  We develop a simplified light source at 461 nm for laser cooling of Sr
without frequency-doubling crystals but with blue laser diodes. An
anti-reflection coated blue laser diode in an external cavity (Littrow)
configuration provides an output power of 40 mW at 461 nm. Another blue laser
diode is used to amplify the laser power up to 110 mW by injection locking. For
frequency stabilization, we demonstrate modulation-free polarization
spectroscopy of Sr in a hollow cathode lamp. The simplification of the laser
system achieved in this work is of great importance for the construction of
transportable optical lattice clocks.
