Abstract FR:

We present the study and the realization of a passively mode-locked dye laser producing pulses shorter than 100 femtoseconds (10-13 s). In a ring cavity with an amplifier medium (Rhodamine 6G) and a saturable absorber (DODCI), a sequence of four prisms controls the group velocity dispersion and allows the generation of very short pulses. Then we have studied the production of femtosecond pulses at other wavelengths directly from the femtosecond dye laser. For the first time, 60 fs pulses at 685 nm and pulses shorter than 50 fs between 775 nm and 800 nm have been produced by passive mode locking. These near infrared pulses have been used to study the absorption saturation kinetics in semiconductors multiple quantum wells GaAs/GaA1As. We have observed a singular behavior of the laser operating at 685 nm and analyzed the produced pulses in terms of optical solitons. To perform time resolved spectroscopy with shortest pulses, we have studied a pulse compressor and a multipass amplifier to increase the pulses energy. Pulses of 20 fs and 10 microjoules (peak power: 0. 5 GW) have been obtained at low repetition rate (10Hz) and pulses of 16 fs and 0. 6 micojoules pulses have been generated at high repetition rate (11kHz) using a copper vapor laser. These pulses have been used to study the absorption saturation kinetics of an organic dye (the Malachite Green).