Abstract: A high power laser source comprises a bar of laser diodes, a submount onto which said laser bar is affixed, and a cooler onto which said submount is affixed. The laser bar has a first coefficient of thermal expansion (CTEbar), the submount has a second coefficient of thermal expansion (CTEsub), and the cooler has a third coefficient of thermal expansion (CTEcool) the third coefficient (CTEcool) being higher than both said first coefficient (CTEbar) and said second coefficient (CTEsub). Contrary to the usual approach with a CTEsub matching the CTEbar, the second coefficient (CTEsub) is selected lower than both said first coefficient (CTEbar) and said third coefficient (CTEcool) according to the invention. A preferred range is CTEsub=k*CTEbar, with 0.4<k<0.9. The submount may consist of or comprise two or more layers of different materials having different CTEs, e.g.