Elimination of the chirp of narrowband terahertz pulses generated by chirped pulse beating using a tandem grating pair laser pulse stretcher

We study the elimination of the chirp of narrowband terahertz pulses generated by chirped laser pulse beating using a laser pulse stretcher with two grating pairs that cancel out the third-order spectral phase. First, we show that positively chirped terahertz pulses can be generated using a pulse stretcher with a grating pair and internal lenses. We then combine this with a second grating pair, the spectral phase of which has the opposite sign to that of the first one. By varying the separation of the second grating pair, we experimentally verify that the chirp of the generated terahertz pulses can be eliminated.