Optical Engineering Science. Stephen Rolt

in Harlow, UK (later Nortel Networks), home of optical fibre communications. I would especially like to acknowledge the help and support of my colleagues, Dr Ken Snowdon and Mr Gordon Henshall during this creative period. Ultimately, the seed for this text was created by a series of Optical Engineering lectures delivered at Nortel's manufacturing site in Paignton, UK. In this enterprise, I was greatly encouraged by the facility's Chief Technologist, Dr Adrian Janssen.

      In later years, I have worked at the Centre for Advanced Instrumentation at Durham University, involved in a range of Astronomical and Satellite instrumentation programmes. By this time, the original seed had grown into a series of Optical Engineering graduate lectures and a wide-ranging Optical Engineering Course delivered at the European Space Agency research facility in Noordwijk, Netherlands. This book itself was conceived, during this time, with the encouragement and support of my Durham colleague, Professor Ray Sharples. For this, I am profoundly grateful. In preparing the text, I would like to thank the publishers, Wiley and, in this endeavour, for the patience and support of Mr Louis Manoharan and Ms Preethi Belkese and for the efforts of Ms Sandra Grayson in coordinating the project. Most particularly, I would like to acknowledge the contribution of the copy-editor, Ms Carol Thomas, in translating my occasionally wayward thoughts into intelligible text.

This project could not have been undertaken without the support of my family. My wife Sue and sons Henry and William have, with patience, endured the interruption of many family holidays in the preparation of the manuscript. Most particularly, however, I would like to thank my parents, Jeff and Molly Rolt. Although their early lives were characterised by adversity, they unflinchingly strove to provide their three sons with the security and stability that enabled them to flourish. The fruits of their labours are to be seen in these pages.

      Finally, it remains to acknowledge the contributions of those giants who have preceded the author in the great endeavour of optics. In humility, the author recognises it is their labours that populate the pages of this book. On the other hand, errors and omissions remain the sole responsibility of the author. The petty done, the vast undone…

Glossary

ACAlternating currentAFMAtomic force microscopeAM0Air mass zeroAM1Air mass one (atmospheric transmission)ANSIAmerican national standards instituteAPDAvalanche photodiodeARAntireflection (coating)ASAstigmatismASDAcceleration spectral densityASMEAmerican society of mechanical engineersBBOBarium borateBRDFBi-directional reflection distribution functionBSBeamsplitterBSDFBi-directional scattering distribution functionCADComputer aided designCCDCharge coupled deviceCDCompact discCGHComputer generated hologramCIECommission Internationale de l'EclairageCLAConfocal length aberrationCMMCo-ordinate measuring machineCMOSComplementary metal oxide semiconductorCMPChemical mechanical planarisationCNCComputer numerical controlCOComaCOTSCommerical off-the-shelfCTECoefficient of thermal expansiondBDecibelDCDirect currentDFBDistributed feedback (laser)DIDistortionE-ELTEuropean extremely large telescopeEMCCDElectron multiplying charge coupled deviceESAEuropean space agencyf#F number (ratio of diameter to focal distance)FATFactory acceptance testFCField curvatureFEAFinite element analysisFELFilament emission lampFELFree electron laserFFTFast Fourier transformFRDFocal ratio degradationFSRFree spectral rangeFTFourier transformFTIRFourier transform infra-red (spectrometer)FTRFourier transform (spectrometer)FWHMFull width half maximumGRINGraded index (lens or fibre)HEPAHigh- efficiency particulate air (filter)HSTHubble space telescopeHWPHalf waveplateIESTInstitute of environmental sciences and technologyIFUIntegral field unitIICCDImage intensifying charge coupled deviceIRInfraredISOInternational standards organisationJWSTJames Webb space telescopeKDPPotassium dihydrogen phosphateKMOSK-band multi-object spectrometerLALongitudinal aberrationLCDLiquid crystal displayLEDLight emitting diodeLIDARLight detection and rangingMTFModulation transfer functionNANumerical apertureNASANational Aeronautics and Space AdministrationNEPNoise equivalent powerNIRSPECNear infrared spectrometerNISTNational institute of standards and technology (USA)NMINational measurement instituteNPLNational physical laboratory (UK)NURBSNon-uniform rational basis splineOPDOptical path differenceOSAOptical society of AmericaOTFOptical transfer functionPDPhotodiodePMTPhotomultiplier tubePPLNPeriodically poled lithium niobatePSDPower spectral densityPSFPoint spread functionPTFEPolytetrafluoroethylenePVPeak to valleyPVAPolyvinyl alcoholPVrPeak to valley (robust)QMAQuad mirror anastigmatQTHQuartz tungsten halogen (lamp)QWPQuarter waveplateRMSRoot mean squareRSSRoot sum squareSASpherical aberrationSISystème InternationaleSLMSpatial light modulatorSNRSignal to noise ratioTATransverse aberrationTETransverse electric (polarisation)TGGTerbium gallium garnetTMTransverse magnetic (polarisation)TMAThree mirror anastigmatTMTThirty metre telescopeUSAFUnited States AirforceUVUltravioletVCSELVertical cavity surface emitting laserVPHVolume phase hologramWDMWavelength division multiplexingWFEWavefront errorYAGYttrium aluminium garnetYIGYttrium iron garnetYLFYttrium lithium fluoride

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1 Geometrical Optics

      1.1 Geometrical Optics – Ray and Wave Optics

In describing optical systems, in the narrow definition of the term, we might only consider systems that manipulate visible light. However, for the optical engineer, the application of the science of optics extends well beyond the narrow boundaries of human vision. This is particularly true for modern instruments, where reliance on the human eye as the final detector is much diminished. In practice, the term optical might also be applied to radiation that is manipulated in the same way as visible light, using components such as lenses, mirrors, and prisms. Therefore, the word ‘optical’, in this context might describe electromagnetic radiation extending from the vacuum ultraviolet to the mid-infrared (wavelengths from ∼120 to ∼10 000 nm) and perhaps beyond these limits. It certainly need not be constrained to the narrow band of visible light between about 430 and 680 nm. Figure 1.1 illustrates the electromagnetic spectrum.

Geometrical optics is a framework for understanding the behaviour of light in terms of the propagation of light as highly directional, narrow bundles of energy, or rays, with ‘arrow like’ properties. Although this is an incomplete description from a theoretical perspective, the use of ray optics lies at the heart of much of practical optical design. It forms the basis of optical design software for designing complex optical instruments and geometrical optics and, therefore, underpins much of modern optical engineering.

      Geometrical optics models light entirely in terms of infinitesimally narrow beams of light or rays. It would be useful, at this point, to provide a more complete conceptual description of a ray. Excluding, for the purposes of this discussion, quantum effects, light may be satisfactorily described as an electromagnetic wave. These waves propagate through free space (vacuum) or some optical medium such as water and glass and are described by a wave equation, as derived from Maxwell's equations:

      (1.1)

      E is a scalar representation of the local electric field; c is the velocity of light in free space, and n is the refractive index of the medium.

      Of course, in reality, the local electric field is a vector quantity and the scalar theory presented here is a useful initial simplification. Breakdown of this approximation will be considered later when we consider