  We explored the issues related to the resolution and the modulation
extinction when filtering the spectrum of a UV femtosecond laser with a
standard ultrashort pulse shaper. We have learned that a higher pulse shaping
resolution often requires a larger working beam size or a higher density
grating for greater dispersion. However, these approaches also introduce more
optical errors and degrade the extinction. In this work, we examined specifics
of each component to determine the best configuration of our spectral filtering
setup. As a proof-of-concept demonstration, we utilized elements available as
standard products and achieved 100 GHz filtering resolution with high
extinction at the UV-A wavelength, which is superb in this wavelength range.
The high extinction spectral filtering is especially important while modifying
a broadband laser for the optical control of molecule's internal state.
