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

Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

An insight into the analogies, state-of-the-art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic-organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high-efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo-, pyro-, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects.

Mutual Insight on Ferroelectrics and Hybrid Halide Perovskites: A Platform for Future Multifunctional Energy Conversion.

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

Part 1 Perovskite type ferroelectrics: single crystals of potassium niobate solid solutions of potassium tantalate niobate lead zinc and magnesium niobate ferroelectrics with a smeared phase transition. Part 2 Ferroelectrics with tetragonal potassium tungsten bronze type structure: single crystals of barium strontium niobate barium sodium niobate single crystals other crystals with tetragonal potassium tungsten bronze type structure nonlinear optical crystals with lamellar structure. Part 3 Some physical aspects of oxygen-octahedra ferroelectrics: photoreactive properties of oxygen-octahedra ferroelectrics relation between ferroelectric and nonlinear optical properties of oxygen-octahedra ferroelectrics.

Ferroelectric Crystals for Laser Radiation Control

Stimulated-Raman conversion of multisoliton pulses in quartz optical fibers

We present the results of research and development in photodynamic therapy and fluorescence diag- nostics performed by the Center of Natural Research, General Physics Institute, Russian Academy of Sciences, in collaboration with several research and medical institutes. The main attention is focused on physical aspects of the problem. We describe schemes and the principle of operation of devices employed by our group in clin- ical and experimental studies. The problems of interaction of laser radiation with biological tissues are consid- ered. The assessment of an outlook for using different photosensitizers is based on their spectral-fluorescent properties, their ability to excite molecular oxygen, and their stability to irradiation with light. Some results of clinical applications of the developed devices and methods are presented.

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Photodynamic Therapy and Fluorescence Diagnostics

Stimulated emission due to the 4I11/2–4I13/2 transition (λ = 2.936 μ) in yttrium aluminum garnet (Y3Al5O12) doped with Er3+ ions (30 wt%) was observed for the first time at 300°K. The output energy from crystals of 50×3 mm dimensions was 0.3 J under free-oscillation conditions and 0.05 J in the case of Q switching. The lifetime of the 4I11/2 level was determined for crystals with 3–30 wt% Er3+. The energy from the higher Er3+ levels relaxed in a cascade manner through 4I11/2 to 4I13/2.

Stimulated emission from Er3+ ions in yttrium aluminum garnet crystals at λ = 2.94 μ

The authors propose a new simple configuration for 1.24 and 1.48 /spl mu/m Raman fibre lasers which are promising pumping sources for 1.31 /spl mu/m Raman amplifiers and Er-doped fibre amplifiers, respectively. Efficient resonant conversion of CW 1.06 /spl mu/m radiation to the first (1.24 /spl mu/m) and second (1.48 /spl mu/m) Raman Stokes in a phosphosilicate fibre is demonstrated for the first time.

A M Prokhorov

Papers

Ferroelectric Crystals for Laser Radiation Control

Stimulated-Raman conversion of multisoliton pulses in quartz optical fibers

Photodynamic Therapy and Fluorescence Diagnostics

Stimulated emission from Er3+ ions in yttrium aluminum garnet crystals at λ = 2.94 μ

CW high power 1.24 [micro sign]m and 1.48 [micro sign]m Raman lasers based on low loss phosphosilicate fibre