Design principles of q-preserving multipass-cavity femtosecond lasers

Abstract

We describe a new class of femtosecond laser cavity designs that are based on a Herriott-type multipass cavity (MPC) to effectively increase the length of a standard laser resonator. MPC laser designs can be used to increase the output pulse energies or to make more compact resonator configurations. A general theory for MPC lasers is developed by analyzing a periodic optical system, and the conditions are established for the case in which the q parameter of a Gaussian beam is left invariant after a single transit through the system. On the basis of this analysis, we determine the design criteria for two-mirror q-preserving MPCs. Practical laser cavity choices are presented and their trade-offs are examined. We also discuss various experimental setups that use these novel MPC designs to increase pulse energies while maintaining compact cavities.