Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

We review the recent developments in the area of optical fiber grating sensors, including quasi-distributed strain sensing using Bragg gratings, systems based on chirped gratings, intragrating sensing concepts, long period-based grating sensors, fiber grating laser-based systems, and interferometric sensor systems based on grating reflectors.

Fiber grating sensors

Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

/pdf/lanthanide-luminescence-for-functional-materials-and-bio-1w9cppwf8r.pdf

Lanthanide luminescence for functional materials and bio-sciences

The historical beginnings of photosensitivity and fiber Bragg grating (FBG) technology are recounted. The basic techniques for fiber grating fabrication, their characteristics, and the fundamental properties of fiber gratings are described. The many applications of fiber grating technology are tabulated, and some selected applications are briefly described.

/pdf/fiber-bragg-grating-technology-fundamentals-and-overview-460zsnwohq.pdf

Fiber Bragg grating technology fundamentals and overview

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

/pdf/science-and-technology-roadmap-for-graphene-related-two-4q9m7czlkc.pdf

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Permanent photorefractive gratings with considerable refractive index modulations (~3×10–4) were written in silica optical fibers doped with very low levels of SnO2(~015 mol %) using ultraviolet (UV) laser radiation at 248 nm The photoinduced refractive index change does not show any sign of saturation even for long exposure times (ie, total fluence >20 kJ/cm2) A comparison with GeO2:SiO2 fibers shows that under similar UV intensities saturation takes place for shorter exposure time and comparable refractive index changes are obtainable for GeO2 concentrations ~10 mol %

Photorefractive index gratings in SnO2:SiO2 optical fibers

Rare-earth-doped fibre lasers and amplifiers have been demonstrated at several wavelengths in the visible and near infrared regions. The authors describe recent advances in the field with particular attention to applications in telecommunications.

Rare-earth-doped fibre lasers and amplifiers

We have demonstrated the feasibility of achieving high-performance fiber polarizers (insertion loss 30 dB), based on polarization mode dispersion in a long-period grating. Chirped operation with 100-nm bandwidth has also been achieved, showing the possibility of a broad-band device.

/pdf/high-performance-optical-fiber-polarizers-based-on-long-4kpyvckj3h.pdf

High-performance optical fiber polarizers based on long-period gratings in birefringent optical fibers

A fibre optic sensor for monitoring high pressures, using an in-fibre grating, has been constructed. The method involves tracking the wavelength of peak reflection from an in-fibre grating as it is pressurised. Experimental trials, under the influence of hydraulic pressure, have been carried out and a wavelength shift of 0.22 nm at 70 MPa pressure was observed. The sensor should be an attractive choice for ultra-high pressure monitoring

Optical fibre sensor for high pressure measurement using an in-fibre grating

We have demonstrated fast formation [~1500 pulses at ~1 (J/cm2)/pulse] of fiber gratings with highly negative index modulations (~−3 × 10−4). We have found that the maximum negative index modulations that are achieved do not depend on the pulse intensities, although the inverse of the time taken to reach the negative index-modulation maximum varies linearly with the pulse intensities. This prompts us to use a three-energy-level system to model the photosensitivity in boron-doped germanosilicate fiber. All the necessary parameters of the model can be determined from a single growth measurement of the average index change, and the model’s prediction fits well the measured index-modulation growth.

/pdf/negative-index-gratings-formed-by-a-193-nm-excimer-laser-lrj4jdfa8j.pdf

Negative-index gratings formed by a 193-nm excimer laser.

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