CC BY
16LS-I-3
Waveguide Lasers Based on Fluoride Films Grown by Liquid
Phase Epitaxy (Invited)
Pavel Loiko1*, Gurvan Brasse1, Alain Braud1, Jean-Louis Doualan1, and Patrice Camy1
1—Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), UMR 6252 CEA-CNRS-
ENSICAEN, Université de Caen Normandie, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France
'pavel.loiko@ensicaen.fr
Fluoride crystals are attractive for doping with rare-earth ions (RE3+) for laser applications in the near-and mid-infrared spectral ranges. They combine good thermal properties, broadband transparency, low refractive index and low phonon energies with suitable spectroscopic properties of the RE3+ ions (in particular, long emission lifetimes and weak non-radiative path). RE3+-doped fluoride materials represent a promising platform for waveguide (WG) lasers. Liquid Phase Epitaxy (LPE) is a well-known method for the growth of single-crystalline thin-films of high optical quality with a great potential for WG applications. In the present work, we review of recent results on WG lasers based on fluoride thin-films grown by LPE.
Single-crystalline thin films of LiYF4 [1] and CaF2 [2] doped with various RE3+ ions (Yb3+, Tm3+, Tm3+/Ho3+, Er3+, etc.) were grown on bulk oriented undoped substrates by LPE using the following solvents: LiF (for LiYF4) and CaCl2, LiF and NaF (for CaF2). For LiYF4, the RE3+ doping level was up to 20 at.%, the thickness of the films was up to ~200 ^m, the refractive index contrast was about 2^10" 3 and the measured passive losses were down to 0.1 dB/cm. The orientation of the films and low lattice mismatch were confirmed by single-crystal XRD. The uniform distribution of RE3+ ions was confirmed by EDX element mapping.
Planar and channel WGs were fabricated. To produce the surface channel (ridge) WGs, the epitaxies were subjected to precision diamond saw dicing, Fig. 1(a). For Tm:LiYF4 / LiYF4 epitaxies, ridge WGs with a square cross-section of -30*30 ^m2 were fabricated in this way.
The laser operation was achieved both in the planar and channel WG geometry. The following emission ranges were studied: ~1 ^m (Yb:CaF2), -1.9 ^m (Tm:LiYF4), -2.1 ^m (Tm,Ho:LiYF4), ~2.3 ^m (Tm:LiYF4), -2.8 ^m (Er:LiYF4). The results on an in-band pumped ridge Tm:LiYF4 waveguide laser are shown in Fig. 1(b,c) for example. In the continuous-wave regime, this laser generated a maximum output power of 2.05 W at 1881 nm with a slope efficiency of 78.3%, a linearly polarized emission (n), a single-mode output and a laser threshold of only 12 mW. The results on passively Q-switched operation of Tm waveguide lasers will be also presented.
The developed family of low-loss fluoride waveguides is of practical importance for further design of integrated light sources generating ultrashort pulses at high repetition rates (GHz-range), as well as potential sensing applications.
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0,5 1,0 1,5 2,0 2,5 Absorbed pump power (W)
Wavelength (nm)
Fig. 1. Channel (ridge) waveguides based on Tm:LiYF4 thin films grown by LPE and microstructured by diamond saw dicing: (a) confocal microscope image (top view); (b) input-output dependences, n - slope efficiency; (c) typical spectra of laser emission, the laser polarization is n. In-band pumping, AP = 1679 nm.
[1] P. Loiko, R. Soulard, G. Brasse, J.-L. Doualan, B. Guichardaz, A. Braud, A. Tyazhev, A. Hideur, P. Camy, Watt-level Tm:LiYF4 channel waveguide laser produced by diamond saw dicing, Opt. Express, vol. 26, pp. 24653-24662 (2018).
[2] P. Loiko, R. Soulard, E. Kifle, L. Guillemot, G. Brasse, A. Benayad, J.-L. Doualan, A. Braud, M. Aguilo, F. Diaz, X. Mateos, P. Camy,
Ytterbium calcium fluoride waveguide laser, Opt. Express, vol. 27, pp. 12647-12658 (2019).
