Abstract
We present spectral interferometric four-wave mixing (FWM) microscopy with a nearly shot-noise limited sensitivity and with the capability of separating FWM signals from fluorescence signals. We analyze the requirements for obtaining the shot-noise limited sensitivity and experimentally achieve the sensitivity that is only 4-dB lower than the shot-noise limit. Moreover, we show that only FWM signals can be extracted through the Fourier filtering even when the FWM spectrum is overlapped and overwhelmed by the fluorescence spectrum. We demonstrate simultaneous acquisition of FWM and two-photon excited fluorescence images of fluorescent monodispersed polystyrene microspheres.
Highlights
In the recent biological research field, there is a growing demand for the development of highresolution, three-dimensional imaging tools for exploring the underlying biological functions
We present spectral interferometric four-wave mixing (FWM) microscopy with a nearly shot-noise limited sensitivity and with the capability of separating FWM signals from fluorescence signals
We analyze the requirements for obtaining the shot-noise limited sensitivity and experimentally achieve the sensitivity that is only 4-dB lower than the shotnoise limit
Summary
In the recent biological research field, there is a growing demand for the development of highresolution, three-dimensional imaging tools for exploring the underlying biological functions. This problem could be solved by introducing a time-gating circuit [10], it may result in an increased complexity of the electronic circuits and/or a degraded SNR due to the loss of a part of the nonlinear signal Another interesting technique is an interferometric detection, where a weak signal electric field is mixed with an intense local oscillator (LO) field and their interference signal is detected with an optical detector with a moderate sensitivity. This technique was introduced for the determination of the real and imaginary parts of nonlinear susceptibility [18] and applied to spectral domain SHG-optical coherence tomography (OCT) [19] In spite of these numerous reports on the interferometric detection of nonlinear signals, there has been almost no report which fully exploits the above-mentioned advantages (i.e. shot-noise limited detection and fluorescence removal).
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