Complete Mode Spectrum Decomposition of Complex‐Structured Light by Computer‐Generated Holography

We report the first study of Multi-Photon Ionization (MPI) using an intense two-color light field whose relative phase is known. The light field was produced by overlapped 80 ps pulses of 1.06 µm and .532 µm at various intensities and the phase difference was measured using non-linear mixing in KD*P. The light was focused into a chamber backfilled with Krypton gas, and the photoelectron energy spectrum was measured. We observed periodic variation of the MPI photoelectron peaks as a function of phase; moreover, the variation was seen to be asymmetric with respect to a change of sign in phase. The degree of asymmetry varied in a regular way as a function of intensity and peak energy. In general, the peak ionization rate was not observed to occur at the phase difference that produced the peak field. These effects were predicted for Hydrogen by Schaffer et al.,1 and are believed to be general in nature. We also report the effect of adding a small circular polarization component to the light field and the implications for a theory recently advanced by Corkum.2E Finally, we discuss the origin of these effects.

We study the problem of deblurring light fields of general 3D scenes captured under 3D camera motion and present both theoretical and practical contributions. By analyzing the motion-blurred light field in the primal and Fourier domains, we develop intuition into the effects of camera motion on the light field, show the advantages of capturing a 4D light field instead of a conventional 2D image for motion deblurring, and derive simple analytical methods of motion deblurring in certain cases. We then present an algorithm to blindly deblur light fields of general scenes without any estimation of scene geometry, and demonstrate that we can recover both the sharp light field and the 3D camera motion path of real and synthetically-blurred light fields.

Compressively sampled light field reconstruction using orthogonal frequency selection and refinement

Light field angular super-resolution based on intrinsic and geometric information

Unlike conventional light sources, lasers possess unique characteristics such as coherence and focused nature. Consequently, numerous applications of laser beams can be enhanced according to their spatial distribution characteristics. This paper presents two patterns of change in the intensity distributions of Hermite Gaussian beams regarding the impact of variables, including relative phase, intensity coefficient, and order of indexes. By conducting simulations in Matlab, we generate various patterns of Hermite Gaussian beams by adjusting parameters such as order indexes, relative phase, and intensity coefficients. The superposition principle is then applied to calculate the spatial intensity distribution of the combined laser beams. Our results indicate that as the order of indexes increases, the complexity of spatial distributions also increases. We analyze the symmetry and rotational properties of the Hermite Gaussian modes, revealing reflection and central symmetries, as well as rotational changes concerning the relative phase. Our discussions focus on exploring the potential for generating complex optical fields and theoretically validating experimental feasibility. We provide a schematic representation of the generation process for complex structured optical fields.

A light-field camera combines optics and computation to provide the ability to perform ranging. Many methods and algorithms, which are time-consuming and noise-sensitive, have been proposed for per-pixel depth estimation. We present a Fourier domain ranging method for light fields (LFs). Instead of estimating the depth for every pixel, we attempt to detect the depths of the different planes at which objects are located. The method is somewhat like using the energy in the focal stack, but it is carried out in a more efficient way. Our method has the advantages of speediness and robustness compared with traditional per-pixel depth estimation methods. In addition to the ranging algorithm, we also demonstrate the idea and application of a region adaptive denoising filter, in which the depth parameters are tuned by the proposed method. We include results for synthetic LFs, the Stanford LF archives, and LFs captured with a Lytro camera, exploiting the algorithm complexity, accuracy, depth resolution, and noise performance of our method. Our method uses less computation and is more robust than per-pixel depth estimation, making it appropriate for many applications, such as autorefocusing and autodenoising.

We present a novel Geometry-aware Neural Interpolation (Geo-NI) framework for light field rendering. Previous learning-based approaches either perform direct interpolation via neural networks, which we dubbed Neural Interpolation (NI), or explore scene geometry for novel view synthesis, also known as Depth Image-Based Rendering (DIBR). Both kinds of approaches have their own strengths and weaknesses in addressing non-Lambert effect and large disparity problems. In this paper, we incorporate the ideas behind these two kinds of approaches by launching the NI within a specific DIBR pipeline. Specifically, a DIBR network in the proposed Geo-NI serves to construct a novel reconstruction cost volume for neural interpolated light fields sheared by different depth hypotheses. The reconstruction cost can be interpreted as an indicator reflecting the reconstruction quality under a certain depth hypothesis, and is further applied to guide the rendering of the final high angular resolution light field. To implement the Geo-NI framework more practically, we further propose an efficient modeling strategy to encode high-dimensional cost volumes using a lower-dimension network. By combining the superiorities of NI and DIBR, the proposed Geo-NI is able to render views with large disparities with the help of scene geometry while also reconstructing the non-Lambertian effect when depth is prone to be ambiguous. Extensive experiments on various datasets demonstrate the superior performance of the proposed geometry-aware light field rendering framework.

Signals from the Global Positioning System (GPS) satellites can be used to make measurements of absolute ionospheric group delay and relative phase advance. These ionospheric parameters have wide application in providing corrections for military systems requiring knowledge of ionospheric time delay and phase scintillation, such as satellite detection radars. Multipath effects from the local environment of the receiving antenna can cause severe contamination of ionospheric group delay measurements made with GPS pseudorandom noise receivers. Measured variations in the multipath effects in some typical clean and reflective environments are presented and shown to be consistent with signal analysis for pseudorandom noise receivers. Measured single reflector multipath is analyzed briefly and shown to correlate well with calculations. Since antennas must frequently be located in environments that are much less than ideal, data analysis procedures were developed for minimizing the impact of multipath on the group delay measurement. These include low‐pass filtering, day‐to‐day correlation, and calibration to relative differential carrier phase advance measurements by using subsets of the absolute ionospheric group delay data. Results of these processes as applied to the test data from various multipath environments are presented.

Wave propagation on the surface of cylinders exhibits interferometric self-imaging, much like the Talbot effect in the near-field diffraction at periodic gratings. We report the experimental observation of the cylindrical Talbot carpet in weakly guiding ring-core fibers for classical light fields. We further show that the ring-core fiber acts as a higher-order optical beamsplitter for single photons, whose output can be controlled by the relative phase between the input light fields. By also demonstrating high-quality two-photon interference between indistinguishable photons sent into the ring-core fiber, our findings open the door to applications in optical telecommunications as a compact beam multiplexer as well as in quantum information processing tasks as a scalable realization of a linear optical network.

Coherent control of electron intersubband transitions by frequency-detuned light fields

Temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviors including slow earthquakes, tremor and low frequency earthquakes1. Laboratory and theoretical studies predict changes in seismic velocity prior to earthquake failure2, however tectonic faults fail in a spectrum of modes and little is known about precursors for those modes3. Here we show that precursory changes of wave speed occur in laboratory faults for the complete spectrum of failure modes observed for tectonic faults. We systematically altered the stiffness of the loading system to reproduce the transition from slow to fast stick-slip and monitored ultrasonic wave speed during frictional sliding. We find systematic variations of elastic properties during the seismic cycle for both slow and fast earthquakes indicating similar physical mechanisms during rupture nucleation. Our data show that accelerated fault creep causes reduction of seismic velocity and elastic moduli during the preparatory phase preceding failure, which suggests that real time monitoring of active faults may be a means to detect earthquake precursors.

One technique for measuring an unknown sensor capacitance is using the phase delay of an RC network with a resistor and the sensor capacitor. By buffering the RC network with CMOS inverters, a square wave signal can be delayed through the circuit in proportion to the unknown capacitance. An EXOR gate can be used to compare the delayed square wave with a reference square wave to produce a pulsewidth-modulated signal where the pulsewidth is proportional to the unknown capacitance. This technique has a nearly linear response when the phase delay is small compared with the period of the square wave. However, this technique becomes severely nonlinear if the phase delay is larger than approximately one eighth of the period (45°), as the capacitor does not get fully charged or discharged every half period. To mitigate this nonlinearity, a novel resistance switching RC phase delay network is used to expand the linear range of the phase delay by accelerating the charging and discharging processes of the sensor capacitor. This approach is demonstrated using a fringing field capacitive sensor to measure the mass of added water and expands the linear operation to a phase delay to 133.56°.

To establish how little information the human visual system requires for recognition, common objects were digitally manipulated in the Fourier domain. The results demonstrate that it is not only possible, but also quite efficient, for a (biological) visual system to exist with very few phase relationships among the component spatial frequencies of the (retinal) image. A visual example is then presented which illustrates how certain phase relationships can hinder, or completely eliminate, the recognition of visual scenes.

The manipulation of solid states using intense infrared or terahertz light fields is a pivotal area in contemporary ultrafast photonics research. While conventional circular polarization has been well explored, the potential of counterrotating bicircular light remains widely underexplored, despite growing interest in theory. In the mid-infrared or multi-terahertz region, experimental challenges lie in difficulties in stabilizing the relative phase between two-color lights and the lack of available polarization elements. Here, we successfully generated phase-stable counterrotating bicircular light pulses in the 14–39 THz frequency range circumventing the above problems. Employing spectral broadening, polarization pulse shaping with a spatial light modulator, and intra-pulse difference frequency generation leveraging a distinctive angular-momentum selection rule within the nonlinear crystal, we achieved direct conversion from near-infrared pulses into the designed counterrotating bicircular multi-terahertz pulses. Use of the spatial light modulator enables programmable control over the shape, orientation, rotational symmetry, and helicity of the bicircular light field trajectory. This advancement provides a novel pathway for the programmable manipulation of light fields, and marks a significant step toward understanding and harnessing the impact of tailored light fields on matter, particularly in the context of topological semimetals.

Free electrons appearing from the ionization process oscillate in an intense laser polychromatic field with large velocity. Smooth decrease of the field amplitude results in a residual velocity, which depends on the particular amount of the electron liberation from the atom. Polar asymmetry of the resultant angular distribution is predicted and calculated for the tunnel ionization by the light field with (Ε 3) ≠ 0.