The ability to control the temporal output from a femtosecond laser can enable the same laser to be used for multiple
functions, for example, the laser used in an optical tweezers system could be used as a constant-intensity source to trap a
biological cell and then be temporarily switched to mode-locked operation to effect photoporation. Here, we report the
rapid switching of a Cr4+:forsterite laser between mode-locked and unmode-locked continuous wave (CW) regimes via
the optical pumping of an intracavity SESAM element. Mode-locking of the laser was initiated by an intracavity
quantum well (GaInAsN) SESAM having an anti-resonant design (ΔR~0.3%, λPL~1310nm) that yielded transform-limited
89fs pulses centered around 1296nm with a repetition rate of 162MHz at an average power of 64mW. Upon
excitation of the SESAM with 600mW of extra-cavity power from an 808nm semiconductor diode laser, switching could
be induced between the unmode-locked and mode-locked regimes. Transitions free of Q-switching or relaxation
oscillations were observed with <200μs switching times for both for the initiation and cessation of mode-locking.
Periods of mode-locked operation of custom duration could be produced by appropriate control of the SESAM pump
diode enabling the generation of bursts of pulses as short as 400μs. Switching was confirmed to originate from local
pump-induced heating of the SESAM by observing the laser going through identical regime switching when the chip
temperature of the 'unpumped' SESAM was raised by ~20°C.
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