Optical-microwave double-resonance spectroscopy of highly excited Rydberg states of ytterbium

Microwave transitions between the neighboring levels that belong to the $^{1}$${\mathit{S}}_{0}$, $^{1}$${\mathit{P}}_{1}$, and $^{1}$${\mathit{D}}_{2}$ Rydberg series of ytterbium are studied for the principal quantum number ranging from 33 to 57. The term values and the quantum defects are determined by means of the general Rydberg-Ritz formula. The determined quantum defects show large linear energy dependence. The Zeeman effect measured for three $^{1}$${\mathit{P}}_{1}$ and one $^{1}$${\mathit{D}}_{2}$ Rydberg states under a weak external magnetic field is discussed.