SANTA CLARA, Calif., March 27 -- Coherent Inc. said its COO, John Ambroseo, will succeed Bernard Couillaud as president and chief executive of the laser product maker on Oct. 1. Couillard will become chairman of Coherent's board of directors, while Henry Gauthier, the current chairman, will become vice chairman of the board. Ambroseo, a 13-year veteran of the company, has been chief operating officer since June 2001.