Exploitable results
In this project we have demonstrated the feasibility of a prototype ultra fast ellipsometer (UFE) based on a Zeeman two frequency laser (HeNe; 633 nm). With a time resolution of about 1 microsecond the UFE is one of the fastest ellipsometers in the world. The accuracy we achieved is a relative accuracy of 0.15 degree in the ellipsometric angles Delta and Psi at a time resolution of 1 microsecond. The ultimate capabilities of the UFE were shown in a measurement with a Pockels cell driven with a small amplitude sine wave of a 100 kHz. A 100 kHz sinusoidal response in delta and psi could be measured having an amplitude of much less than one degree. However the absolute accuracy involving a reference measurement was found to be in the order of 1 degree only, due to a phenomenon we called frequency mixing. Also a two-laser ellipsometer was developed, tested and patented in this project. In this set-up the problem of frequency mixing is avoided. Moreover a much simpler set-up is obtained with less components than the UFE, but maintaining all the advantages of the UFE. Also the time resolution can be adjusted in a very wide range. Apart from application in ellipsometers the two-laser set-up can possibly be used in optical recording having the advantage that phase differences rather than amplitude modulations are measured. In conclusion we can say that the capabilities of the UFE can only be fully appreciated in applications where its time resolution is really necessary (eg in the study of the switching of liquid crystals or magnetised materials, or even in plasma physics).
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