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OPAC 202

Optical Design and Inst.

Topic 12

Beam Expanders

Department of

Optical & Acustical Engineering

Gaziantep University

http://www.gantep.edu.tr/~bingul/opac202

May 2018

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Beam expansion or reduction is a common application

requirement in most labs using lasers or light sources and

optics.

To create a beam expansion unit, it is important to know a

few simple optical relationships, as well as what your input to

output beam diameter ratio requirement is.

Beam Expander

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M = the magnification of the beam expander

f2 = effective focal length of exit lens

f1= effective focal length of entry lens

R1= radius of curvature of entry lens

R2 = radius of curvature of exit lens

h2 = radius of exit spot (image height)

h1= radius of entry spot (object height)

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Keplerian Beam Expander = Keplerian Telescope

(focal lengths of both lenses are positive)

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Keplerian Beam Expander = Keplerian Telescope

Keplerian beam expanders are not recommended for

use with lasers with high pulse energies, since there is

a high power density due to the focused spot size at

the focal point between the lenses. This is because the

high pulse energy density at the focal point can cause

the air to arc.

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Keplerian Beam Expander with relay lens

The image will be inverted and reverted at the output,

the addition of a third lens (relay lens) may be required to

correct the image orientation.

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Keplerian Beam Expander with relay lens

Select the distances as follows:

t1 = f1 + 2fr1

t2 = f2 + 2fr2* where fr1 and fr2 are the relay lens focal lengths.

* The overall length of the beam expander will be increased by the sum of

the focal lengths of the relay lens.

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Keplerian Beam Expander with relay lens

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Galilean Beam Expander = Galilean Telescope

(one negative and one positive lens)

M = -f2 / f1

t =f2 + f1

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Newport Company suggests list of lenses for beam expanders:

EXAMPLE 1: Designing Beam Expander

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We will design a 15x beam expander for λ = 550 nm.

Click Len button.

Select Newport Corp.

Insert KBX022 EFL = 12.70 EPD = 12.70

Insert KPX229 EFL = 200.00 EPD = 76.20

Zemax LDE will look like:

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Consider a paraxial lens having diameter of 20 mm and

focal length of 50 mm.

Uniform illumination

About Apodization Factor

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Apodization is related to beam shape.

Gaussian illumination Gaussian illumination

with apodization factor 2: with apodization factor 5:

About Apodization Factor

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In Zemax Ray Fan, Layout and Spot Diagram

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Optimization

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