[en] In this paper, the model of an intracavity Q-switched second order Raman laser is established, the characteristics of the output 2nd Stokes are simulated. The dynamic balance mechanism among intracavity conversion rates of stimulated emission, first order Raman and second order Raman is obtained. Finally, optimization solutions for increasing output 2nd Stokes pulse energy are proposed. (paper)

[en] A new approach to achieve efficient coupling between photonic crystals and a nanometer waveguide via an asymmetric resonator is proposed. The asymmetric resonator was composed of the photonic crystal and the nanometer waveguide was constructed by elongating a rod of the photonic crystal resonator horizontally. By introducing the asymmetric resonator, the nanometer waveguide served as a part of the resonator, and the coupling between the photonic crystal waveguide and the nanometer waveguide was converted to internal coupling between the photonic crystal devices. The 3D theoretical coupling efficiency reached 91.31%. Such compact, efficient coupling shows great promise for applications in molecular imaging, nanoprobes, integrated photonic circuits and on-chip optical interconnects. (paper)

[en] We propose a new structure design and analysis of high-temperature (>350 K) operating 795 nm vertical-cavity surface-emitting lasers (VCSELs) for ⁸⁷Rb based chip-scale atomic clocks (CSACs). Compositions and thicknesses of the InAlGaAs/AlGaAs multiple quantum wells (MQWs) are optimized for high optical gain at elevated temperatures. The temperature sensitivity of the threshold current is estimated by calculating the temperature dependence of the cavity-mode gain. A self-consistent VCSEL model based on quasi-3D finite element analysis is employed to investigate the temperature distribution and output of the proposed structure. An output of 1 mW with a 3 dB bandwidth of 6 GHz is obtained from a 3 μm aperture VCSEL under 2.4 mA current at temperature higher than 340 K. These findings indicate that high-gain QWs and gain-offset consideration are especially crucial to make high-performance VCSELs at elevated temperatures. (letter)

[en] The influence of external optical feedback (OFB) on the light-current characteristics of the vertical-cavity surface-emitting lasers (VCSELs) was investigated theoretically and experimentally. By calculating the OFB sensitivity parameter, the OFB sensibility of the VCSELs was compared with the edge emitting lasers. Based on the compound cavity theory, the light-current characteristic parameters of the VCSELs with external OFB, such as the threshold current and the slope efficiency, were calculated. The experimental results indicated that the threshold current of the VCSELs with different DBR reflectivities decreased to different degrees, accompanied with a decrease of slope efficiency when under 10% feedback ratio of the external OFB, which is in good agreement with the theoretical calculation. (semiconductor integrated circuits)

[en] A diode laser source with a continuous wavelength (CW) power of 106 W and the beam quality M² of 14.6 is demonstrated by spectrum beam combining (SBC) of three 800 nm LDAs. With the help of relay optics, a wavelength interval of 0.21 nm and a whole spectrum span of 13.9 nm are achieved, which is almost 10 times narrower than those of the structure without the relay optics. This presents a method to obtain a high power and high beam quality SBC laser source with a narrow spectrum. (letter)

[en] A 980 nm bottom-emitting vertical-cavity surface-emitting laser linear array with high power density and a good beam property of Gaussian far-field distribution is reported. This array is composed of five linearly arranged elements with a 200 μm diameter one at the center, the other two 150 μm and 100 μm diameter ones at both sides of the center with center to center spacing of 300 μm and 250 μm, respectively. A power of 880 mW at a current of 4 A and a corresponding power density of up to 1 kW/cm² is obtained. The temperature dependent characteristics of the linear array are investigated. The thermal interaction between the individual elements of the VCSEL linear array is smaller due to its optimized element size and device spacing, which make it more suitable for high power applications. A peak power of over 20 W has been achieved in pulsed operation with a 60 ns pulse length and a repetition frequency of 1 kHz. (semiconductor devices)

[en] A series of compressively strained AlGaInAs quantum well (QW) structures with different annealing treatment durations at 170 °C were investigated by temperature-dependent photoluminescence (PL). An abnormal S-shaped behavior in emission energy and a non-monotone evolution in spectral band width were observed at low temperature. A significant negative linear correlation between full width at half maximum (FWHM) and emission energy at different test temperature was exhibited in samples with different heat treatment durations. The highly linear relation demonstrated that the dependencies and relationships between PL peak energy and FWHM vs temperature are consistent. The anomalous blue shift and concomitant narrowing of FWHM in AlGaInAs QW were affected by lattice strain fluctuations due to the difference of thermal expansion coefficients between adjacent layers and strong carriers’ localization at low temperature.

[en] Highlights: • Multivariate statistics and isotope were used together to trace the pollution. • Limited contribution of agricultural activities to heavy metals in the soils. • Coal combustion and smelting/refining activities were main anthropogenic sources. -- Abstract: Apportioning sources of environmental pollutants is key to controlling pollution. In this study, the sources of heavy metals to 234 agricultural soils from the Jianghan Plain (JHP) (∼22454 km²) in central China were discriminated between using Cd and Pb isotope compositions and multivariate statistical analyses. Concentrations of some metals in JHP soils (0.48 ± 0.2, 48.2 ± 15.9, 0.12 ± 0.23, 48.8 ± 16.4, 36.5 ± 9.8, and 96.8 ± 42.2 mg kg⁻¹ for Cd, Cu, Hg, Ni, Pb, and Zn, respectively) were higher than background concentrations in Chinese soil. The Cd isotope compositions for the JHP soils (δ^114/110Cd values −0.76‰ to −0.25‰) were similar to Cd isotope compositions found for smelter dust and incinerator fly ash, indicating Cd was supplied to the JHP soils by ore smelting and/or refining processes. The Pb isotope compositions for the JHP soils (²⁰⁶Pb/²⁰⁷Pb 1.182–1.195 and ²⁰⁸Pb/²⁰⁶Pb 2.078–2.124) were between the Pb isotope compositions found for Chinese coal and natural sources, which a binary isotope mixing model indicated contributed 52% and 48%, respectively, of the Pb in JHP soils. Cluster analysis and positive matrix factorization indicated that the sources of heavy metals in JHP soils may consist of smelting and/or refining activities, coal combustion, agricultural activities, and natural sources (including Han River sediment and soil parent materials). The isotope fingerprints and multivariate statistical analyses together indicated that coal combustion and smelting and/or refining activities were the main anthropogenic sources of heavy metals polluting JHP soils.

[en] Highlights: • The absorption coefficient of OH⁻ in galss sample is about 0.0011 cm⁻¹. • The luminescence performance at λ~3.5 μm in Er³⁺ doped fluoroindate glass samples is investigated. • The maximum emission cross-section of 4.86 × 10⁻²² cm² was obtained. Under 635 nm laser excitation, the 3.5 μm luminescence, corresponding to the Er³⁺: ⁴F_9/2 → ⁴I_9/2 radiation transition, was demonstrated in Er³⁺ doped fluoroindate glasses prepared by melt-quenching method. The energy transfer mechanisms were investigated and the 3.5 μm emission intensity reached a maximum for an Er³⁺ concentration of 9 mol%. The Er³⁺ energy level lifetimes in fluoroindate glass samples were measured, their oscillator strength parameters were calculated by Judd-Ofelt theory and their emission cross-section at 3.5 μm was obtained. The maximum emission cross-section at 3.51 μm was 4.86 × 10⁻²² cm², which indicated that Er³⁺ doped fluoroindate glass is a potential gain medium for lasing at 3.5 μm.

[en] The periodic gain structure is used as the active region of vertical-cavity surface-emitting lasers, which can enhance the effective coupling between gain regions and internal optical field. The high device performance is achieved. The maximum continuous-wave output power of large aperture device with active diameter up to 400 μm is as high as 1.41 W at room temperature. The low threshold current is only 0.5 A, which is lower than that of the conventional device with three quantum wells