SUCCESS STORY – Laser Beam Steering in Materials Processing, Laser Scanning Microscopy and Ophthalmology-- Steffen Arnold --Laser Beam Steering in Materials Processing, Laser Scanning
Microscopy and Ophthalmology
Piezoelectric Drive Components and their Possibilities

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Laser Beam Steering in Materials Processing, Laser Scanning Microscopy and Ophthalmology-- Steffen Arnold--

Lasers are versatile tools. Nowadays, they are just as
indispensable in materials processing as in eye surgery or
super high resolution microscopy. The different areas ofapplication have similarities, however, since a precise
positioning of the laser beam is always crucial. At the sametime, this laser beam steering and focusing also requires thedrive systems used to be dynamic, reliable and compactlydimensioned, in order to allow simple integration inapplications. It is therefore hardly surprising that piezoelectric
drive components often have no serious alternative for laser
beam steering.
Actuators exploiting this piezo effect move with resolutions inthe sub-nanometer range and response times below one
millisecond, which makes dynamic operation with scanningfrequencies of up to one thousand hertz possible. The motion
is based on crystalline solid state effects and so there are norotating or friction-producing mechanical components. Piezo
actuators are maintenance-free, because they have nomoving parts in the conventional sense. This allows motions
to be carried out in the subnanometer range at high velocity.

Fig. 1

A significant advantage of digital controllers is that all motion
parameters can be specifically influenced using algorithms.
This increases precision and dynamics with simultaneous highease of use. Piezoelectric drive and positioning systems thus
offer interesting possibilities for laser beam steering,
especially since the sensors necessary for high-precision
positioning are also included in the product range of PI.

Precision Solutions for Materials
Processing
Typical applications for materials processing via laser beam
are found in electronics manufacturing, e.g. the production oftemplates that are used for coating PCB's with solder paste(Fig. 2).

Highly dynamic, piezo-drive tip/tilt platform with two orthogonalaxes and optic deflection angles of up to 20 mrad. Up to four
piezo actuators are directly coupled with the moving platform.
The length of the actuators determines the tip/tilt angle range;
the system is therefore scalable (Image: PI)

Moreover, piezo actuators dissipate no power in static
operation, since electrically they act as capacitive loads. It istherefore no wonder that the compact, piezo-basedpositioning systems (Fig. 1) of PI (Physik Instrumente) are themeans of choice today in many laser control applications. Inaddition, the analog or digital controllers adapted to theparticular positioning system allow simple integration into theapplication.

Fig. 2

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

PKF MicroLine series for professional laser processing of circuitcarriers and printed circuit board. (Image: LPKF Laser &Electronics AG)

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SUCCESS STORY – Laser Beam Steering in Materials Processing, Laser Scanning Microscopy and Ophthalmology-- Steffen Arnold--

The requirements here are high; the material must be
removed very precisely with exactly defined edges. Highthroughputs are also obligatory.
Common deflection techniques for the laser beam, such as
the galvanometer scanners that are based on the induction
principle, are suitable for such high-precision applications inprinciple, but also have disadvantages. In order to be able toposition in two axes, two systems have to be switched insuccession, in other words stacked. This results in different
pivot points and the space requirement is relatively large.
Piezo-driven tip/tilt platforms or tip/tilt mirror systems are
the better alternative here since they not only offer therequired accuracy but high accelerations and a great dynamic
bandwidth at the same time as well.

In the case of tip/tilt mirror systems and piezo-based scanningplatforms with several motion axes, piezo drives are used inparallel kinematics positioning systems (Fig. 3). This structure
has various advantages over serial systems: for example,
there is only one moving platform with a common pivot point,
the dynamics are higher and the size is smaller. In addition,
the systems can achieve a higher accuracy than can berealized by switching two single-axis systems in succession –which is usually the case with galvanoscanners, for example.
Integrated high-resolution position sensors ensure highlinearity values of better than 0.25 % over the full travel range
and a repeatability of typically 5 µrad, which corresponds toroughly 0.3 millidegrees.

Laser Scanning Applications inSuper Resolution Microscopy
In laser scanning microscopy, the laser beam also has to bepositioned and focused to excite fluorescence in the sample.
While the precision of galvanoscanners certainly suffices forconfocal methods in most cases, this solution may reach its
limits in the field of super resolution microscopy (Fig. 4).

Fig. 3

In parallel kinematics systems all actuators act directly on thesame platform; basic design with three actuators (Image: PI)

Fig. 4

Super-resolution laser scanning microscopy (Image: PI)

Here there are higher requirements for accuracy withresolutions of around 10 nm with simultaneous highdynamics. Piezo-driven tip/tilt mirrors and platforms (Fig. 1)
demonstrate their advantages again here.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Laser Beam Steering in Materials Processing, Laser Scanning Microscopy and Ophthalmology-- Steffen Arnold--

The S-334 tip/tilt platforms and scanners (Fig. 5), for example,
allow highly dynamic and precise tip/tilt motions of the top
platform in two orthogonal axes with a common pivot point.

A coordinate transformation can be carried out via its internal
hardware so that control is possible in direct proportion to
the deflection angle.

Piezo Ultrasonic Drives for Laser
Beam Steering
Precise laser beam steering and focusing is also an important
topic in medical technology. This makes it possible, forexample, to correct ametropia in up to high diopter ranges
thanks to refractive operation techniques.

Fig. 5The piezo-driven tip/tilt platforms are available with tilting
angles of up to 3°, which are each offered with position sensors
for closed-loop operation or without sensors as fast scanners(Image: PI)

The frictionless piezo drives and flexure guides allow higher
accelerations than conventional drives and offer scanningfrequencies of over 100 Hz over tip/tilt angle ranges of up to3° in position control. The E-616 is a controller speciallydeveloped for piezo tip/tilt mirrors that combines thefunctions of a multi-channel controller and amplifier.

Fig. 6

For this purpose, the shape of the cornea is modeled in the
optical axis by removing small cornea particles with laser
beams so that the resulting refractive power of the cornea(epithelium) matches the length of the eyeball again (Fig.
6).The previously described tip/tilt mirror systems have awide-ranging application area here as well.
The ceramic PILine® ultrasonic motors also open up
interesting possibilities for laser beam steering. They arecharacterized by extremely high velocities and acceleration
with simultaneous very compact dimensions. The patenteddrive principle (Fig. 7) makes them self-locking when at rest.
Linear motors and drives are intended for integration in acustomer system and are generally unguided. There are also
complete solutions, however, that can be integrated ready for
installation in many applications.

In order to compensate for ametropia, the shape of the cornea ismodeled in the optical axis by removing small cornea particles
with laser beams so that the resulting refractive power of thecornea (epithelium) matches the length of the eyeball again(Image: PI)

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Laser Beam Steering in Materials Processing, Laser Scanning Microscopy and Ophthalmology-- Steffen Arnold--

About PI

Fig. 7

Patented functional principle of the PILine® actuators:
Oscillations with ultrasonic frequencies of a piezoceramic
actuator are converted along a friction bar into a linear motion
and thereby drive the movable part of a mechanical structure(Image: PI)

The M-663 precision micro linear stage (Fig. 8), which is also
suitable for XY combinations if necessary, is a good exampleof this. It offers velocities of up to 400 mm/s and travel ranges
up to 19 mm with resolutions up to 0.1 µm.

In the past four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany has become the leading
manufacturer of nanopositioning systems with accuracies in
the nanometer range. With four company sites in Germany
and fifteen sales and service offices abroad, the privately
managed company operates globally.
Over 850 highly qualified employees around the world enable
the PI Group to meet almost any requirement in the field ofinnovative precision positioning technology. All key
technologies are developed in-house. This allows thecompany to control every step of the process, from design
right down to shipment: precision mechanics and electronics
as well as position sensors.
The required piezoceramic elements are manufactured by its
subsidiary PI Ceramic in Lederhose, Germany, one of the
global leaders for piezo actuator and sensor products.
PI miCos GmbH in Eschbach near Freiburg, Germany, is a
specialist for positioning systems for ultrahigh vacuum
applications as well as parallel-kinematic positioning systems
with six degrees of freedom and custom-made designs.

AuthorFig. 8PILine® micropositioning stage with linear encoder for direct
position evaluation (Image: PI)

A contactlessly measuring optical linear encoder guarantees
high linearity and repeatability. With a height of 15 mm, awidth of 30 mm and a length of 35 mm, the micropositioning
stage is very compact and can therefore be easily integrated
in the respective application. This is also certainly due to thefact that PI also provides matching drive electronics andcontrollers, which are perfectly adapted to the micro linear
stage. Such positioning solutions create interesting
possibilities for laser beam steering and focusing which offer
advantages in all areas in which laser processing can be used.

Dipl.-Phys. Steffen Arnold, Head of "Marketing and Products"
at PI (Physik Instrumente)

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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