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

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

Low-T Double-Clad Crystal Fiber Inner cladding material: aluminosilicate glass tube, (ID/OD= 80/130 mm) nD(587.6 nm)= 1.538. T softening= 935 oC Outer cladding material: borosilicate glass tube (ID/OD= 200/330 mm) n(589.3 nm)= 1.474. T softening= 821 oC #120315 #111116 NTUST

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

N-LaSF9-clad Crystal Fibers #120406 YAG+N-LaSF9 #120411 Er:YAG+ N-LaSF9 Barely visible core. Very matched index.

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 #120406 pattern at 532 nm

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)

Er:YAG Crystal Cross-sections 1530 nm Narrow linewidth IEEE JQE 44 , pp. 803-810, 2008.

Er:YAG Energy Level Quasi-three level system. But no re-absorption at 1645 nm. Proc. SPIE 6552, 65520K, 2007. (Dubinskii) IEEE JSTQE 15, pp. 361-371, 2009 1532 nm: 19 to 6544 cm-1

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: 2.6 cm-1/at.% @ 1532 nm For 0.5 at.% doping, absorption coefficient= 1.3 cm-1 @ 1532 nm Absorption cross-section: 1.9x10-24 m2 Emission cross-section: 2.7x10-24 m2 @ 1645 nm, 3.2x10-24 m2 @ 1617 nm (Ref.: JSTQE 15, pp. 361-371, 2009) Absorption cross-section: 1.1x10-24 m2 @ 1470 nm (diode pump) Emission cross-section: 0.55x10-24 m2 @ 1645 nm, (Ref: JQE 46, pp. 1039-1042, 2010)

Er:YAG Crystal

Er:YAG Up-conversion ETU: energy transfer up-conversion IEEE JSTQE 15, pp. 361-371, 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. 361-371, 2009)

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 21 @ 446 nm ? Cr4+:YAG 4.54x1017 4.2 22@ 1060nm 5.5 2 1.2 0.036 [1] Cr:forsterite 2.55 1.36 @ 1060nm 1.16 0.18 0.72 [2] Ti:sapphire 5.7x1018 (0.017 wt.%) 3.15 0.52/0.23(p), 0.22/0.12(s) @ 532/446 nm 2.7 (p), 1.0 (s) [3] Ruby 3000 1.71(p), 0.85(s) @ 554 nm 0.25 [4] Er:silica 10000 0.025 @ 980 nm 0.05 @ 1552 nm [5] Er:YAG 6500 0.19 @ 1532 nm - 0.27 @ 1645 nm [6] Pump saturation power for 10-mm-core fiber: 1. Ce:YAG: 2.56 W 2. Cr:YAG: 11 mW 3. EDF: 6.4 mW 4. Ti:Al2O3: 1.8 W (p), 4.2 W (s) @ 532 nm, 4.8 W (p), 9.2 W (s) @ 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 18 1578-1586 2001 3. P. F. Moulton, JOSA B 3 125-133 1986 4. W. Koechner, Solid-state laser engineering, 1999 5. K. Y. Huang, JLT 26, pp. 1632-1639, 2008. 6. J. W. Kim et al, JSTQE 15, 361-371, 2009. 13 13

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.