Berlin 2001 – scientific programme
Parts | Days | Selection | Search | Downloads | Help
Q: Quantenoptik
Q 29: Application of Short Pulses II
Q 29.2: Talk
Thursday, April 5, 2001, 18:00–18:15, H 2013
Single shot CARS thermometry with chirped femtosecond laser pulses — •T. Lang and M. Motzkus — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching, Germany
A new single shot detection technique based on nonresonant Femtosecond CARS (coherent anti-Stokes Raman scattering) in the gas phase is presented. Chirped probe pulses are used in order to project the temporally evolution of the Raman response function of the sample molecules directly onto the signal spectrum. This linear time-frequency mapping allows to monitor the dynamical response of the excited molecules within a sub-ps time window with a single pulse sequence.
The new technique is applied to ultrafast (<1 ps) and high repetitive (1 kHz) single shot thermometry. With 100 fs laser pulses the Q-branch (Δ v=1, Δ J=0) of the probe molecules is excited coherently, the delayed probe pulses are chirped to 450 fs. The modulation of the signal spectrum reflects the thermal population of the rotational states J in the vibrational groundstate v=0. Using H2 as probe molecule, temperatures in a sample cell between T=300 K and T=1100 K were determined with a resolution of better than ΔT=20 K. High spacial resolution is given by the focal overlap of the incoming laser beams. A time delay between the short pump and the chirped probe pulses is used to discriminate against unwanted interferences from nonresonant background.
The experimetal data are compared in detail with theoretical simulations of the CARS spectra. Furthermore the application to single shot probing of molecular dynamics is discussed.