Abstract
Linear and nonlinear gain characterization of electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs) is presented with spectrally resolved measurements of the gain and with gain saturation measurements of two EP-VECSEL samples with different field enhancement in the quantum-well gain layers. The spectral bandwidth, small-signal gain and saturation fluence of the devices are compared. Using the sample with the larger bandwidth, we have demonstrated the shortest pulses generated from a passively modelocked EP-VECSEL to date. With a low-saturation-fluence SESAM for passive modelocking we have achieved 9.5-ps pulses with 7.6 mW average output power at a repetition rate of 1.4 GHz. With a higher output coupler transmission the pulse duration was increased to 31 ps with an average output power of 13.6 mW. The pulses were chirped mainly due to the group delay dispersion (GDD) introduced by the intermediate DBR, which compensates the optical loss in the structure.
Highlights
Optically-pumped vertical external cavity surface emitting lasers (OP-VECSELs) [1] can offer several watts of average output power in circular, diffraction-limited beams
Using the sample with the larger bandwidth, we have demonstrated the shortest pulses generated from a passively modelocked EP-VECSEL to date
The pulses were chirped mainly due to the group delay dispersion (GDD) introduced by the intermediate distributed Bragg reflector (DBR), which compensates the optical loss in the structure
Summary
Optically-pumped vertical external cavity surface emitting lasers (OP-VECSELs) [1] can offer several watts of average output power in circular, diffraction-limited beams. Their external cavity geometry enables passive modelocking with a semiconductor saturable absorber mirror (SESAM [2, 3]). Such passively modelocked ultrafast VECSELs [4] have generated sub-100-fs pulses in bursts of pulses [5], 107-fs pulses in fundamental modelocking at moderate output powers [6] and multi-Watt average output power with longer pulses around 700 fs to 800 fs [7, 8]. Issues and challenges for further power scaling are discussed as well
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