When methanol microdroplets of 15mm size are irradiated
by intense femtosecond laser pulses of moderate intensities (<2×10^16Wcm^−2), we observe a ‘red-light flash’ from the microplasma. We report on
the presence of a large ‘blue shoulder’ (that extends to about 200 nm from
the incident laser wavelength) in the scattered spectra that corresponds to
the red-light flash. A prepulse is found to be essential for producing the
large blue shift, which is attributed to the rapid subsequent ionization of a
near-critical density preplasma when the main pulse is incident.