Short Constriction Research Articles

Quantized conductance in hybrid split-gate arrays of superconducting quantum point contacts with semiconducting two-dimensional electron systems

A quantum point contact (QPC)—a constriction in a semiconducting two-dimensional electron system with a quantized conductance—is a building block of novel spintronic and topological electronic circuits. QPCs can also be used as readout electronics, charge sensors, or switches in quantum nanocircuits. A short and impurity-free constriction with superconducting contacts is a Cooper-pair QPC analogue known as a superconducting quantum point contact (SQPC). The technological development of such quantum devices has been prolonged due to the challenges of maintaining their geometrical requirement and near-unity superconductor-semiconductor interface transparency. Here, we develop advanced nanofabrication, material and device engineering techniques and report on an innovative realization of nanoscale hybrid SQPC arrays with split gate technology in semiconducting 2D electron systems. We exploit the special gate tunability of the quantum wells, and demonstrate the first experimental observation of conductance quantization in hybrid InGaAs-Nb SQPCs. We observe reproducible quantized conductance at zero magnetic fields in multiple quantum nanodevices fabricated in a single chip and systematically investigate the quantum transport of SQPCs at low and high magnetic fields for their potential applications in quantum metrology, for extremely accurate voltage standards, and fault-tolerant quantum technologies. Published by the American Physical Society 2024

A new species of Thrypticus Gerstaecker, 864 and new records of Dolichopodidae (Diptera) from Turkey

A new long-legged fly species, Thrypticus ozerovi Grichanov sp. nov., from the Antalya Province of Turkey is described and illustrated. The new species appears to be close in habitus to the Turkish endemic T. caeruleus Naglis et Negrobov, 2020, differing from the latter in somewhat smaller body, yellow hind tibia and tarsomeres, with only tarsomere 5 brown; hypandrium relatively broad, without constriction, with arrow-like apex and distinct flexion at apex. Thrypticus caeruleus was described from Aydın and Muğla provinces with body length 1.7 mm, hind tibia and tarsomeres dark brown, hypandrium thin, nearly straight, parallel-sided in distal half, with short constriction in middle. In all, 29 species are recorded from the Antalya, Bolu, Burdur, Kayseri and Sakarya provinces. Six species of long-legged flies are reported from the country for the first time: Diaphorus deliquescens Loew, 1871, Dolichopus linearis Meigen, 1824, Dolichopus planitarsis Fallén, 1823, Gymnopternus silvestris (Pollet, 1991), Medetera media Parent, 1925 and Poecilobothrus annulitarsis Kazerani, Pollet, Khaghaninia, 2017. As a result, the dolichopodid species number in Turkey has increased to 230. It is supposed that the real number of Turkish species possibly may reach 400 to 500 species, based on the faunal richness of adjacent countries.

Numerical Study of the Time-Periodic Electroosmotic Flow of Viscoelastic Fluid through a Short Constriction Microchannel.

Electroosmotic flow (EOF) is of utmost significance due to its numerous practical uses in controlling flow at micro/nanoscales. In the present study, the time-periodic EOF of a viscoelastic fluid is statistically analyzed using a short 10:1 constriction microfluidic channel joining two reservoirs on either side. The flow is modeled using the Oldroyd-B (OB) model and the Poisson-Boltzmann model. The EOF of a highly concentrated polyacrylamide (PAA) aqueous solution is investigated under the combined effects of an alternating current (AC) electric field and a direct current (DC) electric field. Power-law degradation is visible in the energy spectra of the velocity fluctuations over a wide frequency range, pointing to the presence of elastic instabilities in the EOF. The energy-spectra curves of the velocity fluctuations under a DC electric field exhibit peaks primarily beneath 20 Hz, with the greatest peak being observed close to 6 Hz. When under both DC and AC electric fields, the energy spectra of the velocity fluctuations exhibit a peak at the same frequency as the AC electric field, and the highest peak is obtained when the frequency of the AC electric field is near 6 Hz. Additionally, the frequency of the AC electric field affects how quickly the viscoelastic EOF flows. Higher flow rates are obtained at relatively low frequencies compared to under the DC electric field, and the greatest flow rate is found close to 6 Hz. But as the frequency rises further, the flow rate falls. The flow rate falls to a level below the DC electric field when the frequency is sufficiently high.

Droplet breakup in the square microchannel with a short square constriction to generate slug flow

AbstractDroplet breakup in microconstrictions is an important phenomenon in industrial applications. This work aimed to investigate the droplet breakup in the square microchannel with a short square constriction to generate the slug flow, which drew little attention before. Mechanism analysis indicated that this breakup process included the shear‐force‐dominated, squeezing‐force‐dominated, and pinch‐off stages. Nonuniform daughter droplets were generated in the constriction with their interface restricted in the horizontal and perpendicular directions by the microchannel walls. The average relative deviation of the daughter droplet size was <30%, much lower than that for the breakup with the daughter droplet restricted only in one direction. An empirical equation with a deviation of <20% was provided to show the dependence of the daughter droplet size on the operation conditions. The comparison results suggested that the different restriction effects of microchannel wall on daughter droplets led to the different breakup mechanisms in different constrictions.

VP20.01: Altered course of umbilical‐portal‐DV complex in type‐2 DV‐systemic shunts: a cause of concern

Aim of the study was to evaluate the outcome of fetuses who showed the downward and upward displacement of umbilical-portal-DV complex in type-2 DV-systemic shunts as they have an association with Trisomy 21 and poor obstetric outcome. 1050 showing normal umbilical-portal-DV complex on the sagittal view of abdomen and seven patients with altered course of DV complex were included in the second trimester. Normal direction of DV complex (figure 1) seen in 1050 feti. Seven showed altered direction of DV complex. Four of these 7 feti showed downward displacement of DV complex with umbilical vein draining into IVC via a narrow channel (figure 2 a, b). Two of the four had Trisomy 21 and two had normal outcome. Three out of the seven feti showed upward displacement of DV complex with umbilical vein showing short constriction with aliasing before opening into the IVC and spectral Doppler showed triphasic flow as of ductus venosus (figure 3 a, b and c). One out of the three feti with upward displacement of DV had Trisomy 21 and the other had associated structural anomalies and opted for abortion and the third fetus had a normal outcome. All seven cases showed presence of Intrahepatic portal venous system (figure 4). Not only the presence DV but also the alteration in the direction of DV complex is important in type-2 DV-systemic shunts as they have an association with Trisomy 21 and poor outcome. Hence these patients need to be offered amniocentesis to establish chromosomal normalcy. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Biophysical Informatics Approach For Quantifying Phenotypic Heterogeneity In Cancer Cell Migration In Confined Microenvironments.

Cancer cell heterogeneity can manifest genetically and phenotypically. Bioinformatics methods have been used to analyze complex genomics and transcriptomics data, but have not been well-established for analyzing biophysical data of phenotypically heterogeneous tumor cells. Here, we take an informatics approach to analyze the biophysical data of MDA-MB-231 cells, a widely used breast cancer cell line, during their spontaneous migration through confined environments. Experimentally, we vary the constriction microchannel geometries (wide channel, short constriction, and long constriction) and apply drug treatments. We find that cells in the short constriction are similar in morphology to the cells in the wide channel. However, their fluorescence profiles are comparable to those in the long constriction. We demonstrate that the cell migratory phenotype is correlated more to mitochondria in a non-confined environment and more to actin in a confined environment. We demonstrate that the cells' migratory phenotypes are altered by ciliobrevin D, a dynein inhibitor, in both confined and non-confined environments. Overall, our approach elucidates phenotypic heterogeneity in cancer cells under confined microenvironments at single-cell resolution. Here, we apply a bioinformatics approach to a single cell invasion assay. We demonstrate that this method can determine distinctions in morphology, cytoskeletal activities, and mitochondrial activities under various geometric constraints and for cells of different speeds. Our approach can be readily adapted to various heterogeneity studies for different types of input biophysical data. In addition, this approach can be applied to studies related to biophysical changes due to differences in external stimuli, such as treatment effects on cellular and subcellular activities, at single-cell resolution. Finally, as similar bioinformatics methods have been widely applied in studies of genetic heterogeneity, biophysical information extracted using this approach can be analyzed together with the genetic data to relate genetic and phenotypic heterogeneity. The data that support the findings of this study are available from the corresponding author upon reasonable request. Supplementary data are available at Bioinformatics online.

Preparation of Mycobacterium smegmatis porin A (MspA) nanopores for single molecule sensing of nucleic acids.

Mycobacterium smegmatis porin A (MspA), possessing a short (~0.6 nm) and narrow (~1.2 nm) constriction that enables its high spatial resolution of sensing, has emerged as an optimum choice for nanopore sequencing and nano-reactive sensing. However, prepared MspA nanopores cannot be obtained from any commercial vendors. We here provide a highly simplified protocol for MspA preparation. The protocol yields ~10 mg fully oligomerized protein per liter of culture and is straightforward to follow. With the prepared MspA nanopores, discrimination of immobilized ssDNA oligonucleotides can be performed, which serves as a demo application to demonstrate core procedures of single molecule sensing using MspA. This method is also in principle compatible with all other MspA mutants, which might merit the need to develop a variety of MspA based nano-reactive sensors.

Two-dimensional material nanopores as biosensors: Recent progress based on computations and simulations

The passage of molecules through nanoscale pores is ubiquitous in biology. Inspired by this process, nanopore-based biosensors were proposed and have been widely used to probe, analyze or manipulate single biomolecules, such as DNA, RNA and protein. In a typical nanopore experiment, a thin membrane containing a nanoscale pore is used to separate two chambers of conducting electrolyte solution. As a transmembrane voltage bias is applied, analytes (such as DNA and RNA) in solution are driven through the nanopore, leading to changes in recorded ionic current traces. These changes are related to physical or chemical properties of the translocating molecules (analytes) such as structure, configuration and even identity. When DNA molecules are used as the analytes, the ionic current signal could be used to recognize individual bases, and in turn, the DNA sequence. The advantage of nanopore method for sequencing applications lies in its low cost, high efficiency, and ultra-long reads, because it eliminates the need for sample amplification and fluorescence labeling steps. In 1996, Kasianowicz et al. reported the first experiment of single-stranded DNA and RNA molecules passing through the biological pore α -hemolysin. In the following years, many other biological nanopores were used in order to obtain sufficient current and temporal resolution for single-molecule analysis. For example, the MspA nanopore, incorporated with Phi29 DNA polymerase, is able to read the sequence information of a single-stranded DNA (ssDNA) through measured ionic current. The relatively sharp and short constriction of the MspA nanopore compared to other biological nanopores (e.g., α -hemolysin) is regarded as the structural origin for its outstanding sensing ability. In particular, the length of the constriction in the MspA nanopore is equivalent to the distance between neighboring DNA bases in an ssDNA strand. This observation implied that a monolayer of typical two-dimensional (2D) materials such as graphene, with a thickness also equivalent to the spatial interval of DNA bases, is a promising candidate for DNA sequencing. On one hand, 2D material nanopores share inherent advantages of traditional solid-state nanopores, such as high stability over a broad range of temperature, pH and applied electric fields. On the other hand, the extreme thinness of 2D material nanopores is expected to deliver much higher spatial resolution than nanopores in traditional solid-state membranes such as silicon nitride and silicon oxide, which typically contain hundreds of bases in the pores simultaneously. Furthermore, the use of electrically conducting 2D materials offers the possibility to detect analytes at higher bandwidths, namely, by measuring transverse in-plane current through 2D material nanoribbons. During the development of nanopores sensors, computational tools such as first principle calculations and molecular dynamics simulations that can resolve molecular-scale interactions in nanopores have made significant contributions to this area in terms of prediction of novel detection approaches, optimization of device performance and explanation of experimental phenomena, etc. Here, with a standing point of computations and simulations, this review surveys the milestones in the area of 2D material nanopore-based biosensors, and the key experimental progress is also briefly discussed. Not limited to ionic current measurement, several other measurement methods such as transverse current in a nanoribbon and force traces during the pulling of biomolecules through nanopores are also introduced. This review further outlines key factors that restrict the performance of these sensors and discusses challenges and possible solutions. The key challenges include fast biomolecular translocation across nanopores and high noise levels in the recorded signal, etc. Finally, we provide a discussion on the future direction for the field, including the rational choice of 2D material, precise control over molecular movement inside nanopores as well as exploration of new applications.

Effect of Alternating Electric Current on Pulsation Mode of Rat Major Arteries In Situ.

In experiments on narcotized rats, the electrical potential and impedance of isolated segment of the right femoral and/or carotid artery were simultaneously recorded in situ via two extracellular nonpolarizable Ag/AgCl electrodes mounted along the arteries at the interelectrode distance of 4 mm. The active, passive, and intermediate pulsing modes of arterial segment were determined according to the phase relations between its electrical impedance and BP, which was simultaneously measured in the symmetrical part of the respective left artery and used to assess pressure in the examined segment. The study assessed the effect of amplitude (0.2-2.0 mA) of alternating probe current (100 kHz), which was used to measure the electrical impedance of arterial segment, on its pulsing mode. The pulsing mode determined at the initial minimal probe current of 0.2 mA was passive with out-of-phase pulsatile oscillations of electrical impedance and BP. After elevation of the probe current amplitude to maximal level of 2 mA, these oscillations became in-phase indicating transition of the arterial segment to active pulsing mode. This transition was accompanied by appearance of arterial voltage impulses synchronized with BP upstrokes and an 11-fold median increase in the peak-to-peak value of electrical impedance oscillations with the interdecile range of 7-15 (N=28). Under moderate amplitude of probe current (0.3-0.5 mA), the intermediate mode of arterial pulsing was observed featured by a delayed, weak, and short active constriction during BP front, which was insufficient to resist and counterbalance the dilating effect of rising BP. In this case, the pulsatile oscillations of electrical impedance were smaller than those observed in active or passive pulsing modes indicating a possibility to stabilize the arterial diameter during pulsatile oscillations of BP. The effect of alternating electric current on the mode of arterial pulsation is explained with electrical model of smooth muscle cell membrane reflecting the rectifying features of potassium channels and predicting membrane hyperpolarization in response to external alternating current passing across the cell. The visibilities of therapeutic neurotropic and angiotropic stimulation with alternating electric current are discussed.

Pressure of a viscous droplet squeezing through a short circular constriction: An analytical model

The model of a droplet squeezed through a narrow-constricted channel has many applications in pathology, chip/filter/membrane design, drug delivery, etc. Understanding the transient physics of the squeezing process is important in the design and optimization of many micro flow systems. However, available models often ignore the influence of droplet viscosity, and they usually feature low numerical efficiency by solving Navier-Stokes equations. In the present research, we developed a low-dimension analytical model to predict the pressure of squeezing a viscous droplet through a circular constricted channel with acceptable fidelity and low computational cost. Our approach is as follows. We first adapt the Hagen–Poiseuille law to predict the viscosity effect of droplet squeezing. Next, we obtain an analytical expression for the extra pressure caused by only the curvature change obtained. Finally, the general expression of squeezing pressure taking consideration of viscosity and surface tension is expressed. The analytical model we developed is in great agreement with the numerical solutions of the Navier-Stokes equation at a low Reynolds number and low capillary number. These findings have fundamental significance for future applications in engineering and industry.

A spike in mechanotransductive adenosine triphosphate release from red blood cells in microfluidic constrictions only occurs with rare donors.

ObjectiveWan et al (Proc Natl Acad Sci USA, 105, 2008, 16432) demonstrated that RBCs rapidly and transiently release a spike of 300% more ATP shortly downstream from a short microfluidic constriction where the cells experience a sudden increase in shear stress. More recent work by Cinar et al (Proc Natl Acad Sci USA, 112, 2015, 11783), however, yielded no evidence for a similar spike in ATP release downstream of the constriction. Our aim was to determine whether a transient spike in mechanotransduction is the typical response of RBCs to the sudden onset of increased shear.MethodsWe investigate ATP release downstream of a microfluidic constriction for 15 participants using a luciferase‐based photoluminescent assay.ResultsWhile we observe mechanotransductive ATP release from blood drawn from all donors, we find evidence of a spike in ATP concentration after the microfluidic constriction for only 2 of 15 participants. No clear trends in ATP release are found with respect to the magnitude of the applied shear stress, or to the gender, age, or physical activity (Baecke) index of the donor.ConclusionsIn aggregate, all data acquired to date suggest that a spike in mechanotransductive ATP due to a suddenly applied increase in shear stress occurs in blood drawn from only 14% of the population.

Coulomb-blockade peak spacing statistics of graphene quantum dots on SiO2

Extrinsic disorder strongly affects the performance of graphene-based quantum dots. The standard SiO2 substrate is generally considered to be one major factor besides edge-induced disorder. In this report we present the fabrication of lithographically defined quantum dots on SiO2 with short and narrow constrictions and different central island sizes. Low temperature transport measurements display distinct Coulomb-blockade peaks with amplitudes exceeding what is commonly observed experimentally. The analysis of the normalized Coulomb-blockade peak spacing shows a size dependence, which has not previously been observed for devices on SiO2. Furthermore, a quantitative comparison of the peak spacing distribution to the literature shows that one of the two devices compares favorably to a similar sized dot placed on hexagonal boron nitride, which is known to reduce the substrate disorder. Our findings suggest that the other sources of extrinsic disorder, such as lithography residues, may play an important role for the performance of large graphene quantum dots.

Simulation of methane adsorption and diffusion in a carbon nanotube channel

The effect of pore-connectivity feature of nanoporous carbons (NPCs) on the adsorptive and diffusive behavior of methane was studied by a simple constricted carbon nanotube (C-CNT) model using grand canonical Monte Carlo and molecular dynamics simulations. In spite of slight overprediction, C-CNT model can properly predict the adsorption of methane in some real NPCs. The calculated heat of adsorption was well agreed with the reported values for the hypothetical Schwarzite (C168) model and activated carbon. The obtained results show that the most preferred site for the adsorption of methane is the constricted region of the pore. The effect of constriction length on the methane uptake was studied at various pressures. It was shown that at low pressures the methane uptake increased with the length of constriction, while at high pressures the uptake is larger for short constriction. The diffusion coefficients of methane inside the C-CNT were calculated by very long MD simulations (220ns). The calculated methane diffusion coefficients in the C-CNT were one to two orders of magnitude lower than that in the regular slit pores as well as the straight carbon nanotubes. In addition, the diffusion coefficients in the C-CNT were in the same order of magnitude as in the constricted slit and virtual porous carbon (VPC) models of carbon pores. MD simulations revealed that the diffusivity decreases with the constriction length and approaches a constant value for large constriction length.

Nonlinear transport of the Wigner crystal in symmetric and asymmetric FET-like structures

When floating on a two-dimensional surface of superfluid 4He, electrons arrange themselves in two-dimensional crystalline structure known as Wigner crystal. In channels, the boundaries interfere the crystalline order and in case of very narrow channels one observes a quasi-one-dimensional (quasi-1D) Wigner crystal formed by just a few rows of electrons and, ultimately, one row in the “quantum wire” regime. Recently, the “quantum wire” regime was accessed experimentally [D.G. Rees, H. Totsuji, K. Kono, Phys. Rev. Lett. 108, 176801 (2012)] resulting in unusual transport phenomena such as, e.g., oscillations in the electron conductance. Using molecular dynamics simulations, we study the nonlinear transport of electrons in channels with various types of constrictions: single and multiple symmetric and asymmetric geometrical constrictions with varying width and length, and saddle-point-type potentials with varying gate voltage. In particular, we analyze the average particle velocity of the particles and the corresponding electron current versus the driving force or the gate voltage. We have revealed a significant difference in the dynamics for long and short constrictions: The oscillations of the average velocity of the particles for the systems with short constrictions exhibit a clear correlation with the transitions between the states with different numbers of rows of particles; on the other hand, for the systems with longer constrictions these oscillations are suppressed. The obtained results qualitatively agree with the experimental observations. Next, we propose a FET-like structure that consists of a channel with asymmetric constrictions. We show that applying a transverse bias results either in increase of the average particle velocity or in its suppression thus allowing a flexible control tool over the electron transport. The advantage of the asymmetric FET is that it does not have a gate and it allows an easy control of relatively large electron flow. Furthermore, the asymmetric device can be used for rectification of an ac-driven electron flow. Our results bring important insights into the dynamics of electrons floating on the surface of superfluid 4He in channels with constrictions and allow the effective control over the electron transport.

Single-File Transport of Classical Electrons on the Surface of Liquid Helium

Electrons trapped on the surface of liquid helium form a model two-dimensional system. Because the electron density is low (~ 109 cm-2) and the Coulomb interaction between the electrons is essentially unscreened, the system can be regarded as a classical analogue of the degenerate Fermi gas. Electrons on helium have therefore long been used to study many-body transport phenomena in two dimensions. Here we review recent experiments investigating the transport of electrons on helium through microscopic constrictions formed in microchannel devices. Two constriction geometries are studied; short saddle-point constrictions and long constrictions in which the length greatly exceeds the width. In both cases, the constriction width can be tuned electrostatically so that the electrons move in single file. As the width of the short constriction is increased, a periodic suppression of the electron current is observed due to pinning for commensurate states of the electron lattice. A related phenomenon is observed for the long constriction whereby the quasi-one-dimensional Wigner lattice exhibits reentrant melting as the number of electron chains increases. Our results demonstrate that electrons on helium are an ideal system in which to study many-body transport in the limit of single-file motion. [Formula: see text] Special Issue Comments: This article presents experimental results on the dynamics of classical electrons moving on the surface of liquid helium in narrow channels with constrictions, with a focus on the "quantum wire", i.e. single file, regime. This article is related to the Special Issue articles about advanced statistical properties in single file dynamics34 and the mathematical results on electron dynamics in liquid helium.35

Nonlinear Transport of the Wigner Crystal on Superfluid 4He in a Quasi-One-Dimensional Channel

We study transport properties of a Wigner crystal driven by an external force on the surface of superfluid 4 He , in the "quantum wire" regime, i.e. in the quasi-one-dimensional (quasi-1D) case when a typical width of the channel is comparable to the inter-electron separation. Utilizing molecular dynamics simulations, we investigate the electronic transport through the channels with different constrictions: (i) geometrical constrictions with varying shape and size, and (ii) a saddle-point potential with varying gate voltage. The average particle velocity has been calculated as a function of the driving force or gate voltage. We have revealed a significant difference in the dynamical behavior for long and short constrictions. In particular, we found that the oscillations of the average particle velocity in channels with short constrictions exhibit a clear correlation with the transitions between the states with different numbers of rows of particles in the constriction, while for channels with longer constrictions these oscillations are suppressed. The obtained results are in agreement with the recent experimental observations,1 and thus bring new important insights into the dynamics of electrons floating on the surface of superfluid 4 He in channels with constrictions. [Formula: see text] Special Issue Comments: This article presents results on the dynamics of electrons moving on the surface of liquid helium in narrow channels with constrictions, with a focus on the "quantum wire", i.e. single file, regime. This article is connected to the Special Issue articles about advanced statistical properties in single file dynamics39 and the experiments on liquid helium.40

Characterizing wave functions in graphene nanodevices: Electronic transport through ultrashort graphene constrictions on a boron nitride substrate

We present electronic transport measurements through short and narrow (30x30 nm) single layer graphene constrictions on a hexagonal boron nitride substrate. While the general observation of Coulomb-blockade is compatible with earlier work, the details are not: we show that the area on which charge is localized can be significantly larger than the area of the constriction, suggesting that the localized states responsible for Coulomb-blockade leak out into the graphene bulk. The high bulk mobility of graphene on hexagonal boron nitride, however, seems not consistent with the short bulk localization length required to see Coulomb-blockade. To explain these findings, charge must instead be primarily localized along the imperfect edges of the devices and extend along the edge outside of the constriction. In order to better understand the mechanisms, we compare the experimental findings with tight-binding simulations of such constrictions with disordered edges. Finally we discuss previous experiments in the light of these new findings.

Transport spectroscopy of a graphene quantum dot fabricated by atomic force microscope nanolithography

We report low-temperature transport spectroscopy of a graphene quantum dot fabricated by atomic force microscope nanolithography. The excellent spatial resolution of the atomic force microscope allows us to reliably fabricate quantum dots with short constrictions of less than 15 nm in length. Transport measurements demonstrate that the device is dominated by a single quantum dot over a wide gate range. The electron spin system of the quantum dot is investigated by applying an in-plane magnetic field. The results are consistent with a Landé g-factor ∼2 but no regular spin filling sequence is observed, most likely due to disorder.

AB0489 Correlation between vestibular function and raynaud’s phenomenon

BackgroundRaynaud’s phenomenon (RP) is caused by short term constriction of the small arteries in the extremities, usually the fingers. Primary Raynaud phenomenon is a benign condition caused by functional changes...

Suppression of pointing instability in quantum cascade lasers by transverse mode control

We report on a technique that serves to eliminate pointing instability in Quantum Cascade lasers by suppressing the propagation of higher order transverse modes within the laser cavity. This process, achieved via a short and lossy lateral constriction in the waveguide, only allows the fundamental mode to propagate. The beam pointing fluctuations of the modified devices are greatly reduced, with a 10-fold improvement in standard deviation, indicating a stable emitted beam. The far-field pattern has a Gaussian shape, and the slope efficiency of the received power on a 0.87 numerical aperture detector increases by ∼65%, without significant increase in threshold.