CW LIF for measurements of Ar and Xe ion and atom VDFs

  • Xe and Ar ion and atoms and He atom can be detected with available diode lasers
  • Particle velocity resolution is about 60 m/s
  • Time resolved version of diagnostic
  • Confocal version of the diagnostic for measurements in plasmas with limited optical access (spatial resolution ~ 1mm)
  • High sensitivity technique with a detection limit around 1014 m-3

The Laser-Induced Fluorescence (LIF) spectroscopy is an active laser diagnostic with the possibility of spatially and temporally resolved measurements of the fluorescence profile of various species in complex plasmas encountered in laboratory and industrial plasma applications, including plasma processing, electric space propulsion, and many others. The fluorescence profile resembles a Velocity Distribution Function (VDF), which is a fundamental statistical quantity that provides information about the thermodynamic properties of atom or ion populations in plasma. More specifically, from VDF one can extract the temperature, the mean velocity, and the most probable velocity of fluorescent particles.

LIF diagnostics, available at PPPL are based on two diode lasers:

  • TLB-6917 series New Focus tunable diode laser with the center vacuum wavelength of 834.95 nm
  • TOptica DLC DL PRO 670 tunable diode laser with the tuning range of 660 nm - 673 nm

These laser systems can reach Xe atom/ions, Ar ion/atoms, and He atom transitions.

The available systems are capable of collecting the fluorescence light at some angle (usually 90 degrees) with respect to the incident laser beam. The confocal version of the LIF diagnostic has its collection path on the same side as the laser beam entrance. This allows for diagnostic of optically obstructed plasma systems. The diagrams of both setups are shown below.

LIF setup with fluorescence light collection at 90 degrees with respect to the incident laser beam.

Confocal LIF setup for plasma sources with limited optical access.­

  This capability is located at the Princeton Plasma Physics Laboratory.