Abstract

Coupling a mode-locked laser to a nonlinear external cavity has led¹-⁶ the emission of ultrashort pulses whose duration can be reduced by two orders of magnitudes. The method has allowed to generate pulses in the 100 fs range from colour center lasers. With Ti: sapphire lasers, the emission of ultrashort pulses was observed⁶ to be self-starting, e.g. the laser did not require the use of a mode-locking device. Although the nonlinear element in the external cavity is generally an optical fibre, semiconductor amplifiers can also be used¹,⁴. The physical process leading to pulse narrowing has been identified²,⁷: chirping of the pulse circulating in the coupled cavity leads to a time-dependent modulation after interferometric recombination with the pulse circulating in the main cavity.

© 1990 Optical Society of America