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Phase modulation technique for eliminating phase noise in picosecond T2 measurements based on stimulated Raman gain

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2 Author(s)
De Maziere, Martine ; Physics Department, University of Antwerp (Universitaire Instelling Antwerpen), B‐2610 Wilrijk‐Antwerp, Belgium ; Schoemaker, Dirk

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The pump and probe variant of the stimulated Raman gain technique permits the measurement of picosecond dephasing times with low‐power, continuous‐wave mode‐locked lasers, but it suffers by its susceptibility to inevitable randomly induced fluctuations in the relative phases of the interacting laser fields. The resulting severe requirements on optical stability can be circumvented through application of a double‐modulation–detection scheme that we have developed. It is based on rms detection of the T2 signal as generated through application of a low‐frequency phase modulation of precise amplitude, additional to the commonly applied rf modulation with corresponding lock‐in detection. A detailed description of the method and its experimental realization is presented. T2 measurements on the 656 cm-1 vibration of liquid CS2 illustrate its performance. In comparison with previous techniques, precision is improved by about a factor of 4. But more important is the fact that the technique permits to make a continuous recording of the T2 signal, while achieving at the same time a reduction in measurement time by an order of magnitude. Furthermore, optimization of the optical setup is possible, through direct monitoring of the dephasing signal at any delay. Automating the data taking and processing should be straightforward.

Published in:

Journal of Applied Physics  (Volume:58 ,  Issue: 4 )