in Quantum Electronics
Henry Baltes, Peter Günter, Ursula Keller,
Fritz K. Kneubühl †, Walter Lukosz,
Hans Melchior, Markus W. Sigrist
High-Power Optically Pumped VECSELs and MIXSELs.
1st edition 2010. XXVIII, 160 pages, € 64,00.
Ultrafast lasers drive applications in areas as diverse as biology, telecommunication, metrology, or material structuring. So far, multi-Watt power levels required ion-doped dielectric laser materials in combination with additional intra-cavity components for the pulse formation, resulting in high complexity and costs. Modelocked semiconductor lasers have the potential for cost-efficient mass production, a necessary requirement for applications such as biomedical imaging or optical clocking. For modelocked edge-emitters the dispersion, nonlinearities and end facet damage are severe challenges for achieving multi-Watt power levels. Vertical external cavity surface emitting lasers (VECSELs) appear to be better suited, because the pulses propagate mostly in the external cavity and experience only low dispersion and nonlinearities from the vertical propagation through the epitaxial semiconductor layers of only a few m thickness. Since the gain structure and the saturable absorber for the pulse formation, typically a semiconductor saturable absorber mirror (SESAM), are both made of semiconductor material, the integration of both elements into a single structure become possible, leading to very simple ultrafast lasers.
In this thesis we present we the first realization of such a laser, which we refer to as modelocked integrated external-cavity surface emitting laser (MIXSEL). One of the key challenges has been the development of quantum dot (QD) saturable absorbers that enable modelocking with equal mode sizes on gain and absorber. The laser generates 185 mW average output power in 32 ps pulses at a repetition rate of 2.8 GHz. With the development of low saturation fluence quantum dot absorbers, enabling a more sophisticated MIXSEL-structure design, and with improved thermal management, we were able to boost the average output power to 6.4 W. Due to the shorter pulse length of 22 ps, the repetition rate could be increased to up to 10 GHz. We believe that these devices will fill a gap in the performance spectrum of today’s laser technology.
Benjamin Rudin received his diploma degree in physics from the ETH Zurich in 2004. He joined the Institute of Quantum Electronics at ETH Zurich in 2005. His research focused on ultrafast high-power vertical external cavity surface emitting lasers (VECSELs) and modelocked integrated external-cavity surface emitting lasers (MIXSELs) and on measurement methods for timing jitter and amplitude noise. He has written and co-authored more than 40 scientific journal articles and conference proceedings. In his spare time he is designing and constructing electronics and mechanics for autonomous walking robots.
Keywords: VECSEL, MIXSEL, semiconductor disk laser, ultrafast, modelocking
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