Figure 4
Optimization of the flux at 300 eV with the driving wavelength and the gas cell length. (a) Soft X-ray high-order harmonic spectra generated in helium with few-cycles pulses with the OPA central wavelength set at 1300 nm (red, solid) and 1400 nm (green, dashed) in a 4 mm gas cell. (b) Soft X-ray high-order harmonic spectra generated in helium with few-cycles pulses with the OPA central wavelength set at 1300 nm in 1 mm (blue, dotted), 4 mm (red, solid) and 7.5 cm (yellow, dashed) length gas cells. Further optimization of the SWIR HCF gas pressure for HHG with the 7.5 cm cell yields the optimal solid yellow curve.
