1. Topic Report Er:YAG DCF for High Power Laser Kuang-Yu Hsu 許光裕 4/19/2012

2. Outline Er:YAG double-clad crystal fiber
Er:YAG crystal optical properties
Simulation of Pump absorption

3. Low-T Double-Clad Crystal Fiber
Inner cladding material: aluminosilicate glass tube, (ID/OD= 80/130 mm) nD(587.6 nm)= T softening= 935 oC
Outer cladding material: borosilicate glass tube (ID/OD= 200/330 mm) n(589.3 nm)= T softening= 821 oC
#120315
#111116
NTUST

4. High Index Glasses for Er:YAG
Pump: 1532 nm
Lasing: 1617, 1645 nm
N-LaSF9 or N-LaSF41?

5. N-LaSF9-clad Crystal Fibers
# YAG+N-LaSF9
# Er:YAG+ N-LaSF9
Barely visible core. Very matched index.

6. N-LaSF9 CF Samples #120406 pattern at 532 nm No. Core Growth speed
Length
Result
#120418
Er:YAG
10 mm/min
4.4 cm ?
#120411
1 mm/min
12.4 cm
#120406
YAG
4 cm
Guided: 532, 660? nm
# pattern at 532 nm

7. Summary N-LaSF9-clad YAG CF (1 mm/min): guided at 532 nm.
N-LaSF9: no crack issue. A suitable material in fabrication point of view.
N-LaSF9 or N-LaSF41? To be verified. (More samples)

8. Er:YAG Crystal Cross-sections
1530 nm
Narrow linewidth
IEEE JQE 44 , pp , 2008.

9. Er:YAG Energy Level
Quasi-three level system. But no re-absorption at 1645 nm.
Proc. SPIE 6552, 65520K, (Dubinskii)
IEEE JSTQE 15, pp , 2009
1532 nm: 19 to 6544 cm-1

10. Er:YAG Crystal Lasing wavelength: 1645 nm, 2940 nm
Pump wavelength for 1645 nm:
980 nm (LD): thermal loading due to large quantum defect
resonant pumping with reduced quantum defect heating, no Yb-codoped
1470 nm (LD): 10 nm broad bandwidth, poor beam quality, require high Er3+ concent.
1532 nm (clad-pump fiber laser): flexibility in wavelength, beam quality
Concentration: 0.7x1026 m-3 = 0.5 at.%
Absorption coefficient: nm For 0.5 at.% doping, absorption coefficient= nm Absorption cross-section: 1.9x10-24 m2
Emission cross-section: 2.7x nm, 3.2x nm
(Ref.: JSTQE 15, pp , 2009)
Absorption cross-section: 1.1x nm (diode pump)
Emission cross-section: 0.55x nm,
(Ref: JQE 46, pp , 2010)

11. Er:YAG Crystal

12. Er:YAG Up-conversion ETU: energy transfer up-conversion
IEEE JSTQE 15, pp , 2009
Crystal length: 58, 29, 15, 7.0, 3.5 mm for 0.25, 0.5, 1, 2, 4 at.% Er concentrations.
1532-nm pump radius: 220 mm
(Ref.: JSTQE 15, pp , 2009)

13. Parameter Table Cross-section unit: 10-19 cm2 NT (cm-3) tf (ms) spGSA
spESA se
seESA
se(1-fL)/sp
Ref.
Ce:YAG (bulk)
2.94x1019
0.065
446 nm ?
Cr4+:YAG
4.54x1017
4.2
1060nm
5.5 2
1.2
0.036
[1]
Cr:forsterite
2.55
1060nm
1.16
0.18
0.72
[2]
Ti:sapphire
5.7x1018 (0.017 wt.%)
3.15
0.52/0.23(p), 532/446 nm
2.7 (p), 1.0 (s)
[3]
Ruby
3000
1.71(p), 554 nm
0.25
[4]
Er:silica
10000
980 nm nm
[5]
Er:YAG
6500 nm - nm
[6]
Pump saturation power for 10-mm-core fiber:
1. Ce:YAG: W
2. Cr:YAG: 11 mW
3. EDF: 6.4 mW
4. Ti:Al2O3: 1.8 W (p), 4.2 W 532 nm, 4.8 W (p), 9.2 W 446 nm
5. Ruby: 0.7 mW (p), 1.4 mW (s)
6. Er:YAG: 1.3 mW
1. KY Hsu’s current version
2. A. Sennaroglu, JOSA B
3. P. F. Moulton, JOSA B
4. W. Koechner, Solid-state laser engineering, 1999
5. K. Y. Huang, JLT 26, pp , 2008.
6. J. W. Kim et al, JSTQE 15, , 2009. 13 13

14. Summary
Suitable Er:YAG DCF structure is using aluminosilicate & borosilicate as the inner and outer cladding materials.
Pumping Er:YAG at 1532 nm is easy (small saturation intensity).
The core diameter of Er:YAG may be large (~100 mm) for high power laser applications.
Suitable fiber length of cladding-pump Er:YAG crystal fiber (core/inner clad diameter of 200/400 mm) is ~ 30 cm with a pump power of 50 W.