Reconstruction of structures from their scattered intensity distributions is heavily exploited in a range of disciplines, with common methods limited when phase information is lost. Contemporary iterative algorithms depend on a priori knowledge of the object boundaries to solve such inverse scattering problems, but remain highly time-consuming and, at times, inaccurate. The proposed all-optical technology harnesses a digital degenerate cavity laser arrangement that registers the scattered intensity distribution only within the predefined boundaries of the object. The process is ultra-rapid (nanosecond-scale) and bears very high spatial resolution potential.
Reconstruction of objects from their scattered intensity distributions stands at the basis of numerous medical and technological imaging procedures, including tomographic, seismologic, and single-shot X-ray imaging, speech recognition and radar detection. Such inverse scattering procedures are limited when phase information is lost in the process. In cases of objects with a compact support, this loss can be compensated for by using iterative algorithms that rely on a priori knowledge, such as the spatial features or constraints of the object of interest. However, this approach is highly time-consuming.
A novel all-optical phase-retrieval platform based on a digital degenerate cavity laser (DDCL) that incorporates both the intensities of the scattered light and the physical boundaries of an object, to provide a reconstructed image within 100 nanoseconds.
The DDCL is comprised of a ring degenerate cavity laser, that includes a gain medium, two 4f telescopes, an amplitude spatial light modulator (SLM), an intracavity aperture, three reflective mirrors and an output coupler (Figure 1). When placed between the two lenses, the intracavity aperture, shaped in accordance with the compact support constraints, serves as a binary mask that filters out modes that fail to exhibit phase-dependence of their amplifications and losses. Integration of the specific scattered intensity distribution applied on the SLM, within the boundaries of the intracavity aperture, yields the most probable reconstructed object, which can be imaged through the output coupler onto the camera. The ultra-rapid phase retrieval process generates images that exhibit good agreement with the original object, including accurate replication of intensity (brightness) and phase (color code) distributions (Figure 2). The system demonstrated equally effective image reconstruction for objects of uniform, symmetric or asymmetric phase distribution.
Figure 1. Basic digital degenerate cavity laser arrangement for rapid phase retrieval
Figure 2. DDCL-reconstructed uniform (row 1) and random asymmetric (row 2) phase distribution objects (column c), showed good agreement with the intensity and phase distributions of the actual objects (column a).
- Reduced computation time to nanosecond scale
- Image is converged within compact support boundaries
- Light intensity-sensitive
- Can operate on three dimensional objects
- Can operate even if the scattered intensity is distorted
- Can be applied to structures of any wavelengths (from x ray to radio)
- Can perform hundreds of computations in parallel
- Identify Nano structures from their x ray scattered intensity in material science, biology and medicine
- Correct images distorted in scattering media such as biological tissue of turbulent atmosphere
- Reconstruct radio and microwave images
- Correct for aberrations in various imaging systems
- Map to many other optimization problems
We constructed a laboratory prototype and demonstrated with it reconstruction images composed of ~100 pixel with good quality within 100 nanoseconds. We have recently improved our optical design and interfaces so expect better performances. We incorporated computer pre and post processing to further improved the performance. We developed a real time concept that will not require a slow spatial light modulator.