Determination of oxacyanine dyes and rhodamine by a second harmonic generation technique using a femtosecond laser

A second harmonic generation (SHG) technique has been used for a highly sensitive determination on a surface in ambient air. The detection limit (signal: noise = 3) of an oxacyanine dye on a glass plate was 2 pM/cm2, which was equivalent to 0.8% of the monolayer coverage. Rhodamine was found to create a dimer at higher surface concentrations.