Abstract
We explore mode locked operation of a Ti:Sapphire laser with enhanced Kerr nonlinearity, where the threshold for pulsed operation can be continuously tuned down to the threshold for continuous-wave (CW) operation, and even below it. At the point of equality, even though a CW solution does not exist, pulsed oscillation can be realized directly from zero CW oscillation. We experimentally investigate the evolution of the mode locking mechanism towards this point and beyond it, and provide a qualitative theoretical model to explain the results.
Highlights
The ultra-broad gain bandwidth of the Ti:Sapphire (TiS) laser renders it the ‘work-horse’ of the last decades for generation of ultrashort pulses by mode locking (ML) [1]
The ML threshold is defined as the minimum pump power required to initiate pulsed operation
From both figures we see the typical behaviour of mode locked lasers, where the ML threshold is always larger than the CW threshold and CW oscillation must exist to initiate the ML process
Summary
The ultra-broad gain bandwidth of the Ti:Sapphire (TiS) laser renders it the ‘work-horse’ of the last decades for generation of ultrashort pulses by mode locking (ML) [1]. When the pump power crosses a certain threshold, can ML be initiated from a noise-seed (either by a knock on a cavity element or by external injection of long pulses). Another common feature is that the threshold pump power for ML is higher than the CW threshold. Typical mode locked operation requires a certain amount of CW oscillations to exist in the cavity, and only on top of the existing CW can an intensity fluctuation be amplified to create the pulse. We investigate the possibility to push the ML threshold to the extreme, i.e. the possibility of reducing the ML threshold down to the CW threshold and even lower
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