For latest on DM, click "News Room" tab: TechUpdate, Spring 2010
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Technology Highlights and Status
Optical Physics Company(OPC) completed the design, manufacture and test of a Deformable Mirror(DM) for tactical HEL applications. The final product is shown in Figure1. Made entirely of silicon pieces bonded together, it is strong and endures long exposures to an HEL beam without any rippling or waffling effects.
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The key requirements for this DM involved stroke, frequency response, thermal ripple and scatter. The OPC DM significantly exceeds the performance of the awailable products and has an almost vanishingly small level of thermal ripple under 200 seconds of continuous operation to HEL beam exposure. A detailed scatter analysis shows that the facesheet design will add less than 1 ppm of scatter to that of a simple super-polished silicon mirror.
Click the image to enlarge.
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While fabricating and testing this DM, we have developed extensive procedures for assembly and test. We have also worked with our vendors to optimize the fabrication of the key components. As a result, we can confidently move forward to the next stage to manuacture a 30 cm size DM. The technology readiness level(TRL) of this next DM will be TRL 6.
The ability to integrate the actuator drivers onto the backside of this DM is another key advantage. Instead of a rack of electronics, all that will be required will be power and ground plus a bit serial data line to pass actuator commands - much simpler and more compact.
Collectively, work done so far brings the OPC DM to TRL 5 which includes:
- Actuators of the form factor desirable in many HEL applications
- Frequency response out to 7.5 KHz
- Little performance effect after thermal loading comparable to minutes of continuous HEL beam exposure
Note:TRL 6 is defined as the "System/subsystem model or prototype demonstration in a relevant environment." At TRL 6, a representative model or prototype system or system — which would go well beyond ad hoc, ‘patch-cord’ or discrete component level breadboarding — would be tested in a relevant environment.
TRL 5 is defined as the "Component and/or Breadboard Validation in Relevant Environment", where the fidelity of breadboard technology increases significantly. To reach TRL5, the basic technological components are integrated with reasonably realistic supporting elements so that it can be tested in simulated environment.
Advantages of the OPC DM Design over the state of the Art
Current HEL deformable mirrors have a standard architecture consisting of piezo-stacks attached to a thin face sheet through flexures all mounted on a base plate. A thin face sheet is required to minimize the bending stiffness of the mirror in response to the pistoning piezo-stacks. This standard DM design produces significant thermal deformation from three contributing factors, as follows:
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The thin facesheet heats up tremendously compared to the actuators and baseplate resulting in differential expansion. This differential expansion twists the flexure attachments to the actuators creating a ripple in the surface.
- The facesheet and its flexure attachments can have a local mismatch in thermal expansion which creates a local curvature above each actuator and a ripple effect across the surface.
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Any ribbing in the structure of the facesheet will print through under thermal gradients.
In contrast to the standard DM, the OPC DM design does not have any of these thermal weaknesses and withstands 200 second HEL irradiation with < 0.006 mm peak-to-valley surface ripple – even at 200 watts absorbed power.
With a deformable mirror capable of piston-tip-tilt control of each actuator, there are three times as many degrees of freedom as with a standard DM. The benefit here is that the fitting error with the OPC DM will be much less than the current DM
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DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Approved for Public Release 08-MDA-3306 (17 MAR 08)
Material cleared for public release can be reused in its original form any time, any place. Any updating, changing or combining of previously cleared material will form a new document that requires the material be re-submitted for a new public release clearance. Please re-submit any new material with the past clearance documentation. A marked copy of the document indicating where new information is placed will help speed the review.
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