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Laser Launch Facility Mini-Review

Laser Launch Facility Mini-Review. Contributors: Jason Chin, Thomas Stalcup, Jim Bell, Drew Medeiros, and Ed Wetherell. Agenda. 9:00AM Introductions

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Laser Launch Facility Mini-Review

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  1. Laser Launch Facility Mini-Review Contributors: Jason Chin, Thomas Stalcup, Jim Bell, Drew Medeiros, and Ed Wetherell

  2. Agenda • 9:00AM Introductions • 9:05AM Presentations: Overview, 5 min. Beam Generation System, 30 min. Beam Transport System, 20 min Switchyard, 20 min. System performance 20 min. • 10:50AM Break • 11:00AM Open discussion • 12:00PM Committee closed session • 12:45PM Review committee feedback to team

  3. LLF Reviewer Charter • Reviewers: Olivier Martin (WMKO, Chair) Renate Kupke (UCO-Lick) Viswa Velur (Caltech) • Does the LLF team understand the critical requirements? • Does the opto-mechanical design satisfy the requirements? • Is the opto-mechanical design technical feasible to fabricate? • Are the technical risks clearly defined and are there plans to mitigate the risks?

  4. Requirements • Laser Launch Facility Requirements • From three sources within Contour. • 2.0 Overall Laser Guide Star Facility Requirements. • 2.3 Overall Beam Transport System Requirements. • 2.3.6 Diagnostics (within BTS). • Functional requirements • Opto-mechanical system to transmit or relay the laser beams for central projection onto the sky. • Generation of the 7 LGS with proper orientation. • Beam steering and centering. • Diagnostics such as beam quality, laser power, and polarization not included in Laser Units. • Operational range: elevation range (0° to 70° zenith angle).

  5. Requirements • Functional requirements (continued) • Ability to operate with the existing Keck II dye laser. • Meet all ANSI and laser safety related requirements. • Implementation requirements • Does not add any additional vignetting. • Does not impact daily and nightly operations (maintenance and service). • Re-use of a launch telescope similar to the Keck 1 unit. • Performance requirements • Peak power for 3 lasers (4.5KW/cm2) • 0.9” spot size on sky; work in progress to define this in terms of WFE. • 60% throughput, including launch telescope (was 75%). • On-sky laser positioning range of 30” with position tolerance of 0.3”. • Circular Polarization 98%.

  6. Focus of the review • Opto-mechanical designs between the Laser Units and the launch telescope. • Does not include software for the LLF or the motion controller. • Management issues will be presented at PDR. • Assumptions. • Laser Units: 3 lasers providing 25 watts each. Lasers will be housed in one or two laser enclosures situated on the elevation ring. • Re-use of a launch telescope design similar to Keck I; LT design is not included in this review

  7. Definitions • BGS – subsystem within the secondary socket to generate asterism and provide PNS. • BTO – on telescope structure to relay the beams. • SYD – on elevation ring to steer lasers into BGS.

  8. Telescope References

  9. Beam Generation System • Central Asterism Generator (CAG, 4 beams). • Point aNd Shoot (PNS) generator and positioning (3 beams). • Steering of all beams on sky. • Tracking of lasers for non-sidereal objects. • Imaging of pupil on the launch telescope secondary mirror. • Rotator control. • Polarization control (possibly if needed). • Sensing of position to control mirrors in the SYD for telescope flexure. • Beams and asterism diagnostics. • Final (fast) safety shutter.

  10. BGS (Iso-view)

  11. BGS (Iso-view)

  12. CAG

  13. PNS Module

  14. BGS Rotator / Diagnostics

  15. BGS interface at top end (horizon view)

  16. BGS on LTA

  17. BGS Interface with Counterweight

  18. Design Advantages • Design is relatively compact. • Allows for PNS to move about within field; not limited to individual sectors. • Allows for non-sidereal tracking. • BGS fits on top of the launch telescope; minimize independent motion between BGS and launch telescope.

  19. BGS Motion Control • Size and weight constraints require the use of piezo linear motors. • Selection of smaller and lighter stages • The current design uses three PI M-683 piezo ultrasonic stacked stages (1350g). • Stages may have difficulty moving in the vertical direction when stacked. • New design calls for SmarAct stages (183 g). • Option with tensioning system to balance load. • Blocking force can be increased. • Reduce the support required for lighter stages. • New stages should reduce the overall mass by 8.5 Kg. • SmarAct can be controlled by USB, LabView, or RS232. • Risk reduction during DDR phase to test stage and tracking performance.

  20. Risk Assessment • Risk Definitions

  21. BGS Risks • 1. Polarization changing as the K-mirror rotates (3,3) (likelihood, consequence). • Need to understand whether several degrees in angle can adversely affect the polarization due to coatings. • Understand coatings from manufacturers to understand its dependencies. • 2. Ability to fit the components within its volume and meet its weight restriction (2,2). • Need to complete design of supports and determine the final weight. • New smaller stages should minimize this risk. • The counterweight mechanism on the f/15 may need to be modified; resulting in additional cost. $2.5K of procurement and 1 man month of labor. • 3. Air breakdown due to internal focus (2,2). • Further examination is needed to determine allowable peak power at focus. • If needed, the beam expansion optics must be change to reduce power density.

  22. Polarization Control • The launch system introduces an arbitrary polarization shift • This will be compensated by applying a conjugate shift in the system • Currently, this is done per laser in the laser enclosure • Assumes that polarization shift is identical over the multiple paths after the beamsplitter(s). • There are a few surfaces where the incidence angle varies by +/- 2.7 degrees which may result in per-beam polarization variations • If the per-beam polarization shift is too large, control will have to move to the BGS after the beam splitters • This is undesirable, as it would result in adding up to 14 motion devices to the BGS…

  23. BGS Risks • Telescope vibration (2,1) • Known vibration modes need to be verified on its impact. • If needed, input high rate correction into SYD pzt stages. • Diagnostics (2,1) • Further layout is needed to ensure all diagnostics can fit onto breadboard. • Layout of shutter to allow real time diagnostics even if shutter is closed. • PNS motion devices (1,1) • How well they will work in a changing gravity vector. • Test device in house. • Additional risk reduction • Investigate the feasibility of using the BGS design layout for the center launch system project on K2. • Partial implementation of the focus, beam expander and diagnostics.

  24. Beam Transport Optics (BTO) • Relay the 3 beams from the Laser Units to the BGS. • Operate over the elevation ranges of 0° to 70° zenith angle. • Additional requirement to assure this will operate with the current Keck II dye laser. • Install this subsystem in FY’11 as part of the Keck II Center Launch System Project.

  25. Flexure • Important to understand the amount of flexure in the design of the BTO • KOR 90 estimates motion to be 1.7mm with an additional 19” of motion; combined of 2.9mm of motion • Current K2 flexure pointing model shows 19” of flexure for the entire system, telescope, laser, sodium distance, secondary module, telescope pointing model and acquisition system • Recent K2 flexure testing shows a maximum of 2.9 mm motion from the elevation ring to the current L4 position (top ring)

  26. Flexure displacement (LRD)

  27. Closed Loop Operations • Use of PSD to determine beam location at the BGS to control flexure along the BTO • On-Trak PSM2-4 provides 4mm range and 0.1um resolution. • May require modification to sensor packaging to fit into the compact design of the three beams; 25mm separations

  28. Long Relay Design

  29. Long Relay Design (LRD)

  30. Long Relay Design

  31. LRD entry into the secondary +X +Y

  32. LRD considerations • Entry into the secondary socket is from the –Y direction; allows greater freedom in attaching equipment; minimizes any interferences with the telescope as it comes to horizon. • Entry into the secondary socket is oriented for location of the BGS (-Y of the module). • Entry into the secondary socket minimizes interferences with servicing within the f/15 module for operations. • Mounting of light tubes on the telescope in the –Y direction minimizes interferences with the telescope as it comes to horizon. • If an additional laser is needed to be installed at the RBC, it can easily tie into the LRD. • Beam path travel to the top ring at an angle resulting is smaller flexure error. • The –Y direction of the telescope is more difficult to access for installation, alignment and service.

  33. Short Relay Design (SRD) +X +Y

  34. SRD Considerations • Most direct path to the top socket from the Laser Enclosure (LE); • May reduce the number of reflective surfaces by 1. • Re-use existing Keck II L4 launch telescope tube support structure to support new tube. • Easier access to locations on the telescope for installation, alignment and servicing. • Entry into the socket from +y; may impact servicing of f/15 module. • If additional Laser Unit is needed at RBC, an identical BTO is needed. • Entry into the top socket is from the +y direction, opposite of where the BGS is located • Interferences with the telescope as it comes to horizon.

  35. SRD and Telescope Interference • Limitations of volume for opto-mechanical mounts • At the L4 corner, ~20 cm of clearance as the telescope approaches 20 degrees near the Nasmyth deck • At top end socket, ~ 20 cm of clearance as the telescope approaches horizon near the Nasmyth deck Nasmyth Deck Nasmyth Deck

  36. Tube Design Considerations • Tubes exiting the laser enclosure will be larger than those crossing the spiders. • Tubes at the laser enclosure; 3” x 4”. • Tubes at spiders and secondary socket; 1” x 3”. • Exterior of tube will be low emissivity paint. • Interior of tube will be an uncoated dispersive surface. • The attachment points to the telescope will be compliant to not impact the telescope structure performance.

  37. Keck II Center Launch System Applicability • Take advantage of the existing optical trombone on the laser table. • Install a M1 and beam expander prior to the current M3 • Allow for switching between current Keck II laser operations and with new BTO/BGS. New exit location Current M3 New M1

  38. f/15 module modifications • Using either the LRD or SRD designs requires modification to the top end socket. • Infrastructure modifications to support existing glycol, pneumatics, and cabling. • Counterweight design may need to be modified to fit the required volume of the BGS.

  39. BTO Risks • Flexure is larger than expected (2,1) (likelihood, consequence) • Still a possibility; but is significantly reduced due to testing on Keck II. • Design to allow an additional stage for the LRD to compensate for this. • Vibration on the telescope (2,2) • More data needs to be gathered. IF data is mainly concerned with focus (OPD) versus tip-tilt. • Test to move current accelerometers from top end mirror to the LTA in Keck 1. Should provide an idea of expected vibration seen by BGS. • SRD allowable volume (2,1) • Need to finish design to assure volume is sufficient to install opto-mechanics at the pinch points at L4 and the top end locations.

  40. SYD Requirements • Format of the three laser beams to relay via the BTO to the BGS. • Control of beam polarization at the output of the laser for circular polarization on sky. • Support installation of the Laser Units onto the elevation ring. • Support laser alignments. • Control laser beam power for alignment purposes. • Provide a separate method to align BTO/BGS without the requirement of the 589nm Laser Units; rough alignment. • Diagnostics not provided by the Laser Units.

  41. SYD Location • Installation inside existing LE

  42. SYD Layout with Laser Units • 3 Laser Unit heads to be installed on an optical bench. • SYD will be located in the middle of the same platform • Sized similar to existing laser table (6’x5’); can be increased to used existing space for dye lines.

  43. SYD Layout

  44. SYD Design • Quarter and half waveplates to control polarization for each laser • Polarization is not expected to change much in real time. • Afocal beam expander telescope to convert 3mm laser beams to 1.14mm diameter beams for BGS. • BTO flexure will require piezo control of tip/tilt mirrors to properly center beams from SYD to BGS; 0.57” resolution requirement. • Piezo tip/tilt mirrors will also support vibration control if necessary. • Alignment laser for rough alignments. • Dual optics stage to reduce laser power for alignment through system. • Beam dump for excess laser power as well as measurement.

  45. SYD Mounting • Similar mounting to the existing laser table and auxiliary units, estimate 1,700 Kg. • Attach to existing elevation ring supports via pads to elevation ring structure. • Elevation ring was stiffened with internal gussets during K2 laser install

  46. SYD Risks • Laser Units larger than expected (3,3) (likelihood, consequence) • We believe a minimum of 2 lasers can be implemented in the LE; the third is in question. Once Laser Units design is further along, this risk will be retired. • A backup plan is to install a third unit at the RBC location. • Polarization (3,3) • Do not expected to change once system is set in place. Current laser technology has 700:1 linearity ratio. • If the polarization varies due to pointing, up to 14 separate polarization controls may be needed at the BGS. • Further understanding of the coatings is necessary to determine the significance of this risk to meet the 98% circular requirement.

  47. LLF Motion Control • 29 Degrees of Freedom (DOF) in Laser Launch Facility • Precision • millimeter to 10 um linear accuracy • milli-radian to sub micro-radian angular accuracy • Locations • laser enclosure (13 DOF) • secondary (16 DOF) • Types • rotation (asterism rotator, polarization waveplates) • translation (in/out, focus, PnS steering) • tip/tilt (beam steering, asterism pointing, vibration compensation) • servo (most things) • piezo (for precision: beam steering, PnS steering) • tracking (flexure compensation, off loading, sidereal motion, non-sidereal motion)

  48. LLF Motion Control • Actuator choices • traditional linear and rotation stages • Brushed DC servo motors, drive or load encoding, end of travel switches • lots of experience with design and integration • good match with either centralized or distributed motion control architecture • traditional piezo tip/tilt stages • smooth, high precision, high speed actuation, strain gauge readback • experience with design/integration • more suited to centralized MC architecture • care must be taken with high voltage signals • piezo translation stages (PnS steering) • smooth, very precise actuation • not currently used at WMKO • turnkey and OEM type controller/driver solutions available • more suited to distributed MC architecture • should work with centralized architecture, cable length is the concern

  49. Cleanliness of the optics • To achieve the level of throughput, it is imperative the optics remain clean. • 20% throughput gain for clean vs. dirty optics. • The entire system will be sealed for laser safety and cleanliness. • A positive pressure of 1 to 2 CFM of facility dried air is planned for the LLF. • Dried air is already available at the BGS and SYD. • Cleanliness is also important for the optics due to high laser power density.

  50. Safety • Compliance with ANSI Z136.1 standards. • Hazardous radiation containment. • Within cover for BGS • Within beam tubes for BTO • Within laser enclosure for Switchyard • Indicators providing laser status at each service point • Interlocking with safety system to contain radiation hazards.

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