Lidar systems are of major importance for driver assistance systems and autonomous driving, but their obstacle detection range can be heavily impaired by adverse weather conditions like fog. To mitigate the effects of fog, the use of polarized light has been proposed. We simulated a polarized lidar system, taking Mie theory-based scattering functions for different fog types at several wavelengths into account, and investigated the possible increase in contrast between fog backscattering and target returns for different surface types, depending on the target orientation and the polarizer configuration. Fog is modeled as an infinite, homogeneous, scattering, and absorbing medium. The simulated detector registers the time-dependent radiance, resolved by scattering order. Our findings show that the suitable choice of illumination and detection polarization allows the amount of single-scattered light detected to be reduced by two to four orders of magnitude and the contrast between fog and target to be increased significantly. Crucially, this approach delivers robust contrast enhancement regardless of whether the target surface is depolarizing Lambertian or perfectly reflecting.

Coherent backscattering is an interference phenomenon that occurs in the backwards direction of the incident illumination. It arises from photons traveling the same path in opposite directions within a scattering medium. Accurately determining the background signal for normalization can be challenging in such measurements. This study investigates the use of a spatial light modulator to control spatial coherence, effectively switching the interference on and off. This approach enables independent, absolute measurements of both the signal and background across the full angular detection range without modifying the experimental setup. We demonstrate this method experimentally, highlighting the importance of accurate background determination in coherent backscattering measurements using a Fourier-based setup. Additionally, we demonstrate that measurements normalized to the correct background closely match Monte Carlo simulations of the coherent backscattering signal.

Delivering energy deep into turbid media is essential for applications like biomedical imaging, medical treatment, and material processing. We applied wavefront shaping to enhance light penetration by manipulating the phase of incident light. Using feedback-based phase optimization and numerical solutions of Maxwell’s equations, we present an approach that significantly and non-invasively increases the energy density deep inside complex scattering media by minimizing the reflected light, without prior knowledge of the media. In simulations of media with a transport mean free path as low as 43.36μm, we achieved a 2.5-fold enhancement of the energy density at a depth of about 200μm. Light transport through this simulated medium is equivalent to propagation through approximately 4mm of biological tissue with optical properties typically found in the red or infrared wavelength range. By switching between minimized and maximized reflection, the energy density can be modulated by up to a factor of 12 deep inside the scattering medium, while the energy density at shallow depths remains fairly unchanged.