Silica Prism Research Articles

Contrasting damage characteristics in direct incidence and surface plasmon mediated single-shot laser ablation of aluminium films

Thin, oxidised Al films grown on one face of fused silica prisms are exposed, under ambient conditions, to single shots from an excimer laser operating at wavelength 248 nm. Preliminary characterisation of the films using attenuated total reflection yields optical and thickness data for the Al and Al oxide layers; this step facilitates the subsequent, accurate tuning of the excimer laser pulse to the surface plasmon resonance at the Al/(oxide)/air interface and the calculation of the fluence actually absorbed by the thin film system. Ablation damage is characterised using scanning electron, and atomic force microscopy. When the laser pulse is incident, through the prism, on the sample at less than critical angle, the damage features are molten in nature with small islands of sub-micrometer dimension much in evidence; a mechanism of film melt-through and subsequent blow-off due to the build up of vapour pressure at the substrate/film interface is appropriate. By contrast, when the optical input is surface plasmon mediated, predominately mechanical damage results with the film fragmenting into large flakes of dimensions on the order of 10 μm. It is suggested that the ability of surface plasmons to transport energy leads to enhanced, preferential absorption of energy at defect sites causing stress throughout the film which exceeds the ultimate tensile stress for the film; this in turn leads to film break-up before melting can onset.

The optical dielectric function of amorphous carbon films

Amorphous carbon, deposited as a thin film (∼47 nm thick) on a silica prism, has been characterised, for the first time over a range of wavelengths, using attenuated total internal reflection. By measuring angular dependent reflectivities from the prism-carbon interface in the region of the critical angle with subsequent fitting of the data to Fresnel theory, both the real and imaginary parts of the dielectric function are obtained. The wavelength dependence of these two variables has thereby been established between 450 and 840 nm. Extension of this range for the imaginary component to 200 nm, by optical absorption measurements, has allowed discrimination between two different models describing the electron states at the band edge in this material.

THE HIGH-RESOLUTION CROSS-DISPERSED ECHELLE WHITE PUPIL SPECTROMETER OF THE MCDONALD OBSERVATORY 2.7-M TELESCOPE

ABSTRACT A new high-resolution cross-dispersed echelle spectrometer has been installed at the coude focus of the McDonald Observatory 2.7-m telescope. Its primary goal was to simultaneously gather spectra over as much of the spectral range 3400A to 1 micron as practical, at a resolution R = lambda/delta-lambda ≃ 60,000 with signal-to-noise ratio of ~100 for stars down to magnitude 11, using 1-hour exposures. In the instrument as built, two exposures are all that are needed to cover the full range. Featuring a white-pupil design, fused silica prism ross disperser, and folded Schmidt camera with a Tektronix 2048 X 2048 CCD used at either of two foci, it has been in regularly-scheduled operation since April 1992. Design details and performance will be described.

Surface Plasmon Enhanced Laser Ablation of Thin Metal Films

Abstract Surface plasmon enhancement of laser ablation of thin Al films is examined with a view to its application in metal film patterning and nano-structuring. Al films, deposited on silica prisms, are first characterized by attenuated total reflection using a broadband UV source and appropriate interference filter. The films are subsequently subjected to excimer laser radiation of wavelength 248 nm under conditions both of direct incidence from the air side of the film, and of surface plasmon excitation in which light is incident through the prism at greater than critical angle. For a given level of ablation damage in a particular film the fluence required using the surface plasmon technique is 3–5 times less than that needed when direct incidence is used. This is roughly in line with the energy absorbed in the film. From a practical standpoint it is clear that ablation of metal films can be achieved with much lower fluences than has hitherto been possible, thus reducing the requirements on laser output and relaxing the power handling constraints on any input optical elements.

Nonuniformity in void concentration between the initial and final growth stage of sputtered a-Ge films studied using spectroscopic ellipsometry.

In this study $a$-Ge films were sputtered onto 60\ifmmode^\circ\else\textdegree\fi{} vitreous silica prisms. The films were examined by spectroscopic ellipsometry at the prism-film and air-film interfaces. The void fraction was found to be significantly different near these two interfaces for an rf-sputtered film but almost the same for a dc-magnetron-sputtered film. This difference between depositions is related to a higher degree of energetic particle bombardment in the latter case. Previous studies of the thickness dependence of void fraction in the film were done on different films of various thickness, while the present measurements were performed on the same film and thus directly verify the nonuniformity in the void concentration in rf-sputtered films.

Light Guide Systems for the Ultraviolet Region of the Spectrum

AbstractWhereas diverse and highly refined fiber optics have long been in technical use for the conduction of visible light, traditional but expensive silica glass lenses and prisms have had to be utilized until quite recently for the transmission of ultraviolet light. The reason for this was the lack of suitable materials. UV light cannot be transported to any technically useful extent either with pure glass‐glass (core and sheath materials) light guides or with plastic‐plastic light guides. UV light guides for wavelengths down to 200 nm can be produced by combination of a silica glass as the core material with a tetrafluoroethylene‐hexafluoropro pylene copolymer or methylpolysiloxane as the sheath material. Fiber optics of this type constitute a new aid for medical technology, medicine, and many technical and scientific fields, whose range of applications cannot yet be fully envisaged.

Infra-red Spectra of Polar Molecules adsorbed on Titanium Dioxide Pigments

WE have examined the mechanism of adsorption from solution in benzene of some organic molecules on titanium dioxide pigments. Pigments were allowed to come to equilibrium in 0.015–0.030 M solutions in benzene of the compounds. The pigment was filtered off, under reduced pressure, and made into self-supporting disks; their infrared spectra were measured at 30° C with a Unicam SP100 spectrophotometer, using a rock-salt prism-grating double monochromator (1,000–3,650 cm−1) and a silica prism (3,600–3,800 cm−1). Compensation for scatter by the sample was achieved by placing either metal gauzes or blank pigment disks in the reference beam.

Compensation of Inhomogeneity in Polishing Fused Silica Prisms

An experiment is attempted to improve the resolution of a Littrow type spectrograph. It is ascertained that inhomogeneity of fused silica can be compensated successfully by local polishing of the surfaces of prisms, except for those which have very complex inhomogeneity.

Calibration of prism spectrometers in the ultraviolet, visible and near-infrared regions

Emission line spectra of the elements Hg, Cd, Zn, He, Ne and Rb were used in the development of a precise and comprehensive calibration procedure for the fused silica and DF-2 glass prisms covering the range 0.194 μ < λ< 2.33 μ and 0.365 μ < λ < 2.33 μ, respectively. Spectrograms of the emission lines are presented together with experimental conditions necessary to reproduce them, the photon energy and vacuum wavelength of each identified line, as well as other pertinent information. Since the emission lines are very narrow and their wavelength values are accurately known, the precision of the method is determined only by the experimental uncertainty in obtaining the corresponding spectrometer drum readings. Data are reported for 233 lines observed with the fused silica prism and for 341 lines with the DF-2 glass prism. The observations were made with a Perkin-Elmer Model 13-U single-pass spectrometer using Osram spectral lamps. The detectors used were the RCA photomultiplier type 7200 for the ultraviolet and visible regions, the type 1P21 for the visible region (in which it has a better S N ratio than the 7200), and the PbS photoconductive detector for the near infrared. A discussion of experimental aspects is presented including details on spectrometer arrangements and problems of technique. In addition, a procedure was developed to provide a definitive and precise method for plotting the final calibration curves in terms of photon energy versus spectrometer drum reading, based on a modification and extension of the empirical relationship of McKinney and Friedel. A detailed description of the adaptation and the application of this procedure is given, together with the modified equation and typical values of its constants pertinent to each prism.

Three New Spectrophotometers

Spectrophotometers are being used more frequently and for more applications in industrial and research laboratories. Therefore it becomes more important to build various spectrophotometers for specialized applications. This presentation describes three new commercial spectrophotometers, an interference filter colorimeter (range 400 to 700 mμ), a prism spectrophotometer (range 300 to 750 mμ) and a silica prism – glass prism – grating spectrophotometer (range 210 to 5000 mμ).

Synthetic silica prism in the infrared : Davies, M.; J. Chem. Phys. 1950 18 398

Synthetic silica prism in the infrared : Davies, M.; J. Chem. Phys. 1950 18 398