Measuring Ultrafast Polarization Dynamics: POLLIWOG

Abstract

It is well appreciated that by studying the phase and the amplitude of coherent ultrashort signals that are transmitted, reflected or emitted from materials during linear and nonlinear optical experiments one can obtain valuable information about the optical interactions and the fundamental processes in those material systems. Many of the signals of interest (e.g., those from four wave mixing (FWM) experiments) are very weak and require very sensitive measurement techniques. As described in previous chapters, characterization techniques [1–3] that provide both the amplitude and phase of an ultrashort pulse have been developed over the last decade, but each requires a nonlinear process. Consequently, both for practical and for fundamental reasons, they are of no use for very weak signals. Recently, in partial response to this need, a method of completely measuring the intensity and phase of an almost arbitrarily weak coherent signal has been demonstrated by performing spectral interferometry (SI) [4–9] with a well-characterized reference pulse [8,9]. The latter technique has been given the acronym TADPOLE by Fittinghoff et al. [9] and is described in some detail in the previous chapter. As described in Chapter 22, however, TADPOLE (and similar) techniques are scalar in nature. That is, they characterize the amplitude and phase of only a single polarization component.