Characterization of inhomogeneous transparent thin films on transparent substrates by spectroscopic ellipsometry: refractive indices n(λ) of some fluoride coating materials.

By incorporation of an achromatic three-reflection quarterwave retarder to a spectroscopic ellipsometer and application of appropriate calibration and error correction procedures, it has been possible to characterize real thin-film fluoride optical coatings that are inhomogeneous. The refractive index and its dispersion with wavelengths greater than 300-700 nm as well as the depth profile of voids in the film have been determined for AlF(3), CeF(3), HfF(4), LaF(3), ScF(3) and YF(3) films on vitreous silica substrates.

Determination of the optical function n(λ) of vitreous silica by spectroscopic ellipsometry with an achromatic compensator.

Studies of dielectric materials by rotating-element spectroscopic ellipsometry (SE) are beset with a number of problems such as (1) low reflectance and hence low signal-to-noise ratio and (2) an almost zero (or 1800) change in the ellipsometric parameter A on reflection from the sample, which leads to significant errors in the measured parameters. These difficulties were overcome (1) by developing suitable procedures for correcting nonlinearity in the detection system and the deleterious effects of ambient light and (2) by incorporating an achromatic quarter-wave compensator in the SE system, respectively. A new rapid method of aligning and calibrating the compensator has also been developed. Test measurements with such an SE system on a vitreous silica sample revealed that the accuracy of measurements of Δ and Ψ are 0.03° and 0.015°, respectively, over the spectral range of 300-700 nm. The SE data were then analyzed by standard procedures with linear regression analysis to determine the optical function n(λ) (i.e., refractive index and its dispersion with wavelength) of vitreous silica and at the same time to characterize the microroughness of the surface layer of the sample. The refractive index of vitreous silica determined by this technique is within ±0.0004 of the best reported values in the literature over the spectral range of 300-700 nm. The SE data obtained on the vitreous silica sample revealed the presence of a 1.0-nm-thick microrough layer on the surface of the sample.

Determination of the optical constants of an inhomogeneous transparent LaF(3) thin film on a transparent substrate by spectroscopic ellipsometry.

The optical constants of a thin inhomogeneous transparent film of LaF(3) on a transparent vitreous silica substrate have been determined by spectroscopic ellipsometry. To overcome the lack of accuracy in the spectroscopic-ellipsometry measurements of transparent samples, an achromatic compensator was used with a rotating-analyzer ellipsometer. As a result, we were able to determine the depth profile of the film and also determine the refractive index of LaF(3) and its dispersion in the near-UV-visible region to the third decimal place, even though the film thickness was only lambda/4 ( 150 nm).

Optical characterization of a four-medium thin film structure by real time spectroscopic ellipsometry: amorphous carbon on tantalum.

A real time spectroscopic ellipsometry (RTSE) investigation is reported for comprehensive optical characterization of a thin film/substrate system, vacuum-deposited hydrogenated amorphous (diamondlike) carbon on tantalum. Precision RTSE measurements were carried out from 1.6 to 4.0 eV with a time resolution of 3 s and a repetition period of 15 s. Spectra collected during substrate exposure to an Ar(+) beam identify processing conditions for optimum precleaning and provide the bulk dielectric function of the Ta. Spectra collected during alpha-C:H growth to approximately 1700 A by ion beam deposition are best interpreted with a four-medium model (Ta/interface/alpha-C:H/ambient). From the analysis, we deduce the bulk dielectric function for alpha-C:H and an approximate dielectric function for the interface layer, interpreted as a carbide. The time evolution of the bulk and interface layer thicknesses is also determined. The dielectric functions of alpha-C:H deduced assuming a four-medium model and a three-medium model which neglects the interface layer differ by as much as 5%. The capabilities of measurement and analysis reported here represent a major new advance in the optical characterization of thin films.

Temperature dependence of optical constants of MoS(2) for pyrooptical devices.

The temperature sensitivity of the reflectance of MoS(2) under small temperature modulations has been investigated.It is feasible to detect temperature changes of 10(-2) degrees C by monitoring the reflectance, and thus MoS(2) is a potential candidate material for the pyrooptical sensors.

Simultaneous determination of refractive index, its dispersion and depth-profile of magnesium oxide thin film by spectroscopic ellipsometry.

A new method of using the spectroscopic ellipsometry technique to determine (a) the true (or bulk) refractive index of the film material, (b) the dispersion of the above refractive index with wavelength, (c) the thickness of the film, and (d) the distribution of the voids in the film is presented.

Nondestructive depth profiling of ZnS and MgO films by spectroscopic ellipsometry.

Spectroscopic ellipsometric (SE) measurements followed by linear-regression analysis of the SE data obtained on ZnS and MgO films on vitreous silica substrates reveal the distribution of voids (or low-density regions) in these transparent thin films.

Speckle photography of lateral sinusoidal vibrations: error due to varying halo intensity.

The effect of varying halo intensity in speckle photography of lateral sinusoidal vibration using Young's fringes is discussed. An interesting new result is found that, for nonunity contrast or visibility, the relative fringe shift (or the error) for minima is always minimum for the lower-order fringes. Also the error in the fringe maxima position is lowest generally at intermediate fringe orders. However, as the visibility reduces the trend becomes similar to that for the case of minima. For maxima and minima both, the error is less for larger amplitude vibrations and higher visibility.

Direct observation of laser speckles for real-time analysis of lateral motions.

A method for real-time observation of speckle movement for the analysis of lateral motions is suggested. The method involves significant magnification using lenses and a TV-camera monitor system. This approach has the advantages of conventional speckle photography without the need for any chemical processing.

Laser speckle photography for supersensitive dial gauge.

Using laser speckle photography to measure displacement of the needle of a dial gauge can significantly increase the lower measurement range. Experimental results are presented, and the measurement range is discussed.