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 μJ and 50 nJ energy at average power levels of 1 and 2.5 W (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 μJ pulses have a peak power in excess of 10 MW and reach a peak intensity >1015 W cm-2 (when focused down to ∼1 μm2), 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