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selection guide reflective divergence adjustable fixed magnification variable magnification beam shapers focusing objectives
In many laser-based applications, beam expanders are an essential
component of the optical system. They are most often used to decrease
divergence (by a factor of the expansion power) or to create
smaller nal focused spot sizes by expanding the beam before the
nal focusing element. They are also used to increase beam diameter,
therefore reducing power density or facilitating alignment. Variable
magni cation beam expanders are often used to correct for laser
beam diameter variability in mass produced lasers. More information
about beam expanders can be found in Section 6: Laser Beam Expanders
on pages 20-21.
Once you have determined the need for a beam expander, selecting
the correct beam expander can be a daunting task due to the numerous
options available. There are a few key attributes that can help
di erentiate between beam expander families to identify the right one
for your application (Table 1 and Table 2).
Expansion Power
Variable magni cation beam expanders can operate over a range of
expansion powers, or magni cations, but they require more elements
and more complex mechanics, increasing cost, size, and weight. Fixed
beam expanders should be selected where possible, which operate at
a given expansion power.
Wavelength
Ideally, beam expanders should have an anti-re ective (AR) V-coat at
the wavelength of your laser. However, if a close match is not available
or the beam expander is intended for use with multiple wavelengths
or tunable lasers, broadband AR-coated beam expanders are
e ective solutions. Unless a beam expander design itself is achromatic,
di erent wavelengths will collimate di erently, regardless of
the coating, and wavelength changes will require re-adjusting the divergence
of the beam expander.
Focusing Mechanisms
Beam expanders often include divergence adjustment mechanics. Rotating
focusing mechanisms are the most simple and economical option,
but the rotation of the internal optics can lead to beam wander
during adjustment. This e ect is often small enough to be negligible,
but for certain precision applications the minimized beam wander of
non-rotating, or sliding, focusing mechanisms justi es their additional
cost.
Input/output Aperture
The input/output apertures need to be su ciently large to accommodate
your input/output laser beam without clipping. A safety factor of
1,33 is often chosen over the 1/e diameter of the laser beam,1
Transmitted Wavefront Error
Lower transmitted wavefront error indicates higher performance and
should be preferred. However, it is important to understand whether
the quoted wavefront is a nominal design value or real world transmitted
wavefront. Edmund Optics measures transmitted wavefront error
using a Shack-Hartmann wavefront sensor. While a beam expander
with a larger real world wavefront error may look worse on paper than
a beam expander with a smaller quoted nominal value, it could potentially
be the better beam expander in actual use. Finally, be sure to
compare transmitted wavefront error at the same input beam diameter
and wavelength, as transmitted wavefront error scales nonlinearly
with input beam diameter and can degrade rapidly for larger beams.
References
1. Siegman, Anthony E. Lasers. University Science Books, 1986.
Product Family Expansion Powers Wavelengths Focusing Mechanisms Key Differentiator
Scorpii 2X - 10X 355 nm, 532 nm, 1064 nm Completely fi xed Cost driven
Vega 1,5X - 20X
266 nm, 355 nm, 405 nm, 532 nm,
1064 nm, 250 - 532 nm, 500 - 1090 nm,
1030 - 1550 nm, 1900 - 2100 nm
Rotating divergence adjustment Best performance/price value
Arcturus 3X - 20X 633 nm Non-rotating divergence adjustment Ideal for HeNe applications
Draconis 3X - 10X
532 nm, 1064 nm, 260 - 365 nm,
425 - 700 nm, 750 - 1100 nm
Non-rotating divergence adjustment Highest performance
Table 1: Key speci cations of the xed laser beam expanders o ered by EO
Product Family Expansion Powers Wavelengths Focusing Mechanisms Key Differentiator
Research-Grade Variable
1X - 3X
266 nm, 355 nm, 532 nm, 1064 nm,
260 - 365 nm, 425 - 700 nm,
500 - 1100 nm, 750 - 1100 nm
Non-rotating divergence adjustment Variable magnifi cation
2X - 8X
266 nm, 355 nm, 532 nm, 1064 nm,
260 - 365 nm, 425 - 700 nm,
750 - 1100 nm
Non-rotating divergence adjustment Variable magnifi cation
Table 2: Key speci cations of the variable magni cation laser beam expanders o ered by EO
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