Optical turbulence distorts beam amplitude and phase, causing spreading, wandering, and irradiance fluctuations. Reconstructing perturbed beams’ complex fields is experimentally challenging due to these dynamic effects. Our complex phase retrieval technique, using binary amplitude modulation with a DMD and high-speed camera, characterizes collimated beams through turbulence and overcomes interferometric limitations. Conventionally, phase retrieval modulates optical fields via random coded apertures (RCA) to recover amplitude and phase without prior knowledge, solving ill-posed problems with phase-lift algorithms. Our previous approach required ≥20 apertures, increasing acquisition time and complexity. We designed a new coded aperture, reducing time and enhancing quality over traditional RCA. Then we apply a novel deep-learning phase unwrapping algorithm enabling efficient unwrapping of phases with turbulence-induced branch point singularities manifesting as vortices. This is the first experimental observation of turbulence complex wavefronts reconstructed with high spatial resolution and sampling rate. We discuss observed statistical properties and compare with current models.
Any beam that propagates through optical turbulence will experience distortions in both its amplitude and phase, leading to various effects such as beam wandering, beam spreading, and irradiance fluctuations. Reconstructing the complete field of a perturbed beam is a challenging task due to the dynamic nature of these effects. Interferometric wavefront reconstruction techniques—such as those based on holography—are commonly used but are hindered by their sensitivity to environmental disturbances and alignment errors. However, new complex phase retrieval methods based on propagation equations have emerged, which do not require prior knowledge of the beam to be reconstructed and are suitable for amplitude or phase objects, or both. We propose an experimental implementation of a complex phase retrieval technique for characterizing Gaussian beams propagating through optical turbulence, using binary amplitude modulation with a digital micro-mirror device (DMD). This approach is ideal for dynamic applications and has enabled us to achieve experimental high-speed complex wavefront reconstruction of optical beams through controlled real turbulence. This experiment corresponds to the initial step in our research focused on gaining a deeper understanding of optical turbulence from an experimental perspective.
Optical turbulence induces distortions in amplitude and phase in any beam propagating through it, resulting in beam spreading, beam wandering, and irradiance fluctuations among other effects. Due to the dynamic nature of these effects, the complex field reconstruction of a perturbed beam presents a great experimental challenge. Interferometric wavefront reconstruction techniques require very sophisticated assemblies prone to alignment errors due to their high sensitivity to environmental disturbances. This hinders its experimental implementation. New complex phase retrieval methods overcome most of the limitations of interferometric methods: they are suitable for amplitude or phase objects (or both) and their reconstruction algorithms—based on propagation equations—make unnecessary any a-priori knowledge of the beam to be reconstructed. We propose an experimental implementation of a complex phase retrieval technique for the characterization of Gaussian beams propagating through turbulence. This technique is based on binary amplitude modulation using a digital micro-mirror device (DMD) which has proven to be suitable for dynamic applications. To our knowledge, this is the first experimental high-speed complex wavefront reconstruction of optical beams—by binary amplitude modulation—through controlled real turbulence. This experiment represents the first step in our research focused on understanding optical turbulence from an experimental point of view.
We propose new techniques for the reconstruction of complex fields through the development of new iterative algorithms based on propagation equations and the representation of complex objects on orthogonal bases. These techniques use the advantages of the latest phase retrieval techniques and single pixel (SP) detection to retrieve the complex field. These techniques as a whole form a suitable tool for the characterization of dynamically perturbed scalar beams with singular phase profiles.
This research is based in the analysis of the decomposition of Laguerre-Gaussian modes into Hermite-Gaussian modes when propagating through turbulence. This effect can be clearly observed by cancelling the original Laguerre-Gaussian beam with another of different topological charge. The results of the propagations of these beams through Kolmogorov phase masks were analyzed, identifying which turbulences achieved the decomposition. The turbulences were then decomposed into the first 15 Zernike polynomials and used as new "Zernike turbulences". We discovered that the turbulence internal process that allows the decomposition has a high correlation with a phase distortion based on a single Zernike polynomial or a combination of them.
Wavefront reconstruction of Laguerre-Gaussian (LG) beams presents a great challenge due to the singularities in their phase profiles. Interferometric methods are difficult to implement since they require a reference beam and they are very sensitive to mechanical perturbations. Deterministic methods such as those based on the phase-transport or intensity-transport equation are limited to the paraxial approximation. Furthermore, if such beams propagate in atmospheric turbulence, complex dynamic characteristics are added to the problem. We seek to find an implementation of a technique that is capable of dynamically recovering the singular phases of LG beams under such random conditions. In this work, we will demonstrate a phase-retrieval technique that allows the recovery of LG wavefronts in turbulence and will characterize its effectiveness under a range of atmospheric parameters and propagation length. This technique is based on binary amplitude modulation and is suitable for dynamic applications.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.