Abstract
Extracting signals at low single-photon count rates from large backgrounds is a challenge in many optical experiments and technologies. Here, we demonstrate a single-photon lock-in detection scheme based on continuous photon timestamping to improve the SNR by more than two orders of magnitude. Through time-resolving the signal modulation induced by periodic perturbations, 98% of dark counts are filtered out and the < 1 c o u n t / s contributions from several different nonlinear processes identified. As a proof-of-concept, coherent anti-Stokes Raman measurements are used to determine the vibrational lifetime of few molecules in a plasmonic nanocavity. This detection scheme can be applied to all single-photon counting experiments with any number of simultaneous modulation frequencies, greatly increasing SNR and resolving physical processes with picosecond time resolution while keeping the photon dosage small. The open instrumentation package provided here enables low-cost implementation.
Highlights
Transient or time-resolved optical experiments often require elaborate experimental setups designed to measure very low signal intensities over ultrashort time scales, and they often suffer from poor signal-to-noise ratios [1]
In all-optical experiments such as four-wavemixing in semiconductor optical amplifiers [7] or stimulated emission from single nanocrystals [8], the pump pulse train is amplitude-modulated at high frequency fmod
We provide the Field programmable gate array (FPGA) software online [will be provided on acceptance of the paper] under an open source licence to allow for low-cost implementation
Summary
Transient or time-resolved optical experiments often require elaborate experimental setups designed to measure very low signal intensities over ultrashort time scales, and they often suffer from poor signal-to-noise ratios [1]. Increasing the strength of a repetitive perturbation (for instance the optical pulse intensity) to enhance the nonlinear signal is often problematic since this can damage the samples, preventing stroboscopic measurement. By introducing a modulation to the sample, the amplitude and phase of the emerging signal can be determined using phase-sensitive heterodyne detection while noise at other frequencies is rejected [6]. In all-optical experiments such as four-wavemixing in semiconductor optical amplifiers [7] or stimulated emission from single nanocrystals [8], the pump pulse train is amplitude-modulated at high frequency fmod. Optical lock-in detection is used for stimulated-emission-depletion microscopy to enhance contrast in fluorescence microscopy [10], and in many other scenarios
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