Water expansion dynamics after pulsed IR laser heating.

Area of Science:

• Physical Chemistry
• Fluid Dynamics
• Laser-Matter Interactions

Background:

• Understanding water's response to rapid heating is crucial for various applications.
• Previous studies have explored water dynamics under thermal stress, but nanosecond timescales present unique challenges.

Purpose of the Study:

• To investigate the dynamic volume expansion of water heated by a nanosecond pulsed infrared laser.
• To measure the rate of water level increase and analyze the subsequent expansion and contraction phases.

Main Methods:

• Utilized time-resolved interferometry to monitor water level changes.
• Employed nanosecond pulsed infrared (1.9 microm) laser for rapid, localized heating.
• Analyzed Raman spectra to determine bulk hydrogen bond restructuring timescales.

Main Results:

• Observed water expansion at sub-sonic speeds, reaching ~500 nm height increase in <100 ns for a 20 K surface temperature jump.
• The initial expansion phase was slower than hydrogen bond restructuring, indicating an overpressure release limit.
• A subsequent contraction and re-expansion phase driven by hydrodynamic effects was identified, leading to light scattering and droplet spallation.

Conclusions:

• The initial rapid heating of water results in a volume expansion limited by the rate of overpressure release, not solely by hydrogen bond dynamics.
• Hydrodynamic effects govern later stages of the expansion, causing complex morphological changes and material ejection.
• This study provides insights into the fundamental physics of laser-induced water dynamics at the nanosecond scale.