3D transient imaging of flame temperature via single-frame capture of lateral shearing interferometry

Lateral shearing interferograms of only one single frame are proposed to capture transient three-dimensional images of dynamic flames. The interferometric phase at each pixel in one interferogram is derived from the intensity and two calibrated parameters. The phase is extracted pixel by pixel from the light intensity of interferograms of the flames. The refractive index and temperature distribution are reconstructed after unwrapping. The feasibility of light intensity parameter calibration from the extinction interferograms was validated in numerical simulations, and an analysis of error sources for the proposed method was conducted, with the relative uncertainty of temperature determined to be 6.8%. A Bunsen burner was used to confirm the feasibility of the proposed method, with the temperature consistent with that measured by thermocouple and an average error of 26.73 K. The burner was acoustically excited and measured at frame rates of 2 k to 20 k fps. Temperature fluctuations were detected at different frame rates, and the higher accuracy of the proposed method was verified by comparison with the five-step method. The proposed method achieves temperature images in a pixel-wise way, and has the potential to increase the imaging frame rate up to the highest frame rate of the camera.