Growth, Characterization, and Efficient Continuous-Wave Laser Operation in Nd,Gd:CaF₂ Single-Crystal Fibers

Abstract

Nd,Gd:CaF 2 single-crystal fibers (SCFs) of various Nd 3+ and Gd 3+ concentrations were grown by a modified temperature gradient technique (TGT) using a home-designed multi-microchannel crucible. Powder and Laue X-ray diffraction measurements indicated the SCFs consist of pure monocrystalline CaF 2 phase. Distributions of rare earth dopants in SCFs are proven to be uniform by both EDS and spectroscopic measurements. Laser diode (LD) pumped continuous-wave (CW) laser output at ∼1.06 μm spectral region of a highest slope efficiency of 42% and a maximum output power of 1.49 W were achieved. Comparison of laser performances between Nd,Gd:CaF 2 SCFs and bulk crystal was analyzed, indicating the potential of fluoride SCFs in high-power laser applications.

Rare-Earth-Metal (Nd3+, Ce3+ and Gd3+)-Doped CaF2: Nanoparticles for Multimodal Imaging in Biomedical Applications

“…In order to evaluate the optical properties of the NPs, we first measured the absorption spectra of the CaF 2 : Ce, Gd, Nd NPs and CaF 2 : Ce, Gd NPs in aqueous solution at a concentration of 10 mg/mL (Figure 2a). Compared to CaF 2 : Ce, Gd NPs, the CaF 2 : Ce, Gd, Nd NPs showed absorption peaks at 576 nm,734 nm and 795 nm, corresponding to the 4 G 5/2 + 2 G 7/2 , 4 F 7/2 + 4 S 3/2 , and 4 F 5/2 + 2 H 9/2 absorption peaks of Nd 3+ [45,56]. Then, to demonstrate that the doping of Ce increased the luminescence intensity of the NPs, we first tested the luminescence intensity of CaF 2 : Nd and CaF 2 : Ce, Nd under 808 nm laser excitation (300 mW) (Figure 2b).…”

“…However, when the Nd 3+ doping concentration reaches a certain limit, Nd 3+ aggregates and some energy cross-relaxation occurs, which triggers the cluster effect and reduces the luminous efficiency of the nanomaterials [40,41]. In order to overcome this phenomenon, the introduction of optically inactive ions (such as Lu 3+ , Gd 3+ , Y 3+ , Yb 3+ ) can effectively destroy the formation of Nd-Nd clusters, thereby improving the quantum efficiency of the material [42][43][44][45]. Notably, the special properties of certain optically inactive ions also offer the possibility of constructing multimodal probes; however, most current multimodal imaging probes are dual-mode probes, and NIR-II-based imaging systems combining more than two modes are still rarely reported, but our previous study demonstrates that triple-mode imaging probes hold great promise for obtaining complementary information.…”

Mode-locked and free running operation of Nd,Gd:CaF2 crystal fiber laser

“…% [16]. Concentration profiles were flat and were presented in [16]. For comparison, a standard bulk Nd,Gd:CaF2 crystal was available.…”

“…Investigations of high-power laser performance of SCFs also indicate the SCFs are very suitable for both high-power continuous-wave (CW) lasers [14] and high-power ultra-short laser amplifiers [15]. Growth, characterization and efficient continuouswave laser operation in Nd,Gd:CaF2 Single Crystal Fibers was recently reported [16].…”

“…In this work we report laser operation of 790 nm laser diode pumped Nd,Gd:CaF2 single crystal fibers in free running and mode-locked regime. Our crystals were grown by modified temperature gradient technique [TGT] using a home designed multi-microchannel crucible [16].…”