ABSTRACT
To fully understand the transport processes and energy balance of the plasma in high intensity discharge (HID) lamps, the electron gas properties are crucial parameters. The most straight forward way to measure ne and Te is by means of Thomson scattering (TS). In the past, TS has been applied to open plasmas such as ICP, later on to closed plasmas like the QL lamp with extension 'ears' [1]. In May 2003, TS was applied, for the first time, to a real high pressure Hg lamp. The challenges of TS on HID lamps in general are: 1. The small quartz burner wall will cause high intensity false stray light near the detection volume of the TS spectrum. 2. The high intensity plasma radiation from HID lamps will compete with the TS signal. 3. The quartz burner wall can be damaged by the high laser power. 4. The high laser power can create laser induced plasma which disturbs the real plasma inside the lamp. 5. The TS spectrum will be partly collective.
