Generation of 20-fs pulses by a prismless Cr^4+:YAG laser

Ultrafast optical pulses shorter than 20 fs with 400-mW average power at a 110-MHz repetition rate have been generated by a ${\mathrm{Cr}}^{4+}:\mathrm{YAG}$ laser with only double-chirped mirrors for dispersion compensation. The corresponding pulse spectrum has a peak intensity at 1450 nm and extends from 1310 to 1500 nm full width at half-maximum (FWHM). These pulses, which are believed to be the shortest generated to date from a ${\mathrm{Cr}}^{4+}:\mathrm{YAG}$ laser, are only four optical cycles within the FWHM intensity width.