  A Watt-level continuous and single frequency blue laser at 461 nm is obtained
by frequency-doubling an amplified diode laser operating at 922 nm via a LBO
crystal in a resonant Fabry-P\'{e}rot cavity. We achieved a best optical
conversion efficiency equal to 87\% with more than 1 W output power in the
blue, and limited by the available input power. The frequency-converted beam is
characterized in terms of long term power stability, residual intensity noise,
and geometrical shape. The blue beam has a linewidth of the order of 1 MHz, and
we used it to magneto-optically trap $^{88}$Sr atoms on the 5s$^{2}\,^{1}$S$_0$
-- 5s5p$\,^{1}$P$_1$ transition. The low-finesse, linear-cavity doubling system
is very robust, maintains the lock for several days, and is compatible with a
tenfold increase of the power levels which could be obtained with fully-fibered
amplifiers and large mode area fibers.
