LAUSR

The hydroxyl (OH+) radical, with its distinctive 308 nm emission, provides a unique fingerprint for hydrocarbon combustion monitoring. Exploiting the low ultraviolet sky background, OH+-based detection achieves high accuracy without cooling but suffers from narrowband-filter blue shifts caused by light-convergence angles, degrading uniformity and reliability. We propose a differential correction method using a coordinated filter pair-308 nm target and 307 nm reference-engineered to share identical blue shifts. Images from both channels are acquired, and the background (Ioff) is subtracted from the target (Ion). Because broadband background signals (mainly sky scattering) remain nearly equal after blue shift, subtraction cancels them while fully retaining the narrowband OH+ emission present only in the 308 nm channel. Experiments show that this approach cleanly extracts a 1 nm bandwidth 308 nm signal under ideal conditions and markedly improves the signal-to-noise ratio (SNR). The resulting dual-channel synchronized imaging and differential system provides a reliable, engineering-ready solution to mitigate filter blue shift and enhance UV spectral detection accuracy in dynamic scenarios.