Optical Shop Testing

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Ambrose Jonathan Houston
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1 Optical Shop Testing nd Edition (199 ) Edited by Daniel Malacara 1

2 OUTLINE Chapter 1. Newton, Fizeau, and Haidinger Interferometer Fizeau Interferometer 1.3 Haidinger Interferometer 1.4 Absolute Testing of Flats

3 Any arrangement of two surface in contact illuminated by a monochromatic source of light is called a Newton Interferometer 3

4 letαbe the wedge angle and the air gap is αx λ for bright fringe αx + = λ ( comes from reflection) nλ x x for dark fringe αx = nλ the distance between two fringe is d = λ α 4

5 Simulation by ASAP beam divider source test plane reference plane observation plane 5

6 0.005 degree ( dark lines) 0.01degree (5 dark lines) degree (7 dark lines) 0.0degree (10 dark lines) 6

7 R for a large R the sag is for dark fringe x = nλ R x R the distance for nth dark fringe is x n = nrλ sag x and we have the ratio xn xn x x n n+ 1 n x = 4λ R 7

8 x R = λ x R = λ x R = 4λ x R = 8λ 8

9 When maximum error (sag) is less than λ/, with suitable manipulation, we can see fringes of arcs of circle. x R = λ x R = λ 4 9

10 x = R λ (without tilt) x = R λ (tilt 0.05degree) x = R λ 4 (tilt 0.05degree) x = R λ 4 (tilt 0.015degree) 10

11 Estimating peak error peak error = λ 0 If the fringe spacing is d and the peak deviation is k We have peak error = k d λ d k 11

12 Simple way to judge whether the surface is convex or concave (1). Press the edge of test plant gently by a pencil (before press) (after press) 1

13 Simple way to judge whether the surface is convex or concave (). Press the center of test plant gently by a pencil (before press) (after press) 13

14 Different kinds of fringe patterns 14

15 Plane Almost plane Spherical Conical 15

16 Cylindrical Astigmatic 1 Astigmatic 16

17 Fizeau Interferometer Similar to Newton interferometer, when the air gap become large, it becomes Fizeau interferometer. 17

18 Fizeau Interferometer Simulation by ASAP beam divider test plane source reference plane observation plane 18

19 Fizeau Interferometer Liquid reference flats A liquid surface can be used as a reference flat. The liquid surface has a radius of curvature equal to that of the earth. y = R y ( mm) 4 If want the error not exceed /100 ( λ = 5 10 mm ) 4 then y and y 51mm 9 Water is not suitable because of low viscosity Mercury is not suitable because of high reflectivity 19

$If A is wedge angle and N is the refractive index of the glass, then we have NAD= (d is the distance between two dark fringes).$

20 Fizeau Interferometer Testing nearly parallel plates Without the reference flats, we can test small wedge angle by using Fizeau interferometer. If A is wedge angle and N is the refractive index of the glass, then we have NAD= (d is the distance between two dark fringes). Hence the angle A is A = λ ND We can make test plane a slight local expansion, then the straight fringe will form a kink toward the thin side. A D 0

21 Fizeau Interferometer Testing right-angle prisms good prism prism with angular errors 1

$deviation of the fringe from straight, N is the refractive index,and is the wavelength, then the error is given by ε = ( k )( λ )$

22 Fizeau Interferometer If L is the width of the prism, π ± ε is the prism angle, d is distance between two fringes, k is the deviation of the fringe from straight, N is the refractive index,and is the wavelength, then the error is given by ε = ( k )( λ ) d 4NL

23 Fizeau Interferometer ε= 0 degree ε= degree ε=0.01 degree ε= degree 3

24 Haidinger Interferometer Testing a wedge plane with a point source, we can get two virtual sources, which have distance t/n and lateral displacement NAr. 4

25 Haidinger Interferometer If the plate under test has a wedge angle, the center of circle fringe id displaced from the center of the hole by a distance d = N r t A where d =displacement of the Haidinger fringe system A =wedge angle of the plate t =thickness of the glass plate N =refractive index of the glass plate r =distance of the point source from the glass plate 5

26 Haidinger Interferometer A= 0 degree A= degree A= 0.01 degree A= degree 6

27 Reference Optical Shop Testing nd Edition Daniel Malacara Optical Testing Analysis on the Parallelism of DWDM Filter Kuo-Hui Chang 7

Interference- Michelson Interferometer. Interference lecture by Dr. T.Vishwam

Interference- Michelson Interferometer Interference lecture by Dr. T.Vishwam * Measurement of the coherence length of a spectral line * Measurement of thickness of thin transparent flakes * Measurement