ECR Title: ECR: Add half-wave plate to REFL beam path in HAM1	DCC No: E1300419-v1
Date: 5/13/2013
Requester: Peter Fritschel	Impacted Subsystem(s): ISC
Description of Proposed Change(s): Proposed changes: Add a 1” diameter half-wave plate (1064 nm) in the REFL beam path in HAM1. The wave plate will be installed just after the beam splitter that directs most of the REFL beam light into a beam dump.
Reason for Change(s): This will rotate the beam polarization to horizontal in HAM1 (after the splitter). This addresses an interface mis-match where IO delivers the REFL beam into HAM1 with vertical polarization, but ISC had been assuming horizontal polarization. We insert the wave plate after the first splitter so that any back-scattered light from the wave plate is minimized. For the first splitter (M14 in D1000313), will be changed to use a 90/10 R/T splitter coated for s-polarization, available from the iLIGO optics stock.
Estimated Cost: Wave plates: approx. $2k (4 plates from Precision Photonics, WPZ10H-FY) Mounts: might have sufficient mount hardware in hand; if not, new hardware estimated at $1k
Schedule Impact Estimate: None.
Nature of Change (check all that apply): Safety Correct Hardware Correct Documentation	Improve Hardware Improve/clarify Documentation Change Interface Change Requirement
Importance: Desirable for ease of use, maintenance, safety Desirable for improved performance, reliability Essential for performance, reliability Essential for function Essential for safety	Urgency: no urgency desirable by date/event: __June 2013__ Essential by date/event: Immediately (ASAP)
Impacted Hardware (select all that apply): Repair/modify. List part & SNs: ______________________ Scrap & Replace. List part & SNs:_____________________ Installed units? List IFO, part & SNs: _________________ Future units to be built	Impacted Documentation (list all dwgs, design reports, test reports, specifications, etc.): D1000313
Disposition (to be completed by Systems Engineering): TRB CCB Approved Additional information required. Define: [Requester re-submits with new information with the same DCC E-number for the ECR but the next version number.] Concurrence by Project Management: (Acknowledged Electronically in DCC) Project Systems Engineer: Dennis Coyne Project Systems Scientist: Peter Fritschel