ABSTRACT
In this chapter, the authors give a detailed discussion of the design of multipass optical cavities and their application to pulse energy amplification in femtosecond solid-state lasers. The authors focus on special multipass cavity (MPC) configurations that leave invariant the original spotsize distribution of the short cavity. These are referred to as “q-preserving” MPCs. The authors give analytical design rules for the construction of q-preserving MPCs. Finally, the authors discuss different experiments in which MPC configurations were utilized to build compact and/or high-energy mode-locked oscillators. Active and passive mode locking techniques can be used to lock the phase of the oscillating modes. Active mode locking involves synchronized modulation of the cavity loss or gain at the frequency equal to the free spectral range or one of its harmonics.
