High-order Harmonic Generation In Gases

The production of short wavelength radiation has been the focus of considerable experimental and theoretical effort recently. One source is very high-order harmonic production observed when short-pulse, intense optical lasers are weakly focussed into a jet of rare gas atoms
¹
. As long as the confocal parameter of the laser focus was larger than the (propagation) distance through the gaseous medium, a spectrum of odd harmonics was observed in which many orders were of comparable intensity. In these experiments absolute conversion efficiencies for the harmonics were obtained as functions of gas pressure, peak laser intensity and geometry of the laser focus. On the strength of these results it is possible to project that coherent short-wavelength radiation with peak power far in excess of existing synchrotron sources can be achieved. Also, using a tunable, subpicosecond dye laser source, the wavelength of the harmonics can be varied continuously.