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.
Laser 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 laser 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.
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 drive circuit is the CX4000B.
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. Our CX4000B is a cost effective plug & go driver.
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 laser 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.
Safety Interlock and Process Control Laser Shutters
Laser shutters in this group are designed for high optical power and damage thresholds, but with lower emphasis on speed.
The Safety Interlock Laser Shutter is normally kept open for long periods of time, closing only for breaches in the safety system or at the end of an experiment.
The Process Control Laser Shutter is used at frequent intervals, allowing equipment to move or change in between optical exposures. An example would be laser cutting. At various points, the laser shutter would block the laser to allow table repositioning and cutting to resume.
All Safety Interlock and Process Control Laser Shutters are fail-safe and close upon power loss. They are not dependent on gravity to close.
Switching speed requirements for safety and process applications are moderate. The flexure technology used in these products offer inherent fast switching without developing large heat loads in the electromagnet. Typical speeds are a few tens of milliseconds.
Many of these applications can use low power, simple electronic drive systems. See our Application Notes page for more on OEM and user built drive circuits. Our Laser Shutter Controller product CX4000B is the most convenient way to drive the shutter and extract all benefits of the shutter design.
Position sensors are on most of the models, providing a safety or process circuit with verification that the laser shutter did indeed open or close as it was instructed to do from the power circuit.
These position sensors are completely independent of the power circuit. They audit the physical movement of the flexure blade, with either solid-state opto-interrupters for smaller apertures, or mechanical micro-switches for larger apertures.
The solid-state sensors are powered from regulated 5 VDC at about 20 mA current budget. There are two output leads which yield a logic hi or low depending on laser shutter state.
The output signals are logic ready TTL totem pole outputs, able to drive up to about 5 mA. This signal can be used to control software or to drive power electronics for warning light illumination.
The mechanical micro-switches provide contact closure for the open and closed states. There are two leads for each switch. Typically switches are operated at 5, 12, 24 VDC at a few tens of mA, but are rated for use at several Amps. Contact resistance is less than 5 ohms with cable loss included.
Many of these models are driven with user-built circuitry. Switching speed is very dependent on the circuit, with more advanced circuits providing faster speeds. In general, all models close in less than 50 msec, with an approximate rule of 4 msec per mm of aperture diameter.