Nd-doped Phosphate Laser Glass Research Articles

Monolithic edge-cladding process for the elliptical disk of N31-type Nd-doped high-power laser glass

Abstract This paper investigates the monolithic edge-cladding process for the elliptical disk of N31-type Nd-doped phosphate laser glass, which will be utilized under liquid cooling conditions for high-power laser systems. The thermal stress, interface bubbles and residual reflectivity, which are due to high-temperature casting and bonding during the monolithic edge-cladding process, are simulated and determined. The applied mould is optimized to a rectangular cavity mould, and the casting temperature is optimized to 1000°C. The resulting lower bubble density makes the mean residual reflectivity as low as 6.75 × 10−5, which is enough to suppress the amplified spontaneous emission generated in the Nd-glass disk, and the resulting maximum optical retardation is converged to 10.2–13.3 nm/cm, which is a favourable base for fine annealing to achieve the stress specification of less than or equal to 5 nm/cm. After fine annealing at the optimized 520°C, the maximum optical retardation is as low as 4.8 nm/cm, and the minimum transmitted wavefront peak-to-valley value is 0.222 wavelength (632.8 nm). An N31 elliptical disk with the size of 194 mm × 102 mm × 40 mm can be successfully cladded by the optimized monolithic edge-cladding process, whose edge-cladded disk with the size of 200 mm × 108 mm × 40 mm can achieve laser gain one-third higher than that of an N21-type disk of the same size.

Optimized monolithic edge-cladding glass for N31-type Nd-doped high power laser glass

In this paper, six edge-cladding glasses are prepared and analyzed, which are designed to clad the elliptical disk of N31-type Nd-doped phosphate laser glass by monolithic edge-cladding technique. The transition temperatures, soften temperatures, thermal expansion coefficients, high temperature viscosities and refractive indices of the prepared edge-cladding glasses are determined, which must be consistent with these parameters of N31 glass as possible. The residual stresses and residual reflectivities are determined for the cladded N31 elliptical disks and slab samples, which are the most important parameters for the monolithic edge-cladding technique and must be as low as possible to meet the index requirements for high power laser applications. The interface bubbles, edge-cladding interface and the controllability of divalent Cu2+ ions are also discussed. By the optimized edge-cladding glass, it is verified that the elliptical disk of N31-type Nd-doped phosphate laser glass can be successfully cladded by the optimized monolithic edge-cladding glass, which can be utilized securely in a strong liquid cooling to pursue a better high-power laser performance with a higher laser shot rate.

Investigation on Residual Stress in Monolithic Edge-Cladding of Elliptical Nd-Doped Phosphate Laser Glass for High-Peak Power Solid-State Laser

Investigation on Residual Stress in Monolithic Edge-Cladding of Elliptical Nd-Doped Phosphate Laser Glass for High-Peak Power Solid-State Laser

阴离子改性抛光剂对磷酸盐激光钕玻璃抛光的影响

阴离子改性抛光剂对磷酸盐激光钕玻璃抛光的影响

(INVITED) Impurities in large scale produced Nd-doped phosphate laser glasses. I. Cu ions

Impurity ions such as transition metals and rare earth metals in Nd-doped phosphate laser glasses will degrade Nd-laser performance, among which Cu is the most harmful. Divalent Cu2+ not only results in an optical loss at Nd-laser wavelength, but also reduces the energy storage for laser amplification. A large-scale production of Nd-doped phosphate laser glasses is required to meet quality demand and to realize economy of scale. To balance between the controlled impurity level in the glasses and the cost of raw materials for thousands of slabs of meter-scale Nd-doped phosphate laser glasses, it is important to determine an upper limit for Nd-laser degradation due to divalent Cu2+ ions. The absorption edge of Cu singly-doped phosphate glass prepared in an oxidizing atmosphere shows the evidence of monovalent Cu+. X-ray photoelectron spectroscopy is utilized to further verify the existence of monovalent Cu+ ions in Cu, Nd codoped phosphate glass. The results show that both Cu+ and Cu2+ ions most probably coexist in Nd-doped phosphate laser glasses produced in the oxidizing atmosphere to eliminate Pt inclusions in the glasses. Accordingly, this paper discusses the extinction coefficient and the fluorescence quench factor caused by divalent Cu2+ ions, as well as their influence.

(INVITED) Impurities in large scale produced Nd-doped phosphate laser glasses. II. Pt ion and Pt inclusion

Platinum is a special kind of impurity in Nd-doped phosphate laser glasses. Firstly, its presence in the glass depends on the production processes, rather than the purity of the raw materials used. Secondly, there coexist Pt ion and Pt inclusion in the glass, which one is the oxidized and the other is the reduced. The detection for these two kinds of Pt impurities in the large-scale produced Nd-doped phosphate laser glasses can reflect the control level and stability of the processes. To determine more accurately the content of Pt ion in the glass, a hemi-cyanine dye, instead of SnCl2 previously used, is utilized to color Pt ion solution by dissolving the glass. On the basis of such a new hemi-cyanine spectrophotometric analysis, the factor of proportionality between Pt ion content and its absorption coefficient at 400 nm is determined and discussed. To avoid the interference from other cations in the multi-cation solution by dissolving the glass, when doing ICP-MS analysis for Pt, a magnetic poly-ionic liquid is synthesized successfully by bonding an ionic liquid to nano-Fe3O4 particles covered by C. Such a new magnetic poly-ionic liquid can adsorb Pt ions with a better selection. The element distribution of Pt, O and P for differently sized Pt inclusions in the glass is analyzed by EPMA.

Effect of Iron and Copper Impurity Ions on Laser Efficiency of Phosphate Laser Glass

The effect of impurity such as Fe and Cu ions on the optical loss and laser performance of N31-type Nd-doped phosphate laser glass was studied. It was found that the laser slope efficiency decreased in accordance with an e exponential function, and the laser threshold increased in quadratic with the increase of Fe concentration. More- over, the empirical equations between concentration of Fe with laser slope efficiency and laser threshold were obtained. It also showed that laser efficiency was seriously influenced by Cu ion compared with that by Fe ion at the same con- centration. The results are useful for improving the gain performance of laser glass and quantitatively control of the impurity in raw materials in the future.

掺钕磷酸盐激光玻璃的短期水解及其光电子能谱表征

掺钕磷酸盐激光玻璃的短期水解及其光电子能谱表征

Quantitative investigation on single-asperity friction and wear of phosphate laser glass against a spherical AFM diamond tip

The single-asperity friction and wear behaviors of Nd-doped phosphate laser glass against a spherical diamond AFM tip were quantitatively investigated with respect to normal load, friction cycles, and velocity. Specific friction and wear equations were proposed to fit the experiment data obtained in the single-pass nanoscratch and multi-pass reciprocating sliding tests, respectively. The contribution of both the interfacial fiction and the plowing friction under specific sliding conditions was analyzed, and the corresponding wear mechanism was discussed. The results would be useful in understanding the mechanisms of friction and material removal in ultra-precision cutting and polishing of glass materials.

采用显微荧光法研究掺钕磷酸盐激光玻璃的亚表面缺陷

采用显微荧光法研究掺钕磷酸盐激光玻璃的亚表面缺陷

新型掺钕磷酸盐激光玻璃的耐抽运热破坏性质

新型掺钕磷酸盐激光玻璃的耐抽运热破坏性质

Measurement of the figure of merit of indigenously developed Nd-doped phosphate laser glass rods for use in high power lasers

High energy, high power (HEHP) Nd:glass laser systems are used for inertial confinement fusion and equation of state (EOS) studies of materials at high temperature and pressure. A program has been undertaken for the indigenous development of Nd-doped phosphate laser glass rods and discs for HEHP lasers. In this paper, we report the characterization of the Nd-doped phosphate laser glass rods produced under this program and compare the indigenously developed laser glass to LHG-8 laser glass of M/s Hoya, Japan. We experimentally measured the values of the stimulated emission cross-section (σ) and coefficient of intensity-dependent refractive index (n 2) and hence the figure of merit F = σ / n2 of the indigenous phosphate laser glass rods. This value is found comparable to the reported value of identically doped Nd:glass rods.

Further damage induced by water in micro-indentations in phosphate laser glass

Using a microhardness tester, artificial flaws were made by micro-indentation in N31 Nd-doped phosphate laser glass. Indentation fracture toughness, KIC, was estimated as 0.45–0.53MPam1/2 from these indentations. The glasses with indentations were then immersed in ultrapure water to investigate further water-induced damage of these indentations. Stress-enhanced hydrolysis leads to the propagations of radial crack, lateral cracks and microcracks in the subsurface. These crack propagations therefore cause deformation in subsurface to form annular reflections regions around the indentations and further material collapse within imprints. After the residual stresses are exhausted, the leaching plays a more dominated role in glass corrosion in the further immersion. After immersion, the material structure slackens around micro-indentation, which decreases the contact stiffness and results in a lower nano-hardness. For the surface far away from flaws, water immersion presents a weak effect on the near-surface mechanical since the matrix leaching in phosphate glass restricts the formation of hydration layer. During first 20min immersion, due to higher chemical activity and lower fracture toughness, the radial cracks show a faster propagation in phosphate glass compared with that in K9 silicate glass. For further immersion, crack healing occurs in silicate glass but not in phosphate glass. Analysis shows that the formation of hydration layer on crack walls plays an important role in crack healing in glasses.

Effect of copper impurity on the optical loss and Nd 3+ nonradiative energy loss of Nd-doped phosphate laser glass

N31-type phosphate laser glasses doped with different concentrations of Cu were prepared. Their optical loss coefficient at 1053 nm wavelength and nonradiative transition rate from the Nd 3+ 4F 3/2 state were determined and analyzed in detail. The optical loss coefficient per unit of Cu 2+ (cm −1/ppmw) and the fluorescence decay rate (Hz/ppmw) caused by Cu 2+ and Nd 3+ interaction were 0.0024 and 7.9, respectively. Cu impurity affected both optical loss at 1053 nm and fluorescent emission of Nd 3+ 4F 3/2 state seriously in N31 laser glass.

Distribution of electric field and energy flux around the cracks on the surfaces of Nd-doped phosphate glasses

We simulate and calculate numerically the electromagnetic field and energy flux around a surface crack of an Nd-doped phosphate laser glass by using the finite-difference time-domain method. Because of a strong interference between the incident wave and the total internal reflections from the crack and the glass surface, the electric field is redistributed and enhanced. The results show that the electric-field distribution and corresponding energy flux component depend sensitively on the light polarization and crack geometry, such as orientation and depth. The polarization of the incident laser beam relative to the crack surfaces will determine the profile of the electric field around the crack. Under TE wave incidence, the energy flux peak is always inside the glass. But under TM wave incidence, the energy flux peak will be located inside the glass or inside the air gap. For both incident modes, the light intensification factor increases with the crack depth, especially for energy flux along the surface. Because cracks on the polished surfaces are the same as the roots extending down, the probability for much larger intensification occurring is high. The results suggest that the surface laser-damage threshold of Nd-doped phosphate may decrease dramatically with subsurface damage.

Comparison of ion exchange and cw CO_2 laser treatment of Nd-doped phosphate laser glass

We investigate the relation of ion-exchange treatment and laser conditioning of a glass surface. The surface of Nd-doped phosphate laser glass was preirradiated with a cw CO(2) laser and strengthened by the ion-exchange treatment. It is shown that residual compressive stress occurs on the surface as peak-to-valley roughness and the appearance of microcracks decreases. Damage threshold of the glass surface increases by a factor of 1.7-3. The mechanism of laser conditioning is consistent with that of the ion-exchange treatment.

Laser properties of a new average-power Nd-doped phosphate glass

The Nd-doped phosphate laser glass described herein can withstand 2.3 times greater thermal loading without fracture, compared to APG-1 (commercially available Average-Power Glass from Schott Glass Technologies). The enhanced thermal loading capability is established on the basis of the intrinsic thermomechanical properties (expansion, conduction, fracture toughness, and Young's modulus), and by direct thermally induced fracture experiments using Ar-ion laser heating of the samples. This Nd-doped phosphate glass (referred to as APG-t) is found to be characterized by a 29% lower gain cross section and a 25% longer low-concentration emission lifetime. Other measurements pertaining to the concentration quenching, thermal lensing, and saturation of the extraction are also described in this article. It is note-worthy that APG-t offers increased bandwidth near the peak of the 1054 nm gain spectrum, suggesting that this material may have special utility as a means of generating and amplifying ultrashort pulses of light.

Measurements of heating and energy storage in flashlamp-pumped Nd:YAG and Nd-doped phosphate laser glasses

We have experimentally measured the energy stored and the heat generated in flashlamp-pumped Nd:YAG and six different commercially available Nd-doped phosphate glasses. We find that the normalized heating parameter <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</tex> , defined as the heat deposited per unit stored energy, is 1.5-2 times the value expected from the known spectroscopy of the Nd ions in these hosts and the emission spectrum of Xenon flashlamps. We discuss the heat sources in Nd-doped glasses. Using a theoretical model, we calculate the influence of Nd concentration, flashlamp pulse length, and current density on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</tex> , and we point out the effects of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</tex> on practical laser designs.

Gain saturation in Nd-doped phosphate laser glasses

We have studied saturation of gain in several Nd-doped phosphate glasses which are being evaluated for possible use in the Nova laser facility. Phosphate glass of excellent optical quality can be produced in sizes adequate to fabricate the large amplifier rods and disks needed for fusion lasers.