First and second laser beams having respective first and second wavelengths respectively excite palladium isotopes at a ground level to a first excited level then to a second excited level. At first and second excitation steps, palladium isotopes having an odd mass number are selectively excited to the second excited level, with the identity of the ion core state of each of the palladium isotopes retained between the first excited level and the second excited level. The first wavelength and the second wavelength are selected to allow the second excited level to be an autoionization level or, in a case where the second excited level is not the autoionization level, the first wavelength, the second wavelength, and a third wavelength are selected to excite the palladium isotopes at the second excited level to the autoionization level with a third laser beam having the third wavelength at a third excitation step.