Middle Infrared Range Research Articles

Sub-two-cycle gigawatt-peak-power LWIR OPA for ultrafast nonlinear spectroscopy of condensed state materials.

The application of high-power, few-cycle, long-wave infrared (LWIR, 8-20 µm) pulses in strong-field physics is largely unexplored due to the lack of suitable sources. However, the generation of intense pulses with >6 µm wavelength range is becoming increasingly feasible with the recent advances in high-power ultrashort lasers in the middle-infrared range that can serve as a pump for optical parametric amplifiers (OPA). Here we experimentally demonstrate the feasibility of this approach by building an OPA pumped at 2.4 µm that generates 93 µJ pulses at 9.5 µm, 1 kHz repetition rate with sub-two-cycle pulse duration, 1.6 GW peak power, and excellent beam quality. The results open a wide range of applications in attosecond physics (especially for studies of condensed phase samples), remote sensing, and biophotonics.

Far- and mid-infrared examination of nontronite-1 clay mineral – Redox and cation saturation effects

Infrared Spectroscopy is a very useful tool studying clay minerals in a structural level as well as interactions on their surfaces. In this study, middle- and far- infrared spectroscopy was utilised to better understand how iron-bearing smectites and more specifically the nontronite-1 (NAu1) alters upon iron reduction. Changes in the middle-infrared spectral range have been studied extensively, such as the 3570 cm−1, 1020 cm−1 and 823 cm−1, while far-infrared spectral range changes have not drawn much attention. In this study, NAu1 spectra of oxidised, partially, and fully reduced state are presented noting the differences that occur on different vibration bands at this low frequency infrared range. Key changes took place at the region of 430–494 cm−1, as well as the 145 cm−1 band. From the 175 cm−1 to the 380 cm−1 region, vibrating bands disappeared or convoluted in a wider spectral envelope, upon full iron reduction. At the same time, NAu1 is saturated with different cations, such as Na+, Ca2+, K+, isolating effects on vibrating bands, depending on these cations, across the oxidation states and infrared range examined. These effects are more prominent at the region of 1620–1650 cm−1, where adsorbed H2O bending vibration takes place, for the middle-infrared range. Far-infrared range changes, due to the cation present, are less prominent, but recorded and discussed in detail. Eventually, the redox state of iron-bearing clay minerals controls the structural configuration of the lattice and consequently the interaction strength of clay mineral/saturating cations. The increasing interaction strength observed was Ca2+ < Na+ < K+, which will govern clay mineral hydration and cation exchange processes taking place on the clay mineral surface, as demonstrated, and discussed in this study. These outcomes can be useful in agriculture, waste disposal, and the oil & gas industry.

Amino Termination of Ti3C2 MXene Induces its Graphene Hybridized Film with Enhanced Ordered Nanostructure and Excellent Multiperformance

AbstractThe strategy of nacre‐inspired structures or the introduction of polymers can only strengthen and toughen 2D inorganic nanosheets‐based flexible films while mitigating their other properties. Herein, based on bending rigidity discrepancy of reduced graphene oxides (rGO) and Ti3C2 nanosheets, the introduction of amino termination on Ti3C2 (Ti3C2‐NH2) endows 3rGO/7Ti3C2‐NH2 films with enhanced ordered nanostructure and excellent multiperformance. Its interlayer‐ordered nanostructures are consistently confirmed by both wide‐angle X‐ray scattering and polarized Raman spectroscopy. The tensile strength and fracture energy increase by 84.7% and 156.3% compared with those of traditional 3rGO/7Ti3C2 film, respectively. The higher remained stress (81%) after relaxation agrees well with its better nanosheet orientation. The average fatigue cycles to failure approach 16 951 times under 150 MPa maximum tensile loading. Due to a large decrease in the interface thermal resistance, its thermal conductivity approaches ≈48.9 W m−1 K−1. The results also show that the absorbance of Ti3C2‐NH2 based films greatly surpass the maximum of the components in both X‐band frequency and middle infrared range. Particularly, 3rGO/7Ti3C2‐NH2 films exhibit anomalously high absorbance in the middle infrared range (55% for 22 µm thickness). It suggests that this film has good promise as flexible electronic devices with excellent mechanical, EMI shielding, heat dissipation, and thermal accumulation monitoring capabilities.

Bis-tetrabenzoporphyrinates of rare earths: Effective template synthesis, optical, electrochemical properties and conductivity in thin films

The template synthesis of novel bis-tetrabenzoporphyrin complexes of gadolinium, erbium and lutetium is described. The structure of these sandwich-type complexes was confirmed by the elemental analysis, MALDI-TOF mass spectrometry and optical spectroscopy in the visible, near and middle infrared range. The electrochemical behavior was studied by the cyclic voltammetry and compared to that of the structurally similar bis-phthalocyanine lanthanides. The conductivity of thin films of bis-tetrabenzoporphyrin complexes was measured both in the dark and under illumination. Thin films of erbium complex showed the highest photosensitivity, while the films of the gadolinium complex have the lowest resistivity.

Efficient Acousto-Optical Light Modulation at the Mid-Infrared Spectral Range by Planar Semiconductor Structures Supporting Guided Modes

Acousto-optical devices, such as modulators, filters or deflectors, implement a simple and effective way of light modulation and signal processing techniques. However, their operation wavelengths are restricted to visible and near-infrared frequency region due to a quadratic decrease of the efficiency of acousto-optical interaction with the wavelength increase. At the same time, almost all materials with high value of acousto-optic figure of merit are non-transparent at wavelengths larger than 5 {\mu}m, while the transparent materials possess significantly lower acousto-optic figure of merit. Here we propose and demonstrate by calculations how these limitations could be overcome using specially designed planar semiconductor structures supporting electromagnetic modes strongly coupled to the incident light in the Otto configuration. Such approach could be used for a novel efficient acousto-optical device operating in middle infrared range of 8-14 {\mu}m. Acoustic wave excited by a piezoelectric transducer in a semi-conductor prism is utilized to modulate the coupling coefficient of the incident light to the semiconductor structure which results in up to 100% modulation of the transmitted light at the spatial scale less than the ultrasound wavelength. It allows to utilize acoustic waves with short decay distance and therefore, it provides a unique possibility to achieve an efficient acousto-optical modulation at frequencies over several gigahertz, which are unreachable for traditional acousto-optics.

Optical multilayer anti-reflecting coating in the infrared range

The constant expansion of the applicable scope of optical technologies has led to the need to create optical coatings not only with certain frequency characteristics, but also high performance properties. This article contains the results of a research of a thin optical film from an advanced material SrYF4. On the basis of this film, a multilayer coating was synthesized, which has high transparency in the near and middle infrared range. The coating has successfully passed the climatic tests on resistance to cold and heat.

Simulation investigation of strained black phosphorus photodetector for middle infrared range.

In this paper, we design the uniaxially and biaxially strained black phosphorus (BP) photodetectors. Different strains applied in the zigzag or armchair direction can effectively tune the direct band gap of 5-layer of BP. The optical field intensity is modeled to determine the absorption for the BP layer. The strain effect on the band structure of BP is investigated using first-principles method based on density functional theory. The cut-off wavelength of strained 5-layer of BP pin photodetector is extended to middle infrared range with a high responsivity of 66.29 A/W, which means that the strained black phosphorus photodetector provides a new approach for the middle-infrared range optoelectronic devices.

Ultrafast middle-IR lasers and amplifiers based on polycrystalline Cr:ZnS and Cr:ZnSe

Transition-metal-doped II-VI semiconductors possess a unique blend of physical, spectroscopic, optical, and technological parameters. These materials enable high power lasers in important middle-infrared range. Furthermore, they combine superb ultra-fast laser capabilities with high nonlinearity and polycrystalline microstructure, which provides random quasi-phase matching. We developed flexible design of femtosecond polycrystalline Cr:ZnS and Cr:ZnSe lasers and amplifiers in the spectral range 2–3 µm. We obtained few-optical-cycle pulses with a multi-Watt average power in a very broad range of repetition rates 0.07–1.2 GHz. We also report on efficient nonlinear frequency conversion directly in the polycrystalline gain elements of ultra-fast lasers and amplifiers including second harmonic generation with sub-Watt power and generation of an octave-spanning middle-infrared supercontinuum.

Development of an evanescent optical integrated sensor in the mid-infrared for detection of pollution in groundwater or seawater

AbstractThe detection of molecules dissolved in liquid medium can be envisaged by means of an optical integrated sensor operating in middle infrared range. The intended sensor is composed of a cladding and a guiding selenide sputtered layers transparent in middle infrared. Hence, Ge-Sb-Se thin films were selected in view of tailored refractive index contrast, successfully deposited by radio frequency magnetron sputtering and characterized. To maximize the evanescent field at a wavelength of 7.7 µm, a suitable selenide waveguide allowing measuring the optical transmitted power was designed by performing computer simulations based on the effective index method enabling single-mode propagation for a waveguide width between 8 and 12 µm. Selenide sputtered films were micro-patterned using reactive ion etching with inductively coupled plasma process. Finally, optical waveguide surface was functionalized by the deposition of a hydrophobic polymer, which will permit detection of organic molecules in water.

Thermal evolution of ladder-like silsesquioxanes during formation of black glasses

Pyrolysis of ladder-like silsesquioxanes in oxygen-free atmosphere leads to the formation of silicon oxycarbides (black glasses). Black glasses are materials of amorphous silica structure where some amount of O2− ions were replaced by C4− ions. This exchange leads to local increase in bonds density and therefore improvement in mechanical, thermal, and chemical properties. Thanks to this modification, silicon oxycarbide glasses can be used in a variety of applications like: protective coatings and interconnectors in solid oxide fuel cells. Xerogels were prepared by sol–gel method, and ladder-like silsesquioxanes were used as precursors. Samples were burned at 200–1000 °C in inert atmosphere. Structural studies in the middle infrared range (MIR) and SEM with EDX confirmed the presence of SiOC bonds in obtained materials. MIR analysis of solid samples together with TG/dTG measurements allowed defining the process for the formation of black glasses.

Carrier Lifetime in Exfoliated Few-Layer Graphene Determined from Intersubband Optical Transitions

We report a femtosecond transient spectroscopy study in the near to middle infrared range, 0.8-0.35eV photon energy, on graphene and few layer graphene single flakes. The spectra show an evolving structure of photoinduced absorption bands superimposed on the bleaching caused by Pauli blocking of the interband optically coupled states. Supported by tight-binding model calculations, we assign the photoinduced absorption features to intersubband transitions as the number of layers is increased. Interestingly, the intersubband photoinduced resonances show a longer dynamics than the interband bleaching, because of their independence from the absolute energy of the carriers with respect to the Dirac point. The dynamic of these intersubband transitions reflects the lifetime of the hot carriers and provides an elegant method to access it in this important class of semimetals.

Amaranth Milling Strategies and Fraction Characterization by FT-IR

Amaranth nutritional value has been widely recognized, but the required conditions for its processing cannot be adapted to traditional technologies. For the proposal of alternative strategies, the changes of several components should be understood. Enriched starch and lipid–protein fractions of amaranth flour upon different milling treatments were obtained and characterized by attenuated total reflectance–Fourier transform-infrared spectroscopy. Starch- and lipid–protein-enriched amaranth fractions were obtained by abrasive milling; amaranth starch was isolated by wet-milling procedure, and flour samples were obtained from planetary ball milling. Changes on starch, protein, and lipids relative contents, on starch crystallinity and on lipids and protein stability after milling and 6-month storage, were evaluated. The Fourier transform-infrared (FT-IR) spectroscopy peaks of the main grain components were identified in the middle-infrared range. By calculating the ratios between height intensities of selected specific peaks, several characteristics of the samples could be explained: increased protein content and lipid proportion of the enriched fraction; decrease of the starch crystallinity degree by abrasive milling and especially by ball milling due to starch amorphization during these processes; and lipids modification in milled and in 6-month aged samples. FT-IR analysis can be considered a rapid, nondestructive, solvent-free, sensitive, and useful tool to investigate starch, lipid, and protein modifications provoked by processing and storage as well as to determine, based on intensity ratio, the relative proportion of grain components within amaranth milling fractions. The abrasive milling associated to planetary ball milling to obtain modified different fractions is presented as an interesting strategy for the processing of amaranth grain.

Structural Evolution during Evaporation of a 3-Glycidoxypropyltrimethoxysilane Film Studied in Situ by Time Resolved Infrared Spectroscopy

Time resolved infrared spectroscopy has been applied to study in situ the evaporation process of a 3-glycidoxypropyltrimethoxysilane hybrid sol by casting a droplet on a ZnSe substrate; the analysis has been performed in the middle-infrared range and in the near-infrared range. The experiment has allowed following the structural changes induced by water evaporation and the formation of ordered structures within the cast film; the CH(2) scissoring bands have been used as a fingerprint for the disorder to order transition of the hybrid. The experiment has been done using both a fresh sol and an aged sol which produce respectively an amorphous material and a crystalline hybrid material. The analysis has shown that the epoxy groups do not react during the evaporation while the silica structure shows only a slight condensation and an increase in open cage-like species. At the end of evaporation the hybrid has a "soft-like" state which allows structural rearrangements to self-order.

Limiting sensitivity of photodetectors based on A3B5 photodiodes for middle infrared range

The noise of photodetectors based on mid-IR A3B5 photodiodes (PhDs) implemented in a transimpedance amplifier scheme is analyzed. Recommendations concerning the choice of amplifier elements depending on the dynamic resistance of PhDs are given. It is shown that, using modern low-noise amplifiers, it is possible to reach a potential limiting threshold sensitivity of photodetectors only using PhDs with dynamic resistances above 50 Ω.

Identification of pour point depressant by terahertz time-domain spectroscopy

The frequency-dependent absorption coefficients and refractive indexes of three selected pour point depressants (PPDs) are extracted within the spectral range of 0.2–2.5 THz using terahertz time-domain spectroscopy (THz-TDS). The selected PPDs are also characterized by the middle-infrared spectrum. The experimental results reveal that PPD is more sensitive in the THz range than that in the middle-infrared range. Moreover, the different compositions of PPD can be identified according to their different spectral features in the THz range. Due to its properties of better repeatability, shorter testing time, and easier operation, THz-TDS can be used as a complement for identifying the chemical compositions of PPD. OCIS codes: 300.6495, 300.6250. doi: 10.3788/COL201109.S10505.

Optical transmission properties of perforated metal films in the middle-infrared range

We experimentally studied the enhanced optical transmission of perforated silver films in the middle-infrared region. The optical transmission properties of the samples with classical inductive frequency selective surface structures are also affected by both the periodicity and the aperture shape. Our results indicate that the physical operating mechanisms are the same for the plasmon crystal and the frequency selective surface, and both surface plasmon polaritons due to the periodicity and waveguide modes that are present in single holes have effect in the optical transmission enhancement.

Rapid Fabrication of Three-Dimensional Woodpile PhotonicCrystals by Means of Two-Photon Photopolymerization

Two-photon photopolymerization (TPP) of femtosecond laser is apromising method to fabricate three-dimensional woodpile photoniccrystals (PCs). We build micro-fabrication system based on theprinciple of TPP. Three-dimensional woodpile PCs consisting of in-planerod distances ranging from 1000 nm to 2000 nm are fabricated by focusingfemtosecond laser in photosensitive liquid resin ORMOCER. Theproperties of the PCs are also discussed, and fundamental photonic bandgaps in middle-infrared range are measured, whose in-plane roddistances are 1500 nm and 2000 nm. Three-dimensional woodpile PC deviceswith desired defects, such as cross-waveguide and micro-laserstructures, are introduced easily by TPP. We fabricate thethree-dimensional woodpile PCs in the liquid resin at the fast scanningspeed of 120 μm/s.

High performance miniaturized InSb photovoltaic infrared sensors operating at room temperature

A miniaturized InSb photovoltaic infrared sensor (InSb PVS) that operates at room temperature was developed. The InSb PVS consists of an InSb p + - p - - n + structure grown on semi-insulating GaAs (1 0 0) substrate, with a p + - Al x In 1 - x Sb barrier layer between p + and p - layers to reduce diffusion of photoexcited electrons. We found the optimum Al composition and thickness of AlInSb barrier layer to be x = 0.17 and 20 nm, respectively. To improve the signal-to-noise ratio of InSb PVS, 700 serially connected photodiodes were patterned on a 600 × 600 μ m 2 chip. The InSb PVS has a typical responsivity of 1.9 kV/W and an output noise of 0.15 μ V / Hz 1 / 2 . A detectivity of 2.8 × 10 8 cmHz 1 / 2 / W was obtained at 300 K. The InSb PVS was flip-chip bonded on a pre-amplifier IC and finally encapsulated by a dual flat non-leaded (DFN) package with a window, which exposes the backside of the GaAs substrate allowing the infrared light incidence. The device external size is 2.2 mm × 2.7 mm × 0.7 mm and to our knowledge is the smallest uncooled sensor for the middle-infrared range reported until now.

Negative Photoconductivity of Selectively Doped SiGe∕Si : B Heterostructures with a Two-Dimensional Hole Gas in the Middle-Infrared Range

The spectra of lateral photoconductivity in selectively doped SiGe/Si: B heterostructures with a two-dimensional hole gas are analyzed. It is revealed that the lateral photoconductivity spectra of these heterostructures exhibit two signals opposite in sign. The positive signal of the photoconductivity is associated with the impurity photoconductivity in silicon layers of the heterostructures. The negative signal of the photoconductivity is assigned to the transitions of holes from the SiGe quantum well to long-lived states in silicon barriers. The position of the negative photoconductivity signal depends on the composition of the quantum well, and the energy of the low-frequency edge of this signal is in close agreement with the calculated band offset between the quantum-confinement level of holes in the quantum well and the valence band edge in the barrier.

New method for investigations of normal human skin surfacesin vivo using fiber-optic evanescent wave fourier transform infrared spectroscopy (FEW-FTIR)

Fiber-optic evanescent wave Fourier transform infrared spectroscopy (FEW-FTIR) is a new method developed for different applications for surface analysis of materials, including the diagnostics of skin and living tissues. Our technique allows for the detection of inconsistencies in the molecular structure of normal skin surface non-invasively and in vivo . This FEW-FTIR method is direct, non-destructive and fast (seconds). Our optical fibers for the middle infrared (MIR) range are non-toxic, non-hygroscopic, flexible and characterized by extremely low losses. The combination of Fourier transform infrared spectroscopy and advanced fiber technology in the MIR range has opened the door for new powerful diagnostic tools for investigations of many skin surface phenomena, including normal skin, process of aging, allergies and precancerous conditions. Our method could be extended to applications involving the detection of the influence of environmental factors (sun, water, pollution and weather) on the skin surfaces of children and adults. In this study, we have investigated non-invasively more than 118 cases of normal skin in vivo in the range of 1450–1800 cm−1. We compare the FEW-FTIR spectra of palm, hand and elbow tissue. The results of our surface analysis of skin tissue are discussed in terms of structural similarities and differences on a molecular level. Copyright © 1999 John Wiley & Sons, Ltd.