Μm Fiber Laser Research Articles

1.8μm fluorescence characteristics of Tm3+ doped silica glasses and fiber prepared by the glass phase-separation technology

We report Tm3+ doped silica glasses and fiber prepared from mesoporous silica glass by glass phase-separation technology. The Judd–Ofelt parameters and radiation properties of Tm3+ doped silica glasses were calculated and evaluated according to the recorded absorption spectrum. The absorption and emission cross-section, gain spectra and fluorescence lifetime were analyzed. Tm3+ doped large-core double-cladding fiber with a core NA of 0.08 was fabricated by the rod-in-tube method. The measurements show that the fiber has a Tm3+ concentration of 10300 ppm by weight and excellent homogeneity in the fiber core. The 1.8 μm luminescence properties were investigated. It is suggested that the Tm3+ doped silica glass prepared by glass phase-separation technology can be a potential fiber core material to achieve 2 μm fiber laser.

Tm/Al Co-Doped Silica Glass Prepared by Laser Additive Manufacturing Technology for 2-μm Photonic Crystal Fiber Laser

In this article, we demonstrated the Tm/Al co-doped silica glass fabricated by the laser additive manufacturing technology for the first time. The measurements show that the glass was doped with Tm3+ concentration of 1.64 wt% without any crystallization. The Tm3+ and Al3+ were uniformly distributed, and no additional defects were introduced during the fabrication process. The glass exhibits low hydroxyl content level of 11.56 ppm. Using the prepared silica glass as the core rod, a Tm/Al co-doped photonic crystal fiber (PCF) was fabricated and performed 13.9% slope efficiency with nearly 600 mW output laser power. This novel technology provides an alternative method to fabricate Tm-doped fiber materials with high homogeneity and large core size, promoting the further spread and development of 2 μm fiber lasers.

Numerical demonstration of widely tunable femtosecond soliton generation in chalcogenide microstructured fibers

We numerically investigated widely tunable femtosecond solitons spanning from 4.1 to 7.2 µm in designed chalcogenide fibers with two rings of air holes. The core was made of Ge15Sb15Se70 glass and the cladding glass was composed of Ge20As15S65. By using a 4.1 µm fiber laser with a pulse width of 100 fs as the pump light and 1 m long chalcogenide microstructured fibers as the nonlinear media, widely tunable femtosecond solitons spanning from 4.1 to 7.2 µm were observed, and the pulse width of these tunable Raman solitons remained below 150 fs. The efficiencies of the mid-infrared soliton could be up to over 80%, ranging from 4.1–6.8 µm. Through numerical simulations, we also observed red-shifted dispersive waves varying from 10.2 to 8.9 µm. Our simulated results show that the designed chalcogenide microstructured fibers are promising nonlinear media for generating tunable mid-infrared light sources.

Three-Dimensional Wind Measurements with the Fibered Airborne Coherent Doppler Wind Lidar LIVE

A three-dimensional (3D) wind profiling Lidar, based on the latest high power 1.5 µm fiber laser development at Onera, has been successfully flown on-board a SAFIRE (Service des Avions Français Instrumentés pour la Recherche en Environnement) ATR42 aircraft. The Lidar called LIVE (LIdar VEnt) is designed to measure wind profiles from the aircraft down to ground level, with a horizontal resolution of 3 km, a vertical resolution of 100 m and a designed accuracy on each three wind vector components better than 0.5 m.s−1. To achieve the required performance, LIVE Lidar emits 410 µJ laser pulses repeating at 14 KHz with a duration of 700 ns and uses a conical scanner of 30° total opening angle and a full scan time of 17 s.

Graphene mode-locked Tm,Ho-codoped crystalline garnet laser producing 70-fs pulses near 21 µm

Bilayer graphene synthesized by chemical vapor deposition is successfully applied as a saturable absorber (SA) for the passive mode-locking of a Tm,Ho:CLNGG laser at 2093nm. Near transform-limited pulses as short as 70 fs, i.e., 10 optical cycles, are produced at a 89 MHz repetition rate with 69 mW average output power. To the best of our knowledge, these are the shortest pulses ever reported from graphene-SA mode-locked Tm, or Ho-lasers in the 2 µm spectral region, including bulk and fiber lasers.

The glass-forming region and 2.7 μm emission of Er3+-doped TeO2−Ta2O5−ZnO tellurite glass

An Er3+-doped TeO2 − Ta2O5 − ZnO (TTZ) tellurite glass has been investigated to explore its possible application in mid-infrared laser glass and fiber lasers. Glass-forming region of the ternary TTZ glass system was determined based on the thermodynamic calculation and experiments. Physical and optical properties of the TTZ glass were characterized in detail by using Raman, different scanning calorimetry, luminescence spectra, and fluorescence decay curves. An intense 2.7 μm emission was observed in Er3+-doped TTZ glasses upon the excitation of 980 nm laser diode (LD). The excellent thermal stability (△Tmax = 203 °C), low maximum phonon energy (~770 cm−1), high emission cross-section (0.82 × 10−20 cm2) and spectroscopic figure of merit (3.22 × 10−24 cm2s) indicate that the Er3+-doped TTZ glass could be a promising candidate for efficient ~ 3 μm fiber lasers and amplifiers.

Modeling and simulation of a mid-IR 43 µm Raman laser in chalcogenide glass fibers

Raman lasers based on mid-infrared (IR) fibers that operate at the 3–5 µm atmospheric transparency windows are attractive sources for many important applications. In this work, a Raman laser operating in the mid-IR range at 4.3 µm based on an As2Se3 fiber pumped by a 3.92 µm fiber laser has been designed and systematically optimized. The influences of pump power, fiber length, and output coupling efficiency on laser performance are investigated. Simulation results show that a fiber length of 0.75–1.3 m and an output coupler reflectivity of 89%–98% could obtain the optimized output power. The maximum output power of 0.269 W was obtained at a pump power of 1.5 W. The simulated result can be used for theoretical guidance and design optimization of practical chalcogenide fiber Raman lasers.

Endcapping of high-power 3 µm fiber lasers.

Fiber tip photodegradation through OH diffusion currently limits the long term operation of high-power fiber lasers and amplifiers operating near 3 µm. To address this issue, we investigate the resistance to OH diffusion of fluoride and oxide endcaps manufactured out of ZrF$_4$4, AlF$_3$3, GeO$_2$2, SiO$_2$2 and Al$_2$2O$_3$3 fibers. To this extent, the endcaps are spliced at the output of a 20 W continuous-wave fiber laser operating at 2.8 µm and their degradation over a 100 h time period is monitored. While the fluoride-based endcaps underwent failure during the first 10 h, their oxide counterparts survived the experiment, although showcasing degradation which was reflected as an increase of the endface temperature over time. To overcome this issue, we propose a novel method to completely suppress OH diffusion which consists in sputtering a nanoscopic diffusion barrier film made of silicon nitride (Si$_3$3N$_4$4) on the output face of the endcap. The effectiveness of the approach is validated on Al$_2$2O$_3$3, ZrF$_4$4 and AlF$_3$3 endcaps which show no sign of degradation after being used for more than a 100 h at the output of a 3 µm high-power fiber laser.

High-power all-fiber wavelength-widely-tunable Tm3+-doped fiber laser Q-switched by TI-SA

A wavelength widely tunable all-fiber Tm3+-doped double clad fiber laser by using topological insulator (TI) as saturable absorber (SA), for the generation of large energy passively Q-switched pulse, is demonstrated. This 2 μm fiber laser source can generate an average output power as high as 195 mW, corresponding to a pulse energy of ∼3 μJ, and the laser wavelength can be widely tuned from 1935.42 to 2048.85 nm. This high-performance Q-switched operation is implemented by purpose laser cavity optimization and TI-SA protection. Overall, the above results can provide an easily accessible way to develop large energy wavelength tunable passively Q-switched 2 μm fiber laser sources, which possesses important applications in various fields, including manufacturing, spectroscopy, medicine, and the military.

Nd3+-doped antimony germanate glass for 1.06 μm fiber lasers

In this work, a multicomponent GeO2–Sb2O3–BaO (BSG) glass is explored to assess its potential for 1.06 μm fiber lasers. The glass-forming region of BSG system is predicted and determined experimentally based on a thermodynamic method. Benefitting from the incorporation of Sb2O3, this system possesses an exceptionally large glass-forming region, as well as high density and refractive index, wide infrared transmission range and low phonon energy. Furthermore, an efficient near-infrared emission at 1064 nm from Nd3+ has been realized in this oxide glass with relatively long measured lifetime (200.58 ± 1.24 μs) and large emission cross-section (3.015 ± 0.090 × 10−20 cm2), indicating that Nd3+-doped BSG glass is a promising candidate for laser application in 1.06 μm region.

TeO2-WO3-GeO2-NdF3 glasses for 1.06 μm fiber lasers: An optical analysis

The TeO2-WO3-GeO2-NdF3 (TWGNd) glasses containing various amounts of NdF3 were synthesized through melt-quenching method and analyzed for 1.06 μm fiber lasers. The index of refraction increases with the addition of NdF3 content at 5893 Å wavelength. Different spectroscopic and radiative parameters were determined applying the standard Judd-Ofelt theory. The TWGNd glasses exhibit three emission transitions peaked at ∼0.90, ∼1.06 and ∼1.33 μm corresponding to 4F3/2 → 4I9/2, 4I11/2, 4I13/2 transitions, respectively at 808 and 514.5 nm laser excitations. A quenching in luminescence was noticed beyond 1.0 mol% of NdF3 content. The saturation intensities that were used to know the threshold power of input source for laser operation were determined. The observed results show that the TWGNd10 glass has the best choice to develop 1.06 μm fiber lasers.

MoS2 Q-switched 2.8 µm Er:ZBLAN fiber laser

Since the invention of graphene, two-dimensional (2D) materials have attracted great interest in both fundamental science and potential applications. Here, we report the saturable absorption features of 2D (multilayered structure) molybdenum disulfide (MoS2) in the mid-infrared (mid-IR) wavelength region, and use it to passively Q-switch an Er3+-doped ZBLAN fiber laser at 2.8 µm. This MoS2 saturable absorber has a moderate modulation depth of 5% at 2.8 µm, making it an appropriate candidate for light modulating in the mid-IR spectral range. In stable Q-switching, the Er3+-doped ZBLAN fiber laser is widely tuned in both repetition rate and pulse width. Through increasing pump power, the repetition rate and pulse duration are monotonically tuned from 36 to 70 kHz and from 1.84 µs to 806 ns, respectively. The maximum average power is 140 mW (at 70 kHz), giving a pulse energy of 2 µJ and peak power of ~2.48 W. Successful Q-switching operation of this 2.8 µm fiber laser confirms that 2D MoS2 has great potentials as efficient light modulating elements in mid-IR regions.

Compact self-Q-switched, tunable mid-infrared all-fiber pulsed laser.

A compact self-Q-switched wavelength-tunable Ho3+:ZBLAN fiber laser around 3 μm is experimentally demonstrated for the first time. The mid-IR all-fiber cavity is formed by a pair of fiber end-facet mirrors. A 2 m-long heavily-doped Ho3+:ZBLAN fiber pumped by a homemade 1.15 μm fiber laser not only provides mid-IR optical gain, but also functions as an equivalent saturable absorber. Stable self-Q-switched pulses around 2.9 μm are generated at a low threshold of 36.6 mW, and the maximum average power obtained is 3.17 mW, corresponding to a pulse width of 1.54 μs and repetition rate of 67.8 kHz, respectively. By simply increasing the incident pump power, the mid-IR laser wavelength can be continuously tunable from 2927 nm to 2960 nm. Furthermore, when the pump power is fixed at 207.7 mW, a 42 nm wavelength tuning (2923 ∼ 2965 nm) from the self-Q-switched all-fiber laser is also achieved by applying the novel loss-adjusting technique.

Towards power scaling of 28 μm fiber lasers

We report the demonstration of a 2824nm passively cooled erbium-doped fluoride fiber laser delivering a record average output power of 41.6W in continuous-wave operation. The splice-less cavity is based on intra-core fiber Bragg gratings written directly in the active erbium-doped fluoride fiber, which is bidirectionally pumped at 980nm to reduce heat load. To the best of our knowledge, this result is the highest average output power achieved with a mid-infrared fiber laser. The long-term performance of different protective endcaps is also investigated at high-power operation.

Mid-infrared emissions of Dy3+ doped Ga-As-S chalcogenide glasses and fibers and their potential for a 42 μm fiber laser

For developing an ideal efficient and low-threshold medium for fiber lasers operated at 4 μm wavebands, 0.05 wt.% to 0.5 wt.% Dy3+ ions doped Ga0.8As39.2S60 chalcogenide glasses were investigated and a 4.2 μm fiber laser was theoretically studied based on the rate and propagation equations. It was shown that the Ga0.8As39.2S60 glass shows a desirable large Dy3+ ion solubility, which has been increased by an order of magnitude compared to As2S3 glass. Dy-rich nanocrystallines were found when the Dy3+ ions’ concentration is more than 0.3wt.% (i.e. 3000 ppmw), and the concentration quenching was found based on spectral analysis; however, no rapid decreases in lifetimes were observed. 0.3wt.% Dy3+ doped Ga0.8As39.2S60 glass possesses relatively large laser quality factor σemi × τmea = 1.70 × 10−23 cm2·s and excellent thermal stability (ΔT = 182°C), which can be successfully drawn into fibers indicating good potential for mid-infrared fiber laser.

Positive influence of Sm3+ ion on the ~ 2.85 µm emission in Yb3+/Ho3+ co-doped silica-germanate glass

In present work, a novel sensitized ion: Sm3+ activated Yb3+/Ho3+ co-doped silica-germanate glasses have been synthesized by melt quenching method. Absorption spectra and mid-infrared photo-luminescence of prepared glasses were characterized and compared in parallel. Quintuple enhancement of ~ 2.85 µm emission was achieved successfully in Yb3+/Ho3+ co-doped silica-germanate glass with 0.3 mol% Sm3+ addition, which also possesses a large stimulated emission cross section (14.9 × 10–21 cm2). Sensitized effect of Sm3+ and efficient energy transfer (ET) mechanism of Ho3+:5I7→Sm3+:6H13/2 in the co-doped silica-germanate glasses were investigated under 980 nm laser diode excitation. Moreover, decay profiles of Ho3+:5I7 level were measured to further examine the high ET efficiency (η) of Ho3+:5I7 to Sm3+:6H13/2, which confirmed the efficient population inversion of Ho3+ ~ 2.85 µm emission. All results indicate that the Yb3+/Ho3+/Sm3+ tri-doped silica-germanate glass is a promising candidate material for improving the Ho3+ ~ 2.85 µm fiber laser performance.

Experimental study of laser irradiated graphite oxidation using IFTS

Graphite oxidation is investigated at varying porosity and laser irradiance, resulting in surface temperatures of 1500–3100 K. Samples are irradiated using a 1.07 µm fiber laser at irradiances of 1000 and 3600 W/cm2 in dry air environment (20% O2, < 1% H2O) at atmospheric pressure, producing a buoyant flow. Combustion plumes are analyzed using a midwave (MW) imaging Fourier transform spectrometer (IFTS) at 2 cm−1 spectral resolution, 0.5 mm/pixel spatial resolution, and data cube rates of 1 Hz. Spectral signatures from CO and CO2 are predominant in the 1800–2500 cm−1 spectral region. A radiative transfer model is used to infer species concentration and temperature from the hyperspectral data, resulting in 2D characterization of the reacting boundary layer. Plume temperatures of up to 2500 K are observed. CO and CO2 populations are correlated with surface temperature, with a general trend of [CO]/[CO2]=10exp(−5,200/Ts). A simplified model incorporating diffusion transport and surface kinetics is presented to assess the relative strengths of the S1) 2C+O2⇒2CO, S2) C+CO2⇒2CO, and S3) C+O2⇒CO2 surface oxidation mechanisms. The role of kinetic and transport mechanisms is discussed.

Er3+/Tm3+共掺铋硅酸盐玻璃2.0 μm光谱性质

Er₃₊/Tm₃₊共掺铋硅酸盐玻璃2.0 μm光谱性质

BaF2 modified Cr3+/Ho3+ co-doped germanate glass for efficient 2.0 μm fiber lasers

The influence of BaF2 on the physical and spectroscopic properties of Cr3+/Ho3+ co-doped germanate glass is investigated systematically by differential scanning calorimeter, excitation and emission spectra, as well as dynamic decay lifetime. The intense and broad absorption band of Cr3+ provides a selective pump scheme for obtaining an efficient 2.0μm emission of Ho3+, the OH− absorption coefficient, on the other hand, is decreased as low as 1.08cm−1, which both highly conducive to obtain an intense 2.0μm emission of Ho3+. In addition, the crystal-field parameter Dq/B of Cr3+-doped glasses is also calculated to study the influence of BaF2 on the local environment of activators and sensitizers. Further theoretic calculation shows that the largest absorption and emission cross-sections of Ho3+ near 2.0μm are as high as 4.6 and 5.2 (×10−21cm2) in the 10mol% BaF2 modified Cr3+/Ho3+ co-doped glass and the maximum energy transfer efficiency from Cr3+ to Ho3+ is about 42.5%. All results suggest that this BaF2 modified Cr3+/Ho3+ co-doped glass is very suitable for a high-efficient 2.0μm fiber lasers with flexible pump sources.

Tm-doped fiber laser resonantly diode-cladding-pumped at 1620 nm

We report the first demonstration of an efficient, high power, resonantly (in-band) diode-cladding-pumped Tm-doped fiber laser operating on the 3F4 ⇒ 3H6 transition of Tm3+ ion. The laser, pumped by a fiber coupled laser diode module at ~1620 nm, delivered ~15 W of power at 1930 nm with a slope efficiency of 67% versus the absorbed pump power. This presents, to the best of our knowledge, the highest slope efficiency and the highest output power reported so far for resonantly diode-cladding-pumped 2 µm fiber lasers based on double-clad Tm-doped silica fibers. These very preliminary results, obtained with commercial double-clad Tm-doped fibers, unoptimized for in-band pumping at the peak of resonant absorption, indicate a very high potential of resonantly diode-cladding-pumped Tm fiber lasers for major power scaling unaffected by photodarkening. Fiber optimization for resonant pumping at the maximum of the Tm3+ 3H6 ⇒ 3F4 absorption band in silica (1610–1710 nm) can lead to a new generation of Tm fiber lasers with power and wall-plug efficiency, competing with those of high power tandem-pumped Tm-doped fiber lasers, but potentially with a lighter weight and smaller dimensions.