Presented by Lane Carlson 1 M. Tillack 1, T. Lorentz 1, N. Alexander 2, G. Flint 2, D. Goodin 2, R. Petzoldt 2 ( 1 UCSD, 2 General Atomics) HAPL Project Review NRL, Washington D.C. October 30-31, 2007 Progress on Tracking & Engagement Demonstration

Hit-on-the-fly experiment has demonstrated engagement on moving target 1)Engaging moving targets (5 m/s) with a simulated driver beam by using the glint return signal to steer a fast steering mirror. 2)Improved simulated driver beam and target engagement verification system: 1 mm range 7 µm resolution 3)150 µm (1  ) engagement for all targets with ± 1.5 mm placement, (110 µm (1  ) with placement accuracy < ± 1 mm) Prior reported engagement was 20% of targets in range of verification system (150 µm). Final Key Requirement: 20 µm engagement accuracy in (x,y,z) at ~20 m (10 -6 )

We are continuing our effort on the “glint-only” option table-top demo with help from Poisson spot “Remember we have two scenarios…”

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 & driver beam Glint return simulated driver beam

Effort to improve engagement accuracy to 20 µm must address & minimize all uncertainties Initially effort focused on system integration and operation. Now, a more sophisticated control over the experiment is needed to realize 20 µm goal. Working to understand and address all errors and uncertainties: – Environment (air fluctuations) – Sensors (speed, noise) – Target (surface quality, sphericity) – Glint laser/return (repeatability, stability) Most dominant uncertainty so far is deciphering the glint return … Error contributions to engagement accuracy: -Reading glint return off target ~50 µm -Air fluctuations ~10 µm -Verification camera ~7 µm -Mirror pointing ~6 µm Glint off target

Target surface quality and glint laser energy output

Target’s surface roughness plays an important part in glint return Two contributing errors: – Glint laser’s pulse-to-pulse energy output variance – Surface roughness causes certain features to reflect back to PSD. 25 µm patch off target propagates back through optics to PSD Grade 25 SS BB Au-coated 4mm shell Surface features & roughness are important “When we are getting to 20 µm…”

Surface roughness can be correlated to glint return repeatability As surface roughness improves, glint return on PSD is more repeatable (for a stationary target). Rotation of the target on a kinematic stalk introduces sphericity errors. Light-weight shells require vacuum to implement

Glint return on camera shows target’s surface characteristics Surface characteristics are manifested by glint return on PSD. Rough targets may reflect light from a larger region, especially when rotated (a different surface is presented). Grade 25 SS BB glint return RMS roughness ~65 nm Au-coated 4mm shell glint return RMS roughness ~10 nm => Desire a smooth target for more repeatable glint return ~1 mm * * Glint return defocused to prevent PSD saturation ~1 mm * ---Glint returns---

Laser’s output energy and spatial profiles vary considerably Peak-to-peak energy ± 6% (consistent with laser spec’s) Expanded glint beams immediately before overfilling target ~1 cm Spatial profile is inconsistent from shot-to-shot, thus depositing randomly-distributed energy on target. ---Glint beams---

Laser’s energy variation thought to be causing some apparent target motion Same geometrical shape, yet hot spots skew energy centroid ~1 mm => Probable cause of shot-to-shot position variation of µm off rough targets, better for smoother. Glint return off a stationary, Grade 25 (rough) target at PSD location ---Glint returns---

Improving glint laser’s output may improve glint return repeatability All beams ~1 cm A more consistent, flat spatial profile may help improve glint return repeatability. Pointing stability may also be a concern. Current profile Imaging Homogenizer Flat-topped microlens diffuser Desire a smoother beam - more work to be done.

Driver Beam & Engagement Verification Improvements

Target equally eclipsing beamlets New simulated driver beam enables larger field of view Expanded observation range to 1mm. Computes light centroid of inner and outer ring (i.e. “non-concentricity”) Limited observation range (150 µm). Non-linear calibration. Computed light centroid of obscured and un-obscured beamlets. Driver beam overfilling target target Simulated driver beam

Verification algorithm post-processes snapshot to verify target engagement Post-processing algorithm can resolve 7 µm (1  ) engagement with 1mm range Pre-processed image 4 mm target, 4.8 mm beam Triggered camera takes a snapshot as the simulated driver beam engages the target.

Optic improvement yields clearer driver beam, more precise verification Short-pass filter required for glint return created striations. Replacing beam splitter and filter with pellicle eliminated interference.

False steering offset due to large wedge angle is corrected by Poisson spot system Solution: Use Poisson spot system to measure target’s Z-offset at glint location. Give one correction to FSM to modify steering. Wedge correction will not be an issue in a power plant due to long standoff. Simulated dichroic wedge “Z”

Poisson spot system gives one steering correction to FSM X,Y position of Poisson spot Final location at glint illumination time “Z” Target’s Z- position at glint location modifies mirror steering.

Optics In Motion fast steering 1” mirror Improvements to mirror ensure it is is positioned and settled in time for driver pulse Improvements include: – Alignment beam steering closer to PSD center. – Alignment gain improved. – Mirror hardware gain increased. – Dropping accuracy (< ±1mm). Glint return on PSD Commanded mirror position Mirror response Driver pulse Alignment mode Mirror not settled in time Mirror settled in time 5 ms Driver pulse

Current Engagement Results

We have engaged moving targets with a simulated driver beam using the glint return If injection accuracy < ±1 mm, engagement accuracy = 110 µm (1  ) Engagement accuracy so far = 150 µm (1  ) (with injection accuracy of ±1.5 mm) Stainless steel G25 BBs

Dropping water-filled PAMS, Au/Pd-coated sapphire spheres expedites our way to real shells Au/Pd-coated sapphire spheres are heavier and fall straighter in air than “real” shells. An expedient way to simulate higher-quality targets before we go to vacuum. Au/Pd-coated sapphire sphereWater-filled, Au-coated PAMS shell

Near-term effort focuses on completing demo, achieving 20 µm engagement goal In summary: We are using a glint return off a falling target to steer a simulated driver beam to hit it on-the-fly to nearly 100 µm. Verification system has 1mm range, 7 µm resolution. Table-top engagement demo honing in on 20 µm goal. Working on details of glint laser, glint return, and target surface quality. Long-term effort: Increase capabilities to mate with a prototypic injector in vacuum.

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Effort to improve engagement accuracy to 20 µm must address & minimize all uncertainties Contributing errors identified: – Target surface roughness – Laser not at thermal equilibrium – Room temperature & air fluctuations, dirt, optics – Spatial intensity variations in glint beam – Thermal drift of components – Saturating PSD – Asymmetric glint return – FSM not settled We are trying to systematically eliminate errors one-by-one. - One means of quantifying progress is glint return stability. Progress on Reducing Macroscopic Glint Errors (glint return repeatability off a stationary target)