Using a 14-mm thick volume Bragg grating, spectral bandwidth of a cw-operated diode laser array is narrowed to 7 GHz (FWHM). Total output power reaches 13.5 W cw, of which 86% is in the 7-GHz band. With such a narrow bandwidth, it is possible to temperature tune laser frequency across O(2) X(3)Pi --> b(1)Sigma(+) absorption line at 763.8 nm, efficiently generating O(2)((1)Delta) molecules.