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Gas medium ionization and harmonic wavelength tunability in high-order harmonic generation with ultrashort laser pulses

Published online by Cambridge University Press:  09 April 2001

P. CECCHERINI
Affiliation:
INFM—Unità di Padova and Dipartimento di Elettronica e Informatica, Padova, Italy
A. BOSCOLO
Affiliation:
INFM—Unità di Padova and Dipartimento di Elettronica e Informatica, Padova, Italy
L. POLETTO
Affiliation:
INFM—Unità di Padova and Dipartimento di Elettronica e Informatica, Padova, Italy
G. TONDELLO
Affiliation:
INFM—Unità di Padova and Dipartimento di Elettronica e Informatica, Padova, Italy
P. VILLORESI
Affiliation:
INFM—Unità di Padova and Dipartimento di Elettronica e Informatica, Padova, Italy
C. ALTUCCI
Affiliation:
INFM—Unità di Napoli and Dipartimento di Scienze Fisiche, Università di Napoli “Federico II”, Napoli, Italy Dipartimento di Chimica, Università della Basilicata, Potenza, Italy
R. BRUZZESE
Affiliation:
INFM—Unità di Napoli and Dipartimento di Scienze Fisiche, Università di Napoli “Federico II”, Napoli, Italy
C. DE LISIO
Affiliation:
INFM—Unità di Napoli and Dipartimento di Scienze Fisiche, Università di Napoli “Federico II”, Napoli, Italy
M. NISOLI
Affiliation:
INFM—Dipartimento di Fisica, Politecnico di Milano, Italy
S. STAGIRA
Affiliation:
INFM—Dipartimento di Fisica, Politecnico di Milano, Italy
S. DE SILVESTRI
Affiliation:
INFM—Dipartimento di Fisica, Politecnico di Milano, Italy
O. SVELTO
Affiliation:
INFM—Dipartimento di Fisica, Politecnico di Milano, Italy

Abstract

We have investigated the effect of free electrons on the spectral properties of high-order harmonics generated in a neon gas jet by a 30 fs Titanium:Sapphire pumping laser with intensities in the range 5–10 × 1014 W/cm2. The main feature of our observations concerns the possibility of continuously tuning the harmonic wavelength in the spectral region 20–7 nm, by taking advantage of the blue shift of harmonic wavelengths induced by the presence of free electrons to cover the entire spectral region between two consecutive harmonics of the unshifted spectrum. Different amounts of blue shift, which can be as large as 0.3–0.4 nm, are imparted to the given harmonic by simply changing the gas-jet-laser-beam-waist relative position. We have also interpreted our experimental results with a simple model for the generation process based on the “barrier suppression” ionization of an atom exposed to an ultraintense laser field.

Type
ULIA-1 CONFERENCE PAPERS
Copyright
© 2000 Cambridge University Press

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