Optical frequency synthesizer for wide-range frequency scan and its application to high-resolution molecular spectroscopy

In high-resolution molecular spectroscopy, detailed structures and dynamics appear as frequency shifts, line broadening, intensity anomalies, and Zeeman effects. To observe these minute effects, the relative uncertainty of the frequencies should be less than 10-9. However, to comprehensively analyze the rovibronic energy-level structure and dynamics in a single vibronic excited state, the spectrum over the entire single vibronic band, which extends to hundreds of GHz, must be measured. We developed an optical frequency synthesizer (OFS) employing a scanning single-mode Ti:Sapphire laser and an Er comb to satisfy these contradictory demands. The continuous scanning range was not limited in the developed OFS, and wide-range spectra extending across the entire scanning range of the single-mode laser in the OFS were obtained. For a detailed examination of the developed OFS, we measured the D2 transition of Rb atoms. Although continuous scanning generally has an adverse effect on precise frequency determination, the obtained transition frequencies agreed with those obtained in previous studies, where laser frequencies were locked to a specific transition for a long time. To demonstrate the power of the developed OFS in molecular spectroscopy, the rovibronic spectrum of 1,2-benzanthracene was observed over a single band. We successfully obtained spectra in which the rotational lines were well-resolved. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.