We report experimental optical and thermodynamical studies of convection cooling for face-cooling of laser amplifier disks. Amplifier maquettes are used to explore the flow regime in laser relevant conditions, and to measure heat exchange coefficients. We thus benchmark analytical and numerical predictions, based on common models of turbulence. The y+ model appears best suited to compute h in the laminar regime, and RANS in the weakly turbulent regime. By strioscopic imaging, we examine the optical properties of the flows, in particular the onset of a striation instability occurring well before the transition to turbulence. At higher Reynolds numbers, the unstable thermal layer is shown to be pushed back onto the surface, suppressing effectively the wavefront distortions from striations. This super-forced thermal regime maybe of high interest for very high thermal loads