Ultrashort pulse generation in lasers containing an antiresonant ring

Abstract

Mode locking with an antiresonant ring is a powerful technique for producing stable trains of ultrashort pulses. This structure1 was first applied to visible dye lasers by placing a saturable absorber within an antiresonant ring that forms the high-reflectivity end mirror of a linear laser cavity. Nearly transform-limited 65 fs pulses have been generated with enhanced pulse stability.2 By using the additive pulse mode-locking (APM) representation, we describe the antiresonant ring (ARR) as a pulse-shaping reflector, which returns a temporally narrowed pulse to the main laser cavity. When a nonlinear element is incorporated within the ARR, an intensity-dependent reflectivity is predicted. A nonlinear element introduces temporal or spectral pulse shaping of the two counterpropagating fields within the ring. If the pulse shaping is unbalanced for the two fields, then preferential reflection of the high-intensity portions of the incident pulse can occur, resulting in a temporally narrowed pulse being returned to the laser gain medium. Results will be presented for a saturable absorber, a saturable amplifier, and a Kerr-type nonlinearity, such as an optical fiber.