Laser Active Medium Research Articles

Comparative study of various types of laser active media for solar pumping in multi-rod configurations

The Nd:YAG, Ce:Nd:YAG, and Cr:Nd:YAG active media in multi rod configuration are investigated for solar-pumped lasers using simulation methods. A statistical model employing Monte Carlo photon tracing simulates a laser system with multiple rods for combined end-side solar radiation pumping. The model enables one to evaluate efficiency, pump distribution, and output parameters of solar lasers. Simulation analyses is conducted on a three-rod setup using the aforementioned active media. Comparative results demonstrate that Cr:Nd:YAG achieves the highest efficiency, reaching an overall conversion efficiency of 5% at 500 W pump power, which is twice that of Nd:YAG lasers under similar conditions.

Semi-empirical model of a copper bromide vapor brightness amplifier

We propose the semi-empirical mathematical model of the brightness amplifier based on the self-terminating transitions in laser active media. The model is applied to the copper bromide vapor brightness amplifier. The feature of the model is that it allows one to distinguish the amplified spontaneous emission and amplified input optical signal. Due to that we have managed to study the “real” gain and theoretical maximum of contrast for the brightness amplifier depending on temporal and energy characteristics of the input optical signal.

Synchronization under saturable nonlinearity.

In this theoretical work, we introduce a nonlinear gain saturation law representative of the experimentally observed properties manifested by phenomena ranging from aeroacoustic shear layers in self-sustained cavity oscillations to flame heat release rate in thermoacoustic instabilities. Furthermore, this type of saturable gain may be relevant for a wider class of physical systems, such as active laser media in photonics. The nonlinearity discussed herein governs the fullscale behavior of a self-oscillator exhibiting linear loss under large amplitude perturbations, in contrast to the cubic damping and linear gain of the Van der Pol model. A distinctive characteristic of the proposed equation is the simple, well behaved gain term in the slow timescale dynamics.

Spectral analysis and dynamic properties of polyurethanes dyed with rhodamine 6G and rhodamine B as matrices of a solid-state laser element

A comparison was carried out of the nature of intermolecular interactions, elastic properties and gas permeability of the crosslinked polyurethanes doped with xanthene dyes and original polyurethane using IR spectroscopy, dynamic mechanical analysis (DMA) and electron paramagnetic resonance (EPR). The introduced dye can be considered as useful microimpurity which, however, can affect the efficiency of the laser. In IR spectra of polyurethanes the complex band of stretching vibrations of C=O groups is sensitive to the nature of intermolecular interaction of urethane groups. From the analysis of that band it is shown that in the presence of dyes, self-association of urethane groups within the hard segment predominates and the interaction of urethane groups with the oligoether component decreases, which can contribute to increasing the mobility of the flexible component. A decrease in the dynamic storage modulus (E’) and a decrease in the glass transition temperature (Tc) of polyurethanes in the presence of dyes is shown by the DMA method. The results of both DMA and IR spectroscopy indicate a greater increase in the mobility of the elastic component with the introduction of the rhodamine B dye, covalently bound to the polyurethane chain. According to nitroxyl paramagnetic probe data the introduction of both rhodamine B and rhodamine 6G dyes into polyurethanes increases their permeability to vapors of low-molecular weight compounds, but rhodamine 6G has a more prominent effect on this characteristic. This is consistent with DMA data indicating a greater increase in the Mc value in the presence of rhodamine 6G in polyurethane. The obtained results make it possible to determine the optimal composition of the active laser medium and are important in assessing the radiation resistance of the polymer matrix. Its increase is facilitated by a decrease in the storage modulus and an increase in the gas permeability of the polymer, leading to a decrease in pressure in the area of local heating.

Excimer Fluorescence of Acriflavine Dye in Glycerol and Ethylene Glycol.

This research investigates the excimerisation of acriflavine dye in ethylene glycol and glycerol solvents. Acriflavine, a member of the acridine dye family, exhibits unique fluorescence properties with applications in various fields, including cellular nucleus observation, nucleic acid analysis, and dye laser active media etc. The study explores the impact of solvent and concentration on acriflavine's emission properties, with a focus on excimer formation, which can influence its suitability as a dye laser active medium. UV-Visible absorption spectroscopy reveals concentration-dependent absorption profiles, with distinctive monomer bands. Steady-state fluorescence studies demonstrate the emergence of red-shifted excimer fluorescence bands as concentrations increase in both solvents. Temperature-dependent fluorescence studies reveal the dynamics of excimer formation, suggesting dynamic diffusion as the excimerisation mechanism. Time-resolved fluorescence spectroscopy confirms the singlet character of both monomer and excimer states, providing insights into the excimerisation process. Critical concentration values are determined, representing the equilibrium between monomeric and excimeric forms. The study also explores pH-induced spectral shifts, highlighting the influence of acidity on fluorescence properties. Overall, this research deepens our understanding of acriflavine's excimerisation in ethylene glycol and glycerol, offering insights that can enhance its diverse applications, especially in laser technologies.

Organosilicon-Based Ligand Design for High-Performance Perovskite Nanocrystal Films for Color Conversion and X-ray Imaging.

Perovskite nanocrystals (PNCs) bear a huge potential for widespread applications, such as color conversion, X-ray scintillators, and active laser media. However, the poor intrinsic stability and high susceptibility to environmental stimuli including moisture and oxygen have become bottlenecks of PNC materials for commercialization. Appropriate barrier material design can efficiently improve the stability of the PNCs. Particularly, the strategy for packaging PNCs in organosilicon matrixes can integrate the advantages of inorganic-oxide-based and polymer-based encapsulation routes. However, the inert long-carbon-chain ligands (e.g., oleic acid, oleylamine) used in the current ligand systems for silicon-based encapsulation are detrimental to the cross-linking of the organosilicon matrix, resulting in performance deficiencies in the nanocrystal films, such as low transparency and large surface roughness. Herein, we propose a dual-organosilicon ligand system consisting of (3-aminopropyl)triethoxysilane (APTES) and (3-aminopropyl)triethoxysilane with pentanedioic anhydride (APTES-PA), to replace the inert long-carbon-chain ligands for improving the performance of organosilicon-coated PNC films. As a result, strongly fluorescent PNC films prepared by a facile solution-casting method demonstrate high transparency and reduced surface roughness while maintaining high stability in various harsh environments. The optimized PNC films were eventually applied in an X-ray imaging system as scintillators, showing a high spatial resolution above 20 lp/mm. By designing this promising dual organosilicon ligand system for PNC films, our work highlights the crucial influence of the molecular structure of the capping ligands on the optical performance of the PNC film.

Brief Review of Recent Developments in Fiber Lasers

This review covers the recent achievements in high-power rare earth (RE)-doped fiber lasers, Raman fiber lasers, and Brillouin fiber lasers. RE-doped fiber lasers have many applications such as laser cutting, laser welding, laser cleaning, and laser precision processing. They operate in several wavelength ranges including 1050–1120 nm (ytterbium-doped fiber lasers), 1530–1590 nm (erbium- and erbium–ytterbium-doped fiber lasers), and 1900–2100 nm (thulium- and holmium-doped fiber lasers). White spaces in the wavelength spectrum, where no RE-doped fiber lasers are available, can be covered by Raman lasers. The heat power generated inside the laser active medium due to the quantum defect degrades the performance of the laser causing, for example, transverse-mode instability and thermal lensing. It can even cause catastrophic fiber damage. Different approaches permitting the mitigation of the heat generation process are considered in this review. Brillouin fiber lasers, especially multiwavelength Brillouin fiber lasers, have several important applications including optical communication, microwave generation, and temperature sensing. Recent progress in Brillouin fiber lasers is considered in this review.

Studies of luminescence traits and Judd-Ofelt analysis of Sm3+ activated oxyfluoride glasses

Novel Sm3+ activated oxyfluoride glass was synthesized via the melt-quenching approach with subsequent heat treatment. The X-ray diffraction measurement discloses the amorphous nature of prepared glasses. And, FTIR illustrates the molar surplus of Bi2O3 raises the network connectivity by creating bridging oxygen sites in the structure. The Judd-Ofelt (J-O) intensity parameters exhibit Ω4>Ω2>Ω6 trend, witnessing the rigidity of the glass structure and ionic bonding between Sm3+ ions and surrounding ligands. The 4G5/2 → 6H7/2 transition of Sm3+ is the most applicable for reddish-orange lasers due to their higher values of radiative transition probability, branching ratio, and stimulated emission cross-section. The optimum emission intensity is obtained with 30 mol% Bi2O3 and the corresponding decay time is 1.40 ms. Additionally, the F30 glass sample was lit in a reddish-orange region having a CCT value of 1689 K. The thermal luminescence quenching of the prepared glass was studied and the thermal stability parameters activation energy was estimated. Further, the contactless optical thermometry capability of the glass sample was explored within the range of 303 K–603 K using the luminescence intensity ratio (LIR) technique. Thus, the above studies on the glass sample suggest that it can be used as an active medium in lasers, contactless optical temperature sensing, and high-energy scintillator applications.

Development of Eu3+-Doped Oxyfluoride Glass for Active Laser Medium

In this work, Eu3+-doped barium sodium borate oxide and oxyfluoride glasses were fabricated by melt-quenching technique for investigated their physical, optical, photoluminescence and radiative properties. The emission spectra, observed under the 394 nm, show the emission band corresponding to the transitions of 5D0→7F1 (590 nm), 7F2 (613 nm), 7F3 (652 nm) and 7F4 (701 nm). The most intense emission band is the 5D0→7F2 transition at 613 nm. The emission light is shown the reddish-orange color according to the framework of CIE 1931 color space. The Judd-Ofelt analysis confirmed the potential for using the glass samples in this work for use as photonic applications. The results from the emission spectra and radiative properties show that the oxyfluoride glass sample has more lasing potential than the oxide glass sample.

A Review of Cr2+ or Fe2+ Ion-Doped Zinc Sulfide and Zinc Selenide Ceramics as IR Laser Active Media

Zinc chalcogenides doped with Cr2+ or Fe2+ ions are of considerable interest as active media for IR lasers operating in the 2–5 µm wavelength range. Such lasers are in demand in various fields of medicine, remote sensing and atmospheric monitoring, ranging, optical communication systems, and military applications. In recent years, however, the rate of improvement in the characteristics of zinc chalcogenide laser sources has slowed considerably. Unwanted thermally induced effects, parasitic oscillations, and laser-induced damage of the active element have hindered the scaling of output power and efficiency. However, the physical and chemical properties of the materials leave ample room for further improvements. In particular, the control of the dopant concentration profile in the active element is of great importance. Zero concentration of Cr2+ or Fe2+ ions on the radiation input/output surfaces can significantly increase the laser-induced damage threshold; the designed concentration distribution in the element volume allows regulation of heat dissipation and reduction of parasitic oscillations. The zinc chalcogenide ceramic technology seems to be the most suitable to solve this challenge. This review presents and discusses the state of the art in ZnS and ZnSe optical and laser ceramics and the directions for further development of their technology.

Amplification and ellipticity enhancement of high-order harmonics in a neonlike x-ray laser dressed by an IR field

In Khairulin et al. [Sci. Rep. 12, 6204 (2022)] we proposed a method for amplifying a train of sub-femtosecond pulses of circularly or elliptically polarized extreme ultraviolet radiation, composed by high-order harmonics of an infrared (IR) laser field, in a neonlike active medium of a plasma-based x-ray laser, additionally irradiated with a replica of a fundamental frequency laser field used to generate harmonics. Here we present the analytical theory and numerical study of an amplification process of an individual harmonic with either preservation of its polarization state or ellipticity enhancement. We also analyze in detail the spectral-temporal and polarization properties of a sub-femtosecond pulse train formed by a set of elliptically or circularly polarized harmonics during the propagation through the medium. We discuss also the possibility of an experimental implementation of the suggested technique in an active medium of an x-ray laser based on neonlike ${\mathrm{Ti}}^{12+}$ ions irradiated by an IR laser field with a wavelength of 3.2 \textmu{}m.

On the Possibility of Converting Linearly Polarized Attosecond Pulses of High Harmonics into Circularly Polarized Pulses with an Increase in the Energy in an Optically Modulated Neon-Like Active Medium of an X-Ray Plasma Laser

A method is proposed for converting linearly polarized radiation of a single harmonic or a combination of high-order harmonics of an optical field, which form a train of subfemto-/attosecond pulses, into elliptically and, in particular, circularly polarized radiation in an optically modulated neon-like active medium of an X‑ray plasma laser. It is shown that this method can provide a high energy efficiency of radiation conversion due to the amplification of the harmonic field, and is also insensitive to changes in the number of high harmonics that form the amplified pulses. The possibility of experimental implementation of the method is considered on the example of an active plasma of neon-like Ti12+ ions with an unperturbed inverted transition wavelength of 32.6 nm.

Characterization of laser dye concentrations in ZnO nanostructures for optimization of random laser emission performance

Many nanoforms of zinc oxide (ZnO) structures can be synthesized, such as spheres, rods, flowers, disks and walls, as scatter centers in random laser. However, nanoflower and nanowire shapes in this work have received particular interest due to their wide range of applications, including biological, medical cancer cell detection, gas sensors, and biosensors. In this paper, we investigate the optical and morphological properties of two-shaped nanoparticles as scatter centers in the laser active medium on the performance emission of a random laser. Fluorescence and absorption spectra show that 10[Formula: see text][Formula: see text]M for R6G dye and [Formula: see text][Formula: see text]cm[Formula: see text] ZnO NPs are the optimal nanocomposite film concentrations for R6G dye. With excitation energies ranging from 3.44[Formula: see text]mJ to 28.34[Formula: see text]mJ and a repetition rate of 2[Formula: see text]Hz, second-harmonic generation Nd: YAG laser Amplified spontaneous emission (ASE) spectra of the nanocomposite films were observed. The results indicated a minimum bandwidth (Full width at half maximum (FWHM)) of 13[Formula: see text]nm at a threshold energy of 8.65[Formula: see text]mJ for ZnO NW (nanowire) nanocomposite films at [Formula: see text][Formula: see text]cm[Formula: see text] with R6G dye at 10[Formula: see text][Formula: see text]M and Poly(methyl methacrylate) (PMMA). The ZnO NF (nanoflower) nanocomposite film had an FWHM of 11[Formula: see text]nm and a threshold energy of 4.8[Formula: see text]mJ at the same concentrations of R6G dye on PMMA.

Significant enhancement in laser damage resistance of YAG crystal surface by plasma etching.

The high-quality surface of an optical element is a prerequisite for a high-power laser system design. Yttrium aluminum garnet (YAG) crystal is one of the most important materials for solid-state laser active medium. Laser-induced damage threshold (LIDT) of the YAG crystals might substantially limit the maximum output power of the whole laser system. In this research, we show the novel possibility of significant LIDT enhancement via plasma etching of YAG crystal surface for picosecond laser pulse durations. The dependence of the LIDT on the etching depth was investigated. With the optimized etching conditions, the LIDT value was increased by more than three times and reached the intrinsic LIDT of the bulk crystal.

Photoexcimerisation of pure acriflavine dye in water and alcohol

The light emission properties of acriflavine have been extensively utilised in its applications as dye laser active media, as photosensitizer, as fluorescent and FRET (Fluorescence Resonance Energy Transfer) agent for sensing mechanism etc. However, studies on the photochemical and photophysical properties of acriflavine and its aggregates are very limited and little is known about its emission characteristics in different media. The present study was undertaken to acquire a comprehensive understanding of the aggregation process and emission characteristics of the solution of pure acriflavine dye in water and alcohol, namely the propanol, methanol, ethanol and butanol. This study includes confirming the photoexcimerisation of acriflavine by concentration dependent UV–Visible spectroscopy, steady state fluorescence spectroscopy and time resolved fluorescence spectroscopy at room temperature. The present study shows the monomer and excimer fluorescence emission of acriflavine in the range 495–528 nm and 549–587 nm respectively (monomer and excimer emission peak wavelength varies for different solvents). The nature of the excimer emission band of acriflavine around 575 nm for all the solvents has been tested through temperature dependent steady state fluorescence spectroscopy and also from time resolved fluorescence spectra it has been found that the excimer band does not originate from any triplet excited state. The pH dependent emission spectra for fixed concentration of acriflavine in the solvents reveals red shifts in the monomer and the excimer fluorescence maxima. The excimerisation of acriflavine in water, propanol and methanol is found as static process from excited dimers, whereas in ethanol and butanol it is the result of dynamic diffusion process between a photoexcited and a ground state monomer. The excimerisation process of the acriflavine has been quantified by evaluating the monomer-excimer equilibrium concentration i.e., the critical concentration in the cited solvents. At the critical concentration the monomer and the excimer are found to be fluoresced with equal intensity. The acriflavine solutions specifically at the critical concentration in the cited solvents will enhance its photophysical and photochemical applications by extending them up to the new range of excimer emission radiation at the wavelength in-between 549 nm and 587 nm. Hence, this report shows that, by using acriflavine solutions of certain concentrations in any one of the cited solvents as an active medium of a dye laser and thereby obtaining both the monomer and excimer emission band, the wavelength of the laser can be tuned from 495 nm to 587 nm.

Mutual amplification of high-order harmonics in an optically dressed hydrogenlike plasma-based x-ray laser

In a recent work [V. A. Antonov, K. C. Han, T. R. Akhmedzhanov, M. Scully, and O. Kocharovskaya, Phys. Rev. Lett. 123, 243903 (2019)] a method of amplifying a train of attosecond pulses, produced via high-order harmonic generation of an infrared (IR) laser field, in an active medium of a plasma-based x-ray laser dressed by a replica of the IR field of the fundamental frequency was proposed. The specific case of independent amplification of each incident harmonic was considered, corresponding to a dense plasma of multiply charged ions (such as ${\mathrm{C}}^{5+}$ ions) which is strongly dispersive for the IR field. In the present paper, we consider a general case when the laser field modulation leads not only to the direct amplification of high harmonics (HHs), but also to the scattering of the harmonics into each other. The mutual coherent scattering process plays an important role in a relatively low-density plasma with a lower ion charge, corresponding to a weakly dispersive plasma at the frequency of the IR field. Constructive interference between the amplified HHs and the coherently scattered field may result in a significant enhancement of the total output field. We call this effect the mutual amplification of high-order harmonics. Considering the plasma of hydrogenlike ${\mathrm{Li}}^{2+}$ ions with an inverted transition wavelength of 13.5 nm as an example, we analytically and numerically show that synchronization of a coherently scattered field with the radiation of amplified HHs makes it possible to increase the intensity of attosecond pulses by several times compared to the case of an independent amplification of HHs.

Спектральные и люминесцентные свойства Yb-=SUP=-3+-=/SUP=- в растворах CCl_4-GaCl_3-Yb-=SUP=-3+-=/SUP=-

The absorption and luminescence spectra and the luminescence lifetime of the excited state 2F5/2 of Yb3+ ions in CCl4 – GaCl3 – Yb3+ solutions have been measured. Information was obtained on the Stark splitting of levels, on the absorption and stimulated emission cross sections, and on the quantum yield of Yb3+ luminescence. The spectral dependences of the gain cross section are calculated for different relative inverse populations of the 2F5/2 excited state. Based on an analysis of the spectral and laser properties of Yb3+, it was concluded that the use of CCl4 – GaCl3 – Yb3+ solutions as the active medium of a liquid ytterbium laser is promising. Keywords: carbon tetrachloride, ytterbium, absorption, luminescence, lifetimes, Stark splitting, gain cross section

Universal Single-Mode Lasing in Fully Chaotic Billiard Lasers.

By numerical simulations and experiments of fully chaotic billiard lasers, we show that single-mode lasing states are stable, whereas multi-mode lasing states are unstable when the size of the billiard is much larger than the wavelength and the external pumping power is sufficiently large. On the other hand, for integrable billiard lasers, it is shown that multi-mode lasing states are stable, whereas single-mode lasing states are unstable. These phenomena arise from the combination of two different nonlinear effects of mode-interaction due to the active lasing medium and deformation of the billiard shape. Investigations of billiard lasers with various shapes revealed that single-mode lasing is a universal phenomenon for fully chaotic billiard lasers.

Mid-Infrared Laser Generation of Zn1-xMnxSe and Zn1-xMgxSe (x ≈ 0.3) Single Crystals Co-Doped by Cr2+ and Fe2+ Ions-Comparison of Different Excitation Wavelengths.

Two different mid-infrared (mid-IR) solid-state crystalline laser active media of Cr, Fe:ZnMnSe and Cr, Fe:ZnMgSe with similar amounts of manganese or magnesium ions of x ≈ 0.3 were investigated at cryogenic temperatures for three different excitation wavelengths: Q-switched Er:YLF laser at the wavelength of 1.73 m, Q-switched Er:YAG laser at 2.94 m, and the gain-switched Fe:ZnSe laser operated at a liquid nitrogen temperature of 78 K at ∼4.05 m. The temperature dependence of spectral and laser characteristics was measured. Depending on the excitation wavelength and the selected output coupler, both laser systems were able to generate radiation by Cr or by Fe ions under direct excitation or indirectly by the Cr→ Fe energy transfer mechanism. Laser generation of Fe ions in Cr, Fe:ZnMnSe and Cr, Fe:ZnMgSe (x ≈ 0.3) crystals at the wavelengths of ∼4.4 and ∼4.8 m at a temperature of 78 K was achieved, respectively. The excitation of Fe ions in both samples by direct 2.94 m as well as ∼4.05 m radiation or indirectly via the Cr→ Fe ions’ energy transfer-based mechanism by 1.73 m radiation was demonstrated. Based on the obtained results, the possibility of developing novel coherent laser systems in mid-IR regions (∼2.3–2.5 and ∼4.4–4.9 m) based on AB matrices was presented.

Uniform and Non-Uniform Pumping Effect on Ce:Nd:YAG Side-Pumped Solar Laser Output Performance

The Ce:Nd:YAG is a recent active medium in solar-pumped lasers with great potential. This study focuses on the influence of two secondary concentrators: a fused silica aspherical lens and a rectangular fused silica light guide; and consequent pump light distribution on the output performance of a Ce:Nd:YAG side-pumped solar laser. The solar laser head with the aspherical lens concentrated the incident pump light on the central region of the rod, producing the highest continuous-wave 1064 nm solar laser power of 19.6 W from the Ce:Nd:YAG medium. However, the non-uniformity of the absorbed pump profile produced by the aspherical lens led to the rod fracture because of the high thermal load, limiting the maximum laser power. Nevertheless, the solar laser head with the light guide uniformly spread the pump light along the laser rod, minimizing the thermal load issues and producing a maximum laser power of 17.4 W. Despite the slight decrease in laser power, the use of the light guide avoided the laser rod fracture, demonstrating its potential to scale to higher laser power. Therefore, the pumping distribution on the rod may play a fundamental role for Ce:Nd:YAG solar laser systems design.