A method and system for spectroscopic ellipsometry employing reflective optics to measure a small region of a sample by reflecting radiation (preferably broadband UV, visible, and near infrared radiation) from the region. The system preferably has an autofocus assembly and a processor programmed to determine from the measurements the thickness and/or complex refractive index of a thin film on the sample. Preferably, only reflective optics are employed along the optical path between the polarizer and analyzer, a sample beam reflects with low incidence angle from each component of the reflective optics, the beam is reflectively focused to a small, compact spot on the sample at a range of high incidence angles, and an incidence angle selection element is provided for selecting for measurement only radiation reflected from the sample at a single, selected angle (or narrow range of angles). The focusing mirror preferably has an elliptical shape to reduce off-axis aberrations in the focused beam. Some embodiments include both a spectrophotometer and an ellipsometer integrated together as a single instrument. In such instrument, the spectrophotometer and ellipsometer share a radiation source, and radiation from the source can be focused by either the spectrophotometer or the ellipsometer to the same focal point on a sample. Preferred embodiments of the ellipsometer employ a rotating, minimal-length Rochon prism as a polarizer, and include a spectrometer with an intensified photodiode array to measure reflected radiation from the sample, and a reference channel (in addition to a sample channel which detects radiation reflected from the sample).

Focused beam spectroscopic ellipsometry method and system

Radiative cooling during the day: simulations and experiments on pigmented polyethylene cover foils

Refractive index data of ZnS, ZnSe, and ZnTe were searched, compiled, and analyzed. Recommended values of refractive index for the transparent spectral region were generated in the ranges 0.5–14 μm and 93–1000 K for ZnS, 0.55–18 μm and 93–618 K for ZnSe, and 0.55–30 μm at room temperature for ZnTe. Generation of these values was based on a dispersion equation that best fits selected data sets covering wide temperature and wavelength ranges where the available experimental data permit. Temperature and wavelength derivatives of refractive index were calculated from the first derivatives of the equation with respect to temperature and wavelength, respectively. The results are in concordance with the existing data.

/pdf/refractive-index-of-zns-znse-and-znte-and-its-wavelength-and-gd17mzmt99.pdf

Refractive Index of ZnS, ZnSe, and ZnTe and Its Wavelength and Temperature Derivatives

The photoelectronic properties of high‐resistivity n‐type GaAs : Cr are quite similar to those of high‐resistivity n‐type GaAs : O described in the preceding paper. In the low‐temperature region, intrinsic photoconductivity is n type, increases exponentially with 1/T, and can be consistently described by a simple one‐level Shockley‐Read recombination model with a level lying 0.66 eV below the conduction band and a density that is remarkably constant over a variety of different materials. Two levels characteristic of the Cr doping lie at 0.86 eV below the conduction band and at 0.9 eV above the valence band. Low‐frequency photocurrent oscillations are associated with levels at 0.86 and 1.25 eV below the conduction band. The extrinsic photoconductivity at 0.86 eV is produced via two steps: (i) electrons are photoexcited from the ground state to the excited state of Cr+2 (d4) center, and (ii) they are then thermally excited to the conduction band.

Photoelectronic properties of high‐resistivity GaAs : Cr

Chalcogenide glasses transmitting in the infrared between 1 and 20 μ — a state of the art review

New high temperature infrared transmitting glasses

An apparatus designed and built to measure the infrared refractive index of an optical material as a function of wavelength and temperature is described. The values obtained for the thermal change in refractive index of a Si–As–Te glass, a Ge–Sb–Se glass, As2S2 glass, and Kodak Irtran 4 are presented. Treatment of these data and literature values for other ir optical materials from a molar refraction standpoint, were used to establish an empirical relationship for predicting unknown ΔN/ΔT°C values of new optical materials. Measured values range from +300 × 10−5/°C for covalent single crystal germanium to −235 × 10−6/°C for ionic polycrystalline KRS–5.

The thermal change in the nondispersive infrared refractive index of optical materials.

The beginning of transmission for a solid occurs at a wavel ength corresponding to the energy of its forbidden gap. The long wavel ength cut off for the solid is usually determined by a lattice or lattice type absorption of the constituent elements. These two wavelength limits are qualitatively predictable from the position of the constituent elements in the Periodic Table; that is, their atomic masses and electronic configurations. Absorption within the transmission range is usually related to impurities or the perfection of the sample and is thus related to the method of preparation.

A. Ray Hilton

Papers

New high temperature infrared transmitting glasses

The thermal change in the nondispersive infrared refractive index of optical materials.

Infrared transmitting materials

The Depth of Mechanical Damage in Gallium Arsenide

Optical Absorption in Chromium Doped, High Resistivity GaAs in the 0.6 to 1.5 ev Range