(b) Write out the equations for the time dependence of ρ11, ρ22, ρ12 and ρ21 assuming that a light field interaction V = -μ12Ee iωt + c.c. couples only levels |1> and |2>, and that the excited levels exhibit spontaneous decay. (8 marks) (c) Under steady-state conditions, find the ratio of populations in states |2> and |3>. (3 marks) (d) Find the slowly varying amplitude ̃ ρ 12 of the polarization ρ12 = ̃ ρ 12e iωt . (6 marks) (e) In the limiting case that no decay is possible from intermediate level |3>, what is the ground state population ρ11(∞)? (2 marks) 2. (15 marks total) In a 2-level atom system subjected to a strong field, dressed states are created in the form |D1(n)> = sin θ |1,n> + cos θ |2,n-1> |D2(n)> = cos θ |1,n> sin θ |2,n-1>

The Quantum Theory of Light

Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control
of optical quantum systems.

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

From its initial use to describe hydrolysis and condensation processes, the term ‘sol–gel’ is now used for a diverse range of chemistries. In fact, it is perhaps better defined more broadly as covering the synthesis of solid materials such as metal oxides from solution-state precursors. These can include metal alkoxides that crosslink to form metal–oxane gels, but also metal ion–chelate complexes or organic polymer gels containing metal species. What is important across all of these examples is how the choice of precursor can have a significant impact on the structure and composition of the solid product. In this review, we will attempt to classify different types of sol–gel precursor and how these can influence a sol–gel process, from self-assembly and ordering in the initial solution, to phase separation during the gelation process and finally to crystallographic transformations at high temperature.

/pdf/the-evolution-of-sol-gel-chemistry-as-a-technique-for-ml3j7shxr6.pdf

The evolution of 'sol-gel' chemistry as a technique for materials synthesis

A review on developments in dyeing cotton fabrics with reactive dyes for reducing effluent pollution

Persistent luminescence instead of phosphorescence: History, mechanism, and perspective

The modulation of luminescence is essential because unwanted spontaneous-emission modes have a negative effect on the performance of luminescence-based photonic devices. Photonic crystals are promising materials for the control of light emission because of the variation in the local density of optical modes within them. They have been widely investigated for the manipulation of the emission intensity and lifetime of light emitters. Several groups have achieved greatly enhanced emission by depositing emitters on the surface of photonic crystals. Herein, the different modulating effects of photonic crystal dimensions, light-emitter positions, photonic crystal structure type, and the refractive index of photonic crystal building blocks are highlighted, with the aim of evaluating the fundamental principles that determine light propagation. The applications of using photonic crystals to manipulate spontaneous emission in light-emitting diodes and sensors are also reviewed. In addition, potential future challenges and improvements in this field are presented.

Manipulating Luminescence of Light Emitters by Photonic Crystals.

Encoding and Decoding of Invisible Complex Information in a Dual-Response Bilayer Photonic Crystal with Tunable Wettability

The unique brilliant and angle-independent structural colors of morpho butterfly wings were derived from the multilayer interference, diffraction, and scattering of light with a composite structure including ordered and quasiamorphous arrays. Inspired by the biological heterostructure of ordered and quasiamorphous arrays in the wings, a bilayer inverse heterostructure (BLIHS) containing ordered array layers inverse structure (OALIS) and quasiamorphous array layers inverse structure (Q-AALIS) of polyvinylidene fluoride were successfully prepared through the template method. The BLIHS films selectively displayed iridescent structural color derived from Bragg diffraction of OALIS, whereas the color states transform to noniridescent color because of Q-AALIS just by rotating the sample. Furthermore, the patterning process could be realized by using the spray-coating method on the BILIS films as quasiamorphous array layers. By virtue of this novel photonic structure, the switch between hiding and displaying patterns could be easily realized by changing the viewing angles, and the as-prepared films exhibited inherent excellent durability, which is crucial to their potential for practical applications as anticounterfeiting materials.

Biomimetic Structural Color Films with a Bilayer Inverse Heterostructure for Anticounterfeiting Applications

Biological skin systems can perceive various external stimuli through ion transduction Especially, the skin of some advanced organisms such as cephalopods can further promptly change body color by manipulating photonic nanostructures However, the current skin-inspired soft iontronics lack the rapid full-color switching ability to respond to multiple stimuli including tension, pressure, and temperature Here, an intelligent chromotropic iontronics with these fascinating functions is developed by constructing a biomimetic ultrastructure with anisotropic electrostatic repulsion This skin-like chromotropic iontronics can synchronously realize electrical response and optical visualization to mechanical strain and tactile sensation by adjusting the ultrastructure in cooperation with ionic mechanotransduction Notably, it can perform instantaneous geometric changes to thermal stimuli via an anisotropic electrostatic repulsion interior Such a capability allows bionic skin to transduce temperature or infrared light into ionic signals and color changes in real time The design of anisotropic photonic nanostructures expands the intelligent application for soft iontronics at higher levels, providing a concise, multifunctional, interactive sensing platform that dynamically displays stimuli information on its body

Suli Wu

Papers

Manipulating Luminescence of Light Emitters by Photonic Crystals.

Encoding and Decoding of Invisible Complex Information in a Dual-Response Bilayer Photonic Crystal with Tunable Wettability

Biomimetic Structural Color Films with a Bilayer Inverse Heterostructure for Anticounterfeiting Applications

Cephalopod-Inspired Chromotropic Ionic Skin with Rapid Visual Sensing Capabilities to Multiple Stimuli

New Encryption Strategy of Photonic Crystals with Bilayer Inverse Heterostructure Guided from Transparency Response