Development of a compact, low-cost mid-infrared scanning monochromator for spectroscopy

Abstract

The mid-infrared spectral region (2.5–5 µm) remains critical for molecular spectroscopy and thermal imaging applications, yet commercial scanning monochromators for this range typically cost tens of thousands of pounds. This work developed a compact, open-hardware scanning monochromator employing a 300 lines/mm reflective grating mounted on a GT2 belt-driven rotation stage controlled via Arduino with Python-based data acquisition through a PM100D power meter, achieving sub-£200 total hardware cost. Testing with 600 nm and 1550 nm laser sources validated the system's angle-to-wavelength conversion through the grating equation, revealing multiple diffraction orders as expected. The mechanical characterization demonstrated an effective step granularity of 0.98°/command with measured backlash between 0.05–0.10° and repeatability of ±0.05°, translating to approximately 5.7–11.4 nm uncertainty from backlash and 60 nm wavelength increment per command step near 1550 nm. The design successfully met its primary objectives of cost reduction, stable repeatability, and robust operation, though full validation across the 2.5–5 µm target range awaited appropriate sources and detectors while order-sorting filters and stray-light baffling required further refinement. This accessible platform demonstrated that trading ultimate spectral resolution for modularity and affordability creates valuable opportunities for educational laboratories and budget-constrained research groups seeking incremental upgrade paths toward enhanced mid-IR spectroscopic capabilities.