Evidence of a Cooper minimum in the photoionization from the 7s 2S1/2 excited state of potassium

The existence of a Cooper minimum in the experimentally measured photoionization cross sections for the 7s S-2(1/2) excited state of potassium has been reported using a two-step laser excitation technique in conjunction with a time-of-flight mass spectrometer. The photoionization cross sections for the 7s 2S1/2 state have been determined as (9.78 +/- 0.01) x 10(-2), (3.30 +/- 0.49) x 10(-4), (5.47 +/- 0.82) x 10(-3), and (2.06 +/- 0.30) x 10(-2) Mb at the ionizing laser wavelengths 1064, 700, 532, and 355 nm, respectively, that validate the presence of a Cooper minimum at congruent to 1.25 eV above the first ionization threshold. The number density has been determined as N-0 = 2 x 10(11) cm(-3). The experimentally determined absolute values of the cross sections are in qualitative agreement with the theoretical predictions.