Continuous-wave Laser Emission Research Articles

Design of a Broadband Erbium-Doped Fluoroindate Fiber Laser Emitting Up to 3.91 μm

In this paper, for the first time, an erbium-doped fluoroindate fiber laser emitting up to 3.91 μm is designed and optimized by means of a numerical investigation performed via a home-made computer code. It is cladding pumped with red light at 635 nm. The employed fiber is commercially available from Le Verre Fluoré and exhibits a double D-shaped geometry. Continuous-wave laser emission is obtained thanks to the population inversion between the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9/2</sub> and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9/2</sub> energy levels. The model takes into account measured spectroscopic parameters for the absorption, stimulated emission and spontaneous decay processes. The device performance is investigated by varying several parameters, such as the input pump power, the fiber length, the dopant concentration, the output mirror reflectivity and the signal wavelength. The proposed device is very versatile and is optimized for different scenarios, including: the shortest fiber, the highest output power and the lowest threshold. Simulation results show that the best performance in terms of emission bandwidth is obtained for the laser with the lowest threshold, i.e. only 25 mW, predicting a broadband coherent emission in the 3.25-3.91 μm wavelength range and paving the way to the fabrication of a low-cost and easy-to-pump middle infrared fiber laser.

80-μs pulsewidth from a circulation-free diode-pumped liquid organic laser limited by thermal blooming.

Continuous-wave laser emission is challenging to obtain in organic lasers, whether in the solid or liquid form, a limitation caused by long-lived triplet states and by thermal effects. In liquid dye lasers, both issues can be fixed by rapidly flowing the dye, which is technically complex and prevents those lasers to be further miniaturized or easily integrated. Here we address the issue of the maximal pulsewidth that can be obtained in liquid dye lasers in the absence of any dye flow, in a compact and cost-effective diode-pumped laser system. Pulses as long as 80 μs have been obtained, thanks to the combination of a hemispherical resonator design, almost insensitive to thermal-lens effects, and an intentional mismatch between pump and cavity spatial modes. The limitation in pulse duration is shown to be entirely due to thermal blooming, and more specifically to diffraction losses brought by the spherical aberration of the thermal lens.

Comparison between continuous and modulated wave laser emission modes for the selective laser melting of Ti-6Al-4V: Dimensional accuracy, microstructure and mechanical behaviour

This study investigated the difference between the properties of Ti-6Al-4 V alloy parts printed using continuous wave (CW) and modulated wave (MW) laser emission modes, with equivalent input energy densities. Laser powers in this powder bed fusion process, were systematically altered to evaluate the effect of different input energies on the as-built parts. Printed alloy parts were obtained across five equivalent laser energy densities, in the range of 31–51 J/mm3, investigated using the two laser emission modes. The impact of changes in laser emission mode and energy density was examined based on printed part dimensions, microstructure, porosity, hardness and tensile properties. It was demonstrated that microstructural refinement occurs as a function of melt pool size, which was associated with the penetration depth of the laser energy. The microstructure of samples produced using CW laser emission mode were characterised by thinner laths and narrower prior β grains. Tensile testing according to ASTM E8M, obtained at the different energy levels, demonstrated that over the energy density range investigated there was up to a 17.4% increase in yield strength (YS) and a 2.5% increase in Ultimate Tensile Strength (UTS) for the CW printed samples, when compared with those obtained using the MW laser wave emission mode. Comparatively, MW laser emission mode resulted in thicker laths with slightly wider prior β grains, which exhibited an elongation at break of 13.6% during tensile testing at high energy densities. The influence of the laser emission mode on dimensional accuracy was also investigated. Sample printed using the MW laser emission mode showed up to a 50% improvement in dimensional accuracy when compared with that obtained for CW wave laser emission mode.

Diffraction limited 195-W continuous wave laser emission at 2.09 µm from a Tm3+, Ho3+-codoped single-oscillator monolithic fiber laser.

We present a bi-directionally 793-nm diode-pumped Tm3+, Ho3+-codoped silica polarization maintaining double-clad all-fiber laser based on a single-oscillator architecture emitting 195 W at 2.09 µm in continuous wave mode of operation, with a beam quality near the diffraction limit (M2 = 1.08). The power scaling of the laser is only pump-power-limited in the range of the total available pump power (540 W).

An ultra-stable 2.9 μm guided-wave chip laser and application to nano-spectroscopy

We present a configurable guided-wave planar glass-chip laser that produces low-noise and high-quality continuous-wave laser emission tunable from 2.82 to 2.95 µm. The laser has a low threshold and intrinsic power and mode stability attributable to the high overlap of gain volume and pump mode defined by an ultrafast laser inscribed waveguide. The laser emission is single transverse-mode with a Gaussian spatial profile and M2x,y ∼ 1.05, 1.10. The power drift is ∼0.08% rms over ∼2 h. When configured in a spectrally free-running cavity, the guided-wave laser emits up to 170 mW. The benefit of low-noise and stable wavelength emission of this hydroxide resonant laser is demonstrated by acquiring high signal-to-noise images and spectroscopy of a corroded copper surface film with corrosion products containing water and hydroxide ions with a scattering-scanning near-field optical microscope.

Research on the properties and LD-pumped CW laser emission at 2.7 µm in Er3+:KLu(WO4)2 and Er3+/Pr3+:KLu(WO4)2 crystals

Two laser crystals of Er3+:KLu(WO4)2 and Er3+/Pr3+:KLu(WO4)2 were successfully grown using the top-seeded solution growth technique with K2W2O7 as flux. Segregation coefficients of Er3+ ions in Er3+:KLu(WO4)2 and Er3+/Pr3+:KLu(WO4)2 crystals were 0.664 and 0.9, respectively. The density of the Pr3+ ions in the Er3+/Pr3+:KLu(WO4)2 crystal was 1.19 × 1019 cm−3, and the segregation coefficient was 0.18. The absorption and fluorescence spectra of the two crystals with Y-oriented polarization (parallel to the b axis) light were recorded. Judd–Ofelt (J–O) theory was adapted to analyze the main parameters and they were crucial for evaluating the potential of laser crystals with output wavelength of 2.7 µm. Results showed that the Er3+/Pr3+:KLu(WO4)2 crystal had good J–O intensity parameter Ωt (t = 2, 4, 6) and relatively large emission cross section at 2.7 µm. The lifetimes of the 4I11/2 state in the Er3+:KLu(WO4)2 and Er3+/Pr3+:KLu(WO4)2 crystals were fitted to be 87.13 ms and 79.36 ms, respectively. The lifetime of 4I13/2 state decreased sharply from 5.59 s in Er3+:KLu(WO4)2 to 53.19 ms with co-doping of Er3+ ions and Pr3+ ions. Laser oscillation was accomplished at 2.7 µm wavelength using a b-cut Er3+/Pr3+:KLu(WO4)2 crystal sample with size of 4 × 4 × 10 mm3. Finally, a continuous-wave (CW) laser was realized with the highest slope of 15.94%. The center wavelength of the laser output was 2740 nm, and its FWHM was approximately 1.8 nm. Therefore, the Er3+/Pr3+:KLu(WO4)2 crystal has remarkable potential for generating 2.7 µm lasers.

Broadband heterogeneous terahertz frequency quantum cascade laser

The authors demonstrate a broadband, heterogeneous terahertz frequency quantum cascade laser by exploiting an active region design based on longitudinal optical-phonon-assisted interminiband transitions. They obtain continuous wave laser emission with a threshold current density of ~120 A/cm 2 , a dynamic range of ~3.1, and an emission spectrum spanning from 2.4 to 3.4 THz at 15 K.

Continuous-Wave Mid-Infrared Gas Fiber Lasers

Efficient continuous-wave laser emission of acetylene molecules at 3.1 μ m wavelength has been demonstrated in low-loss hollow-core fiber by optically pumping using a fiber-amplified diode laser around 1.53 μ m. In this paper, we report and compare the continuous-wave laser performance of acetylene molecules in the cavity and single-pass configurations. The use of low-loss antiresonant hollow-core fiber makes the single-pass configuration ideal for high-power laser generation and enables over 1.1 W continuous-wave mid-infrared laser output with over 33% slope efficiency relative to the absorbed pump power. The systematic characterization of power-scaling and pump power absorption properties demonstrates that the molecular kinetics inside hollow-core fiber determines the laser performance, and that low fiber attenuation is key to high-efficiency continuous-wave output.

Widely tunable, efficient 2 μm laser in monocrystalline Tm3+:SrF2.

We report on the growth, spectroscopy, and laser operation of monocrystalline Tm3+:SrF2. Spectroscopic investigations confirmed the presence of broad absorption and emission bands caused by inequivalent doped sites, introduced by charge compensation effects which also caused the clusterization of doping ions in the lattice. We obtained continuous-wave laser emission at about 2 μm, with efficiencies comparable with other Tm-doped crystals. We also achieved an uninterrupted tuning range of 180 nm between 1.8 and 2 μm. This characterization indicates that SrF2 enhances the cooperative mechanisms between Tm ions, helping to obtain remarkable laser performances at low doping concentrations.

Visible laser emission from a praseodymium-doped fluorozirconate guided-wave chip.

We report visible continuous-wave laser emission at 636 nm from a praseodymium-doped fluorozirconate glass guided-wave chip laser. This ultra-fast laser inscribed gain chip is demonstrated to be a compact and integrated laser module. The laser module, pumped by 442 nm GaN laser diodes, generates >8 mW lasing output with a beam quality of Mxy2∼1.15×1.1(±0.1). To the best of our knowledge, this is the first visible laser emission from a glass-based waveguide chip laser.

Visible laser operation in a Pr^3+:LiLuF_4 monocrystalline fiber grown by the micro-pulling-down method

We report on the growth and laser operation of a fiber-shaped single crystal of Pr3+:LiLuF4 (Pr:LLF) grown by the micro-pulling-down (µ-PD) method. We checked the optical quality of the crystal by measuring its spectroscopic features, and by observing the profile of a laser beam transmitted through it. Using an InGaN laser diode as pump source, we achieved continuous-wave laser emission in the orange, red, and deep red regions, with slope efficiencies comparable with or exceeding previous reports on this material. To the best of our knowledge, this work represents the first observation of visible laser emissions from a crystal grown by the µ-PD technique.

Deep red diode-pumped Pr³⁺:KY₃F₁₀ continuous-wave laser.

We report the first observation of continuous-wave laser emission at 720 nm, in the deep red region, of a Pr3+:KY3F10 (Pr:KYF) single crystal, pumped with a blue InGaN-based laser diode at 446 nm. We employed a hemispherical cavity with three different output coupling mirrors transmitting 0.7%, 1.4%, and 2.7% of laser radiation. We obtained a maximum output power of 207 mW with a slope efficiency of 24.3%, comparable for the first time to what has been reported for other praseodymium-doped fluoride crystals. The round-trip cavity losses for our sample were estimated to be between 0.3% and 0.6%, a remarkably small value for this material.

Continuous-wave operation up to 20 °C of deep-ridge npn-InGaAsP/InP multiple quantum well transistor laser emitting at 1.5-μm wavelength.

We report continuous-wave (CW) operation up to 20 °C of 1.5-μm wavelength npn-InGaAsP/InP multiple quantum well (MQW) transistor laser (TL) with a deep-ridge structure. With CW laser emission, the common emitter current gain of the device can be over 3.5, which is significantly larger than those of the previously reported long wavelength TLs. It is found that at low base current, the laser operation occurs on the first excited state of the MQWs. At high base current, however, the device shows stimulated emissions on the ground state transition. The trend is contrary to what has been observed in the GaAs based TLs and is explained by the change of carrier flow at different base currents.

Multiple polarization orange and red laser emissions with Pr:BaY₂F₈.

We investigated the polarization of continuous-wave laser emission in the orange region, at 607 nm, and in the red region, at 639 nm and 643 nm, from a Pr:BaY2F8 (Pr:BYF) crystal, pumped by a 445 nm laser diode. We achieved linearly polarized emission along two optic axes of the crystal by changing its orientation with respect to the pump. Simultaneous emission of two orthogonal linear polarizations was observed in the orange region, at the same wavelength, and in the red region, with concurrent emission from the two separate lines.

Continuous-Wave Laser Emission of Pr:${\rm LiYF}_{4}$ at 695.8 nm

We present a diode-pumped Pr: LiYF4 (Pr:YLF) laser at 695.8 nm by suppressing the higher gain transitions near 640, 670, 698, and 721 nm. With an InGaN laser diode as the pump source, the output power of the laser centered at 695.8 nm in σ polarization was up to 51 mW, corresponding to a slope efficiency of 12.6% and a threshold power of 229 mW with respect to absorbed pump power. To the best of our knowledge, this is the first Pr:YLF laser emitting at 695.8 nm in σ polarization.

Investigation of structural dependence of host erbium-doped triangular-lattice PCF on lasing properties and design of high performance laser

A detailed study is presented on the lasing properties of an erbium-doped photonic crystal fiber (PCF) laser. The effects of the host PCF’s structure and laser parameters on continuous-wave laser emission are analyzed by considering the confinement and overlap of pump and signal fields in the gain medium for varying values of pitch, hole diameter, and doping radius. For analysis, we used a finite-difference mode-calculation algorithm devised with standard population and propagation rate-equation solver. Our analysis, applied to an experimentally realized PCF laser, reproduces the observed/reported data, thereby showing the efficacy of our analysis. Finally, a fiber geometry to realize a laser with threshold as low as 6 mW using a short fiber length of 0.52 m is prescribed. The aim of the design is to greatly reduce splice loss with standard single-mode SM28/G.652 fiber while maintaining the optimum performance. These results are new in PCF laser research and should be useful in realizing high performance PCF-based laser devices.

Efficient 1856 nm emission from Tm,Mg:LiNbO_3 laser

Efficient continuous-wave laser emission at 1856 nm from a Tm,Mg:LiNbO(3) crystal slab with high Tm(3+) doping concentration is reported. A maximum output power of 2.62 W is realized with a slope efficiency of 19.6% and the beam quality factor M(2) of 1.7 at room temperature. We believe that this is the first demonstration of watt-level laser operation in Tm,Mg:LiNbO(3) crystal and the output power is four orders of magnitude higher than that reported previously in Tm-doped LiNbO(3) crystal. Performance degradation due to the photorefractive effect under high intensity 1856 nm laser is not observed thanks to the co-doping of magnesium ions. Quantitative analysis about the long-term photorefractive effect is also provided. Multi-wavelength laser operation is realized by using different narrow-band output couplers. This demonstration opens up a viable pathway towards 2-μm integrated optic devices for achieving laser oscillation, electro-optic and nonlinear optical effects within just one sample simultaneously.

Uniformity of the lasing wavelength of heterogeneously integrated InP microdisk lasers on SOI

We report a high lasing wavelength uniformity of optically pumped InP-based microdisk lasers processed with electron-beam lithography, heterogeneously integrated with adhesive bonding on silicon-on-insulator (SOI) waveguide circuits and evanescently coupled to an underlying waveguide. We study the continuous wave laser emission coupling out of the SOI via a grating coupler etched at one side of the waveguide, and demonstrate a standard deviation in lasing wavelength of nominally identical devices on the same chip lower than 500 pm. The deviation in the diameter of the microdisks as low as a few nanometers makes all-optical signal processing applications requiring cascadability possible.

A 200 W INNOSLAB Tm:YLF laser

We report obtaining 200 W of continuous wave laser emission at 1.9 μm from an INNOSLAB Tm:YLF (YLiF4) laser. The slope efficiency is 52.2% with respect to the absorbed pump power. The wavelength of the laser output and the polarization direction can be switched between 1890 and 1908 nm. Due to the stable resonator design in both axes of the slab crystal, the output is strongly elliptical with a Gaussian distribution beam shape along the semi-minor axis and a top-hat-like distribution beam shape along the semi-major axis. This laser source is ideal for pumping a holmium-doped slab crystal in a pulsed INNOSLAB amplifier.

All-solid-state continuous wave doubly linear resonator sum-frequency mixing yellow laser

We report a continuous-wave (CW) yellow laser emission by sum-frequency mixing in Nd:YVO4 crystal. Using type-II critical phase-matching KTP crystal, a yellow laser at 593.5 nm is obtained by 1064 and 1342 nm intracavity sum-frequency mixing. The maximum laser output power of 2.1 W is obtained when an incident pump laser of 18.2 W is used. At the output power level of 2.1 W, the output stability is better than 3.2%.