Ultrabroadband, highly flexible amplifier for ultrashort midinfrared laser pulses based on aperiodically poled Mg:LiNbO_3

Abstract

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:LiNbO(3) amplification crystal has a chirp rate of kappa'=-250 cm(-2) and provides gain over the 800 nm bandwidth centered at 3.4 microm. We were able to generate pulses as short as 75 fs and the pulse energy at the output of the optical parametric amplifier before compression was 1.5 microJ. Low thermal load on the amplification medium allows for operation at a high repetition rate, 100 kHz in our case, and high average power limited only by the available pump power.