Forthcoming Events

11.07.2022 - 15.07.2022, Celeste Hotel, on UCF main campus, Orlando, Florida
05.09.2022 - 09.09.2022, Iseolago hotel, Iseo, Italy.


MUST2022 Conference- succesfully concluded
New scientific highlights- by MUST PIs Chergui and Richardson
FELs of Europe prize for Jeremy Rouxel- “Development or innovative use of advanced instrumentation in the field of FELs”
Ruth Signorell wins Doron prizefor pioneering contributions to the field of fundamental aerosol science
New FAST-Fellow Uwe Thumm at ETH- lectures on Topics in Femto- and Attosecond Science
International Day of Women and Girls in Science- SSPh asked female scientists about their experiences
New scientific highlight- by MUST PIs Milne, Standfuss and Schertler
EU XFEL Young Scientist Award for Camila Bacellar,beamline scientist and group leader of the Alvra endstation at SwissFEL
Prizes for Giulia Mancini and Rebeca Gomez CastilloICO/IUPAP Young Scientist Prize in Optics & Ernst Haber 2021
Nobel Prize in Chemistry awarded to RESOLV Member Benjamin List- for the development of asymmetric organocatalysis
NCCR MUST at Scientifica 2021- Lightning, organic solar cells, and virtual molecules
#NCCRWomen- NCCR MUST celebrates 50 years women’s right to vote in Switzerland
Kick-Off dynaMENT Mentoring for Women in Natural Sciences- with Ursula Keller as plenary speaker

Transient 2D IR spectroscopy from micro- to milliseconds

March 11, 2021

(Featured Article in the Journal of Chemical Physics)
Peter Hamm introduces a new application of 100 kHz Yb-laser systems, transient 2D IR spectroscopy, using the photocycle of bacteriorhodopsin as a demonstration object. This approach utilizes the high repetition rate of these lasers in two ways: First, it directly determines the time resolution of the experiment (10 µs) and, at the same time, enables the measurement of many 2D IR spectra within a reasonable averaging time. Furthermore, the very good stability of the Yb-laser/OPA system allows for hours of measurement time without the need for any readjustments. We have not seen the same level of stability for Ti:S-based laser systems. Data can be taken overnight, and the only limiting aspect at this point is the need to refill the MCT detector with liquid N2.
Currently, 100 kHz is the upper limit for this type of experiment, despite the fact that Yb-laser systems with higher repetition frequencies are available. The pulse shaper, the response time of the MCT detector, and the AD-converter limit the repetition frequency to that value.
The timescales covered by this type of experiment, 10 µs to a few tens of milliseconds, are perfectly suitable for the investigation of a wide range of photo-active proteins. It also matches that of diffusion controlled bimolecular processes, such as protein–ligand interactions or chemical reactions, in the context of artificial photosynthesis. Even when the goal is “only” transient 1D IR spectroscopy, the system outperforms step-scan FTIR spectroscopy or more modern setups based on quantum cascade lasers in terms of measurement time; 1 min was sufficient to collect transient 1D IR data. Admittedly, the present experimental setup is more expensive than, for example, a quantum cascade laser spectrometer, but not by orders of magnitudes (by a factor of 2–3). At the same time, due to the high intensities of femtosecond pulses, an Yb-laser system is much more versatile, as one may reach a very wide frequency range from THz to x rays by some means of nonlinear optics. The improvement over Ti:S lasers is enormous, suggesting that these types of lasers might become the standard for time-resolved mid-IR spectroscopy on all conceivable timescales, from femtoseconds to hours.

FIG. 1. (a) Basic pulse sequence of transient 2D IR spectroscopy. (b) Repetitive pulse sequence used here to measure a sequence of transient 2D IR spectra. IR probe pulses (bottom row) are generated at a repetition rate of 100 kHz (Δt = 10 µs), together with a pair of IR pump pulses (middle row) produced with the help of a pulse shaper on a single shot basis. In total, n2D IR laser shots are needed to construct one 2D IR spectrum. The actinic pump (top row) has a periodicity of na = m × n2D + 1 with any integer number m (m = 1 is shown here).
Reference: Hamm, P. (2021). Transient 2D IR spectroscopy from micro- to milliseconds. J Chem Phys 154, 104201. (10.1063/5.0045294)

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