Optical system design of sheet-beam energy homogenization with long focal-depth based on aberration effect of aspheric lens

Planar laser-induced fluorescence (PLIF) has been widely used in the two-dimensional (2D) accurate measurements of important combustion parameters such as temperature, species concentration and flame structure due to its high spatiotemporal resolution and non-contact diagnosis. Since the sheet-forming optics is an important part of PLIF system, the accuracy and precision of PLIF measurement strongly depend on the uniformity and focal-depth of the shaped sheet-beam. However, the current sheet-beam shaping methods cannot meet the practical requirements of high uniformity and long focal-depth at the same time. To improve the measurement accuracy and precision of PLIF technology, a new sheet-forming homogenization optical system with long focal-depth is proposed and designed based on aspherical aberration effect. By redistributing the central energy of Gaussian beam to the edges of the shaped sheet-beam, the sheet-beam shaping with high uniformity is realized. The working wavelength of the system is 283.553 nm, the working distance is 504 mm, and the total length of the system is 360 mm. The design results show that the size of the shaped sheet-beam is 100 mm × 0.5 mm with the effective focal depth of ±15 mm, the maximum beam uniformity >89% and the energy transmission efficiency >95%, which can better meet the actual requirements of PLIF measurement.