Advances in Single-Crystal Fibers and Thin Rods Grown by Laser Heated Pedestal Growth

Abstract

Single-crystal fibers are an intermediate between laser crystals and doped glass fibers. They have the advantages of both guiding laser light and matching the efficiencies found in bulk crystals, which is making them ideal candidates for high-power laser and fiber laser applications. This work focuses on the growth of a flexible fiber with a core of dopant (Er, Nd, Yb, etc.) and a polycrystalline clad of yttrium aluminum garnet (YAG) that will exhibit good wave guiding properties. Direct growth or a combination of growth and cladding experiments are described. Scattering loss measurements at visible wavelengths, along with dopant profile characterization with damage threshold results, are also presented. For single-pass amplification, a single-pass linear gain of 7.4 was obtained for 29 nJ pulses of 5 ns duration at 1 MHz repetition rate. We also obtained a laser efficiency of over 58% in a diode-pumped configuration. These results confirm the potential for single-crystal fibers to overcome the limitations of the glass fibers commonly used in fiber lasers, making them prime candidates for high-power compact fiber lasers and amplifiers.

Claddings for YAG single crystal high power fiber lasers

“…Ca 3 Ga 2 Ge 3 O 12 green state claddings extruded on both doped and undoped single-crystal YAG fibers were melted and then crystallized in a laser heated pedestal growth (LHPG) apparatus modified by AFRL from an earlier design. 18,19,20 The apparatus had a hot zone of 0.5 mm; speeds of 1.0 to 2.7 mm/min were used. Microstructures of the various cladded fibers and the crystallized YAGgarnet melts were observed with SEM (Quanta, Thermo Fischer, Hillsboro, OR) and TEM (Talos, Thermo Fischer, Hillsboro, OR) with EDX.…”

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

“…One of the most LFZ-developed materials is single crystal Y 3 Al 5 O 12 (YAG) as a laser medium. Despite the fact that it was produced by Fejer et al in 1984 [25], a considerable amount of work has appeared during the last 20 years (Table 1) reporting its growth [35][36][37][38][40][41][42][49][50][51][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72], improving the production efficiency [59,71], and also enhancing its mechanical and optical characteristics [38]. Among those studies, the work of Nie et al, in 2015 [37], who produced YAG single crystals doped with Er 3+ , Ho 3+ , Tm 3+ , Nd 3+ , and Yb 3+ may be highlighted here.…”

“…Focusing on this composition, both Lai et al, in 2009 [60], and Yi et al, in 2010 [61], developed laser gain media and multi-pass ring laser devices, respectively, from single crystal fibers (SCF) with the double-clad structure. The doubleclad structure fabrication has been generally achieved by covering the single-crystal fiber through Sol-Gel and later sintering [49] or basically inserting a diameter-reduced grown rod into silica-or glass-based capillary tubes [35,50,63,66,68]. These kinds of materials, namely, the cladded, single-crystal fibers, have been largely applied as fiber amplifiers of the laser radiation [40,67,70].…”

Efficient 2.76 μm continuous-wave laser in extremely lightly Er-doped CaF2 single-crystal fiber

“…However, there are few reports of crystal fibers concerned with the Er-based 2.8 µm laser. One important reason is that a low dopant concentration and long gain length are required for a single-crystal fiber to spread the absorption of pump light over the long fiber to alleviate the heat loads [31], while reducing the Er 3+ concentration will significantly impair the MIR laser performance of the gain crystals [15,20,21]. Taking this point into consideration, CaF 2 /SrF 2 single crystals possess a unique superiority in that a high-efficiency laser can be obtained at a rather lower Er 3+ doping concentration because of the clustering of Er 3+ ions within these fluorite crystals [32,33].…”