13 research outputs found
Analytical modeling of light transport in scattering materials with strong absorption
We have investigated the transport of light through slabs that both scatter
and strongly absorb, a situation that occurs in diverse application fields
ranging from biomedical optics, powder technology, to solid-state lighting. In
particular, we study the transport of light in the visible wavelength range
between and nm through silicone plates filled with YAG:Ce
phosphor particles, that even re-emit absorbed light at different wavelengths.
We measure the total transmission, the total reflection, and the ballistic
transmission of light through these plates. We obtain average single particle
properties namely the scattering cross-section , the absorption
cross-section , and the anisotropy factor using an analytical
approach, namely the P3 approximation to the radiative transfer equation. We
verify the extracted transport parameters using Monte-Carlo simulations of the
light transport. Our approach fully describes the light propagation in phosphor
diffuser plates that are used in white LEDs and that reveal a strong absorption
() up to , where is the
slab thickness, is the absorption mean free path. In
contrast, the widely used diffusion theory fails to describe this parameter
range. Our approach is a suitable analytical tool for industry, since it
provides a fast yet accurate determination of key transport parameters, and
since it introduces predictive power into the design process of white light
emitting diodes
Entanglement genesis by ancilla-based parity measurement in 2D circuit QED
We present an indirect two-qubit parity meter in planar circuit quantum
electrodynamics, realized by discrete interaction with an ancilla and a
subsequent projective ancilla measurement with a dedicated, dispersively
coupled resonator. Quantum process tomography and successful entanglement by
measurement demonstrate that the meter is intrinsically quantum non-demolition.
Separate interaction and measurement steps allow commencing subsequent data
qubit operations in parallel with ancilla measurement, offering time savings
over continuous schemes.Comment: 5 pages, 4 figures; supplemental material with 5 figure
Deterministic and controllable photonic scattering media via direct laser writing
Photonic scattering materials, such as biological tissue and white paper, are
made of randomly positioned nanoscale inhomogeneities in refractive index that
lead to multiple scattering of light. Typically these materials, both
naturally-occurring or man-made, are formed through self assembly of the
scattering inhomogeneities, which imposes challenges in tailoring the disorder
and hence the optical properties. Here, We report on the nanofabrication of
photonic scattering media using direct laser writing with deterministic design.
These deterministic scattering media consist of submicron thick polymer
nanorods that are randomly oriented within a cubic volume. We study the total
transmission of light as a function of the number density of rods and of the
sample thickness to extract the scattering and transport mean free paths using
radiative transfer theory. Such photonic scattering media with deterministic
and controllable properties are model systems for fundamental light scattering
in particular with strong anisotropy and offer new applications in solid-state
lighting and photovoltaics.Comment: 18 pages, 9 figure
Point singularity array with metasurfaces
Phase singularities are loci of darkness surrounded by monochromatic light in
a scalar field, with applications in optical trapping, super-resolution
imaging, and structured light-matter interactions. Although 1D singular
structures, such as optical vortices, are the most common due to their robust
topological properties, uncommon 0D (point) and 2D (sheet) singular structures
can be generated by wavefront-shaping devices such as metasurfaces. Here, using
the design flexibility of metasurfaces, we deterministically position ten
identical point singularities in a cylindrically symmetric field generated by a
single illumination source. The phasefront is inverse-designed using phase
gradient maximization with an automatically-differentiable propagator. This
process produces tight longitudinal intensity confinement. The singularity
array is experimentally realized with a 1 mm diameter TiO2 metasurface. One
possible application is blue-detuned neutral atom trap arrays, for which this
light field would enforce 3D confinement and a potential depth around 0.22 mK
per watt of incident trapping laser power. Metasurface-enabled point
singularity engineering may significantly simplify and miniaturize the optical
architecture required to produce super-resolution microscopes and dark traps
How to distinguish elastically scattered light from Stokes shifted light for solid-state lighting?
Systematic design of the color point of a white LED
\u3cp\u3eLighting is a crucial technology that is used in our daily lives. The introduction of the white light emitting diode (LED), which consists of a blue LED combined with a phosphor layer, greatly reduces the energy consumption for lighting. Despite the fast-growing market, white LEDs are still being designed with slow, numerical, trial-and-error methods. Here we introduce a radically new design principle that is based on an analytical model instead of a numerical approach. Our model predicts the white LED's color point for any combination of design parameters. In addition, our model provides the reflection and transmission coefficients of the scattered and re-emitted light intensities, as well as the energy density distribution inside the LED. To validate our model, we have performed extensive experiments on an emblematic white LED and found excellent agreement. Our model provides for a fast and efficient design, resulting in reductions of both design and production costs.\u3c/p\u3
How to distinguish elastically scattered light from Stokes shifted light for solid-state lighting?
We have studied the transport of light through phosphor diffuser plates that are used in commercial solid-state lighting modules (Fortimo). These polymer plates contain YAG:Ce+3 phosphor particles that both elastically scatter and Stokes shift light in the visible wavelength range (400–700 nm). We excite the phosphor with a narrowband light source and measure spectra of the outgoing light. The Stokes shifted light is spectrally separated from the elastically scattered light in the measured spectra, and using this technique, we isolate the elastic transmission of the plates. This result allows us to extract the transport mean free path ltr over the full wavelength range by employing diffusion theory. Simultaneously, we determine the absorption mean free path labs in the wavelength range 400 to 530 nm where YAG:Ce+3 absorbs. The diffuse absorption (μ a =1l abs ) \u3cbr/\u3e(μa=1labs)\u3cbr/\u3e spectrum is qualitatively similar to the absorption coefficient of YAG:Ce+3 in powder, with the diffuse spectrum being wider than the absorption coefficient. We propose a design rule for the solid-state lighting diffuser plates
Transport of light through white-LED phosphor plates
\u3cp\u3eEnergy efficient generation of white light has become an important societal issue in recent years. The technology of white-light emitting diodes (LEDs) is one of the main directions (Akasaki I, Amano H, Nakamura S, Blue LEDs – filling the world with new light, http://www.nobelprize.org/, 2014; Schubert EF, Light emitting diodes. Cambridge: Cambridge University, 2006). Key challenges in the white LED usage are understanding scattering, absorption and emission from ab-initio, and extracting the transport properties in the region where both emission and absorption overlap. Physical understanding of multiple light scattering in the LED provides tools to extract optical parameters of this system, and greatly simplify the LED design process. In this work we have been able to measure the total transmission, using a novel technique, in the region where emission and absorption overlap, and to extract transport parameters in the whole visible range.\u3c/p\u3
How to distinguish elastically scattered light from Stokes shifted light for solid-state lighting?
We have studied the transport of light through phosphor diff user plates that are used in commercial solid-state lighting modules (Fortimo). These polymer plates contain YAG:Ce+3 phosphor particles that both elastically scatter and Stokes shift light in the visible wavelength range (400-700 nm). We excite the phosphor with a narrowband light source, and measure spectra of the outgoing light. The Stokes shifted light is spectrally separated from the elastically scattered light in the measured spectra and using this technique we isolate the elastic transmission of the plates. This result allows us to extract the transport mean free path ltr over the full wavelength range by employing di ffusion theory. Simultaneously, we determine the absorption mean free path labs in the wavelength range 400 to 530 nm where YAG:Ce+3 absorbs. The diff use absorption 1/labs spectrum is qualitatively similar to the absorption coefficient of YAG:Ce+3 in powder, with the diff use spectrum being wider than the absorption coefficient. We propose a design rule for the solid-state lighting di ffuser plates