Adaptive Optimization of High Order Harmonic Generation In a Free Propagation Geometry

Adaptive femtosecond pulse shaping has become a powerful tool for optimizing the characteristics of ultrafast pulses [1,2] or ultrafast laser-matter interactions [3]. Recently, it has been shown in high order harmonic generation that specific harmonic orders near the cutoff can be significantly enhanced by optimizing the spectral phase of the driving pulse via adaptive optimization [4]. These experiments were conducted in a waveguide geometry using a hollow core fiber. Nonetheless, it is interesting to consider if adaptive learning can be effective for high order harmonic generation in a free propagation geometry. Here, we present results of experiments that demonstrate that harmonic emission can be tuned more effectively using adaptive optimization than via simple pulse chirping.