Efficient generation of 50-fs red pulses by frequency doubling in LiB3O5

We report frequency-doubling of femtosecond pulses from a mode-locked Cr:forsterite laser with efficiency as high as 44%, using lithium triborate (LiB3O5). The single-pass efficiency is nearly 4 times as large as values obtained previously with femtosecond pulses of nanojoule energies. Red pulses as short as 45 fs are generated with average power > 100 mW at 620 nm. The dependence of the harmonic pulse duration on fundamental pulse duration is investigated over a range from 100 fs to 40 fs.