Laser spot position dependent photothermal mode cooling of a micro-cantilever

We explore the laser spot position (LSP) dependent photothermal mode cooling of a micro-cantilever in a Fabry-P'erot (FP) cavity. Depending on the LSP along the lever, photothermal coupling to the first two mechanical modes can be either parallel or anti-parallel. This LSP dependent behavior is analyzed theoretically by a simple model, which is in quantitatively agreement with our experimental observation. From simulation, the parallel and anti-parallel coupling region is identified along the lever. We conclude that a more efficient mode cooling may be achieved in the parallel coupling region.