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Multi-pulsing instabilities

The high-Q-cavity, the short gain lifetime, and the kinetic-hole burning can also support rather complex multipulse instabilities.

Unfortunately, such multipulse operation sometimes can mimic stable modelocking when only limited diagnostics are available. 

We identify four different modelocking states correlated with a step-like increase of the average output power. Besides an initial fundamental modelocking state, we find stable multipulse operations, such as side pulse, double pulse, and double & side pulse states. Simulations based on the coupled multi-delay differential equations give an explanation!

DownloadRef. [447] (PDF, 2.3 MB)vertical_align_bottom

Optical pump efficiency

For cw InGaAs QW-VECSELs, optical-to-optical pump efficiencies as high as 45% in multimode output and 43.2% in fundamental Gaussian mode output are reported. For femtosecond pulse durations, however, the efficiency is typically reduced to below 1%!

We provide a simple model that explains the observed trade-off between short pulse duration and pump efficiency.

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Modelocking characterisation

Ultrafast VECSELs and MIXSELs are very susceptible to strong “pulsation”, that can be mistaken for clean fundamental modelocking if only limited laser diagnostics are available.

You need full diagnostics - see Section 4.3 in DownloadRef. [396] (PDF, 4.2 MB)vertical_align_bottom for more details.