1-bit photon cross-correlation-based phase-modulation fluorometer using an OFDM signal-modulated excitation light source

Abstract

We propose a phase-modulation fluorometer, which is a combination of a 1-bit photon cross-correlator constructed using a field-programmable gate array and an excitation light source modulated by an orthogonal frequency-division multiplexing signal. Such multiplexing allows us to use multiple modulation frequencies efficiently and selectively within a given baseband. Defined as the inverse of its fundamental frequency, the symbol length of the multiplexing is set equal to the width of the time window of the cross-correlator. Therefore, all temporal waveforms of the subcarriers in the baseband are connected smoothly at both ends of the symbol interval; hence, no spurious sidebands appear in the frequency domain of the subcarriers. The 1-bit cross-correlator brings about fluorescence lifetimes in the photon-counting realm. From a phase difference spectrum between the fluorescence and the reference signal, fluorescence lifetimes for each frequency may be obtained with precision simultaneously. The resolution time and the width of the time window of the cross-correlator are 2.0 ns and 256 ns, respectively. As a proof-of-principle experiment, we measured the fluorescence lifetimes of some standard samples.