CC BY
10LS-I-1
Femtosecond-laser-written 2-^m waveguide lasers
X. Mateos1, E. Kifle1, P. Loiko2, C. Romero3, J. R. Vázquez de Aldana3, U. Griebner4, V. Petrov4, M. Aguiló1, F. Díaz1
1Universitat Rovira i Virgili, Inorganic and Physical Chemistry, Tarragona, Spain 2Université de Caen Normandie, Centre de recherché sur les Ions, les Matériaux et la Photonique, Caen, France
3University of Salamanca, Aplicaciones del Láser y Fotónica, Salamanca, Spain 4Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Berlin, Germany
This work reviews our recent achievements on fabrication, optical characterization and continuous-wave and passively Q-switched 2-p.m laser operation of active waveguides (WGs) produced by femtosecond direct laser writing (fs-DLW) in thulium and holmium doped low-symmetry (monoclinic) crystals. Various depressed-index photonic micro-structures were fabricated, such as buried channel WGs with circular and hexagonal (lattice-like) cladding, surface WGs with a half-ring cladding, and straight WGs and Y-branch splitters.
As active materials for emission near 2 p,m, monoclinic double tungstate crystals, KRE(WÜ4)2 singly doped and codoped with Tm3+ and Ho3+ ions were studied. The WGs were characterized by confocal laser microscopy, p,-Raman and ^-luminescence spectroscopy, confirming well preserved crystallinity of their cores [1].
As for Tm-doped WGs, the best CW laser output was achieved using a circular-cladding Tm:KLu(WÜ4)2 WG which generated 1.07 W at 1.84 p,m with a slope efficiency of 69.5% (fundamental mode, linearly polarized emission). An in-band pumped Holmium WG laser was scaled to 0.21 W at 2.06 p,m with a slope efficiency of 67.2%.
Passive Q-switching of Tm WG lasers was achieved using "fast" (graphene, MoS2, singlewalled carbon nanotubes - SWCNTs) and "slow" saturable absorbers (Cr2+:ZnS). Surface functionalization of Tm WGs by SWCNTs lead to generation of nanosecond pulses through evanescent-field-interaction [2].
References
[1] E. Kifle, X. Mateos, J. R. Vázquez de Aldana, A. Rodenas, P. Loiko, S. Y. Choi, F. Rotermund, U. Griebner, V. Petrov, M. Aguiló, and F. Díaz, Femtosecond-laser written Tm:KLu(WÜ4)2 waveguide lasers. Opt. Lett. Vol., 42, 1169 (2017).
[2] E. Kifle, P. Loiko, J. R. V. de Aldana, A. Rodenas, S. Y. Choi, F. Rotermund, V. Zakharov, A. Veniaminov, M. Aguiló, F. Díaz, U. Griebner, V. Petrov, and X. Mateos, Passively Q-switched fs-laser-written thulium waveguide laser based on evanescent field interaction with carbon nanotubes. Phot. Res. 6, 971 (2018).
