Laser sources operating in the eyesafe wavelength regime around 1.5-1.6 µm have applications in a number of areas including, remote sensing, ranging and free-space communications. For many of these applications, the requirement for high output power is often supplemented by the need for high efficiency and good beam quality. This combination of operating characteristics is very difficult to achieve in conventional diode-pumped solid-state lasers based on erbium doped crystals (sensitised with Yb) owing to the relatively high fractional heat loading which results from the large quantum defect (~ 40%) and energy-transfer-upconversion. To alleviate this problem, attention has recently turned to singly-doped crystals (e.g. Er:YAG) and in-band pumping using an Er,Yb fibre laser. This approach has the advantage that most of the waste heat is generated in the fibre, which is largely immune to thermal effects, and quantum defect heating in the Er-doped crystal is very small (~7%). Using this hybrid laser scheme, we have demonstrated ~60 W of continuous-wave output from an Er:YAG laser at 1645 nm with a slope efficiency of 80 % 1. However, for some remote sensing applications this operating wavelength is a little inconvenient, since there are atmospheric absorption lines due to methane which are in very close proximity necessitating careful selection and control of the lasing wavelength. Er:YAG also has a transition from the same upper level manifold (4 I 13/2) at 1617 nm, which lies in a region of the spectrum where there are no atmospheric absorption lies. However, this transition has a much more pronounced three-level character and hence a much higher threshold pump power, so it has received little attention in spite of its obvious advantages for certain applications. Here, we report preliminary results for power scaling of an Er:YAG laser at 1617 nm in-band pumped by a high-power cladding-pumped Er,Yb fibre laser. The Er,Yb fibre pump laser was constructed in-house with wavelength selection provided by an external cavity containing a diffraction grating in the Littrow configuration. The Er,Yb fibre laser was pumped by two 9-bar pump modules at 975 nm and produced up to 120 W of output in a beam with M 2 ≈ 5. For efficient pumping of Er:YAG, the Er,Yb fibre laser operating wavelength was tuned to the absorption peak at 1532 nm. In this preliminary study, a simple four-mirror folded cavity was employed for the Er:YAG laser comprising a 29 mm long Er:YAG rod with 0.5 at.% Er 3+ concentration mounted in a water-cooled aluminium heat-sink, a plane pump in-coupling mirror with high reflectivity at 1617 nm and high transmission at 1532 nm, two concave mirrors of 100 mm radius of curvature and high reflectivity at 1617nm, a plane output coupler of transmission, 30% at 1617 nm, and a 100 µm thick fused silica etalon. The latter was used to select the 1617 nm line and suppress oscillation on the higher gain 1645 nm line. Figure 1 shows the Er:YAG output power at 1617 nm as a function of pump power. The Er:YAG laser yielded a m...
With the proposal of dual-wavelength pumping (DWP) scheme, DWP Er:ZBLAN fiber lasers at 3.5 μm have become a fascinating area of research. However, limited by the absence of suitable saturable absorber, passively Q-switched and mode-locked fiber lasers have not been realized in this spectral region. Based on the layer-dependent bandgap and excellent photoelectric characteristics of black phosphorus (BP), BP is a promising candidate for saturable absorber near 3.5 μm. Here, we fabricated a 3.5-μm saturable absorber mirror (SAM) by transferring BP flakes onto a Au-coated mirror. With the as-prepared BP SAM, we realized Q-switching and mode-locking operations in the DWP Er:ZBLAN fiber lasers at 3.5 μm. To the best of our knowledge, it is the first time to achieve passively Q-switched and mode-locked pulses in 3.5 μm spectral region. The research results will not only promote the development of 3.5-μm pulsed fiber lasers but also open the photonics application of two-dimensional materials in this spectral region.
Numerical simulations on dissipative-solitonresonance generation in an all-normal-dispersion fiber ring laser are presented. Situations with monotonic and periodical saturable absorption are both considered. The multipulse operation in dissipative soliton laser is found to be caused by the spectral filtering effect that limits the spectral maximum width. And the multipulsing can be fully circumvent by inducing strong peak-power-clamping effect of a sinusoidal saturable absorber in the cavity. When the cavity peak-power-clamping effect is strong enough that the pulse peak-power and the pulse spectral width are both confined at a low value, the spectral filtering effect induced multipulse operation is prevented and the dissipative-soiton-resonance is generated. Otherwise, the spectral filtering effect causes pulse breaking before the pulse peak power reaches the saturation point. Further results show that under the dissipative-soliton-resonance, the generated pulse peak power can be directly controlled by the cavity peak-power-clamping effect, which is determined by the saturation power of the saturable absorber.
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