Omer Tzang

Lock-in detection of photoacoustic feedback signal for focusing through scattering media using wave-front shaping.

Wave-front shaping techniques enable focusing and imaging through scattering media. Unfortunately, most approaches require invasive feedback inside or behind the sample, or use of spatial correlations (memory effect) limiting the application to specific types of samples. Recent approaches overcome these limitations by taking advantage of acoustic waves via the photoacoustic (PA) effect or via photon tagging. We present a fully analog signal processing lock-in scheme for PA detection to improve focusing through scattering media and to efficiently extract nonlinear photoacoustic signals towards wave-front optimization. Our implementation improves PA feedback performance in terms of SNR, speed, and resolution.

Wave-front shaping for nonlinear dynamics control (Conference Presentation)

Recent progress in controlling light propagation in multimode fibers in the linear regime, opened new opportunities for multimode fiber endoscopy. However, nonlinear light propagation in multimode fibers comprises complex intermodal interactions and rich spatiotemporal dynamics. In this work, we demonstrate a wave-front shaping approach for controlling nonlinear phenomena in multimode fibers. Using a spatial light modulator at the fiber’s input and a genetic algorithm optimization, we control a highly nonlinear stimulated Raman scattering cascade and its interplay with four wave mixing via a flexible implicit control on the superposition of modes that are coupled into the fiber. We demonstrate versatile spectrum manipulations that could be used to generate a multi-wavelength, tunable source. The wavefront shaping control allows spectral shifting and modal tuning. A theoretical analysis of modal phase matching in graded index multi-mode fibers is presented and we suggest potential bio-imaging applications.

Material anisotropy as a degree of freedom in optical design

We present an approach for the design of refractive optical elements using materials degrees of freedom that are accessible via engineered materials. Starting from first principles and an unconstrained general material, we specify homogeneous refractive lenses that focus light with diffraction-limited resolution resulting from a tailored anisotropic refractive index. We analyze the performance, physical feasibility, and advantages over isotropic lenses. Materials degrees of freedom enable new flexibility for imaging system designs with lower complexity expanding the existing aspheric and graded index paradigms.