Chirped-pulse oscillators for the generation of high-energy femtosecond laser pulses

This paper reports on a novel approach for producing high energy femtosecond pulses without external amplification. The so-called chirped-pulse oscillator ~CPO! concept is based on an extended-cavity oscillator, operating at small net positive intracavity group delay dispersion ~GDD!, over a broad spectral range by the use of chirped multilayer mirrors. The resultant chirped picosecond pulses are compressed by a dispersive delay line external to the laser cavity. Utilizing this technique, sub-30 fs pulses with an energy exceeding 200 nJ at a repetition rate of 11 MHz were produced. The demonstrated peak power in excess of 5 MW is the highest ever achieved from a cw-pumped laser and is expected to be scaleable to tens of megawatts by increasing the pump power and0or decreasing the repetition rate. The demonstrated source allows micromachining of any materials under relaxed focusing conditions.