Search

Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) of linear geometry generally operate in an antisymmetric mode, which is undesirable due to its double-lobed far-field beam pattern. The antisymmetric mode can be suppressed by designing $2^{\mathrm {nd}}$ -order metal/semiconductor gratings that favor symmetric-mode operation, but using such an approach requires tight tolerances in grating duty cycle that impair fabrication yields. Alternatively, the grating can be designed to favor antisymmetric-mode operation with single-lobe emission by using a central $\pi $ -phaseshift. Here we show that such a design is highly fabrication tolerant. Simulations using COMSOL Multiphysics are performed followed by finite-length analysis using coupled-mode theory and the transfer-matrix method, as well as a semi-empirical QCL model for predicting CW performance. The analysis reveals a device of significantly higher tolerance for fabrication errors, operating in a single-lobe beam pattern to 0.63 W CW, although the emitted power scales less efficiently with length than for symmetric-mode operating devices.

A three-element phase-locked array of ∼5.3 μm-emitting quantum cascade lasers fabricated by a two-step MOCVD process is demonstrated which operates in a diffraction-limited beam to 5.3 W peak pulsed power. To compensate for overetching at the array edges, the fabrication process was modified such that it resulted in array elements of equal width. Then the array operates in a pure in-phase array mode, in agreement with simulations based on the actual device dimensions, which indicate that resonant leaky-wave coupling occurs for this device's geometry. Measured uniform near-field intensity profiles confirm resonant coupling. Simulations indicate that chirping of the element widths would allow for modification of the near-field intensity profile to mitigate the effects of thermal lensing in continuous-wave operation.

A numerical model is developed for a phase-locked array of quantum cascade lasers. The population density is derived from rate equations. The temperature distribution for stationary generation is produced by ohmic heating. It is shown that the results of above-threshold operation modeling by the semi-vectorial beam propagation method are in good agreement with the modal analysis provided by the vectorial-COMSOL solver supplemented with the Rigrod’s model estimations. The wall-plug efficiency and the limits of the single-mode lasing are found. Thermal lensing is shown to be the main reason limiting the single-spatial-mode power under CW-operating conditions.

Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) are attractive sources for realizing watt-range continuous-wave (CW) output powers in the mid-infrared spectral region. Linear GCSE QCLs generally operate in the antisymmetric longitudinal mode [1] , which produces a double-lobed beam pattern. The antisymmetric mode can be suppressed by using a metal/semiconductor, 2 nd- order distributed-feedback (DFB) grating [2] , allowing symmetric longitudinal-mode operation and a single-lobe beam pattern. However, such designs require rather tight tolerances in grating duty cycle which cause fabrication challenges. Nevertheless, we have previously reported experimental results from GCSE QCLs using this approach – a single-lobe, diffraction-limited beam with a peak pulsed output power of ~ 0.4 W from wide ridges (~ 21 µm) [3] . Alternatively, GCSE devices designed to operate in an antisymmetric mode can exhibit a single-lobe beam by using a central π-phaseshift in the gratings [4] . Here we show that 4.6 µm-emitting GCSE QCLs with a central π-phaseshift can be designed to solely operate in an antisymmetric mode for high CW output power, single-lobed beam operation, while maintaining strong intermodal discrimination over a wide range in grating duty cycle.

A ray optics (RO) technique utilizing diffraction grating theory and a transfer matrix method is used to derive a closed form expression for the 1st-order distributed feedback coupling coefficient in practical quantum cascade laser structures. Values of the coupling coefficient obtained using a full-wave finite element numerical method (COMSOL Multiphysics) are in good agreement with those obtained using the RO-derived expression.

Five-element phase-locked arrays of 4.7 μ m-emitting quantum cascade lasers are demonstrated which operate either in a near-diffraction-limited (D.L.) beam to 3.6 W peak pulsed power or in a narrow beam (< 3.5 × D.L.) up to 6.1 W peak pulsed power. Devices are fabricated by a two-step MOCVD process and operate predominantly in an in-phase array mode, in agreement with design-simulation studies. Analysis based on the actual device dimensions indicate that near-resonant leaky-wave coupling occurs. Scaling to a larger number of array elements and optimization for resonant operation is expected to lead to further increases in output power while maintaining high beam quality.

Endoscopic skull base surgery has developed rapidly over the last decade, in large part because of the expanding armamentarium of endoscopic repair techniques. This article reviews the available technologies and techniques, including vascularized and nonvascularized flaps, synthetic grafts, sealants and glues, and multilayer reconstruction. Understanding which of these repair methods is appropriate and under what circumstances is paramount to achieving success in this challenging but rewarding field. A graduated approach to skull base reconstruction is presented to provide a systematic framework to guide selection of repair technique to ensure a successful outcome while minimizing morbidity for the patient.

Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) offer a pathway towards realizing watt-range, surface-emitted output powers in the mid-infrared spectral region with high beam quality. Previously we have reported wide-ridge GCSE QCLs which employed metal/semiconductor, 2nd-order distributed feedback (DFB) gratings with distributed Bragg reflector (DBR) terminations. We report here on the lasing characteristics of narrow-ridge (~7 μm-wide) GCSE devices, which employ the STA-RE-type active-region design, for obtaining single-spatial-mode both laterally and longitudinally. The QCL structure was grown using Metalorganic Chemical Vapor Deposition (MOCVD) and the grating was defined using a combination of e-beam lithography patterning and wet-chemical etching, and the ridge (~7 μm) was dry-etched. The total length of the DFB + DBR regions is 5.1 mm, and was electrically isolated in the DBR regions by employing AlOx. Due to resonant coupling of the guided light to the antisymmetric surface-plasmon modes of the 2nd-order grating, the antisymmetric (A) modes are strongly absorbed; thus, allowing for the symmetric (S) mode to be favored to lase. Initial devices have demonstrated maximum pulse output power from the surface of ~150 mW at 4.88 μm, with only ~10% power emitted from the edge facets. An anti-reflective (AR) coating of a quarter-wavelength Y2O3 layer was applied on the emission window, drastically improving the far-field beam pattern, that resulting in a central, near-diffraction-limited single-lobe beam pattern. COMSOL simulations were performed to further optimize the SE-base design for high CW performance. Parameter sweeps of cladding-layer thickness, grating height, and grating duty cycle were performed, which identified design tradeoffs for the various structural parameters.

Quantum cascade lasers (QCLs) employ intersubband transitions between conduction-band (CB) energy states in multi-quantum-well (MQW) structures, carrier tunneling between adjacent MQW stages, and coherent-light emission from multiple (30–50) stages. Unlike interband-transition semiconductor lasers, QCLs are not affected by Auger recombination in the mid-infrared wavelength range (λ= 3–20 μm); thus, allowing them to readily reach lasing at room temperature (RT). However, using multiple stages leads to high voltages (≥ 10 V) that significantly decrease the wallplug efficiency, η wp . Thus, although pulsed RT operation was obtained in 1996, it took until 2002 to achieve CW RT operation and until 2008 to obtain 1 W CW power.1

Phase-locked array of diode lasers is an attractive way to achieve multi-Watt power single-mode operation. Theoretical analysis of the optical modes of planarized phase-locked quantum cascade laser arrays (QCLA) emitting at 4.8 pm was performed in [1], [2]. These high-index-contract photonic crystal (HC-PC) structures allow global coupling between all array elements. Our numerical modelling predicts that even in the presence of strong thermal lensing under CW operation, 3-element QCLA can achieve more than 1W power.

Errors have been found in subsection 3.2 (i.e., in page 1384) of our paper [Opt. Mater. Express 8, 1378 (2018) 10.1364/OME.8.001378] as far as the identification of the grown layers within one period, for the quantum cascade laser structure shown in Figure 1(a). The correct text is as follows.

Metamorphic buffer layers (MBLs) were used as substrates with lattice constants selected for designing and fabricating intersubband transition sources involving strained superlattices (SLs) such as Quantum Cascade Lasers (QCLs). Chemical mechanical planarization (CMP) was used to prepare the InGaAs-based MBLs for epitaxial growth. Indium enrichment of the InGaAs layer on the MBL surfaces was observed when annealed at the regrowth temperatures. This post-anneal enhancement was eliminated by including a wet-etch treatment after CMP, which results in an epi-ready surface for regrowth. Ten stages of a QCL core region structure, designed for emission at a 3.4 μm wavelength are regrown on a surface-optimized MBL. Such structures exhibit well defined X-ray diffraction pendellosung fringes, and transmission electron microscopy confirms planar superlattice interfaces with layer thicknesses that are in good agreement with the design target.

High-CW-power (i.e., watt-range), mid-infrared (IR) (λ= 3–15 μm) quantum cascade lasers (QCLs) are needed for a wide range of applications, from remote sensing to infrared countermeasures. Many of these applications require single-spatial-mode operation with beam stability to multi-watt-range output powers. Scaling the CW single-mode output power requires optimization of the QCL active region, as well as device architectures allowing for scaling the lateral width. Single-element, edge-emitting QCLs operating in the 4.5–5.0 μm wavelength region generally requires a relatively narrow element width (∼ 5 microns) to maintain stable, single-spatial-mode CW operation up to the 1.5–2.0 watt-range output power levels. Larger width devices operate to high CW output powers (∼ 5W), but suffer from multi-mode operation as well as beam instabilities with drive current [1].

Mid-infrared quantum cascade lasers (QCLs) are a growing industry and are being introduced into the marketplace primarily for low-output-power operation. High-power (> 1 W) continuous wave (CW) QCLs are expected to become commercially viable as they become more efficient and the necessary thermal dissipation requirements are achieved. However, there is a relative lack of knowledge regarding the degradation and failure mechanisms of QCLs under high power CW operation [1,2]. QCLs are expected to have different degradation and failure modes than diode lasers, because nonradiative recombination at the facets is not an issue. To push towards wider commercial adoption, lifetesting and failure analyses of high-power QCLs are performed. Previously reported QCL lifetests were carried out at relatively low output powers (∼200 mW) and revealed activation energies as high as 1.2 eV, with the primary failure mechanism being reported to be oxidation of the front facet [3]. Here, we report on initial constant-power lifetest studies of QCLs emitting at λ ∼ 5.0 μm and operating at 5 times the output power previously reported (i.e. at 1W CW). To mitigate the failure mechanism previously observed and improve device output, both facets have coatings: a high-reflectivity (HR) back-facet coating and a 14% low-reflectivity (LR) front-facet coating. The devices are mounted epi-side-down on copper with indium and tested under constant-power operation in a controlled environment.

A theoretical analysis of the optical and thermal characteristics of planarized phase-locked quantum cascade laser (QCL) arrays emitting at 4.8 μm was performed. Large aperture seven-element designs are established with a reasonably large process window for achieving single in-phase-mode operation. Full-wave optical simulations of these high-index contrast photonic crystal devices were coupled with 2-D heat flow analysis to investigate the influence of thermal lensing on modal behavior. Self-focusing under thermally induced index variations across the array are expected to ultimately limit the single-mode operational range. Anti-resonant reflective-optical waveguide terminations for three-element arrays can decrease the in-phase mode threshold-current density, improve discrimination against array modes composed of coupled first-order element modes, and improve the in-phase-mode near-field uniformity under CW operation.

Carrier-leakage suppression and fast carrier extraction allow quantum cascade lasers to reach internal efficiencies close to fundamental limits (∼ 90 %). Then, CW wallplug efficiencies > 40 % and powers > 10 W become possible.

We have integrated a family of innovative technologies with an aligned set of properties into Tunable Drug Conjugates (TDCs). TDCs are made up of a targeting moiety (e.g. small molecules, peptides, antibodies or antibody fragments), combined with our proprietary Silicon-based linkers (SiLinkers) and novel Payload Cassette (PC) designs which allow for delivery of multiple payloads, preferentially Conditionally Active Payloads (CAPs). CAPs are cytotoxic moieties which cannot readily permeate into normal cells due to their charged state at physiological pH of 7.4; however, at the more acidic pH of the endosome or the tumor microenvironment, the charge is neutralized enabling the CAP to readily permeate into and accumulate within the cancer cells. Our goal is to establish a beneficial Therapeutic Index (TI) and dosing flexibility by creating TDCs around a rapid payload release/rapid systemic clearance approach. Therefore, SiLinker/CAP constructs are designed to concentrate payload in the targeted tumor cell and associated tumor microenvironment while minimizing systemic payload release and rapidly clearing the parent TDC. Folate Receptor alpha (FRα) is overexpressed in multiple cancers, most notably, ovarian, endometrial, and NSCLC. Our optimized FRα-targeting TDCs use folic acid as the ligand and deliver various triple- and hexa-CAP cassettes. The various CAPs were selected from different target classes in order to allow for optimized treatment of different cancer types. We will present comparative cellular data, in vivo xenograft studies in KB, OV90 and IGROV1 models, as well as DMPK parameters of our lead FRα-TDCs. Using our triple- and hexa-PCs, we have achieved cures in in vivo xenograft studies which were durable and lasted even after treatment was stopped. We also demonstrate that in vivo our hexa-PC shows superior efficacy compared to our triple-PC in the moderate FRα expressing models. Based on our data, we believe that the combined properties of our innovative CAP-TDCs and rapid payload release/rapid systemic clearance approach will further increase TI, differentiate from other Drug Conjugates, and ultimately provide a compelling addition to existing Drug Conjugate technologies. Citation Format: Sara C. Sigler, Vinayak Gupta, Hanh N. Nguyen, Michael K. Rood, Jutta Wanner, Doug S. Werner. Optimization of folate receptor alpha-targeting tunable drug conjugates [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 226.

Implementation of the step-taper active-region (STA) design to 8-9 μm-emitting quantum cascade lasers (QCLs) has resulted in both high T0 and T1 values: 220 K and 665 K, and short lower-level lifetimes: 0.12 ps. In turn, the internal differential efficiency ηid, which is the product of the injection efficiency and the differential laser-transition efficiency, reaches values as high as 86 % for both 8.4 μm- and 8.8 μm-emitting QCLs. Such ηid values are 30-50% higher than those obtained from conventional QCLs emitting in the 7-11 μm wavelength range. Achieving both carrier-leakage suppression and miniband-like carrier extraction in mid-infrared (IR) QCLs leads to ηid values close to the fundamental limit of ~ 90 %. In turn, the currently employed fundamental wallplug-efficiency limits over the mid-IR wavelength range have to be increased by ~ 34 % (e.g., the wallplug-efficiency limit at λ= 4.6 μm increases from 29 % to 39 %). Preliminary results from STA-type 4.8-5.0 μm-emitting QCLs include 1.5 W CW operation, and 77 % internal differential efficiency; that is, 30-50% higher than the ηid values obtained from conventional 4.0-6.5μm-emitting QCLs.

Narrow beam (3.2 × D.L. FWHM) is demonstrated up to 5.85 W pulsed output power from a five-element phase-locked array of 4.7 μm-emitting quantum cascade lasers. Devices are fabricated by a two-step MOCVD process and operate predominately in an in-phase array mode, in agreement with design simulation studies.

Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) are demonstrated with high-power, single-lobe surface emission. A 2nd-order Au-semiconductor distributed-feedback (DFB)/ distributed-Bragg-reflector (DBR) grating is used for feedback and out-coupling. The DFB and DBR grating regions are 2.55 mm- and 1.28 mm-long, respectively, for a total grating length of 5.1 mm. The lasers are designed to operate in a symmetric longitudinal mode by causing resonant coupling of the guided optical mode to the antisymmetric surface-plasmon modes of the 2nd-order metal/semiconductor grating. In turn, the antisymmetric longitudinal modes are strongly absorbed by the metal in the grating, causing the symmetric longitudinal mode to be favored to lase, which produces a single lobe beam over a grating duty-cycle range of 36-41 %. Simulations indicate that the symmetric mode is always favored to lase, independent of the random phase of residual reflections from the device’s cleaved ends. Peak pulsed output powers of ~ 0.4 W were measured with single-lobe, single-mode operation near 4.75 μm.

Carboxylesterases (CEs) are ubiquitous enzymes responsible for the detoxification of xenobiotics. In humans, substrates for these enzymes are far-ranging, and include the street drug heroin and the anticancer agent irinotecan. Hence, their ability to bind and metabolize substrates is of broad interest to biomedical science. In this study, we focused our attention on dynamic motions of a CE from B. subtilis (pnbCE), with emphasis on the question of what individual domains of the enzyme might contribute to its catalytic activity. We used a 10 ns all-atom molecular dynamics simulation, normal mode calculations, and enzyme kinetics to understand catalytic consequences of structural changes within this enzyme. Our results shed light on how molecular motions are coupled with catalysis. During molecular dynamics, we observed a distinct C-C bond rotation between two conformations of Glu310. Such a bond rotation would alternately facilitate and impede protonation of the active site His399 and act as a mechanism by which the enzyme alternates between its active and inactive conformation. Our normal mode results demonstrate that the distinct low-frequency motions of two loops in pnbCE, coil_5 and coil_21, are important in substrate conversion and seal the active site. Mutant CEs lacking these external loops show significantly reduced rates of substrate conversion, suggesting this sealing motion prevents escape of substrate. Overall, the results of our studies give new insight into the structure-function relationship of CEs and have implications for the entire family of α/β fold family of hydrolases, of which this CE is a member.

Thermal profiles of a single-element quantum cascade laser (QCL) and a five-element QCL array at different bias currents, under quasi-continuous-wave (QCW) conditions, are obtained using the charge-coupled device (CCD)-based thermoreflectance imaging technique. Peak temperature changes of 55 K and 105 K are measured on the single-element QCL (operating at 1.2 A) and the central element of the QCL array (operating at 4.2 A), respectively. The average facet temperature of the single QCL device shows a linear relationship with the dissipated power, indicating an effective thermal resistance of Rth = 3.0 ± 0.2 K/W (7%) for the device. The thermal transient behavior of the single QCL device, in response to a 35 μs-wide heating pulse, is also measured. From the transient curve, an effective thermal time constant of τth = 9.5 ± 0.4 μs (4%) is obtained. Experimental results are compared to the results obtained from heat-transfer models for both the single-element and array devices. Thermal profiles show a thermal lensing effect at the facet of the single-element QCL. In the array device, a more pronounced heating is observed at the center of the device while the temperature gradually decreases away from the central element.

Metalorganic chemical vapor deposition (MOCVD) growth of InP‐based quantum cascade laser (QCL) structures on a Si (001) substrate is demonstrated by employing a metamorphic InP buffer layer with InAs/InP quantum dots as dislocation filters. Calibration samples consist of a strain‐compensated 11.98 nm In0.365Al0.635As/14.8 nm In0.64Ga0.36As superlattice (SL) structure as well as 5‐stages of the λ ≈ 4.8 µm QCL active region, which are grown atop the metamorphic buffer and are used to assess the structural properties of the SL through high‐resolution X‐ray diffraction and high‐resolution transmission electron microscopy. Full QCL structures with 40‐stage active region are fabricated into edge‐emitting ridge‐waveguide structures and demonstrate low temperature electroluminescence with a FWHM of 48.6 meV.

The step-taper active-region (STA) design concept is implemented for ~5.0 μm-emitting quantum cascade lasers (QCLs) grown by metal-organic chemical vapor deposition (MOCVD). Carrier-leakage suppression yields high characteristic temperatures for the threshold-current density Jth, T0, and for the slope efficiency ηsl, T1: 226 K and 653 K. Resonant-tunneling extraction from the lower level results in miniband-like extraction. In turn, the internal efficiency ηi is found, from a variable mirror-loss study, to be ~77%; thus approaching the ~90% upper limit, when employing only inelastic scattering. Considering interface-roughness and alloy-disorder scattering, the transition efficiency reaches values of ~95%. Then, the injection efficiency is ~81%, and, for λ = 4.6 μm, the wallplug-efficiency ηwp upper limit reaches 41.2%. Results include 4.2 W/A single-facet ηsl and 0.96 kA/cm2Jth values. Buried-heterostructure (BH) QCLs provide single-facet 2.6 W continuous-wave (CW) power and 12% CW ηwp. Optimized 8 μm-emitting, STA-design QCLs provide 2 W/A ηsl, and 1.1 kA/cm2Jth; and BH devices yield single-facet 1 W CW power and 6% CW ηwp.

Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) have been studied since 2000 [1] and generally operate in a two-lobe beam pattern [1,2]. Recently, single-lobe surface emission has been reported either from asymmetrically-coated devices [3] or from chirped-grating, ring-cavity devices [4], but at powers ≤ 0.1 W. Here we present the implementation of a novel concept for high-power, single-lobe surface emission, which employs metal-semiconductor, 2nd-order distributed feedback (DFB) gratings [5]. Initial devices demonstrate ∼ 0.4 W single-lobe, single-mode power from 4.75 µm-emitting GCSE QCLs.

On-chip resonant leaky-wave coupling of quantum cascade lasers (QCLs) emitting at 8.36 μm has been realized by selective regrowth of interelement layers in curved trenches, defined by dry and wet etching. The fabricated structure provides large index steps (Δn = 0.10) between antiguided-array element and interelement regions. In-phase-mode operation to 5.5 W front-facet emitted power in a near-diffraction-limited far-field beam pattern, with 4.5 W in the main lobe, is demonstrated. A refined fabrication process has been developed to produce phased-locked antiguided arrays of QCLs with planar geometry. The main fabrication steps in this process include non-selective regrowth of Fe:InP in interelement trenches, defined by inductive-coupled plasma (ICP) etching, a chemical polishing (CP) step to planarize the surface, non-selective regrowth of interelement layers, ICP selective etching of interelement layers, and non-selective regrowth of InP cladding layer followed by another CP step to form the element regions. This new process results in planar InGaAs/InP interelement regions, which allows for significantly improved control over the array geometry and the dimensions of element and interelement regions. Such a planar process is highly desirable to realize shorter emitting wavelength (4.6 μm) arrays, where fabrication tolerance for single-mode operation are tighter compared to 8 μm-emitting devices.

Three-dimensional above-threshold analyses of high-index-contrast (HC) photonic-crystal (PC) quantum-cascade-laser arrays (QCLA) structures, for operation at watt-range CW powers in a single spatial mode, have been performed. Threeelement HC-PC structures are formed by alternating active- antiguided and passive-guided regions along with respective metal-electrode spatial profiling. The 3-D numerical code takes into account absorption and edge-radiation losses. Rigrod’s approximation is used for the gain. The specific feature of QCLA is that only the transverse component of the magnetic field sees the gain. Results of above-threshold laser modeling in various approximate versions of laser-cavity description are compared with the results of linear, full-vectorial modeling by using the COMSOL package. Additionally, modal gains for several higher-order optical modes, on a ‘frozen gain background’ produced by the fundamental-mode, are computed by the Arnoldi algorithm. The gain spatial-hole burning effect results in growth of the competing modes’ gain with drive current. Approaching the lasing threshold for a competing higher-order mode sets a limit on the single-mode operation range. The modal structure and stability are studied over a wide range in the variation of the inter-element widths. Numerical analyses predict that the proper choice of construction parameters ensures stable single-mode operation at high drive levels above threshold. The output power from a single- mode operated QCLA at a wavelength of 4.7 μm is predicted to be available at multi-watt levels, although this power may be restricted by thermal effects.

In immortal cells, the existence of a mechanism for the maintenance of telomere length is critical. In most cases this is achieved by the reactivation of telomerase, a cellular reverse transcriptase that prevents telomere shortening. Here we report that the telomerase gene (hTERT) promoter is up-regulated during transmission of human T-cell lymphotropic virus type-I (HTLV-I) to primary T cells in vitro and in ex vivo adult T-cell leukemia/lymphoma (ATLL) samples, but not asymptomatic carriers. Although Tax impaired induction of human telomerase reverse transcriptase (hTERT) mRNA in response to mitogenic stimulation, transduction of Tax into primary lymphocytes was sufficient to activate and maintain telomerase expression and telomere length when cultured in the absence of any exogenous stimulation. Transient transfection assays revealed that Tax stimulates the hTERT promoter through the nuclear factor κB (NF-κB) pathway. Consistently, Tax mutants inactive for NF-κB activation could not activate the hTERT or sustain telomere length in transduced primary lymphocytes. Analysis of the hTERT promoter occupancy in vivo using chromatin immunoprecipitation assays suggested that an increased binding of c-Myc and Sp1 is involved in the NF-κB–mediated activation of the hTERT promoter. This study establishes the role of Tax in regulation of telomerase expression, which may cooperate with other functions of Tax to promote HTLV-I–associated adult T-cell leukemia.

Quantum cascade lasers (QCLs) that employ metamorphic buffer layers as substrates of variable lattice constant have been designed for emission in the 3.0- to 3.5-μm wavelength range. Theoretical analysis of the active-region (AR) energy band structure, while using an 8-band k•p model, reveals that one can achieve both effective carrier-leakage suppression as well as fast carrier extraction in QCL structures of relatively low strain. Significantly lower indium-content quantum wells (QWs) can be employed for the AR compared to QWs employed for conventional short-wavelength QCL structures grown on InP, which, in turn, is expected to eliminate carrier leakage to indirect-gap valleys (X, L). An analysis of thermo-optical characteristics for the complete device design indicates that high-Al-content AlInAs cladding layers are more effective for both optical confinement and thermal dissipation than InGaP cladding layers. An electroluminescence-spectrum full-width half-maximum linewidth of 54.6 meV is estimated from interface roughness scattering and, by considering both inelastic and elastic scattering, the threshold-current density for 3.39-μm-emitting, 3-mm-long back-facet-coated QCLs is projected to be 1.40 kA/cm2.

The modal characteristics of nonresonant five-element phase-locked arrays of 4.7-μm emitting quantum cascade lasers (QCLs) have been studied using spectrally resolved near- and far-field measurements and correlated with results of device simulation. Devices are fabricated by a two-step metal-organic chemical vapor deposition process and operate predominantly in an in-phase array mode near threshold, although become multimode at higher drive levels. The wide spectral bandwidth of the QCL’s core region is found to be a factor in promoting multispatial-mode operation at high drive levels above threshold. An optimized resonant-array design is identified to allow sole in-phase array-mode operation to high drive levels above threshold, and indicates that for phase-locked laser arrays full spatial coherence to high output powers does not require full temporal coherence.

Cementifying fibromas are rare fibro-osseous tumors that arise from the periodontal ligament. These tumors are usually small, asymptomatic lesions noted on routine dental radiography, but they can develop into aggressive, expansile masses. The authors report the case of a 12-year-old boy with a tumor involving the maxillary, ethmoid, and frontal sinuses that extended to the right orbit, causing proptosis and disfigurement of the right side of his face. Removal of the tumor with facial reconstruction resulted in significant improvement of vision, despite long-standing disc edema and tension on the optic nerve. On histopathologic examination the lesion was found to be a cementifying fibroma.

Grating-coupled surface-emitting (GCSE) lasers generally operate with a double-lobed far-field beam pattern along the cavity-length direction, which is a result of lasing being favored in the antisymmetric grating mode. We experimentally demonstrate a GCSE quantum-cascade laser design allowing high-power, nearly single-lobed surface emission parallel to the longitudinal cavity. A 2nd-order Au-semiconductor distributed-feedback (DFB)/distributed-Bragg-reflector (DBR) grating is used for feedback and out-coupling. The DFB and DBR grating regions are 2.55 mm- and 1.28 mm-long, respectively, for a total grating length of 5.1 mm. The lasers are designed to operate in a symmetric (longitudinal) grating mode by causing resonant coupling of the guided optical mode to the antisymmetric surface-plasmon modes of the 2nd-order metal/semiconductor grating. Then, the antisymmetric modes are strongly absorbed by the metal in the grating, causing the symmetric mode to be favored to lase, which, in turn, produces a single-lobed beam over a range of grating duty-cycle values of 36%–41%. Simulations indicate that the symmetric mode is always favored to lase, independent of the random phase of reflections from the device's cleaved ends. Peak pulsed output powers of ∼0.4 W were measured with nearly single-lobe beam-pattern (in the longitudinal direction), single-spatial-mode operation near 4.75 μm wavelength. Far-field measurements confirm a diffraction-limited beam pattern, in agreement with simulations, for a source-to-detector separation of 2 m.

Cadmium chloride at 0.25 µg/ml inhibited the proliferation of bovine cor-neal endothelial cells in vitro 24 hr after treatment during the preconfluent stage. The growth curve was significantly lowered with a slight increase in nuclei/mm2 after 1 week. The cadmium-treated cells at 120 hr became elongated and spindle-shaped. This morphologic change was more conspicuous at 168 hr. When cadmium-treated cells were treated simultaneously with 0.25 or 1 µg/ml zinc chloride, their growth curves were significantly elevated, which suggests that zinc reduces cadmium toxicity on this cell type. At 168 hr, however, these zinc-ameliorated cells were morphologically different from the control cells and the growth curves were statistically lower than the control. The present results suggest that the preconfluent model of bovine corneal endothelial cells can be used as a sensitive toxicity evaluation test based on changes in the growth curve of the cells.

Resonant coupling of the transverse-magnetic polarized (guided) optical mode of a quantum-cascade laser (QCL) to the antisymmetric surface-plasmon modes of 2nd-order distributed-feedback (DFB) metal/semiconductor gratings results in strong antisymmetric-mode absorption. In turn, lasing in the symmetric mode, that is, surface emission in a single-lobe far-field beam pattern, is strongly favored over controllable ranges in grating duty cycle and tooth height. By using core-region characteristics of a published 4.6 μm-emitting QCL, grating-coupled surface-emitting (SE) QCLs are analyzed and optimized for highly efficient single-lobe operation. For infinite-length devices, it is found that when the antisymmetric mode is resonantly absorbed, the symmetric mode has negligible absorption loss (∼0.1 cm−1) while still being efficiently outcoupled, through the substrate, by the DFB grating. For finite-length devices, 2nd-order distributed Bragg reflector (DBR) gratings are used on both sides of the DFB grating to prevent uncontrolled reflections from cleaved facets. Equations for the threshold-current density and the differential quantum efficiency of SE DFB/DBR QCLs are derived. For 7 mm-long, 8.0 μm-wide, 4.6 μm-emitting devices, with an Ag/InP grating of ∼39% duty cycle, and ∼0.22 μm tooth height, threshold currents as low as 0.45 A are projected. Based on experimentally obtained internal efficiency values from high-performance QCLs, slope efficiencies as high as 3.4 W/A are projected; thus, offering a solution for watt-range, single-lobe CW operation from SE, mid-infrared QCLs.

A 44-year-old immunosuppressed man developed initial symptoms of intermittent irritation of the left eye three months after cardiac transplantation. Symptoms increased, with decreased vision, photophobia, and lacrimation. Slit lamp examination showed slightly raised, swollen, grayish epithelium in a broad multibranching dendritic pattern associated with fine and medium punctate epithelial erosions that stained slightly with fluorescein. Histopathologic study of the corneal epithelial scraping demonstrated swollen epithelial cells with intranuclear and intracytoplasmic viral inclusions. Viral cultures manifested a cytopathic pattern characteristic of cytomegalovirus 14 days after inoculation on human embryonic lung cells (MRC-5). Pretransplantation cytomegalovirus IgM and IgG serologic titers were negative (less than 1:16 for IgG, no IgM noted) until the onset of symptoms. Subsequently, IgM titers rose against cytomegalovirus consistent with concurrent infection.

The first measurement of the elementary process $\mu^- p \rightarrow \nu_{\mu} n \gamma$ is reported. A photon pair spectrometer was used to measure the partial branching ratio ($2.10 \pm 0.22) \times 10^{-8}$ for photons of k > 60 MeV. The value of the weak pseudoscalar coupling constant determined from the partial branching ratio is $g_p(q^{2}=-0.88m_{\mu}^2) = (9.8 \pm 0.7 \pm 0.3) \cdot g_a(0)$, where the first error is the quadrature sum of statistical and systematic uncertainties and the second error is due to the uncertainty in $\lambda_{op}$, the decay rate of the ortho to para $p \mu p$ molecule. This value of g_p is $\sim$1.5 times the prediction of PCAC and pion-pole dominance., Comment: 13 pages, RevTeX type, 3 figures (encapsulated postscript), submitted to Phys. Rev. Lett

We report the observation of the elementary process {mu}{sup {minus}}{ital p}{r_arrow}{ital n}{nu}{sub {mu}}{gamma} at TRIUMF. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Healon, Viscoat and Amvisc Plus (Amvisc+) are commercial preparations containing hyaluronic acids of different molecular weights and viscosities. Cytotoxicity of these preparations to the corneal endothelium may be a factor in postsurgical recovery of the cornea. Using different in vitro models of bovine corneal endothelial cells (BCEC), three experiments to compare the possible detrimental effects of these viscoelastic agents were designed. In the confluent model, confluent BCEC were exposed to viscoelastic agents and the control to Balanced Salt Solution Plus (BSS+) for one hour and the nuclear density (nuclei/mm2) was assessed at 24 and 168 hours. At both times, the BCEC exposed to Healon showed the highest nuclear densities. In the preconfluent model, BCEC were treated for one hour at 48 hours post-seeding. The nuclear density of the BCEC was assessed at 24 hours. The BCEC exposed to Healon showed the highest density, followed by those exposed to Amvisc+ and then Viscoat. In the proliferation model, BCEC were cultured in media containing 1%, 5%, and 10% viscoelastic agents. The growth curves based on nuclear densities at 0, 24, 72, 120, and 168 hours in all treatment groups did not differ significantly from the control. The results indicate that the undiluted Healon was significantly less toxic in the preconfluent and confluent BCEC models.

The development of cyclophosphamide-induced pulmonary lesions over a 1-year period was studied in mice. Male BALB/c mice received a single intraperitoneal injection of 100 mg/kg of cyclophosphamide. Within 3 weeks there were scattered foci of intraalveolar foamy macrophages. With time, these foci increased in size and, 1 year later, occupied large areas in all lung lobes. There was also diffuse interstitial fibrosis. Chemical determination done 3, 12, 24, and 52 weeks after cyclophosphamide showed that lungs of animals treated with cyclophosphamide had significantly more hydroxyproline per lung than controls. One year after cyclophosphamide pressure-volume curves measured in vivo were shifted down and to the right and total lung volumes were decreased. A single injection of cyclophosphamide produced an irreversible and progressive pulmonary lesion.

This paper investigates the reliability of the upper cervical X-ray marking procedure. The measurement chosen to be examined was atlas laterality. Twenty X-rays were marked by three experienced upper cervical practitioners for the inter-examiner reliability testing, and two of the doctors marked 10 of the films twice for intra-examiner testing. The average measurement for the 60 markings was 1.83 degrees. The average difference between the 3 doctors was 1.05 degrees. The range of error is 57 percent of the average measurement. With interval agreements, it is shown that at the point where all 3 doctors agree 80 percent of the time, the range of error is 2 degrees, this being over 100 percent of the average measurement. The range of error percentages for the 2 intra-examiner tests were 41 percent and 71 percent. It is concluded that with ranges of error of this magnitude any measured differences produced using this system will be just as likely to be from marking error as from actual atlas position change. This should be considered by practitioners who consider these measurements to be objective evidence for demonstrating the results of chiropractic adjustments.