Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

The dependence of the beam propagation factor (M ² parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively studied. Our investigations show that the M ₂ parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration associated with the thermal lens induced by the pump beam. Such dependency of M ² parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd³⁺ -doped GdVO₄ crystal and the values of α and β parameters were estimated from the experimentally measured data points.     

Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe₄₀Ni₄₀B₂₀ and Fe₄₀Ni₃₈Mo₄B₁₈ metallic glass ribbons. 90 MeV ¹²⁷I beam was used for the irradiations. Irradiation doses were 5×10¹³ and 7.5×10¹³ ions/cm². The relative intensity ratios D ₂₃ of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.     

An Anthracene-Based Metal-Organic Framework for Selective Photo-Reduction of Carbon Dioxide to Formic Acid Coupled with Water Oxidation

A Zr-based metal-organic framework has been synthesized and employed as a catalyst for photochemical carbon dioxide reduction coupled with water oxidation. The catalyst shows significant carbon dioxide reduction property with concomitant water oxidation. The catalyst has broad visible light as well as UV light absorption property, which is further confirmed from electronic absorption spectroscopy. Formic acid was the only reduced product from carbon dioxide with a turn-over frequency (TOF) of 0.69 h⁻¹ in addition to oxygen, which was produced with a TOF of 0.54 h⁻¹. No external photosensitizer is used and the ligand itself acts as the light harvester. The efficient and selective photochemical carbon dioxide reduction to formic acid with concomitant water oxidation using Zr-based MOF as catalyst is thus demonstrated here.     

Mesoporous interstitial and substitutional nitrogen-containing titanium dioxide photocatalysts prepared by acid-assisted sol–gel procedure

Two different types of nitrogen-containing TiO₂ were synthesized via an acid-modified sol–gel method. Yellow-colored interstitial and white substitutional nitrogen-containing TiO₂ powders were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller specific surface area and Barrett–Joyner–Halenda pore size distribution analyses, scanning electron microscopy, transmission electron microscopy and UV–vis absorption spectroscopy. The band gaps of interstitial and substitutional nitrogen-containing TiO₂ ceramics were estimated from UV–vis spectroscopy data to be 2.6 and 2.8 eV, respectively. Prepared substitutional nitrogen-containing TiO₂ featured steep light absorption edge with an approximately parallel characteristic to that in pure TiO₂. This fact is due to band-to-band visible light absorption ability of substitutional nitrogen-containing TiO₂. The photocatalytic properties of the produced nitrogen-containing TiO₂ samples were compared for the degradation of Direct Red 28 azo dye. Further studies were also devised to compare the catalytic efficiency of the nitrogen-containing TiO₂ powders with the pure TiO₂ synthesized via the similar sol–gel method. The produced nitrogen-containing TiO₂ samples revealed superior photocatalytic properties in comparison with pure TiO₂ due to their remarkable band gap narrowing, surface oxygen vacancies and much more surface defects. The results also revealed that the substitutional nitrogen-containing TiO₂ is the most effective photocatalyst under ultraviolet and visible light irradiation.     

Theoretical investigation of the molecular structure,vibrational spectra,and molecular docking of tramadol using density functional theory

The optimized molecular structures, harmonic vibrational wavenumbers, and the corresponding vibrational assignments of (1S,2S)-tramadol and (1R,2R)-tramadol are computationally examined using the B3LYP density functional theory method together with the standard 6–311++G(d,p) and def2-TVZP basis sets. The optimized structures show that phenolic rings of both 1R,2R and 1S,2S tramadol adopt planar geometry, which are slightly distorted due to the substitution at the meta-position; and the six-membered cyclohexane adopts a slightly distorted chair conformation. The 1S,2S enantiomer is energetically more favorable than 1R,2R with the energy differences of 1.32 and 1.03 kcal/mol obtained at B3LYP/6–311++G(d,p) and B3LYP/Def2-TVZP levels, respectively. The analysis of the binding pocket in the silico molecular docking with the m-opioid receptor shows that it originated two clusters with the 1S,2S enantiomer and one cluster with the 1R,2R enantiomer of tramadol. The results point to a more stable complex of the m-opioid receptor with the 1R,2R enantiomer of tramadol.     

Low temperature survival of slender naiad (Najas flexilis) seeds

The response to drying and storage at -20 degrees C or in liquid nitrogen was studied in seeds of the freshwater aquatic plant Najas flexilis. The seeds of this species show some desiccation sensitivity, although post-harvest storage in water at 16 degrees C resulted in improvements in desiccation tolerance. There was 63% germination of seeds dried to 9.5% moisture content (30% RH) following this maturation period. Optimum moisture contents for seeds stored at -20 degrees C for 3 months and in liquid nitrogen for 1 week were ~11% and ~15%, respectively.     

Investigation into the rotational bands of ~(185)Pt with the particle-rotor model

Theoretical calculations have been performed for the ν9/2+[624](i13/2) and ν7/2-[503](f7/2) bands of 185Pt in the framework of particle-rotor model. The band properties of signature splitting and configuration mixing have been analyzed. The level energy and signature splitting before the band crossing can be well interpreted by introducing triaxiality. The positive-parity yrast band is pro posed to be dominated by the ν9/2+[624](i13/2) component, while the negative-parity band shows strong mixing of ν7/2-[5...     

Existence results to positive solutions of fractional BVP with $${\varvec{}}$$-derivatives

This paper investigates the existence and uniqueness of positive and nondecreasing solution for nonlinear boundary value problem with fractional q-derivative

$$\begin{aligned}&D_{q}^{\alpha }u(t)+f(t,u(t))=0, \quad {0<t<1, ~3<\alpha \le 4,} \\&u(0)= D_{q}u(0)=D_{q}^{2}u(0)=0, \quad D_{q}^{2}u(1)=\beta D_{q}^{2}u(\eta ), \end{aligned}$$

where \(D_{q}^{\alpha }\) denotes the Riemann–Liouville q-derivative of order \(\alpha \), \(0<\eta <1\) and \(1-\beta \eta ^{\alpha -3}>0\). Our analysis relies a fixed point theorem in partially ordered sets. An example to illustrate our results is given.

     

Numerical simulation of electronic structure,linear and third order nonlinear optical absorption coefficients in the polymeric nanoheterostructure using imaginary time propagation method

In the effective mass approximation, the charge density, the potential profile, the wavefunctions, and the corresponding energy states for zinc sulfide spherical quantum dot have been self-consistently solved, which is embedded in the polymeric media (PVP) by the imaginary time propagation method. Moreover, for the first time, the oscillator strength, linear, third order nonlinear, and total optical absorption coefficients for the transition between intersubbands 1s-1p, 1p-1d, 1d-1f, 1f-1g, 1g-1h, and 1h-1i are investigated with respect to photon energy and the saturation strength has been calculated for every transition too. Calculated result shows that the oscillator strength and the magnitude of optical absorption coefficients are enhanced for transition between intersubbands with higher energies. Also, calculations show that the total absorption coefficient depends on the strength of incident optical intensity and relaxation time.     

Measurement of στ product of solid state laser materials by an alternative method: Application to Nd3+ doped YVO4 crystal for 4 F 3/2→4 I 11/2 transition

In this paper an alternative approach for measurement of στ product for ⁴ F _3/2→⁴ I _11/2 transition of Nd³⁺ doped YVO₄ crystal is reported. In this method a microchip laser is formed by keeping a small piece of the sample in plane-plane resonator and a diode laser (808 nm) is used for pumping. The pump power induced thermal lensing effect is used to make the cavity stable. The cavity mode area is estimated by measuring the thermal lens focal length at the threshold and the average pump area is measured by Gaussian fit to the intensity profiles of the pump beam. The value of στ product of Nd:YVO₄ crystal obtained by this method is within 10% of the reported values. The advantage of this method is that it is a simple method for direct measurement of στ product of laser crystals.