Composition-controlled Recovery Time of SWIR (2 – 2.4 μm) GaSb-based SESAMs

SESAMs (Semiconductor Saturable Absorber Mirrors) in ultrafast laser systems have been extensively used in the near-infrared using GaAs-based SESAMs [1]. The short-wave infrared (SWIR) regime is essential for many sensing and spectroscopic applications, where the GaSb-based material system provides very good performance. So far SESAMs operating at a center wavelength around 2 μm have used InGaSb quantum well layers embedded in GaSb barriers with sufficiently fast recovery times (<30 ps) [2]. These 2- μm SESAMs successfully modelocked lasers [3], [4], but two-photon absorption (TPA) resulted in an early rollover of the nonlinear reflectivity at lower saturation fluences, characterized by the roll-over parameter F2. Replacing the GaSb barrier material with AlAs<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.08</inf>Sb<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.92</inf> reduced TPA, but at the expense of a significantly slower recovery time of 605 ps. We present to our knowledge the first study that systematically investigates the material-composition-dependent recovery times in the 2- μm to 2.4- μm wavelength range [5].