Abstract

Kerr-lens mode locking (KLM)^[1,2] is a powerful technique for generating ultrashort pulses from many different gain media and laser cavity geometries. To date, these lasers all require the use of dispersion compensating intracavity elements to provide net negative dispersion. Pulse shortening is enhanced by a soliton-like interplay between net negative dispersion and self-phase modulation. Analysis has shown^[3] that net negative dispersion (−GVD), while not necessary for pulse formation, has the advantages of generating chirp- free pulses without requiring strong KLM nonlinearities. Pulse formation in the presence of net positive dispersion (+GVD) requires a stronger KLM nonlinearity and results in comparatively longer, chirped pulses. In the +GVD case, minimization of chirp and pulse duration can be achieved by optimizing KLM nonlinearities, and by reducing intracavity dispersion. In this paper, we demonstrate self starting KLM mode locking in compact lasers without the need for intracavity dispersion compensation. Since most techniques for dispersion compensation provide serious limitations to cavity size, the elimination of intracavity dispersion compensation permits a wide range of very compact and simple laser cavity designs. We present a compact positive dispersion Ti:Al₂O₃ laser design that achives high average power, ultrashort pulses at gigahertz repetition rates.

© 1995 Optical Society of America