Subpicosecond ring laser

A ring laser for generating subpicosecond pulses comprising:

• a plurality of reflectors establishing an optical ring cavity, at least one of said reflectors being a partially transmissive output reflector which permits egress of said pulses from said cavity,
• a gain medium positioned within said cavity between a first pair of said reflectors, said first pair comprising curved reflectors effective to focus said pulses onto said gain medium,
• an optical absorber medium of molecules positioned at a location different from said gain medium and between a second pair of said reflectors, said second pair comprising curved reflectors effective to focus said pulses onto said absorber medium so that U.sub.o, the number of photons per square centimeter, is approximately equal to the reciprocal of .sigma., the optical absorption cross section of said absorber medium,
• means for pumping said gain medium to create lasing action in the form of two trains of counterpropagating pulses which overlap in said absorber medium to create therein a transient grating in said molecules, each of said pulses having in said absorber medium a spatial length equal to the product of the pulse time-duration measured at half the maximum pulse amplitude times the velocity of light in said absorber medium,
• the length of the optical path of said pulses in said absorber medium being approximately equal to or less than the spatial length of said pulses therein,
• said absorber medium having a recovery time which is slow compared to the time-duration of said pulses, and
• said reflectors being adapted so that said lasing action occurs in the lowest order transverse mode.