Femtosecond growth dynamics of an underdense ionization front measured by spectral blueshifting

Technical Report · Tue Jun 01 04:00:00 EDT 1993

DOI:https://doi.org/10.2172/10157325· OSTI ID:10157325

Wood, W M; Siders, C W; Downer, M C

A comprehensive report of time-resolved spectral blue shifts of 100-femtosecond laser pulses caused by ionization of atmospheric density N{sub 2} and noble gases subjected to high (10{sup 14} W/cm{sup 2} - 10{sup 16} W/cm{sup 2}) light intensities is presented. Included are data for two experiments: (1) self-shifting of the ionizing laser pulses for varying peak intensities, pressures (1-5 atm.), and gas species; and (2) time-resolved blueshifts of a weak copropagating probe pulse for the same range of ionization conditions. The self-shift data reveal a universal, reproducible pattern in the shape of the blueshifted spectra: as laser intensity, gas pressure, or atomic number increase, the self-blueshifted spectra develop from a near replica of the incident pulse spectrum into a complex structure consisting of two spectral peaks. The time-resolved data reveal different temporal dependence for each of these two features. A quantitative model for a simplified cylindrical focal geometry is presented which explains the presence of the two spectral features in terms of two distinct ionization mechanisms: collisionless tunneling ionization, which dominates early in the ionizing pulse profile, and electron impact ionization, which dominates during the intense maximum of the ionizing pulse. Transient resonant enhancements may also contribute to ionization near the peak of the pulse.

• Research Organization: Texas Univ., Austin, TX (United States). Dept. of Physics
• Sponsoring Organization: USDOE, Washington, DC (United States); Department of Defense, Washington, DC (United States); National Science Foundation, Washington, DC (United States)
• DOE Contract Number: FG05-92ER40739
• OSTI ID: 10157325
• Report Number(s): DOE/ER/40739--T1; ON: DE93013582; CNN: Grant DMR8858388; Grant F49620-89-C-0044
• Country of Publication: United States
• Language: English

Related Subjects

664200
74 ATOMIC AND MOLECULAR PHYSICS
ARGON
CROSS SECTIONS
DYNAMICS
ENERGY SPECTRA
EXPERIMENTAL DATA
HELIUM
KRYPTON
LASER RADIATION
MEDIUM PRESSURE
NEON
NITROGEN
PHOTOIONIZATION
SPECTRA OF ATOMS AND MOLECULES AND THEIR INTERACTIONS WITH PHOTONS
SPECTRAL SHIFT
STRONGLY IONIZED GASES
TIME DEPENDENCE
XENON