Shai Yefet

Kerr lens mode locking without nonlinear astigmatism

We demonstrate a Kerr lens mode-locked folded cavity using a planar (non-Brewster) Ti:sapphire crystal as a gain and Kerr medium, thus cancelling the nonlinear astigmatism caused by a Brewster cut Kerr medium. Our method uses a novel cavity folding in which the intracavity laser beam propagates in two perpendicular planes, such that the astigmatism of one mirror is compensated by the other mirror, enabling the introduction of an astigmatic free, planar-cut gain medium. We demonstrate that this configuration is inherently free of nonlinear astigmatism, which in standard cavity folding needs a special power-specific compensation.

Mode locking with enhanced nonlinearity--a detailed study.

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.

Mode-Locking With Ultra-Low Intra-Cavity Pulse Intensity Using Enhanced Kerr Nonlinearity

Kerr lens mode locking strongly depends upon intensity. Low pulse intensity weakens the nonlinear Kerr lens, and eventually mode locking is not supported. We demonstrate efficient mode-locking in a Ti:Sapphire laser oscillator with record-low intra-cavity pulse intensity (18 GW/cm2) and intra-cavity average power (340 mW). Using an additional nonlinear window in the cavity, the Kerr nonlinearity can be enhanced by an order of magnitude compared to the standard Ti:Sapphire cavity, allowing mode locking with an output coupler reflectivity as low as R = 55% and record-low intra-cavity pulse intensity. Our results provide an important new possibility to control mode-locking in cavities with very low intra-cavity pulse intensity, such as semiconductor laser oscillators and high-repetition rate mode-locked lasers.

Precise spectral shaping of mode-locked oscillations

We demonstrate a powerful method to control the spectrum of a mode-locked laser by placing the gain medium inside an intra-cavity pulse shaper.