First demonstration of Doppler-free 2-photon in-source laser spectroscopy at the ISOLDE-RILIS

Collinear Doppler-free 2-photon resonance ionization has been applied inside a hot cavity laser ion source environment at CERN-ISOLDE. An injection-seeded Ti:sapphire ring laser was used to generate light pulses with a Fourier-limited linewidth for high-resolution spectroscopy. Using a molybdenum foil as a reflective surface positioned at the end of the target transfer line, rubidium was successfully ionized inside the hot cavity. The results are presented alongside previously obtained data from measurements performed at the RISIKO mass separator at Mainz University, where collinear and perpendicular ionization geometries were tested inside an RFQ ion guide. This work is a pre-cursor to the application of the Doppler-free 2-photon in-source spectroscopy method at ISOLDE. This approach aims to take advantage of the unmatched sensitivity of in-source spectroscopy, without the disadvantage of Doppler broadening.