Reversible line broadening phenomena

Figuie 6.2 Lower part Spectral profile of a photochemical hole with and without phonon generation during the detection process. Upper part Directly measured difference between these two profiles as obtained by modulating the IR light at a frequency of 150 Hz. 

The time scale of the hole burning experiments discussed above is several minutes. It is about 3 orders of magnitude larger than the typical thermal relaxation time of the sample as given by 

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If the HCL is run at a high current, an abundance of free atoms form. These free atoms absorb at precisely the resonance lines the hollow cathode is intended to emit an example is shown in Figure 6.28, with the free atoms absorbing exactly at K over an extremely narrow bandwidth (Figure 6.28b). The result is that the line emitted from the HCL is as depicted in Figure 6.28c instead of the desired emission line depicted in Figure 6.28a. The emitted lines are broadened by the mechanisms discussed in Section 6.1.1. The phenomenon of absorption of the central portion of the emission line by free atoms in the lamp is called self-reversal. Such absorption is not easily... 

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