Monolithic and In-Line Method for the Measurement of Time-Dependent Polarization of Ultrashort Pulses

Many recent applications of vector pulses require the characterization of time-dependent polarization of ultrashort laser pulses. For a precise measurement, the relative phase between the vector components is crucial. We propose a monolithic, in-line, single-channel interferometer setup, which allows the full determination of the time-evolving polarization state of the pulse, retrieving with precision the relative phase thanks to its great stability (~10^-3 λ). This is possible due to the use of a birefringent material (3-mm calcite) to delay the x- and y-components of the pulse (Fig. 1a). A linear polarizer (LP) is used to measure three projections with a spectrometer: 0° and 90° for the spectral amplitude of the x- and y-components, respectively, and 45° for the spectral interferences of the delayed components. By analysing the latter using Fourier-transform filtering, it is possible to retrieve the full relative phase (including constant term).