Speaker
Description
Chirality is ubiquitous in nature, and understanding of chiral properties is critical to many applications in modern science and technology, ranging from protein function in biology and enantiomer differentiation in pharmaceutics, to light control in plasmonics and metamaterials all the way to probing magnetic properties in spintronic and superconducting devices. The chiro-optical response of a sample is manifested as the dependence of the complex refractive index on the handedness of circularly polarized light, which can be probed by its imaginary part (circular dichroism, CD) or its real part (optical rotatory dispersion, ORD). The ultrafast chiro-optical response of a sample is of broad interdisciplinary interest, ranging from structural dynamics of proteins to spin dynamics in semiconductors and magnetic materials to the nonlinear response of chiral plasmonic nanostructures. The measurement of time-resolved CD or ORD is however experimentally challenging, because it requires the detection of the small photoinduced change of an already small signal. Here we introduce two novel approaches to ultrafast chiro-optical spectroscopy and microscopy. We first present a broadband ultrafast chiroptical spectroscopy setup which combines time-domain Fourier transform detection and heterodyne amplification using a birefringent common-path interferometer. Our method allows the detection of transient CD and ORD spectra with sensitivity better than 1 millidegree. We then discuss an ultrafast widefield chiro-optical transient absorption microscope which uses a multiplexed off-axis holography scheme with two cross-polarized reference pulses. The holographic nature of the measurement enables retrieval of the electric field of the probe pulse and thus simultaneous detection of the transient CD and ORD signals, which can be reconstructed over a large field of view with high temporal (sub-100-fs) and spatial (sub-µm) resolution.
