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キーワード:
Physics, Optics, physics.optics
要旨:
Much work over the last 25 years has demonstrated that the
interface-specific, alloptical technique, vibrational sum frequency generation
(v-SFG) spectroscopy, is often uniquely capable of characterizing the structure
and dynamics of interfacial species. The desired information in such a
measurement is the complex second order susceptibility which gives rise to the
nonlinear response from interfacial molecules. The ability to detect molecular
species yielding only small contributions to the susceptibility is meanwhile
limited by the precision by which the spectral phase and amplitude can be
determined. In this study we describe a new spectrometer design that offers
unprecedented phase and amplitude accuracy while significantly improving the
sensitivity of the technique. Combining a full collinear beam geometry with a
technique enabling the simultaneous measurement of the complex sample and
reference spectrum, uncertainties in the reference phase and amplitude are
shown to be greatly reduced. Furthermore, we show that using balanced
detection, the signal to noise ratio can be increased by one order of
magnitude. The capabilities of the spectrometer are demonstrated by the
isolation of a small isotropic surface signal from the bulk dominated nonlinear
optical response of z-cut quartz. The achieved precision of our spectrometer
enables measurements not currently feasible in v-SFG spectroscopy.
