2D IR Spectroscopy with Phase-Locked Pulse Pairs from a Birefringent Delay Line
About: The article was published on 2015-01-01 and is currently open access. It has received 4 citation(s) till now. The article focuses on the topic(s): Pulse (signal processing).
Summary (1 min read)
- The heterodyne photon-echo configuration is the most versatile and sensitive but also the most complex way of performing 2D spectroscopy.
- When using a pulse shaper, the phase and delay t1 between the two pulses are fully controlled, and can be changed on a pulse to pulse basis, allowing fast and efficient scanning of t1.
- Besides its compactness and simplicity, advantage of the TWINS configuration is that it naturally produces a pair of perpendicularly polarized pump pulses.
2. Measurement principle
- This effect can be used to generate two orthogonally polarised pulse replicas, and to finely tune their relative delay by adjusting the material thickness.
- This is corrected by the second pair of static wedges, after which the two beams are now parallel and almost collinear.
- For a proof of concept, the authors have selected LiNbO3, which has a transparency window extending up to 5.2 μm, a reasonably high birefringence and is commercially available in the size requested for their experiment.
- The transmitted polarization is sent to the sample and overlapped spatially with the probe beam.
4. Polarization measurements
- Without polarizer in the pump-beam the TWINS setup delivers a pair of pump pulses with very well-defined perpendicular polarizations.
- Scattering signals are suppressed in the YXYX scheme as the probe polarizer (X) acts as a filter to remove all the scattered light coming from the first pump pulse (polarization Y).
- The probe pulse at the sample can also be made very intense without saturating the detector.
- Fig. 4(b) shows the 2D IR measurement of the OD stretch spectrum with perpendicularly polarized pump pulses and a polarizer in the probe beam (polarizations XYXY).
- Since only the anisotropic signal is amplified, isotropic background due to heat is suppressed.
5. Discussion and conclusion
- The TWINS apparatus is simple and compact and allows to generate phase-locked pulses with an extremely high phase stability.
- This can also be exploited to determine angles between transition dipole moments with improved accuracy  and to eliminate diagonal peaks by subtracting signals recorded with polarization orders YXYX and XYYX .
- The current limitations of the set-up are due to the small birefringence and limited spectral transmission of LiNbO3.
- Candidate material with better characteristics are difficult to find for application of the TWINS in the mid-IR.
- The authors are now developing strategies to be able to use smaller crystals and improve the throughput of the sequence, which will permit to utilize calomel for 2D IR spectroscopy with birefringent wedges.
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Cites background from "2D IR Spectroscopy with Phase-Locke..."
...Using different materials with increased longwavelength transparency, such as lithium niobate up to 5 μm  and Hg2Cl2 (calomel) up to 20 μm , it can be extended to the mid-IR, covering the crucial fingerprint region of molecular vibrations....
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Q1. What have the authors contributed in "2d ir spectroscopy with phase-locked pulse pairs from a birefringent delay line" ?
The authors introduce a new scheme for two-dimensional IR spectroscopy in the partially collinear pump-probe geometry. Exploiting the inherent perpendicular polarizations of the two pump pulses, the authors also demonstrate signal enhancement and scattering suppression. 31. T. Steinel, J. B. Asbury, J. Zheng, and M. D. Fayer, “ Watching hydrogen bonds break: a transient absorption study of water, ” J. Phys.