Fiber Amp 2 MDC Bias Control DA12000 AWG RF Amp Seed Modulator Fiber Pre-Amp Fiber Amp 1 Ext. clock sync to RFQ Pump VDRIVE Fiber Port REA Amp RBA Amp Fermi OPG PriTel Yb FA Optical Engines PCF FA Free Space Osc. Keep Alive Trigger sync to RFQ Matching Optics Beam Stacker Transport Optics 15 Hz CW = 2W CW = 48 mW =425 uW 100 mW CW Measured Small signal gain ~ 25 dB both modules Measured peak gain ~ 20 dB

Average power in the Cw pumped amplifiers determined by keep-alive Aveg Power out of PriTel power amplifier is 2 W (measured) Peak Power = * 2.2 us/46 ns Peak power at interface ~ 96W Power interface using 10 um MFD at PtiTel full 2W power is 25 kW/mm2 At 2W: Energy in KA pulse 4.5 uJ Energy in Notch pulse 240 nJ

Fiber Damage Two phenomena – bulk fiber damage threshold usually associated with peak powers in ps and fs pulses with the threshold in the 10’s GW/cm2, – End facet damage – usually due to average power and heating of the silica at the glass-air interface. End facet surface irregularities or polish In fiber to fiber connections mis-alignment can cause heating Dust particles (absorb energy & raise temp)

End facet damage threshold – There seems to be no agreed upon number – NO hard fast number Coastal connections -> clean interface 25 kW/mm 2 (comfortable fluence) -> “dirty” interface 5 kW/mm 2 Diamond -> 1 micron dust particle on core 3 kW/mm 2 How to raise threshold -> increase MFD at fiber-fiber or fiber to air interface – Free space coupling – Expand core – Use coreless end-cap – GRIN fiber end-cap – Different techniques fiber-air and fiber-fiber Apart from manufacturing issues the way to assure survivability -> keep it clean !!! – INSPECT-> CLEAN -> INSPECT -> INSTALL Inspection Tools (currently use) – Optical scope (currently 200x ) -> used for routine/ limited – Video scope (400x) – can save images – cumbersom

125 um

Spare delivery fiber Initial delivery fiber Initial delivery fiber- cleaned

PriTel Delivery Fiber Optical Engines Input fiber (thru the ferrule)

What are we doing/done? The last failure – No smoking gun (can’t identify any setting errors) – Running PriTel at half power (~1W) amplifier behaving well – Could be manufacturing defect (not likely) – Most likely contamination What have we tried ? – We’ve tried expanded core technology on 6 um SM fiber (first interface that failed) – LMA delivery/input fiber 10 um MFD (~8.9 um core diameter) Developing fiber cleaning handling procedure Evaluating strategies for making the connection more robust – Investigated fiber-free space - fiber coupling Tuning can be sensitive Coupling efficiency not very good

– Investigated end-capping Technique to increase MFD and reduce power at tip of fiber Fusion splice ~300 um coreless fiber to end of SM/PM fiber to increase MFD at fiber air interface Mainly used for fiber – free space delivery systems Found only two manufacturers which will consider making fiber connectors with end caps – OM6: They have only made one – Diamond: Developed (2001) fiber connector based on GRIN fiber fused to the end of a SM/PM fiber to increase MFD by x4 to x5. Established product.

Power Solutions: Diamond Technology DIAMOND USA 20-Jul GW/m Computer simulation: The use of a GRIN fiber allows Diamond to use standard connectors with standard SM fibers to transmit powers up to 3W!! SM fiber GRIN fiber SM fiber GRIN fiber splice connector 1 connector 2 Integrated black metal protective caps - Maximizes operator eye safety protection from damaging laser radiation. - Close automatically upon extraction to protect ferrule from dust and scratches

Core Size vs. Max Power Core Size ( µm): Max Power: W W mW mW mW mW DIAMOND USA 20-Jul-1512 Max Power Density ( δ) : 0.3MW/cm 2

Plans Fiber connector – Consulted with both Optical Engines and PriTel. – Proceed to order a set of delivery fiber connectors based upon GRIN technology (plus spare) – We supply Nufern fiber to Diamond (prepare order today) – Cost estimate ~$750/set – Only 1 facility makes these (Switzerland) – Lead time several weeks (dependent on work load of lab) – Order 400x fiber scope & additional cleaning supplies Installation Task – Optical Enclosures

Cabling for timing/RF/ethernet New MEBT floor plates Software Instrumentation Rack cabling Safety

900 um lose tube 1 meter fiber length 3 mm armored cable 900 um lose tube 3 meter fiber length 1 meter fiber length Bulkhead Strain relief E-2000 PS mating adapter w/ screw fixing clip Amplifier Connector w/ armored cable Connector w/ 900 um tube Assembly 1 Assembly 2