INTEGRATION OF IFE BEAMLET ALIGNMENT, TARGET TRACKING AND BEAM STEERING Graham Flint March 3, 2005

BISTATIC TARGET TRACKING CONCEPT l Tracking error is estimated to be ± 5  m or less in all axes l 3-axis tracking is provided throughout acceleration and in-chamber trajectory l Minimizes acceleration of beam-steering elements Bistatic reference #1 Optical Doppler sensor Zero-crossing sensor Target IFE Chamber Centroid sensor (Bistatic reference #2) Optical stop Gaussian beam Electromagnetic target accelerator Laser

PRACTICAL LAYOUT OF TARGET INJECTION AND TRACKING SYSTEM l 3–axis tracking confined to in-chamber trajectory

The laser profile at the aperture is imaged through the amplifiers onto the target If the optical distortion is small, then the image duplicates the aperture Concept of Induced Spatial Incoherence (ISI) Intensity profile at target instantaneous averaged Diffuser Oscillator Amplifiers Target Aperture Intensity profile at aperture instantaneous averaged BASIC LAYOUT OF KrF DRIVE LASER

Target FRONT END ( 20 nsec) LONG PULSE AMPLIFIER (~ 100's nsec) Multiplexer Array (beam splitters) Demultiplexer Array (mirrors) Only three beamlets shown for clarity Last Pulse First Pulse EACH MAIN BEAM DIVIDED INTO BEAMLETS

ASSUMPTIONS l Chamber gas has negligible effect on target trajectory l Target injection accuracy is ±1 mm l Shot-to-shot system drift is less than allowable beam/target alignment budget (200 msec) Optimistic Scenario l Chamber gas has some effect on target trajectory l Target injection accuracy is ±5 mm l Shot-to-shot beamlet co-alignment drift exceeds allowable beam/target alignment budget (5-10 msec) Pessimistic Scenario

TARGET TRACKING AND BEAMLET STEERING CONCEPT (OPTIMISTIC SCENARIO) Coincidence between each outgoing beamlet and target determined ~10 ns before shot Error signals used to co-align beamlets prior to next shot All beamlets (in one beamline) collectively aligned via fast-steering aperture

OPTIMISTIC SCENARIO APPROACH l Single bistatic sensor l 3–axis tracking throughout in-chamber trajectory l Precision better than ± 5  m (all axes) Target tracking l Fast collective steering of all beamlets in a beam line l Two-axis translation of a single lightweight element (~20 mg) l Precision better than ± 5  m (2 axes) Beam steering l Slow (10 Hz) alignment of each beamlet l Each beamlet alignment update based on data from previous shot Beamlet co-alignment

ASSUMPTIONS l Chamber gas has negligible effect on target trajectory l Target injection accuracy is ±1 mm l Shot-to-shot system drift is less than allowable beam/target alignment budget (200 msec) Optimistic Scenario l Chamber gas has some effect on target trajectory l Target injection accuracy is ±5 mm l Shot-to-shot beamlet co-alignment drift exceeds allowable beam/target alignment budget (5-10 msec) Pessimistic Scenario

TARGET TRACKING AND BEAMLET STEERING CONCEPT (PESSIMISTIC SCENARIO) Misalignment between each outgoing beamlet and target determined 2 msec before shot Individual beamlets directed via fast-steering mirrors

TARGET ILLUMINATION VIA COMMON FOOTPRINT ON GRAZING INCIDENCE MIRROR Can combine selectable lead time with large target injection errors Steering mirror speed can be matched to alignment drift rate Allows wide range of target injection velocities

PESSIMISTIC SCENARIO APPROACH l Single bistatic sensor l 3–axis tracking throughout in-chamber trajectory l Target position predicted to ± 5  m at t  -2 msec (all axes) Target tracking l Fast steering of individual beamlets l Two-axis steering mirror immediately ahead of GIM l Coarse adjust commences at t  -20 msec l Fine adjust commences at t  -2 msec l Precision better than ± 5  m (2 axes) Beam steering l Probe beam interrogates entire beamline (t  -2 msec) l Coincidence sensor/retroreflector in each beamlet l Beamlets individually aligned to predicted target location at t  -1 msec Beamlet co-alignment

SUMMARY & CONCLUSIONS l Target tracking and beam pointing with a precision of ±5  m can be achieved l Parts count changes little between “optimistic” and “pessimistic” scenarios l Principle cost tradeoff exists between beamline stability and steering mirror response time l Could be significant cost impact for “fast” versus “slow” steering mirrors l Assessment of IFE vibration/drift environment is an important step in the system definition process

TRANSVERSE TARGET TRACKER VIEWS TARGET ALONG FLIGHT AXIS Typical values: = 532 nm, a = 2 mm, 7m < z < 14 m z = 7 m Centroiding accuracy ~ 2.5  m z = 14 m Centroiding accuracy ~ 5  m Consistent with CCD framing rate of 2000 fps, 1024 x 1024 resolution FLIGHT

LONGITUDINAL TARGET TRACKING BY OPTICAL DOPPLER ALSO VIEWS TARGET ON FLIGHT AXIS Transmit / receive aperture~ 10 mm Maximum target range~ 20 m Laser wavelengths488 nm, 515 nm Subcarrier fringe resolution4.7  m Fringe count rate ~ 43 MHz Photoelectron count rate~ 10 9 W (s -1 ) Laser power W Range resolution ( /4)± 2.5  m FLIGHT

SHARP POISSON SPOT ALLOWS PRECISE TIMING OF ZERO-CROSSING SENSOR l Source/sensor separation~ 0.25 m l FWHM spot diameter~ 12.5  m l Spatial resolution< 1  m