Dear Dr. Soeller,
Three-photon is of course an option, and may work beautifully for many
applications as you pointed out. But for many dyes the three-photon cross
section seems to max out somewhere below 700 nm (e.g. for serotonin etc.,
Maiti et al., Science, vol. 275(1997)530). Also, for some dyes two-photon
around 550 may be better than three-photon around 800, hence the need for an
OPO. Thansk a lot for drawing attention to it though.
Sudipta Maiti

>
>I take it that 3-photon excitation with a Ti::Sapphire is not an option?
>
>  Christian Soeller
>
>--
>Christian Soeller                [log in to unmask] x2770
>Dept. of Physiology              U. Auckland School of Medicine
>Auckland                         New Zealand