  Carrier envelope phase stable 4 fs near-IR pulses with 3 mJ energy were
generated by spectral broadening of circularly polarized 8 mJ pulses in a
differentially pumped 2 m long composite stretched exible hollow ber. The
pulses were characterized using both second-harmonic generation
frequency-resolved optical gating (SHG-FROG) and SHG d-scan methods
