Search

The control of multiply-scattered light has greatly boosted the understanding of optics in complex photonic systems, leading to many applications including imaging, information processing, random lasing, to name just a few. Here, we demonstrate a real-time feedback approach to realize multiple focusing of multiply-scattered light, which is more robust to the inherent background field compared to the time reversal approach. Our method retrieves the optimized wavefront by aligning the high-dimensional vector of the measured pattern with that of the target pattern. Our theoretical simulations and experimental results show that the feedback approach is capable of constructing homogeneous diffraction-limited spots at predefined positions. Moreover, the peak-to-background ratio exhibits a sub- 1 / m decay with m being the number of focuses, indicating the excellent capability of the proposed approach to focus scattered light at multiple positions. This efficient approach provides a promising avenue toward complex control on scattered light in complex photonic media, and therefore would be useful in relevant applications such as optical imaging and optical manipulation. • A real-time feedback approach is developed for realizing diffraction-limited spots at a few predefined positions with multiply-scattered light. • The realized multiple focuses are robust to the random perturbation caused by inherent background light. • The peak-to-background ratio exhibits ∼ 1 / m 0. 62 decay (m: the number of focuses), slower than the well-known 1/m decay. [ABSTRACT FROM AUTHOR]

The exploration of structured light created through autofocusing beams has attracted widespread attention in optical manipulation. Here, we investigate the propagation dynamics of chirped multi-Pearcey beams (CMPBs) in theory and experiment, especially exploring the impact of chirped factors on the autofocusing characteristics of CMPBs. It is found that the autofocusing characteristics of the beams can be significantly modulated by introducing first-order and second-order chirped factors. Specifically, the first-order chirped factor greatly improves the autofocusing coefficient of CMPBs, while the second-order chirped factor introduces multiple autofocusing propagations. By analyzing the transverse power flow of CMPBs both without and with chirped factors, we explain why the chirped factors can remarkably strengthen the autofocusing performance of CMPBs. Finally, our theoretical analysis on trapping force on Rayleigh particles indicates that the introduction of chirped factors optimizes the intensity gradient and trapping capability of CMPBs, potentially enabling multiple longitudinal trapping positions. These findings offer a comprehensive insight into the propagation dynamics of CMPBs, opening avenues for flexible optical manipulation of multiple particles. • The autofocusing characteristics of the CMPBs can be significantly modulated by introducing chirped factors. • The theoretical analysis on trapping force on Rayleigh particles indicates that chirped factors optimize the intensity gradient and trapping capability of CMPBs, potentially enabling multiple longitudinal trapping positions. [ABSTRACT FROM AUTHOR]

The self-focusing transmissions of light beams in five food dye suspensions including Red 40, Red 2, Red 4, Yellow 6, Blue 1 are studied. We qualitatively analyze the key influencing factors of the self-focusing phenomenon with five widely-used food dyes, including the concentration of suspensions, the input-beam power and the kinds of the food dyes. It is found that, the self-focusing phenomenon is mainly attributed to the shift of focus caused by thermal effects. Particularly, Red 40 presents a best nonlinear performance with a 5 cm self-focusing propagation at the wavelength of 532 nm. The significant difference of the self-focusing effects of the five food dyes are further explained by investigating their optical absorption and optical nonlinearity including nonlinear refractive index and absorption coefficient. It is found that a stronger absorption and nonlinearity, originated from the kinds of the dyes or the concentration of the dyes, leads to a stronger nonlinear self-focusing effect. Our work provides a systematic study on the quantitative analysis of the synthetic food colorants with optical nonlinearity, demonstrating a strong nonlinear self-focusing propagation and high nonlinear refractive index in red 40, red 2, red 4. This may have potential applications in nonlinear optics with soft matters. [ABSTRACT FROM AUTHOR]