Experimental measurement of wave packet motion of Shenzhen Double ten laser.
The early measurement of wave packet motion mainly used femtosecond transition state spectroscopy developed by Zewail and his collaborators
Femotosecond Transition-State spectroscopy (F17S), which was first applied to gas
The phase subdivides the system and then extends to the condensed phase macromolecular system. The method starts with a short pulse excitation
Light excites a molecule from its ground bound state to an electron excited state, which generates an unsteady wave in the upper energy state
Packet, wave packet reciprocates within the potential energy curve as localized probability waves.
According to equation (1.31), the wave packet}W prepared by laser with three different pulse widths is further given in FIG. 1.13
The time-dependent evolution of (x, t) 1 "on the excited state several (R) potential curves, in which the shortest pulse excited the wave
The motion path of the packet is similar to that of the classical particle, and the periodicity of the motion is determined by the energy difference between the wood characteristic states of the packet
Determine [see equation ((1.31)]. However, the wave packet prepared by long pulse is a stationary state and does not change with time. The wave
The measurement of the packet motion process also requires another pulsed laser beam, which is delayed relative to the zero moment of the excitation pulse
The amount. For strongly localized wave packets, such as those excited by 42FS pulse width, the wave packets move at some time
Falls within the range of the detection pulse, and at other times falls outside the range of the detection pulse. As shown in figure 1.13
Shown by the dotted line.
FIG. 1.13 Calculation results of evolution trajectory of wave packets prepared by excitation light with three different pulse widths given by equation (1.31)
Dark shaded areas indicate areas of high probability density. The wave packet formed by the laser pulse with pulse width of 42fS has good localization, while the pulse width is
The wave packet formed by the 66-valence laser pulse disperses throughout the potential well without showing any dynamic signs
In the process of wave packet dynamics measurement, time and space resolution must be guaranteed, so the detection of laser
The pulse width must be equal to or less than the excitation pulse width. A second pulsed laser, usually of wavelength X), will contain a wave packet
The intermediate state V2 (R) is excited to a higher excited state, which can easily achieve fluorescence radiation or
The signal size experimentally determined by femtosecond transition state spectroscopy can be measured by the second order perturbation square of mechanics
The following electronic transitions Vi (R)--)V2 (R) and V2 (R) in the theoretical simulation process
->V3 (R) as a function of the amount of time delay between the excitation pulse and the detection pulse, based on the analog measurement of wave packet motion
The measurement results are shown in Figure 1.14. It can be seen that the shorter the pulse width of excitation and detection light used in the experiment, the more localized the wave packet
All right, the experiment measured the modulation depth of the oscillation curve. For the long pulse laser, the measured signal has no
Any wave packet dynamics information. The kinetic curve given in FIG. 1.14 is similar to that shown in FIG. 1.10 for nuclear spacing
Measurement of expected value of change.
FIG. 1.14 Theory of pump-detection measurement signal using three different pulse width laser pulses in femtosecond transition state spectroscopy
The simulation results
In all simulations, the pump light and probe light have the same pulse width. The results show that the rising edge and modulation depth of the measured signal vary with the pulse width
Is changed by the increase of