Toward standoff distance terahertz wave sensing

For standoff distance terahertz wave generation by mixing a 800 nm pulse and its second harmonic (400 nm) in air, a phase compensator, incorporated with a small-angle wedge pair, is used to pre-compensate the temporal walk-off between the 800 and 400 nm pulses due to the normal dispersion of the ambient air. With the phase compensator, we are able to generate intense terahertz waves by sending the two optical pulses 116 meters away and focusing them locally.