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H₂ Sensing Compendium

Optical methods — overview

Optical methods split into the few that can detect H₂ directly and the many that cannot.

Pages, in reading order:

  1. Raman spectroscopy — exploits H₂’s polarizability to give a single-shot multi-gas fingerprint, but its ~10⁻³⁰ cm²/sr cross section leaves unenhanced Raman blind to soil-gas trace levels.
  2. Enhanced Raman — the cavity, fiber, plasmonic, and coherent methods that push Raman toward ppb on the optical bench.
  3. IR absorption and proxies — NDIR, TDLAS, CRDS, and FTIR cannot detect H₂ (homonuclear symmetry zeroes the dipole moment); they are used for the companion gases (CH₄, CO₂, C₂H₆, H₂S) instead.
  4. UV/EUV and fluorescence — H₂’s native electronic bands sit in a vacuum-UV window that air itself absorbs; this page is the physics veto.
  5. Fiber-optic & chemochromic sensors — palladium and tungsten-oxide coatings translate hydrogen exposure into an optical signal; a credible route to electronics-free downhole monitoring.
  6. Exotic optical approaches — LIBS, interferometry, schlieren, acoustic, and UV-flame methods: physically sound, but wellsite-safety or screening tools rather than exploration sensors.