Selective field ionization of high Rydberg states: Application to zero-kinetic-energy photoelectron spectroscopy

摘要

Sequences of pulsed electric fields have been designed and tested that enable a higher selectivity in the pulsed field ionization of high Rydberg states (n >- 100) than has so far been possible. The enhanced selectivety originates from the permutation of the parabolic quantum numbers n_1 and n_2that is induced by a sufficiently rapid inversion of the electric field polarity during a pulse sequence. A reliable procedure, based on numerical simulations of the outcome of pulse field ionization sequences, has been developed to detect and control changes in the parabolic quantum numbers that can occur during a pulse sequence. The procedure can be used to assess under which conditions a clean permutation of the parabolic quantum numbers can be achieved. Unwanted randomization of m, n_1 and n_2, which reduces the selectivity of the field ionization process, can be avoided by minimizing the time intervals during which the electric field in the pulse sequence is almost zero. The high selectivety reached in the pulsed field ionization of high Rydberg states has been used to record pulsed-field-ionization zero-kinetic-energy photoelectron spectra of argon and nitrogen at an unprecedented resolution of 0.06 cm~(-1). This resolution opens new perspectives in photoelectron spectroscopy.