Generation of high beam quality, high-energy and broadband tunable mid-infrared pulse from a KTA optical parametric amplifier

• We achieve the best beam quality in 3–5 μm femtosecond OPA until now.
• The OPA system provides broadband tunable high energy mid-infrared pulses.
• The idler has excellent energy stability of 1.01% rms.

We have demonstrated efficient generation of high beam quality, high-energy and broadband tunable femtosecond mid-infrared pulses using a three-stage collinear optical parametric amplifier (OPA). The white-light continuum (WLC) seeded OPA setup, based on KTA crystal in three stages and pumped by a femtosecond laser pulse at 800 nm, is capable of producing idler wavelength ranging from 2.4 μm to 4.0 μm with energy up to 82 μJ at 3.27 μm, which corresponds to signal energy of 350 μJ at 1060 nm. The output pulse has excellent intensity distribution with measured beam quality factor M2~1.1 for signal and M2~1.7 for idler. To our knowledge, this is the best beam quality reported in 3–5 μm femtosecond OPA until now. The achieved mid-infrared pulse also has a good energy stability with a fluctuation of 1.01% rms over half an hour.