Tracking molecular wave packets in cesium dimers by coherent Raman scattering Page: 2
The following text was automatically extracted from the image on this page using optical character recognition software:
PHYSICAL REVIEW A 86, 023421 (2012)
Pump/Probe * ib'
740 760 780 800 820 840
FIG. 1. (Color online) An experimental setup: (a) A schematic
layout. OPA, optical parametric amplifier; BS1,2, beamsplitter;
DS 1,2, delay stage; Spec., spectrograph; CCD, charge coupled device.
(b) The measured spectra of pump, probe, and Stokes beams. Inset:
A folded-BOXCARS beam arrangement used in the experiment. A
spot on the top right corner (blue) corresponds to the phase-matched
CARS signal and the other spots correspond to the input beams.
We use a commercially available femtosecond Ti:sapphire
regenerative amplifier system (Legend, Coherent) and an
optical parametric amplifier (OPA: OPerA-VIS/UV, Coherent)
to generate passively synchronized 1-kHz pulse trains of the
two colors. The pump and probe beams are produced by
splitting the output beam of the OPA and tuned to center
wavelength 760 nm [see Fig. 1(b)]. The spectral full-width-
at-half-maximum (FWHM) is about 12 nm. For the pump and
probe beams, average power is attenuated to about 1 mW
(corresponds to 1 iJ/pulse) in front of the Cs cell. For the
Stokes beam, we use a small fraction of the regenerative
amplifier output beam. Its spectrum is centered at 805 nm,
and the spectral FWHM is close to 30 nm. The beam passes
through a pulse shaper (Silhouette, Coherent), which corrects
phase distortions along the Stokes beam path down to the Cs
cell by means of multiphoton intrapulse interference phase
scan (MIIPS) . The Stokes pulse energy at the target
is -0.1 J. The relative timing between the pump, Stokes,
and probe pulses is adjusted by the two automated delay
lines. All the beams are focused and overlapped (under ~2 x
10-2 rad angle) inside a 7.5-cm long Cs cell heated up
to 240 C. At this temperature, the number density of Cs2
molecules is about 2.3 x 1013 cm-3 . However we note
that the number density of cesium atoms is approximately two
orders of magnitude higher than that for Cs2 molecules.
The generated CARS signal (near 720 nm) is spatially
filtered and focused by a lens at the entrance slit of a
spectrograph (Chromex Spectrograph 250is) with a liquid-
nitrogen-cooled CCD (Spec-10, Princeton Instruments). For
most of our measurements, the detected signal is spectrally
integrated over a narrow band, filtering the residual pump and
III. THEORETICAL MODEL
In this section, we present a theoretical model suitable
to interpret the time-delayed coherent Raman scattering
measurement. We classify the present problem by the order
of the arrival times of the three input pulses into the cell.
First we consider the case of Stokes-pump-probe configuration
where the Stokes pulse arrives first followed by the pump and
probe pulses. In this case, there are two possible pathways
as shown in Fig. 2. The upper levels, a) and a'), are the
vibrational levels in the excited state, B ' Hu, while the lower
two, Ib) and Ic), are the vibrational levels in the ground state, X
1 Eg. Note that the level here represents many closely spaced
energy levels. The initial population is equally distributed
over all the vibrational levels in the ground state. A reason
is that the cesium dimer is produced by the hot cesium atomic
collisions, which excites the cesium molecules to the upper
vibrational levels in the ground state. A nonradiative relaxation
between vibrational levels enables the molecules being equally
populated over all the ground-state vibrational levels.
The derivations of the equations that describe the both
pathways are similar. In particular, for pathway (a) in Fig. 2,
the Hamiltonian under the near-resonance approximation is
H = Ho+ HI,
where the unperturbed part of the Hamiltonian is
Ho = ha cla')(a' + hao, a)(a + hcb lb)(b + h o c)(cl,
FIG. 2. (Color online) Energy level diagrams for the two possible pathways [(a) and (b)] in the Stokes-pump-probe configuration and the
other two possible pathways [(c) and (d)] in the pump-Stokes-probe configuration. The upper (lower) two levels are the vibrational levels in
the excited (ground) electronic state.
LUQI YUAN et al.
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Yuan, Luqi; Murawski, Robert K.; Ariunbold, Gombojav O.; Zhi, Miaochan; Wang, Xi; Sautenkov, Vladimir A. et al. Tracking molecular wave packets in cesium dimers by coherent Raman scattering, article, August 31, 2012; [College Park, Maryland]. (digital.library.unt.edu/ark:/67531/metadc103258/m1/2/: accessed July 27, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.