Imaging and Aberration Theory
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Imaging and Aberration Theory Lecture 4: Aberration expansions 2018-11-08 Herbert Gross Winter term 2019 www.iap.uni-jena.de 2 Schedule - Imaging and aberration theory 2019 1 18.10. Paraxial imaging paraxial optics, fundamental laws of geometrical imaging, compound systems Pupils, Fourier optics, pupil definition, basic Fourier relationship, phase space, analogy optics and 2 25.10. Hamiltonian coordinates mechanics, Hamiltonian coordinates Fermat principle, stationary phase, Eikonals, relation rays-waves, geometrical 3 01.11. Eikonal approximation, inhomogeneous media single surface, general Taylor expansion, representations, various orders, stop 4 08.11. Aberration expansions shift formulas different types of representations, fields of application, limitations and pitfalls, 5 15.11. Representation of aberrations measurement of aberrations phenomenology, sph-free surfaces, skew spherical, correction of sph, aspherical 6 22.11. Spherical aberration surfaces, higher orders phenomenology, relation to sine condition, aplanatic sytems, effect of stop 29.11. 7 Distortion and coma position, various topics, correction options 8 06.12. Astigmatism and curvature phenomenology, Coddington equations, Petzval law, correction options Dispersion, axial chromatical aberration, transverse chromatical aberration, 9 13.12. Chromatical aberrations spherochromatism, secondary spectrum Sine condition, aplanatism and Sine condition, isoplanatism, relation to coma and shift invariance, pupil 10 20.12. isoplanatism aberrations, Herschel condition, relation to Fourier optics 11 10.01. Wave aberrations definition, various expansion forms, propagation of wave aberrations special expansion for circular symmetry, problems, calculation, optimal balancing, 12 17.01. Zernike polynomials influence of normalization, measurement 13 24.01. Point spread function ideal psf, psf with aberrations, Strehl ratio 14 31.01. Transfer function transfer function, resolution and contrast Vectorial aberrations, generalized surface contributions, Aldis theorem, intrinsic 15 07.02. Additional topics and induced aberrations, reversability 3 Contents . Repetition... Single refracting surface . Adaptation on optical system terms . Primary monochromatic aberration surface contributions . Extension on several surfaces . Lens contributions . Examples 4 Eikonal Overview . Fermat principle: light takes the fastest way P2 between two points L n(x, y, z) ds 0 The variance of the OPL is zero, stationary point P1 . The OPL is the Lagrange function in optics L L n s , n s the equation of motion is x' x y' y . This is the Eikonal equation of geometrical optics d dr n n ds ds . One ray is fixed by 4 parameters object image optical space angle space system (direction) angle . The general 4x4 functional relation (direction) between object and image space is point s s' restricted by the Fermat principle: r point r' only 4 independent variables . A Legendre transform allows to switch between the variables L(x, y, sx , sy ) nsx x'nsy y' L(x, y, x', y') . Every selection of eikonal variables has at least one case, which is singular 5 Eikonal Overview . Point eikonal: spatial coordinates in dL (x, y, x', y') n's 'dx's 'dy' ns dx s dy object and image space are fixed P x y x y the corresponding angles can be calculated LP LP ns nsy by the differential equations x x y L P LP n'sx ' n's ' x' y' y . Small change of initial ray data in the object space: Fermat principle allows to calculate the corresponding change in the image space A' A R' Q L n's'dr' ns dr s' q' Q' dr s q P' dr' R P . Special case q = 90°delivers the Abbe sine condition nsin u y' m n'sin u' y 6 Refracting Surface I: Basic Eikonal Approach . P, P' points on ray . A, A' arbitrary points on axis 2 2 2 2 . s,s' direction unit vectors of the rays sz 1 sx sy , s'z 1 s'x s'y relationship 2 2 2 2 2 . Real surface equation x y x y z 3 (1 b)... contains system parameters R, b 2R 8R . Angle eikonal, gives the optical path length change in P', if the point P is varied dLA (s,s') n r a ds n'r'a' ds' In coordinate representation dLA n x dsx y dsy z a dsz n'x ds'x y ds'y z a' ds'z y Q surface s' s P P' R n r n' M z A a z a' A' O origin 7 Refracting Surface II: Eikonal .Integration of the differential to get the total optical path length dLA n x ds x y ds y z a ds z n''''' x ds x y ds y z a ds z .Result of 4th order Taylor approximation LA na n'a' 2 2 x y a 2 2 n x sx y sy sx sy 2R 2 2 2 x y a' 2 2 n'x s'x y s'y s'x s'y 2R 2 2 2 2 2 1 b 2 2 2 x y sx sy a 2 2 2 n 3 x y sx sy 8R 4R 8 2 2 2 2 1 b 2 2 2 x y s'x s'y a' 2 2 2 n' 3 x y s'x s'y 8R 4R 8 . Elimination of intermediate variables x, y of the intersection point with the help of the law of refraction 8 Refracting Surface III: Law of Refraction 2 x2 y 2 (1 b)x2 y 2 . Implicite surface equation F(x, y, z) z 0 2R 8R3 . Normal unit vector in the intersection point e F(x, y, z) x (1 b) x2 y2 y (1 b) x2 y2 ex 1 2 , ey 1 2 , ez 1 R 2R R 2R . Law of refraction (n s n's')e 0 . Formulation in components y (1 b) x2 y2 (nsy n's'y )(nsz n's'z ) 1 2 0 R 2R x (1 b) x2 y2 (nsx n's'x )(nsz n's'z ) 1 2 0 R 2R y (1 b) x2 y2 x (1 b) x2 y2 (nsx n's'x ) 1 2 (nsy n's'y ) 1 2 0 R 2R R 2R . Solving for x, y in approximation of 4th order ns n's' ns n's' x R x x , y R y y n n' n n' 9 Refracting Surface IV: Eikonal . Resulting Eikonal function of sx, sy, s‘x, s‘y only (0) (2) (4) LA LA LA LA R 2 2 na 2 2 n'a' 2 2 na n'a' nsx n's'x nsy n's'y sx sy s'x s'y 2(n n') 2 2 R 2 2 2 2 2 2 nsx n's'x nsy n's'y nsx sy n's'x s'y 4(n n')2 1 2 2 2 2 2 2 (1 b)R 2 2 na sx sy n'a's'x s'y nsx n's'x nsy n's'y 8 8(n n')3 . Further re-arrangements for better practical usage: 1. introduction of the pupil coordinates xp, yp instead of the image sides directions s‘x, s‘y 2. switch to the image space ray parameters 3. optional switch to circular coordinates 4. according to Seidel substitution of the system parameter by the paraxial properties of the system and the marginal ray 5. Further approximation in 4th order to get a perturbation representation of the paraxial imaging. This allows a decoupling of the surface contributions 10 Refracting Surface V: Paraxial Optics (2) . 2nd order: paraxial optics 1 LA nR n' R x sx a s'x n sx n n' n n' (2) 1 LA nR n' R y sy a s'y n sy n n' n n' (2) 1 LA n' R nR x' s'x a' sx n' s'x n n' n n' (2) 1 LA n' R nR y' s'y a' sy n' s'y n n' n n' a' n' n n' aa' n' n n n' x' x s n' a' R n' x a' a R . Eliminating s'x, s'y a' n' n n' aa' n' n n n' y' y sy n' a' R n' a' a R . Imaging condition: x‘, y‘ independent from ray directions sx, sy n n' n n' 1. imaging equation a a' R 2. magnification na' x' na' x' x , m n'a x n'a 11 Refracting Surface VI: Pupil Coordinates y yp . Change to pupil coordinates object entrance system for optical systems plane pupil surface . Relations arcsin(sy) x x s x x tanu p x , s p s x x z arcsin(sz) y p sz p p y y y p sy y y p tanu y , sy sz p sz p p s x'x' x'x' p p s'x p s tanu'x , s'x s'z p' s'z p' y'y' p s'y y'y' p tanu'y , s'y s'z p' s'z p' . Approximated to 2nd order x x y y s p , s p x p y p x'x' y'y' s' p , s' p x p' y p' 12 Refracting Surface VII: Eikonal . Eikonal of 4th order 4 4 2 2 (s p) 2 s 2 s (s p) 2 L(4) K x2 y 2 S x2 y 2 A xx yy A 8p4 8p4 p p 2 p4 p p s2 (s p)2 s (s p)3 s3 (s p) P x2 y 2 xx yy D x2 y 2 xx yy C x2 y 2 xx yy 4 p4 p p 2 p4 p p 2 p4 p p 2 2 (n'n)b 1 1 1 1 . Coefficients K ns n's' 3 2 2 R Rs s p Rs' s' p 1.