Lasing Characteristics Research Articles

Iterative model for CW fiber lasers

A new iterative numerical model of continuous wave fiber lasers doped with rare-earth ions is proposed. The main advantage of this model is its stability to the choice of initial values of the generated power at the fiber boundaries. The algorithm for solving the system of rate equations is discussed in detail. Simulation results of double-clad fiber lasers obtained using the proposed model are compared with those reported in the literature. The output characteristics of single-mode fiber lasers were modeled and compared with experimentally obtained data.

Single‐Mode Lasing by Selective Mode Structure Breaking

AbstractSingle‐mode lasers are highly desirable for applications in optical communication, quantum information, and photonic computing, but their realization is challenging due to the competition of multiple closely spaced resonant modes in microcavities. This paper proposes a novel approach, termed mode structure breaking, to achieve high‐performance single‐mode lasing in an individual laser cavity. By introducing selective spatial structure defects, the mode structure of competing modes can be broken, enabling single‐mode selection without huge losses. As proof of concept, femtosecond (fs)‐laser ablation is experimentally employed to introduce external angle defects on a microdisk cavity, effectively eliminating mismatched competing modes and thus achieving single‐mode lasing output. The lasing characteristics are further optimized by incorporating a punched hole to suppress remaining high‐order lasing modes. Notably, the fabricated perovskite laser sources, which are called mode‐structure‐breaking lasers, demonstrate excellent single‐mode lasing properties, including stability, an ultralow threshold (≈2.31 µJ cm−2), and a narrow linewidth (≈0.15 nm). Conclusively, this comprehensive study of manipulating lasing mode by breaking mode structure may provide a promising approach to realizing single‐mode lasing in a single structure, which is significant for producing on‐chip laser source arrays for use in photonic integrated circuits.

Correlating thermal history with characteristics of Laser Welded 15-5 PH Stainless Steel

Correlating thermal history with characteristics of Laser Welded 15-5 PH Stainless Steel

Lasing Characteristics of GaInAsP Laser Diodes on Directly Bonded InP/Si Substrates with a Gas out Channel

In this study, the lasing characteristics of GaInAsP laser diodes (LDs) grown on directly bonded InP/Si substrates with a gas out channel (GOC) structure are investigated. GOC InP/Si substrates are fabricated using hydrophilic direct bonding and metal–organic vapor phase epitaxy growth methods and subsequently their surface conditions, bonding strength, and lasing performance are examined. Herein, it is observed that the introduction of a GOC substantially reduces void formation and improves the threshold current density of the LDs. In the results, it is demonstrated that the performance of the GOC InP/Si substrates is comparable to that of InP substrates, highlighting their potential for use in high‐performance optical devices.

915 nm pumping kilowatt fiber oscillator with high optical-to-optical efficiency

We demonstrate an all-fiber oscillator with high optical-to-optical efficiency using laser diodes working at 915nm as the pump sources to reduce the demand for thermal management. When the output power of the bidirectional pumped oscillator is 1.16kW, the optical-to-optical efficiency is as high as 75.4%. In this working state, the output characteristics of the oscillator are observed. The Raman suppression ratio is 41.23dB and the beam quality factor Mx2 = 1.14, My2 = 1.29. Analyzing the time trajectory of the highest power output, there are no significant characteristic peaks in the time domain signal and the frequency domain signal, which indicates that the oscillator has good stability.Improving the output characteristics of the 915nm pumping lasers has a positive significance for the application of non-strict ambient temperature control.

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.

Diagnostics of tin droplet-based laser produced plasma by triple Langmuir probe

Laser produced plasma extreme ultraviolet light source, as the exposure light source for next-generation lithography, faces urgent challenges due to its low conversion efficiency and significant debris contamination. Using a triple Langmuir probe, we conducted a study on the parameters and kinetic characteristics of tin droplet-based laser produced plasma that serves as extreme ultraviolet light source. In this paper, we report a design of triple Langmuir probe circuit based on the BWL (Bulk Wirewound Low-value) sampling resistor, which ensures that high-frequency signals remain undistorted during acquisition. Utilizing the “shadowgraph” method, we calculated the average deflection angles of droplet debris jets under different alignment conditions. Combining the diagnostic results from the probe, we found that the alignment accuracy between the laser and droplet directly influences the parameters of plasma. The parameters and kinetic characteristics of plasma were also diagnosed and analyzed at different angles and distances by moving the probe. Employing the triple Langmuir probe, measurements and analyses of laser produced plasma parameters and kinetic characteristics were achieved, providing a convenient method for diagnosing extreme ultraviolet lithography light sources. This work also offers an effective basis for optimizing the light sources.

Laser Cutting of Titanium Alloy Plates: A Review of Processing, Microstructure, and Mechanical Properties

The growing use of titanium alloys has led to the gradual replacement of traditional processing methods by laser cutting technology, making it the preferred method for processing titanium alloy plates due to its high efficiency, precision, and adaptability. In this review, the characteristics of laser cutting technology and its application in titanium alloy plate processing are summarized, outlining several aspects of the cutting process, microstructure, and mechanical properties of the material after cutting, along with simulation predictions. Previous research categorized laser-cutting input parameters into beam parameters and process parameters, with the commonly used parameters being the laser power, cutting speed, and gas pressure. Various parameter combinations can achieve different cutting qualities, and seven indices can be used to evaluate the cutting process, with the surface roughness and slit width serving as the most common indices. Different auxiliary gases have shown a significant impact on the laser cutting quality, with commonly used gases consisting of nitrogen, argon, and air. Argon-assisted cutting generally results in better surface quality. Due to the rapid temperature change, the titanium alloy microstructure will undergo a non-diffusive martensitic phase transformation during laser cutting, producing a heat-affected zone. Experimental studies and simulations of the mechanical properties have shown that the occurrence of a martensitic phase transformation increases the hardness and residual tensile stress of the material, which reduces the fatigue strength and static tensile properties. In addition, studies have found that the more streaks appear on the cut surface, the lower the fatigue strength is, with fatigue cracks arising from the stripes. Hence, the established analytical solution model and three-dimensional finite element model can effectively predict the temperature distribution and residual stress during the cutting process. This can provide a better understanding of the high residual stress characteristics of the cutting edge and the stripe formation mechanism, allowing researchers to better explore the mechanism of laser cutting.

Evaluating productivity characteristics of laser engineered net shaping titanium alloy

Advances in Additive Manufacturing (AM) technologies have made it possible to reduce the design and prototyping costs to a minimum especially for a low-productivity material like titanium. Titanium alloys are commonly and widely used alloys in the aerospace and biomedical sector due to their advantageous material properties. This paper is an evaluation study of factors affecting the productivity characteristics of Laser Engineered Net Shaping (LENS) titanium alloy (Ti-6Al-4 V) using face milling. Some of the productivity challenges associated with titanium such as rapid tool wear, poor surface finish, and high-power consumption are explored in this paper. All materials processed using AM face the same critical problem that the manufactured part requires a post machining since AM produces relatively poor surface finish. Machining trials are conducted using the combinations of machining parameters such as spindle speed of 800 and 1600 rev/min; feed rate of 50 and 100 mm/min; and a constant depth of cut of 1 mm, respectively. Titanium being a poor thermal conductivity material, the effect of coolant was investigated using wet/dry machining. Data related to the productivity factors and material behavior under a milling trial was recorded and analyzed. The obtained data from the trials include productivity factors such as Metal Removal Rate (MRR), power consumed, and the surface finish for each plate/trial. The power consumed in dry milling was observed to be lower than that in wet milling which is contrary to the observations from conventional wet milling. The paper concludes the trends observed for LENS titanium are opposed to the trends in conventional machining such as increasing cutting speed will result in lower cutting force and power consumed.

A Study on the Manufacture of CNT Composites Bipolar Plate for the Fuel Cell Using a Nanosecond Pulsed Laser

The channels of the graphite-based bipolar plate for hydrogen fuel cells were mainly manufactured through milling due to low forming elongation and processability. However, during the milling process, the machining precision is low due to tool wear and vibration, and there is a risk of breakage. Non-traditional laser processing can solve the problems of tool wear and vibration through non-contact processing. In this study, the interaction characteristics of the nanosecond pulsed laser and CNT composites were observed, and channels and bipolar plates were manufactured. The effect of scanning speed and pulse duration was observed for interaction characteristics. Defects were observed due to high thermal effects at low scanning speed and high pulse duration. Channels were created depending on parallel pitch distance [] and Number of scans (NOS). The channel was evaluated for depth, top width, bottom width, channel angle, material removal rate, and surface roughness, and significant changes were observed depending on . The chemical composition, surface resistance, and contact angle of the laser-processed channel were measured. The laser processed channel was oxidized, and the surface resistance and contact angle increased. Finally, the manufacturability of the CNT composites bipolar plate using laser was examined.

Influence of laser absorptivity of CuCr0.8 substrate surface state on the characteristics of laser directed energy deposition inconel 718 single track

An effective method for fabricating copper-nickel bimetallic liquid rocket engine thrust chambers involves utilizing laser directed energy deposition (LDED) technology. However, the state of the substrate surface significantly impacts the LDED process. This study investigates the effects of various substrate treatments on LDED single tracks, using CuCr0.8 high-copper alloy as the substrate and Inconel 718 as the deposition material. The treatments include polishing, sandblasting, laser etching, and cold spraying. Substrate surface roughness, laser absorptivity, molten pool morphology, and microstructure were characterized, and the mechanisms of laser absorptivity change and the different LDED processes were analyzed. The results indicate that the laser-etched surface exhibits the worst surface roughness (Ra 15.20 ± 0.60 μm), the highest laser absorptivity(80.70% at 1080 nm wavelength), the largest deposition width (947.33 ± 29.85 μm), and the maximum number of fine grains among the four substrates. Additionally, the cold-sprayed surface shows the largest deposition depth (237.33 ± 39.04 μm), the minimum number of fine grains and a higher laser absorptivity (66.20% at 1080 nm wavelength). In situ observations of molten pool formation and flow during LDED was conducted using an in situ high-speed high-resolution imaging system. The mechanisms underlying the alteration in laser absorptivity primarily involve the "trapped light" effect and modifications to the surface material. This research is significant as it provides foundational insights for laser processing of highly reflective materials, offering important theoretical and practical implications for engineering applications.

Crack characteristics of pulsed laser brazed diamond grinding wheel

Experiments on pulsed laser brazing of diamond grinding wheels were carried out in this paper. The crack characteristics and residual stress of brazed layer were detected and evaluated. The influence laws of pulse width, frequency, diamond mixing ratio, number of stacked layers, powder thickness and preheating temperature on crack characteristics were investigated. The pulsed laser characteristic coefficients (peak pulse power density/pulse interval time) and the correlation law between thermal stresses and cracks are discussed. The results show that the pulse width and frequency of the pulsed laser affect the cracking rate by varying the energy input and the time between pulses. The existence of a suitable value for the pulse characteristic coefficient corresponding to pulse width and frequency corresponds to a lower cracking rate. Thermal stress variations due to changes in process conditions at different diamond percentages, number of stacked layers, and preheating temperatures are the main causes of crack rate variations. Cracking is not only affected by thermal stresses, but also by the quality of the formed surface when pulsed laser brazing diamond to nickel–chromium alloy brazing material. For example, the main reason for the variation in cracking rate is the change in the morphology of the molded surface due to the variation in the thickness of the powder spread at different variations in the thickness of the powder spread.

Controllable lasing characteristics in Brillouin random fiber lasers by tailoring gain and random feedback fibers

Brillouin random fiber lasers (BRFLs), the combination of stimulated Brillouin scattering (SBS) gain and random distributed feedback, offer narrow linewidth lasing with simplicity and flexibility. However, BRFLs may not gain broad acceptance unless the fundamental lasing mechanisms governing their operation are fully understood and the lasing properties are effectively manipulated. Here, we demonstrate the control of lasing characteristics in BRFLs by tailoring the SBS gain fiber and the scattering pattern of the random feedback fiber. Experimental results show that BRFLs with 5 cm random fiber gratings (RFGs) feedback exhibit lower intensity fluctuation, longer coherence time, and more stable frequency compared to those with 6 km Rayleigh scattering fiber (RSF) feedback thanks to more correlated phase, lower mode density, and weaker dependence on external variations of RFGs. The low-randomness RFG feedback further improves the coherence time and intensity fluctuation attributed to the small period variation of sub-gratings. Moreover, the BRFL based on the high gain fiber and the strong scattering RFG feedback with low loss achieves high lasing efficiency and low threshold. The frequency jitter, intensity noise, and coherence time are also improved by reducing the gain fiber from 20 km to 1 km due to decreased mode hopping from mode competition. These results clarify the impact of gain and random feedback fibers on BRFL performance, offering insights for optimizing complex laser design for applications requiring high frequency stability and long coherence time.

6-ns level passively Q-switched Nd:KNaY (WO4)2 laser at 1.07 µm

To our knowledge, a compact diode-pumped Nd: KNaY (WO4)2 laser operating at 1.07 µm has been successfully achieved for the first time. The passively Q-switched Nd: KNaY (WO4)2 pulse laser with the narrowest pulse width of 6.23 ns and peak power of 1.34 kW was obtained by experiment, and its laser characteristics were studied in detail. The effect of Cr4+: YAG initial transmission for pulse width of Nd: KNaY (WO4)2 output laser was investigated by theoretical analysis and numerical simulation. Finally, it was found that the theoretical and experimental results are basically in agreement.

Nuclear-excited source of coherent and incoherent radiation with direct nuclear pumping

Uranium fission fragments, as well as the products of 3He(n,p)3H and 10B(n,α)7Li nuclear reactions were utilized in the nuclear reactor for gas ionization and excitation. However, the 6Li(n,α)3H nuclear reaction was less examined. The use of lithium-6 as a surface source of excitation of the gas medium, due to the long path length of tritium nuclei in the gas, allows to excite large volumes of gas as opposed to using 235U or 10B.While investigating the luminescence of noble gases in the core of the IVG.1M research reactor, we noted an appearance of alkali metal lines and a sharp increase in the intensity of these lines at temperatures above 570 K. It was determined that the population of levels of lithium atoms has practically no effect on the population of the 2p-levels of atoms of noble gases. The selectivity of p- and s-levels deactivation by lithium atoms implies the possibility of creating inversion of population at 2p-1s transitions of noble gas atoms. Successful experiments to study the luminescence of gases upon excitation by 6Li(n,α)3H nuclear reaction products allow us to proceed to experiments to achieve the laser action threshold and study the lasing characteristics of gas mixtures at the IGR pulsed nuclear reactor with thermal neutron flux density up to 7∙1016 n/cm2s. For this purpose, an experimental device designs were proposed to perform experiments on the IGR reactor. A step-by-step procedure of fabrication of a nuclear-excited source for excitation of gas mixtures is provided. The results of reactor experiments aimed at determining the spectral and temporal characteristics of optical radiation during excitation of gas mixtures by 6Li(n,α)3H nuclear reaction products are presented.

Numerical simulation of electrically-pumped overgrown III-V microwire lasers on silicon

Electrically-pumped III-V lasers on Si by aspect ratio trapping (ART) techniques have been a promising candidate for Si-based light sources. Although the lasers based on the ART approach enable large-scale integration and are compatible with complementary metal-oxide semiconductor processes, the sub-micron size laser structure suffers from severe metal absorption loss and heat accumulation. In this paper, we propose a novel Si-based III-V multi-quantum well laser by ART methods. The overgrowth of III-V microwires is adopted, with additional {110} quantum wells (QWs) generated during epitaxy. Through numerical simulation, the mode loss of the overgrowth structure is reduced from 3.59 dB/cm to 0.96 dB/cm, the threshold current is decreased by 42.5% and the output power is increased by 91.7% under pulsed conditions. Due to the growth of QWs on {110} planes, the injection efficiency of the device increases, leading to an improvement of performance. The effects of temperature and cavity length on the lasing characteristics of the device under continuous wave (CW) conditions are also analyzed that the proposed structure can realize CW lasing at room temperature. Moreover, the device deterioration caused by growth defects is discussed, which can be improved by high reflection coating. The suggested Si-based overgrowth III-V microwire laser has great potential to integrate high-density electrically-pumped light sources for silicon photonics.

Reactive sintering of coaxial Yb3+:YAG/YAG transparent ceramics

15 at.% Yb3+:YAG/YAG transparent composite ceramics with a coaxial geometry were synthesized by a ceramic forming method combined with the reactive sintering at 1800 °C. Densification peculiarities, microstructure, optical properties, and laser characteristics of composite ceramic samples were studied. Powder mixtures of Yb3+:YAG and YAG stoichiometric compositions demonstrate almost the same densification enabling uniform shrinkage of composite without differential sintering. It was shown that in-line optical transmittance of 15 at.% Yb3+:YAG/YAG composite ceramics reaches 80 % at 1030 nm wavelength. The effective diffusion coefficient of Yb3+ ions in garnet structure has been determined. Efficient laser emission was generated from Yb3+:YAG/YAG composite ceramics with a slope efficiency of ηsa = 0.30.

Ultra-low frequency noise external cavity diode laser systems for quantum applications

We present two distinct ultra-low frequency noise lasers at 729 nm with a fast frequency noise of 30 Hz2/Hz, corresponding to a Lorentzian linewidth of 0.1 kHz. The characteristics of both lasers, which are based on different types of laser diodes, are investigated using experimental and theoretical analysis with a focus on identifying the advantages and disadvantages of each type of system. Specifically, we study the differences and similarities in mode behavior while tuning frequency noise and linewidth reduction. Furthermore, we demonstrate the locking capability of these systems on medium-finesse cavities. The results provide insights into the unique operational characteristics of these ultra-low noise lasers and their potential applications in quantum technology that require high levels of control fidelity.

Design and characteristics of a fiber laser powered repetitive micro-plasma jet triggered gas switch.

To satisfy the need for low jitter in gas switches at repetition rate and enhance insulation reliability during high voltage operation of the trigger, we propose a micro-jet triggering system. This system requires less energy and can use a laser power supply as an energy source. It effectively improves the insulation stability of the trigger when working at high potentials and achieves a good triggering effect with low jitter at low working coefficients. The breakdown characteristics were tested by double-pulse experiments. Ensuring the same operating conditions for both pulses, the pulse interval was varied to obtain the breakdown voltage dispersion at different repetition rates. The results indicate that the dispersion of the breakdown voltages can reach 0.16% at a frequency of 50Hz with a pulse front of 30 μs, representing an order of magnitude reduction compared to the 1.45% at switching self-breakdown, and decreases further as the air pressure rises. In addition, the size of the microcapillary has an impact on the dispersion of breakdown voltage. It was found that for a range of lengths from 2 to 6mm and aperture sizes from 80 to 400μm, the trigger jitter was lower when the length was larger and the aperture was smaller. Furthermore, a trigger life test was performed on the ceramic capillary, and after one million triggers, the system remained stable with no degradation in trigger performance.

Room-Temperature Near-Infrared Lasing from GaAs/AlGaAs Core-Shell Nanowires Based on Random Cavity.

Room-temperature lasing based on low-dimensional GaAs nanowires (NWs) is one of the most critical and challenging issues in realizing near-infrared lasers for nanophotonics. In this article, the random lasing characteristics based on GaAs NW arrays have been discussed theoretically. According to the simulation, GaAs/AlGaAs core-shell NWs with an optimal diameter, density, and Al content in the shell have been grown. Systematic morphological and optical characterizations were carried out. It is found that the GaAs NWs with the additional growth of the AlGaAs shell exhibit improved emission by about 2 orders of magnitude at low temperatures, which can be attributed to the suppression of crystal defects. At room temperature, lasing was observed with a threshold around 70.16 mW/cm2, and the random lasing mechanism was discussed in detail. This work is of great significance for the design of random cavities based on semiconductor NWs, which is important for optoelectronic integration.