Ternary Colquiriite Type Fluorides as Laser Hosts

Abstract

Cryst. Res. Technol. 34 1999 2 145-152The Cr 3+ :LiCaAlF 6 (Cr:LiCAF) and Cr 3+ :LiSrAlF 6 (Cr:LiSAF) laser host crystals can be grown by the CZOCHRALSKI technique. Problems result from the evaporation of lithium-aluminium-fluorides during the growth process and a corresponding stoichiometry shift of the melt towards the CaF 2 (SrF 2 ) corner of the ternary concentration triangle. Both Cr:LiCAF, and to a lower extend also Cr:LiSAF, contain micron-sized defects that disturb the lasing efficiency heavily. The defects are assumed to be related to water and/or oxygen impurities within the starting materials and growth atmosphere and to peculiarities of the LiF -CaF 2 -AlF 3 ternary phase diagram. Cr 3+ :LiCaAlF 6 (Cr:LiCAF) und Cr 3+ :LiSrAlF 6 (Cr:LiSAF) Laser-Wirtskristalle können nach der CZOCHRALSKI-Methode gezüchtet werden. Probleme resultieren aus der Verdampfung von Lithium-Aluminium-Fluoriden während des Züchtungsprozesses und einer damit verbundenen Verschiebung der Schmelzstöchiometrie in Richtung zur CaF 2 -(SrF 2 -) Ecke des ternären Konzentrationsdreieckes. Sowohl Cr:LiCAF als auch in geringerem Umfange Cr:LiSAF enthalten Defekte mit Größen von einigen µm 3 , die die Effizienz des Laser-Effektes drastisch beeinträchtigen. Es wird angenommen, daß die Defekte auf die Verunreinigung von Ausgangsmaterialien und Züchtungsatmosphäre durch Wasser und/oder Sauerstoff sowie einige Besonderheiten des ternären Phasendiagramms LiF -CaF 2 -AlF 3 zurückzuführen sind.

Femtosecond Cr:LiSAF and Cr:LiCAF lasers pumped by tapered diode lasers

“…Especially, the Cr:LiCAF crystal that was used in this study was from a very early growth with relatively high losses (~> 1% per cm). This high level of passive loss in Cr:LiCAF was caused mostly by micron-sized or smaller precipitates arising during the growth process [45][46][47] and it is now possible to grow Cr:LiCAF crystals with passive losses below 0.2% per cm [48]. We also note that, despite the high loss Cr:LiCAF crystal that was available in this study, the slope efficiencies obtained with the tapered diode pumped system (41%), is much higher than what can be obtained (19%) while pumping with broad-stripe single-emitter diodes [31].…”

Low-cost, broadly tunable (375–433 nm & 746–887 nm) Cr:LiCAF laser pumped by one single-spatial-mode diode

“…However, initially, it did not draw much attention, mostly due to the high level of parasitic losses (∼2% per cm) observed in Cr:LiCAF during the early years of its production (for Cr:LiSAF passive losses have been around ∼0.2% per cm) [34][35][36][37][38]. This high level of passive losses in Cr:LiCAF rooted mostly from micrometer-sized or smaller precipitates arising during the growth process [35,36], which obstructed efficient laser operation in this low-gain medium.…”

“…However, initially, it did not draw much attention, mostly due to the high level of parasitic losses (∼2% per cm) observed in Cr:LiCAF during the early years of its production (for Cr:LiSAF passive losses have been around ∼0.2% per cm) [34][35][36][37][38]. This high level of passive losses in Cr:LiCAF rooted mostly from micrometer-sized or smaller precipitates arising during the growth process [35,36], which obstructed efficient laser operation in this low-gain medium. On the other hand, compared to Cr:LiSAF, Cr:LiCAF has several advantages, including a higher intrinsic slope efficiency [39], a higher thermal conductivity [39], a higher thermal quenching temperature [40], a lower thermal lensing [41], a lower quantum defect, a lower excited-state absorption [9,10], and a lower upconversion rate [42].…”

Preparation and characterization of LiAEAlF6:Eu (AE=Mg, Ca, Sr or Ba) phosphors

“…LiCaAlF 6 and LiSrAlF 6 have colquiriite structures. The general formula of the colquiriites is LiMe II Me III F 6 , where Me II stands for Ca, Sr, Cd, Pd and Me III for Al, Ga, Ti, V, Cr, Fe [30]. These quaternary fluorides have received their name from the mineral colquiriite (LiCaAlF6), found in a Bolivian tin mine.…”