Laser-microwave spectroscopy of Cu I atoms in S Rydberg state

For the first time the energy level positions of Cu I atoms have been measured with high accuracy by means of laser-microwave spectroscopy in the 77-136 GHz frequency range. The new measurements cover the range of principal quantum number n = 31-38 for Rydberg series S_1/2. Using our measured frequencies in a joint fit together with the frequencies of optical transitions the quantum defect constants for this series are obtained. The description of our spectrometer, measurement technique and results is presented.