the ablated particles obtained by pulsed-laser-beam irradiation of ibuprofen tablets. Nanosecond and femtosecond laser pulses (KrF excimer laser, λ = 248 nm, FWHM = 18 ns; 600 fs) were applied at various ambient pressures (10−4 mbar to 1 bar). The ablated particles were deposited for further analysis by FTIR, Raman Spectroscopy, XRPD, DSC and SEM. We found that all deposits prepared in vacuum by ns-pulses were chemically identical with ibuprofen, but their morphology varied depending on the applied pressure. At higher pressures (10 mbar to 10−1 mbar) the deposits exhibited similar crystalline morphology as the initial ibuprofen, while at lower pressures (10−2 mbar to 10−3 mbar), the deposits were rather amorphous. Using fs-pulses, molecular decomposition occurred at all background pressures. We have established that PLD with ns-pulses is a promising technique in the field of drug preformulation.

We use laser-induced plasma shock waves to remove Al nanoparticles from a smooth silicon substrate. Our experimental results show that the removal mechanism varies for different substrate regions. We examine the factors influencing particle removal by evaluating the shock-wave spatial distribution and the removal mechanisms. Further, we evaluate the influence of the gap between the laser focus and substrate on the removal results. The effects of the laser focus and substrate particle sizes are also investigated, and the optimum removal conditions are obtained. Our study can aid in better understanding the mechanisms of particle removal from surfaces.

In biomedical engineering, laser-induced periodic surface structures (LIPSSs) have been extensively applied where laser irradiation of selective laser-melted (SLMed) samples to generate LIPSS-covered free-form samples is a promising technique. Using this technique, nanopillars around a spheroidal particle that was not molten during the SLM process have been formed, indicating that nanopillars can be induced around spheroidal particles on a material surface. This study investigates the mechanism of LIPSS and nanopillar formation on SLMed and uneven surfaces experimentally and through finite-difference time-domain simulation. A 50 Hz picosecond laser with 1064 nm fixed wavelengt, 20 ps pulse duration, 0.5 J/cm2 laser fluence, and 400 μm/s scanning speed was employed to irradiate Ti6Al4V alloy samples with 100 μs exposure time. The results show that induced nanopillars form a concentric area around a single particle with curvature radius approximately twice the particle radius. The simulated electric field intensity is ripple-like distributed for particle size beyond 5 μm, with approximately 1 μm periodic length and is close to the laser wavelength. This matches the experimental results from scanning electron microscopy for 800–00 nm LIPSS periodic length, indicating that desired nanostructures can be generated by appropriately designing the surface topography before laser irradiation.

In this paper the distribution of debris generated by a nanosecond UV laser (248 nm) on epoxy resin and the prevention of the corresponding re-deposition effects by parameter selection for a ns-laser scanning process were investigated. In order to understand the mechanisms behind the debris generation, in-situ particle measurements were performed during laser treatment. These measurements enabled the determination of the ablation threshold of the epoxy resin as well as the particle density and size distribution in relation to the applied laser parameters. The experiments showed that it is possible to reduce debris on the surface with an adapted selection of pulse overlap with respect to laser fluence. A theoretical model for the parameter selection was developed and tested. Based on this model, the correct choice of laser parameters with reduced laser fluence resulted in a surface without any re-deposited micro-particles.

Submicrometer spherical particles (SMSPs) are reported to be fabricated by pulsed laser irradiation with a frequency of 10 or 30 Hz onto raw nanoparticles dispersed in liquid. Here, the effect of the pulse frequency on particles obtained by laser irradiation onto the suspension in a vessel, especially at higher pulse frequencies up to 800 Hz, is investigated. At 200 Hz or lower, SMSPs of similar size can be fabricated, as at 10 or 30 Hz, by the same number of pulses. This indicates that the time required for particle fabrication can be greatly reduced and production efficiency can be improved using a high-frequency laser. In contrast, at 400 Hz or above, nanospherical particles (NSPs) are formed in addition to SMSPs, and the mass fraction of SMSPs is drastically decreased. This result suggests that consecutive laser pulse irradiation induces heat accumulation in particles and suspensions, resulting in a temperature increase and partial evaporation of the particles at 400 Hz or above. From the temperature increase of the suspension, the local temperature of the liquid surrounding the particles is believed to be increased by heat dissipation from the heated particles. Calculations suggest that an increase in the local liquid temperature would cause further heating of the particles.

We here show that Ag-Au bimetallic nanoparticles (NPs) can be produced by dewetting an Ag/Au bilayer film coated on glass using a nanosecond-pulsed laser beam. Elemental analysis revealed that the obtained bimetallic NPs are Ag-Au alloys, with two elements well mixed over the whole volume of the particle. The composition of the produced particles was controllable by changing the relative thickness of each layer. The localized surface plasmon resonance (LSPR) peak was red-shifted with an increasing Au content and the LSPR wavelength could be tuned from 415 to 525 nm by varying the alloy composition. A film area of several square centimeters could be transformed into Ag-Au NPs by a single laser pulse of 6 ns duration. This study provides a facile and scalable route to prepare bimetallic NPs for plasmonic and other applications.

Miniaturization and integration of lasers have been a hot topic in recent years. Colloidal quantum dots (CQDS) can be used as laser gain media because of their high luminous efficiency and low threshold. Compact distributed Bragg reflector (DBR) combined with CQDs is used to construct micro laser. In this paper, CdTeSe/ZnS core–shell CQDs were prepared by aqueous synthesis. DBR was fabricated by magnetron sputtering using SiO2 and TiO2 through reasonable design of their thickness and repetition cycle number. CQDs were dropped on the surface of DBR to form a low-cost small-scale surface particle laser (SPL). The output emission of 770 nm and 824 nm dual wavelength laser is realized. The threshold is 11 mW/cm2 and the bandwidth is 1 nm. The micro integrated laser with high intensity and Narrow bandwidth near infrared emission has been completed.

Using an atomic force microscope, the friction and wear of phosphate laser glass against a CeO 2 particle were quantitatively studied both in humid air and in vacuum, to reveal the water molecules induced mechanochemical wear mechanism of phosphate laser glass. The friction coefficient of the glass/CeO 2 pair in air was found to be 5–7 times higher than that in vacuum due to the formation of a capillary water bridge at the friction interface, with a contribution of the capillary-related friction to the total friction coefficient as high as 65–79%. The capillary water bridge further induced a serious material removal of glass and CeO 2 particle surfaces, while supplying both a local liquid water environment to corrode the glass surface and a high shearing force to assist the stretching of the Ce O P bond, accelerating the reaction between water and the glass/CeO 2 pair. In vacuum, however, no discernable wear phenomena were observed, but the phase images captured by AFM tapping mode suggested the occurrence of potential strain hardening in the friction area of the glass surface.

Water-jet laser processing is an internationally advanced technique, which combines the advantages of laser processing with water jet cutting. In the study, the experiment of water-jet laser dicing are conducted with ns pulsed laser of 1064 nm irradiating, and Smooth Particle Hydrodynamic (SPH) technique by AUTODYN software was modeled to research the fluid dynamics of water and melt when water jet impacting molten material. The silicon surface morphology of the irradiated spots has an appearance as one can see in porous formation. The surface morphology exhibits a large number of cavities which indicates as bubble nucleation sites. The observed surface morphology shows that the explosive melt expulsion could be a dominant process for the laser ablating silicon in liquids with nanosecond pulse laser of 1064 nm irradiating. Self-focusing phenomenon was found and its causes are analyzed. Smooth Particle Hydrodynamic (SPH) modeling technique was employed to understand the effect of water and water-jet on debris removal during water-jet laser machining.

Laser dewetting is a simple and efficient method for transforming a metal thin film into nanoparticles. However, the particles obtained via laser dewetting typically exhibit a wide size distribution. This study shows that a combination of thermal and laser dewetting processes can be used to generate more uniform metal nanoparticles. A 10-nm-thick Ag film deposited on glass was irradiated by an Nd:YAG laser pulse to produce nanoparticles with sizes in the range of 35–145 nm. When the film was thermally annealed at 250 °C in an Ar atmosphere before laser irradiation, Ag nanoparticles with a much narrower size distribution were obtained (mean size = 48 nm and standard deviation = 10.5 nm), which was attributed to the island structure formed by the pre-annealing step. X-ray photoelectron spectroscopy confirmed the absence of particle oxidation. An important feature associated with this hybrid dewetting approach was that the obtained Ag nanoparticles showed a strong single plasmonic resonance peak owing to their narrow size distribution. As a plasmonic sensing platform, they exhibited much enhanced refractive index sensitivity and figure of merit than the particles produced via laser dewetting.

Laser shockwave cleaning (LSC) has been gaining increasing attention due to its advantages in decontaminating various micron- and nano-scale contaminated particles on silicon (Si) wafer surfaces. However, the particles in a blind zone right under the laser-induced plasma, the origin of the shockwave, cannot be removed efficiently, thereby impeding the conventional LSC process in industrial wafer cleaning applications. Here, we demonstrate a simple but intriguing method of eliminating the blind zone in nanoparticle removal on Si wafers by employing a double-beam laser shockwave cleaning process (DLSC). The size of the uncleaned blind zone in DLSC is reduced by 98% compared to the traditional single-beam LSC (SLSC) process with a laser pulse energy of 150 mJ and a gap distance between the laser focus and the wafer of 1 mm. The time-resolved, laser-induced plasma evolution reveals that the steady single-laser-beam-induced plasma splits into multiple plasma kernels distributed around the focus point due to the disruption from the second laser beam. The formation of multiple plasma kernels makes it possible to expose the particles in the blind zone to the cleaning-effective zone of the shockwave from a nearby passing plasma. The angle between the two laser beams plays a critical role in eliminating the blind zone. The comparison of the particle removal force between DLSC and SLSC suggests that the horizontal drag force from a nearby passing plasma acts on the particles in the blind zone and facilitates their removal.

Aluminum matrix composites reinforced by in situ ZrB 2 particles were successfully fabricated from an Al-KBF 4 -K 2 ZrF 6 system via a direct melt reaction. A laser surface melting strategy is used to improve the surface strength of the in situ ZrB 2p /6061Al composite, which includes a series of laser-melted composites with different laser power processed by a 2 kW YAG laser generator. XRD and EDS results demonstrated the existence of ZrB 2 nanoparticles in the composite. After laser melting, the penetration depth of the molten pool increases with increasing power density. OM and SEM analysis indicate that the laser melting process yields narrower cellular spacing of the matrix and partly disperses the ZrB 2 particle clusters. Compared with laser-melted matrix alloys, the crystal orientations near the melted layers edge of the composite are almost random due to heterogeneous nucleation in the melt and the pinning effect of laser-dispersed ZrB 2 nanoparticles at the solidification front. Wear test results show that the laser melted layer performs better at wear resistance than both the substrate and the matrix AA6061 by measuring wear mass loss. Compared with composite samples prepared without laser melting, the wear mass loss of the laser melted composites decreased from 61 to 56 mg under a load of 98 N for 60 min.

Optical functional surfaces are key components of nearly every optical device and they have become a special focus in both academia and industry. The no contact, one step, direct, and maskless laser surface texturing technique is one of the most encouraging approaches for realizing the surface functions. We use a high power and high repetition rate ultrafast laser system to produce micro–nano structures on metal surfaces. We demonstrate that metal surface micro–nano structures and correspondingly their optical responses can be facilely tailored by simple controlling the ultrafast laser processing parameters. Nano particles of tens to hundreds nm, sub-micro particles of 0.5–1 μm, fine-micro particles of 1–10 μm, micro particles of 10–50 μm, and coarse-micro particles larger than 50 μm have been fabricated on Cu surfaces. And surface reflection of copper surfaces has been tuned from 10% to 90% in spectra level and from UV to MIR in spectrum range, with unique optical properties like visible selective reflection, linear changing reflection, band reflection, and broadband absorption being achieved. The formation processes of those particle structures as well as the underlying mechanisms for their optical responses are discussed.

The laser induced plasma during the nanosecond Pulsed Laser Ablation in Liquid (PLAL) plays a crucial role in the nanoparticles (NPs) formation and charging. It was demonstrated that during the plasma phase evolution, once the NPs are formed, they are charged with the excess of plasma electrons. Immediately after the plasma phase extinguishes, the NPs will be released in the induced vapor bubble, generated by the fast energy exchanges between the plasma and the liquid. The excess of charge in the NPs preserves them from the agglomeration during the bubble evolution and can induces an electrostatic pressure able to eject the particles outside the cavitation bubble. In this work, the plasma charging effect on the particle releasing in solution, during the bubble evolution, has been investigated. Temporal evolution of laser induced bubble on silver target immersed in water has been measured with the shadowgraph technique. Then, starting from the experimental bubble radius evolution, the releasing of the NPs from the cavitation bubble to the liquid has been modeled by comparing the electrostatic pressure of the charged NPs cloud and the pressure of the cavitation bubble. The following discussion proposes a new insight of the mechanism of NPs releasing in solution.

A high speed repetition rate laser was used in an ‘eclipse’ system configuration for growing ZnO nanowires on Au patterned substrates, using vapor–liquid–solid (VLS) technique. Experimental results have shown that the nanowire length increase in the vicinity of catalyst free areas and the grown length distribution over the catalyst covered areas depend on the number of the laser pulses per train. The results suggest that the nanowire over-growth, attributed to the particle surface diffusion, is effective in the ZnO VLS growth within about 100 μm distances. ‘Glancing angle setup’ obtained for a submillimeter mask-substrate distance could provide control over VLS growing (or actually over ‘non-growing’) locations by suppressing the nanowire grow in the center of the catalyst covered areas.

Femtosecond laser machining of crystalline Si in vacuum resulted in the formation of pillars and particles of ∼100 nm in size at the wall surfaces and the periphery of the ablated hole. These structures were created at a laser fluence below the ablation threshold. The nanopillars and nanoparticles appear to grow from the target surface. The target surface near the particles showed molten features with descending height, indicating significant mass transport from the surface layer to the particles. The nanopillars and nanoparticles likely formed as a result of successive crystal growth processes including amorphization of the laser-irradiated target surface, followed by crystalline nucleation, melting of the amorphous Si surrounding the crystalline particles, and liquid Si creeping over particle surfaces leading to an increase in particle size. By repeating these processes, the particles grow in cumulative laser shots. These particles are the major debris components distributed near micron-sized holes formed at the ablation threshold fluence in vacuum.

A multilayer WSe 1.7 / 57 Fe/ 54 Fe structure was created by sequential pulsed laser deposition on a Si substrate of 54 Fe-rich, 57 Fe-rich, and WSe 1.7 thin films subjected to laser plasma ion implantation (LPII). Electric pulses of negative polarity with amplitude 45 kV were applied to the 54 Fe laser target. The turn-on time of the pulse, with a duration of ~10 μs, was varied in the range of 0–9 μs after the laser pulse. Modeling of the LPII was carried out using the particle in the cell method in a one-dimensional approximation. The initial input characteristics of the plasma (velocity, temperature, concentrations of ions) were measured experimentally. The model adequately describes the ion pulses and results in terms of energy distribution of the ions. The LPII regime, providing an efficient implantation of 54 Fe +2 ions with energies up to 90 keV, was used. Before and after LPII the structure was studied by Rutherford backscattering spectroscopy of 4 He + ions and conversion-electron Mossbauer spectroscopy. LPII treatment induced mixing of W, Se and 57 Fe atoms. 57 Fe–Se phases and non-equilibrium 57 Fe–W compound were detected in a local structure of the interface layer. Thus, LPII may be considered as a promising method in combined laser technology, allowing deposition of coatings and modification of the interface, which may provide an enhanced adhesion and improved tribological properties

Direct laser surface micro/nanopatterning by using Contact Particle Lens Array (CPLA) has been widely utilized. The method involves laser scanning of a monolayer of transparent particles arranged on the substrate to be patterned. Despite the different techniques available for CPLA deposition; the particles monolayer can only be formed on hydrophilic surfaces, which restrict the range of substrates that could be patterned by this method. In this study, a technique for patterning of hydrophobic surfaces by using CPLA has been proposed. In the proposed technique, monolayer of CPLA is formed on a hydrophilic substrate and then transported to a hydrophobic substrate by using a flexible sticky plastic. The transported CPLA is then scanned by a laser for patterning the hydrophobic substrate. The plastic pre-selected for this work was transparent to the laser. Experimental investigations were carried out to generate bumps and bowl shaped patterns using transported particles. Features smaller than the diffraction limit have been generated. The optical near field and associated temperatures around the particles were numerically simulated with a coupled electromagnetic and thermal modelling technique.

Theoretical and experimental results on the heating process of gold nanoparticles irradiated by nanosecond laser pulses are presented. The efficiency of particle heating is demonstrated by in-vitro photothermal therapy of human tumor cells. Gold nanoparticles with diameters of 40 and 100 nm are added as colloid in the cell culture and the samples are irradiated by nanosecond pulses at wavelength of 532 nm delivered by Nd:YAG laser system. The results indicate clear cytotoxic effect of application of nanoparticle as more efficient is the case of using particles with diameter of 100 nm. The theoretical analysis of the heating process of nanoparticle interacting with laser radiation is based on the Mie scattering theory, which is used for calculation of the particle absorption coefficient, and two-dimensional heat diffusion model, which describes the particle and the surrounding medium temperature evolution. Using this model the dependence of the achieved maximal temperature in the particles on the applied laser fluence and time evolution of the particle temperature is obtained.

Particles generated by 2.94 μm pulsed IR laser ablation of liquid 3-nitrobenzyl alcohol were irradiated with a 351 nm UV laser 3.5 mm above and parallel to the sample target. The size and concentration of the ablated particles were measured with a light scattering particle sizer. The application of the UV laser resulted in a reduction in the average particle size by one-half and an increase in the total particle concentration by a factor of nine. The optimum delay between the IR and UV lasers was between 16 and 26 μs and was dependent on the fluence of the IR laser: higher fluence led to a more rapid appearance of particulate. The ejection velocity of the particle plume, as determined by the delay time corresponding to the maximum two-laser particle concentration signal, was 130 m/s at 1600 J/m2 IR laser fluence and increased to 220 m/s at 2700 J/m2. The emission of particles extended for several ms. The observations are consistent with a rapid phase change and emission of particulate, followed by an extended emission of particles ablated from the target surface.

We report results on the pulsed laser deposition of ZnO obtained with the help of a new apparatus that includes in situ reflectron time-of-flight mass spectrometry, with a view to progress the understanding of the role of clusters in the laser deposition of nanostructured materials. Experiments were carried out using a Nd-YAG laser at its fundamental frequency and frequency tripled, with a fluence on target of ∼7.7 J/cm 2 , in vacuum (10 −4 Pa) or oxygen (1 Pa) atmospheres. The results show that under certain conditions there is preferential clusterisation of the material into certain mass numbers and finally that there exists a correlation between cluster presence in the plume and the deposition of nanostructures.

Time-resolved photography was employed to study plasma dynamics and particle ejection of laser-irradiated iron oxide materials. Nano-particle powder, pressed powder pellets and sintered ceramics were ablated in air and Ar gas background by means of short laser pulses (Nd:YAG laser wavelength λ = 1064 nm and pulse duration τ L ≈ 6 ns; KrF laser λ = 248 nm and τ L ≈ 20 ns). Plasma plume dynamics significantly depended on sample morphology. The ejection of non-luminous particles up to several hundreds of microseconds after the laser pulse was observed for powder and pressed powder target materials. Laser-induced breakdown spectroscopy (LIBS) was employed for element analysis of iron oxide powders, pressed pellets and sintered ceramics. LIBS spectra of the different targets were comparable to each other and qualitatively independent of target morphology.

During the operation of the ITER fusion facility, particles with size from 10 nm to 100 μm, mainly composed of carbon, beryllium, and tungsten, will be produced. Since dust could lead to safety issues, it must be periodically removed from the facility in order to keep their quantity below the safety limit requirements. In this context, laser cleaning appeared as a very promising technique, and investigations have to be done to understand the physical processes and optimize the procedure. Several experiments were carried out to improve the understanding of the phenomena involved during the laser-induced removal of Carbon particles. The ejection mechanisms have been experimentally studied for different irradiation conditions with nanosecond laser pulses. The removal efficiency and the fluence threshold were determined by optical microscopy. The influence of the substrate was studied for the dry laser cleaning configuration. This study presents scanning electronic microscopy pictures which show that the particle removal leads to a damage of the substrate. These damages give evidences on the ablation mechanism. The laser shock cleaning was also studied. In this configuration, the laser-induced shock wave can be used to push the particles away from the surface. This technique appears to be very useful to clean shadowed areas.

The laser shock cleaning (LSC) process has been shown to be effective for removing submicron-sized contaminant particles from solid surfaces and thus bears strong potential in various applications. In this work, experimental and theoretical analysis are conducted to reveal the underlying physical mechanisms of the LSC process, with emphasis on the laser-induced hydrodynamics and the effect of external gas-jet injection through a nozzle. A two-dimensional theoretical model is proposed for rigorous simulation of the hydrodynamic phenomena occurring in the LSC process. The hydrodynamics computed by the model is in qualitative agreement with experimental observations and reveal the details of the physics involved in the cleaning process. The effect of gas blowing on the cleaning performance is analyzed both experimentally and theoretically. The results indicate that the gas flow can significantly change the hydrodynamics and increase the cleaning efficiency by reducing the chance of particle redeposition.

Short pulse laser interaction with a metal nanoparticle surrounded by water is investigated with a hydrodynamic computational model that includes a realistic equation of state for water and accounts for thermoelastic behavior and the kinetics of electron–phonon equilibration in the nanoparticle. Computational results suggest that, at laser fluences close to the threshold for vapor bubble formation, the region of biological damage due to the laser-induced thermal spike and the interaction of the pressure wave with internal cell structures can be localized within short distances from the absorbing particle comparable to the particle diameter. This irradiation regime is suitable for targeted generation of thermal and mechanical damage at the sub-cellular level.

Magnetic colloids with nanoparticles inside have been successfully fabricated by laser ablation of a cobalt target immersed in solutions, using an Nd:YAG laser at wavelengths of 532 and 1064 nm. The liquid environment allows formation of the colloids with nanoparticles in uniform particle diameters. Influences of the laser wavelengths and different solutions on efficiency of particle formation were studied. The magnetic properties of the cobalt nanoparticles inside the colloids generated were also investigated. Using proper parameters, this method provides a convenient way for fabricating magnetic fluid as well as metal nanoparticles.

Dry laser cleaning (DLC) is considered as an escape from an adhesion potential under the forces induced by thermal expansion. Important temporal and spatial scales are: period of small oscillations τ0, and equilibrium deformation h0. Possible cleaning regimes are discussed. With laser pulse duration τ τ0 (small particles) cleaning proceeds in the inefficient inertial force regime. If the fronts of the laser pulse are steep enough, tf⪡τ0, cleaning occurs when kinetic energy of the particle exceeds that of adhesion. Utilization of resonance effects by modulation of laser pulse or employing the train of pulses and influence of damping on these regimes are discussed. Effects of the near field focusing by dielectric spheres and decrease in cleaning threshold due to three-dimensional (3D) effects are analyzed and compared with the experimental results for SiO2 particles on Si surface.

A method to monitor laser cleaning is presented in this paper. During laser cleaning of contamination, particles are generated and/or ejected from a substrate based on laser ablation and laser-induced fast thermal expansion of contaminants and/or the substrate. An airborne particle counter is used to detect the particles ejected from the substrate during laser cleaning at the same time as the irradiation of the laser beam. The cleaning threshold, cleaning efficiency, cleanliness of substrate and ablation threshold of substrate can be monitored by particle detection.

Dry laser cleaning is envisaged by semiconductor companies to replace wet-cleans. The influence of beam incidence angle was studied in the case of the removal of weakly absorbing particles on absorbing Si wafers by 248 nm DUV light pulses. By decreasing the beam incidence angle from 80° to 10°, the removal efficiency of 0.15–0.30 μm Si3N4 particles was increased by 30–45%, while no improvement was observed with 0.3 μm SiO2 particles. Based on theoretical calculations, it is proposed that the enhanced removal of particles at grazing incidence is caused by the horizontal component of the beam radiation pressure. The difference between Si3N4 and SiO2 particles is attributed to the influence of particle shape on van der Waals adhesion forces.

We present a comparative study on UV matrix-assisted laser desorption (MALD), laser-induced thermal desorption (LITD), IR laser ablation, and desorption via electrical substrate heating. In order to determine to what extent the material is desorbed as individual molecules or ejected as particles, respectively, the ablated material was intercepted by a trapping plate and the particle size distribution was analyzed by atomic force microscopy (AFM). The ratio of ejected particles to free molecules is strongly dependent on the laser volatilization technique used. High energy densities in the sample, for example in UV MALD, favor molecular desorption leading to very smooth films on the trapping plate. In contrast, IR polymer ablation and LITD of micrometer thick organic films is dominated by ejection of clusters and particulates. Volatization by electrically heated flash filaments is not significantly different from substrate mediated thermal laser desorption (LD). It may allow to miniaturize and simplify mass spectrometric instrumentation for applications requiring desorption–ionization techniques.

Analytical derivation of the thickness profiles of pulsed laser deposited (PLD) thin films starting out from a plausible velocity distribution of the ablated atoms proved to be appropriate in describing PLD in high vacuum. Since the presence of background gases is typical in most applications, there is a need for methods which do not suffer from the limitations of the analytical description, supposing collisionless transfer of the target atoms onto the substrate. We give a microscopic approach to the description of thin film formation by following the `life story' of each ablated particle by Monte Carlo calculations. Bi and In film thickness profiles and TOF and kinetic energy spectra are presented for various pressures of the He, Ar and Xe background. The computer experiments are compared with real experiments on nonreactive PLD. It is demonstrated that the process can be handled satisfactorily in the framework of the hard-sphere collision model used.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP/MS) has been successfully deployed by researchers at the Pacific Northwest Laboratory for the analysis of Hanford nuclear waste. This effort required research to determine the relative importance of the numerous parameters involved in LA-ICP/MS. These factors include laser parameters and sample matrix variables. The precision in relative concentrations was determined as a function of laser wavelength. Ablation at 355 or 266 nm gave precision of 5–10%, while the value for 532 nm was 25% and for 1064 nm was 40%. Analysis of the data for relative fractionation between elements showed large differences in the IR for volatile vs. refractory elements. The UV ablation gave results that were much less dependent on matrix effects and showed minimal or no fractionation. Measurements of the particle distribution produced by laser ablation prior to transfer to the ICP/MS were made as a function of laser wavelength and pulse energy. These results show that the laser wavelength and pulse energies that provide the best precision and accuracy for analysis of glass or tank waste simulant materials produce particle size distributions with the majority of ablated material present as particles from 0.1–1.0 μm in diameter. This size range is important for quantitative transport to the ICP/MS and for complete digestion of the particles in the plasma. The particle counts were used to normalize the mass spectra of glasses having widely different opacities and laser ablation efficiencies resulting in quantitative analysis of these samples.

Unlike traditional laser ablation experiments where solids are volatilized by the focused laser beam, we give the term `inverse laser ablation' to the process of particle formation following the interaction of the laser with a gaseous precursor. Experiments are described where the transition from a normally gas phase species to a normally condensed phase particle takes place within a single gas-phase cluster in a collisionless environment. In addition, by adding reactant molecules to the initial cluster, it is possible to observe and characterize chemical reactions occurring within this novel `test tube'. In this technique, a heterocluster composed of iron pentacarbonyl molecules and potential reactant species is formed by coexpansion in a supersonic jet. Photoionization of the precursor molecules by a picosecond, 266 nm laser pulse efficiently strips away the ligands, leaving metal ions and metal cluster ions (and neutrals) in close proximity to reactant molecules. Subsequent reactions take place which are followed by monitoring the products by time-of-flight mass spectrometry. The reaction with carbon disulfide is described in detail.

The comparative study of the laser ablated Y–Ba–Cu–O high T c superconductor, PbTe(Ga) semiconductor and Sn(Cu) metallic alloy has been carried out using a YAG:Nd 3+ Q-switched laser, an electrostatic probe and OMA in a region of laser power up to 4.8 J/cm 2 and in a region of argon or oxygen pressure up to 0.5 Torr. Ion and electron velocity distributions have been obtained from the probe measurements. Vapor composition and temperature were studied from optical emission spectra. The neutral particle velocity distributions have been calculated from TOF QMS measurements for PbTe(Ga) reported earlier. Two fluxes of the charged particles exist in the region of p =20–100 mTorr: the flux of slow ions and electrons scattered onto the gas molecules, and the flux of the fast non-scattered particles. The position of the ion peaks on the time scale and the average cross section of the scattering in a gas depended on the target material.

The main advantage of the PLD process consists in thin film deposition by a plasma flow with high kinetic particle energy. The energy and mass balance of the particle beam formation generated by laser ablation is the key for qualitative and quantitative understanding of the fundamental processes. Thermal evaporation and inverse bremsstrahlung will be discussed in this context. For experimental estimation of the energy and mass balance several in-situ measuring systems have been installed, in particular the ballistic microbalance and electrical probes. As a representative example the ablation of aluminium and carbon by pulsed Nd:YAG laser irradiation in the intensity range of 108 W/cm2 is presented in more detail.

The thermal effects produced by laser pulses (6 or 18 ns) absorbed by a solid target have been investigated experimentally and theoretically. The energy which is absorbed serves to raise the temperature of the surface. The regimes to be considered are described by the heat-diffusion equation under conditions of what we term `normal vaporization'. Numerical solutions of the heat-diffusion equation lead to the temperature profiles produced within the target. The aim of this work is to present the results on heat flow in terms of the surface temperature and the velocity at which the surface recedes. Experimental data on the recession velocity and of the crater depth in relation to the thermophysical parameters of the metals Al, Cu, Nb, W, and Zn, are reported. The effect of the surface heating has also been examined in terms of the velocities of the plumes emitted from the targets. It is concluded that vaporization from the laser-heated targets is not the only relevant process but that one or both of laser-plume interaction and phase explosion may play a role in determining particle energies.

Controlling the kinetic energy of deposition species is an effective way to improve thin film's physical properties. An apparatus that can select the kinetic energy of laser ablated particles was developed. It was demonstrated that the energy of laser ablated particle was selected by chopping with the slit of rotating disk. This apparatus was applied to thin film deposition and it was useful to improve surface morphology because the number of droplets on the film drastically decreased.

The effect of particle removal from Al mirror surfaces by the influence of pulsed UV laser radiation has been studied. The investigations are closely related to the demands of astronomers, who are looking for a more effective way to clean future very large telescope (VLT) mirrors [1]. A systematic parameter study has been performed in order to determine the irradiation conditions which yield the highest dust removal efficiency (i.e. reflectivity increase) on contaminated samples. The particle removal rate increases with increasing laser fluence, being limited however by the damage threshold of the coating. Data indicate that on Al coated BK7 and Zerodur samples KrF laser radiation yields the optimum result, with cleaning efficiencies comparable to polymer film stripping. The initial reflectivity of the clean coating can nearly be restored, in particular when an additional solvent film on the sample surface is applied.

The behavior of particles ejected in a pulsed-laser deposition (PLD) of a high-temperature superconducting (high- T c )YBa 2 Cu 3 O 7 -δ (YBCO) thin film was investigated by one-dimensional laser-induced fluorescence spectroscopy. It is shown that particles stopped at a finite distance from a target and afterwards they are transported by diffusion. The behavior of ejected particles near the substrate was also examined in-situ during the deposition of high- T c films. Based on these results, a model for the pulse laser deposition of thin films in an ambient gas is presented.

The irradiation of polymeric material by pulsed UV lasers generates characteristic modifications of the surface topography of the polymer beside other effects. The resulting surface properties may have an important impact in textile processing, as they can affect technical properties of synthetic and even natural fibers, e.g. particle and coating adhesion or wetting properties, in a dry process. An overview is given over microscopic and macroscopic properties of the generated surfaces in dependence on laser parameters and material constants. Various understandings of the genesis of the characteristic geometry and structure of irradiated surfaces are compared to experimental observations from polymer films and a number of textile fibers. With respect to specific fiber properties the experimental data give evidence of cooperative transport phenomena in a superheated polymer as the prime driving forces of the effect.

Small sodium particles supported on an insulating LiF crystal are illuminated with visible light of an Ar+ or Kr+ laser. As a result the emission of neutral metal atoms from the particle surface is observed. the strongly resonant character of this emission, centered at about 490 nm, indicates that a surface plasmon excitation precedes the ejection. Time-of-flight measurements show large mean velocities of the emitted atoms. Continued laser illumination of the metal particles leads to an ablation of typically 20% of the initial coverage. The process is explained by a nonthermal mechanism.