2.E Angular Distributions of High-Order Harmonics from Low-Density Gas Targets

Most high-order, harmonic-generation experiments to date have used gas target pressures in excess of 10 Torr. These high pressures have been used to enhance the harmonic signal, which increases quadratically with the pressure. The phase-mismatch factors (caused by both neutral and ionized media) increase with the pressure as does the effect of refraction of the incident laser when the medium becomes ionized. Very few measurements of the angular distributions of the high-order harmonics have been reported.3 The far-field pattern can provide additional insight into the laser propagation, phase matching, and the atomic response.