Abstract
Optically pumped continuous-wave (cw) semiconductor disk lasers (SDLs) have an established commercial impact, and recent progress in ultrashort-pulse operation makes them attractive for applications in frequency metrology. There is, however, a tradeoff between femtosecond pulse lengths and average output power. Quantum-dot (QD) materials could potentially solve this problem---but not just any dots. The authors show that SDLs based on active submonolayer QDs produce record-high cw output power, but without stable mode locking, which is due to fundamental physical reasons.
Highlights
Pumped passively modelocked vertical external-cavity surface-emitting lasers (VECSELs) [1,2,3] and modelocked integrated external-cavity surface-emitting lasers (MIXSELs) [4] are referred to as ultrafast semiconductor disk lasers (SDLs)
Thanks to the high modal gain provided by active (InxGa1-x)As quantum wells (QWs), output powers up to 106 W could be demonstrated in cw operation [7]
Passive modelocking was achieved with semiconductor saturable absorber mirrors (SESAMs) [8] with the first demonstration in 2000 [9]
Summary
Pumped passively modelocked vertical external-cavity surface-emitting lasers (VECSELs) [1,2,3] and modelocked integrated external-cavity surface-emitting lasers (MIXSELs) [4] are referred to as ultrafast semiconductor disk lasers (SDLs). The average enhancement of the electric field intensity in the SML QDs is set to a low value of 0.5 (normalized to 4 outside the structure) and its spectral profile is designed to be flat over a ±30-nm bandwidth around the designed center lasing wavelength [Fig. 1(c), inset] This is not an optimized design for cw performance, where the QD layers will be placed at the antinodes of the standing wave. We characterize the emission wavelength tunability of the SML QD VECSEL by inserting a 1-mm-thick quartz birefringent filter (BRF) at Brewster’s angle inside the optical cavity [Fig. 3(b)] For this experiment, we obtain the broadest tuning range with a reduced ROC of the output coupler of 100 mm and a smaller laser spot size of 125 μm on the VECSEL.
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