Determination of argon metastable densities in an electrosurgical argon plasma by TDLAS

Electrosurgical argon plasma sources have recently shown promising clinical results for the treatment of cervical intraepithelial neoplasia (CIN) without causing significant thermal tissue damage. Despite these findings, the underlying plasma-chemical mechanisms responsible for the therapeutic effects are still insufficiently understood, and quantitative data on key excited species under clinically relevant operating conditions remain scarce. In particular, argon metastable states are expected to play an important role in energy transfer and reactive species formation. In this work, tunable diode laser absorption spectroscopy (TDLAS) is employed to determine the temporal evolution of the argon metastable state densities Ar(1s₅) and Ar(1s₃) in a clinically applied electrosurgical argon plasma with sub-microsecond temporal resolution. Metastable densities in the order of 10²⁰m^-3for Ar(1s₅) and 10¹⁹m^-3for Ar(1s₃) are observed. Both states exhibit pronounced temporal modulations within the discharge pulse, indicating the importance of stepwise excitation and de-excitation processes in the discharge kinetics. The measured densities are in good agreement with those reported in previous studies of similar systems. In addition, pressure-broadened absorption profiles are used to estimate characteristic electron densities and gas temperatures from Stark and van der Waals broadening, respectively. The results provide quantitative insight into the transient plasma chemistry of electrosurgical argon plasmas and support future modelling of reactive species generation relevant for biomedical applications.