Electro-Optic Phase-Sensitive Detection of Optical Emission and Scattering

The limits of time resolution are constantly being reduced with the development of ever shorter laser pulses. In this presentation, we discuss the potential for approaching these limits by experiments in the frequency domain in which microwave electro-optic (EO) intensity modulation and phase-resolved EO demodulation are used to measure the phase shift and depth of modulation of optical emission and scattering. The use of EO phase-sensitive detection greatly expands the utility of fluorometric measurements since a) increased modulation frequencies, related to the frequency of EO modulation rather then the frequency response of the photo detector can be used; b) the frequency range is further extended since harmonics of the applied voltage appear in the modulated light; c) sensitive optical multichannel detection is used and d) purely electronic noise is absent. The experimental method of EO phase-sensitive detection will be discussed as well as two novel measurements which can be made with this apparatus: the measurement of ultrafast dephasing and the separation of Raman scattering from fluorescence.