M. Sheinman: Interferometric Detection for Enhanced Signal-to-Noise Ratio in Widefield Microscopy

A common challenge in microscopy is the measurement of small signals in the presence of large backgrounds. In such cases, the large number of collected photons required to distinguish signals from shot noise associated with the background makes widefield microscopy impractically slow due to the limited full well capacity of cameras. In this talk, I will describe three techniques for enhancing signal-to-background ratio (SBR) interferometrically for widefield detection. The first technique is applied to pump-probe microscopy, in which pump induced changes in a sample result in small modulations in the amplitude and phase of a probe beam, leaving a large unmodulated background. If the transient signal is optically anisotropic, SBR can be enhanced by simply combining cross-polarized probe beams with a linear polarizer. The second technique also enhances SBR in pump-probe microscopy, but without the requirement for an anisotropic response. This is achieved by temporally shearing a probe pulse into sub-pulses arriving before and after the pump pulse, and then recombining the probe pulses for optical subtraction. The final technique enhances SBR in polarized light microscopy, wherein some information about a sample’s optical anisotropy, such as its birefringence, is recovered from several intensity measurements using polarizers and birefringent optics in different states. Here, we demonstrate a method recovering complete information about a sample’s anisotropy exclusively using measurements allowing for enhanced SBR.