UK OPTICAL DESIGNERS’ MEETING
Thursday 16th September 2010
Culham Centre for Fusion Energy, Abingdon, Oxfordshire OX14 3DB
Abstracts
Seeing Beyond Skin in Three Dimensions The optics and optical design of a Gabor domain optical coherence microscope with imbedded liquid lens
Jannick P. Rolland,
The Brian Thompson Chair Professor of Optical Engineering
Professor of Biomedical Engineering
University of Rochester, Institute of Optics
with coauthors Supraja Murali, Panomsak Meemon, Kye-sung Lee, and K.P. Thompson all of, or in affiliation with, the University of Rochester, Institute of Optics
This talk will show recent results in the development of an Optical Coherence Microscope (OCM) that implements a VariOptic liquid lens to embedded in a custom microscope design developed within the ODALab at the University of Rochester and built at General Optics Asia, Ltd. OCM uses a broadband light source in the near-IR to create a virtual slit of the type that enables confocal microscopy by creating a narrow axial coherence function that allows filtering out the scattered light that develops throughout the path of the beam through the skin. While the technology, invented by Fujimoto in 1991 has evolved to achieve micron-level axial resolution, it has had poor lateral resolution, typically 20 microns. To be effective in skin imaging, it is essential to achieve subcellular lateral resolution, which means a few microns. We recently developed a breakthrough approach, Gabor-domain OCM that for the first time results in subcellular resolution in all three dimensions. This talk will present the microscope and liquid lens optical design and testing and show some of the recent results in subcellular imaging through the skin.
Airy Beams and Gouy Phase; Are they only curiosities?
Applying recent advances in the science of beam propagation
Kevin P. Thompson,
Vice President of Optical Engineering Services, Optical Research Associates,
Visiting Scientist, University of Rochester, Institute of Optics
with coauthors Sophie Vo, Kyle Fuerschbach, Charlotte Pachot, Tobias Schmid, Prof. Miguel Alonso, and Prof. Jannick P. Rolland, all of, or in affiliation with, the University of Rochester, Institute of OpticsPart I: Our attention was recently caught by an article on Airy beams. First discovered in 1979 as a special case solution of the Schrodinger wave equation, they were created experimentally in 2006. In addition to being placed in a class of nondiffracting beams, they have been said to have properties that could, if harnessed, result in light “turning corners” as it propagates. On investigation from the ground up (starting from paraxial optics and geometric aberration theory), rather than top down (quantum theory), we have found that in fact these beams do lie within the domain of classical geometric optics and are in fact simply a special, in fact a very special, case of a specific combination of 3rd order Seidel coma and 5th order coma. This talk will highlight where these beams fall in the spectrum of comatic wavefronts and illustrate what confluence of events leads to their special properties. In particular we will comment on how the concept of centroid shift in comatic beams has been perhaps mis-marketed to envision exotic light beams of the future. We will also show how they have been created in the laboratory at the University of Rochester using only an adaptive mirror from Imagine Optics and compare the experimental wavefront measurements with results that use new methodologies in wave propagation that have recently been introduced in CODE V after over 5 years of development.
with coauthors Kye Sung-Lee, John Tamkin Jr., Tobias Schmid, and Prof. Jannick P. Rolland, all of, or in affiliation with, the University of Rochester, Institute of Optics
Part II: We were recently asked if an experiment could be constructed that would verify a theoretical prediction. The premise was that the Gouy phase shift, originally predicted in 1896 for the π (pi) phase shift of a spherical wavefront in passing through focus and experimentally demonstrated would in fact manifest, as also mentioned by Gouy himself, as a π/2 (pi/2) phase shift if an astigmatic beam was studied. Recalling an experimental setup published by Mertz in 1959 based on what is now referred to as a Sagnac triangle interferometer, this team agreed to investigate the Gouy phase shift of astigmatic beams. Here we will summarize the theoretical predictions and then compare them with results of the experiment (accomplished with a collimated beam exiting a ZYGO 4” interferometer, a beam splitter cube, cylinder lenses, and two fold-mirrors) and with comparative simulation results that use a new algorithm for beam propagation far from focus using CODE V.
HARMONI - An Optical Design for a Work-horse First Light Instrument for the European Extremely Large Telescope (E-ELT)
Niranjan Thatte, Fraser Clarke, Matthias Tecza and the HARMONI Consortium
Astrophysics Department, University of Oxford
David Freeman, Optical Design Consultant for Kidger Optics Associates
HARMONI is a visible and near IR Integral Field Spectrograph proposed for the 42 metre European Extremely Large Telescope, operating at one of the Nasmyth foci. It enables the study of galaxy formation from observations of high redshift galaxies at high spatial and moderate spectral resolution to near diffraction limited, high spectral resolution observations of low mass stars and planets. To meet its science objectives, HARMONI needs a large field-of view with interchangeable spatial and spectral scales. This cannot be achieved with a single spectrograph and the field is split in two stages into eight sub-spectrographs each imaging onto a 4k x 4k detector array. The problems of meeting these requirements with a (relatively) low risk optical design will be presented together with an assessment of the optical manufacturing and assembly requirements.
Large Radiation Resistant Optics
Roger B Huxford,
RBH Optics
Thomson Scattering is a very powerful diagnostic tool used for analysing the condition of plasmas generated in Fusion Reactors. Powerful lasers are used to stimulate emissions from the plasma and these emissions are captured by lens systems that are often positioned in hostile and difficult to access locations. This presentation will discuss the requirements, design, manufacture and implementation of the Collection Optics for the United Kingdom Atomic Energy Authority (UKAEA) Culham MAST Thomson Scattering Diagnostic.
Tolerancing Free-Form Optics for Illumination
Andreas Timinger,
OEC AG, Lindwurmstr. 41
80807 Muenchen, Germany
Free form surfaces allow elegant solutions in illumination optics. A complex function of the system, defined e.g. by an asymmetric intensity distribution can be achieved by a single optical element. Common applications are automotive lighting, street lighting or architectural lighting.
Free-form elements are usually manufactured by reproduction techniques, such as injection moulding of plastic. Manufacturing tolerances are crucial to maintain the required function while yielding the lowest price possible at the same time. We implemented a Monte Carlo tolerancing method for illumination systems. Tolerances include typical shape deviations of free-form elements, shape deviations of standard elements and positioning tolerances.
Our procedure consists of the following steps:
An ensemble of systems with random values for all tolerances is defined.
Ray tracing assesses the optical function, such as illuminance distributions or optical efficiency.
Based on this data, a quality definition is derived, e.g. evaluating the illuminance function at different test points and comparing it to the values of the undisturbed system.
Statistical analysis shows the connection between tolerances and performance of the system.
Accuracy classes are defined with values for all considered tolerances.
Examples of different applications are given.
Challenges to lens design for 17micron-FPAs in 8-12micron wavebandOptical Design of Cameras for Earth Observation
N. Schuster and J. Franks
Umicore (Belgium), Electro-Optic Materials
In the 8-12 micron waveband uncooled Focal Plane Arrays (FPA) are available with a 17 micron pixel pitch. They are available with different arrays sizes (e.g. 620 x 480 pixels and 320 x 240 pixels) and with high thermal resolution. Lenses with different focal lengths are required for applications in a variety of markets.
The pixel pitch determines the resolution limit of lenses. However, in the 8-12micron waveband, the impact of diffraction effects is considerable. Different models are discussed.
The interaction of the diffraction limit with energy collection and resolution are considered. The Radiometric f-number (RF) determines the signal on the detector. The relationship between RF and the Traditional f/number (TF) RF2 = TF2 + 0.25 is considered. RF = 1 requires a value of the traditional f-number TF = 0.87.
Examples are given of how these requirements can be handled in practical optical design using Umicore’s standard lenses for 17micron pixel pitch detectors.
Poster Abstracts
Aberrations studies using ray tracing
N. Delerue and Will Powell
University of Oxford (UK)
Accurate modelling and tracing of laser beams passing through optical devices and their transition between subsequent media is essential for many current experiments and applications. Aberrations occur in all optical devices and are particularly significant when laser beams are highly focused on a small area. This poster will firstly look at using fundamental ray tracing optics to map three dimensional optical setups and see its success at portraying these aberrations by comparing results with other methods and theoretical aberration research. Following which an overview of the methods and means by which Gaussian beams fit into the optical picture and how they can be analysed in optical ray tracing method for beam propagation and degradation. The poster will provide an assessment with results from a developed code on using optical ray tracing in optical systems such as lasers.
Development of an Optical and Mechanical Model for The Orion High Power Laser
Paul Jinks, AWE plc, Aldermaston
ORION is a new high power Laser facility currently being commission at AWE Aldermaston. The overall size of the building itself is 100m x 70m by 20m high to accommodate the L-shaped structure. The design process for Orion naturally developed into two high level models: the optical model and the mechanical model; with feedback between the two. This poster shows some examples of how this process was tackled and in particular how the Optical Model was built from commercial Optical Design software.
Comparison of two 10 degree field Catadioptric designs for sky survey
Mehdi Bahrami
National University of Ireland, Galway, Ireland
Time-efficient sky surveys need telescopes with a large field of view but not necessarily diffraction limited resolution. In this study, two Catadioptric designs for this purpose are proposed. Both of these designs are optimised for 10 degree field of view and operate at f/2.5 speed. The first design uses one aspherical mirror and a doublet for correcting the field aberrations. The second design is a two-mirror telescope that is based on Schmidt telescope principle. It contains a Schmidt plate, two spherical mirrors and a doublet as a field corrector. The optical performance of these two telescopes is optimised for wavelength range 0.500 to 0.600 microns. We discuss the advantages and drawbacks of the proposed designs and give recommendations for future survey telescopes.