ABSTRACT
The validity of effective thickness expressions for sample films used in internal reflection spectroscopy is obtained by comparing them to exact computer calculations for various refractive indices, angles of incidence, extinction coefficients, and film thicknesses.
ABSTRACT
Simple equations are given for determining both refractive index and film thickness from a measurement of interference fringe separation where the question of phase change and the order of the fringes can be disregarded. The equations are quite general, since they apply to fringe maxima or minima for either transmission or reflection and can be used for free-standing films or films on substarates of higher refractive index. Advantages of recording fringes via reflection rather than transmission are discussed. A unique attachment for commercial spectrophotometers for making measurements over a wide range of angles of incidence is described.
ABSTRACT
Several variations are given of a relatively simple thin film optical cavity construction which can be designed either to induce absorption in a weak absorber or to induce thermal emission from a weak emitter. In both cases the cavity is very selective with respect to polarization and wavelength.
Subject(s)
Congenital Abnormalities , Dermatoglyphics , Down Syndrome , Female , Humans , Male , Pregnancy , Rubella , TrisomyABSTRACT
A vertical double-pass internal reflection element for internal reflection spectroscopy is described which can be dipped into vessels containing liquids or powders to record their spectra. It has the advantage over the horizontal double-pass internal reflection element in that no additional optical components are required to reorient the spectrometer slit image. Photographs are presented of internal reflection elements showing the actual paths of the light beams outside and inside the internal reflection elements.
ABSTRACT
In internal reflection spectroscopy effective thickness is defined as the thickness of material required to give a spectrum of the same contrast in a transmission measurement as that obtained via internal reflection. Simple expressions for effective thickness are given for bulk materials and for thin films which are useful as guide lines in determining the optimum conditions required to record internal reflection spectra. Depending on angle of incidence and index of refraction, the effective thickness for bulk materials may be much greater or much less than the wavelength of light. Similarly for thin films the effective thickness may be much greater or much less than the actual thickness.
