Abstract

We describe the complete calibration of a ruby laser-based multipoint Thomson scattering system, performed only by rotational Raman scattering from H2 and the measurement of the absolute Raman cross section of some rotational transitions suitable for such calibrations. The absolute calibration factors (for ne measurements by Thomson scattering) have been measured by observing the Stokes J = 1 → 3 rotational transition at Δν = −587 cm−1 (λ = 723.8 nm), with a ≅ 4.5% accuracy. The relative calibration (for Te measurements) has also been performed by Raman scattering, observing the same line in all the spectral channels. The results agree to within ≅ 10% with those obtained by a tungsten lamp and a lock-in detection technique. From a comparison of the results of the two methods, systematic errors on the measured Te and ne of less than ∼10% (for Te up to 200 eV) are inferred. The absolute cross section of the rotational Raman transitions at Δν = −587 cm−1 (λ = 723.8 nm), Δν = −354 cm−1 (λ = 711.8 nm), and Δν = 354 cm−1 (λ = 677.6 nm) has also been measured, by comparison with the intensity of the Rayleigh line. Significant deviations from thermal equilibrium population in Raman levels, expected from the possible occurrence of stimulated Raman emission, are not observed. From the measured data the anisotropic polarizability of H2 at λ = 694.3 nm was estimated to be γ = 2.93 × 10−25 cm3 ± 3%. The absolute cross section of the strongest rotational lines of H2 is also given.

© 1987 Optical Society of America

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