Thermal properties of laser crystal Super KEKB Injector
Thermal properties of laser crystal Super. KEKB Injector Laser RF Gun Review Rui Zhang ACCL Division V, RF-Gun Group Feb 20, 2015
Outline • Introduction to current Yb laser system of Super. KEKB injector laser RF gun • Au-Sn soldering Yb: YAG/Cu bonding composite – Au. Sn soldering material – Soldering components • Thermal effect measurement • Summary Thermal properties of laser crystal
Introduction to current laser system 1 n. J @ 1035 nm Yb-doped fiber oscillator Yb-doped fiber pre amplifier Transmission Grating Stretcher Yb-doped fiber pre amplifier EO Pulse picker double Yb-doped fiber amplifier 51. 9 MHz Synchronization system Yb-doped fiber main amplifier 3 rd stage 2856 MHz trigger From Accelerator RF GUN SHG Yb: YAG thindisk 6 -pass amplifier SHG Yb: YAG thindisk 5 -pass amplifier Yb: YAG thindisk 1 -pass amplifier Yb: YAG thindisk 2 -pass amplifier 5 th stage 4 th stage Introduction to current A 1 laser system
Au. Sn soldering material Au-Sn phase diagram • Eutectic point at 278± 2 ºC • L ↔ [ζ + δ] • Eutectic components: Au 5 Sn and Au. Sn For Au. Sn solder material: • No need for flux • High thermal conductivity and low thermal expansion coefficient • High resistant to corrosion and oxidation • High creep resistance Comparison between Au. Sn, In. Sn, Cu and Yb: YAG Melting point (ºC) Thermal conductivity (W/m/K) Thermal expansion coefficient (10 -6/K) Au. Sn (80: 20) 280 58 16 In. Sn (50: 50) 118 34 20 Copper 396 16. 4 Yb: YAG 11 6. 7 Au-Sn soldering Yb: YAG/Cu bonding composite
Soldering components Coated Yb: YAG laser crystal disk • Diameter: 1/2 inch (12. 7 mm) Under microscope Top surface • Thickness: 0. 5 mm • Yb-ions dopant: 10 a. t. % • Top surface: AR @ 1030 nm and 940 nm Bottom surface • Bottom surface: HR @ 1030 nm and 940 nm, Crcoating and Au-coating Au-Sn soldering Yb: YAG/Cu bonding composite
Soldering components Au-Sn layer Bottom surface Copper plate • Diameter: 1/2 inch (12. 7 mm) • Thickness: 2. 0 mm • Au-Sn layers on top surface: Au-80% and Sn -20% Au-Sn layer after soldering Au-Sn soldering Yb: YAG/Cu bonding composite
Soldering fixtures • Spring (force constant is 0. 05 Kg/mm) • Spring’s deformation length: 10 mm • Total pressure: 1. 21 kg/cm 2 • Vacuum chamber’s vacuum degree: 5. 2× 10 -5 Pa • Polyimide is used for protesting the AR coating Au-Sn soldering Yb: YAG/Cu bonding composite
Yb: YAG/Cu bonding samples analysis Yb: YAG/Cu bonding composite soldered at 310 ºC 500 μm 16 μm Side view. The thickness of bonding layer is ~16 μm Damaged samples Au-coating on the bottom surface of Yb: YAG disk was damaged partly AR-coating on the top surface of Yb: YAG disk was damaged partly Au-Sn soldering Yb: YAG/Cu bonding composite
Optical measurement experimental setup He-Ne laser: • Wavelength: 632. 9 nm • Power: 1. 2 m. W • Mode structure: TEM 00>99% • Enlarged beam diameter: 5 mm Pump laser: • Pump LD peak power: 4 k. W • Pulse width: 600 μs • Repetition rate: 5 Hz Thermal effect measurement
Measurements for soldering quality Before soldering After soldering Wave front interference Beam profile Thermal effect measurement
Thermal effect measurement 1 Old design (without soldering) Wave front without pump Wave front under 450 m. J pump Wave front under 630 m. J pump Wave front under 840 m. J pump New design
Thermal effect measurement 2 Old design (without soldering) Wave front without pump Wave front under 950 m. J pump Beam profile without pump Beam profile under 950 m. J pump New design
Summary • Soldering component ü Fundamental soldering technology – Copper plate with excellent surface quality – Soldering for bigger size laser active medium • Thermal effect measurement ü Available measuring setup – Measurement under high repetition rate pump (50 Hz) The End
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