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.
Highlights
Chiral molecules show optical activity, i.e. they rotate the polarization direction of linearly polarized light
We show the integration of the polarimeter and a probe for linear absorption spectroscopy into an accumulative scheme for femtosecond spectroscopy [21]
The polarimeter probe utilizes the light of a continuous-wave (CW) laser diode, which is modulated by an electro-optic modulator, leading to a continuously varying polarization state. This gives the ability to transform the optical rotation of the sample into a phase difference, which can be rapidly detected by a lock-in amplifier
Summary
Chiral molecules show optical activity, i.e. they rotate the polarization direction of linearly polarized light. Optical rotation is an inherently tiny effect, large optical path lengths in the range of centimeters and high concentrations are commonly employed to reach measurable optical rotation angles 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. We show the integration of the polarimeter and a probe for linear absorption spectroscopy into an accumulative scheme for femtosecond spectroscopy [21] This affords femtosecond laser spectroscopy with rapid and precise detection of optical rotation angles as well as linear absorption. The polarimeter probe utilizes the light of a continuous-wave (CW) laser diode, which is modulated by an electro-optic modulator, leading to a continuously varying polarization state This gives the ability to transform the optical rotation of the sample into a phase difference, which can be rapidly detected by a lock-in amplifier. Adding a small phase retardation after the chiral sample leads to an effective signal amplification such that the measured phase difference corresponds to a sensitive measurement of optical rotation
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