Laser control optimal conditions

In order to interpret the results of our experiments, optimal-control calculations were performed where a GA controlled 40 independent degrees of freedom in the laser pulses that were used in a molecular dynamics simulation of the laser-cluster interactions for Xejv clusters with sizes ranging from 108 to 5056 atoms/cluster. These calculations, which are reported in detail elsewhere [67], showed optimization of the laser-cluster interactions by a sequence of as many as three laser pulses. Detailed inspection of the simulations revealed that the first pulse in this sequence initiates the cluster ionization and starts the expansion of the cluster, while the second and third pulse optimize two mechanisms that are directly related to the behaviour of the electrons in the cluster. We consistently observe that the second pulse in the three-pulse sequence arrives a time delay where the conditions for enhanced ionization are met. In other words, the second pulse arrives at a time where the ionization of atoms is assisted by the proximity of surrounding ions. The third peak is consistently observed at a delay where the collective oscillation of the quasi-free electrons in the cluster is 7t/2 out of phase with respect to the driving laser field. For a driven and damped oscillator this phase-delay represents an optimum for the energy transfer from the driving force to the oscillator. 

A control mechanism has been proposed on the basis of the joint analysis of the experimental and theoretical information. The control scheme leading selectively to the formation of CpMn(CO)3+ is represented in Figure 6(b). The experiment realized with an optimal laser field is simulated by one pump pulse (at 3.49 eV) followed by a probe pulse (at 4.716eV) designed with the adequate properties of phase, frequency, and duration. Within these specific conditions, the quasi-bound state c A is populated selectively and the CO dissociation... 

When the conditions reach the WLC, one can fix the cavity input intensity and measure the cavity transmission linewidth, the experimental results are shown in Fig. 14 (a). It is clear that the Unewidth can be easily controlled with the coupling laser beam power. Another strength with the current mechanism is that one has more freedom to choose the parameters to satisfy the WLC condition in the parameters space as shown in Fig. 7. For a given cavity input intensify, one can always find a set of parameters to balance the linear and nonlinear refractive indices, as well as their derivatives, to reach the WLC condition and make the cavity transmission linewidth maximum. Figure 14 (b) just presents a cross section of the available entire parameter space (such as represented in Fig. 7) in which for each given cavity input intensify (power) a coupling power can always be found to satisfy Eq. (12), i.e., WLC condition, fhe corresponding (optimized) linewidth is shown in the inset of Fig. 14 (b). 

Figure 1 presents a schematic overview of a typical molecular beam time-of-flight mass spectrometer equipped with a laser desorption source. In the studies presented in this book, the sample bar is made from graphite. Accurate positioning of the sample bar with respect to the nozzle is required for optimal performance. It is typically mounted on a double translation stage (Fig. 1). The vertical travel (x-direction) with a typical accuracy better than 0.01 mm allows for optimal cooling with minimal distortion of the molecular beam expansion. The sample bar is typically positioned about 0.1 mm below the aperture of the pulsed molecular beam valve. Travel in the horizontal direction (y-axis) of 50 mm (length of the sample bar) with a position accuracy of about 0.1 mm ensures desorption of fresh sample at every laser shot. Both positioning options can be controlled under operating conditions. Finally, the distance along the molecular beam (z-axis)...

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