www.iap.uni-jena.de

Optical Design with Zemax

Lecture 9: Illumination

2013-06-14

Herbert Gross

Summer term 2013

2

Preliminary Schedule

1 12.04. Introduction

Introduction, Zemax interface, menues, file handling, preferences, Editors, updates,

windows, coordinates, System description, Component reversal, system insertion,

scaling, 3D geometry, aperture, field, wavelength

2 19.04. Properties of optical systems I Diameters, stop and pupil, vignetting, Layouts, Materials, Glass catalogs, Raytrace,

Ray fans and sampling, Footprints

3 26.04. Properties of optical systems II

Types of surfaces, Aspheres, Gratings and diffractive surfaces, Gradient media,

Cardinal elements, Lens properties, Imaging, magnification, paraxial approximation

and modelling

4 03.05. Aberrations I Representation of geometrical aberrations, Spot diagram, Transverse aberration

diagrams, Aberration expansions, Primary aberrations,

5 17.05. Aberrations II Wave aberrations, Zernike polynomials, Point spread function, Optical transfer

function

6 24.05. Optimization I

Principles of nonlinear optimization, Optimization in optical design, Global

optimization methods, Solves and pickups, variables, Sensitivity of variables in

optical systems

7 31.05. Optimization II Systematic methods and optimization process, Starting points, Optimization in Zemax

8 07.06. Imaging Fundamentals of Fourier optics, Physical optical image formation, Imaging in Zemax

9 14.06. Illumination Introduction in illumination, Simple photometry of optical systems, Non-sequential

raytrace, Illumination in Zemax

10 21.06. Advanced handling I

Telecentricity, infinity object distance and afocal image, Local/global coordinates, Add

fold mirror, Scale system, Make double pass, Vignetting, Diameter types, Ray aiming,

Material index fit

11 28.06. Advanced handling II Report graphics, Universal plot, Slider, Visual optimization, IO of data,

Multiconfiguration, Fiber coupling, Macro language, Lens catalogs

12 05.07. Correction I

Symmetry principle, Lens bending, Correcting spherical aberration, Coma, stop

position, Astigmatism, Field flattening, Chromatical correction, Retrofocus and

telephoto setup, Design method

13 12.07. Correction II Field lenses, Stop position influence, Aspheres and higher orders, Principles of glass

selection, Sensitivity of a system correction, Microscopic objective lens, Zoom system

14 12.07. Physical optical modelling Gaussian beams, POP propagation, polarization raytrace, polarization transmission,

polarization aberrations

1. Photometry

2. Illumination calculation

3. Light sources

4. Illumination systems

5. Special illumination components

6. Illumination in Zemax

3

Contents

dW

s

dAS

qS

n

Differential Flux

Differential flux of power from a

small area element dAs with

normal direction n in a small

solid angle d along the direction

s of detection

Integration of the radiance over

the area and the solid angle

gives a power

SSS

S

AdsdL

dAdL

dAdLd

W

W

W

qcos

2

PdA

A

4

Transfer of Energy in Optical Systems

General setup

Optical SystemRadiation

Source

Detector

dA DdAS

in out

PS PD

Ref: B. Drband

Optical System

A2

d2

dA1dW2W2

2

2

2

f

P1

q1

qR

1

W1

Detector

r

dA

5

Illumination Fall-off

Irradiance decreases in the image field

Two reasons:

1. projection due to oblique ray bundles

2. enlarged distances along oblique chief rays

Natural vignetting: smooth function

depends on: 1. stop location

2. distortion correction

entrance

pupil

y yp

chief ray

chief ray

exit

pupil

y' y'p

w'

w

R'Ex

U

axis bundle

off axis

bundle

marginal

ray

E(y) E(y')U'

6

Natural Vignetting

Consideration with the help of entrance and exit pupil:

1. transfer from source to entrance pupil

2. transfer between pupils

3. transfer from exit pupil into image plane

'cos

cos

'' 4

422

w

w

s

s

dA

dA

n

n

dA

dA

AP

EP

EP

AP

object entrance

pupil

exit

pupilimage

sp

dA

dAEN

dAEX

dA'

U w

q

U'

w' q'

system

marginal

ray

chief ray

s'p

7

Natural Vignetting: System with Front Stop

Exact integration:

similar to general formula

including differential magnification

Special case on optical axis

Approximation small aperture

Special case circular symmetry

Appropriate distortion allows to correct the natural vignetting effect

2/1

222

22

tancos1

tancos411

'2)('

uw

uw

dA

dALwE

wEwE 4cos)0(')('

udA

dALE 2sin

')0('

'

''

dh

dh

h

h

dA

dAmA

E L u kh

h

dh

dhw fcorr' sin

'

'cos 2 4

8

Special problems in the layout of illumination systems:

1. complex components: segmented, multi-path

2. special criteria for optimization:

- homogeneity

- efficiency

3. incoherent illumination: non-unique solution

Illumination Systems

Non-Sequential Raytrace: Examples

3. Illumination systems, here:

- cylindrical pump-tube of a solid state laser

- two flash lamps (A, B) with cooling flow tubes (C, D)

- laser rod (E) with flow tube (F, G)

- double-elliptical mirror

for refocussing (H)

Different ray paths

possible

A: flash lamp gas

H

4

B: glass tube of

lamp

C: water cooling

D: glass tube of cooling

5

6

3

2

1

7

E: laser rod

F: water cooling

G: glass tube of cooling

10

Simple raytrace:

S/N depends on the number of rays N

Improved SNR: raytube propagation transport of energy density

Illumination Simulation

N = 2.000 N = 20.000 N = 200.000 N = 2.000.000

N = 100.000

0

1

-0.5 -0.3 -0.1 0.1 0.3 0.50

1

-0.5 -0.3 -0.1 0.1 0.3 0.50

1

-0.5 -0.3 -0.1 0.1 0.3 0.5

N = 10.000 N = 63

NTR

= 63 NTR

= 63 NTR

= 63

CAD model of light sources:

1. Real geometry and materials

2. Real radiance distributions

Bulb lamp

XBO-

lamp

Realistic Light Source Models

-2

0

2-8

-6

-4

-2

0

2

4

6

8

0

0.5

1

z

intensity I

[a.u.]

x

Gaussian Beam Propagation

Paraxial transform of

a beam

Intensity I(x,z)

2

)(2

2 )(

2),(

zw

r

ezw

PzrI

Angle Indicatrix Hg-Lamp high Pressure

cathode

0

800

1200

1600

0 1020

30

40

50

60

70

80

90

100

110

120

130

140

150

160170

180190200

210

220

230

240

250

260

270

280

290

300

310

320

330

340350

400

azimuth angles :

3050

70

90

110

130

150

Polar diagram of angle-dependent

intensity

Vertical line:

Axis Anode - Cathode

XBO-

lamp

Xenon lamp Line spectrum

HG-Xe-lamp

Spectral Distributions

I

1

0.5

0380 580 780 980

I

1

0.5

0380 580 780 980

source

collector condenser objective

lens

object

plane

image

plane

field stop aperture stopback focal plane -

pupil

Khler Illumination Principle

Principle of Khler

illumination:

Alternating beam paths

of field and pupil

No source structure in

image

Light source conjugated

to system pupil

Differences between

ideal and real ray paths

condenser

object

plane

aperture

stopfield

stop filter

collector

source

Illumination Optics: Collector

Requirements and aspects:

1. Large collecting solid angle

2. Correction not critical

3. Thermal loading

large

4. Mostly shell-structure

for high NA

W(yp)

200

a) axis b) field

200

W(yp)

yp

480 nm

546 nm

644 nm

yp

W(yp)

200

a) axis b) field

200

W(yp)

yp

yp

480 nm

546 nm

644 nm

Illumination Optics: Condenser

2. Abbe type, achromatic, NA = 0.9 , aplanatic, residual spherical

3. Aplanatic achromatic, NA = 0.85

y'100m

a) axis b) field

yp

480 nm

546 nm

644 nm

y'100m

yp

x'100m

xp

tangential sagittal

y'100m

a) axis b) field

yp

480 nm

546 nm

644 nm

y'100m

yp

x'100m

xp

tangential sagittal

Fresnel Surfaces

Special description of Fresnel surfaces

with circular symmetry

Bezier spline desciption with corresponding

choice of the control points:

modelling of edges

Mathematically:

- surface sag continuous

- derivative with steps

19

Lighthouse optics

Fresnel lenses with height 3 m

Separated segments

Complex Geometries

Illumination Components

Solar concentrator optics

Ref: Light Presciptions Innovations

Arrays - Illumination Systems

Illumination LED lighting

Ref: R. Vlkel / FBH Berlin

Principle of a light pipe / slab integrator:

Mixing of flipped profiles by overlapping of sub-apertures

Spatial multiplexing, angles are preserved

Number of internal reflexions determine the quality of homogeneity

Rectangular Integrator Slab

length L

width

asquare

rod

virtual

intersection

point

point of

incidence

exit

surface

Ideal homogenization:

incoherent light without interference

Parameter:

Length L, diameter d, numerical aperture angle q, reflectivity R

Partial or full coherence:

speckle and fine structure disturbs uniformity

Simulation with pint ssource and lambert indicatrix or supergaussian profile

Rectangular Slab Integrator

x

I(q)

x'

I(x')q

d

L

Rectangular Slab Integrator

Full slab integrator:

- total internal reflection, small loss

- small limiting aperture

- problems high quality of end faces

- also usable in the UV

Hollow mirror slab:

- cheaper

- loss of 1-2% per reflection

- large angles possible

- no problems with high energy densities

- not useful in the UV

slab integrator

hollow integrator

Array of lenslets divides the pupil in supabertures

Every subaperture is imaged into the field plane

Overlay of all contributions gives uniformity

Problems with coherence: speckle

Different geometries: square, hexagonal, triangles

Simple setup with one array

Improved solution with double array and additional

imaging of the pupil

Flyeye Array Homogenizer

farrD

arr

xcent

u

xray

Dsub

subaperture

No. j

change of

direction

condenser

1 2 3 5

array

4

focal plane of the

array

receiver

plane

starting

plane

farr

fcon

Dill

Dsub

Flyeye Array Homogenizer

condenserarray

spherical surface with

secondary source

points

illumination

field

Simple model: Secondary source of a pattern of point sources

Types of surfaces:

Mirror with facets

Regular lenslet array

Statistical lenslets

Segmented Surfaces and Arrays

bearbeitete

Flche

einfallender

Strahl

Facetten-

spiegel

Flyeye Array Homogenizer

a b

Example illumination fields of a homogenized gaussian profile

a) single array

b) double array

- sharper imaging of field edges

- no remaining diffraction structures

Generation of a ring profile

Axicon:

cone surface with peak on axis

Ringradisu in the focal plane

of the lens

Ring width due to diffraction

fnR )1(

a

fR

22.1

Axicon Lens Combination

R

o

ff

a

R

o

f

Illumination Optics: Condenser

2. Epi-illumination

Complicated ring-shaped components

around objective lens

object

ring lens

illuminationobservation

object

ring lens

illuminationobservationcircle 1

circle 2

Simple options:

Relative illumination / vignetting for systems with rotational symmetry

Advanced possibility:

- non-sequential component

- embedded into sequential optical systems

- examples: lightguide, arrays together with focussing optics, beam guiding,...

General illumination calculation:

- non-sequential raytrace with complete different philosophy of handling

- object oriented handling: definition of source, components and detectors

32

Illumination in Zemax

Relative illumination or vignetting plot

Transmission as a function of the field size

Natural and arteficial vignetting are seen

33

Relative Illumination

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25

y field in

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

relative

illumination

natural vignetting

cos4 w

onset of

truncation

total

illumination

vignetting

Partly non-sequential raytrace:

Choice of surface type non-sequential

Non-sequential component editor with many control parameters is used to describe the

element:

- type of component

- reference position

- material

- geometrical parameters

Some parameters are used from the lens data editor too:

entrance/exit ports as interface planes to the sequential system parts

34

Illumination in Zemax

Example:

Lens focusses into a rectangular lightpipe

35

Illumination in Zemax

Complete non-sequential raytrace

Switch into a different control mode in File-menue

Defining the system in the non-sequential editor, separated into

1. sources

2. light guiding components

3. detectors

Various help function are available to

constitue the system

It is a object (component) oriented philosophy

Due to the variety of permutations, the raytrace

is slow !

36

Illumination in Zemax

Many types of components and options are available

For every component, several

parameters can be fixed:

- drawing options

- coating, scatter surface

- diffraction

- ray splitting

- ...

37

Illumination in Zemax

Starting a run requires several control

parameters

Rays can be accumulated

38

Illumination in Zemax

Typical output of a run:

39

Illumination in Zemax