Saturable absorber design for efficient Q-switch laser operation

Q-switching properties of a laser with a saturable absorber (SA) are investigated. We propose an original method to optimize the transverse concentration profile of the SA inserted in the cavity. The resulting design considerations give the way to an optimal use of the SA over its whole transverse section. The optimization problem is formulated as a variational problem and then solved analytically using the calculus of variations. Replacing an uniform profile by an optimized profile, it is possible with the same number of molecules to increase the absorption at low intensity from a factor 1.9, while transmission at high intensity remains near to 100%. We further demonstrate that the optimization does not affect the transverse pattern properties of the laser emission (M2 near 1).