RESUMO
We report a detailed experimental and theoretical analysis of the $^4{{\rm F}_{9/2}}$ to $^6{{\rm H}_{13/2}}$ lasing transition of a dysprosium (${{\rm Dy}^{3 +}}$)-doped ZBLAN fiber, a strong candidate for future compact and highly efficient yellow laser emission. Experimentally, we used a gallium nitride laser diode emitting at 447 nm as a pump source and measured yellow laser output generated with a maximum slope efficiency of 33%, which is less than half of the Stokes limit (of ${\sim}78\%$). This result is commensurate with two other reports of yellow emission from ${{\rm Dy}^{3 +}}$. As a result, we developed a numerical model to understand and analyze the improvement potential of this fiber laser system. For reliable spectroscopic data input to the numerical model, we measured the absorption and emission cross sections from ${{\rm Dy}^{3 +}}$-doped ZBLAN glass. We investigated the potential causes of the low experimental slope efficiency and found contributions from the background loss of the fiber and excited-state absorption (ESA) of the intracavity yellow light. We estimated the signal re-absorption cross section using the emission cross section and the McCumber relation, which was subsequently used in our numerical model to compare successfully with our experimental results. We show that the ESA can be reduced for future ${{\rm Dy}^{3 +}}$-doped yellow laser systems by cascade lasing or co-doping with a suitable rare earth ion desensitizer.
RESUMO
We report high-energy mid-infrared pulse generation by Q-switching of dysprosium-doped fiber lasers for the first time. Two different modulation techniques are demonstrated. Firstly, using active acousto-optic modulation, pulses are produced with up to 12 µJ energy and durations as short as 270 ns, with variable repetition rates from 100 Hz to 20 kHz and central wavelengths tunable from 2.97 to 3.23 µm. Experiments are supported by numerical modeling, identifying routes for improved pulse energies and to avoid multi-pulsing by careful choice of modulator parameters. Secondly, we demonstrate passive Q-switching by fabricating an inkjet-printed black phosphorus saturable absorber, simplifying the cavity and generating 1.0 µJ pulses with 740 ns duration. The performance and relative merits of each modulation approach are then critically discussed. These demonstrations highlight the potential of dysprosium as a versatile gain medium for high-performance pulsed sources beyond 3 µm.
RESUMO
Rare-earth-doped fiber lasers are emerging as promising high-power mid-infrared sources for the 2.6-3.0 µm and 3.3-3.8 µm regions based on erbium and holmium ions. The intermediate wavelength range, however, remains vastly underserved, despite prospects for important manufacturing and defense applications. Here, we demonstrate the potential of dysprosium-doped fiber to solve this problem, with a simple in-band pumped grating-stabilized linear cavity generating up to 1.06 W at 3.15 µm. A slope efficiency of 73% with respect to launched power (77% relative to absorbed power) is achieved-the highest value for any mid-infrared fiber laser to date, to the best of our knowledge. Opportunities for further power and efficiency scaling are also discussed.
RESUMO
A noncontact scanning probe microscopy method was used to probe local near-surface dielectric susceptibility and dielectric relaxation in polyvinyl acetate near the glass transition. Dielectric spectra were measured from 10(-4) to 10(2) Hz as a function of temperature. The measurements probed a 20 nm thick layer below the free surface of a bulk film. A significant change in the fragility index and moderate narrowing of the distribution of relaxation times were found in the near-surface layer. In contrast to results for ultrathin films confined on or between metallic electrodes, no reduction in the dielectric strength was found, inconsistent with the immobilization of slower modes.
