Mapping the dynamical regimes of a SESAM mode-locked VECSEL with long cavity using time series analysis

Tushar Malica, Jipeng Lin, Thorsten Ackemann, Douglas J. Little, Joshua P. Toomey, David Paboeuf, Walter Lubeigt, Nils Hempler, G Malcom, Gareth T. Maker, Deborah M. Kane

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The different dynamical regions of an optically-pumped SESAM mode-locked, long-cavity VECSEL system with a fundamental pulse repetition frequency of ~200 MHz are investigated. The output power, captured as 250 μs long time series using a sampling rate of 200 GSa/s, for each operating condition of the system, is analyzed to determine the dynamical state. A wavelength range of 985-995 nm and optical pump powers of 10 W-16.3 W is studied. The system produces high quality fundamental passive mode-locking (FML) over an extensive part of the parameter space, but the different dynamical regions outside of FML are the primary focus of this study. We report five types of output: CW emission, FML, modelocking of a few modes, double pulsing, and, semi-stable 4th harmonic mode-locking. The high sampling rate of the oscilloscope, combined with the long duration of the time series analyzed, enables insight into how the structure and substructure of pulses vary systematically over thousands of round trips of the laser cavity. Higher average output power is obtained in regions characterized by semi-stable 4th harmonic mode-locking than observed for FML, raising whether such average powers might be achieved for FML. The observed dynamical transitions from fundamental mode-locking provide insights into instability challenges in developing a stable, widely tunable, low repetition rate, turn-key system; and to inform future modelling of the system.
Original languageEnglish
Pages (from-to)16624-16638
Number of pages15
JournalOptics Express
Issue number13
Early online date14 Jun 2018
Publication statusPublished - 25 Jun 2018


  • mode-locking
  • laser cavity
  • FML


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