Surface integrity of precision ground fused silica for high power laser applications

AbstractSurface integrity of optics used in high power laser systems is vital to their successful application. Reduction of subsurface damage is demanded during their processing. Rapid grinding of large and complex shape optics can be performed using the BoX® ultra precision grinding machine. Importantly, the depth of subsurface damage induced, even at high material removal rates, has been shown to be very small in comparison to previous studies. In this paper, grinding experiments have been conducted to verify the amount of defects beneath ground fused silica surfaces produced under selected processing conditions. The subsurface damage levels were revealed using a sub-aperture polishing process in combination with an etching technique. Observed subsurface damage can be separated in two distinct depth zones characterised as ‘process’ and ‘machine dynamics’ related

Light source selection for a solar simulator for thermal applications: A review

Solar simulators are used to test components and systems under controlled and repeatable conditions, often in locations with unsuitable insolation for outdoor testing. The growth in renewable energy generation has led to an increased need to develop, manufacture and test components and subsystems for solar thermal, photovoltaic (PV), and concentrating optics for both thermal and electrical solar applications. At the heart of any solar simulator is the light source itself. This paper reviews the light sources available for both low and high-flux solar simulators used for thermal applications. Criteria considered include a comparison of the lamp wavelength spectrum with the solar spectrum, lamp intensity, cost, stability, durability, and any hazards associated with use. Four main lamp types are discussed in detail, namely argon arc, the metal halide, tungsten halogen lamp, and xenon arc lamps. In addition to describing the characteristics of each lamp type, the popularity of usage of each type over time is also indicated. This is followed by guidelines for selecting a suitable lamp, depending on the requirements of the user and the criteria applied for selection. The appropriate international standards are also addressed and discussed. The review shows that metal halide and xenon arc lamps predominate, since both provide a good spectral match to the solar output. The xenon lamp provides a more intense and stable output, but has the disadvantages of being a high-pressure component, requiring infrared filtering, and the need of a more complex and expensive power supply. As a result, many new solar simulators prefer metal halide lamps

Parameters Influencing the Output Precision of a Lens-Lens Beam Generator Solar Concentrator

The Lens-Lens Beam Generator (LLBG) is a Fresnel-based optical concentrating technique which provides flexibility in selecting the solar receiver location compared to conventional techniques through generating a powerful concentrated collimated solar beam. In order to achieve that, two successive lenses are used and followed by a flat mirror. Hence the generated beam emerging from the LLBG has a high power flux which impinges on the target receiver, it is important to determine the precision of the system output. In this present work, mathematical investigation of different parameters affecting the precision of the output beam is carried out. These parameters include: Deflection in sun-facing lens and its holding arm, delay in updating the solar tracking system, and the flat mirror surface flatness. Moreover, relationships that describe the power lost due to the effect of each parameter are derived in this study

Design and fabrication of a coating research machine to explore the nanometer scale coating of glass tubes for Concentrating Solar Power (CSP) systems

This paper presents the design and fabrication of a precision designed CSP receiver tube coating machine for research purposes, designed to deposit and examine the properties of novel anti-reflection (AR) coatings possessing a thickness in the nanometre range. The manufacturing process chain and in line thickness control technique are also described

Design and fabrication of a coating research machine to explore the nanometer scale coating of glass tubes for Concentrating Solar Power (CSP) systems

This paper presents the design and fabrication of a precision designed CSP receiver tube coating machine for research purposes, designed to deposit and examine the properties of novel anti-reflection (AR) coatings possessing a thickness in the nanometre range. The manufacturing process chain and in line thickness control technique are also described

Comparison of the subsurface damage induced when precision grinding ULE® and Zerodur® surfaces

A precise and rapid grinding process, with low levels of surface waviness and subsurface damage, can improve the total cycle time for producing large ULE® and Zerodur® optics. In this paper, the subsurface damage level of ULE® and Zerodur® were investigated and compared. Resin bonded diamond cup wheels were employed. The grinding response was characterized by measuring: surface roughness, surface profile and subsurface damage. The amount of defects beneath ULE® and Zerodur® surfaces ground using the selected grinding mode were compared. The observed subsurface damage can be separated in two distinct depth zones, the first 'process' related and the second being 'machine dynamics' related

Wheel Wear and Surface/Subsurface Qualities when Precision Grinding Optical Materials

An ultra precision large optics grinder, which will provide a rapid and economic solution for grinding large off-axis aspherical and free-form optical components, has been developed at Cranfield University. This paper presents representative grinding experiments performed on another machine - a 5 axes Edgetek - in order to verify the proposed BoX(r) grinding cycle. The optical materials assessed included; Zerodur(r), SIC and ULE(r), all three being materials are candidates for extreme large telescope (ELT) mirror segments. Investigated removal rates ranged from 2mm3/s to 200mm3/s. The higher removal rate ensures that a 1 metre size optic could be ground in less than 10 hours. These experiments point out the effect of diamond grit size on the surface quality and wheel wear. The power and forces for each material type at differing removal rates are presented, together with subsurface damage

Subsurface damage in precision ground ULE (R) and Zerodur (R) surfaces

The total process cycle time for large ULE® and Zerodur® optics can be improved using a precise and rapid grinding process, with low levels of surface waviness and subsurface damage. In this paper, the amounts of defects beneath ULE® and Zerodur® surfaces ground using a selected grinding mode were compared. The grinding response was characterised by measuring: surface roughness, surface profile and subsurface damage. The observed subsurface damage can be separated into two distinct depth zones, which are: ‘process’ and ‘machine dynamics’ related