As one of the 1D nanomaterials, Se nanochains have been widely used in photoelectric devices, such as photodetectors, battery devices, and optical sensors due to their excellent photoelectric properties. Among them, ultrafast photonics has attracted much attention due to its wide applications; for instance, environmental monitoring, material processing, biomedical imaging, nonlinear optical generation, and free‐space optical communication. Herein, Se nanochains are fabricated by trapping Se species in the circular 1D channel of AlPO 4 ‐5 (AFI) crystal, and the characteristics of Se@AFI are systemically investigated. In addition, the AFI single crystal loaded with Se nanochains in the channel is successfully prepared as a saturable absorber in the fiber laser. The mode‐locking pulse at 1.5 and 1 μm with the repetition rate of 13.16 and 14.74 MHz can be obtained by integrating the Se@AFI composite material in the cavity. The signal‐to‐noise ratios are both over 70 dB, suggesting the high operational stability of the pulses. These results indicate that Se@AFI has good potential as saturable absorber material with a broad wavelength range for ultrafast pulsed fiber lasers. Our results will also provide a new idea for designing air‐stable ultrafast photonic devices and other composite materials in various fields.
Carbon nanocages with controllable nonlinear saturable absorber properties are synthesized at low carbonization temperature, and can be used for the generation of a Q-switching or mode-locking pulsed fiber laser.
We demonstrate a passively mode-locked erbium-doped fiber laser (EDFL) by using the smallest single-walled carbon nanotubes (SWNTs) with a diameter of 0.3 nm as the saturable absorber. These ultrasmall SWNTs are fabricated in the elliptical nanochannels of a ZnAPO4-11 (AEL) single crystal. By placing an AEL crystal into an EDFL cavity pumped by a 980 nm laser diode, stable passive mode-locking is achieved for a threshold pump power of 280 mW and 73 ps pulses at 1563.2 nm with a repetition rate of 26.79 MHz.
Localised magnetic flux density, magnetising field and power loss are believed to distribute non-uniformly in grain oriented electrical steel. Understanding of the causes of their variation can help reduce the overall power loss of the material.
In this investigation, magnetic domain observation was often used in the study of domain configuration and crystal orientation of the test specimens. Methods of domain observation have been studied and compared in order to select the appropriate method for different parts of the investigation and to improve the understanding of the image observed.
A less destructive local loss measurement sensor has been built for the measurement of localised flux density, magnetising field and power loss. The sensor was tested and evaluated specifically for the measurement of localised magnetic power loss of the high permeability grain oriented electrical steel.
The results obtained from local loss scanning measurements indicated that localised flux density and magnetising field can vary substantially in grain oriented electrical steel under AC magnetisation of 50 Hz. The variation of localised flux density has been found mainly resulted by grain misorientation and local grain arrangement. The transverse component of flux density was detected and has been found increases with increasing grain misorientation. The variation of localised magnetising field has been found mainly influenced by the localised demagnetising field due to formation of free magnetic poles at grain boundaries. It has been proved that both flux density and magnetising field have strong influence on the distribution of localised power loss.
The study of the effect of domain refinement on distribution of localised flux density showed that domain refinement by means of ball scribing on one surface of grain oriented electrical steel can improve the uniformity of distribution of flux density. However, results also inferred that excessive scribing in a confined area can cause obvious uneven distribution of flux density in the direction of the specimen’s thickness.
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