Femtosecond wave-packet dynamics in cesium dimers studied through controlled stimulated emission

We study the dynamics of wave packets in cesium dimers using a femtosecond-controlled pump-probe technique. We implement configurations with one pulse (pump) or two pulses (pump and control) to produce vibrational wave packets on the electronic excited state. The transmission of an additional, variable-delay probe pulse is measured to monitor the time evolution of the wave packets. In the case of the pump-control-probe configuration, a superposition of two independent wave packets is observed. In order to elucidate the observed experimental data, we develop a theory based on the Liouville equation for the density matrix associated with the Franck-Condon factors. Both the numerical and analytical calculations are in good agreement with our experimental results.

Figure 1

Experimental setup layout. CH, chopper; BS, beam splitter; VDFs, variable neutral density filters; DS1,2 delay stages; BPF, variable bandpass filter such as a spectrometer with an adjustable exit slit; PD, photodiode; ADC, analog-to-digital converter.

Figure 2

Energy level diagram of a four-level system.

Figure 3

$|S({\nu }^{\prime },{\nu }^{″})|$ where ${\nu }^{″}$ is the vibrational level in the $X$ ground state and ${\nu }^{\prime }$ is the vibrational level in the $B$ excited state in cesium dimer.

Figure 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.

Figure 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.

Figure 6

Dependence of experimental signal on probe (IR) delay, with different time delay between pump (R1) and control (R2) in pump-control-probe measurements. FFT spectra are on the right.

Figure 7

Numerical results of pump-control-probe measurements with different time delay between pump pulse and control pulse. FFT spectra of the absorption signal are on the right.

Figure 8

Analytical results of pump-control-probe measurements with different time delay between pump pulse and control pulse. FFT spectra of the absorption signal are on the right.