Figure 3
Spectral and temporal characterization of broadband radiation generated by the laser filament.
(a) The OPCPA output spectrum measured by the homebuilt mid-infrared spectrometer (red) and using SHG FROG (blue) along with the spectral phase retrieved from SHG FROG, (b) typical FROG trace and (c) the temporal envelope and the phase of the mid-infrared OPCPA output. (d) The spectrum of the mid-infrared pulse at the output of the OPCPA (shaded area with a dotted contour) and behind the filament produced by a 22-mJ, 100-fs mid-infrared pulse focused by a CaF2 lens with a focusing length of 75 cm (solid line) and 100 cm (dashed line). (e) The spectrum of the mid-infrared OPCPA output (blue line) against the absorption spectrum of the atmosphere (grey shading). The long-wavelength tail of the spectrum of the laser driver is right at the edge of the atmospheric transmission window. Filamentation of the high-peak-power infrared laser pulse in the atmosphere is accompanied by dramatic spectral broadening. Most of the spectrum of broadband radiation generated as a result of this process (red line) falls within the transmission band of the atmosphere, with its long-wavelength tail limited by atmospheric absorption (grey shading).
