Characteristic evaluation of new laser crystals Rui Zhang ACCL Division V, RF-Gun Group Feb 20, 2015...

Characteristic evaluation ofnew laser crystals

Rui　 ZhangACCL Division V, RF-Gun Group

Feb 20, 2015

SuperKEKB Injector Laser RF Gun Review

Outline

• Introduction to current Yb laser system of SuperKEKB injector laser RF gun

• New Yb doped crystal candidates–Cascade laser configuration–Thermal and laser characteristic for new crystals–New Yb doped crystal disk laser–Gain test under cryogenic environment

• Summary

Characteristic evaluation of new laser crystals

Introduction to current Yb laser system

Characteristics of Yb doped laser

• Long fluorescent time

• Wide bandwidth

• High power commercial pump LD source

• High quantum efficiency

• Suitable for fiber laser system

Best candidate for RF-Gun

Yb-doped fiber oscillator

Yb-doped fiber pre amplifier

Yb-doped fiber amplifier

Transmission Grating

Stretcher

EO Pulse picker　double　

Yb:YAG thin-disk 6-pass amplifier


SHG

Synchronization system

2856 MHz triggerfrom accelerator

SHGRF Gun

51.9 MHz

1 nJ @ 1035 nm

Yb-doped fiber main amplifier

BBO


Yb-doped fiber pre amplifier



Introduction for current Yb laser system

Current laser system

New Yb doped crystal candidates

Cascade laser configuration

Cascade Yb laser is a good candidate Tiny thermal lens effect Less re-absorption Higher excitation density Easy to maintain the LD pump system

For 1035 nm band laser– Absorption – Low gain

1035 nm pump source: Q-switch laser


Cascade laser

Pump laser 940 nm Seed laser 1050 nm 10.4%Pump laser 976 nm Seed laser 1050 nm 7.1%

Pump laser 1035 nm Seed laser 1050 nm 1.43%

Superb thermal management!

Experimental setup for testing the gain of cascade laser

Gain test of cascade laser

Quantum defect of Yb cascade laser

Current situation:• Emission cross section of new crystals High dopant and longer effective length• Polarization of pump laser and seed laser Transmission grating and pin hole• Overlap between pump laser and seed laser

Higher energy of pump laser


Thermal and laser characteristic for new crystals Yb:YAG Yb:KGW Yb:BOYS Yb:CaF2

Absorption bandwidth at the zero-line wavelength

(nm)941 968 981 975 979.8

Absorption bandwidth (nm, FWHM) 18 3 3.5 6 6

Peak absorption cross section

(10-21 cm2)8.0 9.4 120

(a-axis)σ 7.3 π 9.4 5.4

Fluorescent lifetime (ms) 0.95 0.75 1.1 2.4Room temperature laser

wavelength (nm) 1030 1026 1066 1049

Emission cross section at laser wavelength

(10-21 cm2)20 22 28

(a-axis) 2 1.7

Emission bandwidth (nm) 10 20 60 70Experimental tuning range

(nm) 1020-1083 1020-1070 1017-1086 1000-1072

Mean refractive index 1.82 2.03 1.75 1.43

Thermal conductivity (W/m/K) 11 3.3 1.8 6.0

Thermal expansion coefficient (10-6/K) 6.7 3.8 5 (a)

20 (c) 18.9

Young Modulus (GPa) 280 115.8 - 76

Yb:CaF2

Yb:KGW


Available new crystals

Yb:CaF2

Crystal Yb:KGW Yb:BOYS Yb:CaF2

Shape Cuboid Cuboid Disk

Dimension (mm) 4×4×20 5×5×18Dia. 12.7

T: 2

Doping concentration (a.t. %) 5.0　 10.5 10.0

Coating √ × ×

Quantity 2　 2 5

Next experiments:• Gain of cascade laser• Gain under cryogenic environment


New Yb doped crystal disk laser

Yb:YAG Yb:CaF2

Fluorescence

Room temperature laser wavelength (nm) 1030 1049

Fluorescent lifetime (ms) 0.95 2.4

Spectral width (nm) 10 70

Fourier minimum pulse width (fs) 165 23

Absorption

Absorption bandwidth at the zero-line wavelength (nm) 941 979

Absorption bandwidth (nm, FWHM) 18 6

Peak absorption cross section (10-21 cm2) 8.0 5.4

Mean refractive index 1.82 1.43

Therma

l

Thermal conductivity (W/m/K) 11 6.0

Thermal expansion coefficient (10-

6/K) 6.7 18.9

Young Modulus (GPa) 280 76

Yb:CaF2 is another good candidate for disk laser

Wide bandwidth Long fluorescent time Possibility of fabricating large size singe crystal

and ceramics (Czochralski or Bridgman) Suitable for high-energy and high power laser

operation Low dispersion behavior and limited nonlinear

effects under intense laser irradiation

× Low emission cross section Cryogenic environment × Thermal conductivity decreases with increasing

of Yb doping concentration


Gain test under cryogenic environmentVacuum chamber Cryogenic equipment Wavelength tunable laser

Vacuum degree: 5.2×10-6 Pa 4 K cryocooler Maximum output power: 20 mW

Gain test schematic design(out of ratio)


Gain test under cryogenic environment

Summary

• New Yb doped crystalsAll candidates have been manufactured (bigger size Yb:CaF2 will be booked)Gain test for Yb:YAG under cryogenic environment– Gain test for Yb:CaF2 under cryogenic environment

• Cascade laser configurationmJ level 1035 nm Q switch laser has been achieved– Gain test for different crystals by use of high doping concentration samples

The End

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Characteristic evaluation of new laser crystals Rui Zhang ACCL Division V, RF-Gun Group Feb 20, 2015...

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