Passive Mode-Locking is the result of the Kerr Effect, which is based on the non-linear intensity
dependent index of refraction. When combined with an appropriately placed slit and a small
perturbation, one can achieve pulses of approximately 10 femtoseconds in duration!!!


A laboratory build "Ti:Sapphire Passive Mode Locked Laser Oscillator" pumped with
a Spectra-Physics Millennia laser, which seeds a BMI alpha-1000 regenerative amplifier.


By Chirp Pulse Amplification, optical pulses 35 fs in duration (with a 1kHz repetition rate,
centered at 800nm, and having an energy ~ 1mJ per pulse) are generated.


The source can be spectrally enhanced by self-phase modulation to produce a white light
continuum by focusing a portion of the amplifier beam into a sapphire plate or a hollow
multi-mode waveguild followed by chirp compression using phase dispersive elements.


To resolve excitations in the experiment, a pump pulse excites the material and a probe measures
the change in the optical properties due to the pump as a function of time delay between
the pump and the probe. Degenerate pump-probe autocorrelation with 2nd harmonic generation!!!