Parameters Of Laser System Research Articles

Optimal design of core parameters of high-power laser systems based on weight analysis

Optimal design of core parameters of high-power laser systems based on weight analysis

Analytical study on the steady-state thermal blooming effect of high-power ytterbium-doped fiber lasers propagating through the atmosphere.

Thermal blooming effect is one of the significant factors affecting the propagation performance of high-power ytterbium-doped fiber lasers (YDFLs) in the atmosphere. In this paper, two 20 kW YDFL systems with typical wavelengths (1070 nm and 1080 nm) are fabricated for propagation comparison experiments, which are used to investigate the thermal blooming effect induced by high-power YDFL propagation through the atmosphere. Under approximately the same laser system parameters (except wavelength) and atmospheric environment, the 1070 nm laser has better propagation characteristics than the 1080 nm laser. Due to the combined effect between the different central wavelengths of the two fiber lasers and the spectral broadening caused by output power scaling, the thermal blooming caused by the different absorptivity of water vapor molecules to the two fiber lasers is the main factor for the variation of the propagation properties. Through theoretical analysis and numerical calculation of factors affecting the thermal blooming effect, and considering the industrial manufacturing difficulty of YDFLs, a reasonable selection of fiber laser parameters can effectively improve atmospheric propagation performance and reduce manufacturing costs.

Thermally-induced transverse mode instability: Hopf bifurcation in high-power fiber laser

The thermally-induced transverse mode instability (TMI) has become a major challenge for further enhancing the output power of single-mode fiber laser. Even though much work has been done over the past decades, the spontaneous generation process of output spot oscillation has not been well understood yet. Here, we establish a new theoretical model of the thermally-induced TMI in a high-power fiber oscillator and provide a new mechanism explanation from the point of view of nonlinear dynamics. Theoretical analysis shows that the spontaneous oscillation (∼kHz) of the output spot caused by the thermally-induced TMI is a limit-cycle oscillation via Hopf bifurcation, and the oscillation frequency is proportional to square root of the relaxation rate γ1 of thermally-induced refractive index grating (RIG) (νTMI∝γ1) when the thermally-induced TMI is initially triggered. Furthermore, the relationship between the threshold power, together with oscillation frequency and several parameters of fiber laser system was also discussed in detail. This work help us better understand the underlying dynamics of the thermally-induced TMI.

Influence of Gain Saturation Effect on Transverse Mode Instability Considering Four-Wave Mixing

Transverse mode instability (TMI) has been recognized as onse of the primary limiting factors for the average power scaling of high-brightness fiber lasers. In this work, a static model of the TMI effect based on stimulated thermal Rayleigh scattering (STRS) is established while considering the four-wave mixing (FWM) effect. The focus of the model is to theoretically investigate the TMI phenomenon and threshold power dominated by FWM. The gain saturation effect and fiber laser system parameters, such as seed power, pumping direction, and core numerical aperture, which have not been considered in the previous perturbation theory model, are also investigated. This work will enrich the perturbation theory model and extend its application scope in TMI mitigation strategies, providing guidance for understanding and suppressing TMI.

Ti:Sa Crystal Geometry Variation vs. Final Amplifiers of CPA Laser Systems Parameters

In this paper, the different Ti:Sapphire crystal configurations of the final amplifiers, depending on the Chirped Pulse Amplification laser system parameters, such as the repetition rates and pulse energy, are discussed. Restrictions placed on the final Ti:Sa amplifiers with a high repetition rate are discussed. The repetition rate of these systems is limited due to the crystal overheating, which leads to stress fracturing or significant beam distortion. The heating density threshold leading to stress fracturing was calculated and taken as the limit of the upper level of the possible pump average power. On the basis of these calculations, the highest repetition rates and corresponding thermolens focal distances were estimated for conventional crystal geometry of the most suitable thicknesses. It was demonstrated that conventional crystal shapes, such as a thin disc, can be used for systems with repetition rates below a few hundred Hz if several Joules of the output pulse energy are required. The rectangular thin crystal plate geometry was more suitable for Ti:Sa amplifiers with repetition rates above 1 kHz. Finally, the parameters of rectangular thin crystal plate Ti:Sa laser amplifier with an output energy above 3 J per pulse for a laser system with more than 100 TW pulse power and 1 kHz repetition rates are presented.

Key parameters of non-ablative fractional laser pretreatments for enhanced topical uptake.

The uptake of topical formulations can be enhanced through laser pretreatments. Newer technologies, such as non-ablative fractional lasers (NAFLs), can target dermal tissues and spare the stratum corneum (SC), which can mitigate common side effects associated with ablative laser treatment. To discuss the parameters of 2 NAFL pretreatment systems (1440-nm/1927-nm diode system or 1550-nm erbium-doped glass/1927-nm thulium system), which can be paired with topicals to improve their cutaneous uptake. The parameters of the 1440-nm/1927-nm diode system and 1550-nm erbium-doped glass/1927-nm thulium system were reviewed, as well as in vivo experiments using both laser systems. Multiple parameters should be optimized to enhance the uptake of various topical formulations and minimize side effects, including wavelength, spot size, density, pulse duration, thermal properties, and topical formulation. Chosen therapeutic parameters must account for patient-specific factors, such as treatment indication, therapeutic area, and Fitzpatrick skin type. In vivo experiments have demonstrated that both laser systems are effective in enhancing the uptake of various topical therapies relative to untreated controls. Individualization of laser system parameters increases efficiency and minimizes risk.

Experimental Analysis of Laser Micromachining of Microchannels in Common Microfluidic Substrates.

Laser micromachining technique offers a promising alternative method for rapid production of microfluidic devices. However, the effect of process parameters on the channel geometry and quality of channels on common microfluidic substrates has not been fully understood yet. In this research, we studied the effect of laser system parameters on the microchannel characteristics of Polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), and microscope glass substrate—three most widely used materials for microchannels. We also conducted a cell adhesion experiment using normal human dermal fibroblasts on laser-machined microchannels on these substrates. A commercial CO2 laser system consisting of a 45W laser tube, circulating water loop within the laser tube and air cooling of the substrate was used for machining microchannels in PDMS, PMMA and glass. Four laser system parameters—speed, power, focal distance, and number of passes were varied to fabricate straight microchannels. The channel characteristics such as depth, width, and shape were measured using a scanning electron microscope (SEM) and a 3D profilometer. The results show that higher speed produces lower depth while higher laser power produces deeper channels regardless of the substrate materials. Unfocused laser machining produces wider but shallower channels. For the same speed and power, PDMS channels were the widest while PMMA channels were the deepest. Results also showed that the profiles of microchannels can be controlled by increasing the number of passes. With an increased number of passes, both glass and PDMS produced uniform, wider, and more circular channels; in contrast, PMMA channels were sharper at the bottom and skewed. In rapid cell adhesion experiments, PDMS and glass microchannels performed better than PMMA microchannels. This study can serve as a quick reference in material-specific laser-based microchannel fabrications.

Automatic detection of coagulation and carbonization in laser applications using machine learning techniques

Laser-induced thermal treatment (LITT) technique is considered to be the most effective method for minimally invasive surgical procedures. However, the parameters of laser systems used in surgical operations need to be adjusted very precisely. Otherwise, irreversible situations may occur especially in the operation of sensitive organs such as the brain. In order to avoid such undesirable situations, artificial intelligence algorithms are used in the fields of engineering, aerospace and automotive, especially in medicine and biomedical. In this study, it was aimed to automatically detect Coagulation (Co) and Carbonization (Ca) states using a total of 140 data obtained as a result of LITT experimental applications (1070 nm and seven different power density values) on ex vivo liver tissue. In the first part of the study, which consists of two main stages, the data set was presented to seven different expert systems based on artificial intelligence (C4.5, KNN, ANN, RF, MLR, SMO-SVM and LWLDS), and automatically Co and Ca formations were determined. Among the proposed expert systems, the C4.5 algorithm showed the best performance with 100% accuracy and 0% error rate. In the second stage of the study, the same data set was given to Attribute Information Gain (AIG) ranking system, which was used to determine the minimum number of feature that would provide the maximum performance, and the gain values of the attributes were calculated. As a result of this application, the most effective feature was found to be Normalized Depth of Thermal Damage (NDeTD) with 100% accuracy rate. Thus, the purpose of using the AIG system has been successfully achieved. As a result, thanks to the expert systems presented within the scope of the study, Co and Ca formations were determined automatically with 100% success rate according to the required parameters without laser application on ex vivo liver tissue. The fact that the aim of the study was realized with the highest success rate is thought to be the first in terms of contributing to the literature. Through this study, as a result of the laser treatment to be applied on cancerous tissue, it can be predicted whether the tissue will suffer irreversible damage and necessary precautions can be taken beforehand.

Modernization of the Thl-100 Laser System to Produce Powerful Terahertz Radiation

This paper presents the results of research on parameters of the THL-100 hybrid laser system of the visible spectrum with a view to modernizing it, in order to achieve the boundary parameters required for the pumping of non-linear crystals and production of the unprecedented THz radiation powers. The laser system consists of the Start-480M Ti:Sa starting complex and photodissociation XeF(C-A) amplifier with a 24 cm aperture. After modernization, the starting complex provides the spectrally limited radiation pulse of 60 fs at the first harmonic (950 nm) at energy of 25 mJ and 50 fs at the second harmonic (475 nm) at energy of 10 mJ. In the case of the positively chirped pulse with duration of 50 ps, the energy at the second harmonic is 3 mJ. When amplifying the negatively chirped radiation pulse in the XeF(C-A) amplifier at the wavelength of 475 nm with duration of 1.8 ps, the power of 40 TW is reached, and the maximum energy is 2 J. When amplifying the positively chirped pulse with duration of 50 ps, the highest energy of 3 J is achieved.

Experimental characterization to fabricate CO2 laser ablated PMMA microchannel with homogeneous surface

Polymethyl methacrylate (PMMA) is widely used for fabrication of microfluidic devices. PMMA, in the recent times, has emerged as an alternative to glass base microfluidic devices owing its convenience in handling, low cost, less weight and excellent optical properties. Due to the high transparency of PMMA and absorption properties in near infrared and UV regions, laser machining can be employed. This work reports characterization of a CO2 laser system, with a wavelength of 10.6 µm, for microfluidic channel fabrication on PMMA. Variety of channels were fabricated by varying CO2 laser system parameters – power, scan speed, pulse frequency and resolution. Power was varied up to its limiting value of 30 W. Surface profile for each of the fabricated channel was recorded and obtained data was analysed. Optimization was done to identify and establish parameters to obtain channels corresponding to specified width and depth. The profile of the channels was observed to have Guassian profile which can be attributed to the Guassian nature of incident laser beam. Effects of post processing using acetone and dichloromethane (DCM) vapour exposure were also studied.

Optimisation of laser assisted forming conditions for improved formability of aerospace materials

ISF technology was gradually considered as a manufacturing technology for fabricating sheet metal parts for both commercial and military aircraft. However, many challenges remain with respect to improving the consistency of the process, such as part thinning and springback. This is especially critical for two phase titanium alloy Ti-6AL-4V which has limited formability at room temperature. Therefore, understanding the correlation of laser system parameters and material properties is a key aspect for successful ISF of non-fractured Ti-6AL-4V. The laser heating is modelled to find the relationships between laser power, beam radius, scan speed, and the resultant temperature. The analysis shows that the temperature from laser heating increases with an increase in power, decreases significantly with an increase in beam radius, and decreases slightly with an increase in scan speed.

Hundred-watts-level monolithic narrow linewidth linearly-polarized fiber laser at 1018 nm

We theoretically and experimentally demonstrated an all-fiber, hundred-watts-level, linearly-polarized, narrow spectral linewidth laser amplifier at a central wavelength of 1018 nm based on master oscillator-power amplifier configuration, which is composed of a laser oscillator and one stage of the fiber amplifier. The laser system can generate 104-W output power with 3- and 20-dB spectral linewidth of ∼0.073 and ∼0.25 nm, respectively, and a higher polarization extinction ratio of ∼17.89 dB at 1018.3 nm was obtained. Theoretical analysis based on the rate equations was used to optimize the parameters of 1018-nm ytterbium-doped fiber laser system for the maximum suppression of amplified spontaneous emission (ASE). The ASE was well depressed based on the optimization for the parameters of the laser system including the seed power, seed spectrum, gain fiber length in the amplifier, etc. And ∼ 27-dB signal-to-noise ratio was achieved at the maximum output power. The slope efficiency for the amplifier stage can reach 79%, and near-diffraction-limited beam quality ( M x 2 ∼ 1.617 and M y 2 ∼ 1.635 ) was obtained.

Femtosecond micro-machining of hydrogels: parametric study and photochemical model including material saturation

We report on the effects of various laser system parameters on the magnitude of phase change induced inside hydrogel-based contact lens materials in the two-photon absorption limit via a laser induced refractive index (LIRIC) technique. In comparison with near infrared writing at 1035 nm where four-photon absorption process dominates, blue writing at 405 nm allows for the achievement of a decent amount of phase change (one wave) with a low power and a fast scan speed due to a more efficient two photon absorption process. Efficacy of the LIRIC process could be further improved by taking advantage of intermediate repetition rate laser pulses instead of high repetition rate (> 60 MHz) pulses or low repetition rate (< 500 KHz) pulses. A generally applicable photochemical model based on multiphoton absorption mechanism and pulse overlapping effect in two dimensions is proposed to predict the scaling behavior of the induced phase change. A modified photochemical model incorporating a saturation factor is developed to account for the behavior at large phase shifts. The modified photochemical model also helps explain the inapparent dependence of the phase change on numerical aperture (NA) at low irradiation doses and the observed sub-linear inverse dependence on scan speed.

Laser Milling Ceramics Dioxide Zirconium and Disilicate of Lithium

The paper considers the possibility of using laser milling technology for precision processing of ceramic samples from pre-sintered and sintered ceramics zirconia and lithium disilicate. To find the best radiation source were compared different lasers. To find highest removal rate with acceptable accuracy was studied influence laser and scanning system parameters on ceramics. Accuracy problem of laser milling was considered. Examples of surfaces of prostheses were made.

The effect of VCSEL intrinsic dynamics on polarization bistability

Abstract This work is devoted to a theoretical study that addresses the influence of the parameters of original laser system on the dynamics of formation of polarized radiation in VCSEL with his institution of symmetrical triangular pulses. The model is based on a sequential process of enhancing radiation in the resonator, taking into account anisotropy of gain and loss. It is shown that all features of polarization hysteresis can be associated with ultimate speed formation characteristics of reinforced radiation with the rapid build-up and decline in current, rather than with the process of competition between two independent polarization modes.

Measurement of gain coefficient and resonator internal loss in Yb:YAG thin-disk-laser

In this paper, the gain coefficient and the resonator internal loss in quasi-three-level active medium lasers were measured by two different methods: the spectroscopic gain analysis (SGA) and generalized Findlay-Clay method (GFCM). Standard Findlay-Clay method was modified and formalized for quasi-three-level active medium lasers. With these methods, the gain coefficient and the resonator internal loss of a Yb:YAG thin-disk-laser (TDL) were obtained and the results were compared, analyzed and discussed. To verify the accuracy of these methods, a numerical code based on the laser rate equations was developed to simulate the cw operation of the TDL and predict the laser system parameters. The obtained values of the resonator internal loss from these methods were used in the simulation to calculate some laser parameters such as laser output power and gain of the active medium. The analyses of measured values showed that the results of SGA have better accuracy. The relative measurement errors of 1.2% and 18.4% for gain coefficient were obtained for SGA and GFCM, respectively.

Effect of Process Parameters and Material Properties on Laser Micromachining of Microchannels.

Laser micromachining has emerged as a promising technique for mass production of microfluidic devices. However, control and optimization of process parameters, and design of substrate materials are still ongoing challenges for the widespread application of laser micromachining. This article reports a systematic study on the effect of laser system parameters and thermo-physical properties of substrate materials on laser micromachining. Three dimensional transient heat conduction equation with a Gaussian laser heat source was solved using finite element based Multiphysics software COMSOL 5.2a. Large heat convection coefficients were used to consider the rapid phase transition of the material during the laser treatment. The depth of the laser cut was measured by removing material at a pre-set temperature. The grid independent analysis was performed for ensuring the accuracy of the model. The results show that laser power and scanning speed have a strong effect on the channel depth, while the level of focus of the laser beam contributes in determining both the depth and width of the channel. Higher thermal conductivity results deeper in cuts, in contrast the higher specific heat produces shallower channels for a given condition. These findings can help in designing and optimizing process parameters for laser micromachining of microfluidic devices.

Transfers from Earth to LEO and LEO to interplanetary space using lasers

New data on some materials at 80ps pulse duration and 1057 nm wavelength give us the option of proportionally combining them to obtain arbitrary values between 35 (aluminum) and 800 N/MW (POM, polyoxymethylene) for momentum coupling coefficient Cm. Laser ablation physics lets us transfer to LEO from Earth, or to interplanetary space using repetitively pulsed lasers and Cm values appropriate for each mission. We discuss practical results for lifting small payloads from Earth to LEO, and space missions such as a cis-Mars orbit with associated laser system parameters.

THL-100 Multi-Terawatt Laser System of Visible Range

Results of investigation of the parameters of the THL-100 hybrid laser system of visible range developed at the IHCE SB RAS in collaboration with the LPI RAS are presented. The laser system consists of the Ti:Sa Start-480M starting complex and the photodissociation XeF(C-A) amplifier with aperture of 24 cm. The starting complex provides 50-fs spectrally limited radiation pulses with energy of the second harmonic (475 nm) up to 20 mJ and 50-ps positively chirped radiation pulses with energy up to 5 mJ. The active medium of the XeF(CA) amplifier is created in the XeF2/N2 mixture upon exposure to VUV radiation of xenon excited by a highpower electron beam. It is demonstrated that record power of 14 TW is attained by amplification of negatively chirped radiation pulse with duration of 1.6 ps in the XeF(C-A) amplifier, and maximum energy of ~3.2 J is realized by amplification of positively chirped radiation pulse.

Fundamental understanding of the interaction of continuous wave laser with aluminium

In welding, the depth of penetration, weld profile and the corresponding thermal cycle are the three basic outcomes that a user wishes to control flexibly. In laser welding applications, controlled application of power and energy density is the key to achieve predictable control of these characteristics. Creation of an analytical model is an important step towards understanding the underpinning science of laser metal interaction in controlling the depth, bead geometry and thereby temperature profile of a weld. The “power factor model”, which correlates the power applied per unit length to the laser metal interaction time, has been originally developed and validated for mild steel, guides a user on the selection laser system parameters, to achieve specific weld profile. This study is performed to extend the power factor–interaction time model to aluminium alloys by understanding the underpinning laser aluminium interaction parameters in terms of power density, interaction time, specific point energy and their correlation with the weld bead profiles. Although the power factor and interaction time showed a rectangular hyperbolic relationship, as observed in low carbon steel, for a specific weld depth and profile, the absolute magnitude and the characteristic profile of the curve is different due to the intrinsic differences in physical and thermal properties of aluminium as compared to steel. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of power and travel speed by keeping the energy input per unit length constant.