Onam is the biggest and the most important festival of Kerala. It is a harvest festival and is celebrated with joy and enthusiam all over the state by people of all communities. According to a popular legend, the festival is celebrated to welcome King Mahabali, whose spirit is said to visit Kerala at the time of Onam...
Holmarc celebrates Onam festival every year with "Pookalam com-petition", "Onam sadhya" and other cultural programmes. This year it was celebrated on 21st Aug 2010.
First prize was awarded for the Pookalam competition to Mr.Josemon & team.
»08/ 06/2010
ELLIPSOMETER
Holmarc has recently developed an ellipsometer for thin film analysis. The same has been introduced in scientific market as a standard product from Holmarc as model number HO-ED-P06
In this issue of News and Events, we would like share the salient features of this instrument with our esteemed readers.
Principle
As all of us know, Ellipsometry is a very sensitive optical technique for thin film metrology. The main advantages of ellipsometry are its non-destructive character, high sensitivity and wide measurement range. The optical parameters like thickness
and refractive indices of a thin film can be determined precisely by this technique.
Ellipsometry makes use of the phenomena that polarization state of light changes upon reflection from a surface and this change depends on the surface characteristics. In the ellipsometer we have developed, an elliptically polarized light is made to incident on the test substrate and the reflected light which is linearly polarized is analyzed for polarization changes.
Construction and Features
The instrument consists of two concentrically rotating arms around a precisely graduated disc fixed to a heavy base. A laser source is held on one arm and the detector assembly on the other arm. The graduated disc has 1 degree scale and 0.1 degree resolution achieved through a vernier. Power supplies for laser source and detector are placed separately. Polarizer, analyzer and quarter wave plate are held in precision rotary stages in the optical path with precise graduations having 0-360 degree range and 0.1 degree resolution. Glan-Thompson Prisms are used for both polarizer and analyzer. Sample is placed on a precision micrometer driven vertical stage with height adjustment range of 10 mm and resolution 0.01 mm. Incident angle for laser source can be adjusted between 30 degree and 90 degree. For null method, detector can be replaced with a miniature screen for visual determination of null point, if required.
Procedure
As shown in the figure right, randomly polarized laser light (532nm) passes through a polarizer (Glan-Thompson Prism) which changes the polarization of light from random polarization to linear polarization. The linearly polarized light then passes through a quarter-wave plate (set the fast axis at 45 degree) which changes the polarization state from linear to elliptical. After reflection from the sample thin film, the elliptically polarized light become linearly polarized and an analyzer (Glan-Thompson Prism) measures the degree of polarization.
Software
Holmarc has developed a unique software to be used along with the instrument for analyzing the data. The software which can be loaded into any personal computer plots the Δ – ψ graph and optical constant can be determined from the plot. It can be used for finding out simple and complex refractive indices
Specifications of Optical & Mechanical Components:
1. Laser
Type = DPSS
Wavelength = 532 nm
Output Power = 5 mW
Polarization = Random
