Development of a broadband reflectivity diagnostic for laser driven shock compression experiments.

Area of Science:

• Materials Science
• Optical Physics
• Laser-Induced Dynamics

Background:

• Investigating dynamic changes in material optical properties under extreme conditions like laser compression is challenging.
• Previous methods struggled with small sample sizes and short timescales inherent in shock experiments.

Purpose of the Study:

• To develop and demonstrate a novel optical reflectivity diagnostic for analyzing materials under dynamic laser compression.
• To overcome limitations in time and wavelength resolution for shock-compressed samples.

Main Methods:

• Constructed a normal-incidence visible and near-infrared shock wave optical reflectivity diagnostic.
• Utilized time-delayed pulses from an ultrafast Ti:sapphire laser, broadened to create broadband light on nanosecond timescales.
• Integrated off-normal incidence velocity interferometry (VIVF) for complementary measurements.

Main Results:

• Successfully demonstrated the diagnostic over the 450-1150 nm wavelength range, capturing up to 16 time-displaced spectra per experiment.
• Achieved 0.5 ns time resolution and 10 nm wavelength resolution in reflectivity measurements.
• Documented the shock-driven semiconductor-to-metallic transition in germanium.

Conclusions:

• The developed diagnostic effectively probes dynamic changes in optical properties of laser-shock compressed materials.
• This technique provides high resolution in both time and wavelength, crucial for understanding transient material behaviors.
• The study successfully characterized a phase transition in germanium using this advanced optical method.