Figure 1.

(Top) Thermal length expansion of a 1 mm Si crystal relative to room temperature (squares) fitted by a T ² polynomial (red line). The coloured ellipses show examples of T _p and T _b corresponding to low-, medium- and high-power regimes (green, yellow and red, respectively). T _ze shows the temperature of minimum thermal expansion. (Bottom) Schematic representation of crystal deformation, switching from concave to flat, and to convex, when power is increased.