Laser Floating Zone: General Overview Focusing on the Oxyorthosilicates Growth

Abstract

This chapter reviews the laser floating zone (LFZ) technique, also known as the laser-heated pedestal growth (LHPG), focusing on the recently produced rareearth-doped oxyorthosilicate fibers. LFZ has been revealed as a suitable prototyping technique since high-quality crystals can be developed in short time with low consumption of precursor materials in a crucible-free processing that ensures to practically avoid by-products. Moreover, additional advantages are the possibility to treat and melt highly refractory materials together with the easy way for tailoring the final microstructural characteristics and this way the macroscopic physical properties. Thus, refractory rare-earth (RE) doped oxyorthosilicates following the formula RE 2 SiO 5 have been recently produced by the LFZ technique for tuning laser emission parameters. The oxyorthosilicates have high chemical stability and allow incorporation of many rare-earth ions yielding different applications, such as laser host materials, gamma ray detectors or scintillators, environmental barrier coatings (EBCs) and waveguides, among others. Thus, different kinds of oxyorthosilicates were produced by the LFZ technique, and the detailed effects of the main processing parameters on crystal's characteristics are discussed in this chapter.

Laser Floating Zone Growth: Overview, Singular Materials, Broad Applications, and Future Perspectives

“…It enabled a circular, crown-shaped laser beam focus and, therefore, uniform radial heating. This term describes a setup of a two-stage pair of reflective linear axicon surfaces [21], which was invented by Martin in 1948 [26] and later improved by Nubling and Harrington in 1997 [27] (Figure 1). Likewise, processing under high-vacuum conditions, achieved for the first time by Brueck et al in 1996 [28], must also be highlighted.…”

“…(1) The extrusion process is the most common way to prepare the precursor rod cylinders for the LFZ process, since it is a simple method, not requiring special equipment or additional hands [21,29]. Thus, the commercial raw oxide powders are mixed, according to the desired stoichiometry, and reduced in grain size with an agate ball mill or similar equipment.…”

“…The growth process can end abruptly or by reducing the laser power gradually. This procedure is very important to reduce the thermal stresses and, therefore, to avoid crack formation [9,21].…”

“…Thus, Harrington reported, for the first time in 2014 [42], the single-crystal production of Gd 3 Ga 5 O 12 (GGG) laser garnet. Recently, Rey-García et al, in 2020 [21], produced, in air atmosphere, gadolinium oxyorthosilicate single crystals, suitable to be employed as laser host matrices. [97], demonstrating the suitability of the fibers produced to be successfully employed for high-temperature sensing, as Ye et al, in 2005 [57], also similarly tested later for YAG:Cr 3+ .…”

“…This setup allows achieving high melting temperatures with a significantly lower energy consumption, as compared to conventional crystallization methods described above [13,14]. However, the LFZ technique allows better control of the temperature gradient compared to OFZ, as well as higher temperatures [21] since the light focus in OFZ is broad and the temperature gradient at the interface between the solid and the liquid is less abrupt. This makes the melt seriously attack the feed rod and spill over to the crystal, eventually making the growth unstable [22].…”