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The pyroelectric effect converts thermal energy into usable electrical energy. It is an ideal and effective strategy to enhance the surface-enhanced Raman scattering (SERS) detection sensitivity by tuning the electromagnetic fields. In this work, a plasmonic metal/ferroelectric hybrid SERS substrate was fabricated by integrating a pyroelectric functional layer composed of BiFeO3 with an electron/heat conduction layer of carbon nanofibers (CNFs) using the electrospinning technique. The initial layer was followed by a plasmonic layer of Ag nanowires, which were uniformly spin-coated on BiFeO3/CNFs. By introducing periodically switched near-infrared (NIR) light, the BiFeO3/CNFs could effectively convert the thermal energy induced by light into pyroelectric charge, which could adjust the electron densities of Ag, and in turn boost the electromagnetic fields at the "hot spots". The hybrid Ag–BiFeO3/CNFs were used to test the Raman signals of methylene blue (MB), and a 5.6-fold enhancement of the SERS signal was achieved compared with that noted without the pyroelectric effect and the following parameters were obtained: an ultra-low detection of 10−13 M, a high enhancement factor of 8.3 × 109, and excellent reproducibility with an RSD of 4.08%. The theoretical calculations revealed that the excellent sensitivity was mainly ascribed to the synergistic light-induced pyroelectric and plasmon effects. In addition, this substrate was also used for the detection of ciprofloxacin (CIP) in milk with a limit of detection as low as 10−10 M. Furthermore, the Ag–BiFeO3/CNFs were used to successfully in situ monitor the photocatalytic reduction of p-nitrophenol (p-NTP) to 4,4′-dimercaptoazobenzene (DMAB) by SERS in real time. This work provides an efficient strategy to develop highly sensitive SERS substrates through pyroelectric-plasmonic hybrid structures, and opens a new avenue for the development of energy harvesters that can be used for extensive applications. [ABSTRACT FROM AUTHOR]

In this study, a double-end pumped high-power passively mode-locked erbium-doped fiber laser (EDFL) was realized by employing a few-layered In2Se3 flakes as a saturable absorber (SA). Herein, the uniform large-scale In2Se3 flakes were synthesized by the physical vapor deposition (PVD) method. The PVD-In2Se3 SA exhibited a remarkable damage threshold of higher than 24 mJ/cm2. Meanwhile, the PVD-In2Se3 SA had a modulation depth and saturable intensity of 18.75% and 6.8 MW/cm2, respectively. Based on the In2Se3 SA, the stable bright pulses emitting at 1559.4 nm with an average output power/pulse energy/pulse duration of 122.4 mW/5.8 nJ/14.4 ns were obtained successfully. To our knowledge, 122.4 mW was the new major breakthrough of mode-locked Er-doped fiber lasers. In addition, this is the first demonstration of the dark-bright pulse pair generation based on In2Se3 SA. The maximum average output power of the dark-bright pulse reached 121.2 mW, which also showed significant enhancement in comparison with previous works. Our excellent experiment results fully prove the superiority of our experimental design scheme and indicate that the PVD-In2Se3 could operate as a promising highly-nonlinear photonic material for a high-power fiber laser. [ABSTRACT FROM AUTHOR]

In this work, we report about high energy and various solitons' operation by using high-efficiency topological insulator bismuth telluride ( B i 2 T e 3 ) nanofilms as broadband saturable absorbers in the passively mode-locked Er-doped fiber laser. The B i 2 T e 3 film was successfully synthesized by chemical vapor deposition (CVD). Excellent characteristics of the dark-bright pulse pairs, bright pulses, and multiharmonics have been investigated experimentally by adjusting the polarization state. At the same time, the maximum average output power was 40.18 mW, and the single-pulse energy was 20.91 nJ. As we all know, it is the various solitons of the first generation with large pulse energy in an Er-doped fiber laser with B i 2 T e 3 as saturable absorber. The experimental results show that CVD B i 2 T e 3 can be used as an excellent candidate in mode-locked fiber lasers.

In this study, the output energy in topological insulators (TIs)-based Erbium-doped fiber laser (EDFL) was improved using two strategies: bidirectional pumped laser cavity and saturable absorber (SA) with high damage threshold and large modulation depth. Using the chemical vapor deposition (CVD) method, Bismuth Selenide (Bi 2 Se 3 ) film was synthesized and improved to a SA. Employing this CVD-Bi 2 Se 3 SA in an EDFL, bright and bright-dark soliton operations were achieved. The average output power/pulse energy was 82.6 mW/48.3 nJ and 81.2 mW/47.5 nJ, respectively. The results demonstrate that CVD-Bi 2 Se 3 can act as an excellent performance material to improve output power performance in TISA-based EDFL.

In this study, a high-energy noise-like mode-locked Yb-doped fiber laser in a linear cavity was achieved with SnS 2 -polyvinyl alcohol film as the saturable absorber. In addition, the nonlinear saturable absorption characteristics of the SnS 2 were investigated experimentally. The saturation intensity and modulation depth were about 6.01  MW/cm 2 and 8.68%, respectively. Under pump power of 422 mW, stable noise-like mode-locked operation with a maximum output power and largest single pulse energy of 9.50 mW and 18.1 nJ, respectively, was obtained. To the best of our knowledge, this study is the first to observe and experimentally investigate noise-like operation in a linear laser cavity. Our study may provide some valuable design guidelines for noise-like operation and create new directions for advanced photonic devices based on SnS 2 .

We reported on the generation of pulse bunch and large-energy dark pulses in a mode-locked ytterbium-doped linear-cavity fiber laser based on Bi 2 Se 3 as a saturable absorber (SA). Bi 2 Se 3 nanosheets were successfully synthesized by the chemical vapor deposition (CVD) method and transferred to the end facet of a fiber connector for the proposed SA. Its saturation intensity and modulation depth were measured to be 52   MW / cm 2 and 14.5%, respectively. By inserting the Bi 2 Se 3 -based SA into the Yb-doped all-fiber linear cavity, stable pulse bunches were observed. In addition, dark soliton operation with a maximum average output power of 32.6 mW and a pulse energy of 61.8 nJ were also achieved. To the best of our knowledge, this is the first demonstration of a dark soliton within a linear cavity with much larger pulse energy than previous works. Our study fully indicated that CVD - Bi 2 Se 3 could be an excellent SA for achieving large-energy pulse operations.