Numerical modeling of laser matter interaction in the presence of an ambient gas

The extraordinary ability of the hydrogen-bond network of water in the condensed phase to thermalize vibrational excitations within several picoseconds, even under supercritical conditions, offers the possibility of creating highly excited thermodynamic states at water surfaces on ultrafast time scales using vibrationally resonant short infrared laser pulses. We experimentally and numerically studied such states created by depositing ~100 ps long pulses tuned to the 3400 cm(-1) O–H stretch vibration at the water/air interface using time-resolved dark-field imaging and time-resolved optical reflectivity. The results are reasonably well described by using a hydrodynamic ablation model under the assumption of impulsive heat deposition. The large thermoelastic stress amplitudes on the order of 1 GPa created within 100 ps by depositing laser pulses with ~1 J cm(-2) fluence were inferred from the numerical simulations. Stresses of this magnitude drive the excited water layer into a very fast expansion resulting in rapid adiabatic cooling and thorough vaporization within a few nanoseconds. The spatial and temporal lengths scales of the ablation plume are nearly ideal for ejecting molecules into the gas phase with minimum perturbation for applications ranging from mass spectrometry and laser surgery to the development of extremely high pressure molecular beams.

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“…7). 47,48 The first region comprises the water layer immediately next to the water/air interface and has pressure P 1 and temperature T 1 .…”

Section: The Interface Fluxesmentioning

confidence: 99%

Vibrationally excited ultrafast thermodynamic phase transitions at the water/air interface

Franjić

Miller

2010

Phys. Chem. Chem. Phys.

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Plasma dynamics of a confined extreme ultraviolet light source

Yeates

Kennedy

2010

Physics of Plasmas

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Laser plasmas were generated by ablation of aluminum targets via a Nd:YAG glass laser, of pulse energy 0.8 J, and duration 15 ns (full width at half maximum) at the fundamental wavelength (1.064 μm). Emission lines in the wavelength range of 27–32 nm (45–37.8 eV) were mapped over a spatial range extending out 1.8 mm from the target surface and for a temporal range of 42 ns after the termination of the laser pulse. Two targets were utilized: a planar surface and a rectangular cavity. The latter was composed of a rectangular shaped cavity of depth 3 mm and height 1.2 mm, cut into an aluminum massive. An irradiance of Ip∼1011 W/cm2 was delivered to both targets and the confining influence of the rectangular cavity upon plasma formation and expansion was studied. Diagnostics of the emitted spectra reveal the unique dynamics of restricted plasma plume expansion, which results in plasma-surface collisions and subsequent plasma rebound within the cavity. These effects give rise to strong enhancement of both continuum and line emission in the contained plasma plume. These enhancements are especially evident for the more highly charged ions. Superior emission from plasma-surface collisions are associated with “forced recombination” during early time scales, while enhanced emission at later stages are associated with plasma plume component rebound and collision.

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Shock formation and the ideal shape of ramp compression waves

et al. 2008

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We derive expressions for shock formation based on the local curvature of the flow characteristics during dynamic compression. Given a specific ramp adiabat, calculated for instance from the equation of state for a substance, the ideal nonlinear shape for an applied ramp loading history can be determined. We discuss the region affected by lateral release, which can be presented in compact form for the ideal loading history. Example calculations are given for representative metals and plastic ablators. Continuum dynamics (hydrocode) simulations were in good agreement with the algebraic forms. Example applications are presented for several classes of laser-loading experiment, identifying conditions where shocks are desired but not formed, and where long duration ramps are desired. * Electronic address: dswift@llnl.gov

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Numerical modeling of laser matter interaction in the presence of an ambient gas

Cited by 3 publications

References 15 publications

Vibrationally excited ultrafast thermodynamic phase transitions at the water/air interface

Vibrationally excited ultrafast thermodynamic phase transitions at the water/air interface

Plasma dynamics of a confined extreme ultraviolet light source

Shock formation and the ideal shape of ramp compression waves

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