Lasing Characteristics Research Articles

Research on cutting force characteristics of laser ultrasonically assisted turning of cemented carbide

Cemented carbide possesses excellent characteristics such as high strength and hardness, but its poor machinability has restricted its widespread application. Laser ultrasonically assisted turning (LUAT) can enhance the machinability of workpieces and is widely used in precision machining of difficult-to-machine materials. In this paper, LUAT is applied to the cutting of cemented carbide, and the characteristics of cutting force in the machining process are studied. A theoretical model of cutting force is established by analyzing the interaction between the cutting tool, chip and workpiece during the turning process. The maximum error was found to be 18.6% by comparing with the experimental data, which better predicted the changing trend of cutting force and verified the accuracy of the model. Furthermore, experiments on LUAT of cemented carbide are carried out using the Taguchi method. The influence of cutting tools and processing parameters on cutting force is analyzed, revealing that the amplitude has the most significant impact on cutting force. The optimal combination of processing parameters is also obtained. Finally, a comparison is made between different turning methods. Compared to conventional turning, laser assisted turning, and ultrasonically assisted turning, the total cutting force in LUAT is reduced by 53.44%, 45.62%, and 21.64%, respectively, resulting in improved surface quality of the workpiece.

Efficient fabrication of high quality SU-8 photoresist based microsphere lasers via emulsion

SU-8 photoresist is a highly important material in the field of microfabrication and photonics owing to its low cost, excellent chemical and mechanical durability, high refractive index and transparency in the visible range. As a result, SU-8 photoresist has been employed as a cavity matrix for microsphere lasers. However, the current fabrication technique of SU-8 based microsphere lasers is complex and time-consuming. Here, we demonstrate a novel, cost-effective fabrication method for dye-doped SU-8 microspheres with diameters ranging from about 15–100 µm. These microspheres exhibit efficient lasing emission under optical pulse excitation. Lasing thresholds of 20–30 µJ mm−2 and quality factors ranging from 1500 to 3000 are achieved. The size dependence of lasing characteristics indicates that the lasing mechanism is due to whispering gallery mode. Interestingly, these microsphere lasers can work in water, presenting promising application prospects in the fields of biological and chemical sensors.

Influence of Franz Keldysh effect on the modulation depth and distortion characteristics of transistor laser

Influence of Franz Keldysh effect on the modulation depth and distortion characteristics of transistor laser

Analysis of phase, microstructure, and mechanical characteristics of selective laser melted AlSi10Mg alloy after post-heat treatment

Analysis of phase, microstructure, and mechanical characteristics of selective laser melted AlSi10Mg alloy after post-heat treatment

Efficient and accurate parameter extraction for quantum-well DFB lasers: a comprehensive approach integrating multiple mathematical models

This study proposes an efficient and accurate method for parameter extraction of quantum well distributed feedback (DFB) lasers by combining the rate equation model, finite element method, transmission matrix method, and traveling wave model (TWM). By fabricating and measuring the companion Fabry-Perot (FP) lasers, material and structural parameters common with the target DFB laser are extracted efficiently. All the intrinsic parameters of the DFB laser are accurately extracted by integrating multiple mathematical models, and the possibility of multiple solutions is avoided. From the extracted parameters, the output characteristics of the DFB laser are simulated using the TWM. The simulation results agree closely with the experimental results, proving the feasibility and accuracy of the proposed method.

Frequency Domain Analysis and Determination for Spectrum Characteristics of Laser With External Phase Modulation

Frequency Domain Analysis and Determination for Spectrum Characteristics of Laser With External Phase Modulation

Reduction of relative intensity noise in a diamond Raman laser

The relative intensity noise (RIN) characteristics of a continuous-wave diamond Raman laser are investigated for the first time. The results reveal the parasitic stimulated Brillouin scattering (SBS) that usually occurred with higher-order spatial modes in the diamond Raman resonator is a pivotal factor impacting the Raman longitudinal modes and deteriorating the RIN level. The diamond Raman laser automatically switches to single-longitudinal-mode operation and the RIN level is significantly decreased in the frequency range of 200 Hz to 1 MHz after the parasitic SBS is effectively suppressed through inserting a spatial aperture or a χ(2) nonlinear crystal into the cavity. Due to the introduction of additional nonlinear loss to the high intensity Raman fluctuations and the non-lasing spontaneous Raman modes, the χ(2) nonlinear crystal enables better performance in the RIN-level reduction compared to the spatial aperture which can only achieve SBS inhibition. The RIN reduction routes are well suited for various crystalline Raman media to achieve high power and low intensity noise laser at different wavelengths.

Modification of the temporal laser source term in two-temperature model

Simulations on the interaction between laser pulses with materials during pulsed laser ablation require information on the characteristics of both laser and material. While details on material properties are extensively studied, the temporal profile of the laser source term is rarely studied and is generally assumed to be Gaussian. This article explores the effects of non-Gaussian temporal laser source terms (TLSTs) in simulating the heat diffusion within a metal upon irradiation of femtosecond pulsed lasers. We employed the Two-Temperature Model (TTM) to simulate the temperature evolution on the surface of copper upon irradiation of a 100-fs laser pulse with different TLSTs at different laser repetition modes (single-shot, burst, and biburst). We used a constant total fluence of 3J/cm 2 in all cases and subsequently calculated the ablation depths based on the resulting temperature values. Our results show that non-Gaussian TLSTs generate lower electron and lattice temperatures, resulting in shallower crater depths compared to a Gaussian TLST. However, under burst and biburst modes, particularly with higher subpulse number repetition time, the results of non-Gaussian TLSTs approximate those of Gaussian TLSTs. To initiate laser ablation in such cases, higher laser fluence might be required. Our work on non-Gaussian temporal profiles in TTM simulations can be applied to other computational methods in describing laser-matter interaction.

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.

Design optimization of Yb-doped fiber lasers for operation in radiation environments

AbstractRadiation hardening should be considered for various active fiber systems operated in adverse environments to reduce their sensitivity to complex ionizing radiations. And, architecture optimization through numerical simulation provides an efficient choice. Here, introducing radiation effects into the conventional fiber laser model, a radiation model concerning the design optimization of low- and moderate-power Yb-doped fiber lasers is developed. And, experiments at different radiation levels up to 750 Gy are carried out for validation, demonstrating the ability of this model to correctly simulate the performance of the Yb-doped fiber laser in harsh environments. Then, with this model, impacts of active fiber length, pump scheme, and pump allocation on the output characteristics of Yb-doped fiber lasers are analyzed numerically. And, optimization of Yb-doped fiber lasers are conducted through architecture design. Simulations show that a proper design with relatively short active fiber and dynamic pump allocation can remarkably improve the radiation tolerance of Yb-doped fiber lasers.

Cascaded All-Fiber Gas Raman Laser Oscillator in Deuterium-Filled Hollow-Core Photonic Crystal Fibers.

Hollow-core photonic crystal fibers (HC-PCFs) provide an ideal transmission medium and experimental platform for laser-matter interaction. Here, we report a cascaded all-fiber gas Raman laser based on deuterium (D2)-filled HC-PCFs. D2 is sealed into a gas cavity formed by a 49 m-long HC-PCF and solid-core fibers, and two homemade fiber Bragg gratings (FBGs) with the Raman and pump wavelength, respectively, are further introduced. When pumped by a pulsed fiber amplifier at 1540 nm, the pure rotational stimulated Raman scattering of D2 occurs inside the cavity. The first-order Raman laser at 1645 nm can be obtained, realizing a maximum power of ~0.8 W. An all-fiber cascaded gas Raman laser oscillator is achieved by adding another 1645 nm high-reflectivity FBG at the output end of the cavity, reducing the peak power of the cascaded Raman threshold by 11.4%. The maximum cascaded Raman power of ~0.5 W is obtained when the pump source is at its maximum, and the corresponding conversion efficiency inside the cavity is 21.4%, which is 1.8 times that of the previous configuration. Moreover, the characteristics of the second-order Raman lasers at 1695 nm and 1730 nm are also studied thoroughly. This work provides a significant method for realizing all-fiber cascaded gas Raman lasers, which is beneficial for expanding the output wavelength of fiber gas lasers with a good stability and compactivity.

Lasing emission from ZnO hierarchical spherical microcavity

We investigated lasing characteristics of ZnO hierarchical micro-spherical particles with diameters of 1–5 μm . The lasing emission consists of a small number of discrete laser peaks unlike conventional random lasing from ZnO nanopowder-assembly. Theoretical calculations based on a many-body theory reveal that the optical gain is achieved at the observed lowest lasing threshold value, 4 mJ⋅cm−2⋅pulse−1 , which corresponds to the excited carrier density ∼2.4×1025 m−3 . Because the carrier density is much higher than the Mott density, the gain origin for lasing is electron-hole plasma recombination. The lasing frequency mode shift ( ∼1.2 meV ) is due to the refractive index change induced by exciting high carrier density up to 6.1×1025 m−3 . By changing hierarchical structures via controlling growth condition and performing the annealing treatment and performing the calculation of scattering efficiency of ZnO particles, we found that the hierarchy of the micro-spherical particle plays a crucial role of the lasing feedback: the strong light scattering at the interface between outer nanoparticles with the sizes of 100–200 nm and smaller ones with the sizes of 10–60 nm consisting in the micro-spherical particle results in a light confinement. Furthermore, it has been confirmed that each discrete lasing mode shows strong gain competition with each other probably due to spatial overlap between the modes. These results suggest that both random scattering and microcavity modes contribute to the lasing oscillation.

Revealing the impact of Hot Isostatic Pressing temperature on the microstructure and mechanical characteristics of Selective Laser Melted CuAlNiMn shape memory alloy

The present research examines the impact of temperature during Hot Isostatic Pressing (HIP) on the mechanical, microstructure, and density characteristics of Cu-based shape memory alloys (SMAs) made by Selective Laser Melting (SLM). HIP improved the density of the built components by 11.5 %, with a reduction in density with an increase in HIP temperature. Pore aspect ratio analysis revealed non-spherical pores at higher temperatures, while spherical and small pores were observed at 950 °C. SEM analysis demonstrated the disappearance of shrinkage porosity and an increase in grain size with higher HIP temperatures. XRD analysis confirmed phase transformation and variation in crystallite size with an increase in HIP temperature. After HIP treatment, microhardness and tensile strength significantly improved, with the 950 °C sample showing the highest values.

The Efficiency of Erbium Lasers in the Removal of Root Canal System and Surface Biofilms: A Systematic Review and Meta-Analysis.

Background: Studies have shown positive effects of erbium lasers in removal of biofilms. A review article was required with quantitative data for confirmation of their effects, but there is still no a comprehensive study reviewing their effects based on the root canal and implant surface. This systematic review and meta-analysis was conducted to evaluate the efficiency of erbium lasers in removal of the root canal system and surface biofilms. Methods: Studies were searched with keywords in databases of PubMed, Scopus, Europe PMC, Cochrane Central, Embase, and Web of Science and screened by referees. Data were included based on mean ± standard deviation and size of control and laser groups. Effect sizes were assessed as standardized mean differences and calculated for each study and for the root and dental surface. Laser characteristics and bacteria were considered as moderators. Results: Nineteen articles in the current study comprised 565 samples (283 control samples and 282 laser samples). The analyses showed the significant effects of erbium lasers on bacterial biofilms on the implant surface [-0.496, 95% confidence interval, CI (-0.720 to -0.273); I2 = 26.94; p = 0.029; Q = 13.28] and root canal [-0.551, 95% CI (-0.656 to -0.445); I2 = 23.89; p = 0.031; Q = 10.46]. Results showed that highest efficiency lasers were obtained at higher wavelengths of 2940 nm, 75-100 mJ energy, and 100-150 μsec and <50-Hz pulses. Conclusions: Erbium lasers can be used to remove biofilms on dental implant surfaces and root canal systems and are safe options for untouchable sites in the root canal.

Research on the Linewidth Characteristics of the Pulse Compression Laser by Stimulated Brillouin Scattering Through the Compact Two-Cell Setup

Research on the Linewidth Characteristics of the Pulse Compression Laser by Stimulated Brillouin Scattering Through the Compact Two-Cell Setup

Analysis of Threshold Characteristics of Short-Wavelength Semiconductor Lasers

Analysis of Threshold Characteristics of Short-Wavelength Semiconductor Lasers

Advances in Semiconductor Lasers Based on Parity-Time Symmetry.

Semiconductor lasers, characterized by their high efficiency, small size, low weight, rich wavelength options, and direct electrical drive, have found widespread application in many fields, including military defense, medical aesthetics, industrial processing, and aerospace. The mode characteristics of lasers directly affect their output performance, including output power, beam quality, and spectral linewidth. Therefore, semiconductor lasers with high output power and beam quality are at the forefront of international research in semiconductor laser science. The novel parity-time (PT) symmetry mode-control method provides the ability to selectively modulate longitudinal modes to improve the spectral characteristics of lasers. Recently, it has gathered much attention for transverse modulation, enabling the output of fundamental transverse modes and improving the beam quality of lasers. This study begins with the basic principles of PT symmetry and provides a detailed introduction to the technical solutions and recent developments in single-mode semiconductor lasers based on PT symmetry. We categorize the different modulation methods, analyze their structures, and highlight their performance characteristics. Finally, this paper summarizes the research progress in PT-symmetric lasers and provides prospects for future development.

Investigating the Microstructural and Mechanical Characteristics of Laser Additive‐Manufactured AlSi10Mg Specimens Through Experimental and Phase‐Field Modeling Approaches

Metal‐based additive manufacturing can make complicated parts that are complex or expensive to cast and process. Rapid cooling rates increase laser powder bed fusion (LPBF's) mechanical properties during manufacturing. The objective of this study is to examine the impact of process parameters in the L‐PBF technique on the characteristics of microstructure and mechanical properties, specifically, on the nanohardness influenced by Si segregation. The microstructures of the produced specimens are examined using field‐emission scanning electron microscopy and the analysis identifies the existence of bimodal equiaxed α‐Al grains, accompanied by Si phases located within their grain boundaries. In addition, the solidified sample exhibits the segregation of secondary precipitates, particularly Mg2Si, which results in enhanced mechanical properties. Both cellular walls and Si precipitates impede the motion and generation of dislocations, thereby influencing the overall behavior of dislocations. The examination of segregation at the top layer is conducted in a comprehensive manner, subsequently using energy‐dispersive X‐ray spectroscopy for analysis. The presence of Mg2Si, Al2MgSi2, and other phases in all samples is confirmed through X‐ray diffraction. The as‐built samples’ residual stress under different process conditions is also investigated. Additionally, the obtained microstructure is compared to a phase‐field model to forecast the evolution of the microstructure.

Passively Q-Switched 1.5- μm Erbium-Doped All-Fibre Laser with Silver Saturable Absorber

This research examines the operation of a passively Q-switched erbium-doped all-fibre laser (EDFL) using a silver (Ag) based saturable absorber (SA) by comparing the output characteristics of the Q-switched laser with those of continuous wave all-fibre lasers. A study was done on how the laser's Q-factor is modified and affects the rate at which pulses are repeated, as well as their output power, width, and energy. The results showed that high-energy Q-switched pulses were successfully generated at the essential 1.5 µm wavelength within the pump power range of 83.6 mW to 171.7 mW, with repetition rates ranging from 33.46 kHz to 77.96 kHz. The EDFL generated a pulse with a width of 4.033 µs and an energy of 2.82 nJ at a pump power of 171.7 mW. The results indicate that Ag may potentially be a good SA for pulse production in the 1.5 µm wavelength area as well as for use in a wide range of applications.

Influence of geometry passive Q-switch based on a nanopowder-polymer on the characteristics of an erbium ring fiber laser

The presented work shows an influence of geometry passive Q-switch based on a nanopowder-polymer on the characteristics of an erbium ring fiber laser. The saturable absorber Bi2Te3 was applied to two types of specially prepared samples of thinned sections of optical fiber, and the resulting structures were built into the ring circuit of an erbium fiber laser. In the first case, the surface of the light guide segment was thinned by chemical etching, and in the second, by mechanical grinding. For the first time, the time-domain optical reflectometry technique was used to control the quality of the resulting sample surface and the resulting losses. For a more complete comparison, a set of different optical splitters was used, providing a change in the feedback coefficient in the resonator from 5 to 95 %. A study in the mode of passive Q-switching using polarized light showed that for both types of modulators there are optimal ratios of the amount of energy output from the resonator to obtain the highest values of the average generation power. The d-shape fiber modulator allows mode-locking to be observed without any additional changes to the laser circuit. The pulse duration in this case was 5 ns with a repetition rate of 4 MHz. A Q-switch based on a chemically thinned fiber segment made it possible to obtain narrower pulses in Q-switching mode (up to 700 ns at 38 kHz), a stable peak position in the transmission spectrum, and an average power of 34 mW.