If coulored crystal slices of SrF2, SrF2: NaF, or SrF2: CeO2 are positioned in a ruby laser resonator, Q‐switching by saturated absorption of colour centres is observed. The centres in question are F2 centres disturbed by natrium or oxygen generally bleaching by continued switching. The switching function is measured for a laser stable F2 centre disturbed by oxygen. From this spectroscopic parameters are calculated. The peak power of the giant pulses is limited by losses due to stepwise absorption, energy transfer, and reabsorption of the fluorescence, primarily due to the modulation parameter, however, which is smaller by orders of magnitude as compared with dye switches. On the other hand it causes the favourably low switching and saturation power of the colour centre switches. There are possibilities for practical applications.
13C‐N.M.R. Spektroscopical Studies on Simply Substituted Flavylium‐Salts
On a series of differently substituted flavyliumsalts 1‐3 their 13C‐NMR‐chemical shifts and their 1J(13CH) coupling constants were recorded and compared with results received by means of semiempirical PPP calculations and using LFE relationships. Both the experimental and theoretical results exhibit concordantly a characteristic alternate electron distribution along the conjugated π‐system of the compounds studies and reveal the distinct influence of donor and acceptor substituents on the electron distribution in both the benzopyrylium and the aryl moiety of the flavylium salts studied.
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