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The high chemical stability of SU-8 makes it irreplaceable for a wide range of applica- tions, most notably as a lithography photoresist for micro and nanotechnology. This advantage becomes a problem when there is a need to remove SU-8 from the fabricated devices. Researchers have been struggling for two decades with this problem, and al- though a number of partial solutions have been found, this difficulty has limited the applications of SU-8. Here we demonstrate a fast, reproducible, and comparatively gen- tle method to chemically remove SU-8 photoresist. An ether cleavage mechanism for the observed reaction is proposed, and the hypothesis is tested with ab initio quantum chem- ical calculations. Also described are a polymer-metal adhesion treatment, and a comple- mentary removal method, based on atomic hydrogen inductively coupled plasma.

In this work, we experimentally demonstrate magnetic modulation of mid-infrared (mid-IR) plasmon resonances in microantenna and hole-array metamaterial platforms made of Ni81Fe19/Au multilayers. The responsible mechanism is the magnetorefractive effect linked to the giant magnetoresistance (GMR) present in this system. Ni81Fe19/Au multilayers experience a modification in the electrical resistivity upon the application of a small magnetic field. This directly translates into a change in the optical constants of the multilayer, making it possible to magnetically modulate the plasmon resonances. Because GMR acts on conduction electrons, the optical modulation occurs in the low energy, mid-IR range, even being possible to extend it to the THz range. Electrodynamical calculations confirm the experimental observations. This approach improves by up to 2 orders of magnitude previous attempts for mid-IR magnetic modulation, is potentially ultrafast due to the characteristic spintronics dynamics, and establishes a roadmap for spintronically controlled devices in the whole mid-IR to THz band., We acknowledge financial support from MINECO through project AMES (MAT 2014-58860-P), Quantum Spin Plasmonics (FIS2015-72035-EXP), PlasmoQuanta (FIS2016-80174-P), and MIRRAS (MAT2017-84009-R). L.B., N.Z., and J.A. acknowledge support from the Basque Department of Education and the UPV-EHU (Grant IT-756-13). A.M. acknowledges support from the Spanish Ministry of Economy and Competiveness (MINECO) under grant TEC2014-51902-C2-1-R. We acknowledge the service from the MiNa Laboratory at IMN and funding from MINECO under project CSIC13-4E-1794 and from CM under project S2013/ICE-2822 (Space-Tec), both with support from EU (FEDER, FSE).

A new design of carbon source using a S-shaped glassy carbon filament for p-doping and carbon deposition is presented. Due to the higher resistivity of the glassy carbon, lower current is needed to produce the same flux as in a source based on pyrolytic graphite filament. The source design is very compact and the use of water cooling is not mandatory. The results and simulations of the new design show a higher flux than the previously reported glassy carbon based source while avoiding hot spots that can cause an early filament degradation. Hole mobility vs doping level relation data on p-doped GaAs layers grown by molecular beam epitaxy using this new carbon source are shown. With this new C source GaAs (001) surface morphology flatness is preserved after depositing C, showing a reduced substrate heating radiation essential for operate in III-V solid source molecular beam epitaxy (MBE) systems., The authors wish to acknowledge the financial support by the Spanish MINECO (MAT2015-67021-R), by MCIU-AEI-FEDER-UE (ENE2017-91092-EXP, RTI2018-096937-B-C22) and by Comunidad de Madrid (P2018/EMT-4308). We acknowledge the service from the MiNa Laboratory at IMN, funding from CM (project S2018/NMT-4291 TEC2SPACE), and from the X-SEM Laboratory, funding from MINECO (project CSIC13-4E-1794), both with support from EU (ERDF, ESF).

Trabajo presentado en el SPIE Nanoscience + Engineering, celebrado en San Diego (California, Estados Unidos), del 6 al 10 de agosto de 2017, Here we present our proposal and initial results on the magnetic field control of plasmon resonances in the mid IR region by the use of the Magneto-Refractive (MR) effect, i.e., a change in the optical properties of the system by magnetic field controlled electrical resistivity. For this we select a Giant Magneto Resistance model system (a Au/Permalloy multilayer), for which changes in resisitivity of the order of 10% by the application of small (of the order of 20 Oe) magnetic fields have been reported. The experiments are carried out in a dedicated magnetic field FTIR (M-FTIR) spectrometer.

The moth-eye structure has been proposed several times as an antireflective coating to replace the standard optical thin films. Here, we experimentally demonstrate the feasibility of a dielectric moth-eye structure as an antireflective coating for high-index substrates, like GaAs. The fabricated photonic crystal has Si3N4 cones in a square lattice, sitting on top of a TiO2 index matching layer. This structure attains 1.4% of reflectance power losses in the operation spectral range of GaAs solar cells (440–870 nm), a 12.5% relative reduction of reflection power losses in comparison with a standard bilayer. The work presented here considers a fabrication process based on laser interference lithography and dry etching, which are compatible with solar cell devices. The experimental results are consistent with scattering matrix simulations of the fabricated structures. In a broader spectral range (400–1800 nm), the simulation estimates that the nanostructure also significantly outperforms the standard bilayer coating (3.1% vs. 4.5% reflection losses), a result of interest for multijunction tandem solar cells., We acknowledge the SGAI-CSIC for the allocation of computational resource and the financial support by MINECO (TEC2015-64189-C3-2-R, AIC-B-2011-0806, FPI grant) and CAM (S2013/MAE-2780).

[Full-text not avalaible yet], Two-dimensional photonic crystal lasers have been fabricated on III–V semiconductor slabs. Tuning of the spontaneous emission in micro and nanocavities has been achieved by accurate control of the slab thickness. Different structures, some of them of new application to photonic crystal lasers, have been fabricated like the Suzuki-phase or the coupled-cavity ring-like resonators. Laser emission has been obtained by pulsed optical pumping. Optical characterization of the lasing modes have been performed showing one or more laser peaks centred around 1.55 μm. Far field characterization of the emission pattern has been realized showing different patterns depending on the geometrical shape of the structures. These kinds of devices may be used as efficient nanolaser sources for optical communications or optical sensors., A.R. Alija thanks a FPU fellowship AP2002-0474 and L.J. Martínez an I3P fellowship. The authors would also like to acknowledge support from European Network of Excellence IST-2-511616-NOE (PHOREMOST) and NMP4-CT-2004-500101 (SANDIE), Spain-Italy Integrated Action HI2004-0367/IT2304, projects NAN2004-08843-C05-04, TEC-2005-05781-C03-01, NAN2004-09109-C04-01, CONSOLIDER-Ingenio 2010(CSD2006-00019), TEC2004-03545 and CARIPLO Foundation.

© 2015 Optical Society of America. Broadband solar cell antireflection coatings made of nanocones are studied in square lattices of ZnS, TiO2 and Si3N4. In the best case, the spectrally integrated transmittance (accounting for both reflection and dielectric absorption losses) for direct solar radiation is 99 %, which represents a four-fold decrease in transmission losses in comparison to a standard antireflective coating bilayer. The dependence of the transmission as a function of nanostructure dimensions is studied, showing a wide maximum, thus leading to a high tolerance for manufacturing errors. This high transmittance is also robust against deviations from normal incidence. Our analysis suggests that the high transmittance is due not only to an effective gradual index effect, but is also due to light coupling to quasiguided modes in the photonic crystal leaking mostly towards the substrate., We acknowledge the SGAI-CSIC for the allocation of computational resource and the financial support by MINECO ( ENE2012-37804-C02-02, FPI grant) and CAM ( (S2013/MAE-2780).

Photoplethysmography and pulse oximetry are techniques based on optical principles, which are widely used in medical practice for non-invasive monitoring. There are some processes which may affect specific organs or parts without a significant repercussion on the information provided non-invasively. Here, we report on the preliminary results obtained by transmittance photoplethysmography in pig intra-peritoneal organs along a surgical intervention, using a measurement system based on two near-infrared laser diodes. Analysis of the signals recorded at 750 nm and 850 nm in the mesentery root, mesocolon, gastric wall and aorta artery has shown the affordability of performing in situ photoplethysmography for visceral perfusion evaluation. © 2006 IOP Publishing Ltd., This work has been partially supported by the Spanish Commission for Science and Technology (CICYT) project TIC98–1025, Asociacion C ´ antabra de Cirug ´ ´ıa, project UNI 2002/15 of University of Las Palmas de Gran Canaria and grant FIS PI040715 of Spanish Ministry of Health. Spanish Programa Ramon y Cajal supports SMLS.

This work describes the application of the Lattice Fringe Spacing Measurement (LFSM) method to the study of complex multiquantum well heterostructures containing both low-misfit and strain compensated short period superlattices in barriers and wells, respectively. 90º-wedge cross-sectional samples have been used. The adequate choice of both experimental conditions and digitized sampling allows the whole heterostructure to be visualized and studied in a single High Resolution Transmission Electron Microscopy (HRTEM) image. Sample preparation and image processing technique are simple and inexpensive, resulting a fast procedure particularly suited for the analysis of large areas. By this way, in a single HRTEM image we have measured, in the growth direction, the lattice spacings at either side of the multiple grown interfaces as well as the period variations of both types of superlattices; in addition, we have measure on the same image the lattice strain in a direction perpendicular to the growth direction by using the LFSM and the Cumulative Sum methods. We have observed local lateral variations within the wells, with regions tensile or compressively strained, while a vestige of the grown SL remains, indicating the occurrence of a strain induced lateral composition modulation process spontaneously produced during the growth of strain compensated short-period superlattices. This is further confirmed in cross-section prepared by the tripod mechanical polisher method., The authors express their sincere thanks to A. Guerrero for his support in the CUSUM program, to J. Thibault who invited them to take benefit of the 4000EX microscope available in the CEN-Grenoble, and to A. Sanz-Hervás, from Depto. Tecnología Electrónica, E.T.S.I.T.-U.P.M., Madrid, for his support in XRD measurements.

The lateral composition modulation of strain compensated (GaInP)m(GaInAs)m short-period superlattices (SPSL) has been investigated. Transmission electron microscopy results show that long-range lateral composition modulation is formed in m=2 SPSL grown at 400°C by atomic layer molecular beam epitaxy. The evolution of photoluminescence (PL) peak with temperature shows a blue shift with increasing temperature; in addition, low-temperature PL is strongly polarized. These properties are attributed to the lateral composition modulation. Quantum wires (QWRs) were formed using (GaInP)m(GaInAs)m SPSL as quantum wells in a multiquantum well heterostructure. The formation of QWR is confirmed by their PL properties. © 2003 Elsevier Science B.V. All rights reserved.

5 páginas, 8 figuras., For the first time, we have obtained the real-time observation, by x-ray topography, of the laser degradation due to the formation of misfit dislocations. We drive the laser diode under a high-energy, high-flux synchrotron micro-x-ray beam. We simultaneously obtain both the laser characteristic curve and the structural characteristics during operation, i.e. the presence of misfit dislocations, laser diode curvature and strain status. From the strain we measure the temperature increase in the epilayer due to the injection current. In other lasers device degradation occurred without the formation of misfit dislocations, but by mass transport, and in other lasers no structural degradation was observed.

5 pages, 7 figures., SnTe-doped InP layers were grown at low temperature by solid-source atomic layer molecular beam epitaxy. The samples were characterized by Hall measurements versus temperature, low temperature photoluminescence, x-ray diffraction, and secondary ion mass spectroscopy. The temperature of the SnTe effusion cell was varied from 320 to 440 °C, and the free electron concentration measured at room temperature ranged between 2.0×1016 cm−3 and 5.6×1018 cm−3 with the corresponding Hall mobility varying from 2320 to 1042 cm2/V s., The authors would like to thank Dr. A. J. Springthorpe, from Nortel Networks, for SIMS measurements, and the Spanish CICYT for financially supporting this research under Contract No. TIC-99-0645-C05-05.

Optimizing the feature sizes of dielectric nanostructures on the top (ZnS) and bottom (SiO2) surfaces of a 1 μm thick GaAs solar cell, we obtain a higher efficiency (34.4%) than a similar cell with a state of the art bilayer antireflection coating and a planar mirror (33.2%). The back side nanostructure increases the photocurrent due to enhanced optical path length inside the semiconductor, while the nanostructure on the front side increases the photocurrent due to lower reflectance losses. © 2013 AIP Publishing LLC., We acknowledge the SGAI-CSIC for the allocation of computational resource and the financial support by MINECO (ENE2012-37804-C02-02, FPI grant) and CAM (S2009/ENE-1477).

A hybrid approach for light trapping using photonic crystal nanostructures (nanorods, nanopillars or nanoholes) on top of an ultra thin film as a substrate is presented. The combination of a nanopatterned layer with a thin substrate shows an enhanced optical absorption than equivalent films without patterning and can compete in performance with nanostructured systems without a substrate. The designs are tested in four relevant materials: Amorphous silicon (a-Si), crystalline silicon (Si), gallium arsenide (GaAs) and indium phosphide (InP). A consistent enhancement is observed for all of the materials when using a thin hybrid system (300 nm) even compared to the non patterned thin film with an anti-reflective coating (ARC). A realistic solar cell structure composed of a hybrid system with a layer of indium tin oxide (ITO) an ARC and a back metal layer is performed, showing an 18% of improvement for the nanostructured device. © 2012 Optical Society of America., We acknowledge financial support by MICINN (grants ENE2009-14481-C02-02, CSD2006- 0004, Innpacto IPT-2011-1467- 420000), and CAM (S2009/ENE-1477).

A hybrid approach for light trapping using photonic crystal (PC) nanostructures (nanorods, nanopillars or nanoholes) on top of an ultra-thin film is presented. The combination of a nanopatterned layer with a thin substrate shows an enhanced optical absorption than equivalent films without patterning and can compete in performance with nanostructured systems without a substrate. The designs are tested in four relevant materials: amorphous silicon (a-Si), crystalline silicon (Si), gallium arsenide (GaAs) and indium phosphide (InP). A consistent enhancement is observed for all of the materials when using a thin hybrid system (300 nm) even compared to the non-patterned thin film with an anti-reflective coating (ARC). A realistic solar cell structure composed of a hybrid system with a layer of indium tin oxide (ITO) an ARC and a back metal layer is simulated, showing an 13% of improvement for the nanostructured device.

The spontaneous emission rate and Purcell factor of selfassembled quantum wires embedded in photonic crystal micro-cavities aremeasured at 80 K by using micro- photoluminescence, under transient and steady state excitation conditions. The Purcell factors fall in the range 1.1 - 2 despite the theoretical prediction of ?15.5 for the figure of merit. We explain this difference by introducing a polarization dependence on the cavity orientation, parallel or perpendicular with respect to the wire axis, plus spectral and spatial detuning factors for the emitters and the cavitymodes, taking in account the finite size of the quantum wires. © 2012 Optical Society of America., We want to acknowledge financial support from the Spanish MICINN through Grants: TEC 2005-05781-C03-01/03, TEC2008-06756-C03-01/03, S-0505-TIC-0191, Consolider-Ingenio 2010 QOIT (CSD2006-0019), and CAM (S2009ESP-1503). The main author, J. C.-F., thanks also the Spanish MCI for his FPI grant BES-2006-12300.

We investigate 1D-2D photonic crystals for light absorption enhancement on thin film photovoltaics (Si, GaAs an InP) by FDTD. A comparison with RCWA and TMM is presented. The absorption is increased substantially for these systems.

A novel monolithically integrated optoelectronic microsensor is fabricated on GaAs substrates by means of a single epitaxial process step (atomic layer molecular beam epitaxy, ALMBE), conventional lithography and selective chemical etching techniques. The microsensor integrates an IR (0.86-1.1 μm) lateral emitting diode linked through a leaky optical waveguide to a photodiode. © 1993.

Strained-layer quantum well lasers have been grown at low substrate temperature (350°C) by atomic layer molecular beam epitaxy (ALMBE). A series of five separate confinement laser structures has been grown. Active regions consist of 80 A of GaAs in which n InAs monolayers are inserted separated by 3 GaAs monolayers, with n = 1, 3, 5 and 7. A sample with 100 Å Ga0.8In0.2As active region was also grown at low temperature for comparison. Structural quality is studied by X-ray diffraction. Optical characterization has been performed, and the results are compared with calculations by a four-band envelope-wavefunction method. Broad area lasers have been fabricated, and their performances are studied as a function of increasing InAs content. Lasers with GaAs active regions including InAs monolayers show threshold currents comparable to that of the GaInAs alloy laser, for n≤5 monolayers. These results prove the feasibility of ALMBE for the low temperature growth of strained layer lasers. © 1993.

Strained-layer superlattices (SLSs) made up of alternated GaxIn1-xAs and GaxIn1-xP, with x=0.22 is an alternative to the quaternary GaxIn1-xAsyP1-y. Strain is near symmetrized when grown on InP substrates. Lattice mismatch to InP (-1.57% GaInP, 1.71% GaInAs) being compensated, the net value of strain in the SLS is expected to be negligible. Using low temperature atomic-layer MBE (Ts = 350°C), P2 and As4 are supplied in successive pulses to group III terminated intermediate surfaces, minimizing competition, by using specially designed, fast operating valved solid source cells. A set of (Ga0.22In0.78 As)m/(Ga0.22In0.78P)m superlattices have been grown, with m ranging from 1 to 10 monolayers. The samples were characterized by X-ray diffraction. Photoluminescence measurements were performed, at 98 and 300 K, the emission wavelength ranging from 1.27 to 1.52 μm at room temperature. These superlattices have been used as pseudoquaternary material in InP/GaInAsP/GaInAs structures emitting at 1.5 μm.

Trabajo presentado en el SPIE NanoScience + Engineering, celebrado en San Diego, California (Estados Unidos), del 2 al 5 de agosto de 2010, In this work we show room temperature continuous (CW) lasing at 1.5 μm in photonic crystal microcavities with a single layer of self-assembled quantum wires (QWRs). Low threshold values in the range of 1-20 μW (depending on the excitation type, pulsed or CW) have been measured, along high quality factors exceeding Q=55000 using L7-type photonic crystal microcavities. Solid-source molecular beam epitaxy has been used for the synthesis of the InP/InAs epitaxial material comprising a single layer of InAs QWRs. The main axis of the cavity is always parallel to the QWRs, which are more than 1μm in length along the [1-10] direction. No lasing has been obtained for L7 cavities with axis parallel to the [110] (i.e., perpendicular to the direction of the QWRs), showing the strong one-dimensional character of the QWRs inside the photonic cavity. Under inhomogeneous pulsed excitation the lasing spectra show asymmetric lineshapes and peak splittings first in the μeV and later in the meV ranges as the excitation power is increased.

In this work we show room temperature lasing at 1.5 µm in photonic crystal microcavities in air bridge membranes with a single layer of self-assembled quantum wires (QWRs). Low threshold values around 10 µW have been measured, along high quality factors Q ∼ 55000 using L7-type photonic crystal microcavities. Solid-source molecular beam epitaxy has been used for the synthesis of the InP/InAs epitaxial material comprising a single layer of InAs QWRs. The main axis of the cavity is always parallel to the QWRs, which grow along the [1-10] direction. No lasing has been obtained for L7 cavities with axis parallel to the [110] (i.e., perpendicular to the direction of the QWRs), showing the strong one-dimensional character of the QWRs inside the photonic cavity. Under pulsed excitation the lasing spectra show asymmetric lineshapes and an evolution related with thermal and absorption saturation effects.

Photoplethysmography (PPG) is a non-invasive optical technique that enables to quantify the arterial blood pulse rate derived from the cardiac pumping action. Although this technique is widely used in the medical practice as part of pulse oximeters, the signal corruption by motion artifacts is a primary limitation in the practical accuracy and applicability of current instruments to monitor pulse rate during intense exercise. Here, we report on the application of transmittance PPG throughout maximal exercise tests in cycle ergometer in male athletes. A specifically developed algorithm has been applied to obtain PPG pulse rates similar to the reference heart rates.

During the last years, much attention has been paid to photonic crystals (PC) for different applications, but only recently they have been proposed and showed useful for applications in solar cells. Little work has been done in the actual manufacture and characterization of a complete solar cell with a two-dimensional photonic crystal (2D-PC) on its front surface, conceived as a periodic distribution of the dielectric constant in the plane (the surface of the solar cell) and involving sub-wavelength motifs. In this case, the photonic crystal effect is different from the one happening in slabs or suspended membranes. Despite the partial vertical confinement, there may be some reasons that can justify the use of photonic crystal front surface with sub-wavelength motifs. Experimental results on actual devices with a photonic crystal nanopatterned layer will be shown, along with reflectivity studies on PC lattices with different symmetries and shapes.

6 páginas, 4 figuras, 1 tabla.-- PACS: 42.55.Px; 73.21.Cd; 73.21.Hb., Waveguides formed by (InP)5/(Ga0.47In0.53As)4 short-period superlattices (SPSL) have been grown and characterized for their use as waveguides in InAs self-assembled quantum wires (QWR) lasers. Atomic force microscopy has been used to characterize both the SPSL and the QWR morphology quality. It is demonstrated that the shape of the QWR strongly depends on the roughness of the SPSL surface and that an atomically flat surface is necessary to obtain a uniform QWR size and shape morphology. Photoluminescence (PL) spectroscopy is also employed as a feedback to achieve the optimum growth parameters in order to obtain high-quality QWR confined by SPSL., This work was financed by Spanish projects MEC TEC- 2005-05781-C03-01, CONSOLIDER-Ingenio 2010 QOIT CSD2006-0019 and CAM S_0505ESP_0200, and by UE SANDIE Network of excellence (Contract no. NMP4-CT- 2004-500101).

4 páginas, 4 figuras.-- Póster presentado a la Conferencia de Dispositivos electrónicos, CDE 2007 celebrada en El Escorial (Españ) del 31 de Enero al 2 de Febreo de 2007., In this work, we present results on the growth by atomic layer molecular beam epitaxy and characterization of lasers with three stacked layers of InAs quantum wires (QWR) as active zone and aluminum free waveguides on (001) InP substrates. The separated confinement heterostructure consists of n-p InP claddings and a waveguide formed by short period superlattices of (InP)5/(GaInAs)4 lattice matched to the InP substrate. The optimum growth conditions (substrate temperature and As and P pressures) have been determined to obtain waveguides with a flat surface in order to get an uniform QWR distribution. Lasing emission is observed at a wavelength of -1.66 mum up to 280K from 40mum x 1000mum devices, with a threshold current density at that temperature of 3.6 kA/cm2., This work was financed by Spanish projects MEC (TEC-2005-05781 -C03-01, Consolider-Ingenio 2010 Project "QOIT", CSD2006-00019) and CAM S 0505ESP_0200, by the SANDIE Net work of excellence (Contract n° NMP4-CT- 2004-500101) and by the European Commission Growth program NANOMAT project, contract no. G5RD-CT-2001-00545.

We present results on the optical characterization of InxGa1−xP layers grown by atomic layer molecular beam epitaxy on GaAs (001) substrates at a growth temperature of 420 °C. Our results show that the optical characteristics of these layers, which do not show ordering effects, are strongly dependent on surface stoichiometry during growth. In this way, we can obtain either highly homogeneous alloys with a predictable band-gap energy or layers with optical properties indicative of spatial localization effects, like an anomalous behavior of photoluminescence peak energy with temperature and a large shift between the emission energy and absorption edge.

1 página, 1 figura.-- Póster presentado al ICTON 2006 celebrado en Nottingham (UK) del 18 al 22 de Junio de 2006.

The transmittance photoplethysmogramms recorded with multiple NIR laser diodes in an athlete along a maximal exercise test by treadmill ergometer and the results after processing, are presented and compared with the established reference techniques.

Maximal effort tests are used to check the fitness of athletes and to assess their status of health. Measurements performed during the test are also useful to understand athlete physiology and to optimise the training protocols. One of the interesting measurements that can be performed is the oxygen saturation and desaturation in blood along with cardiac rate. The task is complicated by the fact that standard instrumentation (oximeters) are affected by movement artefact, and in the case of this kind of tests movements can be so strong and wide that the measurements is invalidated. In this paper, a novel algorithm is proposed which achieve meaningful measurements even in presence of very strong movement artefact.

Photoplethysmography and pulse oximetry are widely used techniques for noninvasive monitoring of heart rate and peripheral oxygen saturation. Over the last years we have been working onto the application of near infrared range wavelengths to replace those of the classical pulse oximeters. The development of laser diodes based sensors, processing algorithms, a calibration procedure, and the comparison with a commercial pulse oximeter, have been followed by a set of experimental studies. The results exposed here demonstrate the applicability of transmittance photoplethysmography and pulse oximetry using laser diodes emitting at specific wavelengths for a wide range of situations.

Pulse oximeters are used for the non-invasive monitoring of arterial blood hemoglobin oxygen saturation. This technique is based on the time variable optical attenuation by a vascular bed due to the cardiac pumping action (photoplethysmography) and the differential optical absorption of the oxy- and deoxy-hemoglobin. The photoplethysmographic (PPG) signals measured at two specific wavelengths are decomposed into its variable or pulsating component (EAC) and the constant or non-pulsating component (EDC) for deriving a parameter related to the arterial blood oxygen saturation (So2). Previously it has been reported a signal processing algorithm for a near infrared (NIR) laser diodes based transmittance pulse oximetry system. The main difficulties in the extraction of the information from the PPG signals are the small value of the signals variation related to their constant values, and the presence of artefacts caused by macro- and micro- movements of the part under analysis. The proposed algorithm permits the numeric separation of the variable and constant parts of the signals for both wavelengths. The EDC is obtained by a low pass filtering, and EAC by a pass-band one, followed by a non-linear filtering based on histogram reduction. In the present work is exposed the analysis of the influence of processing parameters like filters cut-off frequencies and histogram reduction percentage, on the derived So2 values. The test has been conducted both on real and simulated PPG signals. The real PPG has been recorded through experimental studies with human subjects using the NIR laser diodes based transmittance pulse oximetry system. The sources of artefacts and noise in the laser diodes PPG signals are discussed.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on the characteristics of tensile-strained 1.3 μm InGaAsP multi-quantum well lasers with InP/GaInAsP short-period superlattices (SPSLs) in barriers and waveguide. Growth was carded out by all solid source atomic layer molecular beam epitaxy (ALMBE) without growth interruptions. Infinite length threshold current densities are as low as 176 A/cm2 per quantum well for as cleaved broad area lasers. The values for the characteristic temperature T0 are as high as 90 K for cavity lengths of 1200 μm. The improvement in To is attributed to the increased effective barrier height by the short-period superlattices.

A transmittance pulse oximetry system based on near-infrared laser diodes (LD) for monitoring arterial blood hemoglobin oxygen saturation (So 2 ) has been previously reported. In this work we present the results obtained after improvements in the sensor configuration, signal processing algorithm and calibration procedure. The pulse oximetry system also comprises the sensor electronics, and a data acquisition board installed on a handheld personal computer. The two LD chips are mounted on a single metal heat-sink and as photo- detectors are used silicon p-i-n photodiodes with the first amplifier stage situated in their back side. The real time calculation of the parameters related to So 2 is carried out through a numeric separation of the pulsatile and non- pulsatile components of the photoplethysmographic signals for both wavelengths and a non-linear filtering. Patients with respiratory failure conditions were monitored as a part of the calibration procedure in order to cover a wide range of So 2 -values. A calibration curve have been derived through the determination of in vitro arterial So 2 with a significant quantity of experimental points ranging from 60 to almost 100%. The obtained results demonstrate that it is possible to apply the proposed system to monitoring a wide range of oxygen saturation levels.

Here we comment on the paper entitled >A novel laparoscopic pulse oximeter device. An easy, efficient and cost-effective way of detecting arterial structures.> authored by Theodosopoulos et al., and recently published in the April issue of the Journal of Clinical Monitoring and Computing. © Springer 2010.

A transmittance pulse oximeter based on near-infrared laser diodes for monitoring arterial blood hemoglobin oxygen saturation has been developed and tested. The measurement system consists of the optical sensor, sensor electronics, acquisition board and personal computer. The system has been tested in a two parts experimental study involving human volunteers. A calibration curve was derived and healthy volunteers were monitored under normal and apnoea conditions both with the proposed system and with a commercial pulse oximeter. The obtained results demonstrate the feasibility of using a sensor with laser diodes emitting at specific near infrared wavelengths for pulse oximetry.

Beryllium-doped InP layers have been grown by solid source atomic layer molecular beam epitaxy at low substrate temperature. The residual n-type doping was reduced by controlling both the amplitude and the length of the phosphorus pulse. We have shown a well controlled p-type doping and obtained a hole concentration in the range 4×1017–3×1019 cm−3 at room temperature. The electrical and optical properties of InP layers grown at low temperatures were investigated by Hall effect and photoluminescence (PL) measurements. PL spectra for lightly doped samples have a near band emission at 1.41 eV and Be-related emissions around 1.38 eV., This work was supported by Project No. TIC95-0563-C05-05 of the Spanish Government.

6 páginas, 5 figuras, 2 tablas., We present a study of the relaxation behavior of compressive InxGa1−xP layers grown by atomic layer molecular‐beam epitaxy at Ts=420 °C with x=56%±3% and x=67%±3%. Similar (thickness and composition) InxGa1−xP layers were grown under different growth conditions in order to assess the influence of the stoichiometry of the growth front on the structural properties and the relaxation process of this material system. All InxGa1−xP layers were characterized by double‐crystal x‐ray diffraction, transmission electron microscopy, and Nomarski interference. Our results show that surface stoichiometry during growth does not affect the relaxation behavior of InxGa1−xP layers but strongly determines their structural characteristics related to composition modulation features which appear in all our InxGa1−xP layers. We have established an empirical relation between residual strain and thickness. This relation makes predictable the residual strain of more complicated structures which can be introduced as buffer layers in lattice‐mismatched heteroepitaxial systems., The authors wish to acknowledge to the European Community for financial support under ESPRIT Project No. BLES-6854.

6 páginas, 3 figuras., p++/n++ InP tunnel diodes have been fabricated for the first time on InP and Si substrates by solid source Atomic Layer Molecular Beam Epitaxy (ALMBE) at low temperature. The high peak current density exceeding 200 A/cm2 and the low specific resistance exhibited in these diodes indicate that they are appropriate to use as optically transparent interconnects in InP/Ga0.47In0.53As tandem solar cells. This is a very promising result for the use of solid source ALMBE for fabricating these tandem solar cells with a technological process compatible with low temperature technologies, as the conventional silicon technologies.

The electrical and optical properties of undoped InP layers grown at low temperatures by solid source atomic layer molecular beam epitaxy are investigated. Phosphorus surface coverage during epitaxy is controlled by monitoring the evolution of reflection high-energy electron diffraction pattern during growth. An accurate phosphorus supply by means of a valved cracking phosphorus cell is employed. The relation between phosphorus incorporation and the electronic properties of the epilayers is examined, and it is found that, at a substrate temperature of 340°C, residual electron concentration increases linearly with phosphorus flux. Residual doping of InP layers grown at 340°C has been reduced down to 1×1016 cm-3, and Hall mobilities of 3260 cm2/V s at 300 K and 14 830 cm2/V s at 65 K are reported. Low-temperature photoluminescence of low background doping layers is dominated by near band transitions. © 1995 American Institute of Physics.

Photoplethysmography (PPG) is a non-invasive optical technique that can be used to quantify the arterial blood pulse rate. Signal corruption by motion artifacts limits the practical accuracy and applicability of instruments for monitoring pulse rate during intense physical exercise. This study develops and validates an algorithm, which is based on linear filtering and frequency-domain and heuristic analyses, for extracting the heart rate from a PPG signal in the presence of severe motion artifacts. The basis of the hearth beat frequency selection is the observed high harmonic content of movement artifact signals with respect to the PPG-derived heartbeat. The algorithm, implemented in an experimental PPG measurement device, is developed by analyzing a set of PPG data recorded from a group of athletes exercising on a treadmill. An extensive set of tests is carried out during maximal exercise tests on a treadmill to validate the proposed algorithm by comparison with a reference electrocardiography measurement system. The Bland-Altman method is used to compare and evaluate PPG signals. The accuracy of the heartbeat measurement is better than ± 6.5 beats per minute (bpm) ( ≤ 4.2 %) even under maximal exercise conditions.

3 páginas, 2 figuras., InP layers have been grown on Si(001) substrates by using a low temperature process, both for the Si surface preparation (400°C, The authors wish to thank the CEC for their support under ESPRIT III project 6854 'BLES' (buffer layer engineering in semiconductors).

(InP)n/(Ga0.47In0.53As)m lattice-matched short-period superlattices have been used as pseudoquaternary material to confine Ga0.47In0.53As multiquantum wells in a GaxIn1-xAs/GaxIn1-xAs yP1-y/InP heterostructure. The samples have been grown by low-temperature atomic layer molecular beam epitaxy, using fast operating valved solid sources to generate P2 and As4 beams. X-ray diffraction was used to assess the structural quality of the samples. The effect of the superlattice period on the pseudoquaternary band gap is reported. Room-temperature photoluminescence wavelength of the multiquantum well structure is close to 1.55 μm. Growing short-period superlattices results in a much easier method to control band-gap energy than growing alternative quaternary material.

X-ray interference effect and transmission electron microscopy are used to study the relaxation process in a series of laser structures as a function of InAs content in the quantum well. It is shown that the X-ray interference effect is a powerful, fast and non-destructive method to assess the strain status in samples of this kind. A set of strained layer laser structures containing N monolayers of InAs (Nx(InAs)1(GaAs)3 with (N = 1, 3, 5, 7) in an 8 nm quantum well active region and a set of strained layer quantum wells consisting of P monolayers of InAs (Px(InAs)1(GaAs)Q with (P = 2, 4 and (Q = 2, 4) were grown [Dotor et al., J. Crystal Growth 127 (1993) 46] by atomic layer molecular beam epitaxy. X-ray interference effect and cross-section transmission electron microscopy analysis of the samples show that in the series of lasers with N monolayers of InAs the whole laser structure is coherent with the substrate (and consequently dislocation free) for 1 and 3 monolayers of InAs, while a sample with 5 monolayers of InAs is in a certain stage of relaxation (dislocation density nd {all equal to}107 cm-2) and a sample with 7 monolayers of InAs is almost completely relaxed (nd{all equal to}108 cm-2). In strained layer quantum well samples, the influence of the InAs/GaAs thickness ratio (P/Q) on the critical thickness has also been studied. These results are compared with those predicted by theoretical critical thickness models. Optical characterization as well as threshold current measurements of the lasers are correlated with X-ray diffraction and transmission electron microscopy relaxation status results. © 1993.

Dependence on the excitation power and temperature of the photoluminescence emission of GaAs quantum well laser structures using GaAs/AlAs superlattices in the waveguide is reported. The effects related to a quality reduction due to the presence of a thick ternary AlGaAs cladding layer in the bottom of the laser structure were elucidated by comparing to the photoluminescence of a similar waveguide structure, except for the AlGaAs bottom layer. The excitation power dependence shows the strong excitonic origin of the light emission in the temperature range 4-300 K in both structures. Carrier transport mechanisms through the superlattices is analyzed from the evolution of the photoluminescence of the quantum well and the superlattice confining layers; a structure dependent transparency temperature is defined, at which transport changes from tunneling assisted to extended minibands regime. The value of this parameter depends on the localized states in the superlattice minibands, caused by interface roughness.

A single monolayer thick InAs quantum well laser structure has been grown at low substrate temperature by atomic layer molecular beam epitaxy (ALMBE). The laser has an emission wavelength of approximately 884 nm and a threshold current density of 1.97 kA/cm2 at room temperature. This value is lower than values obtained for other monolayer thick quantum well lasers, and it demonstrates the device quality of epitaxial layers grown at 350°C by ALMBE.

GaP/InP strained-layer superlattices (SLS) grown on GaAs substrates are a novel structure with a large lattice mismatch symmetrically shared (+ 3 . 7 (GaP) -3 . 6 (InP)). We present growth and characterization of two types of GaP/InP based heterostructures: i) isolated SLSs and ii) a SLS based QW confined by A1GaAs barriers. Growth by Atomic Layer MBE has allowed to combine P- and As-containing materials in a controllable way preserving flat interfaces at low substrate temperatures. Optical characterization oftheheterostructures ispresented and correlated with akp model obtaining the first estimation for the conduction band offset at the GaP/InP heteroj unction. All superlattices studied have been found to be spatially direct (type I) being this feature very promising for their use as active layer in a semiconductor QW laser. I.

3 páginas, 4 figuras., In this work, the authors present results on the growth by atomic layer molecular beam epitaxy and characterization of lasers with one and three stacked layers of InAs quantum wires (QWRs) as active zone and aluminum-free waveguides on (001) InP substrates. The separated confinement heterostructure consists of n-p InP claddings and a waveguide formed by short period superlattices of (InP)5/(GaInAs)4 lattice matched to the InP substrate. The optimum growth conditions (substrate temperature and As and P pressures) have been determined to obtain waveguides with a flat surface in order to get a uniform QWR distribution. Lasing emission is observed at a wavelength of ~1.66 µm up to 270 K from 15×3000 µm2 devices, with a threshold current density at that temperature of 2 kA/cm2., This work was financed by Spanish project Nos. MEC TEC-2005-05781-C03-01 and CAM S 0505ESP 0200, by the SANDIE Network of excellence (Contract No. NMP4-CT-2004-500101), and by the European Commission Growth program NANOMAT project, Contract No. G5RD-CT-2001-00545.

Pulse oximeters are widely used for noninvasive monitoring of oxygen saturation in arterial blood hemoglobin. We present a transmittance pulse oximetry system based on near-infrared (NIR) laser diodes (750 and 850 nm) for monitoring oxygen saturation of arterial blood hemoglobin. The pulse oximetry system is made up of the optical sensor, sensor electronics, and processing block. Also, we show experimental results obtained during the development of the whole NIR transmittance pulse oximetry system along with modifications in the sensor configuration, signal processing algorithm, and calibration procedure. Issues concerning wavelength selection and its implications for the improvement of the transmittance pulse oximetry technique are discussed. The results obtained demonstrate the proposed system’s usefulness in monitoring a wide range of oxygen saturation levels, SMLS is supported by Programa Ramo´n y Cajal from the Spanish Ministry of Science and Technology.