In laser-induced fluorescence (LIF) experiments on aerospace engine fluorescent materials such as high-temperature coatings and stress-sensing materials—980nm near-infrared excitation generates fluorescence signals in three bands: 540nm (green), 560nm (yellow-green), and 680nm (red).

However, practical detection faces several challenges:

Extremely weak signals prone to interference: Metallic or ceramic substrates reflect and scatter the excitation light. Background noise, including residual engine lubricants, reduces the signal-to-noise ratio (SNR), especially in the red 680nm band. Conventional cameras struggle to distinguish true fluorescence from noise.

Long exposure causes photobleaching and thermal noise: Capturing weak signals may require exposures of hundreds of milliseconds or more. Under high-intensity laser illumination (1–5 W/cm²), fluorescence signals decay quickly (e.g., 540nm signal drops 30% within 10 minutes), and thermal noise from substrates accumulates, affecting measurement stability.