  High-energy femtosecond laser pulses in the mid-infrared (MIR) wavelength
range are essential for a wide range of applications from strong-field physics
to selectively pump and probe low energy excitations in condensed matter and
molecular vibrations. Here we report a four stage optical parametric chirped
pulse amplifier (OPCPA) which generates ultrashort pulses at a central
wavelength of 3000 nm with 430 $\mu$J energy per pulse at a bandwidth of 490
nm. Broadband emission of a Ti:sapphire oscillator seeds synchronously the four
OPCPA stages at 800 nm and the pump line at 1030 nm. The first stage amplifies
the 800 nm pulses in BBO using a non-collinear configuration. The second stage
converts the wavelength to 1560 nm using difference frequency generation in BBO
in a collinear geometry. The third stage amplifies this idler frequency
non-collinearly in KTA. Finally, the fourth stage generates the 3000 nm
radiation in a collinear configuration in LiIO$_3$ due the broad amplification
bandwidth this crystal provides. We compress these pulses to 65 fs by
transmission through sapphire. Quantitative calculations of the individual
non-linear processes in all stages verify that our OPCPA architecture operates
close to optimum efficiency at minimum absorption losses, which suggests that
this particular design is very suitable for operation a high average power at
multi kHz repetition rates.
