Laser sheet imaging, also called planar laser imaging, is one of the most versatile optical imaging techniques and has been frequently used in several different areas. However, when applied to the limited operating space and strong light scattering media, the light originating from indirect reflections, multiple scattering and surrounding backgrounds can produce error especially in intensity-ratio based measurements.

This work is motivated by these challenges, with the overall aim of making laser sheet imaging technique applicable for the study of eliminating the stray light interference. Therefore a novel two-dimensional imaging technique named structured laser illumination planar imaging (SLIPI) is developed based on planar laser imaging but uses a sophisticated illumination scheme i.e. spatial intensity modulation, to differentiate between the intensity contribution arising from useful signals and that from stray light. By recording and dealing with images, the SLIPI method can suppress the diffuse light and retain the useful signals.

In this paper, we first use the MATLAB software to simulate the phase-shift SLIPI method, and the results show that the stray light interference can be eliminated completely. Furthermore, the phase-shift SLIPI is combined with the liquid solution (Rhodamine B solution) laser induced fluorescence (LIF) approach to imagine the concentration distribution. By recording three images, between which this encoding is changed noticeably only for the useful LIF signals, the phase-shift SLIPI method is evidenced to be able to remove the diffuse light contribution, thus improving and enhancing the visualization quality. The instantaneous SLIPI images of rapidly moving samples, a key feature to study dynamic liquid solution diffusion behavior, are also acquired. The lock-in amplifier SLIPI technique is then experimentally studied under Rhodamine B diffused solution, and the phase-shift SLIPI method can remove the unwanted background interferences and achieve the significant improvements in terms of pronounced concentration distribution within the Rhodamine B solution.

The SLIPI technique is relatively inexpensive: the cost does not exceed the cost of an ordinary laser sheet arrangement noticeably, and it can combine with several other linear imaging techniques, such as Rayleigh scattering, particle image velocimetry and laser-induced phosphorescence.