Dynamic real-time optical processing has significant potential for accelerating specific tensor algebra. Here we present the first demonstration of simultaneous amplitude and phase modulation of an optical two-dimension signal in the Fourier plane of a thin lens. Two spatial light modulators (SLMs) arranged in a Michelson interferometer modulate the amplitude and the phase while being simultaneously in the focal plane of two Fourier lenses. The lenses frame an interferometer in a 4f-system enabling full modulation in the Fourier domain of a telescope. Main sources of phase noise and losses are discussed such as native to SLMs non-linear inter-pixel crosstalk, variability in modulation efficiency as a function of projected mask parameters, and Fresnel’s optics limitations. Such a system is of extreme utility in rapidly progressing fields of optical computing, hardware acceleration, encryption, and machine learning, where neglecting phase modulation can lead to impractical bit-error rates.
Here we introduce a free-space optical communication (FSOC) system that is capable of adjustment to alignment drift, varying atmospheric turbulent conditions of multiplexed spatial structured laser beams such as orbital angular momentum (OAM) beams. The detection system is based on heterogeneous convolutional neural network with first Fourier convolution neural network layer implemented in optics as a 4f system driven by kilohertz-fast reprogrammable high-resolution digital micromirror devices (DMDs). We utilize this optical-filtering-based convolutional neural network to realize the training and identification of two co-propagating OAM beams among 12 different multiplexed modes under simulated turbulent condition using modified von K´arm´an atmospheric model. The current implementation shows test accuracy of 95.04% (under weak turbulence) and 87.52% (under strong turbulence).
In this paper we analyze the novel quantum properties of atomic photo-excitations generated by Orbital Angular Momentum (OAM) photons. It was previously predicted for Bessel beams (BB), that transitionsin atomic systems driven by twisted laser beams obey a modified set of position-dependent angular-momentum selection rules. It was also shown, that in the case of perfect alignment of the atom on the beam axis, total angular momentum of the photon must be fully transferred to the internal degrees of freedom of the target, which causes dramatic enhancement of higher-multipole processes. As a result, weak atomic transitions, which are hardly observable in interactions with simple states of light, become accessible with OAM photons. In the current paper, we extend the earlier developed theory to describe atomic photoexcitations by Bessel-Gauss (BG) and Laguerre-Gauss (LG) modes. It allowed us to infer the information about the phase structure of the beam, such as mode content and topological charge. The formalism exhibits a high level of sensitivity to the polarization content of the laser beam, which is on the order of 0.005% of the polarization admixture. The theoretical predictions are confirmed experimentally for photo-excitation of Ca40+ ions, trapped in a micro-structured, segmented Paul trap. The full set of quadrupole transitions from the S-state were generated by 729nm OAM laser beam shaped with a holographic phase-plate with a fork-dislocation. The experiment was conducted by Ferdinand Schmidt-Kaler's group at the University of Mainz.
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