Optical activity spectroscopy such as circular dichroism (CD) and optical rotatory dispersion (ORD) is frequently employed to investigate (bio)-molecular structures and chiroptical responses of materials. Here we present an innovative, simple configuration for the quick and sensitive measurements of broadband optical activity spanning the visible and nearinfrared. A linearly polarized light illuminates a chiral sample to create a chiral free-induction decay field (CFID), along with an orthogonally polarized achiral transmitted field which serves as the phase-locked local oscillator for heterodyne amplifications. A common-path birefringent interferometer varies the relative delay between the chiral and achiral components and a balanced photodetector records their delay-dependent interferogram from which broadband CD and ORD spectra are obtained by the Fourier transform. Using an incoherent thermal light source, we achieve state-of-the-art sensitivity for broadband CD and ORD spectra, with a measurement time of just a few seconds. The setup allows highly sensitive measurements of glucose concentration and real-time monitoring of fast asymmetric chemical reactions. In comparison to standard spectropolarimeters, our setup is considerably faster, more compact, and cost-effective, as it does not require any monochromator, photo-elastic modulator, or lock-in amplifier. The setup also accepts ultrashort pulses, thus paving the way towards broadband transient optical activity spectroscopy and broadband CD imaging.
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