High-throughput accurate-wavelength lens-based visible spectrometer

Area of Science:

• Spectroscopy
• Plasma Physics
• Optical Engineering

Background:

• Charge exchange recombination spectroscopy (CXRS) is crucial for plasma diagnostics.
• Fixed-wavelength spectrometers have limitations in spectral coverage.
• A need exists for advanced spectrometers to complement existing CXRS methods.

Purpose of the Study:

• To prototype a scanning visible spectrometer for CXRS.
• To achieve high spectral resolution and wavelength accuracy.
• To ensure persistent wavelength calibration under varying environmental conditions.

Main Methods:

• Utilized fast f/1.8 200 mm commercial lenses and a large 2160 mm⁻¹ grating for high throughput.
• Employed a stepping-motor controlled sine drive and precision rotary table for grating positioning.
• Incorporated a high-resolution optical encoder for precise grating angle measurement (0.075 arc sec accuracy).

Main Results:

• Achieved a wavelength error of ≤0.005 Å, demonstrating high precision.
• Identified the importance of thermal expansion and air refractive index variations at this precision.
• Developed an automated calibration procedure to determine spectrometer parameters accurately.

Conclusions:

• The prototyped scanning visible spectrometer effectively complements fixed-wavelength systems for CXRS.
• The system demonstrates the capability for precise wavelength measurements crucial for plasma diagnostics.
• Automated calibration and environmental monitoring ensure reliable and persistent spectral measurements.