Seventh-harmonic generation from tightly focused 2 μm ultrashort pulses in air

We report generation of third, fifth and seventh harmonics from air by using tightly focused, ultrashort pulses of short-wave infrared (2 μm) radiation. We have measured the third- and fifth-harmonic efficiencies to be 5×10(-5) and ~1.4×10(-5), respectively, with the ratio of fifth-to-third-harmonic efficiency being close to 0.28. Our experimental results provide confirmation of expectations of the higher-order Kerr effect model.