N131-081 TITLE: Membrane-Based Deformable Mirrors for High Power Laser Systems

TECHNOLOGY AREAS: Space Platforms, Weapons

OBJECTIVE: Develop MicroElectroMechanical Systems (MEMS) or larger scale membrane-based deformable mirrors for use with high power lasers and directed energy weapons.

DESCRIPTION: Deep turbulence conditions will exist in many Navy scenarios where the propagating high energy beam will expedite both phase and scintillation corruption. Scintillation becomes a significant problem in deep turbulence regimes where the atmospheric path has a Rytov number that exceeds 0.3, but is especially bad beyond 1.0. Current deformable mirrors for use with high power lasers utilize relatively thick continuous faceplate mirrors driven by piezoelectric or electro-ceramic actuators. The systems are expensive, bulky, and provide a relatively low number of actuators which restricts the number of modes that can be corrected. A large number of actuators with high bandwidth are needed in deep turbulence. MEMS, or other membrane-based deformable mirrors, have demonstrated low cost, high actuator count deformable mirrors.

The Navy is seeking AO systems which adapt the membrane-based technology to deformable mirrors for high power lasers. The beam control optics should be capable of handling intensity levels of up to 40 kW/cm2 and total laser power exceeding 100 kW for at least 30 seconds. The AO should be able to be addressed at high speed with low latency to compensate for aberrations moving due to high wind velocities, or platform or target motion. Because deep turbulence can have high D/r�0 ratios (where D is the aperture diameter and r0 is the Fried coherence diameter), beam control optics with high actuator density and larger number of actuators are of interest.

Desired Features:
� Capable of producing a one-wave phase discontinuity with minimal optical loss.
� Achromatic and not dependent on polarization.
� Capable of being addressed at speeds in excess of 10 kHz at phase change rates of 20 nm/�s or greater.
� Higher-order beam control optics with large actuator counts (>1000) and high actuator densities (actuator spacing <3 mm) ideally with a path to low cost manufacturing and parallelizable manufacturing.

Required Features:
� When designed to be used in the full high-energy laser beam, laser power handling of >100 kW with ?/20 uncompensated distortion over 30 seconds of high power illumination and less than 15% of the actuator stroke used to compensate thermally induced distortion.
� Capable of handling laser irradiance levels of >40 kW/cm2.
� To facilitate the use of pulsed illuminators, phase modulator should be able to handle peak pulse power >1 GW over the aperture diameter.

Beam control, in the presence of deep turbulence, has typically been addressed with a conventional AO system consisting of a wavefront sensor and a deformable mirror or liquid crystal phase compensator but suffer performance limitations due to atmospheric induced phase and amplitude aberrations. Analysis and demonstration of alternative architectures and comparison against a standard AO architecture is of interest, particularly systems that can feasibly operate in real time with current or near-term technology.

PHASE I: Develop a design of a membrane-based Deformable Mirror system including analysis, modeling, and simulation of system performance addressing the above desired and required features.

PHASE II: Develop a demonstration mirror capable of handling 10 kW/cm and 20 kw total of laser power at 1.06-1.07 micron wavelength. Verify performance against the above desired and required features. Develop an analysis and design of an advanced AO system with phase and amplitude compensation control.

PHASE III: Demonstrate an AO mirror for a 40kW /cm and 100 kW laser system addressing above desired and required features. Demonstrate an advanced phase and amplitude AO control system in the lab.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: An AO system capable of handling high laser power would be of interest to wielding community. Deep turbulence correction for laser propagation is of interest in a large number of communication and laser sensing applications including astronomy, space situation awareness, and Light Detection and Ranging (LIDAR).

REFERENCES:
1. Dimas, Clara, E., Perreault, Julie, Cornelissen, Steven, Dyson, Harold, Krulevitch, Peter, Bierden, Paul and Beifano, Thomas. 2003. "Large Scale Polysilicon Surface Micromachined Spatial Light Modulator." Proceedings of SPIE 4983. http://people.bu.edu/tgb/PDF_files/LargeScale_SLM_SPIE_4983.pdf

2. Dumas, Clara E, Bierden, Paul, Bifano, Thomas, Perreault, Julie and Riemann, G. 2002. "High Speed, Compact Adaptive Optics Using MEMS Silicon Deformable Mirrors." Lasers and Electro Optics, CLEO �02. Accessed June 8, 2012. doi: 10.1109/CLEO.2002.1033440ISBN.

3. Mansell, Justin, Praus, Robert, Maynard, Morris, Praus, Mark and Praus, Stephen. "Progress on Compact Low-Cost Adaptive Optics Systems for Enhanced Imaging and Laser Wavefront Control." DEPS Beam Control Conference, March 2006]

4. Rodriguez-Ramos, L.F., Alonso, A., Gago, F., Gigante, J.V., Herrera, G. and Viera, T. 2006. "Adaptive Optics Real-Time Control Using FPGA." IEEE Field Programmable Logic and Applications. Accessed June 8, 2012. doi: 10.1109/FPL.2006.311250.

5. J. Mansell et al., "High Power Deformable Mirrors," SPIE Conference Mirror Technology Days 2007. http://www.activeopticalsystems.com/docs/Mirror%20Tech%20Days%20070801_asGiven_Compressed.pdf

KEYWORDS: Adaptive optic system; deformable mirror; high energy laser; deep turbulence; Micro Electro Mechanical Systems

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