The Experts below are selected from a list of 3147 Experts worldwide ranked by ideXlab platform
Lionel C Kimerling - One of the best experts on this subject based on the ideXlab platform.
-
optimization based design of surface textures for thin film si solar cells
Optics Express, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian Models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.
-
Optimization-based design of surface textures for thin-film Si solar cells
Optics Express, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian Models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.Massachusetts Institute of Technology. Energy InitiativeUnited States. Air Force Office of Scientific Research (AFOSR MURI for Complex and Robust On-chip Nanophotonics (grant FA9550-09-1-0704)
-
Optimization-based design of surface textures for thin-film Si solar cells — Are conventional Lambertian Models relevant?
2011 37th IEEE Photovoltaic Specialists Conference, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:The efficiency of thin film silicon solar cells critically depends on the optical absorption. In this work, we numerically investigate the light trapping effect in the weak absorption regime for 1.5 μm thick crystalline silicon at normal incidence. Using electromagnetic simulations, we study the impact of different textures on the light absorption enhancement in two-dimensional (2D) device configuration. We discover that the light trapping effect of commercially used textures from Asahi glass is close to the 2D Lambertian result (F = πn), while optimized periodic gratings show better performances, and both rectangular and triangular gratings are capable to exceed the Lambertian result. To further explore the optimal light trapping structures, we develop a simulation method combining finite-difference time-domain (FDTD) calculations and the optimization algorithm (Nlopt-COBYLA). Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, our structure still obeys the conventional πn Lambertian limit when averaged over all the angles.
Xing Sheng - One of the best experts on this subject based on the ideXlab platform.
-
optimization based design of surface textures for thin film si solar cells
Optics Express, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian Models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.
-
Optimization-based design of surface textures for thin-film Si solar cells
Optics Express, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian Models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.Massachusetts Institute of Technology. Energy InitiativeUnited States. Air Force Office of Scientific Research (AFOSR MURI for Complex and Robust On-chip Nanophotonics (grant FA9550-09-1-0704)
-
Optimization-based design of surface textures for thin-film Si solar cells — Are conventional Lambertian Models relevant?
2011 37th IEEE Photovoltaic Specialists Conference, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:The efficiency of thin film silicon solar cells critically depends on the optical absorption. In this work, we numerically investigate the light trapping effect in the weak absorption regime for 1.5 μm thick crystalline silicon at normal incidence. Using electromagnetic simulations, we study the impact of different textures on the light absorption enhancement in two-dimensional (2D) device configuration. We discover that the light trapping effect of commercially used textures from Asahi glass is close to the 2D Lambertian result (F = πn), while optimized periodic gratings show better performances, and both rectangular and triangular gratings are capable to exceed the Lambertian result. To further explore the optimal light trapping structures, we develop a simulation method combining finite-difference time-domain (FDTD) calculations and the optimization algorithm (Nlopt-COBYLA). Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, our structure still obeys the conventional πn Lambertian limit when averaged over all the angles.
Jurgen Michel - One of the best experts on this subject based on the ideXlab platform.
-
optimization based design of surface textures for thin film si solar cells
Optics Express, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian Models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.
-
Optimization-based design of surface textures for thin-film Si solar cells
Optics Express, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian Models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.Massachusetts Institute of Technology. Energy InitiativeUnited States. Air Force Office of Scientific Research (AFOSR MURI for Complex and Robust On-chip Nanophotonics (grant FA9550-09-1-0704)
-
Exploration of Optimization-based Surface Textures for High Efficiency Thin-fFilm Si Solar Cells
Frontiers in Optics 2011 Laser Science XXVII, 2011Co-Authors: Jurgen MichelAbstract:We explore light-absorption behavior of thin-film silicon for normal-incidence, using surface textures to enhance absorption. Using an optimization algorithm, our optimized surface texture enhances absorption (900-1100nm) by 2.7x over the general Lambertian Model.
-
Optimization-based design of surface textures for thin-film Si solar cells — Are conventional Lambertian Models relevant?
2011 37th IEEE Photovoltaic Specialists Conference, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:The efficiency of thin film silicon solar cells critically depends on the optical absorption. In this work, we numerically investigate the light trapping effect in the weak absorption regime for 1.5 μm thick crystalline silicon at normal incidence. Using electromagnetic simulations, we study the impact of different textures on the light absorption enhancement in two-dimensional (2D) device configuration. We discover that the light trapping effect of commercially used textures from Asahi glass is close to the 2D Lambertian result (F = πn), while optimized periodic gratings show better performances, and both rectangular and triangular gratings are capable to exceed the Lambertian result. To further explore the optimal light trapping structures, we develop a simulation method combining finite-difference time-domain (FDTD) calculations and the optimization algorithm (Nlopt-COBYLA). Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, our structure still obeys the conventional πn Lambertian limit when averaged over all the angles.
Steven G Johnson - One of the best experts on this subject based on the ideXlab platform.
-
optimization based design of surface textures for thin film si solar cells
Optics Express, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian Models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.
-
Optimization-based design of surface textures for thin-film Si solar cells
Optics Express, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian Models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.Massachusetts Institute of Technology. Energy InitiativeUnited States. Air Force Office of Scientific Research (AFOSR MURI for Complex and Robust On-chip Nanophotonics (grant FA9550-09-1-0704)
-
Optimization-based design of surface textures for thin-film Si solar cells — Are conventional Lambertian Models relevant?
2011 37th IEEE Photovoltaic Specialists Conference, 2011Co-Authors: Xing Sheng, Jurgen Michel, Steven G Johnson, Lionel C KimerlingAbstract:The efficiency of thin film silicon solar cells critically depends on the optical absorption. In this work, we numerically investigate the light trapping effect in the weak absorption regime for 1.5 μm thick crystalline silicon at normal incidence. Using electromagnetic simulations, we study the impact of different textures on the light absorption enhancement in two-dimensional (2D) device configuration. We discover that the light trapping effect of commercially used textures from Asahi glass is close to the 2D Lambertian result (F = πn), while optimized periodic gratings show better performances, and both rectangular and triangular gratings are capable to exceed the Lambertian result. To further explore the optimal light trapping structures, we develop a simulation method combining finite-difference time-domain (FDTD) calculations and the optimization algorithm (Nlopt-COBYLA). Over a 900–1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian Model for periodic structures in finite spectral range. However, our structure still obeys the conventional πn Lambertian limit when averaged over all the angles.
Michael Oren - One of the best experts on this subject based on the ideXlab platform.
-
Improved Diffuse Reflection Models for Computer Vision
International Journal of Computer Vision, 1998Co-Authors: Lawrence B. Wolff, Shree K. Nayar, Michael OrenAbstract:There are many computational vision techniques that fundamentally rely upon assumptions about the nature of diffuse reflection from object surfaces consisting of commonly occurring nonmetallic materials. Probably the most prevalent assumption made about diffuse reflection by computer vision researchers is that its reflected radiance distribution is described by the Lambertian Model, whether the surface is rough or smooth. While computationally and mathematically a relatively simple Model, in physical reality the Lambertian Model is deficient in accurately describing the reflected radiance distribution for both rough and smooth nonmetallic surfaces. Recently, in computer vision diffuse reflectance Models have been proposed separately for rough, and, smooth nonconducting dielectric surfaces each of these Models accurately predicting salient non-Lambertian phenomena that have important bearing on computer vision methods relying upon assumptions about diffuse reflection. Together these reflectance Models are complementary in their respective applicability to rough and smooth surfaces. A unified treatment is presented here detailing important deviations from Lambertian behavior for both rough and smooth surfaces. Some speculation is given as to how these separate diffuse reflectance Models may be combined.
-
Reflectance analysis for image understanding
1996Co-Authors: Michael OrenAbstract:In this thesis, we study the two primary reflectance components--diffuse and specular reflectance--and their roles in image understanding. In particular, we explore accurate physical Modeling of reflectance and development of scene recovery techniques. One of the most widely used Models for diffuse reflection is the Lambertian Model which predicts that surface brightness is independent of viewing direction. However, it is shown that the Lambertian Model can be a very inaccurate approximation for rough surfaces. A comprehensive Model is developed that predicts reflectance from rough diffuse surfaces. The Model accounts for complex geometric and radiometric phenomena including masking, shadowing, and inter-reflections between points on the surface. Experiments have been conducted on real samples, such as plaster, clay, sand, and cloth, which demonstrate significant deviation from Lambertian behavior. The reflectance measurements obtained are in strong agreement with the reflectance predicted by the proposed Model. The implications of the Model for machine vision and graphics are discussed. A theoretical framework is introduced for the perception of specular surface geometry. When an observer moves in three-dimensional space, real scene features, such as surface markings, remain stationary with respect to the surfaces they belong to. In contrast, a virtual feature, which is the specular reflection of a real feature, travels on the surface. Based on the notion of caustics, a novel feature classification algorithm is developed. Next, using support functions of curves, a closed-form relation is derived between the image trajectory of a virtual feature and the geometry of the specular surface it travels on. It is shown that in the 2D case where camera motion and the surface profile are coplanar, the profile is uniquely recovered by tracking just two unknown virtual features. Finally, these results are generalized to the case of arbitrary 3D surface profiles that are traveled by virtual features when camera motion is not confined to a plane. An algorithm is developed that uniquely recovers 3D surface profiles using a single virtual feature tracked from the occluding boundary of the object. All theoretical derivations and proposed algorithms are substantiated by experiments.
-
Generalization of the Lambertian Model and implications for machine vision
International Journal of Computer Vision, 1995Co-Authors: Michael Oren, Satinder K. NayarAbstract:Lambert's Model for diffuse reflection is extensively used in computational vision. It is used explicitly by methods such as shape from shading and photometric stereo, and implicitly by methods such as binocular stereo and motion detection. For several real-world objects, the Lambertian Model can prove to be a very inaccurate approximation to the diffuse component. While the brightness of a Lambertian surface is independent of viewing direction, the brightness of a rough diffuse surface increases as the viewer approaches the source direction. A comprehensive Model is developed that predicts reflectance from rough diffuse surfaces. The Model accounts for complex geometric and radiometric phenomena such as masking, shadowing, and interreflections between points on the surface. Experiments have been conducted on real samples, such as, plaster, clay, sand, and cloth. All these surfaces demonstrate significant deviation from Lambertian behavior. The reflectance measurements obtained are in strong agreement with the reflectance predicted by the proposed Model. The paper is concluded with a discussion on the implications of these results for machine vision.
-
ECCV (2) - Seeing beyond Lambert's law
Computer Vision — ECCV '94, 1994Co-Authors: Michael Oren, Shree K. NayarAbstract:Lambert's Model for diffuse reflection is extensively used in computational vision. For several real-world objects, the Lambertian Model can prove to be a very inaccurate approximation to the diffuse component. While the brightness of a Lambertian surface is independent of viewing direction, the brightness of a rough diffuse surface increases as the viewer approaches the source direction. A comprehensive Model is developed that predicts reflectance from rough diffuse surfaces. Experiments have been conducted on real samples, such as, plaster, clay, and sand. The reflectance measurements obtained are in strong agreement with the reflectance predicted by the proposed Model.
-
CVPR - Diffuse reflectance from rough surfaces
Proceedings of IEEE Conference on Computer Vision and Pattern Recognition, 1Co-Authors: Michael Oren, Shree K. NayarAbstract:A comprehensive Model that predicts reflectance from rough diffuse surfaces is presented. It is shown that diffuse reflectance from rough surfaces increases as the viewing direction approaches the source direction. This is in contrast to Lambertian surfaces, where radiance is independent of the viewing direction. The new Model is a generalization of the Lambertian Model, and has significant implications for machine vision, graphics, and remote sensing. >
