Provided are methods and systems for operation instability detection in a surface wave plasma source. In an embodiment a system for plasma processing may include a surface wave plasma source configured to generate a plasma field. The system may also include an optical sensor configured to generate information characteristic of optical energy collected in a region proximate to the surface wave plasma source. Additionally, the system may include a sensor logic unit configured to detect a region of instability proximate to the surface wave plasma source in response to the information generated by the optical sensor.