First results on tunneling ionization of H/sub 2/ with a new portable experiment

We have studied the vibrational population of H/sub 2/ after photoionization of H/sub 2/ with a femtosecond laser. A first series of measurements was performed at the fundamental wavelength (800 nm) with both linear and circular polarization and for various intensities of the laser beam. The population obtained in each case differs from the classical Franck-Condon distribution by being shifted towards smaller vibrational numbers. In addition, we used the second harmonic of the laser (400 nm) with linear polarization. In this case, it appears that we witness a transition from the tunneling to the multiphoton regime. At low intensity, almost only nu ' = 0 is observed.