|
Our
patented electro-mechanical laser shutters provide
features not found in other types of mechanical
shutters. This broad-based product line is designed
for the high irradiance produced by lasers. The
standard models meet the requirements of most
commercial laser applications, while our custom
development services provide extended support for
demanding applications.
Shutter Basics
Laser
shutters pass the laser beam undisturbed in the open
position, and dump the laser energy safely into the
shutter body when in the closed position. This
requires well designed thermal properties of the
moving optical element as well as the stationary
absorbing element. By using a lightweight, reflective
optical element to steer the energy to a stationary
absorber, little heat is generated in the moving
reflector. This allows higher optical power handling
and faster switching speeds. The use of a stationary
absorber allows a solid heat conduction path to the
shutter mounting plane.
The shutter
is conduction mounted for cooling, much like a power
semiconductor or laser diode. Heat sink capabilities
depend on both the laser power dumped, and the
shutter’s electrical power dissipation. A rule of
thumb is to use water chiller plates above 50 watts.
The
reflectors and absorbers use geometry, surface
morphology, and atomic absorption properties to
achieve clean operation with high irradiance CW lasers
and high fluence pulsed lasers. Damage threshold and
thermal conductivity are key design properties of
these elements. Some models use near grazing
incidence to spread the optical power over a large
area. Efficient absorption minimizes backscatter out
through the input aperture, enhancing safety.
Position
sensing elements are offered as options on most
products, and standard on some, to monitor the state
of the shutter’s aperture. Mechanical micro-switches
and logic output photo-sensors provide this
independent feedback to process and safety circuits
used by the customer.
Our Patented Technology
The heart
of our shutter technology is a cantilever flexure beam
that is magnetic, has good thermal conductivity,
provides excellent spring properties, and is optically
coated. This optical beam is magnetically pulled to
the open position by a closely coupled cylindrical
toroid electromagnet, with pole curvature that matches
the catenary curve of the flexure beam. This provides
high pulling forces and resultant rapid switching
speeds.
With loss
of electrical power, the stored mechanical energy in
the flexed beam returns it to the closed position,
yielding failsafe closure safety.
Faster
switching speeds are achieved by using stiffer flexing
beams and more powerful electromagnets. Practical
limits apply to electromagnet power dissipation.
Our electromagnets are wet-wound with extremely low
outgas epoxies, which meet NASA outgas specs. This
provides excellent thermal flow out of the windings
and down a thermal path to the shutter mounting base
plate.
A good
thermal path keeps the epoxy polymer at lower
temperature, further reducing outgas properties.
Managing the thermal flow from absorbers and
electromagnets allows the beam to pass through the
aperture with minimum wave front distortion generated
from thermal gradients in the air pocket within the
shutter.
The
cantilever flexure offers the simplest mechanical
movement with the highest reliability. This technology
eliminates the problems associated with friction
pivots, hinges, bearings with lubrication outgas, and
accumulated mass movements on linkage systems. This
technology is scaleable, allowing large aperture
designs for special applications.
Basic
Principle
Shutter Families
We offer
two families of shutters:
The
Modulation/Exposure/Gating
series provide fast
switching speeds and high repetition rates, with
higher electrical power dissipation use. These models
require sophisticated electronic drive circuits to
achieve specified switching performance. Our
controller series offer these drive circuits in a
convenient table top instrument package.
The
Safety Interlock & Process
series are designed for
moderate switching speed applications, at low
repetition rates, typically in safety interlocking or
industrial processing. The electrical power
dissipation is very low. These models are typically
held open for long periods of time and are designed to
be used with very simple drive circuits, most from 12
or 24 VDC. Typical drivers are the capacitor
discharge circuit or a pulse width modulated current
driver chip. We also offer a series of interlock
controllers for use in process and safety systems.
Optically,
the two shutter families are very similar. Power
handling and damage threshold ratings vary little. The
key difference is flexure beam stiffness and
electromagnet power.
We
recommend the shutters to be mounted very near to the
laser for safety purposes, and to take advantage of
switching across the smallest diameter location of the
beam. In cases of very high fluence, the shutter may
be mounted further downstream where divergence has
expanded the beam. Beam seal tubes are typically used
between the shutter and the laser or other optical
elements.
Laser
shutters are optical elements and need the care and
attention of optical elements when in shipment,
handled, stored, and in use. Typical laboratory
conditions provide a clean environment. Precautions
should be taken in some industrial environments where
debris is generated. The optical elements must be kept
clean for proper operation.
Back to top
|
