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High resolution spatially extended 1D laser scattering diagnostics using volume Bragg grating notch filters
J Bak1, J L Suazo Betancourt2, A Rekhy1
1Department of Aerospace Engineering, Texas A&M University, 400 Bizzell St., College Station, Texas 77843, USA.
The Review of Scientific Instruments
|March 1, 2023
Summary
Volume Bragg grating (VBG) filters enable spatially resolved laser light scattering measurements with micrometer resolution along the beam axis. This technique enhances spatial resolution for 1D measurements in various discharge conditions.
Area of Science:
- Optical Physics
- Laser Spectroscopy
- Plasma Diagnostics
Background:
- Volume Bragg Grating (VBG) filters are typically used for point measurements in laser light scattering systems.
- Existing methods offer limited spatial resolution, often in the hundreds of micrometers range, defined by the beam waist.
Purpose of the Study:
- To demonstrate a novel application of VBG filters for achieving high spatial resolution measurements along the beam propagation axis.
- To analytically derive the rejection ring characteristics and explain its utility for 1D laser line rejection.
- To propose and validate methods for extending the measurable region and improving signal collection.
Main Methods:
- Analytical derivation of the VBG filter's rejection ring based on angular acceptance criteria.
- Utilizing the rejection ring for 1D laser line rejection with micrometer-level spatial resolution.
- Employing focused probe beams and exploring techniques like varying collimation lens focal length and using multiple VBG filters.
- Performing 1D rotational Raman and Thomson scattering measurements on pulsed and DC discharges.
Main Results:
- Achieved spatially resolved measurements with micrometer resolution over several millimeters along the beam propagation axis.
- Demonstrated tunable spatial resolution up to several millimeters for 1D measurements using the VBG rejection ring.
- Showcased methods to extend the measurable region, including using multiple VBG filters to minimize signal loss without compromising the solid angle.
- Successfully verified the method through 1D rotational Raman and Thomson scattering measurements in different discharge types.
Conclusions:
- VBG filters can be effectively utilized for high-resolution, spatially resolved laser light scattering measurements.
- The proposed method offers a compact, flexible, and high-throughput system suitable for diverse experimental conditions.
- This technique significantly advances the capability for detailed spatial analysis in plasma and scattering experiments.
