Measuring the velocity of fragments produced by high-repetition-rate nanosecond laser pulses: A technique to visualize the fragments for laser decontamination

Formation of polymeric pillars by using laser interference lithography is compared for nanosecond and picosecond laser pulses. The experimental results are explained by dynamics of laser-excited radicals. The shape of fabricated structures demonstrates that thermal accumulation and oxygen diffusion from the surrounding air make an influence on polymerization when the pulse duration is in the nanosecond range. By using picosecond laser pulses, the thermal accumulation and oxygen diffusion effects are not important for low repetition rate (500 Hz), and they become relevant only at the repetition rates higher than ≥1kHz. It is shown that thermal accumulation is caused by a low-temperature diffusivity and heat accumulation at the polymer-glass interface, and it plays a significant role in the final shape of the structures fabricated using the nanosecond laser pulses.

Recently observed nonlinear-propagation and optical-limiting effects of nanosecond and picosecond laser pulses through a fiber are analyzed with a model that accounts for various molecular photonic-absorption processes including linear, two-photon, intermediate, and excited-state absorptions. Explicit expressions for the laser-induced molecular-level density changes, the thermal–density effects following photoabsorption, and their effects on the laser propagation transmission are obtained for conditions corresponding to the experimental situations. These theoretical considerations are found to correlate very well with experimental results for the transmission of picosecond and nanosecond laser pulses through the nonlinear fiber. Our analyses show that in the picosecond regime, nonlinear photonic absorptions are efficient optical-limiting processes, whereas in the nanosecond regime, thermal–density effects are the dominant contributor. We also identify a particular nonlinear core liquid that gives very low optical-limiting thresholds and clamped transmission for picosecond as well as nanosecond laser pulses.

Metal particles produced by laser ablation for ICP–MS measurements

Rhodopsin is a biomarker for the function of rod photoreceptors, the dysfunction of which is related to many blinding diseases like retinitis pigmentosa and age-related macular degeneration. Imaging rhodopsin quantitatively may provide a powerful clinical tool for diagnosis of these diseases. To map rhodopsin distribution accurately in the retina, absorption by rhodopsin intermediates need to be minimized. We developed nano-second pulsed scanning laser ophthalmoscopy (SLO) to image rhodopsin distribution in the retina. The system takes advantage of the light-induced shift of rhodopsin absorption spectra, which in turn affects the fundus spectral reflection before and after photo-bleaching. By imaging the retina twice, one in the dark-adapted state and the other one in the light-adapted state, the rhodopsin absorption change can be calculated from the differential image, which is a function of the rhodopsin concentration in the rod photoreceptors. The system was successfully applied to in vivo imaging of rat retina in different bleaching conditions to verify its feasibility. Our studies showed that the differential image between the dark- and light-adapted states represents rhodopsin distribution in the retina. We also conducted a dynamic bleaching experiment to prove the importance of reducing light absorption of rhodopsin intermediates. The preliminary results showed that our nano-second pulsed-light SLO is promising in imaging the functional biomarker of the rod photoreceptors. By using nanosecond pulsed laser, in which one laser pulse generates one pixel of the image, the absorption of rhodopsin intermediates can be reduced.

Laser photoionization of triacetone triperoxide (TATP) by femtosecond and nanosecond laser pulses

The upscaling of perovskite solar cells to modules requires the patterning of the layer stack in individual cells that are monolithically interconnected in series. This interconnection scheme is composed of three lines, P1–P3, which are scribed using a pulsed laser beam. The P3 scribe is intended to isolate the back contact layer of neighboring cells, but is often affected by undesired effects such as back contact delamination, flaking, and poor electrical isolation. Herein, the influence of the laser pulse duration on the electrical and compositional properties of P3 scribe lines is investigated. The results show that both nanosecond and picosecond laser pulses are suitable for P3 patterning, with the nanosecond pulses leading to a higher open circuit voltage, a higher fill factor, and a higher power conversion efficiency. It is found that the longer pulse duration resultes in a larger amount of PbI2 formed within the P3 line and a thin Br‐rich interfacial layer which both effectively passivate defects at the scribe line edges and block charge carrier in its vicinity. Thus, nanosecond laser pulses are preferable for P3 patterning as they promote the formation of beneficial chemical phases, resulting in an improved photovoltaic performance.

Multiphoton ionization mass spectrometry of small biomolecules with nanosecond and femtosecond laser pulses

Morphology and topography of perovskite solar cell films ablated and scribed with short and ultrashort laser pulses

We report on a novel organic chromophore with symmetric twistedintramolecular charge transfer (TICT) state on excitation. Theproperties of nonlinear transmission induced by three-photon absorption(3 PA) are demonstrated pumped with nanosecond laser pulse. Large 3 PAcross sections as high as the order of 10−74 cm6s2 havebeen obtained for nanosecond and picosecond laser pulses at 1064 nmfrom intensity-dependent transmission measurements. Similar two emissivebehaviours from one-photon and three-photon excited fluorescence spectraindicate that the linear and nonlinear fluorescences share the same TICTrelaxation process from the excited states. The intensity dependence ofupconversion fluorescence on the incident intensity obeys the cubic lawthat characterizes the three-photon absorption.

Through-silicon via (TSV) is an emerging technology for three-dimensional integrated circuit, system in package, and wafer level packaging applications. In this study, a wet chemical etching (WCE) process has been employed to enhance the sidewall quality of TSVs fabricated using nanosecond (ns) laser pulses. Experimental results show that the TSV sidewall roughness can be markedly reduced, from micrometer scale to nanometer scale. We concluded that the proposed method would enable semiconductor manufactures to use ns laser drilling for industrial TSV fabrication as the desired TSV sidewall quality can be achieved by incorporating the WCE process, which is suitable for mass production.

A photoelectron imaging study of the gas-phase dianion of pyrromethene-556 is presented. The photoelectron spectra and angular distributions following resonant excitation of the S1 excited state with nanosecond and femtosecond laser pulses are compared, and the influence of the repulsive Coulomb barrier (RCB) in both cases evaluated. Photoelectron angular distributions show the effect of molecular alignment due to an allowed electronic excitation and can be understood qualitatively based on the calculated RCB surface using the Local Static Approximation. Comparison between femtosecond and nanosecond excitation reveals marked differences in the photoelectron spectra. While femtosecond experiments confirm that tunneling through the RCB is adiabatic, nanosecond experiments show a broad photoelectron feature peaking near the RCB maximum. This is explained in terms of the lifetime of internal conversion, which has been determined by time-resolved photoelectron spectroscopy to be ~120 ps: as this is faster than the nanosecond laser pulses, multiple photons can be absorbed through the S1 ← S0 transition which leads to large amounts of internal energy and enables electron detachment directly above the RCB. Fragmentation and detachment from the monoanion are also inferred by the presence of photoelectrons emitted at very low kinetic energy. Our results highlight the difficulty in interpreting photoelectron spectra of polyanions in which a resonant state is excited.

Nanosecond and femtosecond laser pulses were combined in an orthogonal preablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS) configuration. Even without full optimization of interpulse alignment, ablation focus, large signal, signal-to-noise ratio, and signal-to-background ratio enhancements were observed for both copper and aluminum targets. Despite the preliminary nature of this study, these results have significant implications in the attempt to explain the sources of dual-pulse LIBS enhancements.

We present results on laser-assisted formation of two- and three-dimensional structures comprised of gold nanoparticles in glass. The sample material was gold-ion-doped borosilicate glass prepared by conventional melt quenching. The nanoparticle growth technique consisted of two steps – laser-induced defect formation and annealing. The first step was realized by irradiating the glass by nanosecond and femtosecond laser pulses over a wide range of fluences and number of applied pulses. The irradiation by nanosecond laser pulses (emitted by a Nd:YAG laser system) induced defect formation, expressed by brown coloration of the glass sample, only at a wavelength of 266 nm. At 355, 532 and 1064 nm, no coloration of the sample was observed. The femtosecond laser irradiation at 800 nm also induced defects, again observed as brown coloration. The absorbance spectra indicated that this coloration was related to the formation of oxygen deficiency defects. After annealing, the color of the irradiated areas changed to pink, with a corresponding well-defined peak in the absorbance spectrum. We relate this effect to the formation of gold nanoparticles with optical properties defined by plasmon excitation. Their presence was confirmed by high-resolution TEM analysis. No nanoparticle formation was observed in the samples irradiated by nanosecond pulses at 355, 532 and 1064 nm. The optical properties of the irradiated areas were found to depend on the laser processing parameters; these properties were studied based on Mie theory, which was also used to correlate the experimental optical spectra and the characteristics of the nanoparticles formed. We also discuss the influence of the processing conditions on the characteristics of the particles formed and the mechanism of their formation and demonstrate the fabrication of structures composed of nanoparticles inside the glass sample. This technique can be used for the preparation of 3D nanoparticle systems embedded in transparent materials with potential applications in the design of new optical components, such as metamaterials and in plasmonics.

Laser cleaning of manmade contaminants from stone samples have been performed experimentally using picosecond (ps) and nanosecond (ns) laser pulses. Regarding the surface roughness after laser cleaning, optimal cleaning parameters using ps laser have been obtained. Discoloration effect induced by ns laser cleaning of stone sample is improved with the usage of ps laser. The comparison on the roughness and elemental analysis of the cleaned area in the experiment also demonstrates the advantages and effectiveness of ps laser cleaning of stone samples.

Characteristic properties of heating monocrystalline semiconductors by nanosecond laser pulses