Ultrabroadband, highly flexible amplifier for ultrashort midinfrared laser pulses based on aperiodically poled Mg:LiNbO3

We present an amplification medium for optical parametric chirped-pulse amplification that allows for ultrabroadband gain in a collinear configuration. Our approach is based on aperiodic quasi-phase-matching (QPM). For the first demonstration of this method in a mid-IR optical parametric chirped-pulse amplifier, we chose a QPM grating design with a linear chirp of its associated spatial frequencies. The resulting 7.4-mm-long, aperiodically poled Mg:LiNbO3 amplification crystal has a chirp rate of κ′=−250cm−2 and provides gain over the 800nm bandwidth centered at 3.4μm . We were able to generate pulses as short as 75fs and the pulse energy at the output of the optical parametric amplifier before compression was 1.5μJ . Low thermal load on the amplification medium allows for operation at a high repetition rate, 100kHz in our case, and high average power limited only by the available pump power.