Flemingtherkelsen7395

A flat-amplitude multi-wavelength random Raman fiber laser with broad spectral coverage and a high optical signal-to-noise ratio (OSNR) is challenging and of great interest. In this Letter, we theoretically and experimentally proved that broadband pumping can help realize a broader, flat-amplitude multi-wavelength random Raman fiber laser. The influence of pump bandwidth, tunability of the spectral envelope, and channel spacing are investigated. As a result, with a 40 nm pump bandwidth, a spectral coverage of 1116-1125 nm with 19 laser lines and 31 dB OSNR is achieved, and the standard deviation in the peak intensities of the central nine lines is $\sim1.1\;\rm dBm$∼1.1dBm. This technique can also be applied to the multi-wavelength Raman (or random Raman) fiber lasers at other wavelengths and provide a reference for multi-wavelength applications in sensing, communication, and optical component testing.In this Letter, we propose and realize a novel concept for a high-peak-power highly efficient fiber amplifier in the 1.55 µm spectral range. The amplifier is based on the simultaneous utilization of Er-doped, Yb-free, and Er-Yb codoped large-mode-area fibers spliced together. Using this approach, we demonstrate the amplification of single-frequency 160 ns pulses at 1554 nm to a peak power of 3.7 kW with a pump-to-signal conversion efficiency of 23.6% relative to the launched multimode pump power at 976 nm.Microwave metasurfaces comprising overlapping layers of circular patches arranged in a hexagonal array are found to support edge modes akin to edge plasmons. GX15-070 nmr The coupling of these edge modes across small gaps between two such arrays is explored. This phenomenon, well known at optical frequencies, is verified here for the first time, to the best of our knowledge, at microwave frequencies.We describe theoretically and verify experimentally a novel, to the best of our knowledge, class of diffraction-free pulsed optical beams that are "omni-resonant" they have the remarkable property of transmission through planar Fabry-Perot resonators without spectral filtering, even if their bandwidth far exceeds the cavity linewidth. Ultrashort wave packets endowed with a specific spatiotemporal structure couple to a single resonant mode independent of its linewidth. We confirm that such "space-time" omni-resonant wave packets retain their bandwidth (1.6 nm), spatiotemporal profile (1.3-ps pulse width, 4-µm beam width), and diffraction-free behavior upon transmission through cavities with resonant linewidths of 0.3 nm and 0.15 nm.Monoclinic (wolframite-type) monotungstate crystals are promising for rare-earth doping. We report polarized room- and low-temperature spectroscopy and efficient high-power laser operation of such a $\rm Yb^3 + \,\rm MgWO_4$Yb3+MgWO4 crystal featuring high stimulated emission cross section ($\sigma _\rm SE\; = \;6.2\; \times \;10^ - 20\;\rm cm^2$σSE=6.2×10-20cm2 at 1056.7 nm for light polarization $\rm E\;||\;N_m$E||Nm), large Stark splitting of the ground state ($765\;\rm cm^ - 1$765cm-1), large gain bandwidth (26.1 nm for $\rm E\;||\;N_g$E||Ng), and strong Raman response (most intense mode at $916\;\rm cm^ - 1$916cm-1). A diode-pumped $\rm Yb^3 + \,\rm MgWO_4$Yb3+MgWO4 laser generated 18.2 W at $\sim1056\;\rm nm$∼1056nm with a slope efficiency of $\sim89\% $∼89% and a linearly polarized laser output.The unique ring-shaped intensity patterns and helical phase fronts of optical vortices make them useful in many applications. Here we report for the first time, to the best of our knowledge, efficient Raman frequency conversion between vortex modes in a twisted hydrogen-filled single-ring hollow core photonic crystal fiber (SR-PCF). High-fidelity transmission of optical vortices in an untwisted SR-PCF becomes more and more difficult as the orbital angular momentum (OAM) order increases, due to scattering at structural imperfections in the fiber microstructure. In a helically twisted SR-PCF, however, the degeneracy between left- and right-handed versions of the same mode is lifted, with the result that they are topologically protected from such scattering. With launch efficiencies of $\sim75\% $∼75%, a high damage threshold and broadband guidance, these fibers are ideal for performing nonlinear experiments that require the polarization state and azimuthal order of the interacting modes to be preserved over long distances. Vortex coherence waves of internal molecular motion carrying angular momentum are excited in the gas, permitting the polarization and OAM of the Raman bands to be tailored, even in spectral regions where conventional solid-core waveguides are opaque or susceptible to optical damage.Our group proposes an improved misalignment measurement scheme using the moiré beat signal. Compared with the coarse-fine moiré-based alignment methods, this scheme could complete the nanometer-scale alignment within a centimeter-scale scope in one step. Moreover, it could also fundamentally eliminate the influence from the field of view of the observation lens. These merits make it suitable for the high-precision large-scope misalignment sensing in the proximity, x-ray, and nanoimprint lithographies. The experimental results are given to verify the feasibility and rationality.Gold nanorod (Au NR) is an attractive material due to its superior physical and chemical properties. Various applications in diagnostics and biomedicine have been demonstrated. The single-pulse laser is commonly used to reshape nanoparticles in a solvent; however, the laser-material reaction mechanisms underlying nanoparticle reshaping remain unclear. Here, we report the reshaping of Au NRs by ultrafast pump-probe-like double-pulse laser irradiation to understand the reaction dynamics. We demonstrate the enhancement of double-pulse-induced reshaping, which provides an opportunity to design new Au NR structures. It shows that the reshaping enhancement is dependent on the delay time ($\tau _s$τs) between a pair of separated pulses. The absorption peak wavelength of Au NRs exposed to the shaped double pulse was lower than that of using a single pulse of the same total fluence when $\tau _s$τs was less than the electron-phonon relaxation time. This phenomenon was mainly attributed to changes in electronic heat transport and electron-phonon coupling, which affected the pulse delay-dependent nanorod (NR) temperature.