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 polarisation effects in light propagation. If one imagines waves propagating from a central point, the wave equation offers solutions of the following form:
Equation (1.2) represents a spherical wave of angular frequency, ω, and spatial frequency, or wavevector, k. The velocity that the wave disturbance propagates with is ω/k or c/n. In free space, light propagates at the speed of light, c, a fundamental and defined constant in the SI system of units. Thus, the refractive index, n, is the ratio of the speed of light in free space to that in the specified medium. All points lying at the same distance, r, from the source, will oscillate at an angular frequency, ω, and in the same phase. Successive surfaces, where all points are oscillating entirely in phase are referred to as wavefronts and can be viewed at the crests of ripples emanating from a point disturbance. This is illustrated in Figure 1.2. This picture provides us with a more coherent definition of a ray. A ray is represented by the vector normal to the wavefront surface in the direction of propagation. Of course, Figure 1.2 represents a simple spherical wave, with waves spreading from a single point. However, in practice, wavefront surfaces may be much more complex than this. Nevertheless, the precise definition of a ray remains clear:
