Light field

About: Light field is a research topic. Over the lifetime, 5357 publications have been published within this topic receiving 87424 citations.

Advanced optical trapping by complex beam shaping

Abstract: Optical tweezers, a simple and robust implementa- tion of optical micromanipulation technologies, have become a standard tool in biological, medical and physics research labo- ratories. Recently, with the utilization of holographic beam shap- ing techniques, more sophisticated trapping configurations have been realized to overcome current challenges in applications. Holographically generated higher-order light modes, for exam- ple, can induce highly structured and ordered three-dimensional optical potential landscapes with promising applications in op- tically guided assembly, transfer of orbital angular momentum, or acceleration of particles along defined trajectories. The non- diffracting property of particular light modes enables the op- tical manipulation in multiple planes or the creation of axially extended particle structures. Alongside with these concepts which rely on direct interaction of the light field with particles, two promising adjacent approaches tackle fundamental limita- tions by utilizing non-optical forces which are, however, induced by optical light fields. Optoelectronic tweezers take advantage of dielectrophoretic forces for adaptive and flexible, massively parallel trapping. Photophoretic trapping makes use of thermal forces and by this means is perfectly suited for trapping ab- sorbing particles. Hence the possibility to tailor light fields holo- graphically, combined with the complementary dielectrophoretic and photophoretic trapping provides a holistic approach to the majority of optical micromanipulation scenarios.

Recording and controlling the 4D light field in a microscope using microlens arrays

Abstract: Summary Byinsertingamicrolensarrayattheintermediateimageplane of an optical microscope, one can record four-dimensional light fields of biological specimens in a single snapshot. Unlike a conventional photograph, light fields permit manipulation of viewpoint and focus after the snapshot has been taken, subject to the resolution of the camera and the diffraction limit of the optical system. By inserting a second microlens array and video projector into the microscope’s illumination path, one can control the incident light field falling on the specimen in a similar way. In this paper, we describe a prototype system we have built that implements these ideas, and we demonstrate two applications for it: simulating exotic microscope illumination modalities and correcting for optical aberrations digitally.

A single ion as a nanoscopic probe of an optical field

Abstract: In near-field imaging, resolution beyond the diffraction limit of optical microscopy is obtained by scanning the sampling region with a probe of subwavelength size. In recent experiments, single molecules were used as nanoscopic probes to attain a resolution of a few tens of nanometres. Positional control of the molecular probe was typically achieved by embedding it in a crystal attached to a substrate on a translation stage. However, the presence of the host crystal inevitably led to a disturbance of the light field that was to be measured. Here we report a near-field probe with atomic-scale resolution a single calcium ion in a radio-frequency trap that causes minimal perturbation of the optical field. We measure the three-dimensional spatial structure of an optical field with a spatial resolution as high as 60 nm (determined by the residual thermal motion of the trapped ion), and scan the modes of a low-loss optical cavity over a range of up to 100 m. The precise positioning we achieve implies a deterministic control of the coupling between ion and field. At the same time, the field and the internal states of the ion are not affected by the trapping potential. Our set-up is therefore an ideal system for performing cavity quantum electrodynamics experiments with a single particle.

Image transfer through a scattering medium

Abstract: 1 Introduction.- 1.1 A Brief History.- 1.2 Structure of the Book.- 1.3 Notes on Terminology.- 2 Radiation Field and Scattering Medium Characteristics.- 2.1 Radiation Field.- 2.2 Optical Parameters of a Volume Element.- 2.3 Radiation Transfer Equation.- 2.4 Similarity Principle and Modeling.- 2.5 Corollaries of the Optical Reciprocity Theorem.- 3 Light Scattering in Semi-Infinite Media and Plane Layers Illuminated by Infinitely Extended Plane Sources.- 3.1 Basic Equations.- 3.2 Asymptotic Regime in Deep Layers.- 3.2.1 Asymptotic Attenuation Coefficient and Angular Radiance Distribution.- 3.2.2 The Light Field in Absolute Units.- 3.3 Reflection from a Semi-Infinite Medium.- 3.3.1 Nonabsorbing Media.- 3.3.2 Weakly Absorbing Media.- 3.3.3 Absorbing Media with Strongly Anisotropic Scattering.- 3.4 Reflection and Transmission by Layers of Finite Thickness.- 3.5 Reflection and Transmission by Optically Thick Scattering Layers.- 3.5.1 Nonabsorbing Media.- 3.5.2 Weakly Absorbing Media.- 3.5.3 Absorbing Media with Strongly Anisotropic Scattering.- 3.6 Approximate Indicatrix Model Solutions.- 3.6.1 Forward Peak Truncation. Similar Media.- 3.6.2 Transport Approximation.- 3.6.3 Quasi-Single Scattering Approximation.- 3.6.4 Small-Angle Solution Iteration.- 3.6.5 Sobolev Approximation. Conservative Scattering.- 3.7 Two-Stream Approximation.- 3.7.1 Irradiance Coefficients. Boundary Conditions.- 3.7.2 Four-Parameter Variant of the Two-Stream Approximation.- 3.7.3 Two-Parameter Variant of the Two-Stream Approximation.- 4 Radiation Transfer in Scattering Media Illuminated by Localized Sources.- 4.1 Transfer Equation for a Narrow Beam. Spatial Radiance and Irradiance Distribution Moments.- 4.2 Local and Asymptotic Properties of Transfer Equation Solutions.- 4.3 The Diffusion Equation.- 4.3.1 Derivation of the Diffusion Equation.- 4.3.2 Solution of the Diffusion Equation for an Isotropic Point Source.- 4.3.3 Radial Irradiance Distribution from a Monodirectional Point Source.- 4.4 Small-Angle Approximation.- 4.4.1 Various Approaches.- 4.4.2 Transfer Equation in the Small-Angle Approximation.- 4.4.3 Solution of the Small-Angle Transfer Equation.- 4.4.4 Irradiance and Radiance of a Medium Illuminated by an Infinitely Extended Source.- 4.4.5 The Spread Function and its Moments.- 4.4.6 Light Flux.- 4.4.7 Radiation Fields in Scattering Media with Fluctuating Optical Parameters.- 4.4.8 The Merits and Weaknesses of the Small-Angle Approximation.- 4.5 Small-Angle Diffusion Approximation.- 4.5.1 Transfer Equation in the Small-Angle Diffusion Approximation.- 4.5.2 Light Fields Generated by an Infinitely Wide Source.- 4.5.3 Characteristics of Light Fields Produced by Narrow Beams.- 4.5.4 Oblique Medium Illumination.- 4.5.5 Light Fields in Media with Depth-Dependent Optical Characteristics.- 4.5.6 The Scope of the Small-Angle and Small-Angle Diffusion Approximations.- 4.5.7 Modified Small-Angle Diffusion Approximation.- 4.6 Notes on Multiple Backscattering.- 4.7 Generalized Multiple Scattering Theory Parameters and Applicability of Approximate Solutions.- 4.8 Nonstationary Radiation Field from Localized Pulsed Sources.- 4.8.1 The Nonstationary Transfer Equation.- 4.8.2 Pulse Propagation in Optically Thick Media.- 4.8.3 Pulse Reflection from a Semi-Infinite Scattering Medium.- 4.8.4 Forward Pulse Spread in a Strongly Anisotropic Scattering Medium.- 4.8.5 Mean Time and Variance of Photon Paths.- 5 Elements of Vision Theory.- 5.1 Image Quality Characteristics.- 5.1.1 Contrast and Signal-to-Noise Ratio.- 5.1.2 Threshold Contrast.- 5.1.3 General Image Quality Criterion.- 5.1.4 Threshold Signal-to-Noise Ratio.- 5.1.5 Signal-to-Noise Ratio in a Medium with Fluctuating Optical Parameters.- 5.2 Image Transfer Characteristics.- 5.2.1 Point Spread Function. Optical Transfer Function.- 5.2.2 Aspect Invariance of a System.- 5.2.3 Image Recording Techniques.- 5.2.4 Aspect Invariance Applicability.- 5.2.5 PSF and OTF Measurements.- 5.3 Active Vision Systems.- 5.3.1 Basic Relations.- 5.3.2 Classification of Vision System.- 5.3.3 Comparison of Vision Systems.- 5.3.4 Systems with Scattered Light Suppression.- 5.4 Visual Perception. Real Object Detection and Discrimination Range.- 5.4.1 The Johnson Criteria.- 5.4.2 Object Detection Range.- 5.4.3 Object Discrimination Range.- 5.5 Television and Location Target Detection Systems.- 5.5.1 Location in a Given Direction (Laser Echo-Ranging).- 5.5.2 Image Forming Location.- 5.6 Basic Characteristics of the Eye and Other Photodetectors.- 5.6.1 The Human Eye as a Radiation Receiver.- 5.6.2 Photographic and Photoelectric Recording.- 5.6.3 Notes on Infrared Imaging.- 6 Optical Transfer Function of a Scattering Medium.- 6.1 OTF of a Homogeneous Layer.- 6.1.1 OTF within the Small-Angle Approximation.- 6.1.2 The Small-Angle Diffusion Approximation.- 6.1.3 The Diffusion Approximation.- 6.1.4 MTF Dependence on Optical Medium Parameters.- 6.1.5 Scattering Layer MTF under Pulsed Source Illumination.- 6.2 OTF of an Inhomogeneous Layer.- 6.2.1 The Small-Angle Approximation.- 6.2.2 OTF of an Inhomogeneous Strongly Scattering Layer.- 6.2.3 MTF Dependence on the Scattering Layer Position along the Observation Path.- 6.2.4 Stochastic Medium MTF.- 6.3 Scattering Layer OTF along an Oblique Path. Phase Transfer Function.- 6.4 Nonlinear Distortions in Thick Scattering Layers.- 6.5 Object Image Contrast.- 6.5.1 Small Object Contrast.- 6.5.2 Contrast in the Johnson Striped Test Object.- 6.5.3 Finite Object Contrast as a Function of the Scattering Layer Position along the Observation Path.- 6.6 The Function ? in Object Detection and Discrimination.- 7 Image Transfer in Coherent Light.- 7.1 Coherent-Holography Imaging Through a Scattering Medium.- 7.1.1 Time-Averaged Holography.- 7.1.2 Limited Time Coherence (LTC) Method.- 7.1.3 Reference-Free Image Plane Holography (RFIPH).- 7.2 Comparison of Holographic and Incoherent Vision Systems.- 7.2.1 Mutual Coherence Function as Related to Radiance.- 7.2.2 Quality Characteristics of Rough Object Images in Reference Wave Holography.- 7.2.3 Contrast and Signal-to-Noise Ratio in Time-Averaged Holography and the Limited Time Coherence Technique.- 7.2.4 Contrast and Signal-to-Noise Ratio as Functions of the Averaging Time and Optical Parameters of a Scattering Medium.- 8 Viewing in Atmosphere.- 8.1 Optical Parameters of the Atmosphere.- 8.1.1 Cloudless Atmosphere.- 8.1.2 Cloud and Fog.- 8.2 Light Source Visibility.- 8.3 Object Visibility in Sunlight.- 8.3.1 Meteorological Visibility Range.- 8.3.2 Visibility Range in Clouds.- 8.4 Vision Characteristics in Cloud and Fog.- 8.4.1 OTF and Single-to-Noise Ratio.- 8.4.2 Cloud Microstructure Effect on the OTF and SNR.- 8.4.3 Estimation of Cloud OTF from Microstructure Data.- 8.5 Viewing Through Stochastic Clouds.- 8.5.1 Viewing System OTF and Signal Power Fluctuations.- 8.5.2 Irradiance and Radiation Flux Fluctuation Variances.- 8.5.3 Signal-to-Noise Ratio.- 9 Underwater Vision and Location in Sea Water.- 9.1 Optical Properties of Sea Water.- 9.1.1 Experimental Data.- 9.1.2 Simple Model of Optical Sea Water Characteristics.- 9.2 Object Visibility in Sea Water.- 9.2.1 Light Source Visibility.- 9.2.2 Range of Visibility of a Sunlit Object at Ocean Depth.- 9.2.3 Sekky's Disc Depth of Visibility.- 9.3 Underwater Television.- 9.3.1 Underwater TV Systems.- 9.3.2 MTF and Valid Signal and Noise Energy in Underwater Vision Systems.- 9.3.3 Limiting Ranges of Underwater Vision.- 9.4 Image Transfer Through a Rough Sea Surface.- 9.4.1 Rough Sea Surface Model.- 9.4.2 Image Transfer Characteristics.- 9.5 The Range of Optical Pulsed Location in Sea Water.- 10 Image Quality Problems in Photographic Layers and Luminescent Screens.- 10.1 Optical Parameters of a Photographic Layer.- 10.1.1 Undeveloped Layer.- 10.1.2 Exposed Developed Layer.- 10.2 Modulation Transfer Function of Photographic Materials.- 10.2.1 Optical and Photographic Modulation Transfer Functions.- 10.2.2 Empirical and Approximate MTF Formulas.- 10.2.3 MTF Dependence on the Optical and Emulsion Parameters of Photographic Materials.- 10.3 Optical Parameters of a Luminescent Screen.- 10.4 Modulation Transfer Function of Luminescent Screens.- 10.4.1 Nonscattering Luminescent Screens.- 10.4.2 Screens Weakly Absorbing Exciting Radiation.- 10.4.3 Screens Strongly Absorbing Exciting Radiation.- 10.4.4 Modulation Transfer Function of Cathode-Ray Screens.- 10.4.5 Influence of Technological Screen Parameters on MTF.- List of Symbols and Abbreviations.- References.

Light-field-driven currents in graphene

Abstract: The ability to steer electrons using the strong electromagnetic field of light has opened up the possibility of controlling electron dynamics on the sub-femtosecond (less than 10-15 seconds) timescale. In dielectrics and semiconductors, various light-field-driven effects have been explored, including high-harmonic generation, sub-optical-cycle interband population transfer and the non-perturbative change of the transient polarizability. In contrast, much less is known about light-field-driven electron dynamics in narrow-bandgap systems or in conductors, in which screening due to free carriers or light absorption hinders the application of strong optical fields. Graphene is a promising platform with which to achieve light-field-driven control of electrons in a conducting material, because of its broadband and ultrafast optical response, weak screening and high damage threshold. Here we show that a current induced in monolayer graphene by two-cycle laser pulses is sensitive to the electric-field waveform, that is, to the exact shape of the optical carrier field of the pulse, which is controlled by the carrier-envelope phase, with a precision on the attosecond (10-18 seconds) timescale. Such a current, dependent on the carrier-envelope phase, shows a striking reversal of the direction of the current as a function of the driving field amplitude at about two volts per nanometre. This reversal indicates a transition of light-matter interaction from the weak-field (photon-driven) regime to the strong-field (light-field-driven) regime, where the intraband dynamics influence interband transitions. We show that in this strong-field regime the electron dynamics are governed by sub-optical-cycle Landau-Zener-Stuckelberg interference, composed of coherent repeated Landau-Zener transitions on the femtosecond timescale. Furthermore, the influence of this sub-optical-cycle interference can be controlled with the laser polarization state. These coherent electron dynamics in graphene take place on a hitherto unexplored timescale, faster than electron-electron scattering (tens of femtoseconds) and electron-phonon scattering (hundreds of femtoseconds). We expect these results to have direct ramifications for band-structure tomography and light-field-driven petahertz electronics.