Time-resolved Doppler broadening

The most time consuming parts of the forward model are the calculation of the absorption coefficients and the calculation of the radiative transfer. A spectral resolution of Av = 0.0005 cm 1 is considered necessary in order to resolve the shape of Doppler-broadened lines. To avoid repeated line-shape and radiative transfer calculations at this high resolution, two optimizations have been implemented ... 

But experiments to resolve the fine structure of the Balmer lines were difficult as you all know, resolution was impeded by the Doppler broadening of components. So ionized helium comes into the picture, because, as Sommerfeld s formula predicted, fine structure intervals are a function of (aZ)2, so in helium they are of order four times as wide as in hydrogen and one has more chance of resolving the Doppler-broadened lines. So PASCHEN [40], in 1916. undertook an extensive study of the He+ lines and in particular, 4686 A (n = 4->3). Fine structure, indeed, was found and matched against Sommerfeld s formula. The measurements were used to determine a value of a. But the structure did not really match the theory in that the quantum numbers bore no imprint of electron spin, so even the orbital properties - which dominated the intensity rules based on a correspondence with classical radiation theory - were wrongly associated with components, and the value of a derived from this first study was later abandoned. 

We will now consider different laser spectroscopy methods. We will first discuss techniques in which a reasonable resolution is sufficient and where relatively broad-band lasers (0.1-0.01 A) and Doppler-broadened samples are used. We will then describe how resonance techniques can be combined with laser excitation. In the following sections, time-resolved spectroscopy will be considered. Lifetime measurements and structure determinations using such techniques will be described. In this context a comprehensive survey of methods for determining the radiative properties of atoms and molecules is made. 

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