Novel AlGaAs/CaF 2 SESAM Device for Ultrashort Pulse Generation

A novel ultrabroadband AlGaAs/CaF 2 semiconductor saturable absorber mirror (SESAM) covering nearly the entire Ti:sapphire gain spectrum is demonstrated. This device supports sub-10-fs pulse operation of a laser. In contrast to previous SESAMs of comparable bandwidth, our device can be monolithically grown by molecular beam epitaxy and requires no post-growth processing. GaAs is used as semiconductor saturable absorber material. The high defect concentration of the material is due to the lattice-mismatched growth on a fluoride surface with (111) orientation. With a time response of 1.2 ps for carrier trapping, a saturation fluence of 36 μJ/cm 2 and a modulation depth of up to 2.2%, the GaAs saturable absorber is well-suited for all-optical switching in SESAM devices used for ultrashort pulse generation.