  A carrier envelope phase stable near-single cycle mid-infrared laser based on
optical parametric chirped pulse amplification and hollow-core-fiber
compression is demonstrated. 4 {\mu}m laser pulses with 11.8 mJ energy are
delivered from a KTA based OPCPA with 100 Hz repetition rate, and compressed to
be ~105 fs by a two-grating compressor with efficiency over 50%. Subsequently,
the pulse spectrum is broadened by employing a krypton gas-filled
hollow-core-fiber (HCF). Then, the pulse duration is further compressed to 21.5
fs through a CaF2 bulk material with energy of 2.6 mJ and stability of 0.9%
RMS, which is about 1.6 cycle for 4 {\mu}m laser pulse. The near-single cycle 4
{\mu}m laser pulse CEP is passively stabilized with ~370 mrad based on a CEP
stable 4 {\mu}m OPA injection.

Optics