Laser Performance Research Articles

Enhancing high-temperature performance of Inconel 718 LDED samples through hybrid laser polishing post-treatment

ABSTRACT A hybrid laser polishing post-treatment was introduced to enhance the surface quality and high-temperature performance of laser directed energy deposition (LDED) Inconel 718 samples. The surface morphology and microstructure were analysed before and after laser polishing, and the result showed that the surface roughness was reduced by 97.4% and the grains of the recrystallized layer were refined through this post-treatment. Furthermore, the wear resistance, corrosion behaviour, and tensile strength of the laser polishing LDED Inconel 718 samples at the high-temperature of 650°C were investigated detailed. The result showed that the high-temperature tensile strength saw an increase of 14.97%, while both the high-temperature wear resistance and corrosion performance of Inconel 718 exhibited improvements compared to the as-fabricated samples.

Spectroscopy and efficient dual-wavelength laser performances of a Nd:GYSAG crystal.

We reported on the spectral properties and dual-wavelength laser performances of a novel, to the best of our knowledge, Nd:Gd1.8Y1.2ScAl4O12 (Nd:GYSAG) crystal for the first time. The absorption spectra, emission spectra, and fluorescence lifetime were systematically investigated. Further, a continuous-wavelength (CW) laser output power up to 5.02 W was obtained under an absorbed pump power of 9.45 W with slope and optical-to-optical efficiencies of 59.4% and 53.1%, respectively, at 1061.2 and 1063.2 nm. A stable passively Q-switched (PQS) laser employing Cr:YAG as a saturable absorber (SA) was realized. The maximum average output power of 0.756 W with a slope of near 34.4% was obtained with the pulse width, pulse energy, and peak power of 14.0 ns, 128.1 µJ, and 9.15 kW, respectively. The results indicate that the Nd:GYSAG crystal is an excellent laser medium for generating a high-efficiency dual-wavelength laser and has potential in terahertz (THz) laser generation.

Linearly Polarized Broadband Emission and Multiwavelength Lasing in Solution-Processed Quantum Dots.

A miniature laser with linear polarization is a long sought-after component of photonic integrated circuits. In particular, for multiwavelength polarization lasers, it supports simultaneous access to multiple, widely varying laser wavelengths in a small spatial region, which is of great significance for advancing applications such as optical computing, optical storage, and optical sensing. However, there is a trade-off between the size of small-scale lasers and laser performance, and multiwavelength co-gain of laser media and multicavity micromachining in the process of laser miniaturization remain as significant challenges. Herein, room-temperature linearly polarized multiwavelength lasers in the visible and near-infrared wavelength ranges are demonstrated, by fabricating random cavities scattered with silica in an Er-doped Cs2Ag0.4Na0.6In0.98Bi0.02Cl6 double-perovskite quantum dots gain membrane. By regulating the local symmetry and enabling effective energy transfer in nanocrystals, multiwavelength lasers with ultralow thresholds are achieved at room temperature. The maximum degree of polarization reaches 0.89. With their advantages in terms of miniaturization, ultralow power consumption, and adaptability for integration, these lasers offer a prospective light source for future photonic integrated circuits aimed at high-capacity optical applications.

Prediction of mid-infrared 2.72 μm lasing in heavily Er3+-doped fluorotellurite glass

Fluorotellurite glasses heavily doped with Er3+ are prepared in less demanding conditions as compared with fluoride glasses. Specifically, the effects of PbF2 added in the system of AlF3–MgF2–CaF2–SrF2–BaF2–TeO2 (AMCSBYT) are systematically studied on the correlation between glass structure and mid-infrared (MIR) luminescent properties of Er3+. These PbF2-modified glasses with an improved thermal stability and a noticeably reduced phonon energy as compared with telluride glasses exhibit an intense MIR emission at 2.72 μm and a long radiative decay lifetime. Calculation and analysis based on the Judd-Ofelt theory provide deeper insights into the interdependence of luminescent properties and glass structure. Numerical simulation is conducted for a MIR fiber laser based on the experimental data derived from the proposed glass. The 2.72 μm lasing output of 0.68 W is predicted with a slope efficiency of 3.38 %. It is expected that the performance of the fiber laser can be further optimized such that the output power can be increased over 1.0 W. The results emphasize the potential of the PbF2-modified fluorotellurite glass as a promising gain material for 2.72 μm fiber lasers.

III-nitride m-plane violet narrow ridge edge-emitting laser diodes with sidewall passivation using atomic layer deposition

A novel deep-ridge laser structure with atomic-layer deposition (ALD) sidewall passivation was proposed that enhances the optical characteristics of 8-µm ridge width III-nitride violet lasers on freestanding m-plane GaN substrates. The internal loss was determined using the variable stripe length method, where the laser structure with ALD sidewall passivation showed lower internal loss compared to the conventional shallow-ridge laser design. ALD sidewall passivation plays a critical role in device improvements; compared to the lasers without ALD sidewall passivation, the lasers with ALD sidewall passivation yield improved optoelectrical performance and longer lifetime under continuous-wave operation at high current density. This work demonstrates the importance of ALD sidewall passivation to laser performance, which enables high energy efficiency.

Investigation on the performance of deep ultraviolet edge emitting laser diodes using graded undoped AlGaN electron blocking layer (EBL)

P-AlGaN EBLs are usually used to control the overflow of electrons from the multiple quantum wells (MQWs) in AlGaN-based deep ultraviolet (DUV) edge-emitting laser diodes (EELDs). They're specially designed to prevent the excess flow of electrons from the MQW. This control is essential for maintaining the laser's efficiency and performance. Using optimized parameters of Al composition through theoretical calculations using Crosslight software helps certify the electrically driven EELD functions effectively within the desired operational range. In this study, the traditional p-AlGaN EBL within the electrically driven EELD is substituted with an undoped AlGaN EBL. This modification aims to raise the effective barrier height of the conduction band, and thus effectively stopping the electron leakage while improving the injection of holes. By optimizing the aluminum composition in the current research, efforts are made to lower the threshold current (Ith) and elevate the overall enactment of the graded undoped AlGaN EBL EELD. Various structural designs, including both conventional and undoped configurations, have been successfully created and analyzed in this study. Particular attention was given to investigating the impact of grading techniques applied to the electron-blocking layer. The graded undoped AlGaN EBL EELD performed better than the highly doped AlGaN EBL EELD due to the minimized free carrier absorption loss. Specifically, it shows higher slope efficiency (S.E) of 1.45 W/A and a significantly lower Ith of 790 mA. A new AlGaN EBL EELD design was tested with different layers. The ones with a graded undoped EBLs performed better than traditional AlGaN EBL EELD, improving power efficiency. The graded undoped EBLs setup also reduced the threshold current compared to traditional AlGaN EBL EELD.

2.1 µm multi-quantum well laser epitaxially grown on on-axis (001) InP/SiO2/Si substrate fabricated by ion-slicing

A cost-effective method to achieve a 2-3 µm wavelength light source on silicon represents a major challenge. In this study, we have developed a novel approach that combines an epitaxial growth and the ion-slicing technique. A 2.1 µm wavelength laser on a wafer-scale heterogeneous integrated InP/SiO2/Si (InPOI) substrate fabricated by ion-slicing technique was achieved by epitaxial growth. The performance of the lasers on the InPOI are comparable with the InP, where the threshold current density (Jth) was 1.3 kA/cm2 at 283 K when operated under continuous wave (CW) mode. The high thermal conductivity of Si resulted in improved high-temperature laser performance on the InPOI. The proposed method offers a novel means of integrating an on-chip light source.

The dazzling/damage mechanism of InGaAs detectors by near-infrared continuous laser

To investigate the dazzling/damage mechanism of InGaAs detectors by continuous laser, InGaAs detectors irradiated by continuous laser were analyzed theoretically and verified experimentally. Constructing the dazzling model of InGaAs detectors, saturated pixel data at different power levels were obtained. After comparing these data with verified experiments, it was observed that the magnitude and regularity of saturated pixel were relatively consistent at the same power levels. A finite element theoretical model of laser-irradiated InGaAs detectors was designed by Comsol. After calculation, the corresponding laser damage threshold for InGaAs detector was about 9.13 × 105 W/cm2 and 2.63 × 105 W/cm2 for irradiation times of 40 ms and 400 ms, respectively. These values were in relatively good agreement with the experimentally obtained damage thresholds of 1.07 × 106 W/cm2 and 3.95 × 105 W/cm2. The verified experiments confirmed the validity of the simulation methods and the dazzling/damage model employed in this paper. This study serves as a reference for further research on the laser irradiation effects and damage mechanisms of InGaAs detectors, as well as for laser protection and performance optimization in imaging systems.

Lasing from a Large-Area 2D Material Enabled by a Dual-Resonance Metasurface.

Semiconducting transition metal dichalcogenides (TMDs) have gained significant attention as a gain medium for nanolasers, owing to their unique ability to be easily placed and stacked on virtually any substrate. However, the atomically thin nature of the active material in existing TMD lasers and the limited size due to mechanical exfoliation presents a challenge, as their limited output power makes it difficult to distinguish between true laser operation and other "laser-like" phenomena. Here, we present room temperature lasing from a large-area tungsten disulfide (WS2) monolayer, grown by a wafer-scale chemical vapor deposition (CVD) technique. The monolayer is placed on a dual-resonance dielectric metasurface with a rectangular lattice designed to enhance both absorption and emission, resulting in an ultralow threshold operation (threshold well below 1 W/cm2). We provide a thorough study of the laser performance, paying special attention to directionality, output power, and spatial coherence. Notably, our lasers demonstrated a coherence length of over 30 μm, which is several times greater than what has been reported for 2D material lasers so far. Our realization of a single-mode laser from a CVD-grown monolayer presents exciting opportunities for integration and the development of real-world applications.

Terahertz Biosensor Engineering Based on Quasi-BIC Metasurface with Ultrasensitive Detection.

Terahertz (THz) sensors have attracted great attention in the biological field due to their nondestructive and contact-free biochemical samples. Recently, the concept of a quasi-bound state in the continuum (QBIC) has gained significant attention in designing biosensors with ultrahigh sensitivity. QBIC-based metasurfaces (MSs) achieve excellent performance in various applications, including sensing, optical switching, and laser, providing a reliable platform for biomaterial sensors with terahertz radiation. In this study, a structure-engineered THz MS consisting of a "double C" array has been designed, in which an asymmetry parameter α is introduced into the structure by changing the length of one subunit; the Q-factor of the QBIC device can be optimized by engineering the asymmetry parameter α. Theoretical calculation with coupling equations can well reproduce the THz transmission spectra of the designed THz QBIC MS obtained from the numerical simulation. Experimentally, we adopt an MS with α = 0.44 for testing arginine molecules. The experimental results show that different concentrations of arginine molecules lead to significant transmission changes near QBIC resonant frequencies, and the amplitude change is shown to be 16 times higher than that of the classical dipole resonance. The direct limit of detection for arginine molecules on the QBIC MS reaches 0.36 ng/mL. This work provides a new way to realize rapid, accurate, and nondestructive sensing of trace molecules and has potential application in biomaterial detection.

Enhancing solar laser performance through multirod configurations

Enhancing solar laser performance through multirod configurations

High-Reliability Uncooled InGaAlAs Lasers with Unpumped Current Blocking Regions Near Cavity Facets

The facet heating of high-power laser diodes significantly influences device reliability. To mitigate facet temperature, current blocking (CB) regions are employed at both cavity facets of the laser. In this paper, we investigate the device characteristics of uncooled InGaAlAs lasers with CB facets. We observe two types of light versus current (LI) curves and propose corresponding physical models. Our findings demonstrate the high reliability performance of uncooled lasers with proper engineering design and CB process.

Effect of back opening ratio and layout design on the performance of laser ablated point contact cell

In this paper we investigate the effect of the opening ratio and the back layout design on the electrical performance of the solar cell. First, the point contact solar cells are optimized by adjusting the laser opening ratio and the virtual-to-real ratio on each grid line of back side. The experimental results show that the open-circuit voltage (Voc) of the solar cell increases as the opening ratio decreases. Analysis of the PL images also shows that the damage to the passivation layer causes the Voc to drop. By characterizing the resistance of the back line, we found that laser drilling can cause an increase in the resistance of the back line. This can also lead to the FF loss. Then, by reducing the contact area of the bus-bar at the backside, the carrier recombination of the solar cell is reduced and the Voc of the cell is increased, resulting in a 0.07% increase in cell efficiency. Finally, the simulation shows that the openings lead to an increase in the recombination current (J01) at the base of the cell, which affects the efficiency of the cell.

Growth, thermal, spectroscopy and ∼2.7 μm multiwavelength laser output of Er:GYAP crystal

We demonstrate the growth, thermal, spectroscopy and laser performance of a Er3+ doped Gd0.1Y0.9AlO3 (Er:GYAP) disorder crystal grown by Czochralski method. The crystal with space group Pbnm and lattice parameters of =0.5185 nm, =0.5327 nm, =0.7378 nm, α=β=γ=90° and =0.203784 nm3 are obtained by fitting powder X-ray diffraction data. The Mohr’s hardnesses along three axes are 6.94, 7.27, and 7.44. The thermal expansion coefficient of axis is 4.20 × 10–6 K–1 and the density is 5.88 g/cm3. The thermal conductivities are characterized as =6.24, =5.57, and =6.83 W/(m·K). Meanwhile, the refractive index, absorption and emission spectra in triaxial directions are determined. Besides, level lifetimes of 4I11/2 and 4I13/2 are 0.86 and 2.83 ms. Finally, the ∼2.7 μm multiwavelength laser outputs are observed with maximum average power of 628 mW and beam quality factors / of 1.42/1.45. The results prove that the Er:GYAP crystal is a promising gain medium for generating mid-infrared lasers.

Polarized spectral properties and 2.3 µm laser performance of the Tm:YVO4 crystal

The polarized spectral properties and ∼2.3 µm high-power continuous-wave laser operation of Tm3+-doped yttrium orthovanadate crystal (Tm:YVO4) are reported. For the 3H4 → 3H5 transition, the stimulated-emission cross-section σSE is 1.01 × 10−20 cm2 at 2276 nm corresponding to a large emission bandwidth of 52 nm (for π-polarization). Pumped by a 794 nm laser diode, the 1.5 at.% Tm:YVO4 laser delivered 5.52 W at 2.29 µm with a slope efficiency of 19.9%, a laser threshold of 8.70 W, and a linear laser polarization (π). The Tm laser operated on the cascade scheme (on the 3H4 → 3H5 and 3F4 → 3H6 transitions) which was mainly responsible for the observed high laser slope efficiency. We also report on the first passively Q-switched Tm:YVO4 laser at 2.3 µm by employing porous nano-grained cuprous selenide (PNG-Cu2Se) as a saturable absorber. The shortest pulse duration and the highest single pulse energy amounted to 706 ns and 3.65 µJ, respectively, corresponding to a pulse repetition rate of 62.8 kHz.

Single-mode lasers based on pseudo-cubic perovskite CsPbBr3 microcrystals

The performance of perovskite lasers is often influenced by both the gain medium and the optical cavity. Therefore, a cavity with a unique structure and efficient feedback is essential for studying high performance of lasers. We successfully synthesized smooth-surface pseudo-cubic CsPbBr3 microcrystals on a silicon substrate by chemical vapor deposition method. The pseudo-cubic CsPbBr3 microcrystals exhibit a microcavity structure resembling a cube, where three-dimensional total internal reflection can be achieved within the microcavity. This provides a highly promising foundation for exploring high-performance lasers. The pseudo-cubic CsPbBr3 microcrystals demonstrate stimulated emission at a wavelength of 536.2 nm, achieving a full width at half maximum of 0.47 nm for a single-mode laser at room temperature. Additionally, the pseudo-cubic CsPbBr3 microcrystals exhibit remarkable stability that optical properties remain largely unchanged after long-term exposure to air. The perovskite microcavity with this novelty structure has been rarely reported in previous studies, and it also serves as an ideal cavity for lasers with broad prospects for integrated optoelectronic devices due to excellent optical properties and significant stability. This research not only deepens our understanding of unconventional CsPbBr3 microlasers but also provides strong support for future related research and technological development.

Efficient continuous-wave and passively Q-switched Nd:GSAG laser operating at 1.3 μm

We report on the laser performance of neodymium-doped gadolinium scandium aluminum garnet (Nd:GSAG) crystals at 1.3 μm for the first time, to the best of our knowledge. An efficient continuous-wave (CW) laser at 1336 nm and on output power of up to 2.01 W was obtained under an absorbed pump power of 4.89 W with slope and optical-to-optical efficiencies of 43.4 % and 41.1 %, respectively. Furthermore, a passively Q-switched (PQS) laser with a Co:MgAl2O4 crystal serving as a saturable absorber in a compact plano-plano resonator cavity was examined. A maximum average output power of 0.2 W was obtained with a pulse width, pulse energy, and peak power of 34.4 ns, 22.2 µJ, and 645 W, respectively. Our results indicated that Nd:GSAG crystals are promising for producing high-efficiency CW lasers and effective PQS lasers at 1336 nm.

Enhanced Nonradiative Charge Recombination in Microfiber-Based Bismuthene.

After the first report of a graphene-based passive mode-locking ultrafast fiber laser, two-dimensional materials as efficient saturable absorbers offer a new horizon in ultrafast fiber laser. However, the interactions on atomic scale between these two-dimensional materials and fiber and the fiber effect on the carrier dynamics have not been realized. To figure out the exact role of fiber and the carrier dynamics affected by the fiber substrate related to ultrafast photonics, bismuthene, a newly reported 2D quantum material used in a passive mode-locking fiber laser, deposited on α-quartz has been investigated. We surprisingly found that the α-quartz substrate can strongly accelerate the nonradiative electron-hole recombination of bismuthene in theory, and the transient absorption spectra of bismuthene on normal glass and α-quartz further verify the substrate effect on carrier dynamics of bismuthene. The discovery provides new thinking about substrate effect to regulate the performance of ultrafast mode-locking fiber lasers as well as ultrafast photonics.

High-Quality Solution-Processed Quasi-2D Perovskite for Low-Threshold Lasers.

Spin-coated quasi-two-dimensional halide perovskite films, which exhibit superior optoelectronic properties and environmental stability, have recently been extensively studied for lasers. Crystallinity is of great importance for the laser performance. Although some parameters related to the spin-coating process have been studied, the in-depth understanding and effective control of the acceleration rate on two-dimensional perovskite crystallization during spin-coating are still unknown. Here we investigate the effect of solvent evaporation on the microstructure of the final perovskite films during the spin-coating process. The crystallization quality of the film can be significantly improved by controlling solvent evaporation. As a result, the prepared quasi-2D perovskite film exhibits a stimulated emission threshold (pump: 343 nm, 6 kHz, 290 fs) of 550 nm as low as 16.2 μJ/cm2. Transient absorption characterization shows that the radiative biexciton recombination time is reduced from 738.5 to 438.3 ps, benefiting from the improved crystallinity. The faster biexciton recombination significantly enhanced the photoluminescence efficiency, which is critical for population inversion. This work could contribute to the development of low-threshold lasers.

Performance improvement of GaN-based vertical cavity surface emitting laser by employing a hole storage layer and enhancing the carrier transport behavior

In this paper, the transport behavior of carriers between multiple quantum wells (vertical) and inside a single quantum well (radial) in a GaN-based Vertical Cavity Surface Emitting Laser (VCSEL) is investigated, and a new device structure with a hole storage layer is proposed to enhance the laser performance. The theoretical results indicate that the vertical transport capability of holes is the key factor for total stimulated recombination rate and hole leakage. The VCSEL with a double-QW structure exhibits better output performance compared to the devices with three or more QWs owing to the lower light absorption loss and the stronger optical field in the active region. Furthermore, a thicker undoped GaN layer is proposed to be added as the hole storage layer to mitigate hole leakage for the VCSEL with a double-QW structure. This new structure can increase the tilt of energy band in the region of the hole storage layer and effectively improve the uniformity of radial distribution of holes in QWs. Therefore, it is beneficial to reduce the threshold current and enhance the laser output power.