Femtosecond wave-packet dynamics in cesium dimers studied through controlled stimulated emission Page: 5
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FEMTOSECOND WAVE-PACKET DYNAMICS IN CESIUM ...
1.2
FWHM = 31 nm 31 nm 17 nm 9.1 nm
acq 31.0
E 0.8
17 nm o.
v 0.0
4.9 nm
S.o 4.9 nm 2.9 nm 1.5 nm
2.9 nm .
,YAAAAAAAA. ,',A'. E 0.8
S1.51 V 0.6
0.4
0 5 10 15 20 25
Probe pulse delay (ps) 0 40 80 120 0 40 80 120 0 40 80 120
Frequency (cm 1) Frequency (cm'1) Frequency (cm-1)
FIG. 4. The time dependence of the signal observed with one pump beam is shown on the left. The spectral width of the probe beam is
varied from 31 to 1.5 nm by using a spectrometer with an adjustable exit slit. The observed temporal behavior of the spectrally selected wave
packet is changed from a simple decay (probe 31 nm) to decay and revival (probe 1.5 nm). The FFT spectra of the recorded time-domain
profiles are shown on the right.i.e., at the vibrational frequency We in the excited B state and
its overtone. This can be understood from the analytical result
in (28). Because the near resonance of the pump pulse and the
electronic transitions between vibration states a), a'), and Ib)
and that of the probe pulse and the transitions between states
a), Ia'), and Ic), the sin(o,,,a At) term becomes much larger
than the sin(cocb At) term. Furthermore, due to the exponential
functions in the equation, the term with frequency, cWaa,, around
the vibrational frequency of the B excited state, 34 cm-1,
contributes most to the signal while terms with higher-order
harmonic frequency contribute less to the signal. Therefore,
both experimental and theoretical results show a high peak at
34 cm-1 but a much lower peak at 68 cm-'. The dephasing of
the oscillation amplitude is also shown in theory. It is the result
of the vibrational anharmonicity term, We Xe. However, the
dephasing rate from experiment and that from theory does not
match quite well. The possible reason is that we do not include
rotational levels in our model. Besides the anharmonicity of the
molecular internuclear potential, the ro-vibrational coupling
also does effects on the dephasing of the wave-packet motion
[34].
Numerical Result
Numerical Result o 1
C01 4 1 2
( - Frequerncy (m'rnC
C)
Cl)Analytical Result
0 5 10 15
Probe pulse delay (ps)Analytical Resuh
0.4
1 .2
20
a 40 r n o 1L
Freqrency (cm 'FIG. 5. Dependence of the absorptions of the probe pulse with
width 31 nm, calculated both with the numerical simulation and
the analytical solution, on the probe pulse delay in pump-probe
measurements. Corresponding FFT spectra are shown on the right.Next, we evaluate the results of our pump-control-probe
measurements and simulate the observed dynamics by ex-
tending the model above. We assume that two wave packets,
generated by pump and control pulses, are independent.
The experimentally recorded signal for different time delays
between pump and control pulses is shown in Fig. 6. The
time delay between pump pulse and control pulse is changing
from 0 to T, where T is the period of the signal oscillation
in the pump-probe measurements, which is about 1 ps. The
acquisition bandwidth used for observing the signal is 1.5 nm.
The superposition pattern between two wave packets in the
cesium dimer can be seen. When the time delays between
pump pulse and control pulse are 0 and T, two FFT peaks are
found in the FFT spectra. One is at the frequency 34 cm-1
and the other one is at 68 cm-1, which are the same with
the results in pump-probe measurements. However, when the
time delays between pump pulse and control pulse are T/4
and 3T/4, only the peak at 34 cm-1 is surviving. When the
delay time become half of the period, say T/2, the first peak
at 34 cm- disappears but the peak at the second-harmonic
frequency 68 cm-1 appears again. Both numerical simulation
(Fig. 7) and analytical calculation (Fig. 8) show the similar
results with the experiment. Therefore, we are convinced that
two wave packets generated by the pump and control pulses
are independent and they produce the superposition pattern as
shown above.
Such superposition pattern can also be read using the
analytical result for pump-probe measurement [Eq. (28)].
Since two wave packets generated by pump and control
pulses are independent, this superposition pattern shown
above is the result of the superposition of the sine func-
tions listed in this equation. When the time delays between
pump pulse and control pulse are T/4 and 3T/4, the
second-harmonic frequency terms, with frequency 68 cm-1
and period T/2, are destructive. On the other hand, when
this time delay becomes T/2, the frequency terms, with
frequency 34 cm-1 and period T, generate a destructive
superposition. Therefore, with different time delays between
pump and control pulses, FFT peaks appear or disappear
accordingly.053405-5
PHYSICAL REVIEW A 81, 053405 (2010)
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Yuan, Luqi; Ariunbold, Gombojav O.; Murawski, Robert K.; Pestov, Dmitry; Wang, Xi; Patnaik, Anil K. et al. Femtosecond wave-packet dynamics in cesium dimers studied through controlled stimulated emission, article, May 12, 2010; [College Park, Maryland]. (https://digital.library.unt.edu/ark:/67531/metadc103267/m1/5/?rotate=90: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.