Fused Silica Block Research Articles

Investigation of the origin of anomalous eutectic formation by remelting thin-gauge samples of an Ag-Cu eutectic alloy

Sandwiched between two fused silica blocks, thin-gauge samples of Ag-39.9 at.%Cu eutectic alloy were solidified over a range of undercoolings. Subsequently, the samples that consisted consistently of fully lamellar eutectic were rapidly heated to a target temperature below the eutectic temperature. Increasing the initial undercooling prior to solidification or the target temperature of heating led to more anomalous eutectic and worse orientation of phases in the final microstructure. It is conclusively indicated that the formation of anomalous eutectic in bulk samples results from remelting of the primary lamellar eutectic.

Filamentation and supercontinuum emission with flattened femtosecond laser beam by use of microlens array in fused silica

The high power supercontinuum from femtosecond filamentation has attracted great attention for recent years due to its various applications. In our previous researches, we have used microlens array to obtain filament-array in fused silica and to generate the high spectral power supercontinuum. To further improve the ability to generate the high power supercontinuum by using microlens array, in this work we adopt flattened femtosecond laser beam with a flat-top energy distribution to generate filament-array in fused silica and supercontinuum. By using a laser beam shaping system consisting of aspherical lenses, the Gaussian intensity distribution of initial femtosecond laser beam is converted into a flat-top distribution. The flattened laser beam is focused by a microlens array into a fused silica block, and consequently a filament array is formed in the block. Our experimental results show that compared with the filaments formed by a Gaussian laser beam, the filaments formed by the flattened beam have a uniform distribution and almost the same onset due to the initial uniform energy distribution across the section of the laser beam. Furthermore, the spectral stability of supercontinuum emission is used to evaluate the damage of the fused silica block. It is demonstrated that the flattened beam with a pulse energy of 1.9 mJ does not induce permanent damage to the fused silica block, while the Gaussian beam with a relatively low pulse energy of 1.46 mJ leads to the damage to the block. Therefore, a higher incident laser pulse energy is allowed in the case of flattened laser beam, and consequently stronger supercontinuum generation than in the case of the Gaussian laser beam can be expected. In our experiments, the relative spectral intensity of flattened beam generated supercontinuum in the visible range is about twice higher than that for the Gaussian beam case. The conversion efficiencies of the supercontinuum for the two kinds of laser beams are further analyzed. The conversion efficiencies are 49% and 55% for the cases of Gaussian and flattened beams respectively. In this work, we demonstrate the formation of filament array with uniform distribution in fused silica, and, as a proof of principle, we also demonstrate the high power supercontinuum generation with high conversion efficiency from the filamentation, by using flattened femtosecond laser beam as the incident laser and microlens array as the focusing element. This approach provides a way to obtain a high power femtosecond supercontinuum source which is of great importance in many applications such as some absorption spectroscopies based on coherent supercontinuum light.

Generation of sub-two-cycle millijoule infrared pulses in an optical parametric chirped-pulse amplifier and their application to soft x-ray absorption spectroscopy with high-flux high harmonics

An optical parametric chirped-pulse amplifier (OPCPA) based on bismuth triborate (BiB3O6, BIBO) crystals has been developed to deliver 1.5 mJ, 10.1 fs optical pulses around 1.6 μm with a repetition rate of 1 kHz and a stable carrier-envelope phase. The seed and pump pulses of the BIBO-based OPCPA are provided from two Ti:sapphire chirped-pulse amplification (CPA) systems. In both CPA systems, transmission gratings are used in the stretchers and compressors that result in a high throughput and robust operation without causing any thermal problem and optical damage. The seed pulses of the OPCPA are generated by intrapulse frequency mixing of a spectrally broadened continuum, temporally stretched to approximately 5 ps then, and amplified to more than 1.5 mJ. The amplified pulses are compressed in a fused silica block down to 10.1 fs. This BIBO-based OPCPA has been applied to high-flux high harmonic generation beyond the carbon K edge at 284 eV. The high-flux soft-x-ray continuum allows measuring the x-ray absorption near-edge structure of the carbon K edge within 2 min, which is shorter than a typical measurement time using synchrotron-based light sources. This laser-based table-top soft-x-ray source is a promising candidate for ultrafast soft x-ray spectroscopy with femtosecond to attosecond time resolution.

High-energy, sub-nanosecond linearly polarized passively Q-switched MOPA laser system

This study introduces a linearly polarized laser with a 0.6J output energy and a 420ps pulse width. Accordingly, [111]-cut Nd:YAG and [110]-cut Cr4+:YAG crystals are used to fabricate a linearly polarized seed laser. One side of both crystals is configured with a Brewster angle to enhance the extinction ratio of polarization. The output energy and the pulse duration of the seed laser are 2.51mJ and 552ps, respectively. The seed laser pulse is compressed to 420ps using a fused-silica block, while its energy is amplified to 600mJ. The output energy instability over a 90min operation is ±4.7%.

Refractories for Coke Oven Wall – Operator’s Perspective

After a successful campaign of more than 40 years, the walls of Coke Plant 2 of Tata IJmuiden are being replaced. Our paper addresses the issues of the selection and sourcing of the refractory materials for the new walls. Material properties formalised in the specification are reviewed. Those are compared with the properties of alternative silica refractories available on the market. Both conventional silica bricks and relatively new fused silica blocks are evaluated. The discussion is based on thermo-physical data obtained in-house and from plant experience. It is argued that, due to specific lining design and material properties, the coke oven wall refractories are not off-the shelf products that can be sourced on a short notice from any supplier. An extensive pre-order effort is mandatory before the acceptable material and supplier are selected and the order is placed.

Modeling of Grout Propagation in Transparent Replica of Rock Fractures

Abstract This paper presents an experimental investigation on the injection of chemicals into rock fractures by using a transparent replica to visualize grout propagation. The fractured rock mass is simulated by using fused silica blocks, fused silica grains and mineral oils. Fused silica blocks in a cubic form are used to form rock mass and the fused silica grains are used to fill the space between these blocks to simulate fractures with a certain aperture. In addition, a mixed mineral oil that has the same refractive index as that of the fused silica blocks and grains is used to simulate fluid and groundwater. The experimental setup consists of a Plexiglas container, loading frame, grout injection system, and three black and white charge-coupled device (CCD) cameras. A modified urea-formaldehyde resin and an acid solution are mixed together as the grout. The point source of the grouting is simulated by using an injection needle inserted into the model. As the silica blocks are impermeable, the grout instead propagates into the fractures that are filled with silica sand. Propagation images during the grouting are captured by using the CCD cameras. Digital image processing is then applied to analyze the grayscale pictures to detect the edge of the grout front and calculate the grout penetration length at different times. The shape of the boundary of the grout–groundwater interface is found to be spherical when the fractures are filled with porous transparent materials. The results indicate that the flow velocity calculated by using a modified cubic law is in good agreement with the measured penetration length in the images. The results also verify the possibility of the use of a transparent replica to visualize grout propagation inside a fractured rock mass so as to understand grout propagation during grouting.

Generation of ultrashort intense optical pulses at 1.6 μm from a bismuth triborate-based optical parametric chirped pulse amplifier with carrier-envelope phase stabilization

We describe a few-cycle intense optical parametric chirped pulse amplifier (OPCPA) in the IR that is based on bismuth triborate (BiB3O6, BIBO) crystals. Two Ti:sapphire chirped pulse amplification systems are used to generate seed and pump pulses for the OPCPA. Carrier-envelope phase (CEP)-stabilized seed pulses in the IR are produced by difference frequency mixing of white light spanning from the visible to near IR range. The seed pulses, which have a nearly one octave-spanning spectrum around 1.6 μm, are temporally stretched in an acousto-optic programmable dispersive filter and amplified up to 550 μJ in two BIBO-based parametric amplifiers without losing their bandwidth. After compression in a fused silica block, we obtained 9.2 fs optical pulses with a repetition rate of 1 kHz, which comprise less than two optical cycles at 1.6 μm. These optical pulses were used to generate extreme ultraviolet (XUV) high harmonics in krypton. We succeeded in measuring the CEP dependence of the XUV radiation near the silicon L edge around 100 eV, verifying the passive stabilization of the CEP of the sub-two cycle IR pulses. The XUV spectra consist of two half-cycle cutoffs and show a clear transition from a modulated structure to a continuum near the cutoff. The continuum-like spectra as well as their CEP dependence indicate that they originate in a single recombination burst, showing that few-cycle IR OPCPA light sources are capable of generating attosecond pulses in the XUV region.

Etching and forward transfer of fused silica in solid-phase by femtosecond laser-induced solid etching (LISE)

We present a femtosecond laser-based technique for etching and forward transfer of bulk transparent materials in solid-phase. Femtosecond laser pulses with λ = 800 nm were focused through a fused silica block onto an absorbing thin film of Cr. A constraining Si wafer was pressed into tight contact with the Cr film to prevent lift-off of the film. A combination of the high temperature and pressure of the Cr, and compressive stress from the Si, resulted in etching of smooth features from the fused silica by cracking. Unlike in conventional ablative or chemical etching, the silica was removed from the bulk as single solid-phase pieces which could be collected on the Si. Using this so-called laser-induced solid etching (LISE) technique, 1–2 μ m deep pits and channels have been produced in the silica surface, and corresponding dots and lines deposited on the Si. The threshold fluence for etching was found to be ≈ 0.4 J/cm 2 with ≈ 130 fs duration pulses. The morphology of the etched features are investigated as functions of fluence and exposure to multiple pulses.

Energy spectrum evolution of a diffuse field in an elastic body caused by weak nonlinearity.

We study the evolution of diffuse elastodynamic spectral energy density under the influence of weak nonlinearity. It is shown that the rate of change of this quantity is given by a convolution of the linear energy at two frequencies. Quantitative estimates are given for sample aluminum and fused silica blocks of experimental interest.

Fabrication and characterization of pH sensor based on side polished single mode optical fiber

Abstract Fabrication and characterization of side-polished single mode optical fiber pH sensor utilizing evanescent field absorption spectroscopy and dye doped sol–gel immobilization technology are presented. The sensor is prepared by fixing the fiber in a groove made on one of the surfaces of a fused silica block. To make the surface sensitive to pH it is polished up to the core of the fiber and a film containing a mixture of three pH sensitive dyes is coated on it using sol–gel technology. The influence of the radius of curvature of the groove on the sensitivity of the sensor is studied. The decrease in the radius of curvature of the groove increases the sensitivity. This occurs due to the increase in the evanescent field and hence its interaction with the pH sensitive dyes entrapped in the film. The advantage of the side-polished single mode optical fiber sensor is that only 0.1 ml of sample is sufficient to measure the pH of the fluid. This is important when the procurement of the sample in large quantity is not possible.

Mechanical quality factors of fused silica resonators

We have measured the room temperature resonant quality factors Q for a large set of resonant modes for each of several fused silica blocks and one fused silica cylinder. The modal frequencies ranged from 7.8 to 50 kHz. Our best results were obtained when the samples were suspended in a single loop of fine wire. For every sample tested we have measured at least one mode with Q⩾107. Our highest Q for any sample measured was (1.86±0.06)×107 for a block resonating at 26.4 kHz. Our tests included several different types of high purity fused silica, but could not detect any significant differences in mechanical loss. We believe our Q measurements are limited by losses due to our suspensions, as Q depends strongly on the shape of each resonant mode and the proximity of each mode’s nodal regions to the wire suspension points.

Empirical Study of the Effect of Diffraction on Velocity of Propagation of High-Frequency Ultrasonic Waves

The effect of diffraction in increasing the velocity of propagation over the plane wave value is determined experimentally by phase comparison of reflected longitudinal waves in fused silica blocks. It is shown that the parameters of transducer diameter, path length traveled, and frequency can usually be adjusted to keep the fractional excess velocity under 0.02% for measurements in the 20–100-Mc range. This consideration is of particular importance in connection with precision measurement of elastic moduli.