Target Engagement Graham Flint - General Atomics Tom Lehecka - Penn State Electro-Optics Center Bertie Robson - NRL HAPL Project Review Oak Ridge National Laboratory March 21-22, 2006

Overall Concept for Target Engagement in a Semi-Rigid Environment Offset target is illuminated in flight by a Q-switched glint laser. Each coincidence sensor views the glint via the rear surface of a wedged dichroic mirror. Disparities between beamlet alignment and glint signals are used to reposition the fast-steering mirrors. Coincidence sensors verify pointing of redirected beamlets. Offset Target Chamber N-S axis Coincidence sensors ASE Source Alignment Laser Target injection / tracking subsystem Target glint source Dichroic mirror Cat’s eye retroreflectors Wedged dichroic mirrors Grazing incidence mirrors Segmented vacuum window Focusing mirrors Slow steering mirrors in the amplifier chain continuously center each alignment beamlet upon its coincidence sensor. Integrated injection / tracking subsystem places the target within a defined volume which is centered upon the chamber’s nominal center. Amplifier / multiplexer/fast steering mirrors

Geometric Correction associated with a Single Glint Reference Source Beamlet displacement from chamber axis:  Glint offset: a = r sin  /2 For negligible offset error (as   π):  a < 5  m For IFE ( r = 2.35 mm):  r/r ≤ 0.2% Current specification:  r/r ≤ 1.0% Target r Chamber axis   /2 Glint offset a

Null-Referenced In-Flight Measurement of Target Diameter, Transit Time and Velocity Corresponding diametric precision < 0.1% Requirement for glint offset correction 0.2% Velocity determination precision (0.5 m separation) ~ Target placement precision~ 100  m Assumed target velocity 100 ms -1 Image velocity (10x) 1000 ms -1 Mask slit width 25  m Transit time precision < 25 nsec tt Time Signal #1 Signal #2 Detector mask Detector #1 Detector #2 Monochromatic Illumination Source Target Trajectory 10X Telecentric Objective

Coincidence Sensor Views Target Glint via Common Footprint on Grazing Incidence Mirror Target injection / Tracking subsystem Target glint source Dichroic mirror Beamlet Target at t = 0 Target at t = -1.2 ms Grazing incidence mirror Wedge angle ~ 1 mrad Dichroic mirror has long wavelength pass first surface, high reflecting rear surface. Mirror wedge angle compensates for combination of target offset and glint parallax. Except for monolithic dichroic mirror, main laser and coincidence sensor share a common optical path. Common path eliminates sensitivity to vibration at frequencies below ~50 Hz.

Coincidence Sensor / Retroreflector Schematic and Performance Sensor clear aperture 100 mm Sensor effective focal length 15 m Sensor field at chamber center 4.5 mm X 4.5 mm Target-to-beamlet error (1  ) 24  m 3.2  collective centroid error (48 beamlets)11  m Position Sensitive Detector Main beamlet Target glint return Virtual return from beamlet LWP blocking filter Cat’s eye retroreflector Alignment laser beam Vacuum window 10X Microscope objective Coincidence Sensor

End-to-end Target Engagement Strategy SINGLE BEAMLET ENGAGEMENT PRECISION COLLECTIVE BEAMLINE CENTROID PRECISION BEAMLET STEERING MAXIMUM EXCURSION (PREC ) BEAMLET POINTING PRECISION COINCIDENCE SENSOR FIELD OF VIEW (PRECISION ) FAST STEERING MIRROR COMMAND PRECISION ELECTROSTATIC FINE STEERING VOLTAGE PREC ) POST-STEERING TRAJECTORY PRECISION TARGET TRACKING POISSON SPOT (X & Y AXES) CROSSING SENSOR/ OPTICAL DOPPLER (Z AXIS) TARGET LAUNCH (MECH. / EM SLING SHOT) DEMONSTRATED PERFORMANCE (MECHANICAL)  3.2  ( 99.9 % CONFIDENCE LEVEL ) Precision I II III