Effect Of Laser Cleaning Research Articles

Some applications of SIMS in conservation science, archaeometry and cosmochemistry

Some applications of SIMS in conservation science, archaeometry and cosmochemistry are described. Ultra-low energy SIMS depth profiling and TOF-SIMS imaging are used to study the corrosion of low-lime glass vessels from the V&A museum. Static SIMS and focused ion beam (FIB) SIMS are used to study the effects of laser cleaning on museum artefacts. Archaeological glass from Raqqa, Syria is studied with FIB-SIMS and micrometeorite impacts on space vessels are studied with FIB and FIB-SIMS. The new analytical challenges provided to the SIMS community by these materials are presented and the ethical issues associated with sampling and destructive analysis discussed.

Design, construction and performance of all niobium superconducting radio frequency electron gun

Over the past several years Advanced Energy Systems, BNL, and JLab have been collaborating on the development and testing of a fully superconducting, all-niobium RF gun driven by a laser. This paper will review the simulations, design of the gun, and present results of its performance under various operating conditions. Cavity Q of 10 8 at 4 K and QE of 10 −5 at 248 nm, charge up to 0.3 nC/RF cycle and 5 nC in 12 ns have been obtained. Even at these large charges, no effects of cavity quenching have been observed. Measurements of the cavity quality factor at various operating temperatures and quantum efficiency of Nb at superconducting temperature at various cavity field gradients, laser wavelengths and laser powers are presented. Effects of laser cleaning of the cathode and future tests using this gun will also be discussed.

Microfocus X-ray Diffraction of Historical Parchment Reveals Variations in Structural Features through Parchment Cross Sections

We propose a new method of investigating variation of preservation within a parchment sample, which allows a more detailed analysis of alteration of the material structure. X-ray diffraction analysis of parchment typically involves the sample aligned with the plane of the parchment perpendicular to the direction of the X-ray beam, with a beam size of approximately 200 μm and an image consisting of the composite diffraction features from the entire thickness of the sample. Here we describe the use of microfocus X-ray beams, with a beam size of 1.5 μm vertically × 15 μm horizontally, to carry out surface-to-surface scans of thin sections of parchment. Up to 200 images can be taken in a single cross-sectional scan of a 300 μm thick parchment section. This allows for X-ray diffraction analysis of features present only in specific areas of the parchment, such as at the surface. The orientation of collagen fibrils in the plane of the parchment, the effects of laser cleaning (including possible laser induced damage), mineral phases and crystalline lipids present in samples, and parchment structure under an inked region are investigated. It is shown that the long collagen fibril axis lies parallel to the parchment surface throughout the sections. Laser cleaning appears not to damage the collagen in parchment, while laser-damaged samples display gelatinization of the collagen at the surface. Polymorphs of calcium carbonate were detected in several samples but in most cases were not confined to the surfaces, as would be expected if the chalk finishing process was the main source of mineral phases in parchment. Crystalline lipid is found in most samples and appears to exhibit a preferential alignment with the plane of the phospholipid bilayer arranged parallel to the long fibril axis of collagen. The d spacing of the lipid is variable throughout a parchment section, indicating fluctuations in the hydration state, phase, or biochemical composition of the lipid. Ink affects the parchment to a depth of approximately 90 μm, as measured by principal components analysis, disrupting the structure of the collagen to this depth. These features demonstrate the ability of this technique to examine diagenesis of individual components of parchment on a scale not previously studied.

Laser cleaning of parchment: structural, thermal and biochemical studies into the effect of wavelength and fluence

Laser cleaning of parchment is a novel technique that has the potential to provide contactless, chemical-free cleaning of historically important documents. However, the effect of laser cleaning on the collagenous structure of parchment is still poorly understood, as is the effect of the wavelength or the energy density (fluence level) used to clean parchment. In this study, small angle X-ray scattering (SAXS), shrinkage temperature (Ts) measurements by the micro hot table technique and SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of parchment samples after laser cleaning reveal the effect of cleaning to the structural, thermal and molecular characteristics of parchment, respectively. The effect of cleaning at infrared (1064nm), green (532nm) and ultraviolet (266nm) wavelengths at a range of fluence levels is investigated. SAXS is used to investigate the removal of dirt from parchment. Laser cleaning at IR or green wavelengths appears not to alter the collagen diffraction pattern from SAXS, the shrinkage activity or shrinkage temperature from Ts measurements or the molecular integrity of parchment as shown by SDS-PAGE. However, parchments cleaned at the ultraviolet wavelength display structural damage and a reduction in hydrothermal stability and molecular integrity.

Effectiveness of Laser Cleaning for Grinding Wheel Loading

A new method for cleaning loaded grinding wheels is introduced by applying CO2 laser irradiation on the wheel surface. It demonstrates that effective cleaning can be achieved by the selection of adequate laser power flux and suitable irradiation duration. Fusion and evaporation of clogged chips play an important role in the laser cleaning process. It is suggested that high laser power irradiance and short irradiation duration are essential for effective wheel cleaning.

Spectroscopic Analysis of Pigments and Binding Media of Polychromes by the Combination of Optical Laser-Based and Vibrational Techniques

Four spectroscopic techniques, Fourier transform Raman (FTR), Fourier transform infrared (FT-IR), laser-induced breakdown spectroscopy (LIBS), and laser-induced fluorescence (LIF), are employed to characterize the pigment and binding media composition of polychromes. Raman spectra allow the assignment of the main pigments; these are α-HgS (vermilion), 2PbCO3·Pb(OH)2 (lead white), As2S3 (orpiment), Pb3O4 (lead red), and amorphous Carbon. The IR spectra can readily identify the pigment 2PbCO3·Pb(OH)2, the binder CaSO4·2H2O (gypsum) and, in combination with the Raman results, the presence of organic constituents of the binding media such as aliphatic esters, free acids, carbohydrates, and amides. The elemental analysis provided by LIBS corresponds to the pigments identified by the previous techniques and shows in addition the presence of some Hg, Fe, and Pb containing components. The presence of a Hg derivative in some of the sampled areas is supported by the LIF analysis; the fluorescence spectrum is mainly assigned to the binding media with the spectral intensity and shape modified to some extent by the contribution of pigments. In some of the samples studied, a peak assigned to α-HgS is observed. The effect of low intensity KrF laser irradiation of the samples is examined; the combined observations point toward a laser cleaning effect except in the areas that contain the pigment 2PbCO3·Pb(OH)2.

Determination of damage thresholds to prevent side effects in laser cleaning of pliocene sandstone of Siena

The present work reports a basic investigation aimed at optimizing laser cleaning interventions on pliocene sandstone of Siena. Irradiation trials were performed with a short free running Nd:YAG laser, on quarry samples and on samples from Palazzo Spannocchi presenting black crust. The physical parameterization associated with a detailed petrographic and mineralogic diagnostics of the induced effects, allowed the irradiation thresholds for damage phenomena to be derived and their nature understood. The experimental results reported here allow the definition of the best irradiation conditions and the laser parameter ranges for a safe and controlled black crust removal from pliocene sandstone.

Sputtered magnesium as a photocathode material for rf injectors

In this article, we report the investigation of sputtered magnesium as a suitable photoelectron emitter in a rf injector. The measurements were conducted on a 20 μm thick Mg layer, ion sputtered on a copper substrate. UV laser induced damage threshold measurements on this sample indicate that laser energy densities of up to 100 μJ/mm2 at 266 nm, the irradiated surface is indistinguishable from the unirradiated surface. For laser energy densities in the range of 100–300 μJ/mm2, slight roughening of the surface was evident. At 600 μJ/mm2, damage is visible, with the depth estimated to be ∼1 μm. This damage threshold is six times larger than that of the bulk magnesium and approaches that of copper. Systematic laser cleaning has improved the quantum efficiency of the surface from 2×10−5 to 2×10−3. This combination of high quantum efficiency and high damage threshold of sputtered magnesium produces a record current density of 25 kA/mm2 for a metal cathode. The effect of laser cleaning on sputtered Mg, the sample preparation technique for reliable performance, and the parametric dependence of quantum efficiency are reported as well.

Laser cleaning of surface contaminants

Laser cleaning effect can be produced on a surface using pulsed laser irradiation, with pulse duration typically 1 to 100 ns, fluence typically tens to hundreds of mJ/cm 2, and wavelengths typically in the 200 to 300 nm range. A thin liquid film can be used to enhance the removal efficiency of small particulates; this is called `steam laser cleaning'. A manufacturing-worthy tool that can provide both steam laser cleaning as well as dry laser cleaning is built and tested successfully. The basic mechanism of steam laser cleaning is studied.

A practical excimer laser-based cleaning tool for removal of surface contaminants

A laser-cleaning tool capable of removing surface contaminants such as submicron-sized particulates and organic films has been constructed and implemented in practical use. An industrial-grade KrF excimer laser is utilized to irradiate the solid surface to be cleaned. The nanosecond-pulsed laser irradiation, shortly after the deposition of a thin liquid film on the surface, induces explosive vaporization of the liquid and removal of particulates (steam cleaning). The ultraviolet (UV) irradiation also causes ablative photodecomposition of organic film contaminants on the surface (dry cleaning). Hence, cleaning can best be done with the combination of these two laser-cleaning modes. The excimer laser cleaning tool is constructed with an aim toward practical use: It includes a computer-controlled laser beam scanning system and a stable liquid film deposition unit, providing a cleaning rate of over 200 cm /min. Semiconductor, metal, and ceramic sample surfaces, contaminated with 1-/spl mu/m sized alumina particles and micron-thick epoxy films, are tested by laser cleaning. The effectiveness of laser cleaning is compared with ultrasonic technique. The cleaning strategy and the probability of thermal damage due to laser cleaning are discussed. >

Appearance of opacity and damage of optical materials by carbon dioxide laser pulses

The thresholds of the appearance of opacity and damage in the bulk and on the surface of some materials used in the infrared range were determined. A laser cleaning effect was observed for materials whose surface optical strength exceeded the breakdown threshold of air near the surface. This made it possible to raise the opacity threshold to the bulk damage threshold. The opacity threshold of such a cleaned surface fell as a result of adsorption of contaminants from air.

Investigation of the optical strength of gold coatings

An investigation was made of the influence of the substrate material, coating thickness, and conditions during evaporation and annealing on the optical strength of gold coatings illuminated with CO2 laser pulses (interaction time ~ 100 nsec). It was found to be possible to prepare gold coatings whose optical strength was comparable with those of bulk metallic mirrors. Breakdown at the surface of a mirror could occur without causing any damage. Laser cleaning effect was also observed.