Laser Gain Research Articles

Investigation on SBS suppression in a kilowatt single-frequency-amplified Tm-fiber MOPA with distributed pumping

In this Letter, we present a novel distributed pumping scheme (DPS) for effective stimulated Brillouin scattering (SBS) suppression in a kilowatt-level, single-frequency-amplified Tm-fiber master oscillator power amplifier (MOPA). Theoretical analysis of laser gain distribution and temperature variation along the cascaded hybrid active fiber in the DPS indicates enhanced power scalability. By incorporating distributed pumping and pseudo-random binary sequence (PRBS) phase modulation, an output power of 1025 W at 1998 nm was successfully achieved with a spectral linewidth of 480 MHz and signal-to-noise ratio of >46 dB. Further power scaling is primarily limited by high-intensity self-pulses originating from the spectral spikes. Over an ∼60 min time scale, the power stability (RMS) was measured to be approximately 0.48%. A diffraction-limited beam quality factor M2 is estimated to be ∼1.20. Additionally, the dynamic process of backward Stokes light generation under varying phase modulation conditions was revealed. The concept presented herein paves a new pathway for the generation of kilowatt-level single-frequency laser sources across a broad spectral region.

Preparation and performance study of a Tm3+-doped silica optical fiber by sol-coating and laser drawing technology

High-concentration Tm3+-doped silica optical fibers have significant application value in areas such as single-frequency lasers. This paper investigates the sol-coating in the silica capillaries process and CO2 laser drawing technology and successfully fabricates a Tm3+-doped single-mode silica optical fiber. The core composition adopts a Tm-La-Al-Si system; the Tm3+ doping concentration is 0.5 mol%; the core and cladding diameters are 5 and 130 µm, respectively; and the numerical aperture (NA) is 0.28. A laser seed source with a wavelength of 1940 nm is established, and the laser gain characteristics of the optical fiber are tested. The small-signal net gain coefficient at the wavelength of 1940 nm is measured to be 0.15 dB/cm. The sol-coating method employed in this study enhances the doping concentration of Tm ions, while the laser drawing technique mitigates ion diffusion effects. The results indicate that this Tm3+-doped silica fiber preparation method offers a novel, to the best of our knowledge, approach for manufacturing high-concentration doped silica fibers and holds significant reference value for related research fields.

Three-Dimensional Laser Creation of a Near-IR Laser-Gain Medium Based on Hydride Donor/Acceptor Complexes Made of Coupled Laser-Induced Silver Nanoclusters with Ytterbium Ions.

Femtosecond laser inscription in a ytterbium-doped silver-containing phosphate glass is demonstrated by achieving 3D highly localized laser-induced silver photochemistry. The produced fluorescent silver nanoclusters lead to high optical contrast in the visible range, showing that the coinsertion of Yb3+ ions is not detrimental to the silver-based photochemistry. We demonstrate efficient energy transfer from these silver nanoclusters to the rare-earth Yb3+ ions, leading to near-IR background-free fluorescence emission. Indeed, we demonstrate the 3D-localized near-IR emission of homogeneously distributed Yb3+ ions thanks to their spatially selective excitation by colocalized silver nanoclusters. This creation of hybrid donor/acceptor systems, composed of coupled laser-inscribed silver nanoclusters and Yb3+ ions, respectively, allows for the 3D-distribubed creation of a laser-active gain medium. The reported effective laser gain results from the silver nanocluster-mediated excitation of the Yb3+ lasing ions, demonstrating the energy-transfer-based achievement of inversion population and optically induced transparency of the material. This opens the route for the all-optical fabrication of near-IR micron-scale multiscale architectures compatible with the development of new laser-active media especially for integrated waveguides and active photonic integrated circuits. This includes perspectives of versatile 3D laser-integrated architectures allowing for evanescent coupling under lasing operation with their environment, to achieve enhanced photonic sensing abilities beyond those offered by usual conventional planar of unidirectional architectures.

Continuous-wave electrically pumped multi-quantum-well laser based on group-IV semiconductors

Over the last 30 years, group-IV semiconductors have been intensely investigated in the quest for a fundamental direct bandgap semiconductor that could yield the last missing piece of the Si Photonics toolbox: a continuous-wave Si-based laser. Along this path, it has been demonstrated that the electronic band structure of the GeSn/SiGeSn heterostructures can be tuned into a direct bandgap quantum structure providing optical gain for lasing. In this paper, we present a versatile electrically pumped, continuous-wave laser emitting at a near-infrared wavelength of 2.32 µm with a low threshold current of 4 mA. It is based on a 6-periods SiGeSn/GeSn multiple quantum-well heterostructure. Operation of the micro-disk laser at liquid nitrogen temperature is possible by changing to pulsed operation and reducing the heat load. The demonstration of a continuous-wave, electrically pumped, all-group-IV laser is a major breakthrough towards a complete group-IV photonics technology platform.

Monocular Vision-Based 3D Reconstruction Method for Parts in Opto-Mechanical Assembly

Abstract In automated assembly, accurately capturing multi-dimensional parameters of parts is essential. Traditional methods include teaching methods or laser-based approaches, with the former relying on experience for pre-calibration and the latter being costly. This paper proposes a low-cost, monocular vision-based method for 3D reconstruction in opto-mechanical assembly. Taking the laser crystal component, including the laser gain medium and its heat sink, in a solid-state laser as an example, a monocular camera is firstly mounted on a robot and captures images of parts from specific angles. Due to the reflective properties of metal surfaces, some image information is lost. To address this problem, a 2D gamma function-based adaptive illumination correction algorithm is then proposed. Next, the improved SIFT algorithm is used to extract and match feature points from the collected images. Subsequently, the SFM approach generates a sparse point cloud, which is then densified using the CMVS/PMVS algorithm. Finally, the Poisson surface reconstruction algorithm is used to complete the 3D reconstruction of the laser crystal heat sinks. Experimental results indicate that the adaptive correction algorithm for non-uniform illumination images can extract more feature points and improve the number of matches. The reconstructed 3D model has high accuracy, providing important technical support for the next step in achieving automated opto-mechanical assembly.

Effect of Lu content on microstructure and spectral properties of Yb:(LuxSc1-x)2O3 solid-solution sesquioxide transparent ceramics

Yb³⁺-doped (Lux,Sc1-x)2O3 materials demonstrate superior performance in generating short pulse lasers because of the broader emission spectra than single-component sesquioxide, making them a promising laser gain material for high-power ultrafast lasers. By adjusting the concentration of Lu/Sc, laser gain materials with different widths of emission spectra can be obtained. In this work, 5 at.% Yb:(LuxSc1-x)2O3 nano-powders with varying Lu concentrations (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9)were successfully synthesized by the co-precipitation method. Subsequently, Yb:(LuxSc1-x)2O3 transparent ceramics were produced through a combination of vacuum pre-sintering and hot isostatic pressing (HIP) post-treatment at 1700 °C. Influence of Lu content on densification process, microstructure changes and optical transmittance of Yb:(LuxSc1-x)2O3 ceramics was investigated in detail. The average grain sizes of ceramics pre-sintered at 1700 °C decrease from 3.42 μm to 1.43 μm, and all ceramics have a relatively uniform microstructure. After HIP post-treatment, the optimum in-line transmittance of Yb:(LuxSc1-x)2O3 ceramics reaches 77.6 % at 1100 nm when x value = 0.1. With the increase of Lu content, the emission wavelength experiences a gradual blueshift from 1041 nm to 1034 nm. Notably, the Yb:(Lu0.6Sc0.4)2O3 ceramics exhibited the broadest emission bandwidth of 18 nm, which is 1.5 times of the Yb:Sc2O3, suggesting their immense potential for applications in ultrashort pulse lasers.

Improved temporal characteristics for post-compressed pulses via application-tailored nonlinear polarization ellipse rotation.

Intense ultrashort laser pulses with high temporal quality are essential for fundamental science. Nonlinear polarization ellipse rotation (NER) is one way to ensure this high temporal quality, by suppressing weaker signals beyond the duration of the main pulse up to a few orders of magnitude. Post-compression schemes have revolutionized ultrafast lasers, enabling the generation of pulses with durations beyond the limit supported by laser gain media. However, high compression ratios lead to the formation of new pre- and post-pulses. Both NER and post-compression depend on the optical Kerr effect. This makes the combination of the two in a single setup both advantageous and straightforward. While NER cannot suppress the new pre- and post-pulses generated in post-compression, we show via simulations and experimental data that by combining the two, it is possible to shape the output spectrum and counteract temporal contrast degradation.

Mid-infrared arrayed waveguide gratings using a quantum cascade laser gain medium as core material

Mid-infrared photonics is a widely researched field with several applications, such as chemical sensing and spectroscopy. The development of photonic integrated circuits for the mid-infrared can enable the reduction in device size, weight, and power (SWaP) consumption. This paper demonstrates arrayed waveguide gratings working in the mid-infrared regime (5–5.4 µm). Our devices are fabricated on an InP-based quantum cascade laser platform with the gain medium as the waveguide core. To minimize the propagation losses caused by free carrier absorption and intersubband absorption in the unbiased QCL structure, we exposed the photonic chips to proton implantation. The performance of three sets of AWGs with different etch depths was characterized. The lowest waveguide losses were measured to be 2 dB/cm. The best performing 7×1 AWG and 13×1 AWG designs featured insertion losses of −2dB and −2.5dB, respectively. This study showcases the feasibility of applying such a platform for easy integration with active components like lasers and photodetectors, paving the path for on-chip mid-infrared applications.

Enhancing yellow-green emission in Eu/Tb co-doped tellurite glasses controlled by Lu2O3

In this research, Lu2O3 was incorporated into Eu3+ and Tb3+ co-doped tellurite glasses to enhance structural stability and modify the yellow-green emission. A series of microstructural analyses, including Differential Scanning Calorimetry (DSC), Raman spectroscopy, and density measurements, confirmed that the addition of Lu2O3 causes the long-chain or cyclic Te–O–Te network structure to break, resulting in the formation of more [TeO3], which in turn leads to an increase in non-bridging oxygens (NBO) and lowers the phonon energy of the matrix material. Fluorescence spectral characterization revealed that both green and yellow luminescence intensities peaked when Lu2O3 concentration reached 15 %. Additionally, the Judd-Ofelt theory supports its superior laser performance. With the addition of Lu2O3,The radiative transition probability (Arad), lifetime (τrad), and branching ratio (β) of the excited states of Tb3+ and Eu3+ have all been enhanced. Under the regulation of 15 % Lu2O3, The maximum absorption cross-section of at 544 nm is 1.88 × 10−20 cm2, and the maximum emission cross-section is 2.14 × 10−20 cm2. At 611 nm, the maximum absorption cross-section is 1.05 × 10−20 cm2, and the maximum emission cross-section is 1.44 × 10−20 cm2. The decay curve indicates a fluorescence lifetime enhancement from 0.6 ms to 1 ms with Lu2O3. These results underscore the potential of Lu2O3 modulated Eu3+/Tb3+ co-doped tellurium glass as an effective yellow-green laser gain medium.

Effect of the Al(PO3)3 content on the optical properties of Tm3+-doped fluorophosphate glass

A series of glasses composed of xAl(PO3)3-(30-x)AlF3-55ReF2 (Re = Ca, Sr, Ba) −15YF3-1TmF3 (x = 11, 12, 13, 14, and 15 mol%) were implement employing the traditional melt-quenching method. The effect of Al(PO3)3 content on the physical and fluorescence character of fluorophosphate glass was studied. The thermal and spectral properties of the glass were analyzed by differential scanning calorimetry, absorption spectra and fluorescence spectra. The structure of the glass was analyzed by Raman and nuclear magnetic resonance (NMR) spectra. The Judd-Ofelt theory was used to analyze the local environmental changes of rare earth ions. The thermal stability and gain of glass samples doped with 12 mol% Al(PO3)3 are 127 °C and 2.46 × 10−21 cm2 ms, and the emission cross section is 4.79 × 10−21 cm2. The results show that the fluorophosphate glass is an ideal candidate material for 2 μm laser gain medium.

9.4 μm emitting quantum cascade lasers grown by MOCVD: Performance improvement obtained through AlInAs composition adjustment

Metal-organic chemical vapor deposition (MOCVD) is a prevalent technique for the epitaxial growth of quantum cascade lasers (QCLs), with the material quality being paramount to the overall device performance. Previous studies have indicated that the actual aluminum (Al) content in InAlAs barrier layers grown via MOCVD often diverges from the specified design values, particularly for layers with a thickness below 1 nm. To address this discrepancy, the Al content within the InAlAs layers can be fine-tuned by modifying the MOCVD growth parameters. This study undertakes an exhaustive analysis of QCL devices, comparing those with and without aluminum content compensation, through a combination of simulation and experimental approaches. The results demonstrate that the implementation of the Al compensation methodology facilitates the alignment of the QCL device wavelength with the intended design value. This approach also enhances the laser transition efficiency and gain coefficient of the QCL device, thereby improving its slope efficiency and threshold current density. The final QCL device exhibits a wavelength of 9.4 μm, with a maximum continuous wave (CW) and pulsed optical power and wall-plug efficiency (WPE) of 1.26 W and 7.4% and 2.08 W and 10.1%.

Growth, spectroscopy properties, and laser operation of single crystal fiber: Nd3+-doped CNGG

Nd3+-doped calcium niobium gallium garnet single crystal fibers (Nd:CNGG SCFs) with varying Nd3+ concentrations were successfully grown using the laser-heated pedestal growth (LHPG) method. The study thoroughly examines the fundamental physical structure, optical properties, and laser characteristics of the as-grown Nd:CNGG SCFs. Results indicate that the Nd:CNGG SCF exhibits broader absorption and emission full width at half maximum (FWHM) compared to bulk single crystals. Moreover, pumped by a commercial 808 nm laser diode, continuous-wave laser operation at 1061 nm with a half-height width of 1.86 nm was achieved. The laser output power reached 1.04 W at an absorbed power of 7.46 W, with a slope efficiency of 25.4% relative to the absorbed pump power. These findings suggest that Nd:CNGG SCF holds promise as a practical and potent candidate for laser gain medium, offering significant research potential in the field of lasers.

Growth, first-principles calculations and optical properties of a novel near-infrared Ho: NLGW laser crystal

A rigid structure was constructed using an isotopic doping strategy, and a novel near-infrared 1 at% Ho3+: NaLa0.93Gd0.06(WO4)2 (Ho: NLGW) laser crystal with a size of Φ 18 mm × 30 mm was successfully grown by the Czochralski method. X-ray rocking curves and Rietveld refinement indicate that the grown crystal possesses high crystalline quality and crystallizes in the I41/a space group with lattice parameters: a = b = 5.3518 Å, c = 11.6438 Å and V = 333.5051 Å3. The Ho: NLGW crystal exhibits a low coefficient of thermal expansion (8.472 × 10−6 K−1), and the c-axis thermal conductivity increases from 1.235 W/(m × K) to 1.404 W/(m × K). The thermal properties of the Ho: NLGW crystal surpass those of other Ho3+-doped tungstate series and mainstream near-infrared laser crystals, suggesting that it is easier to obtain excellent laser gain. For revealing the excellent thermal properties, the elastic moduli of the NLW and NLGW crystals have been calculated by first principles. With the introduction of Gd3+, the structural stiffness of the NLW as a whole has been increased to optimize the mechanical properties in each axial direction and to obtain the reason for the larger Debye temperature. Finally, the transmission, absorption and near-infrared emission spectra of the Ho: NLGW crystal were investigated. The crystal exhibits a high transmittance of 88.5 % and an emission cross-section of 0.84 × 10−20 cm2 calculated according to the J-O theory. Experimental results indicate that the grown Ho: NLGW crystal can achieve large laser output more easily and are expected to be an excellent medium for 2 μm solid-state lasers.

Mid-Infrared Emission in Ge/Ge1-xSnx/Ge Quantum Well Modeled Within 14-Band k.p Model

Band structure and gain in a Ge/Ge1-xSnx/Ge quantum well are described theoretically using a 14-band k.p model. It has been shown that the quantum well width and the α-Sn concentration considerably modify the conduction and valence subband structure, and, as a result, the optical gain changes with the insertion of a very small concentration of α-Sn. In particular, we have determined the necessary injection carrier density Nj and the critical α-Sn concentration for elevated high gain lasing. It is found that for Nj = 1.5 × 1018 cm−3, we achieved a maximum peak gain for α-Sn concentration of the order 0.155. We can predict that Ge/Ge1-xSnx/Ge QWs should be manufactured with an α-Sn concentration less than 0.155 in devices for optoelectronics applications such as telecommunication and light emitting laser diodes.

High-efficiency 1.6 μm-band fiber laser based on single Er3+-doped tungsten tellurite glass with high mechanical strength through tailored glass network

In this study, the correlation between the Raman structure, thermal stability, and mechanical properties of TeO2-ZnO-La2O3–WO3 glasses with varying WO3 contents are systematically established. By exploring the critical point in the transformation process of glass network structural units, the optimal glass components of 74TeO2-12ZnO-5La2O3–9WO3 glass possess the maximum thermal stability (158 °C) and the highest mechanical properties at the same time. The maximum Vicker hardness and Young's modulus of the optimal glass can reach up to 4.007 GPa and 56.212 GPa, which are higher than those of the well-known TeO2-ZnO-Na2O (TZN) and TeO2-ZnO-La2O3 (TZL) glasses. Furthermore, the 0.5 mol% Er3+-doped glass at this critical point (TZLW-0.5Er) exhibits a higher laser figure of merit (54.29 × 10−21 cm2 ms), a larger laser gain bandwidth value (116 nm) and higher emission cross-sections at 1600 nm (2.52 × 10−21 cm2) and 1625 nm (1.06 × 10−21 cm2) than other host glasses. Finally, high-efficiency laser outputs at 1600 and 1625 nm based on TZLW-0.5Er glass fiber are successfully achieved by simulation. These results show the greater practical potential of TZLW-0.5Er glass with higher mechanical strength compared to TZN and TZL fibers for the 1.6 μm-band laser.

All-solid continuous-wave Nd: YVO4-diamond intracavity Raman laser

We demonstrated a continuous intracavity diamond Raman laser operating by linear-cavity and V-cavity design. The diamond crystal as the Raman medium and Nd: YVO4 as the laser gain medium was utilized to achieve high beam quality Stokes output with narrow line width. By employing linear and V-shaped cavity, we achieved Stokes light outputs of 1.68 and 2.26 W, respectively. Compared to the linear cavity, the V-shaped cavity has a higher conversion efficiency of 11.07% and a narrower linewidth of 0.07 nm. Mechanism for linewidth of different cavity design and methods for further increasing power range and high quality are discussed.

Dynamic gain and frequency comb formation in exceptional-point lasers

Exceptional points (EPs)—singularities in the parameter space of non-Hermitian systems where two nearby eigenmodes coalesce—feature unique properties with applications such as sensitivity enhancement and chiral emission. Existing realizations of EP lasers operate with static populations in the gain medium. By analyzing the full-wave Maxwell–Bloch equations, here we show that in a laser operating sufficiently close to an EP, the nonlinear gain will spontaneously induce a multi-spectral multi-modal instability above a pump threshold, which initiates an oscillating population inversion and generates a frequency comb. The efficiency of comb generation is enhanced by both the spectral degeneracy and the spatial coalescence of modes near an EP. Such an “EP comb” has a widely tunable repetition rate, self-starts without external modulators or a continuous-wave pump, and can be realized with an ultra-compact footprint. We develop an exact solution of the Maxwell–Bloch equations with an oscillating inversion, describing all spatiotemporal properties of the EP comb as a limit cycle. We numerically illustrate this phenomenon in a 5-μm-long gain-loss coupled AlGaAs cavity and adjust the EP comb repetition rate from 20 to 27 GHz. This work provides a rigorous spatiotemporal description of the rich laser behaviors that arise from the interplay between the non-Hermiticity, nonlinearity, and dynamics of a gain medium.

First fluoride ceramics lasing at 605 nm at ambient temperature fabricated from chemically synthesized powders

Laser ceramics have emerged as promising candidates of solid-state laser gain media. However, most laser ceramics are currently focused on lasing in the infrared wavelength range. The very limited options of host materials and the increased optical scattering losses at shorter wavelengths within ceramics have greatly limited the development of visible laser ceramics. Here we report visible laser ceramics with a composition of 0.5%Pr3+,5%Y3+:SrF2, in which a visible (orange) laser oscillation at 605 nm has been successfully achieved at room temperature pumped by InGaN blue laser diodes with a maximum slope efficiency of 8.1%. The ceramics were fabricated by vacuum hot pressing (VHP) of wet-chemistry synthesized 0.5%Pr3+,5%Y3+:SrF2 powders, followed by hot isostatic pressing (HIP). It was found that the visible laser ceramics exhibited a lower optical scattering loss along the processing pressure direction of the VHP process, indicating a uniaxial anisotropy in optical transmission within the ceramics. To our best knowledge, the current work is the first report on visible laser ceramics lasing in the orange region at ambient temperature, fabricated from chemically synthesized powders, which could pave the way for future scientific research on and industrial applications of more sophisticated and cost-effective visible laser ceramics.

Geometric Landscape Annealing as an Optimization Principle Underlying the Coherent Ising Machine

Given the fundamental importance of combinatorial optimization across many diverse domains, there has been widespread interest in the development of unconventional physical computing architectures that can deliver better solutions with lower resource costs. However, a theoretical understanding of their performance remains elusive. We develop such understanding for the case of the coherent Ising machine (CIM), a network of optical parametric oscillators that can be applied to any quadratic unconstrained binary optimization problem. We focus on how the CIM finds low-energy solutions of the Sherrington-Kirkpatrick spin glass. As the laser gain of this system is annealed, the CIM interpolates between gradient descent on coupled soft spins to descent on coupled binary spins. By combining the Kac-Rice formula, the replica method, and supersymmetry breaking, we develop a detailed understanding of the evolving geometry of the high-dimensional energy landscape of the CIM as the laser gain increases, finding several phase transitions in the landscape, from flat to rough to rigid. Additionally, we develop a novel cavity method that provides a geometric interpretation of supersymmetry breaking in terms of the reactivity of a rough landscape to specific external perturbations. Our energy landscape theory successfully matches numerical experiments, provides geometric insights into the principles of CIM operation, and yields optimal annealing schedules. Published by the American Physical Society 2024

Using a multiple regression model for predicting the soft X-ray laser gain coefficient from laser plasmas

Using a multiple regression model for predicting the soft X-ray laser gain coefficient from laser plasmas