Search of “chlorophyll forms” in vivo by non-linear laser spectroscopy

Induction of a non-linearity in the long-wavelength part of the S₀ —S₁ absorption band of chlorophyll in vivo by a monochromatic pulse results in a simultaneous band shape change in the whole range of investigation (645 – 680 nm). Such homogeneous broadening behaviour at least for time periods ⩾0.5 ns (pulse duration) does not support the hypothesis of many small sub-bands representing “chlorophyll forms”. The band shape changes at different excitation intensities indicate two excited state absorptions of antenna chlorophyll.