Assessment of ultra-high resolution optical coherence tomography for monitoring tissue effects caused by laser photocoagulation of ex-vivo porcine retina

Retinal laser photocoagulation is an established and successful treatment for a variety of retinal diseases. While being a valuable treatment modality, laser photocoagulation shows the drawback of employing high energy lasers which are capable of physically destroying the neural retina. For reliable therapy, it is therefore crucial to closely monitor the therapy effects caused in the retinal tissue. A depth resolved representation of optical tissue properties as provided by optical coherence tomography may provide valuable information about the treatment effects in the retinal layers if recorded simultaneously to laser coagulation. Therefore, in this work, the use of ultra-high resolution optical coherence tomography to represent tissue changes caused by conventional and selective retinal photocoagulation is investigated. Laser lesions were placed on porcine retina ex-vivo using a 577 nm laser as well as a pulsed laser at 527 nm built for selective treatment of the retinal pigment epithelium. Applied energies were varied to generate lesions best representing the span from under- to overtreatment. The lesions were examined using a custom-designed optical coherence tomography system with an axial resolution of 1.78 μm and 70 kHz Ascan rate. Optical coherence tomography scans included volume scans before and after irradiation, as well as time lapse scans (Mscan) of the lesions. Results show OCT lesion visibility thresholds to be below the thresholds of ophthalmoscopic inspection. With the ultra-high resolution OCT, 42% - 44% of ophthalmoscopically invisible lesions could be detected and lesions that were under- or overexposed could be distinguished using the OCT data.

Size, strain, and band offset engineering in GaAs(Sb)(N)-capped InAs quantum dots for 1.3 - 1.55 µm LEDs and LDs

The optical and structural properties of InAs/GaAs quantum dots (QD) are strongly modified through the use of a thin (~ 5 nm) GaAsSb(N) capping layer. In the case of GaAsSb-capped QDs, cross-sectional scanning tunnelling microscopy measurements show that the QD height can be controllably tuned through the Sb content up to ~ 14 % Sb. The increased QD height (together with the reduced strain) gives rise to a strong red shift and a large enhancement of the photoluminescence (PL) characteristics. This is due to improved carrier confinement and reduced sensitivity of the excitonic bandgap to QD size fluctuations within the ensemble. Moreover, the PL degradation with temperature is strongly reduced in the presence of Sb. Despite this, emission in the 1.5 !lm region with these structures is only achieved for high Sb contents and a type-II band alignment that degrades the PL. Adding small amounts of N to the GaAsSb capping layer allows to progressively reduce the QD-barrier conduction band offset. This different strategy to red shift the PL allows reaching 1.5 !lm with moderate Sb contents, keeping therefore a type-I alignment. Nevertheless, the PL emission is progressively degraded when the N content in the capping layer is increased

IFE Plant Technology Overview and contribution to HiPER proposal

HiPER is the European Project for Laser Fusion that has been able to join 26 institutions and signed under formal government agreement by 6 countries inside the ESFRI Program of the European Union (EU). The project is already extended by EU for two years more (until 2013) after its first preparatory phase from 2008. A large work has been developed in different areas to arrive to a design of repetitive operation of Laser Fusion Reactor, and decisions are envisioned in the next phase of Technology Development or Risk Reduction for Engineering or Power Plant facilities (or both). Chamber design has been very much completed for Engineering phase and starting of preliminary options for Reactor Power Plant have been established and review here.

Improvement of Mechanical Properties and Life Extension of High Reliability Structural Components by Laser Shock Processing

Profiting by the increasing availability of laser sources delivering intensities above 109 W/cm2 with pulse energies in the range of several Joules and pulse widths in the range of nanoseconds, laser shock processing (LSP) is being consolidating as an effective technology for the improvement of surface mechanical and corrosion resistance properties of metals and is being developed as a practical process amenable to production engineering. The main acknowledged advantage of the laser shock processing technique consists on its capability of inducing a relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly, the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Following a short description of the theoretical/computational and experimental methods developed by the authors for the predictive assessment and experimental implementation of LSP treatments, experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (specifically Al and Ti alloys) under different LSP irradiation conditions are presented. In particular, the analysis of the residual stress profiles obtained under different irradiation parameters and the evaluation of the corresponding induced surface properties as roughness and wear resistance are presented.

Estudio de la inserción de regeneradores 1r en un enlace óptico WDM punto a punto mediante herramientas CAD

El objetivo de este proyecto es estudiar el posicionamiento óptimo de un amplificador óptico dopado con Erbio (EDFA, Erbium-Doped Fiber Amplifier) en un enlace de fibra óptica punto a punto a través de la herramienta de simulación VPI photonics. Primero, se han expuesto los principios físicos que definen el funcionamiento de este tipo de amplificadores 1R. Posteriormente se han realizado lo que hemos denominado escenarios, en los que se han diseñado distintos casos de estudio.

A proposal for multi-tens of GW fully coherent femtosecond soft X-ray lasers

X-ray free-electron lasers1,2 delivering up to 131013 coherent photons in femtosecond pulses are bringing about a revolution in X-ray science3?5. However, some plasma-based soft X-ray lasers6 are attractive because they spontaneously emit an even higher number of photons (131015), but these are emitted in incoherent and long (hundreds of picoseconds) pulses7 as a consequence of the amplification of stochastic incoherent self-emission. Previous experimental attempts to seed such amplifiers with coherent femtosecond soft X-rays resulted in as yet unexplained weak amplification of the seed and strong amplification of incoherent spontaneous emission8. Using a time-dependent Maxwell?Bloch model describing the amplification of both coherent and incoherent soft X-rays in plasma, we explain the observed inefficiency and propose a new amplification scheme based on the seeding of stretched high harmonics using a transposition of chirped pulse amplification to soft X-rays. This scheme is able to deliver 531014 fully coherent soft X-ray photons in 200 fs pulses and with a peak power of 20 GW.

Experimental characterization of Fresnel-Köhler concentrators

Most cost-effective concentrated photovoltaics (CPV) systems are based on an optical train comprising two stages, the first being a Fresnel lens.

Understanding intermediate-band solar cells

The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. To make this possible, these cells incorporate an energy band that is partially filled with electrons within the forbidden bandgap of a semiconductor. Photons with insufficient energy to pump electrons from the valence band to the conduction band can use this intermediate band as a stepping stone to generate an electron-hole pair. Nanostructured materials and certain alloys have been employed in the practical implementation of intermediate-band solar cells, although challenges still remain for realizing practical devices. Here we offer our present understanding of intermediate-band solar cells, as well as a review of the different approaches pursed for their practical implementation. We also discuss how best to resolve the remaining technical issues.

Freeform Optical Surfaces: Report from OSA's First Incubator Meeting

Just as business incubator programs are designed to support the development of fledgling companies, OSA?s new incubator meeting series is structured to encourage the growth of exciting new areas within optics. The first one was devoted to the topic of freeform optics-a field that is actively evolving due to recent technological advances.

Electrically tunable delay for trains of optical pulses

A technique to implement an electrically tunable delay line with high bandwidth for trains of ultrashort optical pulses is presented. The system is based on the temporal self-imaging effect in fiber gratings and electrooptic modulation.

Photovoltaic performance of the dome-shaped Fresnel-Köhler concentrator

In order to have a cost-effective CPV system, two key issues must be ensured: high concentration factor and high tolerance. The novel concentrator we are presenting, the dome-shaped Fresnel-Köhler, can widely fulfill these two and other essential issues in a CPV module. This concentrator is based on two previous successful CPV designs: the FK concentrator with a flat Fresnel lens and the dome-shaped Fresnel lens system developed by Daido Steel, resulting on a superior concentrator. The concentrator has shown outstanding simulation results, achieving an effective concentration-acceptance product (CAP) value of 0.72, and an optical efficiency of 85% on-axis (no anti-reflective coating has been used). Moreover, Köhler integration provides good irradiance uniformity on the cell surface and low spectral aberration of this irradiance. This ensures an optimal performance of the solar cell, maximizing its efficiency. Besides, the dome-shaped FK shows optimal results for very compact designs, especially in the f/0.7-1.0 range. The dome-shaped Fresnel-Köhler concentrator, natural and enhanced evolution of the flat FK concentrator, is a cost-effective CPV optical design, mainly due to its high tolerances. Daido Steel advanced technique for demolding injected plastic pieces will allow for easy manufacture of the dome-shaped POE of DFK concentrator.

Beam-steering array optics with the SMS method

In this work, a new design concept of SMS moving optics is developed, in which the movement is no longer lateral but follows a curved trajectory calculated in the design process. Curved tracking trajectory helps to broaden the incident angle?s range significantly. We have chosen an afocal-type structure which aim to direct the parallel rays of large incident angles to parallel output rays. The RMS of the divergence angle of the output rays remains below 1 degree for an incident angular range of ±450. Potential applications of this beam-steering device are: skylights to provide steerable natural illumination, building integrated CPV systems, and steerable LED illumination.

1000x shadow-free mirror-based Köhler concentrator

A new design for a photovoltaic concentrator, the most recent advance based on the Kohler concept, is presented. The system is mirror-based, and with geometry that guaranties a maximum sunlight collection area (without shadows, like those caused by secondary stages or receivers and heat-sinks in other mirror-based systems). Designed for a concentration of 1000x, this off axis system combines both good acceptance angle and good irradiance uniformity on the solar cell. The advanced performance features (concentration-acceptance products ?CAP- about 0.73 and affordable peak and average irradiances) are achieved through the combination of four reflective folds combined with four refractive surfaces, all of them free-form, performing Köhler integration 2 . In Köhler devices, the irradiance uniformity is not achieved through additional optical stages (TIR prisms), thus no complex/expensive elements to manufacture are required. The rim angle and geometry are such that the secondary stage and receivers are hidden below the primary mirrors, so maximum collection is assured. The entire system was designed to allow loose assembly/alignment tolerances (through high acceptance angle) and to be manufactured using already well-developed methods for mass production, with high potential for low cost. The optical surfaces for Köhler integration, although with a quite different optical behavior, have approximately the same dimensions and can be manufactured with the same techniques as the more traditional secondary optical elements used for concentration (typically plastic injection molding or glass molding).