Precise and rapid detection of optical activity for accumulative femtosecond spectroscopy

Abstract

We present polarimetry, i.e. the detection of optical rotation of light polarization, in a configuration suitable for femtosecond spectroscopy. The polarimeter is based on common-path optical heterodyne interferometry and provides fast and highly sensitive detection of rotatory power. Femtosecond pump and polarimeter probe beams are integrated into a recently developed accumulative technique that further enhances sensitivity with respect to single-pulse methods. The high speed of the polarimeter affords optical rotation detection during the pump-pulse illumination period of a few seconds. We illustrate the concept on the photodissociation of the enantiomers of methyl p-tolyl sulfoxide. The sensitivity of rotatory detection, i.e. the minimum rotation angle that can be measured, is determined experimentally including all noise sources to be 0.10 milli-degrees for a measurement time of only one second and an interaction length of 250 µm. The suitability of the presented setup for femtosecond studies is demonstrated in a non-resonant two-photon photodissociation experiment. 3682-3692 (1991). 9. S. Milder, S. Bjorling, I. Kuntz, and D. Kliger, "Time-resolved circular dichroism and absorption studies of the photolysis reaction of (carbonmonoxy)myoglobin," Biophys. J. 53, 659-664 (1988

Precise and Rapid Detection of Optical Activity for Accumulative Femtosecond Spectroscopy

“…1b shows enantiodifferentiating signals at high signal-to-noise ratio, indicating that the photodestruction can be monitored successfully, which is furthermore corroborated by the simultaneously acquired linear absorption signal (data not shown, see Ref. [10]). By comparing to the noise level of the optical rotation while the capillary is only filled with solvent, we can determine the resolution of the polarimeter experimentally to 0.10 milli-degrees (mdeg) at an optical path length of 250 µm with only one second of measurement time.…”

“…The detected signal can be calculated via the Jones formalism leading to a sinusoidal signal as a function of the EOM voltage, whose amplitude and phase is determined by a lock-in amplifier. The phase of the signal only depends on the (known) retardation setting of the VWP and the optical rotation α of the sample, enabling us to calculate the optical rotation change ∆α directly [10]. Besides the detection of ∆α, the linear absorption (beam which is detected by the spectrometer in Fig.…”

Recent advances in ultrafast time-resolved chirality measurements: perspective and outlook

“…In accumulative femtosecond spectroscopy the stable photoproduct is accumulated by irradiating the sample with femtosecond pump pulses for a couple seconds and then probed . Femtosecond accumulative spectroscopy has also been successfully employed to measure optical activity ; however, this was a steady‐state experiment and no femtosecond time‐resolved chirality changes have been measured. To measure the optical activity the detection of optical rotation of light polarization, i.e.…”

Optical discrimination of racemic from achiral solutions

“…Details on the mode of operation and data recording can be found in ref. 32. The main components of the polarimeter are a continuous-wave (CW) 405 nm laser diode, a linear polarizer, an electro-optic modulator (EOM), a Berek-type variable wave plate, and another linear polarizer working as analyzer.…”

“…The main concept of the present work is to use accumulative femtosecond (fs) spectroscopy 30,31 for creating an enantiomeric excess (ee) from the originally racemic solution and to rapidly detect the resulting OA with an extremely sensitive polarimeter. 32 In the literature, several optical routes are known for generating ee. 33 Optical ee generation has been demonstrated almost a century ago using long-term illumination with incoherent circularly polarized light [34][35][36] leading to asymmetric photodecomposition.…”