ABSTRACT
We demonstrate efficient pulse-energy extraction from a partly quenched erbium-doped aluminosilicate fiber amplifier. This has a high erbium concentration that allows for short devices with reduced nonlinear distortions but also results in partial quenching and thus significant unsaturable absorption, even though the fiber is still able to amplify. Although the quenching degrades the average-power efficiency, the pulse energy remains high, and our results point to an increasingly promising outcome for short pulses. Furthermore, unlike unquenched fibers, the conversion efficiency improves at low repetition rates, which we attribute to smaller relative energy loss to quenched ions at higher pulse energy. A short (2.6 m) cladding-pumped partly quenched Er-doped fiber with 95-dB/m 1530-nm peak absorption and saturation energy estimated to 85 µJ reached 0.8 mJ of output energy when seeded by 0.2-µs, 23-µJ pulses. Thus, according to our results, pulses can be amplified to high energy in short highly Er-doped fibers designed to reduce nonlinear distortions at the expense of average-power efficiency.
ABSTRACT
We experimentally demonstrate 15 dB of Raman amplification of 1115 nm pulses in an orbital angular momentum mode (OAMM) with charge l=+2, S=+1 in 5 m of step-index 25 µm-diameter-core fiber. The total output reaches 4.5 kW of peak power and 68.5 µJ of energy in â¼15 ns pulses at 4 kHz repetition rate. An Yb-doped fiber source pumps the Raman amplifier at 1060 nm with 60 ns pulses. Using a spatial light modulator for modal decomposition, we measure 83% purity for the amplified target OAMM of selected polarization. To the best of our knowledge, this is the first time high energy, peak power, gain, and purity are achieved in a fiber Raman amplifier for a single OAMM.
ABSTRACT
We report the first demonstration of Raman amplification in a fiber of a single Bessel-like higher order mode using a multimode pump source. We amplify the LP08-mode with a 559-µm2 effective mode area at a signal wavelength of 1115 nm in a pure-silica-core step-index fiber. A maximum of 18 dB average power gain is achieved in a 9-m long gain fiber, with output pulse energy of 115 µJ. The Raman pump source comprises a pulsed 1060 nm ytterbium-doped fiber amplifier with V-value ~30, which is matched to the Raman gain fiber. The pump depletion as averaged over the signal pulses reaches 36.7%. The conversion of power from the multimode pump into the signal mode demonstrates the potential for efficient brightness enhancement with low amplification-induced signal mode purity degradation.
ABSTRACT
Stokes polarimetry measurements are carried out to calculate the spatial and angular Goos-Hänchen and Imbert-Fedorov shifts of a Gaussian beam reflected at glass-air interface, by measuring the phase difference between the TE and TM components and the amplitude of reflection. Variation of the beam shifts as a function of input beam polarization is also measured. The results obtained here are in good agreement with the theoretical predictions and the results obtained using a position sensitive detector. The polarimetric measurement method is accurate, independent of the intensity distribution of the beam, and opens up a new method to study the beam shift problem.
ABSTRACT
We report the formation and annihilation of vectorial topological dipole mediated by plasmons in structure-free metal surfaces using a polarization singular optical beam. The measured far-field behavior is due to the strong angular and polarization dependence of the reflection coefficient and the phase shift experienced by the spatially inhomogeneous polarized beam around the plasmon resonance. The threshold polarization ellipticity (σth) anticipated for the dipole formation is experimentally verified.
