Numerical model of hybrid mode-locked Tm-doped all-fibre laser

Abstract: Ultrafast Tm-doped fibre lasers have been actively studied for the last decade due to their potential applications in precise mid-IR spectroscopy, LIDARs, material processing and more. The majority of research papers is devoted to the comparison between a numerical modelling and experimental results; however, little attention is being paid to the comprehensive description of the mathematical models and parameters of the active and passive components forming cavities of Tm-doped all-fibre lasers. Thus, here we report a numerical model of a stretched-pulsed Tm-doped fibre laser with hybrid mode-locking and compare it with experimental results. The key feature of the developed numerical model is employment of the experimentally measured dispersion coefficients and optimisation of some model parameters, such as the bandwidth of the spectral filter spectral filtering and the saturation power of the active fibre, for a conformity with the experiment. The developed laser emits 331.7 fs pulses with a 23.8 MHz repetition rate, 6 mW of average power, 0.25 nJ of pulse energy, and a 21.66 nm spectral bandwidth at a peak wavelength of 1899.5 nm. The numerical model characteristics coincide with experimentally achieved spectral width, pulse duration, and average power with inaccuracy of 4.7%, 5.4%, and 22.9%, respectively. Moreover, in the discussion of the work the main possible reasons influencing this inaccuracy are highlighted. Elimination of those factors might allow to increase accuracy even more. We show that numerical model has a good agreement with the experiment and can be used for development of ultrafast Tm-doped fibre laser systems

Octave-Spanning Supercontinuum Generation in As2S3–Silica Hybrid Waveguides Pumped by Thulium-Doped Fiber Laser

Broadband supercontinuum sources are of interest for various applications. The near-infrared region (1–3 μ m) is specifically useful for biomedical diagnostics. One of the promising media for supercontinuum generation in the infrared region is the strongly guiding nonlinear waveguide with an arsenic trisulfide core (As 2 S 3 ) and a fused silica cladding. The geometrical and chemical properties of such a waveguide allow to finely tune the dispersion landscape and nonlinearity through the core diameter variations. Here we report the generation of octave-spanning supercontinuum in As 2 S 3 -silica hybrid nanospike waveguides pumped by a thulium-doped all-fiber femtosecond laser and amplifier system at 1.9 μ m wavelength. The widest supercontinuum was obtained in the wavelength range from 1.1 to 2.5 μ m (full width at -10 dB) in the waveguide with a core diameter of 1.7 μ m. Generation of significant dispersive waves, as well as third harmonics component, is observed. Numerical simulation shows that the generated supercontinua are coherent in the entire spectral range and can be exploited to create a self-referenced laser comb

All-fiber ultrafast amplifier at 1.9 μm based on thulium-doped normal dispersion fiber and LMA fiber compressor

The duration reduction and the peak power increase of ultrashort pulses generated by all-fiber sources at a wavelength of 1.9 µm are an urgent tasks. Finding an effective and easy way to improve these characteristics of ultrafast lasers can allow a broad implementation of wideband coherent supercontinuum sources in the mid-IR range required for various applications. As an alternative approach of sub-100 fs pulse generation we present an ultrafast all-fiber amplifier based on a normal-dispersion germanosilicate thulium-doped active fiber and a large-mode-area silica-fiber compressor. The output pulses have the following characteristics: the pulse duration of 71 fs, the central wavelength of 1.9 µm, the repetition rate of 23.8 MHz, the energy per pulse period of 25 nJ, the average power of 600 mW, the maximum estimated peak power of 220 kW, and a random output polarization. The pulse intensity and phase profiles were measured via the second-harmonic-generation frequency-resolved optical gating technique. The dynamics of ultrashort pulses propagation in the amplifier was analyzed using numerical simulation

Thermo-optical and lasing characteristics of Cr2+-doped CdSe single crystal as tunable coherent source in the mid-infrared

We report on a comprehensive characterization of Cr2+-doped CdSe single crystal as an efficient active material for tunable laser applications in the mid-infrared spectral region. Optical gain, thermo-optical behavior, power efficiency, scalability and wavelength tunability have been thoroughly investigated. Using an antireflection-coated crystal pumped by a Tmfiber laser at at 1.94 μm, 1-W CW output power and 50% slope efficiency at 2.65 μm emission wavelength have been obtained in a diffraction-limited output beam. An output peak power of 2.5 W has been achieved without significant beam distortion in a quasi-CW regime. Exploiting an intra-cavity diffraction grating in a Littrow configuration, a maximum tuning range of 900 nm from 2.22 to 3.12 μm, limited by the finite bandwidth of resonator components, has been demonstrated with an uncoated crystal

Antireflection microstructures on ZnSe for mid- and far-IR fabricated by femtosecond laser ablation assisted with wet chemical etching

Abstract Most infrared materials used in high-power systems, such as optical parametric generators, have high values of refractive indices, which result in high Fresnel losses. The performance of conventional antireflection coatings is limited when used in high-power and ultra-broadband systems. An alternative approach is to fabricate antireflection microstructures (ARMs) that allow for a broadband increase in transmittance without reducing the damage threshold of the material. In this work, ARMs were fabricated on the surface of ZnSe crystals using the femtosecond laser ablation assisted with wet chemical etching method. This allowed to produce high aspect ratio microstructures that increase the transmittance up to 98% in the mid- and far- infrared regions

Octave-Spanning Supercontinuum Generated in As2S3-Silica Waveguides Pumped by Tm-doped All-fibre MOPA

International audienceFiber-based supercontinuum sources in the mid-IR wavelength range are highly desirable for many applications [1] - [3] . Here we report the generation of octave-spanning supercontinua in As 2 S 3 -silica hybrid waveguides pumped by a thulium-doped all-fiber master-oscillator-power-amplifier (MOPA). The narrow As 2 S 3 core of the step-index waveguide has an extremely high nonlinearity, and by balancing its anomalous geometrical dispersion against the normal dispersion of the glass, the zero dispersion wavelength of the guided mode can be shifted towards the pump wavelength by suitable design. The \"nanospikes\" at both ends of the hybrid waveguide (see Fig. 1a ) are used to boost the launch efficiency into the fundamental core mode [3] , [4] . A thulium-doped all-fiber MOPA centred at 1.9 μm [5] , [6] was used as pump source. It emits pulses with a duration of 78 fs and a maximum peak power of 200 kW at a repetition rate of 23.8 MHz. Dual nanospike waveguides with core diameters d = 1.7 μm and 1.2 μm were tested in the experiment. The length of both waveguides was 3 mm. Fig. 1b plots the calculated dispersion parameter of the two waveguides. For d = 1.7 μm the pump lies within ~ 50 nm of a zero dispersion wavelength, in which case for a launched energy of ~32 pJ the measured spectrum at the output extends from 1.1 μm to 2.5 μm at the –10 dB level. The total output average power was measured as ~ 1.2 mW. When d = 1.2 μm, the pump wavelength lies in between two zero dispersion wavelengths, and for 23 pJ launched energy the spectrum extends from 1.7 μm to 2.3 μm, while a weak dispersive wave appears at 963 nm. In both cases the third harmonic components are visible at 630 nm (inset of Fig. 1c ), which fall within the bandgap of the As 2 S 3 material, limiting further increase of the pump energy. Numerically simulated spectra (black-dotted curves) calculated for the experimental pulse energy agree well with the measurements

Fabrication of an antireflection microstructure on AgClBr polycrystalline fiber by single pulse femtosecond laser ablation

Polycrystalline infrared (PIR) fibers are used for numerous applications, one of those being power delivery for CO2 lasers. However, the fiber tip surface's transmittance cannot be increased with conventional antireflection coatings due to the surface unevenness. Antireflection microstructures (ARMs) offer an alternative way of increasing transmittance. In this work, ARMs were fabricated on the fiber tip surface of an AgClBr fiber by single-pulse femtosecond laser ablation. A single-surface transmittance of 92.8% at 10.6 μm, a CO2 laser operation wavelength, was achieved. The proposed method can help significantly improve the systems' efficiency, where power delivery for CO2 lasers or sources operating in the wide wavelength range is required

Laser performance of Cr 2+ :CdSe crystal with anti-reflection coating

We demonstrated a continuous-wave laser using an anti-reflection coated Cr 2+ :CdSe crystal with transmission of 98 % at wavelength range from 2.0 to 2.7 μm and with relatively large laser damage threshold of 30 MW/cm 2 for the first time. A maximum output power of 1 W at wavelength 2450 nm with an optical-optical efficiency of 48 % and a slope efficiency of 50 % was obtained when the incident pump power was 2.1 W