Na Modification of Lanthanide Doped Ca₃Nb_1.5Ga_3.5O₁₂-Type Laser Garnets: Czochralski Crystal Growth and Characterization

Abstract

The Na+-Yb3+ (or Er3+) co-substitution of Ca2+ in Ca3Nb1.5Ga3.5O12 (CNGG) laser crystal is studied. In contrast to other garnets whose structural disorder is exclusively based on the presence of differently sized cations on the same crystal sites, Na+ incorporated in the dodecahedral site (a site also shared by Ca2+ and trivalent lanthanides) creates diverse electric charge distributions over the dodecahedral sublattice, which adds to the disorder associated with Nb5+ and Ga3+ simultaneous occupation of the octahedral and tetrahedral sites. The currently determined cationic compositions of Czochralski grown congruent CNGG and Na-modified CNGG crystals show that Na+ incorporation reduces the cationic vacancy concentration on dodecahedral and octahedral sites but does not affect that in tetrahedral sites. Physical properties of interest for laser design (optical transmission, elastic constants, hardness, specific heat, thermal conductivity, thermal expansion, refractive index dispersion, group velocity dispersion, and thermo optic coefficients) have been systematically determined at cryogenic temperatures and above room temperature. Na+ incorporation into CNGG decreases the crystal growth temperature, promotes Yb3+ doping, and importantly, increases the Yb3+ optical bandwidth, offering good prospects for the implementation of ultrashort pulses in mode-locked laser oscillators.

A roadmap for laser optimization of Yb:Ca3(NbGa)5O12-CNGG-type single crystal garnets

“…Crystal growth details can be found in our previous works. 19,21 Rocking curves of the 100 XRD of CNGG-type crystals were recorded at room temperature in a Texture Analysis Diffractometer Bruker D8 Advance with Cu Ka radiation.…”

“…The crystalline complexity provides a large number of oxygen and cationic environments around Yb 3+ with a large impact on its optical band broadening. Furthermore, Na 21 and Li 22,23 CNGG modifications (hereafter CNNGG and CLNGG crystals, respectively) have been also developed. Na + enters in the dodecahedral site, potentially helping in the charge compensation of Ca 2+ substitution by Yb 3+ , 21 while Li + exclusively sits at the tetrahedral sites, removing tetrahedral cationic vacancies.…”

“…Furthermore, Na 21 and Li 22,23 CNGG modifications (hereafter CNNGG and CLNGG crystals, respectively) have been also developed. Na + enters in the dodecahedral site, potentially helping in the charge compensation of Ca 2+ substitution by Yb 3+ , 21 while Li + exclusively sits at the tetrahedral sites, removing tetrahedral cationic vacancies. 19 Laser characterization of Yb:CNGG-type crystals has been demonstrated in continuous wave (cw), Q-switched and modelocked operation regimes.…”

Generation of 84-fs pulses from a mode-locked Tm:CNNGG disordered garnet crystal laser

“…Active rare-earth ions such as Nd 3 , Yb 3 , and Tm 3 , can be used as dopants to substitute for the Ca 2 ions in dodecahedral sites. The lattice disorder in these type of crystals results from the random distribution of Nb 5 and Ga 3 ions in the octahedral and tetrahedral sites [13]. In the spectral range near 1 μm, pulse durations of 45 and 55 fs were obtained from mode-locked lasers based on Yb-doped CNGG and CLNGG [14,15], respectively, and 534, 660, and 900 fs from Nd-doped CLNGG-CNGG, CNGG, and CLNGG garnets, respectively [16][17][18].…”

“…Considering that CNGG and CLNGG have similar spectral properties to other dopants, we decided to study the modelocked laser performance of Tm:CNGG. We additionally introduced Na into the crystal (hereafter Tm:CNNGG) to decrease the temperature of crystal growth and promote Tm 3 incorporation [13,20].…”