Double-resonance-ionization mapping of the hyperfine structure of the stable Cu isotopes using pulsed narrowband Ti:sapphire lasers

We present two approaches to enhance the resolving power for measuring hyperfine structure constants using resonance ionization spectroscopy. The first method employs a 2D-resonance ionization spectroscopy scanning technique with pulsed, narrowband Ti:sapphire lasers (1 GHz linewidth), allowing us to resolve hyperfine components that cannot be separated using the standard 1D-scanning method across only one optical transition. In a second refinement, the resolving power is further enhanced through the use of a ring design of the laser cavity. This layout leads to a reduction of the laser linewidth from 1 GHz to below 50 MHz, resulting in experimental linewidths of about 150 MHz. Motivated by the current nuclear physics interest in radioactive Cu isotopes, the hyperfine structure of the 3d¹⁰4s4pt0ex²S1/2 ground state and the 3d⁹4s4p4pt0ex⁴P3/2ᵒ and 3d¹⁰6s4pt0ex²S1/2 excited states in stable Cu isotopes were studied using both approaches. The hyperfine A parameter of the 3d¹⁰6s4pt0ex²S1/2 state was measured with values of $296(18)$ MHz for ⁶³Cu and $307(18)$ MHz for ⁶⁵Cu.