Spectral Redshift in Harmonic Generation from Plasma Dynamics in the Laser Focus
F. BrandiPhysics Department, University of Pisa, Largo B. Pontecorvo 3, 56127-Pisa, Italy. [email protected]F. GiammancoPhysics Department, University of Pisa, Largo B. Pontecorvo 3, 56127-Pisa, ItalyW. UbachsLaser Centre, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands†
2006en
ABI
Annotatsiya
High-precision spectral measurements on the 9th harmonic generated in xenon gas are compared with calculations of the plasma dynamics resulting from multiphoton ionization in the laser focus. For the regime of 300 ps pulses and above-saturation intensities a novel mechanism producing redshifts in the harmonics is uncovered and explained. Ions play a double role: the nonlinear susceptibility of the ions is decisive for the harmonic intensity, while their mutual repulsion and the associated increase of the index of refraction is identified as the cause of the redshift.
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