Narrow Divergence Research Articles

Polarized single-lobed surface emission in mid-infrared, photonic-crystal, quantum-cascade lasers

We report single-mode, surface-emitting, mid-IR, photonic-crystal (PhC), quantum-cascade lasers with linearly polarized and highly directional single-lobed emission. A metallic square-lattice photonic crystal with elliptical air holes and pi phase shift was used as the resonator. The 2D feedback coupling--necessary for the operation of the photonic-crystal resonator--is induced by the mismatch between the modes supported by metalized and nonmetalized regions and yields single-mode output with a side-mode suppression ratio >30 dB. The elliptical air holes modify the relative intensities of the TM field components (H(x) and H(y)) in the PhC plane, thus yielding linearly polarized emission. The pi phase shift allows the system to produce a single-lobed pattern in the far field with a narrow divergence angle (2.4 degrees x 1.8 degrees). The emission is perfectly orthogonal to the device surface, and the maximum operating temperature--still limited by the metallic ohmic losses--is 240 K.

Theoretical demonstration of DBR-assisted super-periodic photonic-crystal light-emitting diodes with narrow divergence angles

Highly-directive light-emitting diodes showing high extraction efficiency are designed and demonstrated based on a two-dimensional super-periodic photonic-crystal structure. With this specific design, a super-periodic photonic-crystal structure can generate a highly directional beam by satisfying the multiple-resonance conditions of distributed Bragg reflectors and the topmost slab. Dependence of the power efficiency on the thickness of the topmost slab and the etching depth of the photonic-crystal holes is then analyzed by the three-dimensional finite-difference time-domain method. From subsequent analyses, it has been determined that >80% of the extracted power could be funneled into a small divergence angle of 30°.

Optimization of a Tip with Carbon Nanofibers for Improved Field Emission Properties

To obtain a good field emission (FE) performance, the shape of a Pd/W tip substrate with carbon nanofibers is optimized. We succeeded in maximizing FE current by adjusting the apex angle of the tip. When the apex angle of the tip substrate is nearly 50°, a high FE efficiency and a narrow divergence emission angle for the convergence of the electron beam are obtained, which can be potentially used for the cathode of electrical devices with a low power consumption and a high FE efficiency.

Directional random-laser emission from Bragg gratings with irregular perturbation

Here we report the laser actions inside an active organic-inorganic grating with some irregular perturbation. In an optical excitation experiment, band-edge and random-laser emissions were both observed. The laser thresholds of the two laser actions are very close, which shows that random laser sometimes can operate with a threshold comparable to band-edge emission. Owing to the diffraction of the grating, directional emission with a narrow divergence angle was also obtained.

S0304-1-5 白色放射光による超細粒鋼の疲労き裂近傍のひずみ分布測定(回折法による材料評価)

For engineering components with cracks, it is very important to evaluate the reliability for fracture. The X-ray diffraction method is now widely used to measure non-destructively the loading and residual stresses in crystalline materials. Synchrotron radiation sources provide the X-rays with extremely high intensity as well as a narrow divergence. The high intensity X-rays with a narrow divergence enables stress measurements in a localized region. In the present study, strain distribution near the fatigue crack in SUF plate was measured by polychromatic X-ray from synchrotron radiation at SPring-8. The spatial resolution in the direction parallel to the crack propagation direction was 0.1 mm. The measured strain distribution was compared with that calculated by the FE analysis. The strain distribution measured at several applied stress levels agreed very well with the calculated results.

High-Brightness Quantum Well Tapered Lasers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> High-power quantum well lasers with high brightness in the spectral range between 650 nm and 1080 nm will be presented. Improved layer structures with a narrow vertical far-field divergence down to angles of 15 <formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula> (full-width at half-maximum) were developed. For these layer structures, optimized tapered lasers were processed to achieve laterally a nearly diffraction-limited beam quality with beam propagation factors smaller than 2. Depending on the emission wavelength, the tapered devices reach an output power up to 12 W and a brightness of <formula formulatype="inline"><tex Notation="TeX">$\hbox{1 GW}{\cdot}\hbox{cm}^{-2}{\cdot}\hbox{sr}^{-1}$</tex></formula>. </para>

Evidence from Internally Transcribed Spacer Sequence Analysis of Soybean Strains that Extant Bradyrhizobium spp. Are Likely the Products of Reticulate Evolutionary Events

The internally transcribed spacer (ITS) sequences of several members within each of 17 soybean bradyrhizobial serogroups were determined to establish whether the regions within all members of each serogroup were identical. The rationale was to provide a sequence-based alternative to serology. The objective also was to link the extensive older literature on soybean symbiosis based on serology with ITS sequence data for more recent isolates from both soybean and other legumes nodulated by rhizobia within the genus Bradyrhizobium. With the exception of serogroup 31 and 110 strains, sequence identity was established within each serogroup. Variation ranged from 0 to 23 nucleotides among serogroup 31 strains, and the regions in the type strains USDA 31 (serogroup 31) and USDA 130 (serogroup 130) were identical. Sequence identity was established among most strains within serogroup 110. The exceptions were USDA 452 and USDA 456, which had ITS sequences that were identical with those of the serotype 124 strain, USDA 124. Perhaps this would imply that USDA 452, USDA 456, and serogroup 31 strains are members of rhizobial lineages resulting from genetic exchange and homologous recombination events. This conclusion would be supported by the construction of a phylogenetic network from the ITS sequence alignment implying that the genomes of extant members of the genus Bradyrhizobium are likely the products of reticulate evolutionary events. A pairwise homoplasy index (phi or Phi(w)) test was used to obtain further evidence for recombination. The ITS sequences of USDA 110 and USDA 124 were more divergent (53 nucleotides) than this region between the type strain Bradyrhizobium japonicum USDA 6(T) and the proposed species Bradyrhizobium yuanmingense (28 nucleotides) and Bradyrhizobium liaoningense (48 nucleotides). Therefore, support for assigning discrete species boundaries among these three proposed species appears limited, considering the evidence for recombination, the narrow divergence of the ITS sequence, and their relative placement on the phylogenetic network.

Freeform surface lens design for uniform illumination

A method of designing refractive freeform surface lenses for uniform illumination is described. Using Snell's law, the differential equations are given to denote the relationship between the directions of the normal of the freeform surface and the input/output ray vectors; the Runge–Kutta formulae are used to calculate it. Moreover, two optical models for uniform illumination are discussed. By this process, uniform, narrow divergence half-angle, high-usage illumination over the given area is achieved. Some practical examples are also included in this paper.

Combining Directional Light Output and Ultralow Loss in Deformed Microdisks

A drawback of optical modes in microdisk cavities is their isotropic light emission. Here we report a novel, robust, and general mechanism that results in highly directional light emission from high-quality modes. This surprising finding is explained by a combination of wave phenomena (wave localization along unstable periodic ray trajectories) and chaotic ray dynamics in open systems (escape along unstable manifolds) and applies even to microlasers operating in the common multimode regime. We demonstrate our novel mechanism for the limaçon cavity and find directional emission with narrow angular divergence for a significant range of geometries and material parameters.

Resolution among major placental mammal interordinal relationships with genome data imply that speciation influenced their earliest radiations.

BackgroundA number of the deeper divergences in the placental mammal tree are still inconclusively resolved despite extensive phylogenomic analyses. A recent analysis of 200 kbp of protein coding sequences yielded only limited support for the relationships among Laurasiatheria (cow, dog, bat and shrew), probably because the divergences occurred only within a few million years from each other. It is generally expected that increasing the amount of data and improving the taxon sampling enhance the resolution of narrow divergences. Therefore these and other difficult splits were examined by phylogenomic analysis of the hitherto largest sequence alignment. The increasingly complete genome data of placental mammals also allowed developing a novel and stringent data search method.ResultsThe rigorous data handling, recursive BLAST, successfully removed the sequences from gene families, including those from well-known families hemoglobin, olfactory, myosin and HOX genes, thus avoiding alignment of possibly paralogous sequences. The current phylogenomic analysis of 3,012 genes (2,844,615 nucleotides) from a total of 22 species yielded statistically significant support for most relationships. While some major clades were confirmed using genomic sequence data, the placement of the treeshrew, bat and the relationship between Boreoeutheria, Xenarthra and Afrotheria remained problematic to resolve despite the size of the alignment. Phylogenomic analysis of divergence times dated the basal placental mammal splits at 95–100 million years ago. Many of the following divergences occurred only a few (2–4) million years later. Relationships with narrow divergence time intervals received unexpectedly limited support even from the phylogenomic analyses.ConclusionThe narrow temporal window within which some placental divergences took place suggests that inconsistencies and limited resolution of the mammalian tree may have their natural explanation in speciation processes such as lineage sorting, introgression from species hybridization or hybrid speciation. These processes obscure phylogenetic analysis, making some parts of the tree difficult to resolve even with genome data.

Y-coupled quantum cascade lasers

Spectroscopy at midand far-infrared wavelengths is important for environmental sensing (trace analysis, pollutants), medical diagnostics (blood analysis, breath control), and is a promising candidate for future high-security applications (airport security, identification of hazardous chemicals).1 Sensing chemical components in gases and liquids requires powerful coherent light sources with narrow spectral bandwidth and small divergence.2, 3 In the past decade, this demand has promoted quantum cascade lasers (QCLs), which enhance the performance and shrink down the dimensions of today’s midand farinfrared sensor systems.4 In contrast to conventional semiconductor lasers, QCLs can be designed to hit the target wavelength of a spectroscopic application. The coupling of semiconductor lasers results in an increased output power,5 stable single-mode operation, and wavelength tunability.6, 7 When integrated in a spectroscopic measurement system, monolithic coupling schemes can maximize the sensitivity, selectivity, and applicability of the sensor. However, a homogeneous laser beam is essential to avoid complicated optics and high losses of light. Therefore, the light inside the laser cavity has to be understood and controlled. Figure 1 shows a sketch of a Y-coupled QCL with corresponding dimensions. Two laser waveguides (branches) spaced by 60μm merge into a single trunk towards a single facet. The Yshaped QCLs have a waveguide width of 10μm and imply a bending radius of 8.3mm. The lasers were fabricated from a gallium arsenide/aluminum gallium arsenide heterostructure by lithography, etching, sputtering, and evaporation techniques.8 The devices were operated with 100ns current pulses at 78K. Their emission wavelength peaks at 10.5μm. To analyze the output beams on both sides of the laser, both the single and double facets were imaged with a midinfrared micro-bolometer camera. The image of the single facet Figure 1. Sketch of the Y-shaped quantum cascade laser (QCL) with corresponding dimensions. Near-field images illustrate the intensity distributions emitted from (left) the single facet and (right) the double facet.

Minimization of Damping in the Electrooptic Frequency Response of High-Speed Zn-Diffusion Single-Mode Vertical-Cavity Surface-Emitting Lasers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We utilize the Zn-diffusion technique to fabricate a single-mode high-speed 850-nm vertical-cavity surface- emitting laser. With this technique, we are able to minimize the thermal effect without greatly scaling down the diameter of the oxide- confined aperture. The demonstrated device has a 9-<emphasis><formula formulatype="inline"> <tex>$\mu$</tex></formula></emphasis>m active diameter with which we can attain a bandwidth of 8 GHz, a small differential resistance (<emphasis><formula formulatype="inline"><tex>$\sim$</tex></formula></emphasis>47 <emphasis><formula> <tex>$\Omega$</tex></formula></emphasis>), and a maximum output power of 3 mW. The single-mode characteristics can be sustained under dynamic operation for the whole bias current range. The dynamic measurement results indicate that with this single-mode device the damping-limited bandwidth of our multimode control can be eliminated without a Zn-diffusion aperture. A larger intrinsic bandwidth (32 versus 21 GHz) is also obtained due to the minimization of damping. The narrower divergence angle (8<emphasis><formula formulatype="inline"><tex>$^{\circ}$</tex> </formula></emphasis> versus 20<emphasis><formula formulatype="inline"><tex>$^{\circ}$</tex> </formula></emphasis>) means that the device exhibits a larger alignment tolerance and much lower coupling loss (9 dB) when used with the standard multimode fiber than those of the control sample. </para>

Fabrication of InGaAlAs MQW buried heterostructure lasers by narrow stripe selective MOVPE

Fabrication of InGaAlAs MQW buried heterostructure (BH) lasers by narrow stripe selective MOVPE is demonstrated in this paper. High quality InGaAlAs MQWs were first grown by narrow stripe selective MOVPE without any etching process and assessed by analysing the cross sections and PL spectrums of the InGaAlAs MQWs. Furthermore, BHs were fabricated for the InGaAlAs MQW lasers by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good device characteristics, with a high internal differential quantum efficiency of 85% and a low internal loss of 6.7 cm−1. Meanwhile, narrow divergence angles of the far field pattern are obtained for the fabricated lasers.

THE PHOTOBIOLOGICAL BASICS BEHIND LIGHT-EMITTING DIODE (LED) PHOTOTHERAPY

Phototherapy is, in its broadest sense, the use of light for any kind of surgical or nonsurgical treatment, but it is the athermal and atraumatic therapeutic application of light which is now accepted as the working definition of phototherapy. The early light-emitting diodes (LEDs) were unsuitable for clinical applications because of low unstable output powers, broad wavebands and very high angles of divergence. In the late 1990’s, the Space Medicine Programme in the United States National Aeronautics and Space Administration (NASA), developed the ‘NASA LED’ with much higher output powers, a much narrower divergence and quasimonochromatic output. With the ability to mount multiple LEDs in planar arrays, large areas of tissue can be irradiated in one hands-off session, unlike the time-consuming and therapist-intensive punctal application with laser diodes. These arrays deliver almost laser-like wavelength specificity and with clinically useful penetration depths and intensities, three of the most important considerations when considering cellular targets in the light of the first law of photobiology which states that without absorption, there can be no reaction. In the past few years, LED-based systems have been successfully applied in an increasingly large number of fields, and three major wavelengths have emerged with a good photobiological basis and proven clinical utility: blue, around 415 nm; red, around 633 nm, and near infrared, around 830 nm. Each has its own specific cellular target or targets and biological action spectrum and reaction, but it has become even more clear that no single wavelength can accomplish everything and combination LED therapy has proved necessary for greatest efficacy. The application of LEDs has ushered in a new and exciting era in phototherapy, and offers a versatile and inexpensive therapeutic modality either as a stand-alone therapy, or as an adjunctive approach to enhance the good results of existing surgical modalities.

Design and characterization of an atomic beam source with narrow angular divergence for alkali-earth targets

A new atomic beam source for use in laser-based experiments is described and characterized. The physically collimated source which has been tested using calcium, produces an atomic beam with low angular divergence and narrow transverse Doppler profile, as measured using fluorescence techniques with a near resonant laser beam. The low angular divergence of the source is essential for new experiments which study super-elastic scattering of electrons from laser prepared targets within a magnetic field, since the atomic beam must pass through a narrow gap between the coil windings. The beam density for calcium is calculated to be 2.8 × 109 atoms cm−3 when the source is operated at a temperature of 1090 K. This is sufficient to produce good electron energy loss and super-elastic scattering signals, while ensuring negligible radiation trapping within the atomic beam.

Development of Supersonic Metastable Helium Pulsed Beam Source for Plasma Diagnostics

A supersonic metastable helium (2 1S) pulsed beam source, which consists of an electromagnetic valve, a collimation skimmer, and discharge electrodes for production of a plasma, has been constructed, which is essential for the direct measurement of electric fields in plasmas by means of polarization laser-induced fluorescence spectroscopy. A supersonic helium atomic beam with a short pulselength (∼300 µs), narrow divergence (∼1.1°), and high density of ∼1.4×1014 cm-3 has been achieved. In order to generate metastable atoms in this beam source, a Penning-type discharge was employed, which is suitable for producing stable plasma with high temperature, even at low gas densities, due to the particular configuration of electrodes together with a magnetic field. Spectroscopic observations indicated that the temporal behaviors of neutral atom and ion emissions were almost the same as that of the helium atom profile, and on increasing the discharge voltage applied between electrodes, the spectral intensity increased approximately linearly. Moreover, the fact that the ion emission can also be observed showed that it was probable that a high-temperature plasma was generated by the Penning discharge.

Imaging in turbid media with intensity-modulated lasers

We describe the formation of a narrow beam for intensity-modulated electromagnetic radiation propagating through highly scattering materials. We propose to use this beam to reconstruct images, similar to X-ray back-projection techniques. For sufficiently high modulation frequency, the photon density wave is primarily carried by photons that suffer small or no large-angle scattering, which gives rise to the beam’s narrow divergence. The beam-narrowing concept is supported by large-scale numerical simulations to examine the quality of the imaging.

Vertical-cavity surface-emitting lasers (VCSELs) with high-power and single-spot far-field distributions at 850-nm wavelength by use of petal-shaped light-emitting apertures

In this letter, we demonstrate a vertical-cavity surface-emitting laser (VCSEL) with a petal-shaped light-emitting aperture, which is realized by the Zn-diffusion technique, at a wavelength of 850 nm. The demonstrated device behaves like a two-dimensional VCSEL array and each light-emitting unit can have high coherence of in-phase lasing to form a near fundamental supermode emission. The measured far-field distributions of such a device exhibit single-lobe (spot), high-power (>7.5 mW), and narrow divergence angle (~6deg) performance under a wide range of bias current. The ratio of in-phase lasing mode to total lasing modes, which include isolated single mode, in-phase, and out-of-phase modes, has also been analyzed by the measured far-field distributions and the theoretically calculated patterns

A crypticBacillusisolate exhibited narrow 16S rRNA gene sequence divergence withBacillus thuringiensisand showed low maintenance requirements in hyper‐osmotic complex substrate cultivations

A cryptic Bacillus (K90) isolate obtained from soil samples from the Kuwait desert exhibited lower maintenance requirements in complex substrate cultivations than Bacillus thuringiensis. A mathematical model was used to estimate apparent maintenance coefficients (m(c)) and these were found to be 0.336 and 0.041/h for B. thuringiensis and K90, respectively. The results also showed that the values of apparent maintenance coefficients were inversely related to the specific growth rates. Furthermore, 16S rRNA gene sequencing showed that K90 exhibited 99.81% sequence similarity to that of B. mojavensis and 92.9% with B. thuringiensis. It is evident from the dendrogram that the evolution of B. mojavensis (K90) (B. subtilis group), which may have originated after B. licheniformis could have been influenced by prolonged hyper-osmotic conditions, while B. thuringiensis that evolved before B. oleronius exhibited greater sensitivity as implied by the higher maintenance coefficient obtained for the hyper-osmotic cultures. As K90 exhibited low maintenance requirements in hyperosmotic cultures, close phylogenetic relationship with B. thuringiensis, along with the reported property of encapsulation of insecticidal crystal proteins (Cry) in Bacillus strains and endophytic nature of B. mojavensis, strongly suggest that K90 could be a promising surrogate host for the transgenic delivery of "Cry" proteins.

Coherent radiation of relativistic nonlinear Thomson scattering

The condition for the coherent addition of the relativistic nonlinear Thomson scattered (RNTS) radiations from a group of electrons is derived. Numerical calculations show that under such a condition, all the characteristics of RNTS radiation by a single electron are maintained, leading to the generation of intense attosecond x rays. Such an attosecond x ray is produced in a specific direction with a very narrow angular divergence. An x-ray radiation of ∼1016W∕cm2 with a pulse width of 7.7 as is expected for an oblique irradiation of a 20 fs linearly polarized laser pulse of 4×1019W∕cm2 on a 7 nm thick film target. For the proof-of-principle experiment, the radiation characteristics from a 50 nm thick film target are presented and discussed.