LAUSR

A methodological study is presented on a noninvasive photometric diagnostic for determining trends in electron density and sheath dynamics in single (1f) and a dual (2f) radio frequency capacitively coupled (CCRF) argon plasmas. The 1f discharges are operated at 13.56 and 27.12 MHz, respectively, while the 2f discharge is driven by both frequencies simultaneously with a variable phase angle between them. A camera is used to measure the sheath extension in front of the powered electrode at different gas pressures and RF‐amplitudes. It was found that sheath thicknesses decrease with rising pressure and increase with frequency. The 2f sheath behavior reflects the influence of both driving frequencies. By fitting the Child–Langmuir law to the sheath width data, electron densities are estimated and compared to Langmuir probe measurements. The results indicate that the photometric method offers only a rough approximation of electron density trends. However, the simple photometric method effectively indicates the general trends and provides valuable insight into the plasma behavior, especially regarding the influence of pressure and RF‐power. In the 2f discharge, the results show a strong dependence of the DC‐self‐bias on the phase variance, as well as pronounced asymmetries in the sheath around , which can be attributed to asymmetric ionization behavior. These findings demonstrate the potential of the simple photometric approach for investigating the interplay between plasma parameters in CCRF discharges and illustrate internal plasma characteristics and controllable process parameters such as pressure, power and phase.