In The Mid-infrared Research Articles

Extraction of optical constants from mid-IR spectra of small aerosol particles

A direct method for extracting optical constants in the mid-infrared (IR), using small particle's spectra is presented. The method is based on the direct extraction of the optical constants from the measured spectra using the Rayleigh approach for absorbance cross section of small particles. This was achieved by using an experimental system combining a scanning mobility particle sizing system attached to a long-path IR cell, allowing simultaneous measurements of aerosol size distribution and their IR spectra. The inversion procedure was tested on crystalline ammonium sulfate aerosols, for which high resolution set of optical constants was obtained and were found to be in good agreement with recently published data. Since the extraction of the k and n spectra is deduced from the refractive index dependent complex function, the exact band features can be obtained, unlike the commonly used iterative methods that modify simultaneously both band features and scale of k and n during the calculation procedure. The suggested procedure is simple to apply; nevertheless, it is sensitive to scaling errors of the final constants resulting from uncertainties in total particle volume measurements.

Mid-Infrared Semiconductor Quasi-Phase-Matching Wavelength-Conversion Devices

Recent progress of semiconductor-based quasi-phase-matching (QPM) wavelength conversion devices is reviewed.Compound semiconductors are promising materials for generating coherent light in the mid-infrared (IR) region because of their transparencies in the long-wave IR range and high second-order nonlinearities.Bulk-type and waveguide-type QPM devices have been developed using Ga As, and their high potentials are now being demonstrated. Wider-bandgap semiconductors are also studied as materials for the next-generation wavelength conversion devices.

GaAsSbN–GaAsSb–InP Type-II “W” Quantum Wells for Mid-IR Emission

A GaAsSbN-GaAsSb-InP type-II ldquoWrdquo quantum well (QW) structure is proposed for achieving emission in the mid-infrared (IR) wavelength region. Simulation studies based on the band anticrossing model and a 10-band k-p Hamiltonian demonstrate that emission wavelengths as long as 3 mum could be achieved on an InP substrate, limited primarily by strain relaxation considerations. The incorporation of nitrogen into GaAsSb grown on InP leads to band-gap narrowing and a deepening of the conduction band offset. The energy band structure, interband emission wavelengths, and optical matrix elements are evaluated for a GaAsSbN-GaAsSb-InP SL structure design. A structure design utilizing the lowest Sb content for the GaAsSbN electron wells and the highest Sb content for the GaAsSb hole wells, within strain limitations, provides the longest wavelength emission. The electron and hole effective masses of bulk GaAsSbN are extracted from the computed energy band structure as a function of Sb and N composition. The electron effective mass of GaAsSbN is found to remain nearly constant with N for low N-composition alloys. The heavy- and light-hole effective masses decrease slightly with increasing N composition.

Manganese pentacarbonyl bromide as candidate for a molecular qubit system operated in the infrared regime

Our concept for a quantum computational system is based on qubits encoded in vibrational normal modes of polyatomic molecules. The quantum gates are implemented by shaped femtosecond laser pulses. We adopt this concept to the new species manganese pentacarbonyl bromide [MnBr(CO)5] and show that it is a promising candidate in the mid-infrared (IR) frequency range to connect theory and experiment. As direct reference for the ab initio calculations we evaluated experimentally the absorption bands of MnBr(CO)5 in the mid-IR as well as the related transition dipole moments. The two-dimensional potential-energy surface spanned by the two strongest IR active modes and the dipole vector surfaces are calculated with density-functional theory. The vibrational eigenstates representing the qubit system are determined. Laser pulses are optimized by multitarget optimal control theory to form a set of global quantum gates: NOT, CNOT, Pi, and Hadamard. For all of them simply structured pulses with low pulse energies around 1 microJ could be obtained. Exemplarily for the CNOT gate we investigated the possible transfer to experimental shaping, based on the mask function for pulse shaping in the frequency regime as well as decomposition into a train of subpulses.

Spatially resolved photoluminescence and transmission spectra of HgCdTe

We report new high-resolution scanning photoluminescence (PL) experiments in the mid-infrared (IR) portion of the spectrum. The samples investigated were Hg0.7Cd0.3Te epilayers grown on Cd0.96Zn0.04Te substrates. The influence of macrodefects and the annealing of samples on the PL signal were studied. Transmission spectra were used to map the optical path variations of the epilayer.

Chalcogenide double index fibers: fabrication, design, and application as a chemical sensor

Double index chalcogenide fibers, based on tellurium, arsenic, and selenium, have been made by an original technique. This technique, based on the build-in-casting method, is achieved in a sealed silica ampoule. In view of the low attenuation obtained in the mid-infrared (IR), these fibers are used to implement Fiber Evanescent Wave Spectroscopy (FEWS). As the IR light is only propagated through the core of the waveguide, a chemical etching is applied in order to remove the glassy cladding of the sensing zone. IR spectra of ethanol and chloroform, recorded with such sensor, are presented showing the high sensitivity of the method.

Application of Fourier transform infrared ellipsometry to assess the concentration of biological molecules.

Spectroscopic ellipsometry is a noninvasive optical characterization technique mainly used in the semiconductor field to characterize bare substrates and thin films. In particular, it allows the gathering of information concerning the physical structure of the sample, such as roughness and film thickness, as well as its optical response. In the mid-infrared (IR) range each molecule exhibits a characteristic absorption fingerprint, which makes this technique chemically selective. Phase-modulated IR ellipsometry does not require a baseline correction procedure or suppression of atmospheric CO2 and water-vapor absorption bands, thus greatly reducing the subjectivity in data analysis. We have found that ellipsometric measurements of thin films, such as the solid residuals left on a plane surface after evaporation of a liquid drop containing a given compound in solution, are particularly favorable for dosing purposes because the intensity of IR absorptions shows a linear behavior along a wide range of solution concentrations of the given compound. Our aim is to illustrate with a concrete example and to justify theoretically the linearity experimentally found between radiation absorption and molecule concentration. For the example, we prepared aqueous solutions of glycogen, a molecule of huge biological importance currently tested in biochemical analyses, at concentrations ranging from 1 mg/l to 1 g/l which correspond to those found in physiological conditions. The results of this example are promising for the application of ellipsometry for dosing purposes in biochemistry and biomedicine.

Optical Conductivity of CeNiSn, CeRhSb, and CeRhAs

The optical reflectivity spectra of the Kondo semiconductors CeNiSn, CeRhSb, and CeRhAs have been measured in a wide photon energy range to obtain the optical conductivity spectra σ(ω). For CeNiSn and CeRhSb, two pronounced peaks in the mid-infrared (IR) region and small pseudogaps in the far-IR region were observed at low temperatures ( T ). The two peaks are attributed to optical transitions related with the two bands arising from the spin–orbit splitting of Ce 4 f . For CeRhAs, σ(ω) exhibits a gap which develops gradually with cooling. The observed (pseudo)gap widths and T dependent variations are largest for CeRhAs and smallest for CeNiSn, well corresponding to their Kondo temperatures. For CeNiSn and CeRhSb, the T dependence of σ(ω) in the far-IR suggests the formation of a narrow Drude peak caused by a c – f mixing. The results may indicate that the pseudogap is opened in a heavy quasiparticle band.

IR-biosensor: flat silver halide fiber for bio-medical sensing?

Cylindrical optical fibers, made of various materials, have been used for decades for chemical and biological sensing. Optical fibers transparent in the mid-infrared (IR) enable absorption measurements in remote locations. New techniques will enable the use of IR fibers for measurements in ATR-mode. If the fiber is in contact with a sample that has characteristic absorption lines, the total transmission of the fiber and sample of these lines will decrease. In this way the absorption of a sample can be determined using a non-destructive method. This work proves that flattened silver halide fibers could be useful as sensing elements in analytical systems. First measurements using flattened IR-fibers have been carried out on biological targets. The experimental set-up used was made up of an FTIR-spectrometer, fiber optic cables and an external detector. A segment of 1.9 cm at the center of the fiber was flattened to approximately 100–150 μm. Transmission spectra of flattened fibers have been compared to those of the cylindrical fibers. IR-spectra were recorded for biochemical compounds such as glucose, bovine serum albumin (BSA), gelatin and bio-fluids, and native tissue was compared to coagulated tissue. Spectral differences were obtained indicating a possible use for the study of thermal damage in tissues.

Delocalized polarons in self-assembled poly(3-hexyl thiophene) nanocrystals

We have studied the characteristic properties of charged excitations (polarons) in thin films of regioregular poly(3-hexylthiophene) (RRPHT) by optical spectroscopies. We found that the increased interchain coupling that exists in self-assembled lamellae in these films drastically changes the properties of the polaron excitations. The traditional self-localized polaron in one-dimension delocalizes in two-dimensions, resulting in a much-reduced relaxation energy and multiple absorption bands, the most dominant being in the mid-infrared (IR) spectral range. Also it has associated IR and Raman active vibrations with reverse absorption bands [anti-resonances (AR)] compared with the continuum electronic band. The AR are attributed to the electron–phonon interaction.

Characterization of Plant Carbohydrates and Changes in Leaf Carbohydrate Chemistry Due to Chemical and Enzymatic Degradation Measured by Microscopic ATR FT-IR Spectroscopy

Leaf litter decomposition is largely effected by the enzymatic action of fungal colonizers of leaf material. Microscopic attenuated total reflectance (ATR) infrared spectroscopy would be a useful tool to evaluate changes in leaf litter carbohydrate chemistry over time during the colonization process at the scale of resolution of the fungal hyphae. This paper reports the first studies to use microspectroscopy in the mid-infrared (IR) region to perform analyses within an area of 250 × 250 μm to gain spectra of single species of sugars and complex carbohydrates (cellulose, hemicellulose, lignin) to identify characteristic IR reflectance peaks and to be able to separate the species in complex media. Changes in leaf surface carbohydrate chemistry were interpreted from spectra obtained from leaf material that underwent the following: (1) treatment with acetone (to remove surface waxes), (2) treatment with enzymes, and (3) observation after colonization by fungi. Analysis of spectra obtained from random locations or from the same points on the leaf surface over time permitted changes in carbohydrate chemistry to be detected. Comparative analysis of spectra was carried out by using time-series analysis of variance of selected characteristic peak heights and multivariate statistics.

Si–Te acousto-optic modulator for the 1.7–10.6 μm IR region

New amorphous Si 20Te 80 glass alloy has been synthesized and investigated. A modulator based on the amorphous Si–Te acousto-optic cell and operating in the mid-infrared (IR) region has been manufactured and tested using CO 2 (10.6 μm) , He–Ne (3.39 μm) gas lasers and 3.3 μm (based on InGaAsSb/InAsSbP double heterostructure), and 1.87 μm , (based on GaInAsSb) diode lasers. A modulation efficiency ∼90% at relatively small acoustic power with short enough response time (not longer than 0.3 μs ) make possible to use the modulator in many applications, e.g. for modulation and deflection laser radiation, for optical gas sensor applications, for diode laser spectroscopy to make mode selection or wavelength selection within lasing pulse.

Time-resolved studies of electron–phonon relaxation in metals using a free-electron laser

Here we report recent experiments on ion emission from metals (Ti, Nb, Mg) using a free-electron laser that delivers a train of subpicosecond micropulses in the mid-infrared (IR). The laser intensities for the surface damage and ion emission thresholds are used as markers for the onset of energy transfer to the lattice for ablation. Numerical calculations based on the Anisimov two-temperature model are used to evaluate the electron temperature T e and the lattice temperature T i . The results are discussed in terms of the Hertz–Knudsen equation for vaporization and a model based on laser-induced multiple electronic transitions.

Fiber‐optic evanescent wave fourier transform infrared (FEW‐FTIR) spectroscopy of polymer surfaces and living tissue

AbstractThe new method of fiber‐optic evanescent wave Fourier transform infrared (FEW‐FTIR) spectroscopy has been applied to studies of polymer surfaces and the diagnostics of normal, precancerous and cancerous tissue. This technique using optical fibers and fiber‐optic sensors operating in the attenuated total reflection (ATR) mode in the mid‐infrared (IR) region of the spectrum (850 – 1850 cm−1) has found recently application in the area of tissue diagnostics. The method is suitable for noninvasive and rapid (seconds) direct measurements of the spectra of normal and pathological tissues in vitro, ex vivo, and in vivo.The FEW‐FTIR technique is an ideal diagnostic tool for different types of soft, porous, foam, and rough polymer surfaces. Inhomogeneous coatings and defects on polymer surfaces as well as layer structures have also been detected by this method. It is convenient to apply this method to analyze large pieces of soft plastics and/or surfaces covered by plastics, since these types of surfaces are comparatively hard to analyze by traditional absorption spectroscopy. The FEW‐FTIR technique is non‐destructive, fast (15 seconds), and remote (up to a fiber length of 3m). In addition, it is sensitive enough to detect any changes in the vibrational spectra of a polymer surface, without heating and damaging it. The surfaces of polyethylene crumpled bags and rumpled films have been investigated in the range of 2000 – 1000 cm−1. The distinct spectra of these surfaces as well as spectra of polytetrafluoroethylene have been recorded. The spectra of white and colored foams and different plastics have also been studied. Weak but distinct spectra have been recorded for carbon fibers (black, narrow fibers with a diameter of about 10 μm). Using the FEW‐FTIR technique, measurements can be taken without preparing the sample. High quality spectra have also been obtained for the bulk and surfaces of apple, banana, grapefruit, and other food products. The method is expected to be further developed for geological and microelectronic applications.

Synthesis and growth processes for zinc germanium diphosphide

Zinc germanium diphosphide (ZnGeP 2) has useful properties for wavelength conversion devices in the mid-in-frared (IR) spectral range. It has a high figure of merit as an optical parametric oscillator (OPO) and it also performs efficiently as a frequency doubler. Present crystal growth technology has been restricted to small volume charges because of the pressure limits of quartz containment vessels. The authors discuss a new approach to synthesis based on direct injection of phosphorus through a B 2O 3 encapsulant and reaction with the zinc germanium melt, resulting in synthesis of a large melt (350 g) of ZnGeP 2. When crystallization is followed by cooling the congruent melt down through the α-β transition temperature (952°C) as is typical for bulk growth processes, the result is the growth of partially disordered material. An alternative approach for the growth of ZnGeP 2 below the phase transition temperature by chemical vapor transport (CVT) is discussed. The results of crystal growth below the α-β phase transition temperature are reported.

Glycine Series as a Model to Study near Infrared Reflectance Spectra1

Near infrared reflectance (NIR) spectra supply the basic information utilized to relate vibrational information of functional groups to the quality analysis of forages and feedstuffs. The spectra are used to quantify the mathematical relationship between functional group information and the chemical analyses currently in use. This paper was developed using the amino acid glycine and its di‐, tri‐, and tetrapeptide forms to demonstrate that the information due to various chemical functional groups appearing in the mid‐infrared region could be located and identified in the NIR region. Spectra for the glycine series were obtained on a spectro‐computer system. Absorption peak assignment was conducted using mathematical calculations and direct comparison with published spectra. The region from 1000 to 1900 nm was found to be an overtone region and 1900 to 2600 nm a combination region. Three regions of the spectra contained primarily carbon information. They were 1000 to 1460,1600 to 1900, and 2240 to 2600 nm. The N regions were 1460 to 1590 and 1900 to 2230 nm. These findings verify that the fundamental information originating in the mid‐infrared (IR) region is contained in the NIR region in a complicated form as overtones and combinations of the primary IR absorption. A better understanding of these principals will be useful in future quantitative research with forage and feed.

Some optic and electrooptic properties of PLZT and PSN ferroelectric ceramics in the infrared

The change of the scattering coefficient in the mid-infrared (IR), as compared to the visible region, is estimated from the theory of electromagnetic wave scattering in inhomogeneous dielectric media. It has been found that the coefficient of light scattering by domains and grains at a wavelength λ = 5 μm is decreased by a factor of about 102 as compared to its value at λ = 0.5 μm. Experimental studies have been performed on electrooptic (EO) properties of ferroelectric ceramics PLZT 10/65/35, the sample thickness being up to 15 mm. Dispersion of the EO effect in the IR region has been studied in PLZT 8/65/35 and PSN ceramics at temperatures beyond Tt—the temperature of disappearance of the macroscopically polarized state.

Prospective Vitreous Materials For Infrared Fiber Optics

Fiber optics operating in the mid-infrared (IR) offer the potential for lower losses and better tolerance to nuclear radiation than current silicate-based fibers. Moreover, mid-IR fibers may be useful for a variety of shorter distance applications such as laser surgery, spot welding, and infrared integrated optics. Although a wide array of potentially highly transmissive mid-IR materials are available in bulk form, most are not suitable for fiber fabrication. Recently, however, a variety of new multicomponent glasses based on the fluorides of heavy metals have been developed, which may offer the best prospects to date for high performance mid-IR fibers. A critical comparison of the advantages as well as the problems associated with various prospective materials and fiber fabrication techniques is given.