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The carrier recombination behavior of GaN-based blue laser diodes (LDs) is studied and analyzed by experiments and simulation calculations before lasing, with a particular focus on the role of Auger recombination. It is found that Auger recombination plays a crucial role in the decrease in differential efficiency and threshold current of GaN-based blue LDs. The theoretical calculation results show that a large Auger recombination rate may lead to a dominant recombination channel before lasing, which could exceed the radiation recombination and result in an obvious decrease in the differential efficiency. Such a high Auger recombination will dissipate a large number of carriers in the quantum well, resulting in deterioration of device performance, a higher threshold current and a lower efficiency. This work presents a method to evaluate Auger recombination through differential efficiency and also provides evidence that suppressing the Auger recombination rate is beneficial to improve the performance of blue LDs. [ABSTRACT FROM AUTHOR]

In recent years, an increasing number of experimental results have been published for a wide variety of systems in which high-precision, ultra-fast, and ultra-short laser pulses techniques have been used to study time-resolved dynamical processes. In the absence of a theoretical prediction of the time distribution of the transition probabilities, the lifetimes τ are generally extracted by fitting the decay time with an exponential, bi-exponential or three-exponential function. In fitting the data, the short-time behavior is generally neglected. The purpose of this study is to show that an explicit formula for the time distribution of the transition probability can be determined rigorously using time-dependent perturbation theory. A formula that perfectly fits an important subset of the experimental results from t = 0 to t = ∞ . We show that by following a route different from the usual procedure for deriving transition amplitudes and Einstein coefficients in time-dependent perturbation theory, one ends up with a time-dependent factor, that is, a temporal distribution function of the transition probabilities, and for the Einstein coefficients. The time distribution reported here looks in the time domain similar to the Planck distribution in the frequency domain. In fact, the behavior of the time distribution, with a maximum at 2 τ ln ⁡ 2 , and with τ playing the role of temperature, resembles the behavior of the Planck frequency distribution. We present several examples to demonstrate that the theoretical formula allows for easier fitting of the experimental results reported in the literature. We also show that the time distribution explains the difference in resonance heights between the experimental and theoretical blue laser spectra. [ABSTRACT FROM AUTHOR]

Recent progress in the in situ synthesise of various nanomaterials has gained tremendous interest and wide applications in various fields. For the first time to the best of our knowledge, this work reports a methodology of ultra-fast in situ synthesis of cobalt–cobalt oxide-reduced graphene oxide (Co−Co3O4−rGO (CC–rGO)) composite by laser ablation. The photothermal reduction technique was leveraged to develop the CC–rGO. For this, a low-cost 450 nm blue diode laser was irradiated onto a grade 1 filter paper in the presence of cobalt ions readily patterns the carbon matrix of paper to the composite material. Moreover, the variation of cobalt concentrations from 0.1–0.5 M led to structural and morphological changes. Standard techniques were adopted for thorough characterizations of developed sensor material for conductivity analysis, specific surface area, crystal-structural information, surface morphology, and chemical composition. The observed results were highly promoting towards the electrochemical sensing applications. Further, the developed sensor was found to be highly selective toward detecting a vital bio analyte alkaline phosphatase (ALP). The sensors performance was highly significant in the linear range of 10–800 mU l−1 with a detection limit of 10.13 mU l−1. The sensors applicability was further validated in actual human serum samples via a recovery-based approach. In the future, the developed in situ material methodology can begin a rapid composite material synthesis at a larger scale. [ABSTRACT FROM AUTHOR]

Atmospheric frosting and icing pose significant problems for critical and common-use infrastructures. Passive anti-frosting and anti-icing strategies that require no energy input have been actively sought, with no viable and permanent solutions known yet. Bioinspired superhydrophobic (SH) materials have been considered promising path to explore; however, the outcome has been less than compelling because of their low resistance to atmospheric humidity. In most cases, condensing water on an SH surface eventually leads to mechanical locking of ice instead of ice removal. Hybrid strategies involving some form of limited energy input are being increasingly considered, each with its own challenges. Here, we propose the application of plasmonic heating of silver nanowires (AgNWs) for remote frost removal, utilizing an SH hybrid passive-active system. This novel system comprises a durable nanocomposite covered with a hydrophobized mesh of AgNWs, protected against environmental degradation by a tin oxide (SnO2) shell. We demonstrate the frost removal ability at âˆ'10 °C and 30% RH, achieved by a combination of plasmonic heating of AgNWs with a non-sticking behavior of submicrometric droplets of molten frost on the SH surface. Heating was realized by illuminating the mesh with low-power blue laser light. Adjustment of the nanowire (NW) and shell dimensions allows the generation of surface plasmon resonance in illuminated NWs at a wavelength overlapping the emission maximum of the light used. In environmental stability tests, the nanostructures exhibited high atmospheric, mechanical, and thermal stability. The narrow-wavelength absorption of the structure in the blue light range and the reflective properties in the infrared range were designed to prevent protected surfaces from overheating in direct sunlight. [ABSTRACT FROM AUTHOR]

In recent years, plasma-induced non-equilibrium electrochemistry (PiNE) has been increasingly used for the synthesis of nanomaterials. In this study, we investigated the effect of solution pH on the formation of AuNP/MWCNT nanocomposites synthesized by PiNE. It is found that resulting nanocomposite morphology can be manipulated by the solution pH with pH 2 giving the most uniformly distributed AuNP along the MWCNT surface during the nanocomposite formation. The detailed mechanisms of AuNP/MWCNT nanocomposites formation under different pH have been discussed. For selected AuNP/MWCNT, we further evaluated the photothermal conversion performance under a blue laser (wavelength 445 nm) and the material biocompatibility using HeLa cells. The promising photothermal capability and biocompatibility of the composite sample point to their potential future applications such as solar thermal conversion and healthcare technology. [ABSTRACT FROM AUTHOR]

An NO2 photoacoustic sensor system with a high reflective mirror based on a low power blue diode laser is developed in this work. The excitation power is enhanced by increasing the number of reflections. Comparing with a traditional photoacoustic system, the pool constant is improved from 300.24 (Pa⋅cm)/W to 1450.64 (Pa⋅cm)/W, and the signal sensitivity of the photoacoustic sensor is increased from 0.016 μV/ppb to 0.2562 μV/ppb. The characteristics of temperature and humidity of the new photoacoustic sensor are also obtained, and the algorithm is adjusted to provide a quantitative response and drift of the resonance frequency. The results of this research provide a new method and concept for further developing the NO2 photoacoustic sensors. [ABSTRACT FROM AUTHOR]

This work presents the theoretical study on strain-free chirped short-period superlattices (C-SPSLs) as the top waveguide core and cladding layers for InGaN laser diodes (LDs) emitting at 450 nm. The total 530 nm thick layers of reference LD containing 100 nm p-GaN waveguide, 30 nm Al0.15Ga0.85N electron blocking layer (EBL) and Al0.065Ga0.935N cladding layers are replaced by 300 nm thick C-SPSL which contains the 33-periods of 10 monolayers (ML) GaN/ 2 ML In0.18Al0.82N, 48-periods of 6 ML GaN/2 ML In0.18Al0.82N, and 97-periods of 2 ML GaN/ 2 ML In0.18Al0.82N. The optical confinement factor of reference LD is 3.28% whereas for C-SPSL LD it is 3.42%. The better optical confinement at reduced thickness using C-SPSL is due to the high refractive index contrast. The strain in the C-SPSL is negligible. The electron leakage has reduced from 2.54 kA cm−2 to 0.166 kA cm−2 at ∼10 kA cm−2 injected current density, whereas the hole transportation has improved by 2.31 kA cm−2. The C-SPSL configuration also favors the electron blocking effect, thus EBL is not required in C-SPSL design. The light output power at a current injection of 500 mA (10 kA cm−2) is 248 mW for the new structure and ∼143 mW for reference LD. The slope efficiency is improved from ∼0.55 to ∼0.89 W A−1. Also, the dynamic resistance from I–V characteristic is ∼1.12 Ω which is lowered to ∼0.94 Ω. [ABSTRACT FROM AUTHOR]

Direct laser writing technique has become a well-established, multi-functional and flexible method for fabricating high quality diffractive optical elements. We propose and build a maskless direct laser writing system with the ability to produce a sub-micron feature size. The high precision lithography is realized by using the astigmatic autofocus method. The minimum feature size of the system, breaking through the diffraction limit with the chromium layer, can achieve 300 nm with the 405 nm blue laser. A 50 × 50 mm2 chromium grating mask with a period of 1 μm and line width of 300 nm is fabricated. This facility will be useful for the fabrication of large-scale submicron diffraction optical elements in the future. [ABSTRACT FROM AUTHOR]

We have grown triply doped Mg:Fe:Mn:LiTaO3 crystals with near stoichiometry using the top seeded solution growth technique. The defect structure was investigated by infrared absorption spectra and Curie temperature. Using a blue laser as the source, excellent photorefractive properties were obtained. Nonvolatile holographic storage properties were investigated using the dual wavelength technique. We got a very high fixed diffraction efficiency and nonvolatile holographic storage sensitivity. The blue light has more than enough energy to excite holes of deep (Mn) and shallow (Fe) trap centers with the same phase, which enhance dramatically the blue photorefractive properties and the nonvolatile holographic storage. Mg2+ ion is no longer damage resistant at blue laser, but enhances photorefractive characteristics. [ABSTRACT FROM AUTHOR]

In this paper we describe the fabrication and characterization of glass optical waveguides and integrated grating couplers. The fabrication can be carried out using low-cost materials and equipment normally found in undergraduate physics and engineering laboratories. Particular use is made of the recent availability of low-cost blue lasers, which are used to write holographic gratings in photoresist. Fabrication and then measurements on the waveguides can be used to demonstrate several areas of great technological and physical importance, including photolithography, holography, optical wave-guiding, tunneling, phase-matching and wave interaction with periodic structures. Components fabricated as described here have been used in undergraduate and graduate classes in optics. The fabrication processes are appropriate for undergraduate projects. [ABSTRACT FROM AUTHOR]

We present a 397-nm frequency-doubling system with a quasi-phase-matched KTP crystal (PPKTP) which fea-tures tunable, narrow linewidth, high power, and excellent mechanical stability. Using 20-mm and 30-mm-long PPKTP crystals, we establish two experimental setups based on different external cavity parameters. By testing the beat signal of these two lasers, the linewidth for the system is measured to be less than 2.5 MHz. The maxi-mum power of blue light can be achieved up to 40 mW. With these performance characteristics, the constructed blue laser system is useful for applications in cold atom physics and precision measurements. [ABSTRACT FROM AUTHOR]

The fabrication process and characteristics of gallium nitride (GaN) based gain-guided blue laser diodes (LDs) are studied, in which an ion implantation process is adopted to confine carrier injection into the active region. The implantation of helium ions with an energy of 85 keV, an angle of 0°, and a dosage of 4.7 × 1014 cm−2 is conducted in the experiment. The specific contact resistivity of p-type ohmic contact of implanted sample is determined to be 2.2 × 10–4 Ω cm2, which is comparable with the un-implanted sample. Then, both ion-implanted gain-guided and ridge waveguide LDs are fabricated at the same time. Similar threshold current density and slope efficiency are obtained, while the operation voltage of ion-implanted gain-guided LDs is 0.2 V lower than the ridge waveguide LDs at 0.56 kA cm−2. The ridge waveguide LDs show multi-mode operation after lasing. However, for ion-implanted gain-guided LDs, the far-field pattern indicates a single lateral mode operation up to twice of the threshold current, and the peak optical output power of blue single mode LDs at 450 nm exceeds 200 mW under pulsed condition. [ABSTRACT FROM AUTHOR]

We demonstrate a 446.5 nm GaN semiconductor laser with sub-MHz linewidth. The linewidth reduction is achieved by locking the laser to a magnesium fluoride whispering gallery mode resonator characterized with 109 quality factor. Self-injection locking ensures single longitudinal mode operation of the laser. [ABSTRACT FROM AUTHOR]

Due to large coherence length, high detection sensitivity and feasible design, a narrow-linewidth single-frequency laser in the blue spectral range is essential for underwater communication and high-resolution atomic/molecular spectroscopy. By exploiting the efficient frequency doubling of a 978 nm Yb-doped phosphate fiber laser in a fiber-coupled 10 mm long periodically poled LiNbO3, an all-fiber single-frequency blue laser at 489 nm with an ultra-compact and practical design is demonstrated. Over 68 mW of stable narrow-linewidth blue radiation is generated with a conversion efficiency of 30.3%. The estimated laser linewidth is less than 15 kHz, while the measured relative intensity noise is less than –139 dB Hz−1 at frequencies above 20 MHz. The obtained blue laser output is naturally stable with a power stability of ±1.5% over a period of 120 min. [ABSTRACT FROM AUTHOR]

Using a quantum dot in quantum well (QD-in-QW) active region, current injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) lasing simultaneously in blue and green were achieved at room temperature (RT). Lasing was first achieved at 545 nm with a threshold current of ∼2 μA, and with a further increase of current, another lasing peak at 430 nm came out with a threshold current of ∼5 mA. The energy difference between the two lasing peaks originating from QDs and QWs is 609 meV. According to the spontaneous emission spectra measured under different injected currents, a model of energy states in QD-in-QW is proposed to describe the distribution of carriers in this structure. Using this model, the evolution of emission intensity, shift of peak energy, variation of linewidth and the lasing characteristics can be well explained. [ABSTRACT FROM AUTHOR]