Counter-propagating fs/ps CARS for sub-100  µm resolution gas-phase thermometry.

Area of Science:

• Spectroscopy
• Fluid Dynamics
• Laser Physics

Background:

• Coherent anti-Stokes Raman scattering (CARS) is a powerful technique for gas-phase temperature measurements.
• Traditional CARS geometries suffer from limited spatial resolution, hindering analysis of fine-scale thermal structures.
• Hybrid femtosecond/picosecond (fs/ps) CARS offers enhanced signal generation but requires optimized phase-matching.

Purpose of the Study:

• To demonstrate a novel counter-propagating (CoP) phase-matching configuration for fs/ps CARS.
• To achieve ultra-high spatial resolution for gas temperature measurements.
• To enable spatially resolved measurements of steep temperature gradients in gas flows.

Main Methods:

• Development and implementation of a CoP phase-matching geometry for fs/ps CARS.
• Quantification of the spatial resolution of the CoPCARS system.
• Measurement of gas temperature profiles in a high-velocity microscale jet using CoPCARS.

Main Results:

• The CoP configuration yields spatial resolution on the order of 10s of µm, an improvement of over an order of magnitude compared to traditional methods.
• The measurement volume location and size can be easily controlled by adjusting pulse timing and duration, respectively.
• Spatially resolved gas temperature measurements were successfully performed across steep temperature gradients in a microscale jet.

Conclusions:

• The demonstrated CoP fs/ps CARS technique provides unprecedented spatial resolution for gas thermometry.
• This method overcomes limitations of conventional CARS, enabling detailed studies of complex thermal phenomena.
• The CoPCARS system offers a versatile and powerful tool for microscale fluid dynamics and combustion research.