Investigation of fading and recovery of fluorescence intensity at 73.5 K.

Fading and recovery of Af-feulgen stained sperm heads are investigated at 73.5 K. The fast fluorescence signals are measured and stored by two coupled transient recorders. 100% recovery was reached after a dark time of 3 s. This shows that the photodecomposition is mainly caused by change of the probability density of energy level and not by destruction of the chromophore groups. The recovery effect allows measurement of the fluorescence intensity of the same sample more than 50 times. Therefore the unaffected spectrum can be measured directly, provided that between the short-term measurements at constant wavelength an appropriate dark phase has been put into operation.