Approaching the microjoule frontier with femtosecond laser oscillators

Broadening the ultrashort laser pulse in a Kerr-lens mode-locked laser by net positive round-trip group-delay dispersion has proven to be a powerful concept for scaling the pulse energy directly achievable with a femtosecond laser oscillator without external amplification. Drawing on this concept, we demonstrate here Ti : Sa chirped-pulse oscillators delivering sub-40 fs pulses of 0.5 mu J and 50 nJ energy at average power levels of 1 and 2.5W ( repetition rate: 2 and 50 MHz), respectively, which to the best of our knowledge constitute the highest pulse energy and average power achieved with a femtosecond (< 100 fs) laser oscillator to date. The 0.5 mu J pulses have a peak power in excess of 10MW and reach a peak intensity > 10(15) W cm(-2) ( when focused down to similar to 1 mu m(2)), both of which represent record values from a laser oscillator. These pulse parameters appear to be limited merely by the pump power available, affording promise of scaling chirped- pulse femtosecond Ti : Sa oscillators to microjoule pulse energies and - by simultaneous spectral broadening - towards peak power levels of several hundred megawatts.