Vibrational circular dichroism signal enhancement using self-heterodyning with elliptically polarized laser pulses

Abstract

Vibrational circular dichroism (VCD) spectra were recorded using elliptically polarized ultrashort laser pulses, produced with the help of a photoelastic modulator. The short polarization axis of the elliptical light acts as a phase-locked local oscillator field, heterodyning the chiral signal generated by the field along the long polarization axis. This leads to VCD signals that increase linearly with the ellipticity of the probe pulses and enhanced signal to noise, which is expected to improve recently reported transient VCD scans. An analogous scheme allows for vibrational optical rotary dispersion measurements. The techniques are compared with similar approaches using both a linear response picture and the Jones matrix calculus.

Precise and rapid detection of optical activity for accumulative femtosecond spectroscopy

“…Such conditions are disadvantageous for femtosecond spectroscopy, especially if one wants to apply pulse-shaping techniques, where small volumes and short path lengths are needed to achieve high intensities for nonlinear excitations and to avoid pulse distortion upon propagation through the sample. In this paper, we do not probe ultrafast chirality changes, as demonstrated (or proposed) by probing ultrafast changes in optical rotation [1][2][3][4] or circular dichroism [1][2][3][4][5][6][7][8][9][10][11][12], but we rather make use of optical rotation changes due to a stable photo- product as a probe for ultrafast dynamics initiated with femtosecond laser pulses. For an experimental implementation of this concept, we present an accumulative polarimeter setup with short path length that is fast and sensitive enough to overcome the mentioned complications.…”

Linear dichroism amplification: Adapting a long-known technique for ultrasensitive femtosecond IR spectroscopy

“…Our technique for modulating the polarization of mid-IR pulses will also be useful in analogous all-IR pump-probe or 2D-IR experiments. 21 A closely related experiment has in fact already been performed by Xiong and Zanni, who could enhance signals significantly by placing a polarizer into the probe beam in a 2D-IR experiment with collinear pump beams of perpendicular polarization. 22 …”

Time-domain measurement of optical activity by an ultrastable common-path interferometer

“…When a linearly polarized light field impinges on an achiral medium, it drives a time-varying material polarization that in turn radiates a light field, the achiral-free induction decay (AFID); interference of the AFID with the input field gives rise to linear absorption/refraction. A chiral medium, conversely, radiates a small light field with perpendicular polarization, known as chiral FID (CFID), which changes the polarization state of the output light, turning it from linear to elliptical [5,6]. As the CFID field is very weak, CD and CB are orders of magnitude smaller than the corresponding achiral absorption/refraction, making their experimental measurement challenging.…”

“…The largest amplification is possible with intense light sources like lasers, and this measurement principle has been used previously to significantly enhance CD (and CB) signals in frequency-domain measurements with wavelength selection both before [5,18] and after [19,20] the sample. On the other hand, if only CD signals are measured, the second polarizer (P 2 in Fig.…”