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The decoration of noble metal nanoparticles (NPs) on the surface of metal oxide semiconductors to enhance material characteristics and gas-sensing performance has recently attracted increasing attention from researchers worldwide. Here, we have synthesized porous silicon (PS)/WO3 nanorods (NRs) functionalized with Pd NPs to enhance NO2 gas-sensing performance. PS was first prepared using electrochemical methods and worked as a substrate. WO3 NRs were synthesized by thermally oxidizing W film on the PS substrate. Pd NPs were decorated on the surface of WO3 NRs via in-situ reduction of the Pd complex solution by using Pluronic P123 as the reducing agent. The gas-sensing characteristics were tested at different gas concentrations and different temperatures ranging from room temperature to 200 °C. Results revealed that, compared with bare PS/WO3 NRs and Si/WO3 NRs functionalized with Pd NPs, the Pd-decorated PS/WO3 NRs exhibited higher and quicker responses to NO2, with a detection concentration as low as 0.25 ppm and a maximum response at room temperature. The gas-sensing mechanism was also investigated and is discussed in detail. The high surface area to volume ratio of PS and the reaction-absorption mechanism can be explained the enhanced sensing performance.

We present a narrow linewidth, all-fiber polarization-maintained amplifier chain seeded by a phase-modulated single-frequency laser, which is a narrow linewidth. Different from previous phase-modulation techniques, the phase-modulation signal is generated by simply imposing an excited signal to an acoustic-optical driven source. Theoretical simulation results show that this method can suppress stimulated Brillouin scattering (SBS) to a better degree, and the output power can be boosted to about 1.2 kW in terms of the SBS threshold. By amplifying the phase-modulated seed based on master-oscillator power-amplification configuration in experiments, a 560 W output laser is achieved with slope efficiency of 87.2% and linewidth of <5  GHz. Further power scaling is limited by mode instability instead of an SBS effect. At maximal output power, the beam quality (M² factor) and polarization extinction ratio is measured to be within 1.3 and 14 dB, respectively.