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Diffraction-limited mirrors used to produce ultra-high resolution holographic gratings

Optical Surfaces Ltd. is a leading international manufacturer of large diameter, ultra-smooth off-axis parabolic mirrors for demanding applications.

Looking to develop their next generation of ultra-high resolution holographic diffraction gratings – Wasatch Photonics (Logan, Utah, USA) commissioned Optical Surfaces Ltd. to manufacture two large diameter off-axis parabolic mirrors – key components in their production process.

Diffraction-limited mirrors used to produce ultra-high resolution holographic gratings

Widely used as optical components to separate light into its component wavelengths, Wasatch Photonics’ holographic diffraction gratings are key components in spectrometers, hyperspectral imaging systems, spectral-domain optical coherence tomography, and other photonics technologies. Holographic gratings are typically generated by imaging a series of closely spaced parallel lines into a light-sensitive material using an interferometric set-up. Producing holographic diffraction gratings of spectroscopic quality requires a stable optical bench and laser as well as the highest quality optical components (mirrors, collimating optics).

Dr. Aris Kouris, Sales Director at Optical Surfaces Ltd said, “In order to produce diffraction gratings using a holographic method, you need to produce a reference collimated beam at a relative angle to another collimated beam. The two collimated beams interact to produce an interference pattern, which is recorded on the holographic recording medium. If an ultra-high-resolution grating is required, it is important that the two beams are extremely well collimated with little wavefront error. However, another parameter that is also important is the slope error, which is a measure of the ‘smoothness’ achieved on the surface form. This quality parameter is critical to produce very high resolution, low noise gratings using the holographic method.”

He added, “Originally Wasatch Photonics contacted us to manufacture two 152mm diameter off-axis parabolic mirrors to a high specification (better than Lambda/10 P-V at 633nm) and we did so. These optical components were required as part of a test project to produce ultra-high resolution holographic gratings of 140mm diameter. In early tests it became apparent that the Lambda/10 P-V surface accuracy alone was not sufficient to produce holographic gratings of sufficient quality. After consultation on the matter, we suggested that improving the slope errors on the mirrors might be beneficial. After Wasatch Photonics shipped back the two 152mm diameter mirrors, we re-worked them to the improved slope error targets. The improved off-axis parabolic mirrors resulted in the customer being able to produce great quality ultra-high-resolution holographic gratings”.

Dr Kouris concluded, “As a result of this successful trial – Wasatch Photonics recently placed a follow-up order with Optical Surfaces Ltd. to produce two new 420mm diameter off-axis parabolic mirrors of similar quality to enable them to produce even larger ultra-high resolution holographic gratings”.

These projects are an example of the collaborative development approach taken by Optical Surfaces in collaborating with key customers, a process which continues beyond delivery of the quoted product. According to Process Engineering Manager Andrew Clawson of Wasatch Photonics, “Validation of any component or tool that comes into our facility is an important part of our quality program and allows us to maintain high standards of quality from start to end of our manufacturing process. Working with a supplier like Optical Surfaces who shares our philosophy of ‘getting it right’ and continuous improvement makes this so much easier and gives us the confidence that we have the right partners to deliver on newer, bigger projects.”

For further information on large off-axis parabolic mirrors with diffraction-limited surface quality please visit www.optisurf.com/index.php/products/off-axis-paraboloids/ or contact Optical Surfaces Ltd. on +44-208-668-6126 / sales@optisurf.com.

Wasatch Photonics holographic gratings deliver high efficiency, low polarization dependence, and uniform performance over broad bandwidths (UV / Visible / NIR) and large clear apertures – all in a robust, field-tested package. Drawing upon multiple patented design technologies, Wasatch Photonics offers the flexibility to recommend the best transmission grating for your unique application. For further information please visit https://wasatchphotonics.com/product-category/gratings-and-diffractive-optics/.

Elliptical Optical Flats & Coated Flat Mirrors

Optical Surfaces Ltd. is a leading manufacturer of large, high precision optical flats and coated flat mirrors including a range of non-circular shapes such as elliptical and octagonal.

Elliptical Optical Flats & Coated Flat Mirrors

Light weighted elliptical flat mirror

When the maximum possible clear aperture is required in a folded Newtonian or Cassegrain telescope design, the optical component of choice is an elliptically shaped coated flat mirror. Elliptical flat mirrors are used to fold and re-direct optical beams. Due to the elliptical geometry of the coated substrate, the aperture of a circular beam can be rotated by 45˚ around the minor axis without truncation.

Manufactured from highly stable optical materials such as Zerodur® or ClearCeram®-Z, Optical Surfaces talented optical engineers can regularly achieve surface accuracies of better than ʎ/10 peak to valley on elliptical optical flats up to 600mm length (long axis).

The most common coating on optical flats is aluminium which offers reasonable reflectivity in the UV, visible and mid-infrared spectral wavebands. Protected silver coatings provides the highest reflectivity for coated flat mirrors operating in the visible and protected gold is the most efficient coating for infrared applications.

Optical Surfaces Ltd. has for over 50 years, supplied uncoated optical flats, and coated flat mirrors to renowned astronomy and defence groups worldwide. The company’s unique thermally stable production environment has made them pre-eminent in applications requiring optical flats and coated flat mirrors. All optical flats from Optical Surfaces Ltd. come with full quality testing assurance. Optics up to 600 mm diameter are provided with a Fizeau interferometric test report, larger flats are quality assured using the Ritchey-Common test procedure.

For further information please visit www.optisurf.com/index.php/products/flats-and-windows/flats/ or contact Optical Surfaces Ltd. on +44-208-668-6126 or sales@optisurf.com.

Fast Focusing On-Axis Parabolic Mirrors

Optical Surfaces Ltd. is a leading producer of on-axis parabolic mirrors for ground-breaking applications in fundamental, high-power laser physics research.

Fast Focusing On-Axis Parabolic MirrorsBenefiting from an ultra-stable manufacturing environment and employing proprietary production techniques the highly experienced and skilled engineers at Optical Surfaces can, depending on the surface accuracy required, generate very fast focusing on-axis parabolic mirrors (< f 0.7).

On-axis parabola are the fast-focusing mirror of choice suitable for both broadband and multiple wavelength applications due to their completely achromatic performance. To optimise their performance – Optical Surfaces offers a range of protective mirror coatings including metallic, multilayer dielectric and ultra-hard coatings for the most demanding high-power lasers. Manufactured from materials including glass, ceramic, and silica – fast focusing on-axis parabolic mirrors from Optical Surfaces are designed to optimise the performance of ultra-high power pulsed lasers. All surface accuracies are checked by interferometer and are guaranteed to be better than λ/10 p-v wave accuracy with low scatter.

In combination with the latest dielectric coating technology – Optical Surfaces fast focusing on-axis mirrors provide minimum pulse distortion and the maximum usable bandwidth. For use with high-power femtosecond lasers operating at 750 to 850 nm, these fast-focusing mirrors can be used at power densities of up to 100 mJ/cm2 for continuous 50-fs pulses without deterioration. Production approved to ISO 9001-2015 the quality and performance of fast focusing on-axis parabolic mirrors from Optical Surfaces Ltd. is second to none.

Optical Surfaces Ltd has been producing optical components and systems for more than 50 years and is today accepted as one of the world’s leading manufacturers of high-precision optics for fundamental, high-power laser physics research.

For further information on fast-focusing on-axis parabolic mirrors please visit https://www.optisurf.com/index.php/on-axis-parabolic-mirrors/ or contact Optical Surfaces Ltd. on +44-208-668-6126 / sales@optisurf.com.

Growing Demand for Ultra-High Precision Optics

Optical Surfaces Ltd. (Kenley, UK) reports how strong demand for high precision optics and optical systems from the astronomy, fundamental physics and defence communities has enabled it to exceed its annual sales target after just 7-months of 2022. This follows a 20% growth in sales achieved in the previous 2 years.

Founded in 1962, Optical Surfaces Ltd is internationally recognised as a leading manufacturer of ultra-high precision optical components and opto-mechanical instruments. Optical Surfaces Ltd is especially renowned for its expertise in large diameter optics, off-axis parabolic mirrors, reference flats, beam expanders, optical collimators, and challenging prototypes.

Dr Aris Kouris, Sales Director commented “Our ISO 9001 approved manufacturing workshops and test facilities being deep underground in a series of tunnels excavated from solid chalk, where temperature remains constant and vibration is practically non-existent, gives us a natural advantage. Couple this with regular investment in optical research and development, state-of-the-art testing equipment and talented staff enables Optical Surfaces Ltd. to produce challenging one-off and small batches of optics and optical systems that deliver performance at the edge of what is possible”.

For further information please contact Optical Surfaces Ltd. on +44-208-668-6126 / sales@optisurf.com.

Ultra-High Precision Optics

Ultra-High Precision Optics

Ultra-High Precision Optics

Ultra-High Precision Optics

High magnification beam expander for small aperture applications

30x magnification A1-Series reflective beam

30x magnification A1-Series reflective beam

Optical Surfaces Ltd. has developed a new compact beam expander that uniquely delivers high magnification (x30) from small aperture (2mm) high power laser beam lines.

Traditionally the combination of small aperture and high beam magnification is difficult to manufacture because the optics associated with such a beam expander are difficult to test using state of the art interferometers. The difficulty arises from the fact that small aperture laser beams, when highly magnified, generate artifacts within the interferometer making it extremely hard to distinguish and analyse what are true errors and what are artificial errors.

Working with a customer, Optical Surfaces Ltd. examined the options to manufacture a small aperture beam expander able to deliver artifact-free high magnification. The options presented to the customer were to use either a transmissive (lens-based) or a reflective (mirror-based) beam expander approach to their application. Drawing upon over 50 years’ experience of serving the high-power laser community, Optical Surfaces Ltd. advised that the use of reflective beam expanders would be particularly useful for high energy applications with lasers operating within the femtosecond pulses regime. This is because the wavelength bandwidth in such applications is relatively large, and a reflective solution allows fully achromatic operation. Also, the coatings on a lens-based beam expander may not be suitable to withstand the high energy intensities typically encountered in such applications, in contrast to the proven hard dielectric coating options available for reflective mirrors.

Working on this project – Optical Surfaces Ltd has developed a proprietary method to suppress the artefacts shown by interferometers during testing thereby making it possible to manufacture such a high magnification (30x) reflective beam expander for small aperture applications.

The new 30x magnification A1-Series reflective beam expander incorporates high precision off-axis mirrors which have constant focal lengths, regardless of the wavelength of light being focused. Unlike lens-based beam expanders, the new high magnification beam expander can be used with collimated polychromatic light without the need of any fine focus adjustment.

Supplied housed in a robust aluminium cover – the 30x magnification A1-Series beam expander comes with provision for secure fixing to an optical table. Alignment aids are provided to ensure correct beam pointing and tracking during integration. Manufactured to better than lambda/5 transmitted wavefront accuracy, the 30x magnification reflective beam expander produces no central obscuration and highly efficient transmission is obtained, unspoilt by diffraction patterns.

For further information on the 30x magnification A1-Series reflective beam expander please visit www.optisurf.com/index.php/products/reflective-beam-expander/ or contact Optical Surfaces Ltd. on +44-208-668-6126 / sales@optisurf.com.

Reference Flat Mirrors for Satellite Telescope Performance Verification

A large diameter mounted reference flat mirror

A large diameter mounted reference flat mirror

Optical Surfaces Ltd. reports how its high precision reference flat mirrors are enabling testing and precise alignment of Earth observation satellite telescopes.

Today, satellite images play a major role in gathering information about the Earth’s ecosphere. This data, obtained by satellite-based optical telescopes provides valuable information about geological features, urban development, weather phenomena, and increasingly reliable prediction of crop yields, which are being impacted by the effects of climate change.

To obtain accurate information, with high spatial resolution, it is vital that these earth observation satellite telescopes undergo a rigorous process of testing and alignment before they are launched into space.Reference flat mirrors are a proven method of measuring the surface accuracy or the transmitted wavefront of optics. However, there are very few suppliers who can produce large flat mirrors with the ultra-high precision specifications required to verify the wavefront performance of an Earth observation telescope during its assembly and be used as an alignment aid.

An Earth Observation satellite being constructed

An earth observation satellite being constructed (courtesy: SSTL)

Dr Aris Kouris, Sales Director at Optical Surfaces Ltd said “We have been producing large optical components and systems for more than 50 years and are widely accepted as one of Europe’s leading manufacturers of high-precision optics for satellite deployment and astronomical research. Our skilled staff have many years’ experiences of producing the large diameter (up to 600mm) flat mirrors with surface accuracies of lambda / 15 at 633nm are often required to test Earth observation satellite telescope systems”. He added “Our ISO 9001-2015 approved manufacturing workshops and test facilities are deep underground in a series of tunnels excavated in solid chalk where temperature remains constant and vibration is practically non-existent, this gives us a natural advantage when producing and testing high precision reference flat mirrors”.

For further information on high precision reference flat mirrors for performance verification and alignment of satellite telescopes please visit www.optisurf.com/index.php/products/flats-and-windows/flats/ or contact Optical Surfaces Ltd. on +44-208-668-6126 / sales@optisurf.com.

High Precision Prototype & Custom Optics

Program of Investment

Benefiting from a uniquely stable manufacturing environment – Optical Surfaces Ltd. can routinely produce challenging prototype and custom optics to the highest levels of precision possible.

The company’s ISO 9001-2015 approved manufacturing workshops and test facilities are deep underground in an area excavated from solid chalk. This provides an environment where the temperature is naturally constant, and vibration is extremely low. These are important considerations when making, mounting, and testing high precision optics.

Light Weighted Mirrors

Working with these natural advantages Optical Surfaces can supply high precision off-axis parabolic, spherical, and flat mirrors, etalons, aspherics, reference flats, windows, collimators, and beam expanders for the most demanding applications. With such stable conditions testing, particularly with long path lengths, becomes quantifiable and reliable. Investment in large aperture interferometers allow detailed direct testing of optics up to 600mm in diameter. Topographic and fringe analysis provides precise testing of surface roughness and confirms the wavefront of various surface forms. A rolling program for calibration of test optics where possible to national standards ensures that the quality of prototype and custom optics from Optical Surfaces is second to none.

Combining these natural advantages, with its team of experienced and knowledgeable optical craftsmen, Optical Surfaces Ltd has over the last 50 years produced the ultra-high precision prototype and custom optics that lie behind technological breakthroughs in areas including fundamental physics, astronomy, space, defence, medical, material sciences and the environment.

For further information on high precision prototype and custom optics please contact Optical Surfaces Ltd. on +44-208-668-6126 / sales@optisurf.com.

Telescope System for Zettawatt Equivalent Laser

Optical Surfaces Ltd has been selected by the Gérard Mourou Center for Ultrafast Optical Science (CUOS) at the University of Michigan (USA) to provide beam expander optics for its ground-breaking Zettawatt-Equivalent Ultrashort pulse laser System (ZEUS).Sponsored by the U.S. National Science Foundation, the ZEUS laser facility is being constructed to allow a Petawatt laser pulse from one of its beamlines to collide with a beam of GeV-energy electrons generated by its other beamline. In this collision, the electrons will encounter a Zettawatt (1021 watt) equivalent laser power as measured in their rest frame.

Telescope System for Zettawatt Equivalent Laser

CUOS researchers performing multidisciplinary research on the applications of ultrashort laser pulsers (courtesy; University of Michigan).

John Nees, a research scientist at CUOS said “The construction of the ZEUS facility began in 2020 and is slated to be operational in 2024. Among its numerous challenges, the Chirped-Pulse Amplified (CPA**) laser system requires an ‘aberration-free’ telescope to deliver the fully amplified pulses at a safe fluence to the 3 Petawatt compressor where their power is increased 50,000-fold for experimental use. The telescope comprises a 170 mm diameter convex aspheric mirror and a 255 mm positive spherical mirror used in an off-axis design. As a leading manufacturer of ultra-high precision Petawatt laser optics we selected Optical Surfaces Ltd. to fabricate the precision mirror substrates that will be coated and used to expand the pulsed beam diameter from 140 mm to 305 mm”. He added “I really did appreciate Optical Surfaces energetic responses to my inquiries as I was planning the telescope. Their knowledgeable input gave me a good comfort level in moving the project forward”.

Director of Sales at Optical Surfaces Ltd. – Dr Aris Kouris commented “We are honoured to be selected by CUOS as the supplier of high precision beam expander for this prestigious project. With this ZEUS laser system, the CUOS team is excited about the possibility of probing quantum electrodynamics, the reigning explanation of how the universe operates at the subatomic level. In addition, ZEUS could help develop new methods and technologies for use in medicine, defence, material science and astrophysics”.

Off-axis beam expander optics (courtesy: Optical Surfaces Ltd)

Off-axis beam expander optics.

Globally, only a few optical manufacturers can produce off-axis optics as part of the delivery system of sufficient surface quality to enable ultra-high-power lasers to focus their massive energy onto targets only a few microns in size. Under these extreme conditions the laser-matter interactions can produce energetic beams of electrons and protons as well as bright, coherent sources of x-rays which enable researchers to address fundamental questions in areas including plasma physics, x-ray radiography, proton therapy and fast ignition experiments. Using in-house production techniques developed over the last 50 years and benefiting from a highly stable manufacturing environment largely immune from vibration and thermal variation, the company’s experienced and skilled engineering team can produce fast-focusing off-axis mirrors with unmatched surface accuracy, surface quality and surface slope errors.

The company’s ISO 9001-2015 approved manufacturing workshops and test facilities are deep underground in a series of tunnels excavated in solid chalk. This provides an environment where temperature is naturally thermally stable, and vibration is extremely low. With such stable conditions testing of high precision mirrors, particularly with long path lengths, becomes quantifiable and reliable. In addition to these natural advantages, Optical Surfaces has invested in an extensive range of test equipment and have developed methods to ensure accurate and reliable testing.

For further information on the pioneering work of the Gérard Mourou Center for Ultrafast Optical Science (CUOS) at the University of Michigan visit https://zeus.engin.umich.edu/. To discuss development of ultra-high precision optics for your high-power laser facility please contact Optical Surfaces Ltd on +44-208-668-6126 or sales@optisurf.com.

** The invention of the Chirped Pulse Amplification (CPA) laser system was the basis for awarding the 2018 Nobel Prize in Physics to Gérard Mourou and Donna Strickland. See https://www.nobelprize.org/prizes/physics/2018/summary/

Large Optical Windows for Military Sensing Applications

Optical Surfaces Ltd is an established manufacturer and supplier of large-area windows of optical quality for military sensing applications.

Optical windows are a critical component in a variety of defence applications including aerial surveillance, reconnaissance and targeting. For over 50 years – Optical Surfaces Ltd has been working with materials including fused silica, BK-7 and Germanium to produce defence grade windows up to 600mm in diameter.

Large Diameter Reference Optical Flats

A large diameter reference optical flat being quality tested

Typically, large diameter optical windows for defence applications are used to provide
environmental protection for sensitive internal sensing systems. To transmit light with minimal disruption, these large diameter optical windows must exhibit low surface roughness, minimal transmitted wavefront errors, and high transmission at the desired operational wavelength range.

Benefiting from an ultra-stable production environment and proprietary polishing techniques – Optical Surfaces Ltd. can routinely produce large diameter optical windows with typical wavefront error of up to lambda/20 p-v, surface roughness of less than 10 Å rms and surface finish of 40/20 to 10/5 scratch / dig.

Dr Aris Kouris – Sales Director of Optical Surfaces Ltd commented “To enable us to quality test large diameter optical windows – we developed a 600mm Fizeau interferometer. This is a capability that only a few optical testing and manufacturing centres around the world possess. Housed in an ultra-stable testing environment, this interferometric set-up allows direct qualification of large diameter optical windows by testing them directly over their complete aperture without the need to use time-consuming combination methods”.

For further information on large diameter windows for military sensing applications please visit www.optisurf.com/index.php/products/flats-and-windows/windows/ or contact Optical Surfaces Ltd. on +44-208-668-6126 / sales@optisurf.com.

Infrared Collimators for performance testing of Thermal Cameras

Optical Surfaces Ltd. is a leading supplier of off-axis parabolic and flat mirrors, the key optical elements in Infrared (IR) collimators commonly used for evaluating the performance of thermal imaging systems.

Infrared Collimators for performance testing of Thermal CamerasThe function of an IR collimator is to generate a thermal image closely resembling the thermal scene at a test plate. Performance tests often performed on Thermal Imaging systems include measurement of the Minimum Resolvable Temperature Difference (MRTD) and the Modulation Transfer Function (MTF). The importance of MRTD testing lies in the fact that it relates to a thermal imaging system’s effectiveness for discerning details in a scene. MRTD values provide estimates of resolution capability allowing comparison of one thermal imaging system with another. The MTF is a tool for optical designers to quantify the overall imaging performance of a system in terms of resolution and contrast. Knowledge of the MTF curves of the lenses and camera sensors involved in a thermal imager may be used for quantification and optimization of the system performance.

Parabolic mirrors are the most common type of aspheric used in optical instruments. They are free from spherical aberrations, and therefore can focus a parallel beam to a point or a point source to infinity. Off-axis parabolic mirrors provide an unobstructed aperture allowing complete access to the focal region as well as reducing the size and minimising the weight of a design. They are especially suitable for infrared waveband applications due to their completely achromatic performance. Using proprietary polishing techniques, the team of experienced engineers and craftsmen at Optical Surfaces Ltd. can routinely produce a surface accuracy of better than lambda/20 p.v. and surface roughness of less than 1nm on off-axis parabolic mirrors produced for IR Collimators.

Working with high-stability materials such as Fused Quartz and Zerodur, in a unique thermally stable manufacturing environment, Optical Surfaces Ltd can routinely achieve a surface accuracy of better than lambda/10 p.v. and surface roughness of less than 1nm on flat mirrors. Over the years – Optical Surfaces has developed expertise to mitigate the uncertainties associated with coating to ensure flatness of mirrors, and hence is able to improve the performance of flat mirrors used in IR Collimators.

For further information on ultra-smooth off-axis parabolic and flat mirrors for high performance IR Collimator systems contact Optical Surfaces Ltd. on +44-208-668-6126 / sales@optisurf.com.

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