Fig. 2.

Dependence of high-harmonic spectrum with the laser peak field. Dependence of high-harmonic spectrum with the peak field of the driving laser for a fused silica and b crystalline quartz. For crystalline quartz, the spectral minimum seen around 17 eV persists for different peak fields. c is the comparison of fused silica and quartz for their total yield (from ~14 to ~25 eV) with different peak fields. At modest fields the total yield is similar, but the intensity scaling is significantly different and eventually crystalline quartz becomes more efficient