Source for ultrafast continuum infrared and terahertz radiation

A compact and stable method for generating high-intensity linearly polarized continuum mid-IR and terahertz light using ultrafast femtosecond (fs) laser pulses is demonstrated. Continuous light generation from 3300 cm(-1) (100 THz, 3 microm) in a sub-100 fs laser pulse is facilitated by nonlinear mixing of the fundamental, second harmonic, and third harmonic of an ultrafast amplified laser source through filamentation in air. Including the third harmonic in the mixing scheme leads to a tenfold increase in the generated IR power. The compact optical configuration utilizing a delay plate in a collinear geometry serves to simplify alignment and increase stability, making it a practical source for transient IR spectroscopy.