Coherence properties of high order harmonic radiation

摘要

The results of a series of experiments to characterize the coherence properties of xuv radiation produced by high-order harmonic generation in helium, neon and argon are reported and compared to predictions from an effective order model. The harmonics exhibit smooth, near gaussian spatial profiles, and have a divergence that is approximately constant ( < 12 mrad) in the plateau region and decreases ((approx)4 mrad) in the cutoff for f/17 focusing. For a bandwidth limited, 140 fsec incident pulse, we measure a harmonic line width of (Delta)(lambda)/(lambda) (approx) 2 (times) 10(sup (minus)3) at 30.3 nm. By reducing the spectral width of the driving pulse, harmonics with (Delta)(lambda)/(lambda) (approx) 2 (times) 10(sup (minus)4) can be produced. Absolute conversion efficiency as high as 10(sup (minus)7) for harmonic radiation as short as 20 nm has been achieved by using 400 fsec, 526 nm pulses from an Nd:Glass laser.