High-power continuous-wave cr(4+):forsterite laser

The temperature and pump power dependence of infrared luminescence of Cr(4+):forsterite are measured. It is demonstrated that temperature-dependent fluorescence in Cr(4+):forsterite is the major reason for saturation of the output power of a continuous-wave laser. At higher pump intensities the temperature rise inside the crystal becomes significant, and even outside cooling does not help to prevent significant reduction of the laser performance. These measurements serve as a guideline to construct a high-power continuous-wave Cr(4+):forsterite laser.     

Efficient continuous-wave radiatively cooled cr(4+):forsterite lasers at room temperature

Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr(4+):forsterite laser at elevated temperatures are presented. From a Cr(4+):forsterite crystal with a differential absorption coefficient of 0.57 cm(-1), as much as 900 mW of cw output power has been obtained at 1.26 mum and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mum. No chopping of the pump beam was necessary. An efficient radiative cooling technique was further employed to cool the laser and no subsequent power fading was observed. To the author's knowledge, the measured absorbed power slope efficiency of 29.5% represents the highest cw power performance reported to date from a Cr(4+):forsterite laser pumped by a Nd:YAG laser around room temperature. The role of the low differential absorption coefficient in the reduction of thermal loading is further elucidated by presenting comparative cw power performance data with a second Cr(4+):forsterite crystal having a differential absorption coefficient of 1.78 cm(-1) in the temperature range between 12 and 35 degrees C. Finally, some interesting multipulse effects of the laser observed in the millisecond regime during quasi-cw operation at 50% duty cycle are described.     

Intracavity frequency-doubled femtosecond cr(4+):forsterite laser

The generation of femtosecond optical pulses centered at ~620 nm directly from an all-solid-state laser oscillator is reported. Red pulses with pulse widths of the order of 170 fs were obtained with 24-mW average power at an 81-MHz repetition rate. They were achieved by intracavity frequency doubling of a mode-locked Cr(4+):forsterite laser with a 1-mm-thick beta-BaB(2)O(4) crystal. The process of laser mode locking was modified by surface coating the doubling crystal.     

Ultrabroadband operation of a cr(4+): forsterite laser by use of a spatially dispersed resonator

Ultrabroadband (half-width of 88 nm) nanosecond Cr(4+):forsterite oscillation was achieved simultaneously in the 1170-1340-nm range (1085 cm(-1)) by use of a spatially dispersed resonator with an intracavity prism pair. The laser demonstrates 4.8% real pump-to-laser efficiency. The oscillation build-up time for different spectral components is around 20 ns and varies by only 2.5 ns in the 1190-1260-nm region, which indicates that the ultrabroadband laser represents a complex multifrequency laser system with nonlinear spectral mode interaction.     

The thermal regime of solid continuous-wave lasers

A method is presented for the calculation of the temperature field of continuous-wave lasers, given constant thermophysical characteristics for the active medium and that these are dependent on temperature.     

Pulse amplification of a single-frequency cr:forsterite laser

Stable single-longitudinal-mode operation of a tunable gain-switched Cr:forsterite oscillator-amplifier system is reported. A novel coupled-cavity oscillator configuration provides a low-threshold fluence of 0.3 J cm(-2), making the system attractive for laser media with low gain or high parasitic loss. Nearly transform-limited pulses with instrument-limited bandwidths of 150 MHz have been obtained across a 100-nm wavelength range, limited by the cavity optics. A range of forsterite crystals with Cr(4+) concentration in the 3-21 x 10(18)-cm(-3) range has been used for investigation of amplifier performance in single- and double-pass configurations.     

Broadly tunable continuous-wave orange-red source based on intracavity-doubled Cr4+:forsterite laser

The operation of a room-temperature, continuous-wave, intracavity frequency-doubled Cr4+:forsterite laser capable of producing broadly tunable output in the orange-red region of the electromagnetic spectrum is described. Intracavity doubling was achieved in a periodically poled lithium niobate crystal that had gratings with different periods. Tunable second-harmonic output could be obtained between 613 and 655 nm. At a wavelength of 630 nm, intracavity doubling yielded as much as 45 mW of continuous-wave output. To the author's knowledge, this represents the highest second-harmonic-power generation obtained to date with a continuous-wave Cr4+:forsterite laser.     

The effect of thermal loading on the yield surface of aluminium. An experimental investigation

Summary Paper presents the results of an experimental investigation dealing with the effects on the motion and deformation of the room temperature yield curve and on the plastic strain resulting from a substantial penetration of the yield surface by: (1) loading paths with constant stress combined with variable temperature and (2) isothermal loading paths. The results are interpreted with the help of the concept of the equilibrium stress-strain curves which is expanded to include both increasing and decreasing stress as well as changing temperature.With 17 FiguresThis research was supported by the National Science Foundation.     

An investigation of the features of loading in thermal fatigue

Experimental investigations were made of the loading of materials under conditions of thermal fatigue. An interpretation of the results obtained is given. A generalizing parameter describing the fatigue strength of the investigated materials is established. Certain practical recommendations are given.Translated from Problemy Prochnosti, No. 10, pp. 17–22, October, 1994.     

Impact loading of plates — An experimental investigation

The impact of projectiles at sub-ordnance velocities against mild steel, stainless steel and aluminium plates, has been studied in a series of experiments. The projectile mass, nose shape and hardness have been shown to have an important effect on penetration as does the target rigidity and support condition. All materials exhibit a clear ‘kink’ effect related to a change from energy absorption by plastic deformation to perforation with well-defined shear bands and no appreciable bulging.     

三种络合沉淀剂对NaYF4:Tm3+,Yb3+发光性能的影响

分别采用EDTA、柠檬酸和H2C2O43类络合沉淀剂,共沉淀法制备了NaYF4:Tm3+,Yb3+材料,用X射线衍射(XRD)分析,扫描电镜(SEM)观察和荧光光谱分析研究了不同络合剂,沉淀温度和燃烧温度对NaYF4:Tm3+,Yb3+材料发光性能,粒度及形貌的影响.研究结果表明,采用H2C2O4为沉淀剂制成草酸盐前躯体,然后在600℃下煅烧5h,即可得到发光效果较好的NaYF4:Tm3+,Yb3+材料.     

Use of broadband, continuous-wave diode lasers in cavity ring-down spectroscopy for liquid samples

Cavity ring-down spectroscopy (CRDS) is an extremely sensitive absorption technique that has been applied primarily to gas samples, which are characterized by having narrow absorption features. Recently, CRDS has also been applied to liquid samples, which have broad absorption features. The use of small inexpensive diode lasers as light sources for liquid samples is demonstrated. The low cost coupled with the ease and technical straightforwardness of application gives this technique wide appeal.     

Comparative investigation towards machinability improvement in hard turning using coated and uncoated carbide inserts: part I experimental investigation

The investigation of low cost uncoated and coated carbide insert in the hard turning of hardened AISI D2 steel (≥55 HRC) will definitely open up a new arena as an economical alternative suitable to industrial machining sectors. Thus, this paper reports the comparative machinability assessment for the hard turning of AISI D2 steel ((55 ±1) HRC) by coated and uncoated carbide insert in a dry environment. Micro hardness and abrasion tests were carried out to assess resistance capability against wear. The above test results confirmed the greater wear resistance ability of Al₂O₃ coated carbide insert over uncoated carbide. Based on the extensive investigation of comparative machinability, the coated carbide insert (TiN-TiCN-Al₂O₃) outperformed the uncoated carbide insert with regard to surface roughness, flank wear, chip-tool interface temperature, and chip morphology. Abrasion and diffusion were observed as the principal tool wear mechanisms in the investigated range. The uncoated carbide failed completely due to the severe chipping and quick dulling of the cutting edge, which led to its unsuitability for machining hardened steel. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0215-z     

An experimental investigation of the sequence effect in block amplitude loading of cross-ply composite laminates

The Palmgren–Miner rule has been shown to be inexact in many cases for various composite materials. Several empirical models have been conceived to account for this discrepancy, as well as the effect of block sequence. The approach taken here is based on the underlying mechanisms. A cross-ply laminate was used as a model material. In general, composites show both initiatory and progressive mechanisms under fatigue loading. The former is active at high static stresses, whereas the latter predominates at lower stress amplitudes where they are given sufficient time to propagate. Initiatory mechanisms give rise to damage from which the progressive mechanisms can start, and conversely the progressive mechanisms continually alter the local stress state which results in further damage accumulation caused by the initiation controlled mechanisms. In a cross-ply laminate, the initiatory mechanism is the formation of transverse cracks, and the progressive mechanism is mainly delamination growth initiated from the transverse cracks. In an experimental investigation of carbon fiber/epoxy cross-ply laminates, the interaction of these mechanisms has shown why a sequence of high–low amplitude levels results in shorter lifetimes than a low–high order. Such a sequence effect seems to be a common behavior for many other composite materials, and can be mechanistically explained by a similar kind of interaction. Advantages and drawbacks of the mechanistic approach compared with empirical rules are also discussed.     

an experimental investigation into the mechanics of deep semielliptical surface cracks in mode i loading

An experimental investigation was made of the surface deformation and extent of plastic yielding associated with relatively deep semielliptical surface cracks in plates subjected to tensile loading. Data were gathered from sheet Ti-6A1-4V and Fe-3Si, the latter material being employed to study, by the electrolytic etching technique, the plastic zones in various planes intersecting the crack. Available analytical models were applied to calculate the stress intensity factors, and the experimental data were used to examine various models for predicting plastic zone sizes.     

Theoretical and experimental study on passive mode-locking composite Nd:GdVO4/Nd:GdVO4/Nd:GdVO4 lasers

Stable passive mode-locking multi-segment composite Nd:GdVO₄ lasers with a semiconductor saturable absorber mirror were demonstrated for the first time. For the composite crystals, the output power increased linearly with the increase of the incident pump power, showing excellent thermo-mechanical performances. While for the conventional crystal, power saturation was observed when the incident pump power exceeded 8.79 W. The maximum average output power of 1.465 W was achieved by Nd(0.1%):GdVO₄/Nd(0.5%):GdVO₄/Nd(1%):GdVO₄ composite crystal at an incident pump power of 9.28 W. The largest pulse energy of 14.90 nJ and the highest peak power of 0.53 kW with a pulse duration of 28.0 ps were also obtained by using the same composite crystal, revealing that the multi-segment composite crystal with a proper combination of Nd³⁺-doped concentrations could obtain the optimal laser performance.     

An experimental investigation of the thermal conductivities of esters of carboxylic acids

This paper gives the results of an experimental investigation of the thermal conductivities of a homologous series of esters of saturated monobasic acids. Equations for calculating the thermal conductivity of liquids in relation to temperature and composition are presented.     

Synthesis of nanocrystalline forsterite (Mg2SiO4) powder by combined mechanical activation and thermal treatment

This study investigates the synthesis of single-phase nanocrystalline forsterite powder by mechanical activation with subsequent annealing. To produce forsterite powder, a mixture of talc and magnesium oxide powders was first milled by a planetary ball mill, and then annealed at 1000 and 1200 °C for 1 h. The synthesized powder was characterized by X-ray diffraction (XRD), simultaneous thermal analysis (STA), scanning electron microscopy (SEM), and atomic absorption spectrometry (AAS). The initial temperature of forsterite crystallization was reduced to about 825 °C after 20 h of mechanical activation. The forsterite powder synthesized by 5 h of mechanical activation with subsequent annealing at 1000 °C for 1 h had crystallites 40 nm in size. The particle size of this sample was less than 500 nm.     

An experimental investigation of the thermal conductivity of highly porous graphitic carbons

This paper gives the results of an investigation of the thermal conductivity of graphitic carbons of different porosity (up to 78%) by the static method involving a radial heat flux from an internal rod heater in the temperature range 500–2200°K.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 4, pp. 696–701, April, 1970.