We discover that emission efficiency of Tm-doped upconversion nanoparticles can be enhanced through the use of a laser cavity. With suitable control of the lasing conditions, the population of the intermediate excited states of the Tm can be clamped at a required value above the excitation threshold. As a result, upconversion efficiency for the 300-620 nm emission band of the Tm-doped nanoparticles under 976 nm excitation can be enhanced by an order of magnitude over the case without a laser cavity. This is because the intrinsic recombination process of the intermediate excited states is suppressed and the surplus of excitation power directly contributes to the enhancement of multiphoton upconversion. Furthermore, our theoretical investigation has shown that the improvement of upconversion emission efficiency is mainly dependent on the cavity loss, so that this strategy can also be extended to other lanthanide-doped systems.

Lanthanide-doped nanocrystals (NCs), which found applications in bioimaging and labeling, have recently demonstrated significant improvement in up-conversion efficiency. Here, we report the first up-conversion multicolor microcavity lasers by using NaYF4:Yb/Er@NaYF4 core-shell NCs as the gain medium. It is shown that the optical gain of the NCs, which arises from the 2- and 3-photon up-conversion processes, can be maximized via sequential pulses pumping. Amplified spontaneous emission is observed from a Fabry-Perot cavity containing the NCs dispersed in cyclohexane solution. By coating a drop of silica resin containing the NCs onto an optical fiber, a microcavity with a bottle-like geometry is fabricated. It is demonstrated that the microcavity supports lasing emission through the formation of whispering gallery modes.

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We propose a scheme for bifurcation control in microcavities based on the interplay between the ultrafast Kerr effect and a slow nonlinearity, such as thermo-optical, free-carriers or opto-mechanical nonlinearity. We demonstrate that Hopf bifurcations can be efficiently controlled with a low energy signal via four-wave mixing. Our results show that new strategies are possible for designing efficient micro-cavity based oscillators and sensors. Moreover, they provide new understanding on the effect of coherent wave mixing in the thermal stability regions of optical micro-cavities, fundamental for microcavity based applications in communications, sensing and metrology, including optical micro-combs. © 2017 Optical Society of America OCIS codes : (140.3945) Microcavities; (190.4380) Nonlinear optics, fourwave mixing; (190.3100) Instabilities and chaos; (190.4870) Photothermal effects; (190.1450 The interplay between slow and fast nonlinearities in optical microcavities [1-2] has attracted considerable attention in the last two decades [1][2][3][4][5][6]. Thanks to the micro-cavities' ability of strongly enhancing the optical field, bi-stable, self-pulsing (SP) and chaotic regimes can be observed at low powers [3,4]. Starting from the pioneering works in whispering-gallery mode resonators by Il' Chencko and co-workers [3], thermal oscillators have been studied in micro-cavities having different geometries. They are usually modelled with one or two temporal relaxation constants [3,4,[7][8][9]. Amongst other effects, regenerative self-pulsing [10] and giant selfpulsation [11] have been reported, with applications, for example, to sensing [12]. In the generation of micro-combs [13] the control of the thermo-optical nonlinearity is fundamental for reaching coherent regimes, such as temporal cavity solitons. [14][15][16].In semiconductor cavities, the free-carrier nonlinearity has a typical time response in the microsecond regime [6,17,18] and its contribution to self-pulsing regimes has been studied under different conditions [19], including with pulsed excitation [20].Finally, opto-mechanical nonlinearities have also been efficiently employed for designing oscillators in the microwave regime [21]. Recently, Monifi et al. [5] have experimentally demonstrated control and transfer of nonlinear dynamics and chaos between two cavity modes via mechanical oscillation.In this framework, the control of multi-stable or self-pulsing regions, usually arising at a bifurcation in the parameter space, is critical for achieving the desired performance. Specifically, relocating a bifurcation at a desired parameter value is a general problem in applied nonlinear science that has been approached with different methods [22].In this letter, we study the effect of a parametric interaction, specifically four-wave mixing (FWM), on the nonlinear dynamics of a micro-cavity based oscillator exhibiting both Kerr nonlinearity and an intensity-dependent nonlinearity with a first order timeresponse, such as a thermal nonlinearity. We propose ...

Detection of H2O2 is important for the applications in environmental protection, pharmaceutical industries, food production, and clinical control. Current colorimetric assay of H2O2 based on enzyme or nanomaterials always needs TMB or other peroxidase substrate as coloration species. Furthermore, the corresponding response time including incubation process is in order of minute. In this study, we report on the synthesis of heavily Ti(3+)-doped TiO2 composed of spherelike nanoparticles by pulsed laser ablation method. This TiO2 can directly detect H2O2 without using TMB or any other peroxidase substrate and is free from incubation process. In addition, the detection sensitivity is compatible with or better than that of the natural enzyme or other nanomaterials. Hence, the self-doped TiO2 nanoparticles provide a novel, direct, ultrafast approach for H2O2 assay application.

SUMMARYInvestment involves the maximisation of return on one's investment whilst minimising risk. Good forecasting, which often requires expert knowledge, can help to reduce risk. In this paper, we propose a genetic programming-based system, EDDIE (Evolutionary Dynamic Data Investment Evaluator), as a forecasting tool. Genetic programming is inspired by evolution theory, and has been demonstrated to be successful in other areas. EDDIE interacts with the users and generates decision trees, which can also be seen as rule sets. We argue that EDDIE is suitable for forecasting because apart from utilising the power of genetic programming to efficiently search the space of decision trees, it allows expert knowledge to be channelled into forecasting, and it generates rules which can easily be understood and verified. EDDIE has been applied to horse racing and achieved outstanding results. When experimented on 180 handicap races (real data) in the UK, it out-performed other common strategies used in horse race betting by great margins. The idea was then extended to financial forecasting. When tested on historical S&P-500 data EDDIE achieved a respectable annual rate of return over a three and a half year period. While luck may play a part in the success of EDDIE, our experimental results do indicate that EDDIE is a tool which deserves more research. © 1998 John Wiley & Sons, Ltd. key words: finance; forecasting; genetic programming; horse racing; investment INTRODUCTION Financial investment is concerned with risking money in order to gain more money. The objective is to minimise risk and maximise Return On Investment (ROI). Information can often help us to reduce risk. For example, to predict the future price of a share, useful information include; its past and present prices, price-earning ratios, price-to-book values, dividends, market indices, who said what in the public domain, etc. The aim of our research is to build tools to help investors to make best use of the information available to them. Such tools should improve the productivity of the users by allowing them to examine more sets of rules in less time. To some users, such tools could help them to do what they did not have the knowledge to do without such tools.Many factors could directly or indirectly affect the future price of an investment. Such factors are often inter-related, which adds to the difficulty of analysis. The combinatorial explosion problem prevents one from examining combinations of all the factors and their possible ways of interaction. We have developed EDDIE

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