Extending the supercontinuum spectrum down to 200 nm with few-cycle pulses

By focusing 805 nm pulses of low energy (0.2-1 mJ) into atmospheric-pressure argon, a supercontinuum is generated with a short- wavelength cutoff of 640, 250 and 210 nm for initial pulse durations of 45, 10 and 6 fs, respectively. It is shown numerically that the large shift of the UV cutoff and many features of the spectrum are caused by terms beyond the slowly-varying- envelope approximation (SVEA). Their effect on pulse compression and filament length is also discussed.

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