• Korean Journal of Optics and Photonics
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• v.33 no.6
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• pp.267-274
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• 2022

In this paper, we report the design and fabrication of binary diffractive optical elements (DOEs) for random-dot-pattern projection for Schlieren imaging. We selected the binary phase level and a pitch of 10 ㎛ for the DOE, based on cost effectiveness and ease of manufacture. We designed the binary DOE using an iterative Fourier-transform algorithm with binary phase optimization. During initial optimization, we applied a computer-generated pseudorandom dot pattern of uniform intensity as a target pattern, and found significant intensity nonuniformity across the field. Based on the evaluation of the initial optimization, we weighted the target random dot pattern with Gaussian profiles to improve the intensity uniformity, resulting in the improvement of uniformity from 52.7% to 90.8%. We verified the design performance by fabricating the designed binary DOE and a beam projector, to which the same was applied. The verification confirmed that the projector produced over 10,000 random dot patterns over 430 mm × 430 mm at a distance of 5 meters, as designed, but had a slightly less uniformity of 84.5%. The fabrication errors of the DOE, mainly edge blurring and spacing errors, were strong possibilities for the difference.

• Fire Science and Engineering
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• v.32 no.6
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• pp.22-27
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• 2018

The flame length in coaxial diffusion flame configurations was investigated when the kerosene fuel flow rate, temperature of the oxidizer stream, and inert gas concentrations in the oxidizer stream were varied. The diffusion flame was photographed using a Schlieren camera under each of the experimental conditions and the obtained images were then digitized to measure the flame length. The measured flame lengths were proportional to the kerosene fuel flow rate and increased with increasing temperature of the oxidizer stream. In addition, increases in the inert gas concentration in the oxidizer stream resulted in stretching of the flame. In particular, the flame was further elongated in the oxidizer steam diluted with helium gas. Inert substitutions in the oxidizer stream that can adjust the viscous drag are believed to be one of the important mechanisms that affect the length of the coaxial diffusion flames.