High fluence ultrafast dynamics of hot carriers in semiconductor saturable absorber mirrors

Summary form only given. Ultrafast dynamics in semiconductor saturable absorber mirrors have important implications for pulse shaping and stabilization in mode-locked lasers. At excitation fluences below complete absorption saturation, the observed bleaching is described in terms of population dynamics and state filling. However, recently the presence of two-photon absorption, free carrier absorption, and diffusion dynamics have been revealed at fluence levels above the saturation fluence. Since the fluence incident on such mirrors in many ultrafast lasers is several times the saturation fluence, high fluence dynamics in these structures are important. A detailed study of the ultrafast dynamics of InGaAs/InP saturable absorber mirrors at high excitation fluences is presented. The investigated structure is an antireflection-coated InP /spl lambda//2 layer containing four, centered, InGaAs quantum wells, on a GaAs/AlAs distributed Bragg reflector. In a degenerate pump-probe experiment the quantum wells are resonantly excited (/spl lambda/=1.54 /spl mu/m) with 130-fs pulses. The observed bleaching at 5 /spl mu/J/cm/sup 2/ is qualitatively similar to low fluence studies of similar structures. The structure exhibits ultrafast thermalization (<150 fs), a 1 ps cooling time, and a 50 ps recombination time.