  We present a laser system with a linewidth and long-term frequency stability
at the 50 kHz level. It is based on a Ti:Sapphire laser emitting radiation at
882 nm which is referenced to an atomic transition. For this, the length of an
evacuated transfer cavity is stabilized to a reference laser at 780 nm locked
to the $^{85}$Rb D$_2$-line via modulation transfer spectroscopy. Gapless
frequency tuning of the spectroscopy laser is realized using the sideband
locking technique to the transfer cavity. In this configuration, the linewidth
of the spectroscopy laser is derived from the transfer cavity, while the
long-term stability is derived from the atomic resonance. Using an optical
frequency comb, the frequency stability and linewidth of both lasers are
characterized by comparison against an active hydrogen maser frequency standard
and an ultra-narrow linewidth laser, respectively. The laser system presented
here will be used for spectroscopy of the $1s^{2}2s^{2}2p\ ^{2}P_{1/2} -\
^{2}P_{3/2}$ transition in sympathetically cooled Ar$^{13+}$ ions at 441nm
after frequency doubling.
