Optical window geometry

In the earliest SFG experiments [Tadjeddine, 2000 Guyot-Sionnest et al., 1987 Hunt et al., 1987 Zhu et al., 1987], a first-generation data acquisition method was used, and, because of the limited signal-to-noise ratios, IR attenuation by the electrolyte solution was a substantial handicap. So, in earlier SFG studies, as in IRAS studies, measurements were performed with the electrode pressed directly against the optical window [Baldelli et al., 1999 Dederichs et al., 2000]. With the in-contact geometry, the electrolyte was a thin film of uncertain and variable depth, probably of the order of 1 p.m. However, the thin nonuniform electrolyte layers can strongly distort the potential/coverage relationship and hinder the ability to study fast kinetics. 

The electrochemical cell used in our laboratory has been fully described elsewhere (5). The cell body is made of chemically inert Kel-F and the electrode is mounted on a piston so that its surface can be pushed to the optical window, to a spacing of the order of 1-3 microns, in order to minimize the signal from the bulk electrolyte. For Raman scattering spectroscopy the window is of flat fused quartz, and the exciting laser beam is incident at about 60°. The scattered light is collected off-normal, but the geometry is not critical for SERS due to the high sensitivity. Details on the SERS measurements in our laboratory have been reported previously (6,7). 

DLC coatings are already in production in several areas (optical and IR windows) and appear particularly well-suited for abrasion and wear applications due to their high hardness and low coefficient of friction. They have an extremely smooth surface and can be deposited with little restriction of geometry and size (as opposed to CVD diamond). These are important advantages and DLC coatings will compete actively with existing hard coatings, such as titanium carbide, titanium nitride, and other thin film... 

X is, due to the plane-parallel geometry of the sample cell, the wavelength of light in air. With a plane-parallel geometry of the sample cell and the optical axis perpendicular to the windows, the refractive index n of the sample does not appear in Eq. (9), since, according to Snell s law,... 

The 4Ii3/2 - 4Iis/2 infrared emission band of Er3+ ions in fluorozirconate glass is displayed in Fig. 11. The band maximum is located at 1.53 /an and the width at half-maximum is as broad as 60 nm, which favors the use of this transition for optical amplification in the third telecommunication window. In bulk geometry, 1.6 jtm CW-laser action is reported for a Cr, Yb, Er-codoped fluoroaluminate glass slab pumped by a krypton laser [114],... 

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