Chirped-Pulse Oscillators - Generating Microjoule Femtosecond Pulses At Megahertz Repetition Rate by Alma Fernandez Gonzalez
The maximum energy achievable directly from conventional Ti:sapphire oscillators has been limited by the onset of instabilities such as cw-generation and pulse splitting because of the high intensity in the laser medium. Generation of microjoule pulses at megahertz repetition rates are of special interest in many areas of science and technology. The main subject of this book is the development of high energy Ti:sapphire oscillators at megahertz repetition rate. The main concept that was applied to overcome the difficulties pointed out above was to operate the laser in the positive dispersion regime. By operating the laser in this regime, intracavity picosecond pulses are generated that can be externally compressed down to femtosecond pulse durations. The long pulse duration inside the laser offers an elegant way to reduce pulse instabilities by decreasing the intracavity intensity via pulse stretching. Drawing on this concept, Ti:sapphire chirped-pulse oscillators delivering sub-50-fs pulses of 0.5 ?J and 60 nJ energy are demonstrated at average power levels of 1 and 4 W (repetition rate: 2 MHz and 70 MHz), respectively. The 0.5 ?J pulses have a peak power in excess of 10 MW. By locking a 76-MHz chirped-pulse oscillator to a femtosecond-enhancement cavity 7.8 ?J pulses with 55 fs pulse duration were achieved. High harmonic generation was demonstrated in a Xenon target placed close to the enhancement cavity focus.