Simultaneous recording of the spectral, temporal, and polarization properties of emission spectra

Abstract

We describe a system that records simultaneously the temporal profile of both linear polarization components of all wavelengths in an emission spectrum. Our excitation source is the vacuum ultraviolet storage ring of the National Synchrotron Light Source at Brookhaven National Laboratory, which provides a continuous spectrum of ultraviolet, visible and near-infrared light consisting of 1 ns FWHM pulses at a repetition rate of --50 MHz, and with identical temporal profiles at all wavelengths, although any source with similar temporal properties could be used. A single excitation band is selected by a monochromator and linearly polarized before reaching the sample. Fluorescence can be monitored either along an axis perpendicular to the excitation beam, or at near normal incidence. A polarizer divides the fluorescence into components with polarizations parallel and perpendicular to the polarization of the incident beam. The emission spectrum is dispersed by an imaging spectrograph, and detected with a resistive-anode imaging photomultiplier operated in a single photon counting mode. The time of arrival of a photon is derived from signals originating in the micro-channel plates that function as the "dynodes" of the photomultiplier, while the location of the centroid of the electron cascade on the anode of the detector indicates both the wavelength and polarization of the detected photon. Simultaneous acquisition of the time-resolved emission spectra for both polarization components is more efficient than conventional approaches and reduces the complications in data analysis that can arise when the properties of a sample change during the time when sequential data-sets are collected.