Development of an optical thermography system using a pumped two-dye fluorescence technique

Abstract

This work demonstrates the development of a novel backside thermography technique based on the temperature sensitivity of laser-induced fluorescence in flowing two-dye solutions. The approach utilizes visible light and optically transparent packaging materials to obtain spatially resolved transient thermal measurements. This makes it a relatively simple, inexpensive, and flexible approach for lab-scale experimental characterizations using economical cameras and optics. Additionally, both heating and cooling of the thermography stage can be achieved by passing temperature-controlled water through plastic packaging components. A custom-built experimental setup was designed, constructed, and used to study the performance of seven two-dye Rhodamine B (RhB)-Rhodamine 110 (Rh110) fluorescent solutions. The effect of dye concentration ratio on sensitivity, maximum frame rate, and excitation area was characterized. Using an optimal dye concentration of unity, it was shown that frame rates of 265–3200 Hz are achievable for excitation areas with diameters of 15.5–4.3 mm, respectively, using the current setup. The calibrated system was used to demonstrate in-situ measurements showing the importance of two-dye light compensation, as well as backside thermography using a simple droplet contact method to investigate temporal response. Experiments were conducted in the range of 25–55 °C with a spatial resolution of 30 µm. The experimental uncertainty of the temperature measurements was calculated to be ±2.1 °C and the technique's ability to account for error due to light fluctuations and non-uniform illumination was demonstrated. Finally, the effect of dye photobleaching during prolonged testing was studied and it was shown that photobleaching can be reduced, and even eliminated, by maintaining a nominal low flow rate of the pumped two-dye solution.