I'm an undergraduate student currently going on a project to build a simple and basic ellipsometry.
After thorough research from papers, I found that most of the light source used is a HeNe laser, or a Xenon lamp. I tried to find the reason for that, but I just can't find one.
Can anyone explain how is noble gases laser are more preferred in ellipsometry than the cheaper ones like the LED lasers used for pointer ? As far as I'm reading the datasheets, I can only find that the important determining factor of a laser is the wavelength, its power spectrum, and its power.
Why does some lasers work best in ellipsometry and why isn't there anyone using LED laser as light source?
Thanks
The choice of a light source stems from, among other things, a need for a long lasting, stable, high flux and well characterized source. Since the ellipsometric parameters Delta and Psi, and hence polarization state, are functions of wavelength along with material properties, it is preferred that the wavelength of light be known and stable. In the case of monochromatic ellipsometers an additional degree of accuracy can be afforded if the FWHM of the source spectrum is as small as possible. In the case of LEDs, you will find that the FWHM value far exceeds this by several orders of magnitude. If you have the facilities, I would encourage you to do the experiment. Using a decent spectrometer, scan xenon, LED and laser light sources and compare their spectra.
A. Kramer
I might be able to do the experiment. I'm just getting a little confused with the physics in ellipsometry so I can't really get what the wavelength of the laser is for.
So it all comes down to the stability of the wavelength, right?
Thanks, Alan Kramer.
As is the case with a lot of applied physics, the road to understanding the relations between experiment and model is quite long. A good start is through a text on modern optics like the one Guenther produced. From that, along with a few diversions, "Ellipsometry and Polarized Light" by Azzam and Bashara.
Good luck,
Alan
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