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In this study, we realize the high-power output of a single-mode 894 nm vertical-cavity surface-emitting laser (VCSEL) at high temperature. The effects of the dimensional parameters of oxide aperture and surface relief on the transverse mode and threshold gain of VCSEL were analyzed. Through collaborative optimization of the oxide aperture and relief, the VCSEL with 8 µm oxide aperture diameter and 5 µm surface relief inner diameter can operate at high temperature of 365 K with single-mode output power of 2.02 mW and side-mode suppression of 29.2 dB. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence (LIF) technique has been widely used to measure the polycyclic aromatic hydrocarbons (PAHs) in sooting flames, but the assignment of the LIF signals measured in flames to specific PAH species is hard to obtain. Investigation on the LIF spectra of gas-phase PAH mixtures could be helpful to analyze LIF spectra measured in flames for more detailed PAH information. In this study, the LIF spectra of gas-phase PAH mixtures containing naphthalene, phenanthrene, pyrene, fluoranthene were experimentally investigated in an optical cell at 673 K and 1073 K. The experimental results indicated that the integral fluorescence intensity of each PAH was in direct proportion to its mole fraction. Moreover, the LIF spectra of PAH mixtures were linearly superposed from the spectra of their components weighted using mole fractions. The component concentrations of the PAH mixtures were able to be fitted from the LIF spectra using multiple linear regression method, and most of the relative errors were less than 5%. In the light of these results from gas-phase PAHs, the LIF spectra of flame-formed PAHs measured in a laminar premixed ethylene flame were discussed. Considering the temperature effects on LIF spectra and simulated PAH concentrations in the flame, the lighter PAHs will contribute to the fluorescence signals shorter than 450 nm measured in the flame. Using the multiple linear regression method established in this study, the relative ratios of naphthalene, phenanthrene and pyrene can be fitted from the LIF spectrum of the flame. In this way, more selective information of these lighter PAHs can be obtained from the LIF spectrum measured in flames. On the other hand, fluorescence signals in the flame longer than 450 nm are possibly emitted from the PAHs with five-membered-ring structures or (and) nanoparticles and nascent soot particles, which are still ambiguous and needs to be further investigated in future works. [ABSTRACT FROM AUTHOR]

The laser-induced fluorescence technique is widely used in the measurement of polycyclic aromatic hydrocarbons (PAHs) in sooting flames. One of the main limitations is the absence of the PAH fluorescence spectra at elevated temperatures. In this study, fluorescence spectra and photophysical properties of five typical PAHs were experimentally studied in the temperature range of 673-1373 K in an optical cell. The experimental results indicated that the fluorescence spectra of PAHs were greatly sensitive to PAH structures and were likely to shift to the red and became broader as temperature increases. Further, we also observed that absorption cross sections of PAHs increased linearly as a function of temperature. Fluorescence quantum yields, which were calculated using integral fluorescence intensities and absorption cross sections, decreased monotonically with increasing temperature. However, the descent gradients of different PAHs were quite different, e.g., naphthalene, fluoranthene and fluorene were more sensitive to temperature, and their fluorescence production was much lower at elevated temperature compared with phenanthrene and pyrene. In order to investigate the fluorescence quantum yields at higher temperatures (up to 2000 K), which cannot be measured in the optical cell, a multistep decay model was established and optimized based on experimental results. At temperatures between 1373 and 2000 K, the extrapolation results indicated that fluorescence quantum yields of phenanthrene and pyrene would be two orders of magnitude higher than those of naphthalene, fluorene and fluoranthene. This contributed to explaining that the PAH fluorescence signals emitted from phenanthrene and pyrene were stronger than those emitted from naphthalene in flames, although the concentrations of phenanthrene and pyrene were much lower than that of naphthalene in flames. [ABSTRACT FROM AUTHOR]