Yb YAG Regenerative Amplifier for A 1 Ground

Yb: YAG Regenerative Amplifier for A 1 Ground Laser Hut Super. KEKB Injector Laser RF Gun Review Rui　Zhang ACCL Division V, RF-Gun Group Nov 20, 2015

Outline • Back ground and introduction – Feasibility analysis and corporation – Current Yb laser system of A 1 ground laser hut • Yb: YAG regenerative amplifier – Cavity design – Experimental setup introduction • Next step work – Ring cavity – Cryogenic experiment • Summary Yb: YAG regenerative amplifier 2 of 11

Feasibility analysis and corporation • Feasibility analysis – In the picosecond or femtosecond domain, the regenerative amplifier is very powerful – Strong amplification factor can help relieve stress of multi-pass amplifier stages and reduce thermal effect • Corporation with Hi. LASE – Beamline B of Hi. LASE gets excellent laser amplification by use of Yb: YAG thin disk regenerative amplifier 1 – The parameters of Hi. LASE beamline B are very similar with our experiment Parameters of thin disk beamline B Schematic of the current status of Hi. LASE beam line B 1. M. Chyla, et. al “Composite Yb: YAG/Si. C-prism thin disk laser, ” Optimization of beam quality and optical-to-optical efficiency of Yb: YAG thin-disk regenerative amplifier by pulsed pumping Method Regenerative amplifier with one thin disk laser head Seed repetition rate 50 MHz Seed pulse width 500 ps Seed output power 2 W @ 1030 nm Pump power 1 k. W @ 969 nm Repetition rage of pump 1 k. Hz Achieved energy 45 m. J Next milestone energy 100 m. J Under development Add second thin disk laser head into regenerative amplifier Yb: YAG regenerative amplifier 3 of 11

Current laser system of A 1 ground laser hut Fiber part Repetition frequency 114. 24 MHz 1064 nm oscillator (ANDi type) Menlo 1030 nm oscillator (ANDi type) Wavelength selection 1030 nm & 1064 nm Repetition frequency 10 MHz Grating stretcher (Transmission) SOA pulse picker Yb single mode fiber amp Yb-doped double clad fiber amp ASE rejection grating pair Repetition frequency 10 Hz EO module pulse picker 1064 nm 1030 nm Nd: YAG regenerative amplifier Yb: YAG Thin disk regenerative amplifier Output@1064 nm Output@1030 nm YAG crystal part Yb: YAG regenerative amplifier 4 of 11

Yb: YAG regenerative amplifier: Cavity design • Timing and cavity length Seed laser repetition rate: 10 MHz 100 ns Pockels cell rise time: 10 -15 ns Length>3 m As to linear cavity: cavity length > 1. 5 m Regenerative amplifier cavity length is 1. 6 m • Match of pump size and laser spot size Pump size: 6 x 6 mm For getting higher gain, laser spot size should be bigger on the surface of Yb: YAG disk Yb: YAG regenerative amplifier 5 of 11

Yb: YAG regenerative amplifier: Cavity design case I: Heatsink Yb: YAG disk DM End mirror PC f=300 QWP PBS f=1000 LD Stack • Low threshold cavity oscillation and high output power • Output laser beam pattern is excellent • Bad tolerance for thermal lens effect • Strange beam focus occurred and the dichroic mirror was damaged Yb: YAG regenerative amplifier 6 of 11

Yb: YAG regenerative amplifier: Cavity design case II: • Low threshold cavity oscillation and high output power • Big output laser beam spot • Very excellent tolerance for thermal lens effect • Suitable to seed laser injection Yb: YAG regenerative amplifier 7 of 11

Yb: YAG regenerative amplifier: Experimental setup Yb: YAG disk soldering laser head • Old design − Strong residual stress − Adhesion between soldering composite and heatsink decreased the heat removal • New design − Weak residual stress − More efficient thermal management can be realized − Suitable for Peltier cooler in vacuum chamber Yb: YAG regenerative amplifier 8 of 11

Yb: YAG regenerative amplifier: Experimental setup PBS Faraday rotator HWP Telescope Seed from fiber part Heatsink Yb: YAG disk DM End mirror PC QWP PBS Yb: YAG regenerative amplifier 9 of 11

Next step work • Ring cavity (design is completed) – Long cavity length and laser beam size inside cavity – Cycle amplification and one-way transmission, lower ASE intensity (IASE~1/L), excellent contrast ratio – Compare with linear cavity, more gain can be achieved under the same saturation flux – Lower losses associate with thermally induced aberrations – More stored energy can be obtained because of absence of spacing hole burning • Cryogenic experiment – Peltier cooler can be adopted to current disk laser head – All the experiment equipment are available Yb: YAG regenerative amplifier 10 of 11

Summary • Different cavities (linear and ring) are designed and built for purchasing high gain and more stable operation in A 1 ground laser hut • High quality Yb: YAG disk laser head has been achieved • Yb: YAG regenerative amplifier cavity is completed and amplification is going to be carried out • Ring cavity regenerative amplifier and cryogenic experiment are carrying out at the same time THANK YOU! Yb: YAG regenerative amplifier 11 of 11