We present a 3D tomography technique for in vivo observation of microscopic samples. The method combines flow in a microfluidic channel, illumination through a slit aperture, and a Fourier lens for simultaneous acquisition of multiple perspective angles in the phase-space domain. The technique is non-invasive and naturally robust to parasitic sample motion. 3D absorption is retrieved using standard back-projection algorithms, here a limited-domain inverse radon transform. Simultaneously, 3D differential phase contrast images are obtained by computational refocusing and comparison of complementary illumination angles. We implement the technique on a modified glass slide which can be mounted directly on existing optical microscopes. We demonstrate both amplitude and phase tomography on live, freely swimming C. elegans nematodes.

From night vision and objects overwhelmed by sunlight to jammed signals and those that are purposely encrypted, detecting low-level or hidden signals is a fundamental problem in imaging. Here, we develop and exploit a new type of stochastic resonance, in which nonlinear coupling allows signals to grow at the expense of noise, to recover noise-hidden images propagating in a self-focusing medium. The growth rate is derived analytically by treating the signal–noise interaction as a photonic beam–plasma instability and matches experimentally measured resonances in coupling strength, noise statistics and modal content of the signal. This is the first observation of nonlinear intensity exchange between coherent and spatially incoherent light and the first demonstration of spatial coherence resonance for a dynamically evolving signal. The results suggest a general method of reconstructing images through seeded instability and confirm information limits predicted, but not yet observed, in nonlinear communications systems.

It is well known that one cannot image directly through a nonlinear medium, as intensity-dependent phase changes distort signals as they propagate. Indirect methods can be used1, 2, 3, 4, 5, 6, but none has allowed for the measurement of internal wave mixing and dynamics. Recently, the reconstruction of nonlinear pulse propagation in fibres was demonstrated by generalizing the techniques of digital holography7, 8 to the nonlinear domain9. The method involves two steps: (1) recording the total field (both amplitude and phase) exiting a nonlinear medium and (2) numerically back-propagating the wavefunction. Here, we extend this process to two-dimensional spatial beams and experimentally demonstrate it in a self-defocusing photorefractive crystal, giving examples in soliton formation, dispersive radiation and imaging. For known nonlinearity, the technique enables reconstruction of wave dynamics within the medium and suggests new methods of super-resolved imaging, including subwavelength microscopy and lithography. For unknown nonlinearity, the method facilitates modelling and characterization of the optical response.