Abstract
We report on the first femtosecond vertical external cavity surface emitting laser (VECSEL) exceeding 1 W of average output power. The VECSEL is optically pumped, based on self-assembled InAs quantum dot (QD) gain layers, cooled efficiently using a thin disk geometry and passively modelocked with a fast quantum dot semiconductor saturable absorber mirror (SESAM). We developed a novel gain structure with a flat group delay dispersion (GDD) of ± 10 fs2 over a range of 30 nm around the designed operation wavelength of 960 nm. This amount of GDD is several orders of magnitude lower compared to standard designs. Furthermore, we used an optimized positioning scheme of 63 QD gain layers to broaden and flatten the spectral gain. For stable and self-starting pulse formation, we have employed a QD-SESAM with a fast absorption recovery time of around 500 fs. We have achieved 1 W of average output power with 784-fs pulse duration at a repetition rate of 5.4 GHz. The QD-SESAM and the QD-VECSEL are operated with similar cavity mode areas, which is beneficial for higher repetition rates and the integration of both elements into a modelocked integrated external-cavity surface emitting laser (MIXSEL).
Highlights
We have made significant progress in compact ultrafast lasers with the invention and development of semiconductor saturable absorbers mirrors (SESAMs [1,2,3]), a family of optical devices that allow for very simple, self-starting passive modelocking of ultrafast diode-pumped solid-state lasers
The quantum dot (QD)-semiconductor saturable absorber mirror (SESAM) and the QDVECSEL are operated with similar cavity mode areas, which is beneficial for higher repetition rates and the integration of both elements into a modelocked integrated external-cavity surface emitting laser (MIXSEL)
We have demonstrated a femtosecond QD-SESAM modelocked QD-vertical external cavity surface emitting laser (VECSEL) with 784-fs pulses at high average output power levels of more than 1 W
Summary
We have made significant progress in compact ultrafast lasers with the invention and development of semiconductor saturable absorbers mirrors (SESAMs [1,2,3]), a family of optical devices that allow for very simple, self-starting passive modelocking of ultrafast diode-pumped solid-state lasers. Ultrafast VECSELs are a promising alternative to diode pumped solid-state lasers as they offer the possibility for cost-efficient mass production using a simple and compact laser cavity setup with both the semiconductor gain and absorber integrated within one wafer (i.e. the modelocked integrated external cavity surface emitting laser – MIXSEL) [5, 6] They benefit from the power scalability of the thin disk geometry [7] and general semiconductor properties such as large wavelength flexibility with bandgap engineering and epitaxial growth techniques. In this paper we demonstrate the first femtosecond operation of a modelocked VECSEL at 1 W average output power Both the SESAM and the gain element are based on QDs. The structure was designed for both large gain bandwidth and low dispersion to support shorter pulses. 2.5 GHz 2.8 GHz 4.0 GHz 10.0 GHz 50.0 GHz 0.9 GHz 1.0 GHz 3.0 GHz 1.2 GHz 1.0 GHz 3.0 GHz 2.6 GHz
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