Capturing the 3D secrets of a flickering candle: Based on digital holographic microscopy

The temperature distribution of flames has long been a fascinating topic of study. To quantitatively analyze the temperature field of flames, traditional methods include infrared devices, thermocouples and thermometer. However, these conventional techniques provide only cross-sectional snapshots while lacking the capability to offer real-time 3D temperature field visualization. This paper proposed a different approach to measure the 3D temperature field with accurate data and details by applying the digital holography. First, based on digital holography and the equations of thermodynamics, we derived the equation between the phase difference and temperature. Then we built a transmission off-axis digital holographic microscopy in the experimental section to perform static and dynamic flame measurements. To calibrate the actual temperatures and test our theorys accuracy, we also took photographs of the flames as a standard reference using an infrared thermal imager. Finally, we obtained a quantitative 3D distribution of the temperature field and a qualitative dynamic process of 3D temperature field. Our results show that the temperature decreases from the center of the flame and follows a general pattern. The comparison with infrared imaging shows that digital holography offers an accurate measurement of the temperature.