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In order to solve the toxic and hazardous issues of the agents in the chemical reduction process of graphene oxide (GO), disodium guanosine 5′-monophosphate (GMP-2Na) was used as an ideal reducing agent for the synthesis of functionalized GO (FGO) for lipase immobilization. At the condition of low amount adsorption of GMP-2Na indicated by the N1s spectra of X-ray photoelectron spectroscopy (XPS), the C/O atomic ratio of the FGO increased from 2.09 to 3.12, indicating the reduction of GO. As the amount of GMP-2Na increased, the intensity of the characteristic peak of GO in the XRD pattern decreased, and the I D /I G peak intensity of Raman spectra increased during the functionalization process. It was found that when the concentration of GMP-2Na is 0.20 mg/mL, the degree of hydrophobicity of FGO is conducive to the formation of optimal conformation of lipase. After immobilization, the activity of the immobilized enzyme reaches twice the value of free enzyme. At the same time, the protein loading reaches to 600 mg/g. The immobilized enzyme showed enhanced durability since no obvious decrease was observed after incubation for 8 h at pH 6.0 and pH 7.0. After storage for 35 days, the activity of GO-G@ enzyme was 54.47% higher than that of free enzyme. GO reduced by GMP-2Na provides a possibility to obtain a highly efficient lipase immobilization carrier.

We report on the development of a 940-nm diode laser bar based on epitaxially stacked active regions by employing a tunnel junction structure. The tunnel junction and the device parameters were systematically optimized to achieve high output and power conversion efficiency. A record quasi-continuous wave (QCW) peak power of 1.91 kW at 25 °C was demonstrated from a 1-cm wide bar with a 2-mm cavity length at 1 kA drive current (200 μs pulse width and 10 Hz repetition rate). Below the onset of the thermal rollover, the slope efficiency was as high as 2.23 W/A. The maximum power conversion efficiency of 61.1% at 25 °C was measured at 300 A. Reducing the heatsink temperature to 15 °C led to a marginal increase in the peak power to 1.95 kW.

The continuous-wave 100 W-class 808 nm laser diode arrays with extremely high power conversion efficiency of 68% were reported at the heatsink temperature of 25 °C. To the best of our knowledge, this was the highest power conversion efficiency at continuous-wave 106 W 808 nm laser diode array with 50% fill factor so far. An asymmetric broad waveguide epitaxial structure with very low internal optical loss of 0.5 cm −1 was presented. In order to improve the efficiency, various fill factor devices were studied. The 50 W laser diode array with 30% fill factoir and 1.0 mm cavity length demonstrated power conversion efficiency of 71% at heatsink temperature of 15 °C.

Semiconductor lasers with high power conversion efficiency (PCE) and output power are heavily investigated driven by more energy-efficient commercial applications. In this paper, an asymmetric broad area laser (A-BAL) design is studied and compared with a conventional symmetric broad area laser (S-BAL) design for 808 nm single emitter laser diodes. We present a comparative theoretical and experimental investigation by studying the thermal effects on the laser parameters. The output characteristics and efficiency loss paths for the designs were analyzed. The leakage of carriers was identified as the primary source of the PCE reduction with temperature. Suppressing this leakage by optimization of the A-BAL design, a record continuous-wave PCE of 68% at 25 °C and 60.4% at 75 °C were achieved for a single emitter laser with 10 W output power. These devices deliver high efficiency at high temperatures with reliable operation achieving 2000 h of an accelerated aging lifetime without failures.

Broad-area diode lasers with high output power and low lateral divergence angle are highly desired for extensive scientific and industrial applications. Here, we report on the epitaxial design for higher output power and a flared waveguide design for reduced divergence, which leads to high power operation with a low lateral divergence angle. A vertically asymmetric epitaxial structure was employed and optimized for low internal optical loss and high efficiency to realize high output power operation. Using a flared waveguide design, the lateral divergence angle was efficiently reduced by decreasing the number of high-order lateral optical modes significantly. The flared waveguide design introduces a smooth modification of the ridge width along the cavity without deteriorating laser performance. Based on the optimized epitaxial and waveguide design, we scaled the waveguide width to realize high continuous-wave power of 34.5 W at 25 °C. A low lateral divergence angle of 8° and high power conversion efficiency of 60% were achieved at the operating power level of 25 W. The life test data (30 A at 45 °C for 39 units, 0 failures in 1000 h) demonstrated reliable operation illustrating the efficient design for reduced lateral divergence angle and high operating power.

A novel black phosphorus (BP) solution saturable absorber (SA) is fabricated by the liquid-phase-exfoliated method and successfully used for passively Q-switched (QS) Nd:YVO4 laser. Compared with a traditional solid SA, a BP solution SA possesses more excellent optical transparency and higher damage resistance. The shortest pulse duration and highest average output power are measured to be 119 ns and 1.23 W, respectively. To the best of our knowledge, both of them are the best results among QS solid-state lasers with BP-based absorbers so far. The repetition rate is in the range of 533.2 to 722 kHz. The results indicate the potential application of the BP solution SA into high-power solid-state pulse lasers.

The report presents the high power mode-locking operation in an anomalous-dispersion fiber laser with a novel WS 2 saturable absorber (SA) based on fluorine mica (FM) substrate. Compared to organic host material such as polymer, FM has higher softening temperature, heat dissipation and laser damage threshold. By employing the SA, a stable mode-locked fiber laser is achieved. The duration of the pulse broadens from 2.816 ns to 3.654 ns almost linearly with increasing pump power. The average output power and single pulse energy can increase up to 33.5 mW and 4 nJ at the maximum pump power respectively. The results indicate that WS 2 /FM material is an ideal SA for high power Er-doped fiber (EDF) lasers.

High-power GaAs-based semiconductor lasers are the most efficient source of energy for converting electrical into optical power. 940nm diode lasers are used directly or as pump sources for Yb:YAG solid-state lasers, and are widely used in laser cladding and other fields. Improving electro-optic conversion efficiency and reliable output power are urgent requirements for current research hotspots and industrial laser systems. In this paper, we use an asymmetric epitaxial structure of InGaAs/AlGaAs, which reduces the optical loss and resistance, and adopt better cavity surface technology to present 940nm 1-cm quasi-continuous micro-channel cooling (MCC) laser bars. The lasers are tested under a high duty cycle of 9.6% (600us,160Hz) at 25°C with output power of 660.05W, electro-optic conversion efficiency of 64.71% at 600A and slope efficiency of 1.16 W/A. The peak efficiency reaches 72.4%. The increased efficiency results from a lower threshold current and a lower series resistance. Furthermore, the output power of 1025W (1000A) has been confirmed at a duty cycle of 4% (400us,100Hz).

Compared to the traditional chemical reduction method, a green and efficient strategy was successfully applied to regulate the surface heterogeneity of graphene oxide (GO). In this work, different kinds of amino acids were used to reduce and modify GO. The reduction and adsorption disparities of amino acids contributed to the difference of structural heterogeneity in terms of density, thermal tolerance and disorder of the oxygen-containing groups of GO. The modification also resulted in discrepancies in surface properties of the GO samples, such as hydrophobicity and surface charge. The functionalized GO was employed as a carrier for the immobilization of lipase from Thermomyces lanuginosus (lipase TL). The storage stability, the temperature and pH sensitivity of the immobilized biocatalysts and the free lipase TL were studied. Lipase immobilized on functionalized GO demonstrates superior enzymatic loading and relative activity compared to GO, with a maximum increase of 70% and 47%, respectively. The relative activity of lipase immobilized on functionalized GO was 19.21 times more than that of commercial immobilized lipase TLIM. Through molecular dynamics simulations we concluded that the increase in the relative activity of lipase TL is mainly related to its adsorption orientation and slight conformational change. Thus, our research offered a green and effective strategy to regulate the heterogeneity of nanomaterials for a suitable microenvironment to enhance the performance of immobilized lipase.

The package structure critically influences the major characteristics of semiconductor lasers, such as thermal behavior, output power, wavelength, and far-field distribution. In this paper, a new single emitter package structure called F-mount is designed and compared with the conventional package structure C-mount. The influence of package structure on their performances is characterized and analyzed. The thermal resistances of lasers with different package structures are calculated through simulation, and are contrasted with experimental results. Some devices are also tested for the maximum output power level. Under the continuous wave (CW) condition, the maximum power of F-mount reaches 12.6 W at 808 nm while the output power only reaches 10.9 W for C-mount. Under the condition of 0.5% duty cycle (100 μs, 50 Hz), the catastrophic optical mirror damage level reaches 58.7 W at 74 A for F-mount, and 54.8 W at 57 A for C-mount are reported for the first time. It is experimentally found that there is an obvious wavelength difference between the two type structure lasers: about 1.37 nm in CW mode and 2.89 nm in quasi CW mode. Theoretical analysis shows that red-shift and blue-shift is a result of external strain in the package process of F-mount and C-mount, respectively. It is also found that the package structure has an effect on the divergence angle of slow axis far fields, but little impact on that of fast axis far fields. The analysis shows that package structure has a strong influence on the performance of the laser; therefore, the package should be optimized to achieve better performance for some special applications.

The whispering-gallery-mode (WGM) photonic crystal microcavity can be potentially used for miniaturized photonic devices, such as thresholdless lasers. In this paper, we use plane wave expansion (PWE) method and study the WGM of H2 photonic crystal microcavities which are formed by removing seven center air holes in a photonic crystal. The WGM in these large-size cavities has some advantages compared with single defect WGM in the view of real device applications. We analyze the nearby air hole effect on WGM and conclude that WGM is more sensitive to moving towards the outside rather than moving towards the inside of a nearby air hole. In our case, if a nearby air hole is moved 0.1a away from the center, the WGM will disappear. If a nearby air hole is moved 0.6a towards the center, however, the WGM will still exit. We also analyze the structure with an air hole (rm= 0.2a) in the center of the microcavity, and we find that the WGM is not affected by the central hole sensitively. As we increase rm, the WGM remains unchanged until rm is 0.64 times greater than period a. It is found that the tolerance of WGM to the displacement of nearby air holes and the occurance of central holes is large enough to fabricate electrical injection structure.

A method based on the theory of transfer matrix to design the integrated microlens for the collimation of vertical-cavity surface emitting laser (VCSEL) array is presented. The integrated microlenses fabricated on the substrate directly and on a certain polymer material which is on the substrate are considered. The relationships between the radius of curvature, beam waist and the divergence angle after collimation are obtained with the help of ZEMAX. The results show that the devices with the divergence angle of 15° (1/e2) and beam waist of 2 μm can be improved to those with the divergence angle lower than 1°, and the devices with beam waist of 10 μm can be improved to those with the divergence angle lower than 3°, which is a good reference for manufacturing high-power devices with small divergence angle. The conclusions including increasing the thicknesses of both the substrate and polymer material and reducing the diameter of oxidized layer are drawn, which will be an important guidance for experiment research.

A 980 nm bottom-emitting vertical-cavity surface-emitting laser (VCSEL) array with a nonuniform linear arrangement is reported to realize high power with a Gaussian far-field distribution. This array is composed of five symmetrically-arranged elements of 200 μm, 150 μm, and 100 μm diameters, with the center spacing of 300 μm and 250 μm respectively. This structure makes it possible to discriminate against the higher order array supermodes. The theoretical simulation of the far-field distribution is in good agreement with the experimental result. An output power of 880 mW with a power density of 1 KW/cm2 is obtained. The divergence angle is below 20° in the range of operating current from 0 A to 4 A. The comparison between this nonuniform linear array and the conventional two-dimensional array is carried out to demonstrate the good performance of the linear array. A peak power of over 20 W is achieved under a short pulsed operation with a repetition frequency of 1 kHz.

This paper presents a stable all-fiber Q-switched Er-doped fiber (EDF) laser with WS2/fluorine mica (FM) as the saturable absorber (SA). The SA device is obtained by depositing WS2 nanosheet layers onto a 20 µm thick one-layer FM substrate using a thermal decomposition method. The modulation depth (MD) of the SA is 8.22% and the non-saturable loss (NL) is 16.38%. By inserting the SA into the EDF laser cavity, stable Q-switched operation is achieved with a central wavelength of 1567 nm. The repetition rate can be tuned from 20.98 kHz to 33.74 kHz and the pulse duration can be adjusted from 8.3 µs to 6.98 µs by increasing the pump power. The maximum output power and the maximum pulse energy are measured to be 2.07 mW and 61.4 nJ, respectively. The experimental results evidently show that the WS2/FM can be regarded as a high-performance SA for fiber lasers.

With the continuous increase of the output power of semiconductor laser array, the heat generation in the active region also increases continuously, which influences the performances and lifetime of semiconductor laser array seriously. In order to improve the performances and lifetime, understanding of the thermal behavior of high power semiconductor laser array packages and optimizing the thermal performance are crucial. By means of numerical analysis, a three-dimensional thermal model has been established, and the static and transient thermal characteristics in continuous-wave (CW) and quasi-continuous-wave (QCW) modes also have been studied systematically for a hard solder, conduction-cooled-packaged 808nm semiconductor laser array. Based on the thermal modeling and analysis, the approaches to reduce thermal resistance have been proposed. The results show that: compared with copper-tungsten (CuW), adopting the copper-diamond composite material as the submount can decrease the thermal crosstalk behavior between emitters, and reduce the thermal resistance by about 30%. In addition, a novel thermal design for the packaging structure of the mounting heat-sink is demonstrated, which has the ability of reducing the thermal resistance of the devices significantly.

Laser cladding has become a useful tool in materials processing for improving the surface properties of the substrate materials, and has been widely used in industry in recent years. In this paper, we study the 3000W CW laser cladding system based on the high power diode lasers. The beam control method is proposed to reduce the collimated beam pointing errors caused during the packaging of the laser stack. At the input current of 84A, the output power and the optical coupling efficiency of this laser cladding system are 3738W and 93.7%, respectively, and at work face the beam spot size is 2.5mm*7.9mm with symmetry intensity distribution. The laser cladding system is also used in cladding the nickel powder onto the iron substrate and the nickel powder can be clothed onto steel plate uniformly.

Vertical-cavity surface-emitting lasers emitting at 808 nm with unstrained GaAs/Al0.3Ga0.7As, tensilely strained GaAs(x)P(1-x)/Al0.3Ga0.7As and compressively strained In(1-x-y)Ga(x)Al(y)As/Al0.3Ga0.7As quantum-well active regions have been investigated. A comprehensive model is presented to determine the composition and width of these quantum wells. The numerical simulation shows that the gain peak wavelength is near 800 nm at room temperature for GaAs well with width of 4 nm, GaAs0.87P0.13 well with width of 13 nm and In0.14Ga0.74Al0.12As well with width of 6 nm. Furthermore, the output characteristics of the three designed quantum-well VCSELs are studied and compared. The results indicate that In0.14Ga0.74Al0.12As is the most appropriate candidate for the quantum well of 808-nm VCSELs.

Whispering-Gallery-Mode (WGM) photonic crystal microcavity is a kind of photonic crystal application and can potentially be used for miniaturized photonic devices, such as thresholdless lasers. In this paper we study the WGM of photonic crystal microcavities focusing on the so called H2 cavities which are formed by removing seven air holes. The WGM in these large-size cavities has some advantages compared with single defect WGM in the view of real device applications. We further add a central air hole in the cavity region to analyze the effect on WGM in the microcavity by finite difference time domain (FDTD) and plane wave expansion (PWE). It is found that the tolerance of WGM is large enough for the fabrication of electrical injection structure.

A new beam-shaping technique is proposed to improve the beam quality of a high-power diode laser area light source. it consists of two staggered prism arrays and a reflector array, which can cut the slow axis beam twice and rearrange the divided beams in fast axis to make the beam quality of both axes approximately equal. furthermore, the beam transformation and compression can be carried out simultaneously, and the assembly error of this technique induced by the machining accuracy of prism's dimensions also can be greatly decreased. by this technique, a fiber-coupled system for one three-bar laser diode stack is designed and characterized. the experimental results demonstrate that the laser beams could be transformed into the required distribution with similar to 93.4% reshaped efficiency and coupled into a 400 mu m/0.22 na fiber, which are consistent with the theory. (c) 2013 society of photo-optical instrumentation engineers (spie)

A 980 nm bottom-emitting vertical-cavity surface-emitting laser (VCSEL) with a p-contact diameter is reported to achieve high power and good beam quality. A numerical simulation is conducted on the current spreading in a VCSEL with oxidation between the active region and the p-type distributed Bragg reflector. It is found that, for a particular oxide aperture diameter, somewhat homogeneous current distribution can be achieved for a VCSEL with an optimized p-contact diameter. The far-field divergence angle from a 600 microm diameter VCSEL is suppressed from 30 degrees to 15 degrees, and no strong sidelobe is observed in the far-field pattern by using the optimized p-contact diameter. There is a slight rise in threshold and optical output power that is due to the p-contact optimization. By improving the device packaging method, the maximum optical output power of the device is 2.01 W.