A Tunable Catadioptric Spectrometer with Bragg-Condition-Preserving Rotation for High-Resolution Spectroscopy.

Area of Science:

• Optics and Photonics
• Spectroscopy
• Instrument Development

Background:

• Conventional transmission spectrometers have fixed configurations, limiting simultaneous high spectral resolution and broad wavelength coverage.
• Volume Phase Holographic (VPH) grating spectrometers offer high throughput but often lack tunability.
• There is a need for compact, tunable spectrometers that maintain high performance across a wide spectral range.

Purpose of the Study:

• To theoretically analyze and experimentally validate a novel tunable catadioptric transmission spectrometer.
• To demonstrate simultaneous achievement of high spectral resolution and broad wavelength tunability.
• To showcase the application of the spectrometer in resolving closely spaced spectral features.

Main Methods:

• Developed a catadioptric grating assembly combining a VPH grating and a planar reflector with synchronous rotation for wavelength scanning.
• Theoretically derived optical configuration and structural parameters for optimal performance.
• Constructed a prototype spectrometer and performed spectral response and resolution measurements.

Main Results:

• The prototype spectrometer demonstrated wavelength tunability from 410 nm to 650 nm by adjusting the rotation angle.
• High diffraction efficiency was maintained across the entire tuning range.
• Achieved spectral resolutions of 0.1 nm (2400 g/mm) and 0.18 nm (1500 g/mm).
• Successfully resolved closely spaced Raman peaks of CH4 and C2H6 in gas Raman spectroscopy.

Conclusions:

• The proposed tunable catadioptric spectrometer effectively combines excellent wavelength tunability with high spectral resolution.
• This novel design overcomes the limitations of conventional fixed-configuration spectrometers.
• The spectrometer shows significant potential for applications requiring precise spectral analysis, such as gas spectroscopy.