Ultrabroadband AIGaAs/CaF[sub 2] semiconductor saturable absorber mirrors.

Ultrabroadband semiconductor saturable absorber mirrors (SESAMs) are required to support self-starting sub-10-fs-pulse generation with Ti:sapphire lasers. Conventional Al[sub x]Ga[sub 1-x]As/AlAs SESAMs are limited by the reflection bandwidth of about 60 nm of the bottom Bragg mirror. In this letter, we demonstrate a GaAs saturable absorber which is epitaxially grown on CaF[sub 2] using molecular-beam epitaxy. Even though the difference of the thermal expansion coefficient is very large, we were able to demonstrate good modulation depth with small nonsaturable losses. This is interesting for ultrabroadband SESAMs because the large refractive-index difference between CaF[sub 2] and Al[sub x]Ga[sub 1-x]As results in very broadband Al[sub x]Ga[sub 1-x]As/CaF[sub 2] Bragg mirrors extending over about a 400-nm-wide reflection bandwidth for a center wavelength of 850 nm. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]