Mid-infrared Transitions Research Articles

High-quality AlGaN/GaN superlattices for near- and mid-infrared intersubband transitions

A pulsed layer-by-layer deposition (PLLD) technique possessing triple growth rates compared to conventional growth techniques is developed by metal−organic chemical vapor deposition to realize high-quality high-aluminum content ordered AlXGa(1−X)N (0.5 < X). X-ray diffraction, photoluminescence, and transmission measurements are employed to demonstrate control over aluminum content, structural uniformity, and optical quality in the ordered AlXGa(1−X)N. To show the feasibility of device applications, AlXGa(1−X)N as barrier and GaN as well are employed in superlattices demonstrating intersubband transitions in the infrared regime. Effects of well width and barrier aluminum content on the intersubband absorption characteristics are reported.

Temperature dependence of middle infrared absorption lines in silver halide crystals doped with Pr3+, Dy3+, and Nd3+ ions

The electron-phonon coupling was investigated for mid-infrared transitions in silver halide crystals doped with Pr, Dy, or Nd. The temperature dependence of the absorption spectral line widths and the line shifts were measured in mid-infrared absorption lines in these crystals. It was shown that in each case the temperature dependence is consistent with the two-phonon Raman process model having a single characteristic Debye temperature. This Debye temperature was found to be in the range of 142–155.5 K. It was also found that below 50 K the line widths are caused by inhomogeneous crystal strains.

Stark shifts in mid-infrared type II quantum well transitions

We have studied electric field induced (Stark) shifts in mid-infrared (IR) transitions that occur in type II AlSb/InAs/GaSb quantum wells. Because of the spatial separation of the electron and hole wave functions in the type II system, the potential drop between the layers dominates the shift in the real-space-indirect transition energies when an external electric field is applied. This can result in either a redshift or a blueshift, depending on the ordering of the quantum well layers within the intrinsic region of a p-i-n diode. The case in which a reverse bias on the diode yields a blueshift in the transition energy is of particular interest for IR electro-optic device applications. The modulator section of an integrated source/waveguide modulator would strongly absorb at zero bias and could be biased into transparency, and bistable optical switches could be made more efficient than with redshifting devices. We have used low temperature current-voltage, capacitance-voltage, and photocurrent measurements to characterize a type II quantum well structure that exhibits a blueshift in the lowest energy transitions that is roughly linear with applied bias and is comparable to the potential drop across the structure.

MOLECULAR HYDROGEN IN THE DISK OF THE HERBIG Ae STAR HD 97048

We present high-resolution spectroscopic mid-infrared observations of the circumstellar disk around the Herbig Ae star HD97048 obtained with the VLT Imager and Spectrometer for the mid-InfraRed (VISIR). We conducted observations of mid-infrared pure rotational lines of molecular hydrogen (H2) as a tracer of warm gas in the disk surface layers. In a previous paper, we reported the detection of the S(1) pure rotational line of H2 at 17.035 microns and argued it is arising from the inner regions of the disk around the star. We used VISIR on the VLT for a more comprehensive study based on complementary observations of the other mid-infrared molecular transitions, namely S(2) and S(4) at 12.278 microns and 8.025 microns respectively, to investigate the physical properties of the molecular gas in the circumstellar disk around HD97048. We do not detect neither the S(2) line nor the S(4) H2 line from the disk of HD97048, but we derive upper limits on the integrated line fluxes which allows us to estimate an upper limit on the gas excitation temperature, T_ex < 570 K. This limit on the temperature is consistent with the assumptions previously used in the analysis of the S(1) line, and allows us to set stronger contraints on the mass of warm gas in the inner regions of the disk. Indeed, we estimate the mass of warm gas to be lower than 0.1 M_Jup. We also discuss the probable physical mechanisms which could be responsible of the excitation of H2 in the disk of HD97048.

Ethylene in the circumstellar envelope of IRC+10216

AbstractEthylene (C2H4) is a symmetric molecule that is best detected using mid-infrared transitions. We report on observations of the 10.5 μm ν7 band using the cryogenic grating spectrograph TEXES. These confirm the previous ethylene detection in the IRC+10216 circumstellar shell. We detect 18 ethylene lines. The lines are both narrow and weak with depths of no more than ~2%. The ethylene lines suggest an excitation temperature of ~80 K.

Comparison of the Mid-Infrared Magneto-Optical Response of Ga1−x Mn x As Films Grown by Molecular Beam Epitaxy and Ion Implantation and Pulsed Laser Melting

We have carried out mid-infrared magneto-optical studies of Ga1−xMnxAs films grown using two different techniques: low temperature molecular beam epitaxy (LT-MBE) and a combination of ion-implantation and pulsed laser melting (II-PLM). The second method is a high temperature growth technique which minimizes the formation of Mn interstitials. Both samples exhibit a ferromagnetic response with similar Curie temperatures (TC). The samples show qualitatively similar behavior in below bandgap Faraday and Kerr measurements, which probe the valence band structure of the materials. This suggests that the same mid-infrared transitions are dominating the magneto-optical response of both samples.

High pressure study of ZnSe:Cr2+ crystals: the origin of the 1.25 eV luminescence

High pressure studies of Cr2+ luminescence in ZnSe crystals were performed at low temperatures. Inaddition to the mid-infrared luminescence transitions from the first excited5E level, higher energy luminescence was also observed. These two luminescencebands exhibit similar pressure coefficients but of opposite signs, which identifythe origin of the higher energy band as the transitions from the second excited3T1 level. At higher pressures, increased covalence effects are observed, which result inthe appearance of an additional peak in the luminescence due to changes in the spin–orbit coupling strength.

Neon Abundances in the HiiRegions of M33

We present neon abundances for 25 H II regions of M33, measured from line profiles of the mid-infrared transitions of [Ne II] and [Ne III] taken with the Infrared Space Observatory Short-Wavelength Spectrometer. The distribution of neon abundances as a function of galactocentric radius is best described as a step, -0.15 dex relative to the solar neon abundance from 0.7 to 4.0 kpc and -0.35 dex from 4.0 to 6.7 kpc, with estimated intrinsic scatter of 0.07 dex. The nearly flat neon abundance distribution differs from the steep oxygen abundance gradient found by previous investigators. Unless the oxygen abundance determinations are wrong, the chemical evolution of the galaxy has been radially dependent.

Observation of photoinduced intersubband transitions in one-dimensional semiconductor quantum wires

We report on midinfrared intersubband transitions between the quantized levels of undoped ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum wires that are grown on nonplanar substrates. Using photoinduced infrared absorption spectroscopy, we were able to resolve two absorption lines in the 120--160 meV range. The first absorption line follows the polarization selection rules for intersubband transitions and exhibits photoinduced excitation profile that resembles the photoluminescence excitation spectrum of the quantum wires. The second absorption resonance, at a higher energy, is not polarized and resembles the photoluminescence spectrum of the side quantum wells. Based on these results and energy level calculations, we assign the first absorption resonance to intersubband transition between the quantized subbands of the quantum wires. The origin of the second resonance is less clear. We propose a model that attributes this resonance to an interface localized exciton mode that arises from interface roughness of the side quantum wells and the wires.

Investigation of mid-infrared intersubband transitions in CdS : Cl/ZnSe quantum wells

We report on the first investigations of intersubband transitions in cubic type-II CdS/ZnSe multiple quantum wells. The samples are n-type doped with chlorine and were grown by molecular-beam epitaxy on GaAs(0 0 1) substrates using CdS and ZnSe compound sources. In case of infrared measurements in waveguide geometry, the different refraction indexes in the middle infrared of GaAs substrate and CdS/ZnSe heterostructure increase the electric field component in growth direction and cause a strong absorption of the infrared beam due to intersubband transitions. The measured energies and oscillator strengths of the intersubband transitions agree well with the theoretically expected values. Thereby, we used for the effective electron mass at the Γ-point of cubic CdS a value of (0.19±0.04) m 0, which has been determined by a combination of Hall and infrared reflectance measurements at nearly normal incidence on highly n-type doped simple CdS layers. Furthermore, first results of our pump-probe measurements on lightly doped CdS/ZnSe multiple quantum wells are presented.

Electronic Properties and Mid-Infrared Transitions in Self-Assembled Quantum Dots

We present a detailed model of the electronic properties of single and vertically aligned self-assembled pyramidal InAs/GaAs quantum dots (SADs) which is based on the self-consistent solution of three-dimensional (3D) Poisson and Schroedinger equations within the local (spin) density approximation. Nonparabolicity of the band structure and a continuum model for strain between GaAs and InAs results in position and energy dependent effective mass. In single SADs, shell structures obeying Hund's rule for various occupation numbers in the pyramids agree well with recent capacitance measurements. The electronic spectra of SADs of various shapes have been determined with intraband level transitions and mid-infrared optical matrix elements. In the case of two vertically aligned pyramidal SADs, we show that quantum mechanical coupling alone between identical dots underestimates the magnitude of the coupling between the dots, which in large part is due to piezoelectricity and size difference between SADs.

Cross relaxation and upconversion coefficients of the mid-infrared transitions of Pr3+:LaCl3

Short pulse laser-induced fluorescence experiments on the lowest-energy electronic states (υ&amp;lt;10−4 cm−1) of trivalent praseodymium ions are reported. Crystals of lanthanum trichloride with a range of Pr3+ concentrations were examined. We compute cross relaxation and upconversion coefficients for the metastable energy levels using a standard rate equation analysis. The limitations of the rate equation approach are examined with a focus on the underlying dynamics of this rare-earth system. The implications of these results for laser emission in the 1.3–7.2 μm spectral range are discussed.

Fabrication and spectroscopy of erbium doped gallium lanthanum sulphide glass fibres for mid-infrared laser applications

Gallium lanthanum sulphide based glasses are proposed as high quality hosts for rare-earth doped, mid-infrared fibre lasers, that would offer compact and rugged sources for gas sensing, atmospheric transmission, and medical applications. The infrared emission spectroscopy of erbium doped glasses and fibres shows the potential of this glass host for the above applications. Mid-infrared transitions at 2.0, 2.75, 3.6, and 4.5mm have been detected and characterized.

Spectroscopy of potential mid-infrared laser transitions in gallium lanthanum sulphide glass

This paper presents experimental results on the mid-infrared emission of rare-earth doped gallium lanthanum sulphide glasses and fibres. Measured fluorescence includes the 3.4 μm transition ( 1G 4 → 3F 4 ) in Pr 3+-doped Ga: La: S fibre, the 3.6 μm transition ( 4F 9 2 → 4I 9 2 ) in Er 3+-doped Ga: La: S fibre, and the 4.3 μm transition ( 6H 11 2 → 6H 13 2 ) in Dy 3+-doped Ga: La: S bulk glass. Fibre lasers with these emission wavelengths would be of interest for gas sensing applications.

How Predictable Are IR Transition Moment Directions? Vibrational Transitions in Propene and Deuterated Propenes

Transition moment directions of mid-infrared transitions in four isotopomers of propene, CH2CHCH3, CH2CDCH3, CD2CHCD3, and CD2CDCD3, have been determined from linear dichroism spectra recorded in stretched polyethylene as solvent. The results were compared with expectations based on bond directions and with results of ab initio calculations at levels of approximations ranging up to CCSD/6-311G**. The former procedure is found to be unreliable, even for high frequency vibrations. With rare exceptions, the highest levels of ab initio theory agree with the experimental directions to within about ±20°, and for intense transitions, to within the experimental uncertainty of about ±(5−10)°.

Influence of ionized impurities on the linewidth of intersubband transitions in GaAs/GaAlAs quantum wells

In this letter, we report the influence of silicon donors on the linewidth of intersubband transitions 1–2 in GaAs/Ga0.75Al0.25As square quantum wells. We clearly demonstrate that the relative position between the ionized impurities and the center of the quantum wells is a major factor on the linewidth of the mid-infrared (10 μm) transitions. Besides, it is shown that the scattering processes are more influenced by temperature when donors are far from the quantum well (QW).

Infrared optical properties of the 10-K organic superconductor (BEDT-TTF)2

Low-temperature polarized bolometric absorption measurements have been performed on the ${\mathit{T}}_{\mathit{c}}$=10.4 K organic superconductor \ensuremath{\kappa}-(BEDT-TTF${)}_{2}$[Cu(NCS${)}_{2}$], where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene. The ratio of the absorption at 5.3 K to that at 10.5 K from 10 to 40 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ showed no evidence of a conventional BCS gap. Polarized-reflectivity measurements at temperatures between 10 and 295 K are also reported for both the protonated and deuterated compounds, between 200 and 8000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The 10-K spectra were calibrated by a technique of simultaneously measuring the reflectivity R and the absorptance, 1-R. The resulting conductivities display vibrational features superimposed on an electronic background. This background shifts from mid-infrared interband transitions, when the dc conductivity is low, to far-infrared intraband transitions as the dc conductivity increases. The vibrations have been assigned to a mixture of normally inactive ${\mathit{a}}_{\mathit{g}}$ modes and normally active ${\mathit{b}}_{2\mathit{u}}$ modes of the BEDT-TTF molecule. A few of both types couple strongly to the charge carriers. One in particular has a very temperature-dependent frequency due to the changing intensity of the mid-infrared band.

Infrared transition frequencies for methyleneimine, CH2NH

view Abstract Citations (2) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Transition Frequencies for Methyleneimine, CH 2NH Halonen, L. ; Duxbury, G. Abstract Frequencies, intensities, and simulated low-temperature spectra have been calculated for strong mid-infrared (9 - 12 μm) transitions of the CH2NH molecule. The parameters used are derived from the recent detailed analysis of the high-resolution room temperature Fourier transform spectra of CH2NH. Publication: The Astrophysical Journal Pub Date: April 1986 DOI: 10.1086/164138 Bibcode: 1986ApJ...303..897H Keywords: Imines; Infrared Spectra; Line Spectra; Methylene; Optical Transition; Coriolis Effect; Fourier Transformation; Interstellar Gas; Low Temperature; Atomic and Molecular Physics; INFRARED: SPECTRA; LABORATORY SPECTRA; LINE IDENTIFICATIONS; MOLECULAR PROCESSES full text sources ADS |

Dual-wavelength He–Ne laser running at 770 and 339 μm

Two mid-infrared laser transitions in a He-Ne discharge have been investigated. They form part of a cascade transition and therefore have a power dependence, which has been examined and shown to satisfy the relationship P(7.70) = 410 + 0.63 x P(3.39), where P(7.70) and P(3.39) are the powers of the 7.70- and 3.3 9-microm lines, respectively, in micro-watts.

Interaction of far-infrared and mid-infrared laser transitions in the NH3 laser

Laser emission on the conventional 12.8-μm NH3 laser transition, optically pumped by the CO2 9R16 line, can be completely quenched and replaced by emission at 12.2μm. Cascading far-infrared laser transitions in the excited ammonia ν2 state are shown to be responsible for the shift in wavelength.