Nonadiabatic Alignment Of OCS Molecule

The controlling of the spatial distribution of molecules is of significant in the regimes of both molecular reaction dynamics and strong field physics. The free rotating molecules distributes isotropically in space, by which many important stereo dynamics informations are shielded. People can obtain valuable spatial angular dependent information of molecules by investigating the processes of dynamics in the laboratory coordinate system only if the spatial orientation of molecules is controlled. As early as the 1990 s, researchers took advantage of magnetic field, electric field, or the laser-field methods, to align and orient molecules. Thereafter, researchers have developed many experimental methods, such as nonhomogeneous magnetic field, nonhomogeneous electrostatic field, homogeneous electrostatic, laser-field technology for the different intentions of the investigation.With the assistance of ultrashort-pulse laser, molecule can be aligned in the field-free condition and no interference will be generated for other experiments. Combining electrostatic hexapole apparatus with ultrashort femtosecond pulsed laser, this thesis analyzes the nonadiabatic alignment dynamics of OCS molecule. In order to improve the alignment degree, a supersonic molecular beam is used to reduce molecular rotational temperature. There still exist many different rotational states after molecular beams are cooled in the beam and these different rotational states exhibit different alignment degrees, which reduces the overall accuracy of molecular alignment in the beam. In order to get single rotational state, we apply a hexapole electrostatic field to select and focus the molecules in the same rotational state, and the application of rotational state selection can improve the accuracy of molecule alignment degree effectively. At last, the nonadiabatic alignment dynamics induced by femtosecond laser can be obtained through a pump-probe method.OCS molecule is chosen as the object studied in this thesis, the rotational temperature of OCS is reduced to 8 k after supersonic cooling. The speed of central molecular beam is about 750 m/s. Two obvious focused peaks are observed in the measured focusing curve. We identify the stronger peak to the OCS molecule vibration ground state, which can be achieved at a focusing voltage of 14 kV. We then use a femtosecond laser pulse to align the OCS molecules. By means of theoretical simulation we learnt that the degree of alignment in condition of single rotational state is higher than that of average thermal disturbed states. The laser used in the experiment possessed the following character: light intensity is13 21.0′10 W cm, central wavelength is 800 nm and pulse width is 275 fs. And the OCS molecules in 10 state are aligned. Revival curve of alignment is obtained by means of controlling translation stage and changing the time delay between alignment laser and probe laser. The result shows that curve of alignment matches well with theoretical simulation, and the highest alignment degree obtained in the experiment is <cos~2θ> = 0.89. The present experiment provides a useful way for further studies on molecular ionization/dissociation in strong laser field in the view of molecular coordinate.