Widefield pump-probe microscopy with coherent background subtraction by angle-compensated temporal shearing

TL;DR

This paper introduces a novel widefield pump-probe microscopy technique using a unique common-path interferometer with angle compensation, significantly improving signal-to-noise ratio and background subtraction for label-free imaging.

Contribution

The authors develop a new common-path interferometer with negligible dispersion that enables enhanced pump-probe imaging with improved signal-to-noise ratio and background suppression.

Findings

Signal-to-background ratio increased by over 100%

Signal-to-noise ratio improved by about 70%

First demonstration of a dispersion-free common-path interferometer for widefield pump-probe microscopy

Abstract

Pump-probe microscopy enables label-free imaging of structural and chemical features of samples. However, signals in pump-probe microscopy are typically small and often must be measured in the presence of large backgrounds. As a result, achieving measurements with a high signal-to-noise ratio is challenging, particularly when using sensors that are easily saturated, such as CMOS cameras. We present a method for enhancing signal-to-noise ratio while avoiding detector saturation. In this approach, temporally separated (sheared) reference and probe pulses transmit through a sample before and after the arrival of a pump pulse. The probe and reference pulses are then temporally recombined with opposing phases and nearly matched amplitudes, resulting in interferometric background subtraction. This recombining operation is performed by a novel common-path interferometer. Unlike previous techniques for temporal shearing, this interferometer demonstrates negligible phase and group delay dispersion with angle of incidence, allowing convenient widefield imaging. To our knowledge, this is the first common-path interferometer with such a property. We demonstrate the technique by measuring transient absorption signals in gold nanorod films with a signal-to-background ratio enhanced by over 100% and a signal-to-noise ratio enhanced by about 70%.