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This paper examines infrared spectroscopic effects for the standoff detection of an explosive material, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), inkjet printed on an aluminum surface. Results of a spectroscopic study are described, using multiple optical setups. These setups were selected to explore how variations in the angles of incidence and collection from the surface of the material result in corresponding variations in the spectral signatures. The goal of these studies is to provide an understanding of these spectral changes since it affects standoff detection of hazardous materials on a reflective substrate. We demonstrate that variations in spectral effects are dependent on the relative surface concentration of the deposited RDX. We also show that it is reasonable to use spectroscopic data collected in a standard laboratory infrared spectrometer outfitted with a variable angle reflectometer set at 0° as reference spectra for data collected in a standoff configuration. These results are important to provide a systematic approach to understanding infrared (IR) spectra collection using standoff systems in the field, and to allow for comparison between such data, and data collected in the laboratory. Although the precise results are constrained to a specific material system (thin layers on a reflective substrate), the approach and general discussion provided are applicable to a broad range of IR standoff sensing techniques and applications.

Sugarcane is one of the major agro-industrial crops with huge variations in state-wise cane production, productivity and sugar recovery. Twenty-five elite selections of sugarcane clones along with nine commercial checks (early and mid-late maturity group) were evaluated for different cane and sugar yield contributing traits. Analysis of variance revealed significant differences among genotypes along with low ( 20%) genotypic coefficient of variations for all studied traits suggested explicitly the presence of wide variation in genetic material used in the study. All the traits exhibited higher estimates (> 60 %) of heritability (h2b) except sucrose content (26.17 %); while genetic advance (%) of mean was observed low ( 20%) for commercial cane sugar, cane yield, germination, single cane weight, no. of shoots and no. of millable canes. Commercial cane sugar showed significant positive genotypic and phenotypic correlation with germination (%), no. of shoots, no. of millable canes, Stalk length, single cane weight, cane yield and sucrose (%). Cane yield (1.130, 0.995) had highest positive direct effect followed by sucrose (%) (0.308, 0.198). It is suggested that these traits can be considered as main determinant traits. High indirect effects of no. of shoots, no. of millable canes, stalk length, single cane weight through cane yield may be used for indirect selection for improving commercial cane sugar.

Inverse vulcanization is the method by which molten sulfur can be combined with comonomers to form stable polymers termed “organically modified chalcogenide” or “ORMOCHALC” polymers. One advantage to ORMOCHALC polymers is that they can possess important optical properties, such as high refractive index and strong infrared (IR) transmission, while being easier to fabricate than glass materials with similar optical properties. In the present work, a new ORMOCHALC is fabricated by using tetravinyltin as a comomoner with sulfur. This is the first example of an organometallic molecule being used as a comonomer to develop ORMOCHALCs. The result is an ORMOCHALC polymer that has the highest refractive index reported for a “sulfur and comonomer” polymer and that demonstrates unprecedented transmission in the IR region.

Recent years have seen the increasing use of noninvasive respiratory support in preterm infants with the aim of minimizing the risk of mechanical ventilation and subsequent bronchopulmonary dysplasia. Respiratory distress syndrome is the most common respiratory diagnosis in preterm infants, and is best treated by administration of surfactant. Until recently, this has been performed via an endotracheal tube using premedication, which has often included opiate analgesia; subsequently, the infant has been ventilated. Avoidance of mechanical ventilation, however, does not negate the need for surfactant therapy. Less invasive surfactant administration (LISA) in spontaneously breathing infants is increasing in popularity, and appears to have beneficial effects. However, laryngoscopy is necessary, which carries adverse effects and is painful for the infant. Conventional methods of premedication for intubation tend to reduce respiratory drive, which increases the likelihood of ventilation being required. This has led to intense debate about the best strategy for providing appropriate treatment, taking into account both the respiratory needs of the infant and the need to alleviate procedural pain. Currently, clinical practice varies considerably and there is no consensus with respect to optimal management. This review seeks to summarize the benefits, risks, and challenges associated with this new approach.

Sugarcane on one side considered important for crop diversification and important for human civilization while on other sugar industry is facing a long term losses in terms of monetary issues. Moreover, farmer is also not clear about which techniques is to adopt for practising the sugarcane cultivation for precision farming. Therefore, range of new sugarcane cultivation technologies pertaining to its cultivars, fertilization, weed control, insect-pest and disease control needs to be invented and recommended to the cane farmers. Precision farming is an approach where inputs are utilised in precise amounts to get increased average yields, compared to traditional cultivation techniques. Adoption of precision agriculture in sugarcane has been slow due to a wide range of uncertainties and conflicting opinions. There is need to reduce cost of cultivation and to improve the canes yield and quality by adopting precision sugarcane techniques. In developing countries like India, Pakistan etc. precision agricultural techniques if adopted, is a powerful tool and should be started with a basic, affordable and effective integration of technologies and practices. Present article aims to review published and unpublished information on precision sugarcane farming must be applied for improving the cane yield and quality so as to improve livelihoods of the cane farmers.

Studies on the reflectance spectra of different mixtures of sand and silt were performed in the infrared spectral region of 7–25 µm to explore the behavior of a second reststrahlen band occurring between 17 and 25 µm with respect to different mixtures of sand and silt. The reflectance spectrum of all samples exhibited reststrahlen bands within both the long wavelength infrared (LWIR) and the very long wavelength infrared (VLWIR) regions of the reflectance spectrum. Results demonstrate that both LWIR and VLWIR reststrahlen bands increase in area as the fraction of sand increases to 80%. More importantly, the data demonstrate that the VLWIR reststrahlen band, like that in LWIR, exhibits a significant and reproducible decrease in reflectivity for mixed soil versus weathered soil.

There are limited fiber-based single-mode laser sources over the visible and near infrared range. Nonlinear conversion through four-wave mixing in photonic crystal fibers allows for the generation of new wavelengths far from a pump wavelength. Utilizing an all-fiber spliced configuration, we convert 1064 nm light into a W-level signal in the 750 nm – 820 nm spectral region. We demonstrate over 7.9 watts in the signal band, out of a custom photonic crystal fiber with M2

This study investigates the embedded nanoparticles’ morphology and distribution effects on the effective refractive index (RI) of composite. The study is based on the FEA model for the Fabry-Pérot interference cavity made from the nanocomposite film. The composites’ effective RI can be derived from the simulation reflection spectrum. In constant particle volume fraction condition, the embedded particles with a larger diameter, locating at the region with high electric field and having longer side length along the electric field oscillating direction, are identified as the factors to reinforce the effective RI. For 4 μm incident light-wave, as controlling the diameter from 24.8 nm to 212 nm, distribution from middle-gathered (high electric field region) to top-bottom gathered (low electric field region), and the rectangular cylinder particle shortest side along electric field oscillating direction to longest side along electric field oscillating direction, the effective RI increasing from 1.687 to 1.719, 1.638 to 1.745 and 1.66 to 1.901, respectively. The underlying RI shifting principle is recognized from the light scattering loss by embedded nanoparticles. This discovering provides one novel idea for next-generation real-time RI tuning structure and device.

Mid-wavelength infrared (MWIR, λ = 3 – 5 μm) materials are of great importance due to their applications in optical sensors and devices for military, industry, and non-invasive medical diagnostics. Specifically, MWIR polarimetry are used in biometric recognition and camouflaged detection. Recently, sulfur based organically modified chalcogenides (ORMOCHALC) polymers have been utilized to fabricate MWIR polarizers with competitive extinction coefficient to commercial polarizers, which are mostly made of expensive, brittle, and heavy inorganic materials. On the other hand, to adjust or reinforce the refractive index of the polymer, the chalcogenide content (i.e., sulfur, selenium) needs to be increased, which may result in adverse effects on the thermomechanical characteristics, including Young's modulus and lower glass transition temperature. This reduced thermomechanical stability compromises the structural integrity of ORMOCHALC-based optical devices. In this study, an ORMOCHALC polymer, poly(S–r–DIB), was reinforced with the zinc sulfide (ZnS) nanoparticles to simultaneously improve the refractive index and the thermomechanical properties. The addition of 20 wt% ZnS nanoparticles improves the pure polymer's glass transition temperature (Tg) from 9.6 °C to 31.4 °C, and the refractive index by Δn= 6.58 %. Then, subwavelength wire-grid polarizers were fabricated based on the pure ORMOCHALC first by a simple thermal imprinting method followed by metal deposition. The resulted MWIR polarizer showed a high extinction coefficient which is comparable with commercial polarizers. However, the structural integrity of the polarizers was compromised due to lower glass transition temperature. Finally, finite element analysis was conducted on the possible wire-grid polarizer fabrication utilizing optically and mechanically reinforced composites, as demonstrated in this study. If fabricated, these nanoparticles reinforced polarizers will possess superior structural integrity compared to ORMOCHALC polarizers. Moreover, these polarizers show a spectral selectivity as the transmission curve's resonance wavelength depends on the composite's refractive index, which is tunable by controlling the nanoparticles content. The resonance peak redshifted from 3.12 μm to 3.3 μm for the pure polymer to 20% ZnS reinforced ORMOCHALC polarizer. The extinction coefficient of the polarizer also improved in multiple wavelength bands in the MWIR. These polarizers with superior extinction coefficient, spectral selectivity, and improved thermomechanical stability demonstrate a broader prospect in MWIR optics.

The polymer nanocomposites have attracted increasing attention in the optical components that are miniaturized and integrated with wearable or portable electronics due to the polymer processibility and the tunability of the refractive index (RI) by adding nanoparticles. However, the lack of models predicting the composites’ RI attributed to the morphology, physical properties, as well as volume fraction of the nanoparticles poses difficulties in the design. This study investigates the effect of the size and agglomeration condition of the nanoparticles on the effective RI based on a Finite Element Analysis (FEA) method simulating the Fabry-Perot resonance within the composite film. The result showed that larger particles (or particle clusters) could reinforce the RI of nanocomposites compared with the well-dispersed small particles. The particle-cluster model had lower RI than the single-solid-particle model with the same effective particle diameter, demonstrating that the particle cluster provides less scattering intensity than the single-solid-particle.

Present research was conducted to modify and evaluate commercially available tractor-operated sugarcane trench planter available in Uttar Pradesh as per needs of local conditions prevailing in Punjab for sugarcane cultivation. Prominent modifications included alteration in shape of soil-covering unit and installation of safety grate. During preliminary evaluation, effect of three cutting roller(s) peripheral speeds (0.69 m/s, 0.81 m/s and 0.93 m/s) and three forward speeds (2.26 km/h, 2.6 km/h and 3.0 km/h) was assessed on three popular varieties of sugarcane (Co0118, CoPb93 and CoJ-85) for cane length, cane diameter, sett length, bud damage (%), number of sett cut and sett damage (%). Thereafter, the field evaluation of modified sugarcane trench planter was carried out by selecting one cutting roller(s) peripheral speed (0.69 m/s) and two forward speeds (2.26 km/h and 3.0 km/h) on above varieties. The selected dependent variables were cane length, cane diameter, sett length, bud damage (%), sett damage (%), overlap/gap and germination (%). Results revealed that average sett length increased with the decrease in diameter of cane and cutting roller peripheral speed. However, bud damage (%) increased with the increase in cutting roller peripheral speed. Bud damage (%) in variety Co0118 was higher due to relatively more toughness (hardness) of cane. Average overlapping decreased with the increase in forward speed. Practically, no sett damage was observed in the study. It was found that germination (%) of cane planted by machine was more than the conventional planting. Average germination on 45 DAP (days after planting) on left and right side of trench in different varieties, viz. Co0118, CoPb93 and CoJ-85, were 50.71%, 43.00%, 48.50% and 48.11%, 38.68%, 43.15%, respectively. Economic analysis showed that there was 25.01% reduction in cost of planting and 58.02% reduction in labour cost as compared to conventional method of sugarcane planting followed under Punjab conditions.

We report the latest progress on fabrication of rare earth doped single crystal yttrium aluminum garnet (YAG) core/undoped YAG cladded fibers. Rare-earth doped single crystal core fibers were grown with laser heated pedestal growth methods. In a second step, epitaxial methods were used to grow a single crystalline undoped YAG cladding onto the core fiber. Hydrothermal and liquid phase epitaxy methods utilize the core doped fiber as the seed. X-ray diffraction of cladding reveals an equilibrium (110) morphology. Energy-dispersive X-ray spectroscopy analysis shows there is minimal diffusion of rare-earth dopants into the cladding structure. The use of scandium doping is shown to substitute at the Al3+ site, thereby allowing an additional tunability of refractive index of core structure material besides conventional Y3+ site dopants. The use of these epitaxial growth methods enables material compatibility, tuning of refractive index, and conformal growth of cladding structures onto core fibers for optical devices.

NRL is developing new materials that transmit across wide wavelength ranges and will present recent results. MILTRAN is a new rugged optical ceramic that transmits visible through LWIR and is 3.5 times harder than ZnS and is well suited as an internal lens element. NRL-series moldable glasses transmit SWIR through LWIR and may be bonded to each other in an adhesive-free thermal process. NRL-200-series glasses transmit visible through MWIR and expand the glass map for multispectral lens designs. These new materials enable greater flexibility for designers of lenses for advanced defense applications and potentially reduce the size, weight and cost of next-generation optics.

At the Naval Research Laboratory, we have developed several rugged oxide materials for optics applications. These materials include cubic sesquioxides (Y2O3 and Lu2O3) and spinel ceramics which transmit in the UV, visible, SWIR and MWIR wavelength region. These materials have superior mechanical and optical properties compared to the currently used materials on various Navy / DoD systems. The transparent and rugged ceramics are fabricated by the Hot press/HIP method using ultra-pure powder synthesized in-house and the resulting ceramics typically have excellent optical quality with no birefringence. In this paper, we present the optical properties of these rugged transparent ceramics and lens designs using these materials will be also discussed.

Solid-state laser based on Er-doped gain medium, is a promising approach to designing directly diode-pumped eye-safer pulsed sources in the spectral range ~1.45-1.65 m. This approach allows obtaining spectrally broad laser outputs with high efficiency, if required by application (e.g., anti-speckle), without resorting to nonlinear conversions. All-fiber laser solutions for high PRF pulsed laser sources is deemed desirable, but it may result in high design complexity, especially on the Master Oscillator (MO) end, hence it is not appropriate in cases where low complexity is of major importance. Presented here are the results obtained with pulsed hybrid MOPA comprised of a bulk crystalline Er-based MO and Er-doped fiber amplifier.

We computationally investigate random motheye structures for fused silica from 0.4 to 1.0 μm. We found that increasing the randomness of the diameter and height can further suppress the reflection at the air-glass interface.

This guest editorial introduces the Special Section on Advances in Gradient Index Optics Technology.

We present a method of post-deposition tuning of the optical properties of thin film dielectric filters and mirrors containing chalcogenide glass (ChG) layers by thermally adjusting their refractive index. A common challenge associated with the use of ChG films in practical applications is that they suffer from slight run-to-run variations in optical properties resulting from hard-to-control changes in source material and deposition conditions. These variations lead to inconsistencies in optical constants, making the fabrication of devices with prescribed optical properties challenging. In this paper, we present new work that takes advantage of the large variation of a ChG films’ refractive index as a function of annealing. We have carried out extensive characterization of the thermal index tuning and thickness change of arsenic selenide (As2Se3) ChG thin films and observed refractive index changes larger than 0.1 in some cases. We show results for refractive index as a function of annealing time and temperature and propose a model to describe this behavior based on bond rearrangement. We apply thermal refractive index tuning to permanently shift the resonance of a Fabry-Perot filter and the cutoff wavelength of a Bragg reflector. The Bragg reflector, consisting of alternating As2Se3 and CaF2 layers, exhibits high reflectance across a ∼550 nm band with only five layers. Modeling results are compared with spectroscopic measurements, demonstrating good agreement.

We demonstrate efficient pulse-energy extraction from a partly-quenched erbium-doped aluminosilicate fiber amplifier. This has a high erbium-concentration, which allows for short devices with reduced nonlinear distortions, but which also results in partial quenching and thus significant unsaturable absorption, even though the fiber is still able to amplify. Although the quenching degrades the average-power efficiency, the pulse energy remains high, and our results point to an increasingly promising outcome for short pulses. Furthermore, unlike unquenched fibers, the conversion efficiency improves at low repetition rates, which we attribute to smaller relative energy loss to quenched ions at higher pulse energy. A short (2.6 m) cladding-pumped partly-quenched Er-doped-fiber with 95-dB/m 1530-nm peak absorption and saturation energy estimated to 85 {\mu}J, reached 0.8 mJ of output energy when seeded by 0.2-{\mu}s, 23-{\mu}J pulses. Thus, according to our results, pulses can be amplified to high energy in short highly-Er-doped fibers designed to reduce nonlinear distortions, at the expense of average-power efficiency, Comment: Manuscript submitted to Optics Express. Peer-Review extended up to March, 31

There is a need for robust optical materials with very low reflectivity and high transmission in the visible and infrared wavelength regions for use with high energy lasers. High power continuous-wave (CW) and high pulse energy laser optical systems can suffer damage from untreated optics due to undesirable Fresnel reflections. Sub-wavelength antireflective structured surfaces (ARSS) have been shown to have a higher laser-induced damage threshold than traditional AR coatings, which are necessary for high energy (multi-kW) laser components. Previous optimization of the etching process for ARSS on fused silica, among other optical materials, has yielded controlled and repeatable parameters, resultant from formation of varying depth and density profiles by randomly removing material from the surface. The “grass-like” boundaries result in gradient-index functionalities for incident optical beams, which simultaneously reduces reflection and increases transmission of the substrate. In this study, we investigate resultant optical properties of B270 Superwhite substrates, whose surfaces are modified using reactive ion etching, in order to enhance broadband transmission and lower reflectivity, thus increasing their utility for visible and near-infrared wavelength regions. We report results for ARSS fabricated directly onto the surface of 1” diameter, B270 Superwhite optical windows. Initial trials yielded single-side random ARSS (rARSS) treated samples with transmission enhancement of up to 3% from 400-1800 nm, nearing that of rARSS enhancement of fused silica, with maximum enhancement 80% that of the theoretical value between 700-900 nm.

The proliferation of chemical threats in the modern world requires the development of new, low cost, flexible sensors, with the ability to be widely deployed. Ideally these sensors will be capable of both proximate and standoff sensing of threats (i.e. not require intimate contact with the chemical) without the need for highly trained/specialized operators. To meet this unique set of requirements, we are developing a bio-inspired chemical sensing method modeled on human color vision. This bio-inspired approach provides the ability to quickly and reliably discriminate between chemicals based on the interaction of infrared chemical absorption bands with selected broadband infrared filters. Here we describe the capabilities of a prototype bio-inspired sensor for standoff detection of threat chemicals on surfaces versus common interferents. We discuss the design and operation of the bio-inspired sensor and preliminary data demonstrating its ability to discriminate between a nerve agent simulant dimethyl methylphosphonate (DMMP) and the common background interferent US Army insect repellant (containing N,N-Diethyl-meta-toluamide (DEET)) in a laboratory environment. We discuss paths forward for this technology, as well as how the bio-inspired sensing approach can result in high-confidence discrimination of threats at proximate standoff distances.

NRL is developing new glasses that transmit within the visible to LWIR range for use in multispectral imaging. We had previously developed NRL glasses which transmit in 0.9 to > 12 µm in wavelength, with refractive index ranging from 2.38 to 3.17, to expand the glass map and provide compact solutions to multispectral imaging systems. These glasses were specifically designed to have comparable glass molding temperatures and thermal properties so that they can be laminated and co-molded into optics with reduced number of air-glass interfaces (lower Fresnel reflection losses). These NRL glasses also have negative or very low dn/dT, making it easier to athermalize the optical system. A set of NRL glasses can be diffused to make infrared graded index (IR-GRIN) optics. Our multispectral optics designs using these new materials demonstrate reduced size, complexity and improved performance. The glass database compatible with Zemax and CodeV is available for distribution. We are adding n

Rugged optics and window materials with good visible and IR transmission are needed for several sensing and imaging application. Some of the applications require very thick windows or windows in complex geometries, which impose additional limitations on material selection. Magnesium aluminate spinel (MgAl2O4), or spinel for short, is a rugged window material with excellent transmission in ultraviolet to midwave infrared (0.18 – 5.5 m) wavelengths. Spinel is comparable to sapphire and ALON in its ruggedness while having superior transmission near 5 m in wavelength. With its cubic crystal structure, spinel is isotropic unlike sapphire which is birefringent. We have been developing high optical quality spinel ceramics in different shapes and sizes. Current status of these efforts in making spinel windows in large sizes and conformal shapes for several imaging applications will be discussed.

A common challenge in metastructure fabrication is precisely tuning of the frequency of a device’s resonance. Slight variations in device dimensions or material properties can lead to a deviation in resonance frequency in comparison to design. We present a method of tuning a dielectric metastructure’s resonance by thermally adjusting the refractive index of a chalcogenide glass (ChG) material. Several characteristics of ChGs make them good candidates for use in dielectric metastructures. They exhibit high linear refractive indices, enabling high index contrast devices; they have large optical nonlinearities, making them useful for tunable devices and nonlinear frequency conversion; and they have wide transmission windows extending from the visible through the long-wave infrared. Recently, we have carried out extensive characterization of the index tuning of arsenic selenide (As2Se3) ChG thin films and observed refractive index changes larger than 0.1 in some cases. We use this refractive index change to permanently shift the resonance of a Fabry-Perot filter and the cutoff wavelength for a Bragg reflector. We then demonstrate thermal tuning to shift resonance positions for a metasurface (MS). We compare finite element modeling results with measurement results and show good agreement. This tuning mechanism has potential for use in MS devices where a precise resonance frequency is required.

We have studied the in-situ radiation-induced degradation and recovery of the output optical power of actively-pumped erbium-doped fiber amplifiers (EDFAs) pumped at both 980 and 1480 nm during and after radiation exposure. The EDFs have high Er concentrations corresponding to 20 – 60 dB/m peak Er3+ absorptionat 1.532 μm suitable for high power cladding-pumped applications. The fibers were made with a wide range of glass compositions, including the addition of specific dopants to reduce clustering and improve efficiency. Radiation tolerance of nanoparticle doped fibers is superior to those fabricated by solution doping. The effects of photo-annealing have been explicitly studied, and an nth-order kinetic model has been used to predict end-of-life degradation. More robust statistical kinetics modeling of accelerated lifetime data has been used to predict on-orbit performance in more realistic scenarios, such as Geosynchronous Earth Orbit.