Based on the open-aperture Z-scan measurement, we firstly uncovered the saturable absorption property of the topological insulator (TI): Bi2Se3. A high absolute modulation depth up to 98% and a saturation intensity of 0.49 GWcm(-2) were identified. By incorporating this novel saturable absorber material into an erbium-doped fiber laser, wavelength tunable soliton operation was experimentally demonstrated. Our result indicates that like the atomic layer graphene, the topological insulator Bi2Se3 could also operate as an effective saturable absorber for the passive mode locking of lasers at the telecommunication band.

The third order nonlinear optical property of Bi₂Se₃, a kind of topological insulator (TI), has been investigated under femto-second laser excitation. The open and closed aperture Z-scan measurements were used to unambiguously distinguish the real and imaginary part of the third order optical nonlinearity of the TI. When excited at 800 nm, the TI exhibits saturable absorption with a saturation intensity of 10.12 GW/cm² and a modulation depth of 61.2%, and a giant nonlinear refractive index of 10⁻¹⁴ m²/W, almost six orders of magnitude larger than that of bulk dielectrics. This finding suggests that the TI:Bi₂Se₃ is indeed a promising nonlinear optical material and thus can find potential applications from passive laser mode locker to optical Kerr effect based photonic devices.

We establish a general propagation model to describe the spin Hall effect of light beam in left-handed materials (LHMs). A spin-dependent shift of the beam centroid perpendicular to the refractive index gradient for the light beam through an air-LHM interface is demonstrated. For a certain circularly polarized component, whether the transverse shift is positive or negative depends on the magnitude of the refractive index gradient. Very surprisingly, the spin Hall effect in the LHM is unreversed, although the sign of refractive index gradient is reversed. The physics underlying this counterintuitive effect is that the spin angular momentum of photons is unreversed. Further, we reveal that the angular shift in the LHM is reversed due to the negative diffraction. These findings provide alternative evidence for that the linear momentum of photons is reversed, while the spin angular momentum is unreversed in the LHM.Comment: 7 pages, 4 figure

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BackgroundThe purpose of this research is to identify the bowel symptoms and self-care strategies for rectal cancer survivors during the recovery process following low anterior resection surgery.MethodsA total of 100 participants were investigated under the structured interview guide based on the dimensions of “symptom management theory”.Results92% of participants reported changes in bowel habits, the most common being the frequent bowel movements and narrower stools, which we named it finger-shaped consistency stools. The 6 most frequently reported bowel symptoms were excessive flatus (93%), clustering (86%), urgency (77%), straining (62%), bowel frequency (57%) and anal pendant expansion (53%). Periodic bowel movements occurred in 19% participants. For a group of 79 participants at 6 to 24 months post-operation, 86.1% reported a significant improvement of bowel symptoms. Among 68 participants of this subgroup with significant improvements, 70.5% participants reported the length of time it took was at least 6 months. Self-care strategies adopted by participants included diet, bowel medications, practice management and exercise.ConclusionsIt is necessary to educate patients on the symptoms experienced following low anterior resection surgery. Through the process of trial and error, participants have acquired self-care strategies. Healthcare professionals should learn knowledge of such strategies and help them build effective interventions.