Indeed, for a pulse centered in the low-frequency region, e.g. infrared (IR) λ λ = 800 nm, its minimum time duration is around t p u l s e = λ λ c = 2.67 fs, where c is the speed of light; whereas, for a light field with central wavelength in the extreme ultraviolet (XUV) at λ λ = 30 nm the minimum duration is around t p u l s e = 100 as.