Density Diagnostic for Plasma and Neutral Gas:

Second-Harmonic Dispersion-Interferometer (SHDI)

The Figure shows a simplified diagram for the SHDI which uses a single laser beam source and homodyne detection. The result is the SHDI has a common-beam path, in a design that is less complex, more stable, and lower cost. The SHDI's lower limit sensitivity depends on the thickness and index of refraction of the sample and SHDI's have been used to measure the density of neutral-gas jets and plasma electron density. Indeed, most optically transparent and dispersive mediums can be sampled and measured, including liquids and solids.

The SHDI is currently available in two instrument configurations for:
1-Dimensional, line-of-sight measurements and for 2-Dimensional, transverse imaging.
Photos of the 1D- and 2D-SHDIs are shown below. The principal characteristics of the SHDIs are as follows:

  1. The instrument can measure large, and small sample sizes, from mm's - m's .
  2. The time resolution can range from Δt ~ ns - seconds.
  3. The phase resolution can range from, ΔΦ ~ 10-2 - radians.
  4. Bandwidth and sensitivity can be tailored for measurements.
  5. The recording rate can approach 100's fps.
  6. User-friendly software provides for quick-image visualization and data analysis.
  7. Large vibration isolation tables are unnecessary.
  8. The optical units may be mounted directly on the experiment.
  9. The system is designed for the application, in order to keep cost low.
  10. The 2D SHDI can sample mm2 – cm2 areas.
  11. Large sample gradients, beam deflections, and fringe jumps may limit the spatial resolution.
    12. Download the SHDI Brochure

    1-Dimensional Line-of-Sight Measurements

      Length (Optical Unit1): 150 mm
      Length (Optical Unit2): 150 mm
      Width: 80 mm
      Bandwidth: ≤ 1 MHz
      Electron Density: ∫ nexdl ≥ 1014 cm-2
        Neutral Density: ∫ n0xdl ≥ 1016 cm-2

    2-Dimensional Line-of-Sight Measurements

      Length: OU1 - 400mm, OU2 - 500 mm
      Width: 80 mm
      Pulse Duration: 1 ns
      Sampling Rate: 100 fps
      ∫ nexdl ≥ 1014 cm-2
      ∫ n0xdl ≥ 1016 cm-2