1. Presented by Lane Carlson 1 M. Tillack 1, T. Lorentz 1, J. Spalding 1, D. Turnbull 1 N. Alexander 2, G. Flint 2, D. Goodin 2, R. Petzoldt 2 ( 1 UCSD, 2 General Atomics) HAPL Project Review PPPL, Princeton, NJ December 12-13, 2006 Progress on Target Tracking & Engagement Demonstration

2. Omnipresent Target Engagement Requirement All individual tracking and engagement components have been operated successfully. All components necessary for a glint-only hit-on-the-fly demo have been integrated and are operational. Final Key Requirement: 20 µm engagement accuracy in (x,y,z) at ~20 m (10 -6 )

3. Current tabletop target engagement demo is complete with one simulated driver beam Glint laser now in operation Poisson & fringe counting systems not used in glint-only demo

4. Hit-on-the-fly experiment has demonstrated engagement on moving target 1)Update time of Poisson spot centroiding algorithm down from 10 ms to 3.5 ms in software. 2)Fringes off falling target counted over 3 mm. 3)Using crossing sensors, the timing & triggering system triggers all necessary lasers/components on-the-fly. 4)Engaged moving targets with a simulated driver beam by using the glint return signal to steer a fast steering mirror. 5)Verification system has been used to measure error in target engagement. 150 µm range 6 µm resolution

5. A range of tracking/engagement scenarios call for different requirements Sub system Example #1 Ultra -FSM Example #2 FSM Achieved (1  ) Target Injector (prob. TBD)± 1 mm± 5 mm4 mm Poisson spot centroiding (x,y position) N/A± 100 µm, 5 ms update time 5 µm, 3.5 ms Fringe counting (z position)N/A± 100 µm5 µm over 5 mm Crossing sensors (zero crossing, velocity prediction) ± 0.7 µs, ± 70 µm ± 10 µs, ± 1 mm 45 µm Glint/coincidence sensor± 10 µm FSM pointing precision± 5 µm, ~2 ms ± 6 µm, 2 µs Target engagement± 20 µm 150 µm ~20% of time Example #1: no in-chamber gas, glint provides final mirror steering Example #2: in-flight, pre-steering corrections by Poisson, fringe counter

6. #1 Transverse Target Tracking Using Poisson Spot Centroid

7. Reduced region of interest (ROI) technique further improves update time 4mm sphere on translation stage Update time reduced from 10 ms to 3.5 ms by implementing a “dynamic ROI” in software. Number of pixels to process is reduced from 307k to 10k. The smaller ROI assumes the target will not move more than a few pixels between frames. ROI is recalculated each frame to follow the Poisson spot centroid. 30x less pixels

8. New centroiding algorithm implements dynamic ROI 2) Brightness & contrast adj. 3) Threshold pixels above a certain value 4) Remove border objects 1) Capture image  Target position update time: 3.5 ms (5 µm 1  )  Closing in on goal of 1-2 ms 6) Dynamic ROI drawn 7) Pixels outside ROI excluded 5) Particles filter, centroid computed 8) Subsequent frames contain reduced number of pixels

9. #2 Axial Target Tracking Using Interferometic Fringe Counting

10. Similar intensities Fringe counting has been demonstrated over 3 mm Lower-noise photo-detector Higher-power laser (60 mW) => Fringes off falling target counted over 3 mm Mini drop tower setup Target releasing from vacuum needle Free-falling target Signal processing required to obtain countable signal 5 ms/div 20 µs/div time 5 V/div

11. #3 Crossing Sensors & Axial Position Prediction

12. Crossing sensors & real-time operating system compute predicted target location on-the-fly Last time: Established crossing sensors to be sufficiently precise (45 µm 1  ) to trigger glint laser. Overview of Timing Sequence: Timing sequence initiated by target crossing C1. C2 crossing yields target velocity. Velocity info used to trigger alignment beam, glint laser, verification camera, and driver beam. C1 C2 Glint Driver Disparity between predicted and actual target location is detected by PSD and corrected by steering mirror…  Timing and triggering system fully operational for our demo

13. #4 Glint System

14. New Wave 35 mJ, 1064 nm glint laser All necessary components have been integrated for glint-only target engagement demo Optics In Motion fast steering mirror Simulated wedged dichroic mirror Pulsed diode laser (simulated driver) Glint laser - final component of hit- on-the-fly demo has been installed

15. Wedged dichroic mirror compensates for glint/chamber center offset target at glint location Verification camera Simulated wedged dichroic mirror target at “chamber center” 1 cm glint beam Co-axial glint return and driver simulated driver beam

16. We have engaged moving targets with a simulated driver beam Targets fully engaged ~20% of the time (in 150 µm verification range) Last time we used a simulated glint return from a stationary target to steer a mirror. Now, we have used the “real” glint return signal from a moving target (5 m/s) to steer a simulated driver beam to engage the target. But does not meet the 20 µm spec yet… Snapshots of engaged targets 150 µm diam. verification beamlets 40% 20% 150 µm verification range outside range

17. Effort to improve engagement accuracy to 20 µm must address & minimize all uncertainties Errors & uncertainties from every subsystem contribute to engagement accuracy. We are working to understand errors and to address each one. – Air fluctuations, sensor noise, bandwidth limitations, response times… PSD signal with ground-looping Erratic 50 mV signal translates to significant mirror steering! (100s microns) Most dominant uncertainty so far is deciphering the glint return on PSD… Error contributions to engagement accuracy: -Reading glint return (PSD, LabView) ~100’s µm -Air fluctuations ~20 µm -Verification camera ~12 µm -Mirror pointing ~6 µm  Resolved by plugging all electrical components into same circuit

18. Glint return is used to make one final steering mirror correction depending on PSD reading Glint return on PSD gives target’s final position. LabView reads PSD signal, then calculates steering gain to give FSM. LabView loop time is 50 ± 20 µs due to non-deterministic operating system. Glint return on PSD X Glint return on PSD Y Glint laser q-switch Steering signal to FSM X-axis 100 µs/div Inconsistent voltage readings grossly and falsely steer the mirror. 2V/div

19. Peak-hold circuit picks off PSD voltage more consistently than software Peak-hold circuit holds the peak voltage until LabView can read it. Also researching other ways to read glint (photo-diode, quad-cell) Signal held by peak det. (not mirror command) Glint returns on PSD 50 µs/div => More work must be done on glint return characterization, PSD response, error/noise reduction. Rise time may also influence reading consistency 2V/div

20. #5 Engagement Verification for Hit-on-the-fly Demo

21. No target Target offset to the right ~ 100 µm Target equally eclipsing beamlets Applet post-processes snapshot to verify target engagement accuracy Applet computes light centroid of obscured and un-obscured beamlets. Resolution of 6 µm, 150 µm range target PSD beamlets imaginary target shadow

22. Summary of progress & plans #1 Moving target engaged by simulated driver beam #2 Transverse Tracking System Using Poisson Spot: Progress: Improved update time to 3.5 ms using dynamic ROI Plans: Implement into system to help pre-steer mirror # 3 Axial Tracking & Triggering Prediction: Progress: Faithfully triggering glint, simulated driver beam & verification camera. Also, fringes off moving target counted over 3 mm #4 Glint System: Progress: Glinted target & steered FSM to engage in-flight target Plans: Better characterize glint return & PSD response to meet 20 µm goal #5 Target Engagement Verification: Progress: Engagement verification resolution of 6 µm, 150 µm range Future Goals to Consider: - increase speed capability to couple with a 50 m/s injector - add more driver beamlines at different angles.