Laser Active Medium Research Articles

Wettability and Surface Roughness Analysis of Laser Surface Texturing of AISI 430 Stainless Steel.

Due to its wide applicability in industry, devising microstructures on the surface of materials can be easily implemented and automated in technological processes. Laser Surface Texturing (LST) is applied to modify the chemical composition, morphology, and roughness of surfaces (wettability), cleaning (remove contaminants), reducing internal stresses of metals (hardening, tempering), surface energy (polymers, metals), increasing the adhesion (hybrid joining, bioengineering) and decreasing the growth of pathogenic bacteria (bioengineering). This paper is a continuation and extension of our previous studies in laser-assisted texturing of surfaces. Three different patterns (crater array-type C, two ellipses at 90° overlapping with its mirror-type B and 3 concentric octagons-type A) were applied with a nanosecond pulsed laser (active medium Nd: Fiber Diode-pumped) on the surface of a ferritic stainless steel (AISI 430). Micro texturing the surface of a material can modify its wettability behavior. A hydrophobic surface (contact angle greater than 90°) was obtained with different variations depending on the parameters. The analysis performed in this research (surface roughness, wettability) is critical for assessing the surface functionality, characteristics and properties of the stainless steel surface after the LST process. The values of the surface roughness and the contact angle are directly proportional to the number of repetitions and inversely proportional to the speed. Recommendations for the use of different texturing pattern designs are also made.

White Light Emission of Dy3+ Doped Oxy-Fluoride Phosphate Glass System for Active Laser Medium

Dy3+ doped oxy-fluoride phosphate glass was prepared by melt quenching technique. The glass samples were subjected to FTIR, absorption, and photoluminescence. The absorption spectrum shows several absorption peaks but strong absorption peak observed at wavelength 1280 nm NIR region. Strong yellow emission at 572 nm corresponding to 4F9/2→6H13/2 and blue emission at 482 nm corresponding to 4F9/2→6H15/2 were observed. The analysis of Judd–Ofelt study was applied to establish the intensity parameters and radiative properties of Dy3+ doped oxy-fluoride phosphate glass. The J–O result suggests that the oxy-fluoride phosphate glass has the potential use as an active laser medium.

Model of Epidemic Kinetics with a Source on the Example of Moscow.

A new theoretical model of epidemic kinetics is considered, which uses elements of the physical model of the kinetics of the atomic level populations of an active laser medium as follows: a description of states and their populations, transition rates between states, an integral operator, and a source of influence. It is shown that to describe a long-term epidemic, it is necessary to use the concept of the source of infection. With a model constant source of infection, the epidemic, in terms of the number of actively infected people, goes to a stationary regime, which does not depend on the population size and the characteristics of quarantine measures. Statistics for Moscow daily increase in infected is used to determine the real source of infection. An interpretation of the waves generated by the source is given. It is shown that more accurate statistics of excess mortality can only be used to clarify the frequency rate of mortality of the epidemic, but not to determine the source of infection.

Recent Progress of Quantum Dot Lasers Monolithically Integrated on Si Platform

With continuously growing global data traffic, silicon (Si)-based photonic integrated circuits have emerged as a promising solution for high-performance Intra-/Inter-chip optical communication. However, a lack of a Si-based light source remains to be solved due to the inefficient light-emitting property of Si. To tackle the absence of a native light source, integrating III-V lasers, which provide superior optical and electrical properties, has been extensively investigated. Remarkably, the use of quantum dots as an active medium in III-V lasers has attracted considerable interest because of various advantages, such as tolerance to crystalline defects, temperature insensitivity, low threshold current density and reduced reflection sensitivity. This paper reviews the recent progress of III-V quantum dot lasers monolithically integrated on the Si platform in terms of the different cavity types and sizes and discusses the future scope and application.

Simulation of Kinetic Processes, Optical and Neutron Properties of the Nuclear-Excited Dusty Plasma of Noble Gases

A model of kinetic processes in the argon-xenon gas plasma with the admixture of uranium nanoclusters is developed. This dusty plasma seems to be perspective as an active laser medium in the technologies of direct conversion of the nuclear energy into coherent light. The process of formation of quasistationary states in plasma and the influence of uranium nanoclusters are considered in the developed mathematical model of the kinetic processes in the argon-xenon gas excited by nuclear fission fragments. The suggested system of equations allows one to describe the kinetic processes in the plasma with presence of the uranium dust in a self-consistent way. The model include the evolutionary equations for the distribution function of electron velocities and for concentrations of a different components of plasma, including charged uranium nanoclusters. The model takes 44 components of plasma and 507 plasma-chemical processes into account. The method of solution of such equations is suggested, and the program complex realizing this method is developed. The influence of the dust concentration on the optical and neutronic properties of the plasma media is studied in calculations. The calculation of the neutron multiplication factor for the laser active infinite medium containing uranium dust particles is performed with the use of MCNP-5 code. The neutron cross-sections needed for calculations were taken from the ENDF/b-VI library. The attenuation of electromagnetic waves by uranium dust particles was calculated in the frame of the Mie theory for various spherical particle sizes and different wavelengths. Real and imaginary parts of the refraction coefficient for uranium needed for this calculation were taken from the experimental and theoretical works.

Enhanced Amplification of Attosecond Pulses in a Hydrogen-like Plasma-Based X-ray Laser Modulated by an Infrared Field at the Second Harmonic of Fundamental Frequency

In a recent work (Antonov et al., Physical Review Letters 123, 243903 (2019)), it was shown that it is possible to amplify a train of attosecond pulses, which are produced from the radiation of high harmonics of the infrared field of the fundamental frequency, in the active medium of a plasma-based X-ray laser modulated by a replica of the infrared field of the same frequency. In this paper, we show that much higher amplification can be achieved using the second harmonic of the fundamental frequency for modulating of a hydrogen-like active medium. The physical reason for such enhanced amplification is the possibility to use all (even and odd) sidebands induced in the gain spectrum in the case of the modulating field of the doubled fundamental frequency, while only one set of sidebands (either even or odd) could participate in amplification in the case of the modulating field of the fundamental frequency due to the fact that the spectral components of the high-harmonic field are separated by twice the fundamental frequency. Using the plasma of hydrogen-like C5+ ions with an inverted transition wavelength of 3.38 nm in the water window as an example, it is shown that the use of a modulating field at a doubled fundamental frequency makes it possible to increase the intensity of amplified attosecond pulses by an order of magnitude in comparison with the previously studied case of a fundamental frequency modulating field.

All-laser-microprocessed waveguide Cr:ZnS laser

We report the proof-of-concept of an operational laser active medium with a depressed cladding waveguide manufactured in the volume of a Cr2+:ZnS single-crystalline sample and antireflection microstructures fabricated on its facets exclusively by femtosecond laser processing techniques. This allowed us to achieve transmittance in a broad range from 2 to 8 µm, approaching a maximum of over 90% near 2.5 µm, and lasing at 2275 nm at the average output power of 20 mW for the absorbed pump power of 500 mW with the slope efficiency of 5.5 %. This demonstration opens up a route towards the industrial fabrication of compact integrable laser sources and sensors based on II-VI materials.

Диэлектрический барьерный разряд в смеси He-Ne низкого давления. Спектроскопия послесвечения

The paper considers the possibility of using a low-pressure dielectric barrier discharge (DBD) as a plasma source for the active medium of a He-Ne laser. The results of a spectroscopic study of the decay stage of a DBD plasma of a cylindrical configuration with a pronounced inverse population of the upper level of the 2p55s configuration, which makes the line of 632.8 nm one of the brightest in the visible region of the spectrum, are presented. It is shown that in the early stage of the DBD afterglow, the distribution of the populations over the 2p55s and 2p54d levels of the neon atom is due to the excitation transfer mechanism Не(21S0) +Ne -- > He(11S0) + Ne*. In the late afterglow with the departure of helium atoms Не(21S0), emission in the visible region of the spectrum is formed mainly by transitions from levels of the 2p53p configuration, the population of which is associated with Не(23S1) atoms. At this stage, the population of the 2p55s and 2p54d states by electron-ion recombination processes is ineffective and does not lead to the formation of population inversion. As an optimal solution in terms of the 632.8 nm line brightness in the afterglow, it is proposed to use a discharge with electrodes along the outer surface of a cylindrical discharge tube, initiated at frequencies that exclude the recombination stage of the afterglow.

Steady-state cooperative effects in a continuously generating superradiant Raman laser

A generalized model of the continuously generating superradiant Raman laser is considered. The model includes competing individual and cooperative atomic processes arising from the interaction of atoms with external light fields. We show that proper selection of the model parameters leads to cooperative effects in the atomic active laser medium. We calculate the steady state values of the atomic polarization and two-atom correlations. Using the quantum regression theorem, we determine the spectral characteristics of the collectively emitted light. We use cumulant expansion to estimate the higher-order correlations between atoms. Keywords: superradiant laser, correlated states of atoms, cooperative effects, cumulant expansion.

Кооперативные эффекты при стационарной генерации сверхизлучательного рамановского лазера

A generalized model of the continuously generating superradiant Raman laser is considered. The model includes competing individual and cooperative atomic processes arising from the interaction of atoms with external light fields. We show that proper selection of the model parameters leads to cooperative effects in the atomic active laser medium. We calculate the steady state values ​​of the atomic polarization and two-atoms correlations. Using the quantum regression theorem, we determine the spectral characteristics of the collectively emitted light. We use cumulant expansion to estimate the higher-order correlations between atoms.

Luminescence of Ti-Sapphire coatings prepared by plasma electrolytic oxidation and their application in temperature sensing

15 µm thick Ti-Sapphire coatings were synthesised at room temperature by the plasma electrolytic oxidation (PEO) method for 20 min from the pure aluminium substrate and with the addition of the TiO2 particles in various concentrations in the supporting electrolyte. The coatings are featured by microscopic pores typical for PEO surfaces. The dominant is the alpha phase of alumina with the small presence of the gamma phase. The estimated average crystalline size is 41 nm. Ti is uniformly distributed in these polycrystalline ceramic coatings and does not affect morphology or phase content. Photoluminescence of PEO-created coatings shows typical absorption, excitation, and emission features of Ti-Sapphire with two broad-overlapping excitation bands in the green and blue spectral region due to the Jahn-Teller splitting of the 2Eg level and the Stokes shifted emission centred at 720 nm. 2Eg energy state splitting is equal to 2195 cm−1 and 10 Dq ≈ 19,300 cm−1. The highest emission intensity was observed in the coating prepared with the 0.1 g/L TiO2 powder concentration, i.e. 0.32 at% of incorporated Ti3+. Emission spectra recorded at temperatures ranging from 100 K to 300 K revealed the Mott-Seitz temperature dependence of emission intensity with the 1180 cm−1 activation energy. The fit to the McCumber-Sturge relation gave, for the first time, the value of Debye temperature of 594 K of Al2O3:Ti. Non-contact, luminescence temperature sensing from the temperature-induced changes in the emission bandwidth gave a high sensitivity of 3.2 cm−1 K−1 and 0.19 K temperature resolution. The PEO created Ti-sapphire coatings are a promising multifunctional barrier level – optical temperature sensor material for applications in harsh environments or on large aluminium surfaces. It shows potential to be used as a planar waveguide Ti-Sapphire laser active medium.

Optical absorption and photoluminescence investigations Dy3+ doped oxyfluoride phosphate glass system for active laser medium and solid-state lighting materials

This article reports on the optical, photoluminescence, and radiative properties of Dy3+ doped oxyfluoride glass. The composition of glass is: 20Li2O–10AlF3–69P2O5–1Dy2O3 (LAPD). The glass has been prepared using the melt-quenching technique at 1100°C with a total mass of 15 grams in an alumina crucible. Judd–Ofelt analysis was used to determine the intensity parameters and radiative properties of Dy3+ ion in glass. The CIE 1931 chromaticity diagram coordinate is calculated to define the color coordinate of emission in a glass sample. Based on research, it is expected to produce glass material that is applied as an active laser medium and solid-state lighting materials.

Effect of Nd2O3 doping on spectroscopic characteristics of zinc barium boro-tellurite glass for laser medium application

The ZnO-BaO-B2O3-TeO2 (ZBBoT) glass samples were prepared, and their properties affected by varied concentrations of Nd2O3 doped in were investigated. The traditional melt quenching process was conducted to synthesize the samples which were explored to identify their density, molar volume, refractive index, absorption, photoluminescence (PL) and PL decay spectral profiles. The optical absorption has been used to derive the Judd-Ofelt (J-O) parameters (Ωλ, λ = 2, 4 and 6). The trend of J-O parameter is Ω2 > Ω6 > Ω4. Moreover, the J-O parameters are used to predict the radiative properties which are significant for the assessment of the suitability of a glass for laser emission. The emission of glasses exhibited 2 peaks at 1060, and 1345 nm. Based on research, it is expected to produce glass material that is applied as an active laser medium and solid-state lighting materials.

Formation of Intense Attosecond Pulses in the Sequence of a Resonant Absorber and Active Medium of a Plasma-Based X-Ray Laser Modulated by an Optical Field

Formation of Intense Attosecond Pulses in the Sequence of a Resonant Absorber and Active Medium of a Plasma-Based X-Ray Laser Modulated by an Optical Field

Plasmonic enhancement of Ag NPs in a different active media

Improvement of the laser output of the laser active media (dye lasers) through the study of the emission spectrum of plasmonic resulting from using a laser beam with a different energies, in addition to study the spectrum that resulting from the interaction of the exciton with the plasmon and its effect on the laser output. It was used (RhB dye) with different concentrations, and then studied the absorption spectrum of these samples by using UV-VIS spectrometer, and then the emission spectrum by using fluorescence spectroscopy. It was used a better concentration of dye (1*10-5 M) to mix with different concentrations of Ag NPs that have been prepared by the ablation method. To get a different concentrations of Ag NPs it was changed the pulse number (500, 600, 700, 800, 900) p and keep the energy constant at (600 mJ), it will play a major role in changing the emission and the absorption spectrum properties. It was found a strong dependence of the emission characteristics (the emission intensity, threshold for lasing) on the concentration of Ag NPs.

Photoluminescence studies on dysprosium doped glass ceramics containing α-Na3AlF6 crystalline phase for white light emission

The present work focuses on Dy3+ doped 20SiO2-(20-x) B2O3–10Al2O3–10ZnO–30NaF–10ZnF2 glass ceramics (GCs), a white light emitting material prepared by conventional melt-quenching technique and thermal treatment. The glass ceramics exhibited good morphological evolution of α-Na3AlF6 crystals at elevated temperatures. Bandgap values are obtained lower for glass ceramics compared to precursor glass which almost tends to come closer to the bandgap value of semiconductor. A good photoluminescence (PL) performance is monitored in glass ceramics with increased emission intensity having two dominant peaks at 482 and 575 nm. Stimulated emission cross section in glass ceramics obtained higher for the level 6H13/2 characterize their significance in laser active media. Quantum efficiency is achieved greater than 80% for glass ceramics ensures their appropriateness for LEDs application. In particular, the yellow to blue intensity, colour coordinates and colour correlated temperature have been evaluated for glass ceramics. With the formation of α-Na3AlF6 crystalline phase surrounded by Dy3+ ions, the PL properties in glass ceramics is enhanced notably. The obtained glass ceramics should be acknowledged as a promising material in white-LEDs and optoelectronic devices applications.

Influence of Detuning of the Seeding VUV Radiation from the Resonance on Formation of Subfemtosecond Pulses in the Active Medium of the Plasma-Based X-Ray Laser Dressed by an Intense IR Field

Influence of Detuning of the Seeding VUV Radiation from the Resonance on Formation of Subfemtosecond Pulses in the Active Medium of the Plasma-Based X-Ray Laser Dressed by an Intense IR Field

Laser destruction of polymeric materials

This work analyzes the properties of polymers, which make them indispensable in the manufacture of elements used in optics, since the main requirement for polymers is stability when exposed to laser radiation. Currently, polymers are used as active laser media. The most commonly used is polymethyl methacrylate, which is highly transparent and the most resistant in relation to laser exposure.

Achieving Optical Gain of the CsPbBr3Perovskite Quantum Dots and Influence of the Variable Stripe Length Method

High-quality inorganic cesium lead halide perovskite quantum dot (CsPbBr3 PQD) thin films were successfully deposited directly from a powdered source and used as an active laser medium following the examination of their distinctive surface and structural properties. To determine the suitability of the CsPbBr3 PQDs as an active laser medium, amplified spontaneous emission (ASE) and optical gain properties were investigated under picosecond pulse excitation using the variable stripe length (VSL) method. The thin film of CsPbBr3 PQDs has exhibited a sufficient value of the optical absorption coefficient of ∼0.86 × 105 cm–1 near the band edge and a direct band gap energy Eg ∼2.38 eV. The samples showed enhanced emission, and ASE was successfully recorded at a low threshold. The light emitted from the edge was observed near 2.40 and 2.33 eV for the stimulated emission (SE) and ASE regimes, respectively. The nonradiative decay contributes excitons dominant over biexcitons in the sample edge emission above the ASE threshold, making it practical for CsPbBr3 PQDs to be used as optical gain media without undergoing repeated SE processes above the threshold over long periods. A high value of the optical gain coefficient was recorded at 346 cm–1.

Formation of Intensive Attosecond Pulses in the Sequence of a Resonant Absorber and Active Medium of a Plasma-Based X-Ray Laser Modulated by an Optical Field

Formation of Intensive Attosecond Pulses in the Sequence of a Resonant Absorber and Active Medium of a Plasma-Based X-Ray Laser Modulated by an Optical Field