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Abstract:We reported on the generation of femtosecond pulse in an anomalous-dispersion fiber ring laser by using a polyvinyl alcohol (PVA)-based Topological Insulator (TI), Bi 2 Se 3 saturable absorber (SA). The PVA-TI composite has a low saturable optical intensity of 12 MW/cm 2 and a modulation depth of ~3.9%. By incorporating the fabricated PVA-TISA into a fiber laser, mode-locking operation could be achieved at a low pump threshold of 25 mW. After an optimization of the cavity parameters, optical pulse with ~660 fs centered at 1557.5 nm wavelength had been generated. The experimental results demonstrate that the PVA could be an excellent host material for fabricating

The vector meson ρ in the presence of external magnetic field has been investigated in the framework of the Nambu-Jona-Lasinio model, where mesons are constructed by infinite sum of quark-loop chains by using random phase approximation. The ρ meson polarization function is calculated to the leading order of 1/Nc expansion. It is found that the constituent quark mass increases with magnetic field, the masses of the neutral vector meson ρ 0 with spin component sz = 0, ±1 and the charged vector meson ρ ± with sz = 0 also increases with magnetic field. However, the mass square of the charged vector meson ρ + (ρ − ) with sz = +1 (sz = −1) decreases linearly with magnetic field and drops to zero at the critical magnetic field eBc ≃ 0.2GeV 2 , which indicates the possible condensation of charged vector meson in the vacuum. This critical magnetic field is much lower than the value eBc = 0.6GeV 2 predicted by a point-like vector meson. We also show that if we use lowest Landau level approximation, the mass of the charged vector meson ρ ± for sz = ±1 cannot drop to zero at high magnetic fields.