Relative Absorption Coefficients Research Articles

A Method of Evaluating NV centers Concentration by UV–Vis Transmittance Spectra

The ultraviolet-visible (UV-Vis) spectrum was not generally considered an available method for measuring the concentration of negatively charged nitrogen-vacancy (NV-, NV center). In this study, we propose the idea of evaluating the concentration of NV center by the slope of the UV-Vis spectrum. To establish this new method we synthesized diamonds with different NV center concentrations by the chemical vapor deposition (CVD) method. We then measured the zero-phonon line (ZPL) intensity of PL spectra at 637 nm and estimated the concentration of the NV centers as a baseline for comparison to our new UV-Vis method. The UV-Vis transmission spectra were then measured and transformed to relative absorption coefficient spectra. Slopes of the transformed UV-Vis spectra between 400 nm and 800 nm were calculated and compared with the ZPL intensities. The results show a strong positive correlation between the slopes of the absorption spectra and the ZPL intensities of PL spectra at 637 nm. Therefore, this paper demonstrates the feasibility of estimating the concentration of the NV centers from measuring the transmission UV-Vis spectrum.

Thienoguanosine brightness in DNA duplexes is governed by the localization of its ππ* excitation in the lowest energy absorption band

Thienoguanosine (thG) is an isomorphic fluorescent guanosine (G) surrogate, which almost perfectly mimics the natural G in DNA duplexes and may therefore be used to sensitively investigate for example protein-induced local conformational changes. To fully exploit the information given by the probe, we carefully re-investigated the thG spectroscopic properties in 12-bp duplexes, when the Set and Ring Associated (SRA) domain of UHRF1 flips its 5′ flanking methylcytosine (mC). The SRA-induced flipping of mC was found to strongly increase the fluorescence intensity of thG, but this increase was much larger when thG was flanked in 3′ by a C residue as compared to an A residue. Surprisingly, the quantum yield and fluorescence lifetime values of thG were nearly constant, regardless of the presence of SRA and the nature of the 3′ flanking residue, suggesting that the differences in fluorescence intensities might be related to changes in absorption properties. We evidenced that thG lowest energy absorption band in the duplexes can be deconvoluted into two bands peaking at ∼350 nm and ∼310 nm, respectively red-shifted and blue-shifted, compared to the spectrum of thG monomer. Using quantum mechanical calculations, we attributed the former to a nearly pure ππ* excitation localized on thG and the latter to excited states with charge transfer character. The amplitude of thG red-shifted band strongly increased when its 3′ flanking C residue was replaced by an A residue in the free duplex, or when its 5′ flanking mC residue was flipped by SRA. As only the species associated with the red-shifted band were found to be emissive, the highly unusual finding of this work is that the brightness of thG in free duplexes as well as its changes on SRA-induced mC flipping almost entirely depend on the relative population and/or absorption coefficient of the red-shifted absorbing species.

The Effect of Annealing Temperature on the Structural and Optical Properties of Si/SiO2 Composites Synthesized by Thermal Oxidation of Silicon Wafers

In this article, silicon wafers were thermal treated in air at temperatures from 800 to 1200 °C. The annealed samples were investigated using X-ray diffraction, FTIR and optical reflection spectroscopy. Unique result obtained includes that possibility of employing the thermal oxidation of silicon to obtain Si/SiOx composites with various energy gaps suitable for the manufacture of semiconductor devices. In addition, we found that the splitting of longitudinal optical and transverse optical stretching motions effect on the relative absorption coefficient. On the other hand, it has been found that, the intensity of the silicon peak in XRD spectra is proportional to the relative absorption coefficient of amorphous silicon oxide.

Influence of ion chelator and CO2-rich environment on self-healing capabilities of cement-based materials

Ion chelator is a kind of crystalline additive which can accelerate the precipitation of calcium carbonate in cracks of cement-based materials. In this paper, the influences of ion chelator and CO2-rich environment on self-healing capabilities of cement mortar were investigated. The mortars with or without ion chelator were subjected to two gas environments (air and CO2-rich) and three exposure conditions (no water, water contact and water immersion), respectively. The self-healing rate of cracks, water permeability and water absorption of the healed mortars, and microstructure of self-healing product were used to assess the self-healing capability of mortars. The results indicated that the self-healing ability of the mortars cured in CO2-rich environment is stronger than that of the mortars cured in air environment. The excellent self-healing ability of the mortars with ion chelator needs to be stimulated by water contact or water immersion. The relative permeability coefficient and water absorption coefficient of mortar with ion chelator in the CO2-rich environment under water contact or water immersion conditions were significantly reduced. In addition, the bottom surface crack of mortar has better self-healing ability than the top surface crack of mortar. The bottom surface crack up to 0.46 mm can be healed after curing for 28 d when the mortars with ion chelator were cured in the CO2-rich environment under water immersion condition. Scanning electron microscopy showed that the particle sizes of self-healing products (CaCO3) in bottom surface crack were larger than that in top surface crack.

Binding energies and optical absorption of donor impurities in spherical quantum dot under applied magnetic field

Abstract In this study, we have calculated the binding energies of the ground-1s and first few excited impurity states such as 2s, 1p, 2p, 1d, and 2d, as well as the wave functions and energies of an electron in spherical quantum dot which has finite confinement potential under applied magnetic field. Furthermore, we calculated the impurity related optical absorption coefficients for 1s → 1p, 1p → 2s, 2s → 2p, 1p → 1d, and 2p → 2d transitions between higher impurity states than those available in the literature. The calculations have been made in the framework of the effective mass approximation via the diagonalization method by using the complete basis of functions obtained as the exact solutions of the infinite QD in the absence of the magnetic field. Considering the two-level approach, the optical response was treated in the density matrix expansion. The results show that the external magnetic field strongly affects the impurity binding energies in large dot radii and the optical absorption coefficients. Furthermore, it has been observed that the change of dot radius has a significant effect on the optical absorption coefficients.

Double-layer targets for forming the beams of the high-energy photons on the electron accelerator of M-30 microtron

Purpose. The bremsstrahlung received at electron accelerators is widely used to study the characteristics of photonuclear reactions and to solve a wide spectrum (series) of applied problems. Basically the output of bremsstrahlung depends on the electron energy, the material of the target converter (Ta) and its effective thickness. The optimum thickness of the converter (when the output of the bremsstrahlung is at its maximum) is significantly less than the electron path in it. This is the reason for the presence of high-energy electrons in bremsstrahlung. Therefore, there is a need to clean the bremsstrahlung beams from residual electrons. The aim of the work is to experimentally determine the optimal parameters (thicknesses) of double-layer targets for obtaining separated bremsstrahlung beams for an energy range of 6.5 – 17.75 MeV in electron accelerator M-30 microtron. Methods. Experimental studies of the relative absorption coefficient of electrons in the investigated materials (C (reactor graphite), Al, Ta) were carried out on the M-30 microtron using the transmission method. The measurements of the outputs of the electrons from the accelerator and the residuals that have passed through the layer of absorbing material were carried out using a pass-through chamber and a Faraday cup, respectively. Studies of the absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) using activation detectors have been carried out. Results. The electron absorption coefficients in single- (C (7 – 46 mm), Al (8 – 48 mm), Ta (0.1 – 1 mm)) and in double-layer targets (Ta (1 mm) + C (7 – 39 mm) and Ta (1 mm) + Al (8 – 40 mm)) were measured for the electron energy 6.5 – 17.75 MeV. The values of the total electron absorption thickness for C, Al, and Ta are in good agreement with the calculated values of the practical electron path (database «ESTAR») for the indicated energy range. The experimentally established values of the thicknesses of materials (C and Al at a thickness of Ta – 1 mm) of doublelayer targets, which ensure the complete absorption of electrons for the indicated energy range. The absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) for bremsstrahlung energy of 17.5 MeV was evaluated. Conclusions. The optimal parameters (thicknesses) of double-layer targets (Ta (1mm) + C (20 mm) and Ta (1 mm) + Al (20 mm)) or (Ta (1mm) + C (39 mm) and Ta (1 mm) + Al (32 mm)) were established experimentally to form the separated bremsstrahlung beams in the electron accelerator – M-30 microtron for energy region 6.5 ч 17.75 MeV. The use of two-layer targets allows us to carry out procedures to form of high-energy photon beams with the parameters necessary for performing specific experimental studies on electronic accelerators, which will increase the accuracy and reliability of the results.

Interlayer distance effects on absorption coefficient and refraction index change in p-type double-δ-doped GaAs quantum wells**Project supported by PISA 2016–1 UJAT and PRODEP Folio UJAT-245 of México.

In the framework of the Thomas–Fermi (TF) approach, a model for the p-type double-δ-doped (DDD) system in GaAs is presented. This model, unlike other works in the literature, takes into account that the Poisson equation associated with the system is nonlinear. The electronic structure is calculated for heavy and light holes. The changes in the electronic structure result of the distance d between the doped layers are studied. In particular, the relative absorption coefficient as well as the relative refractive index change is calculated as a function of the incident photon energy for heavy holes. The effect of the interlayer distance exhibits, in the absorption coefficient, a red shift of the peak position and a decrease in amplitude when the distance increases. In addition, the relative refractive index change node has a red shift as well as the interlayer distance increases. The calculations show that the effect of the separation between layers has a greater influence on the linear terms. These results are very important for theoretical calculations and engineering of optical and electronic devices based in δ-doped GaAs.

Near-infrared in vitro measurements of photosystem I cofactors and electron-transfer partners with a recently developed spectrophotometer.

A kinetic-LED-array-spectrophotometer (Klas) was recently developed for measuring in vivo redox changes of P700, plastocyanin (PCy), and ferredoxin (Fd) in the near-infrared (NIR). This spectrophotometer is used in the present work for in vitro light-induced measurements with various combinations of photosystem I (PSI) from tobacco and two different cyanobacteria, spinach plastocyanin, cyanobacterial cytochrome c6 (cyt. c6), and Fd. It is shown that cyt. c6 oxidation contributes to the NIR absorption changes. The reduction of (FAFB), the terminal electron acceptor of PSI, was also observed and the shape of the (FAFB) NIR difference spectrum is similar to that of Fd. The NIR difference spectra of the electron-transfer cofactors were compared between different organisms and to those previously measured in vivo, whereas the relative absorption coefficients of all cofactors were determined by using single PSI turnover conditions. Thus, the (840nm minus 965nm) extinction coefficients of the light-induced species (oxidized minus reduced for PC and cyt. c6, reduced minus oxidized for (FAFB), and Fd) were determined with values of 0.207 ± 0.004, - 0.033 ± 0.006, - 0.036 ± 0.008, and - 0.021 ± 0.005 for PCy, cyt. c6, (FAFB) (single reduction), and Fd, respectively, by taking a reference value of + 1 for P700+. The fact that the NIR P700 coefficient is larger than that of PCy and much larger than that of other contributing species, combined with the observed variability in the NIR P700 spectral shape, emphasizes that deconvolution of NIR signals into different components requires a very precise determination of the P700 spectrum.

Application of biological preparation for bioremediation of oil-contaminated soils of the tank farm

The paper presents the results of an experiment on the biological purification of permafrost soils from oil pollution with use biological preparations on the basis of hydrocarbon-oxidizing microorganisms. Biological preparations were used in two modifications - in liquid form as a suspension and in dry form as a suspension immobilized on organic granules. It has been established that dry form of a biological preparation is more effective for the purification of permafrost soils from oil than a liquid microbial suspension. For 1 month in dry conditions and a strongly alkaline soil environment, the use of a dry biological preparation allowed reducing the concentration of oil pollution by up to 60 %. The change of the chemical structure of extracts of soil samples was investigated with use the method of IR-Fourier spectroscopy. The increase of the relative absorption coefficients of oxygen-containing groups and bonds pointed (indicated) on the course of oxidative destruction.

Optical absorption coefficient in n-type double δ-doped layers GaAs quantum wells

The superposition principle is one of the cornerstones of physics. In low-dimensional systems, it is routinely used to model the potential profile. That is the case of coupled [Formula: see text]-doped quantum wells, for which, several works have studied the transport and optoelectronic properties. However, the Poisson equation determines the potential profile is not linear, and the superposition principle is not at all valid. The aim of this work is to correct some of the inconsistencies of the mentioned models for coupled [Formula: see text]-doped quantum wells. In the framework of Thomas–Fermi approximation, we calculated the potential profile, the wave functions, the energy values and the relative absorption coefficient for the double system compared to an isolated delta system in terms of impurity density and distance between [Formula: see text]-wells. We found a red shifting in the absorption coefficient when the interlayer distances increase, in addition, an enhancement in the absorption coefficient is detected for a specific separation distance. Our results agree with ab-initio calculations reported for the electronic structure.

Double-layer targets for forming the beams of the high-energy photons on the electron accelerator of M-30 microtron

Purpose. The bremsstrahlung received at electron accelerators is widely used to study the characteristics of photonuclear reactions and to solve a wide spectrum (series) of applied problems. Basically the output of bremsstrahlung depends on the electron energy, the material of the target converter (Ta) and its effective thickness. The optimum thickness of the converter (when the output of the bremsstrahlung is at its maximum) is significantly less than the electron path in it. This is the reason for the presence of high-energy electrons in bremsstrahlung. Therefore, there is a need to clean the bremsstrahlung beams from residual electrons. The aim of the work is to experimentally determine the optimal parameters (thicknesses) of double-layer targets for obtaining separated bremsstrahlung beams for an energy range of 6.5 ÷ 17.75 MeV in electron accelerator M-30 microtron. Methods. Experimental studies of the relative absorption coefficient of electrons in the investigated materials (C (reactor graphite), Al, Ta) were carried out on the M-30 microtron using the transmission method. The measurements of the outputs of the electrons from the accelerator and the residuals that have passed through the layer of absorbing material were carried out using a pass-through chamber and a Faraday cup, respectively. Studies of the absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) using activation detectors have been carried out. Results. The electron absorption coefficients in single- (C (7 ÷ 46 mm), Al (8 ÷ 48 mm), Ta (0.1 ÷ 1 mm)) and in double-layer targets (Ta (1 mm) + C (7 ÷ 39 mm) and Ta (1 mm) + Al (8 ÷ 40 mm)) were measured for the electron energy 6.5 ÷ 17.75 MeV. The values of the total electron absorption thickness for C, Al, and Ta are in good agreement with the calculated values of the practical electron path (database «ESTAR») for the indicated energy range. The experimentally established values of the thicknesses of materials (C and Al at a thickness of Ta – 1 mm) of doublelayer targets, which ensure the complete absorption of electrons for the indicated energy range. The absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) for bremsstrahlung energy of 17.5 MeV was evaluated. Conclusions. The optimal parameters (thicknesses) of double-layer targets (Ta (1mm) + C (20 mm) and Ta (1 mm) + Al (20 mm)) or (Ta (1mm) + C (39 mm) and Ta (1 mm) + Al (32 mm)) were established experimentally to form the separated bremsstrahlung beams in the electron accelerator – M-30 microtron for energy region 6.5 ÷ 17.75 MeV. The use of two-layer targets allows us to carry out procedures to form of high-energy photon beams with the parameters necessary for performing specific experimental studies on electronic accelerators, which will increase the accuracy and reliability of the results

Validation of MODIS-Aqua bio-optical algorithms for phytoplankton absorption coefficient measurement in optically complex waters of El Rincón (Argentina)

El Rincón is a highly productive area in the inner-shelf of the Argentine Sea, southern Buenos Aires Province (39°S–62.5°W; 41.5°S–60°W), regarded as the habitat for commercially valuable fish species and important for local artisanal fisheries. The aims of this work were to characterize for the first time the in situ absorption coefficient of phytoplankton (aph(λ)) in relation to phytoplankton composition and chlorophyll-a (Chl-a) concentration, and to evaluate the satellite retrieval of aph(443) using two atmospheric correction algorithms and three bio-optical semi-analytical algorithms in order to define which is more suitable for the study area. A total of 28 oceanographic cruises were performed between November 2013 and March 2017 and the sampling included physical variables (temperature, salinity, suspended particulate matter, SPM), Chl-a, phytoplankton absorption and composition. The phytoplankton community was mainly dominated by chain-forming diatoms from the microplankton size class (40–80%), while a single coccolithophore, Gephyrocapsa oceanica (cell diameter <10 µm) was a key component (up to 40%) of the nanoplankon. In situ Chl-a (mean 1.8 mg m−3) and aph (443) (mean 0.052 m−1) generally covariated with no clear seasonality. Their correlation was rather low (R2 = 0.52) and with high scattering, in agreement with the high interannual variability of phytoplankton composition. Further, the relative low mean specific absorption coefficient of phytoplankton (aph*(443), 0.032 m2 (mg Chl-a)−1) and (aph*(676), 0.014 m2 (mg Chl-a)−1) denoted the presence of big cells and pigment packaging effect. Aside from the optical complexity of these waters, reasonable results were found using the Quasi Analytical Algorithm in retrieving aph coefficient (R2 = 0.55, Bias = 19%) and switching the atmospheric correction algorithm depending on the distance to the coast, the depth and turbidity. The results found in this paper present for the first time the phytoplankton composition and absorption of algal material characteristics and the derived implication on the performance of bio-optical algorithms in the optically complex waters of El Rincon.

Impact of light absorption and temperature on self-focusing of zeroth-order Bessel–Gauss beams in a plasma with relativistic–ponderomotive regime

The influence of light absorption and temperature on self-focusing of zeroth-order Bessel–Gauss beams through plasma, with relativistic–ponderomotive regime, is investigated in this paper. The nonlinear differential equation for beam-width is established by using parabolic equation approach under Wentzel–Kramers–Brillouin (WKB) paraxial approximation and solved numerically. The numerical results show the effects of beam parameter, relative density plasma, intensity parameter, absorption coefficient and plasma electron temperature on self-focusing of zeroth-order Bessel–Gauss beams in plasma. The self-focusing of Gaussian beams in the considered plasma is also deduced as a particular case in the present work.

On the eccentricity effects on the intraband optical transitions in two dimensional quantum rings with and without donor impurity

Using the plane wave expansion in the frame of the effective mass approximation, a straightforward method is presented to calculate the energy levels and the corresponding wavefunctions in a two dimensional GaAs/AlxGa1-xAs eccentric quantum rings (QRs) with and without donor impurity. The transition energy and their related optical absorption coefficients are calculated. The obtained results show that the transition energy between the ground state and the first two excited states and their related optical matrix are strongly influenced by the eccentricity and the donor position. The resonant peaks of the absorption coefficients for electron are blueshifted, while for QRs with an off center impurity the resonant peaks are red or blueshifted depending on the donor positions and eccentricity. In addition, we have found that a small eccentricity acts on the QRs qualitatively as a weak radial electric field. Moreover, an electric field is no longer able to reproduce perfectly the eccentricity effect when the eccentricity becomes relatively strong. Finally, our results are qualitatively similar to those reported in recent works dealing with concentric QRs under a radial electric field.

Structure and properties of CdO–B2O3 and CdO–MnO–B2O3 glasses; Criteria of getting the fraction of four coordinated boron atoms from infrared spectra

IR spectra of CdO–B2O3 and xCdO·(50 − x)MnO·50B2O3 glasses (0 ≤ x ≤ 50mol%) have been analyzed. The fraction N4 of four coordinated boron atoms obtained from the integrated area under the IR spectra of CdO–B2O3 glasses is markedly higher than the reported NMR values. In both cases, N4 does not change with CdO content. The difference between N4 values of both techniques has been correlated with the relative absorption coefficient of BO4 unit with respect to BO3 unit, as suggested by Chryssikos et al. N4 data of xCdO·(50 − x)MnO·50B2O3 glasses could be used to calculate the fraction of modifier and former CdO and MnO in the borate matrix, as a function of composition. There is a linear increase in both the density and molar volume with increasing CdO content. The change has been correlated with the contribution of CdO and MnO. Electric conduction is assumed to take place via hopping of small polarons. There is a decrease in conductivity with increasing CdO concentration, which suggests that the electrons related to Cd sites are more localized than those at Mn sites.

Measurement of line strengths in the à 2A’ ← [formula omitted]2A” transition of HO2 and DO2

The absorption spectrum of the à 2A’ ← X˜2A” 000–000 band of HO2 and DO2 radicals has been measured in the range 6941–7077 cm−1 with a resolution of around 0.005 cm−1. HO2 and DO2 radicals were generated from the reaction of Cl-atoms with CH3OH and CD3OD, respectively, whereby Cl-atoms were generated by pulsed photolysis of (COCl)2 at 248 nm. One time-resolved absorption curve was measured by cw-Cavity Ring Down Spectroscopy (cw-CRDS) for each wavelength. The relative absorption coefficient for each wavelength was then obtained from the ring down time τ, extrapolated to t = 0 s with respect to the photolysis pulse, and the ring down time τ0 before the photolysis pulse. Absolute absorption coefficients were quantified for several selected lines relative to a well characterized absorption line of HO2 at 6638.21 cm−1 by a second cw-CRDS absorption path. The maximum absorption cross section at 50 Torr Helium was for HO2 the transition N Ka Kc J = 11 0 11 11.5 ← 11 1 11 11.5 with σ7000.28 cm−1 = 2.12 × 10−19 cm2 and for DO2 the doublet transition N Ka Kc J = 18 1 18 18.5 ← 18 0 18 18.5 and 18 1 18 17.5 ← 18 0 18 17.5 with σ7019.83 cm−1 = 2.97 × 10−19 cm2. The full spectrum has been very well reproduced by employing spectroscopic data from earlier works.

Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties.

A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn2+ enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb2+ and Bi3+ induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was determined from the IR spectra after deducing the relative absorption coefficient of boron tetrahedral versus boron trigonal units, α = α4/α3, using NMR literature data of the diamagnetic glasses.

The Electronic States of U(4+) in U(PO4)Cl: An Example for Angular Overlap Modeling of 5f(n) Systems.

Detailed experimental data on UPO4Cl comprising single-crystal UV/vis/NIR spectra and temperature-dependent magnetic susceptibilities form the basis for the investigation of the electronic structure of the U(4+) cation in UPO4Cl. For modeling of the observed physical properties the angular overlap model (AOM) was successfully employed. The computations were performed using the newly developed computer program BonnMag. The calculations show that all electronic transitions and the magnetic susceptibility as well as its temperature dependence are well-reproduced within the AOM framework. Using Judd-Ofelt theory BonnMag allows estimation of the relative absorption coefficients of the electronic transitions with reasonable accuracy. Ligand field splitting for states originating from f-electron configurations are determined. Slater-Condon-Shortley parameters and the spin-orbit coupling constant for U(4+) were taken from literature. The good transferability of AOM parameters for U(4+) is confirmed by calculations of the absorption spectra of UP2O7 and (U2O)(PO4)2. The effect of variation of the fit parameters is investigated. AOM parameters for U(4+) (5f) are compared to those of the rare-earth elements (4f) and transition metals (3d).

InGaAs/GaAs quantum well intermixing using proton irradiation for non-absorbing mirror

We report a proton irradiation-induced intermixing on InGaAs/GaAs quantum well (QW) heterostructures with thick upper cladding layers. Proton irradiation was performed with different dose, followed with annealing. Proton irradiated and annealed sample shows the blue-shift of the photoluminescence (PL) spectra and the blue-shift energy was increased up to about 30 meV with increasing dose, but was insensitive to the annealing temperature. Finally, we calculated that the relative absorption coefficient at the laser wavelength for the irradiated sample with dose of 1 × 1016/cm2 was 0.045, suggesting such proton irradiation-induced intermixing is a promising approach for fabricating non-absorbing mirror.

Diffuse-Reflectance Spectroscopy Using a Frequency-Switchable Terahertz Quantum Cascade Laser

We demonstrate diffuse-reflectance (DR) spectroscopy of powders using a discretely-tunable terahertz-frequency quantum cascade laser (THz QCL) with a heterogeneous active region. DR signatures were obtained at frequencies of 3.06, 3.21, 3.28, and 3.35 THz, and the relative absorption coefficients were inferred at each frequency using a Kubelka-Munk (KM) scattering model. The spectral lineshapes reproduce the absolute Beer-Lambert (BL) absorption spectra of a range of materials, which were also measured using conventional transmission-mode THz time-domain spectroscopy. It is shown that the DR technique works reliably for materials that include pharmaceutical compounds and foodstuffs, with BL absorption coefficients in the range 2-10 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . This method is potentially suitable for automated material identification, without any requirement for a priori knowledge of the refractive index or scattering properties of the sampled material.