Extended Wavelength Range Research Articles

Optical features of human skin revealed by optoacoustic mesoscopy in the visible and short-wave infrared regions.

Detailed assessment of skin conditions or the efficacy of skin treatments could greatly benefit from noninvasively assessing the distribution of cutaneous and subcutaneous structures and biomolecules. We considered ultrawideband raster scan optoacoustic mesoscopy with an extended wavelength range from visible to short-wave infrared and observed previously unseen high-resolution images of lipids colocalized with water, melanin, and hemoglobin distribution in human skin. Based on this contrast, the technique resolves subcutaneous fat, the pilosebaceous unit with complete hair strand and bulb, dermal microvasculature, and epidermal structures. We further visualize melanoidins that form via the Maillard reaction in the ultrathin stratum corneum layer, analyze their absorption spectrum, and separate them from the melanin layer. The suggested method may allow novel interrogation of skin conditions, possibly impacting diagnostics and medical and cosmetic treatments.

Pre-launch calibration results of the TROPOMI payload on-board the Sentinel-5 Precursor satellite

Abstract. The Sentinel-5 Precursor satellite was successfully launched on 13 October 2017, carrying the Tropospheric Monitoring Instrument (TROPOMI) as its single payload. TROPOMI is the next-generation atmospheric sounding instrument, continuing the successes of GOME, SCIAMACHY, OMI, and OMPS, with higher spatial resolution, improved sensitivity, and extended wavelength range. The instrument contains four spectrometers, divided over two modules sharing a common telescope, measuring the ultraviolet, visible, near-infrared, and shortwave infrared reflectance of the Earth. The imaging system enables daily global coverage using a push-broom configuration, with a spatial resolution as low as 7×3.5 km2 in nadir from a Sun-synchronous orbit at 824 km and an Equator crossing time of 13:30 local solar time. This article reports the pre-launch calibration status of the TROPOMI payload as derived from the on-ground calibration effort. Stringent requirements are imposed on the quality of on-ground calibration in order to match the high sensitivity of the instrument. A new methodology has been employed during the analysis of the obtained calibration measurements to ensure the consistency and validity of the calibration. This was achieved by using the production-grade Level 0 to 1b data processor in a closed-loop validation set-up. Using this approach the consistency between the calibration and the L1b product, as well as confidence in the obtained calibration result, could be established. This article introduces this novel calibration approach and describes all relevant calibrated instrument properties as they were derived before launch of the mission. For most of the relevant properties compliance with the calibration requirements could be established, including the knowledge of the instrument spectral and spatial response functions. Partial compliance was established for the straylight correction; especially the out-of-spectral-band correction for the near-infrared channel needs future validation. The absolute radiometric calibration of the radiance and irradiance responsivity is compliant with the high-level mission requirements, but not with the stricter calibration requirements as the available on-ground validation shows. The relative radiometric calibration of the Sun port was non-compliant. The non-compliant subjects will be addressed during the in-flight commissioning phase in the first 6 months following launch.

LED for hyperspectral imaging - a new selection method.

Hyperspectral imaging (HSI) has become a sophisticated technique in modern applications such as food analyses, recycling technology, medicine, pharmacy and forensic science. It allows one to analyse both spatial and spectral information from an object. But hyperspectral cameras are still expensive due to their extended wavelength range. The development of new light-emitting diodes (LED) in the recent past enables another approach to HSI using a monochrome camera in combination with a LED-based illumination. However, such a system has a lower spectral resolution. Additionally, the growing supply of LED on the market complicates the selection of LED. In this paper, we propose a new time efficient selection method for the design process of an illumination. It chooses an optimised LED combination from an existing database to match a predefined spectral power distribution. Therefore, an algorithm is used to evaluate various LED combinations. Furthermore, the method considers the spectral behaviour of each LED in dependence of forward current and temperature of the solder point. Our method has already shown promise during the selection process for even spectral distributions which is demonstrated in the study. Additionally, we will show its potential for HSI illuminations.

Fast and slow propagations of surface plasmon polaritons on metallic mesh gratings

Surface plasmon polariton (SPP) generations on silver-based metal–insulator–metal (MIM) cross mesh gratings were studied by polychromatic and monochromatic specular reflection. Centimeter area scale mesh grating samples were made using soft-lithography imprinting with a varied micro-sized array pitch. The mesh structures support multiple SPP orders with a periodicity-influenced mode generation. For the (±1, 0) SPP modes steep dispersions thus high SPP group velocities Vg were obtained over an extended wavelength range of propagation. Vg were found to achieve a maximum at frequencies closer to the mesh periodicity.

Infrared and visible scintillation of Ho3+-doped YAG and YLF crystals

In our effort to develop a new kind of detector for low-energy, low-rate energy deposition events we have investigated the cathodo- and radioluminescence of Ho:YAG and Ho:YLF single crystals in an extended wavelength range from 200 nm to 2200 nm. The emission spectra of both crystals show a much more intense emission in the infrared range than in the visible one. We estimate an infrared light yield of several tens of photons/keV when exciting the crystals with X-rays of energy ≈ 30 keV. The main reason of this high value is due to the Ho3+ ions energy levels scheme that allows efficient cross relaxation processes to occur even at low dopant concentration.

Photocatalytic Degradation Mechanism of Tetracycline by Ag@ZnO/C Core–Shell Plasmonic Photocatalyst Under Visible Light

A series of hamburger-like Ag@ZnO/C core–shell plasmonic photocatalysts have been synthesized via a simple solvothermal method for degradation of tetracycline (TC) under visible light irradiation, possessing high photocatalytic activity and good stability. The presence of localized surface plasmon resonance (LSPR) in the Ag core has increased the photocatalytic activity over an extended wavelength range. The plasmon-induced resonant energy transfer (PIRET) and direct electron transfer (DET) have facilitated the excitation and separation of photogenerated [Formula: see text] pairs, which has been further confirmed by electrochemical investigations. The presences of hydroxyl radicals ([Formula: see text]), superoxide radicals ([Formula: see text] and singlet oxygen (1O[Formula: see text] in the photocatalytic reaction system of Ag@ZnO/C photocatalyst have been demonstrated by electron spin resonance (ESR) measurements. All of the experiment results indicate that the ternary structure of Ag@ZnO/C can effectively enhance the photocatalytic activity. Furthermore, the effects of introduced Ag contents and carbon source dosage were researched by comparative photocatalytic experiments, and the potential structures of photodegradation products were studied by HPLC-MS.

Generating structured light with phase helix and intensity helix using reflection-enhanced plasmonic metasurface at 2 μm

Mid-infrared (2–20 μm) light has been attracting great attention in many areas of science and technology. Beyond the extended wavelength range from visible and near-infrared to mid-infrared, shaping spatial structures may add opportunities to grooming applications of mid-infrared photonics. Here, we design and fabricate a reflection-enhanced plasmonic metasurface and demonstrate efficient generation of structured light with the phase helix and intensity helix at 2 μm. This work includes two distinct aspects. First, structured light (phase helix, intensity helix) generation at 2 μm, which is far beyond the ability of conventional spatial light modulators, is enabled by the metasurface with sub-wavelength engineered structures. Second, the self-referenced intensity helix against environmental noise is generated without using a spatially separated light. The demonstrations may open up advanced perspectives to structured light applications at 2 μm, such as phase helix for communications and non-communications (imaging, sensing) and intensity helix for enhanced microscopy and advanced metrology.

A Stable Plasmonic Cu@Cu2 O/ZnO Heterojunction for Enhanced Photocatalytic Hydrogen Generation.

The localized surface plasmon resonance (LSPR) effect has been widely utilized in photocatalysis, but most reported LSPR materials are based on noble metals of gold or silver with high chemical stability. Plasmonic copper nanoparticles that exhibit an LSPR absorbance at 600 nm are promising for many applications, such as photocatalysis. Unfortunately, plasmonic copper nanoparticles are affected by serious surface oxidation in air. Herein, a novel lollipop-shaped Cu@Cu2 O/ZnO heterojunction nanostructure was designed, for the first time, to stabilize the plasmonic Cu core by decorating Cu@Cu2 O core-shell structures with ZnO nanorods. This Cu@Cu2 O/ZnO nanostructure exhibited significantly enhanced stability than that of regular Cu@Cu2 O, which accounted for the remarkably enhanced photocatalytic H2 evolution rate through water splitting, relative to pristine ZnO nanorods, over an extended wavelength range due to the plasmonic Cu core.

Plasmonic enhancement of dye-sensitized solar cells by using Au-decorated Ag dendrites as a morphology-engineered

In this study, Cu and Ag dendrites, as well as Ag dendrite decorated with gold nanoparticles (NPs) are designed for improving the efficiency of plasminic TiO2 dye sensitized solar cells (DSSCs). The main challenge in plasmonic DSSCs is adjusting the plasmonic peak at suitable position. Herein, it is shown that how an engineered structure can enhance the efficiency of DSSC by an intense plasmonic effect in extended wavelength range. This is addressed by engineering plasmonic peak of noble metal through controlling their morphology. Moreover, the importance of the protection of the morphology-controlled nobel metal additive by Polyvinylpyrrolidone (PVP) polymer against corrosive electrolyte is shown. PVP-capped Ag dendrites, PVP-capped Cu dendrites and PVP-capped Ag dendrites decorated by gold NPs are prepared and are applied in dye sensitized solar cells.

Wavelength-Dependent Nonlinear Optical Properties of Ag Nanoparticles Dispersed in a Glass Host

The linear and nonlinear optical properties of metal nanoparticles are highly tunable by variation of parameters such as particle size, shape, composition, and environment. To fully exploit this tunability, however, quantitative information on nonlinear absorption cross sections is required, as well as a sufficient understanding of the physical mechanism underlying these nonlinearities. In this work, we present a detailed and systematic investigation of the wavelength-dependent nonlinear optical properties of Ag nanoparticles embedded in a glass host, in which the most important parameters determining the nonlinear behavior of the system are characterized. This allows a proper quantification of absorption cross sections and elucidation of the excitation mechanism. Based on small-angle X-ray scattering measurements average particle diameters of 3 and 17 nm are estimated for the studied samples. The nonlinear optical properties of the nanoparticle–glass composite are studied in an extended wavelength range ...

Broadband Absorption Enhancement in Modified Grating Thin-Film Solar Cell

A novel design of a highly efficient modified grating thin-film solar cell (SC) is reported and analyzed using a 3-D finite difference time domain (3-D FDTD) method. The modified grating has side wings and is covered by 1-D silicon nanorods. The suggested grating has a great potential to harvest the light into the nanoscale active layer. Further, the light trapping through the suggested design is significantly enhanced by the photonic nanorods. The modified grating and nanorods produce an absorption enhancement in different parts of the solar spectrum. Furthermore, the nanorods are considered as a second grating to obtain multiple light trapping which increases the optical path length. Additionally, the nanorods can couple the incident light into the discrete modes of the active layer over an extended wavelength range. Therefore, a broadband absorption enhancement for the suggested SC is achieved. The effects of the structure geometrical parameters on the absorption, ultimate efficiency, and short circuit current of the proposed design are investigated. The performance of the reported SC using crystalline silicon, hydrogenated amorphous silicon, and gallium arsenide is also studied. The numerical results show that high efficiency of 43.114% can be achieved using gallium arsenide with short circuit current density of 35.27 mA/cm2.

Cathodo- and radioluminescence of Tm3+: YAG and Nd3+: YAG in an extended wavelength range

We have studied the cathodo- and radioluminescence of Nd:YAG and of Tm:YAG single crystals in an extended wavelength range up to ≈5μm in view of developing a new kind of detector for low-energy, low-rate energy deposition events. Whereas the light yield in the visible range is as large as ≈104photons/MeV, in good agreement with literature results, in the infrared range we have found a light yield ≈5×104photons/MeV, thereby proving that ionizing radiation is particularly efficient in populating the low lying levels of rare earth doped crystals.

Advanced modeling of a moderate-resolution holographic spectrograph.

In the present article we consider an accurate modeling of a spectrograph with a cascade of volume-phase holographic gratings. The proposed optical scheme allows us to detect spectra in an extended wavelength range without gaps, providing relatively high spectral resolution and high throughput. However, modeling and minimization of possible cross-talk between gratings and stray light in such a scheme represents a separate task. We use analytical equations of the coupled-wave theory together with rigorous coupled-wave analysis to optimize the gratings parameters and further apply the latter together with a non-sequential ray-tracing algorithm to model propagation of beams through the spectrograph. The results show relatively high throughput up to 53% and the absence of any significant cross-talk or ghost images, even for ordinary holograms recorded on dichromated gelatin.

Porous BN/TiO2 hybrid nanosheets as highly efficient visible-light-driven photocatalysts

Porous boron nitride (BN) nanosheets, which possess extreme large surface areas, high thermal conductivity and special chemical activities, have demonstrated advantages in water cleaning and energy storage. However, they are usually considered as an underachieving catalytic material for photocatalysis and other photovoltaic conversion applications due to their wide bad gap of 5.5eV. Here, we report a novel porous BN/TiO2 hybrid nanosheets with the formation of new BOTi bondings between the boron dangling bonds at the open edges of pores of porous BN nanosheets and nanosized TiO2 particles. Such highly active bondings make the hybrid nanosheets responsive to an extended wavelength range from UV to visible light (λ>420nm) spectrum and also substantially enhance the photocatalytic effect (up to 99%) for degradation of organic molecules. In addition, the porous BN/TiO2 hybrid nanosheets exhibit excellent cycling stability up to 5 cycles maintaining high visible-light photocatalytic activity (97%). These results provide new insights for design of advanced hybrid photocatalysts with actively chemical bonding species, which can be applied in environmental protection, water splitting, and photo-electrochemical conversion.

Nanoscale Dielectric Function of Fe, Pt, Ti, Ta, Al, and V: Application to Characterization of Al Nanoparticles Synthesized by Fs Laser Ablation

Development and applications of new nanomaterials and nanocomposites that include metal nanoparticles have received much attention in the last years. However, there are relatively few studies concerning basic physical characteristics of the dielectric function at the nanoscale, which is needed for predicting their optical and plasmonic response. The size-dependent complex dielectric function of metal Fe, Pt, Ti, Ta, Al, and V nanoparticles (NPs) is calculated for the first time for an extended wavelength range from UV to FIR, based on experimental bulk complex refractive index measurements in the mentioned range at room temperature. Calculation is based on a “top-down” approach, based on a stepwise modification of the Drude model. Bulk plasma frequency (ω p) and damping constant (γ free) in this model are determined using a method that improves the relative uncertainties in their values and provide an insight about the wavelength range over which the metal may be considered Drude like. Validation of ω p and γ free values is demonstrated by the improved accuracy with which the experimental bulk dielectric function is reproduced. For nanometric and subnanometric scales, dielectric function is made size dependent considering size-corrective terms for free and bound electron contributions to the bulk dielectric function. These results are applied to analyze the synthesis of Al NP suspensions using a 120-fs pulse laser to ablate an Al solid target in n-heptane and water. The presence of Al, Al-Al2O3, and air-Al core-shell structures is also reported for the first time in these type of colloids. Analysis of the structure, configuration, sizing, and relative abundance was carried out using optical extinction spectroscopy (OES). Sizing results are compared with those provided by atomic force microscopy (AFM) studies.

Continuous and high-precision atmospheric concentration measurements of COS, CO<sub>2</sub>, CO and H<sub>2</sub>O using a quantum cascade laser spectrometer (QCLS)

Abstract. Carbonyl sulfide (COS) has been suggested as a useful tracer for gross primary production as it is taken up by plants in a similar way as CO2. To explore and verify the application of this novel tracer, it is highly desired to develop the ability to perform continuous and high-precision in situ atmospheric measurements of COS and CO2. In this study we have tested a quantum cascade laser spectrometer (QCLS) for its suitability to obtain accurate and high-precision measurements of COS and CO2. The instrument is capable of simultaneously measuring COS, CO2, CO and H2O after including a weak CO absorption line in the extended wavelength range. An optimal background and calibration strategy was developed based on laboratory tests to ensure accurate field measurements. We have derived water vapor correction factors based on a set of laboratory experiments and found that for COS the interference associated with a water absorption line can dominate over the effect of dilution. This interference can be solved mathematically by fitting the COS spectral line separately from the H2O spectral line. Furthermore, we improved the temperature stability of the QCLS by isolating it in an enclosed box and actively cooling its electronics with the same thermoelectric chiller used to cool the laser. The QCLS was deployed at the Lutjewad atmospheric monitoring station (60 m; 6°21′ E, 53°24′ N; 1 m a.s.l.) in the Netherlands from July 2014 to April 2015. The QCLS measurements of independent working standards while deployed in the field showed a mean difference with the assigned cylinder value within 3.3 ppt COS, 0.05 ppm for CO2 and 1.7 ppb for CO over a period of 35 days. The different contributions to uncertainty in measurements of COS, CO2 and CO were summarized and the overall uncertainty was determined to be 7.5 ppt for COS, 0.23 ppm for CO2 and 3.3 ppb for CO for 1-minute data. A comparison of in situ QCLS measurements with those from concurrently filled flasks that were subsequently measured by the QCLS showed a difference of −9.7 ± 4.6 ppt for COS. Comparison of the QCLS with a cavity ring-down spectrometer showed a difference of 0.12 ± 0.77 ppm for CO2 and −0.9 ± 3.8 ppb for CO.

Plasmonic spectrum on 1D and 2D periodic arrays of rod-shape metal nanoparticle pairs with different core patterns for biosensor and solar cell applications

Simulations of surface plasmon resonance (SPR) on the near field intensity and absorption spectra of one-dimensional (1D) and two-dimensional (2D) periodic arrays of rod-shape metal nanoparticle (MNP) pairs using the finite element method (FEM) and taking into account the different core patterns for biosensor and solar cell applications are investigated. A tunable optical spectrum corresponding to the transverse SPR modes is observed. The peak resonance wavelength (λres) can be shifted to red as the core patterns in rod-shape MNPs have been changed. We find that the 2D periodic array of core–shell MNP pairs (case 2) exhibit a red shifted SPR that can be tuned the gap enhancement and absorption efficiency simultaneously over an extended wavelength range. The tunable optical performances give us a qualitative idea of the geometrical properties of the periodic array of rod-shape MNP pairs on SPRs that can be as a promising candidate for plasmonic biosensor and solar cell applications.

Focus on lasers and imaging

Focus on lasers and imaging

Mid-infrared photodetectors operating over an extended wavelength range up to 90 K.

We report a wavelength threshold extension, from the designed value of 3.1 to 8.9μm, in a p-type heterostructure photodetector. This is associated with the use of a graded barrier and barrier offset, and arises from hole-hole interactions in the detector absorber. Experiments show that using long-pass filters to tune the energies of incident photons gives rise to changes in the intensity of the response. This demonstrates an alternative approach to achieving tuning of the photodetector response without the need to adjust the characteristic energy that is determined by the band structure.

Normal‐dispersion microcombs enabled by controllable mode interactions

AbstractWe demonstrate a scheme incorporating dual‐coupled microresonators through which mode interactions are intentionally introduced and controlled for Kerr frequency comb (microcomb) generation in the normal‐dispersion region. Microcomb generation, repetition rate selection, and mode locking are achieved with coupled silicon nitride microrings controlled via an on‐chip microheater. The proposed scheme shows for the first time a reliable design strategy for normal‐dispersion microcombs and may make it possible to generate microcombs in an extended wavelength range (e.g. in the visible) where normal material dispersion is likely to dominate. image