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In this work, ultrafast Yb-doped fiber laser was realized using multi-layer palladium diselenide (PdSe2) film as the saturable absorber, which was prepared by simple selenization of palladium film deposited by magnetron sputtering method. The prepared polycrystalline PdSe2 film has a thickness of about 12 nm. At a pump power of 180 mW, the obtained mode-locked fiber laser based on the PdSe2 film has a central wavelength of 1063.75 nm, a pulse width of 615 ps, a repetition rate of 17.66 MHz, and an output power of 4.43 mW, respectively. These results indicate that PdSe2 has great potential in applications of ultrafast lasers. [ABSTRACT FROM AUTHOR]

Lead-free double perovskites (DPs) have received a lot of attention owing to their good stability and environmental friendliness. They have been widely used in the field of optoelectronics because of their high quantum efficiency and long carrier migration distance. However, the application of lead-free DPs in ultrafast photonics is rarely explored. Cs2AgBiBr6, a typical lead-free double perovskite, has advantages such as toxicity free of Pb, high stability, and strong nonlinear absorption, showing great potential application in ultrafast photonics. However, to date, there is no reported research on the application of Cs2AgBiBr6 in ultrafast optical devices. Herein, we prepared Cs2AgBiBr6 nanocrystals, tested their ultrafast nonlinear absorption properties, and further prepared them as a saturable absorber (SA) to achieve stable mode-locking pulses in Er-doped fiber lasers. The results show that it has a low saturation intensity (0.75 MW/cm2), resulting in a low starting threshold power (50 mW) for mode-locking. The obtained pulsed fiber laser shows a pulse width as narrow as 452 fs. In addition, the Cs2AgBiBr6 SA has unique advantages in long-term stability and it was found that this Cs2AgBiBr6 SA can still work well after 10 months. In general, our results prove that Cs2AgBiBr6 is an excellent nonlinear optical material and has good application potential in ultrafast photonics. [ABSTRACT FROM AUTHOR]

The challenge related to degradation under ambient conditions has greatly constrained Ti3C2Tx quantum dots (QDs) from being used in optical applications. Herein, Ti3C2Tx QDs with an average size within 10 nm were synthesized by exploiting the minimally intensive layer delamination united liquid-phase exfoliation methods. Then, polyvinyl alcohol (PVA) was employed to encapsulate Ti3C2Tx QDs to prepare a saturable absorber (SA) applied in ultrafast laser systems. As verified by balanced twin-detector measurements, the Ti3C2Tx QDs/PVA SA exhibited an ultra-low saturation intensity of 4.3 kW cm−2. By incorporating the Ti3C2Tx QDs/PVA SA into an erbium-doped fiber laser cavity, both Q-switched and mode-locked lasers with high operational stability were easily obtained. Furthermore, the Ti3C2Tx QDs/PVA SA could still easily realize the stable passive mode-locked state with the narrowest pulse width of 654 fs beyond 12 months, which sufficiently demonstrates its versatility and long-term stability. Thus, this work provides a facile approach for MXene QD based practical optoelectronic devices. [ABSTRACT FROM AUTHOR]

Transition metal carbides and nitrides (MXenes) have attracted significant attention in photoelectric applications due to their highly tunable electronic and optical properties influenced by a flexible compositional or surface functional group regulation. Ti3C2Tx MXenes (-F, -OH, =O terminated) used in previous ultrafast photonic studies are usually synthesized via a generic hydrofluoric acid (HF) etching strategy, which may cause numerous defects and thus impedes the optoelectronic properties of Ti3C2Tx. In this contribution, inspired by a much higher conductivity and carrier mobility of Ti3C2Tx (-F, -OH, =O, -Cl terminated) prepared from a minimally intensive layer delamination method (MILD) etching strategy, we further optimized it with a liquid-phase exfoliation (LPE) method to synthesize pure Ti3C2Tx quantum dots (QDs) for ultrafast photonic. Compared to the other QDs saturable absorber (SA) devices performed at 1550 nm, our SA device exhibited a relatively low saturation intensity (1.983 GW/cm−2) and high modulation depth (11.6%), allowing for a more easily mode-locked pulse generation. A distinguished ultrashort pulse duration of 466 fs centered at the wavelength of 1566.57 nm with a fundamental frequency of 22.78 MHz was obtained in the communication band. Considering the SA based on such a Ti3C2Tx QDs tapered fiber is the first exploration of Er3+-doped fiber laser (EDFL), this work will open up a new avenue for applications in ultrafast photonics. [ABSTRACT FROM AUTHOR]

Platinum ditelluride (PtTe2) has many applications in phototransistors, photodetectors, photocatalysis and other fields due to its interesting semiconductor-to-semimetal transition property, ultrashort excited carrier lifetime, high carrier mobility, excellent air stability, and so on. However, the ultrafast nonlinear optical properties of PtTe2 and its application in ultrafast photonics have been rarely explored so far. In this work, PtTe2 nanosheets were prepared and two kinds of saturable absorbers (SAs) were further fabricated, namely the PtTe2/PVA film and PtTe2 coated tapered fiber. The results showed different nonlinear absorption properties for the two SAs. The modulation depth and saturation intensity were determined to be 0.9% and 55.7 MW cm−2 for the PVA film, and 8.9% and 1.39 GW cm−2 for the tapered fiber, respectively. More importantly, Q-switched and mode-locked Er-doped fiber lasers were realized using the PtTe2/PVA film and PtTe2 coated tapered fiber SAs, respectively. The pulse widths of the Q-switched and mode-locked fiber lasers are 2.63 μs and 959 fs, respectively. These results confirm that PtTe2 has great potential in ultrafast photonic applications, and moreover, the PtTe2 coated tapered fiber SA is more suitable for mode-locked fiber lasers because of its lower nonsaturable absorption loss and larger modulation depth by contrast to the PVA film SA. [ABSTRACT FROM AUTHOR]

Objective: To study the lead exposure of people living in a lead high exposure area from local diet, and to assess its health risks., Methods: Thirty five subjects were selected by random from a mining area and another 30 subjects were selected from a non-polluted area. The exposure of lead was estimated by the content of lead in drinking water and vegetables, and health risks was estimated by the levels of lead in blood and urine., Results: The content of lead in drinking water and vegetables in the mining area was 20.6 microg/L and 1.61mg/kg (geometric mean) respectively, which were higher than that in the unpolluted area (6.0 microg/L and 0.56 mg/kg, geometric mean) (P < 0.01). The daily lead exposure of male and female inhabitants in the mining area from diet was 16.88 microg/kg and 16.09 microg/kg respectively, which was higher than that in the unpolluted area (P < 0.01), but the sex difference was not significant statistically (P > 0.05). Blood lead and urine lead of inhabitants in the mining-area were higher than those in the unpolluted area. The health risks for male and female inhabitants in the mining area were 4.73 and 4.51., Conclusion: The health risks of lead exposure caused by diet (drinking water and food) were relatively high in the mining area.