Broadband femtosecond parametric amplification in KTA close to mid-IR transparency cutoff

We report an increase in conversion efficiency and significant broadening of signal and idler bandwidth in the collinear KTA optical parametric amplifier operating close to mid-IR transparency cutoff (5.2 μ m) for a visible and near IR pump. Using a 1.24 μ m pump we have produced 2 μ J idler pulses at 3.8 μ m central wavelength with a bandwidth supporting 65 fs transform limited duration. Further tuning to mid-IR up to 5 μ m could be achieved with a 620 nm pump. (paper)