Time-stretched photonic Doppler velocimetry

Area of Science:

• Plasma Physics
• High-Energy-Density Science
• Optical Diagnostics

Background:

• Inertial confinement fusion (ICF) facilities achieve implosion speeds exceeding 100 km/s.
• Accurate measurement of material velocities in ICF is critical but technically challenging.
• Existing velocimetry techniques are often limited by detector bandwidth, restricting the measurable velocity range.

Purpose of the Study:

• To develop and demonstrate a novel velocimetry technique for measuring high material velocities in ICF.
• To overcome the bandwidth limitations inherent in conventional diagnostic methods.
• To enhance the precision and range of velocity measurements in dynamic experiments.

Main Methods:

• Implementation of time-stretched spectral interferometry for velocimetry.
• Encoding the velocity signal onto a chirped laser pulse.
• Temporal stretching of the laser pulse to reduce the beat frequency prior to detection.
• Experimental validation on an imploding liner experiment at the Sandia National Laboratories' Z machine.

Main Results:

• Successfully demonstrated the time-stretched spectral interferometry technique.
• Measured beat frequencies exceeding 50 GHz.
• Achieved these measurements using a detector with a 20 GHz bandwidth, significantly extending the measurable range.
• Validated the technique's effectiveness in a high-speed implosion scenario.

Conclusions:

• The developed time-stretched spectral interferometry technique effectively increases the measurable velocity range for diagnostics.
• This advancement is crucial for accurately characterizing high-velocity phenomena in ICF and related high-energy-density experiments.
• The technique offers a promising solution for overcoming detector bandwidth limitations in advanced velocimetry.