Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 180
6.1.2. Ellipsometry
6.1.2.1. Method and instrumentation
Refractive index measurements were performed using a Rudolph Research AutoEL R -II
automatic ellipsometer at 632.8 nm. The ellipsometer was calibrated using a Rudolph
Research standard silica sample on a silicon substrate (part no. A9291, serial no. 1772)
with a stated refractive index of 1.460; the measured index of the standard lay within
1.460 + 0.002. Samples were prepared by the same method described in section 6.1.1.1.
When a large population of measurements were made for a particular sample (e.g. 15 or
25), 3 to 5 measurements were taken at one point, and then the same number taken from
other points over the samples surface.
6.1.2.2. Theory of operation
Ellipsometry is typically used to measure the thickness and optical constants (such as n,
refractive index) of thin films. However, it can also be used to measure the refractive
index of bulk glass samples. Monochromatic light (633 nm in this study) of an angle
between 0 and 90° is reflected from the surface of a sample, and its polarisation analysed.
The change in polarisation is expressed as two functions, Ψ, which is a complex
dielectric function relating to the ellipticity of the reflected light, and ∆, which is related
to the phase of the reflected light. Equation (6.19) shows the relationship between these