Terahertz beats of vibrational modes studied by femtosecond coherent Raman spectroscopy (original) (raw)
Related papers
Terahertz quantum beats in molecular liquids
Chemical Physics Letters, 1987
With ultrashort pulses of less than 100 fs it is possible to excite coherently several vibrational modes of polyatomic molecules simultaneously. The femtosecond time resolution of the experiment allows the study of pronounced high-frequency beat phenomena up to 10 THz. The frequency difference between vibrational modes separated by more than 300 cm-' may be determined with high precision.
Nonlinear terahertz coherent excitation of vibrational modes of liquids
The Journal of Chemical Physics, 2015
We report the first coherent excitation of intramolecular vibrational modes via the nonlinear interaction of a TeraHertz (THz) light field with molecular liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then measured in a terahertz Kerr effect spectrometer via phase-sensitive, heterodyne detection with an optical pulse. The spectrometer reported here has broader terahertz frequency coverage, and an increased sensitivity relative to previously reported terahertz Kerr effect experiments. Vibrational coherences are observed in liquid diiodomethane at 3.66 THz (122 cm(-1)), and in carbon tetrachloride at 6.50 THz (217 cm(-1)), in exact agreement with literature values of those intramolecular modes. This work opens the door to 2D spectroscopies, nonlinear in terahertz field, that can study the dynamics of condensed-phase molecular systems, as well as coherent control at terahertz frequencies.
Femtosecond Raman time-resolved molecular spectroscopy
Comptes Rendus Physique, 2004
The applicability of several femtosecond time resolved non-linear coherent techniques such as Raman induced polarization spectroscopy (RIPS), degenerate four-wave mixing (DFWM) and coherent anti-Stokes Raman spectroscopy (CARS) for molecular spectroscopy is presented. All methods rely on the initial coherent excitation of molecular states producing wavepackets, whose time evolution is then measured. In the case of RIPS and DFWM only pure rotational transitions are involved, whereas in CARS vibrational states can be excited. First the methodology of concentration and temperature measurements using RIPS in gas mixtures involving N 2 , CO 2 , O 2 , and N 2 O is shown. In addition some applications are given for the two closely related techniques DFWM and CARS. DFWM is suitable to extract the rotational constants of molecules to a high accuracy as is demonstrated by measurements on CO 2 and pyrimidine, which is a biological building block. CARS can be used to study higher order molecular constants and to sensitively determine temperature in, e.g., H 2 up to 2000 K. Finally, CARS is applied for the investigation of pressure dependent lineshape models, which are important for the temperature evaluation from spectroscopic data. To cite this article: B. Lavorel et al., C. R. Physique 5 (2004). 2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2018
Coherent Raman nanosecond spectroscopy system was developed Epi-detected 3CBCRS method was applied to measure low frequency vibrational modes Volumetric Brag Filters were used to record coherent Raman spectra on the-600-600 cm-1 range Phase retrieval methods were applied to calculate Raman like spectra Carbon tetrachloride and Calcite samples were used to characterize the versatility of the method GRAPHICAL ABSTRACT The figure below shows the recorded low frequency epi-detected 3CBCRS spectra of CCl4 and fused quartz using perpendicular polarization geometry.
Modulated coherent Raman beats
Physical Review A
The authors study the phenomenon of coherent Raman beats in ' NH, using a CO& laser and Stark switching. In particular, a three-level system in which the two upper levels always remain split by a few MHz is prepared by switching the transitions into resonance with a short Stark pulse whose bandwidth is large enough to coherently excite both transitions. When one of the coherently excited levels regains in resonance with the laser after the Stark pulse, this system exhibits a qualitatively new effect which has not been seen heretofore. For Stark shifts on the order of the upper-state splitting or smaller, the Raman beat is amplitude modulated at a frequency related to the optical nutation frequency. This is interpreted as being due to an interaction between the two-photon coherent Raman beat process and a single-photon optical nutation process which occurs simultaneously. Numerical calculations as well as a simple analytic model are presented to support this interpretation. By reducing the laser power, one can make the modulation of the Raman beat disappear. From the Raman signal in this regime the permanent electric dipole moment of ' NH3 in an excited vibrational state is determined and the Raman beat decay rate measured. By comparing the latter result with a delayed optical nutation measurement we show that phase-changing collisions are negligible for the transition studied.
Chemical Physics Letters, 1998
We propose a non-linear experiment using the non-linear interaction with THz pulses, the generation of which has recently become well established. In the lowest non-linear process, we have two controllable delay times. This is another Ž. optical analogue of two-dimensional 2D NMR as the recently developed 2D Raman spectroscopy. Our model calculation for liquid water demonstrates the striking capability of the proposed technique, clearly distinguishing two types of anharmonicity in the low-frequency modes.
Femtosecond stimulated Raman spectroscopy
2010
Femtosecond stimulated Raman spectroscopy (FSRS) is a new ultrafast spectroscopic technique that provides vibrational structural information with high temporal (50-fs) and spectral (10-cm −1) resolution. As a result of these unique capabilities, FSRS studies of chemical and biochemical reaction dynamics are expected to grow rapidly, giving previously unattainable insight into the structural dynamics of reactively evolving systems with atomic spatial and femtosecond temporal resolution. This review discusses the experimental and theoretical concepts behind FSRS, with an emphasis on the origins of its unique temporal and spectral capabilities. We illustrate these capabilities with vibrational studies of ultrafast electronic dynamics, as well as the direct structural observation of nonstationary vibrational wave-packet motion in small molecules and in complex biochemical reaction dynamics. Reaction coordinate: specific path on one or more potential energy surfaces that describes the geometric and electronic changes occurring in a chemical transformation
Coherent two-dimensional terahertz-terahertz-Raman spectroscopy
Proceedings of the National Academy of Sciences of the United States of America, 2016
We present 2D terahertz-terahertz-Raman (2D TTR) spectroscopy, the first technique, to our knowledge, to interrogate a liquid with multiple pulses of terahertz (THz) light. This hybrid approach isolates nonlinear signatures in isotropic media, and is sensitive to the coupling and anharmonicity of thermally activated THz modes that play a central role in liquid-phase chemistry. Specifically, by varying the timing between two intense THz pulses, we control the orientational alignment of molecules in a liquid, and nonlinearly excite vibrational coherences. A comparison of experimental and simulated 2D TTR spectra of bromoform (CHBr3), carbon tetrachloride (CCl4), and dibromodichloromethane (CBr2Cl2) shows previously unobserved off-diagonal anharmonic coupling between thermally populated vibrational modes.