(a) Side view of an as-grown Cr:YAG single crystal fiber with a diameter grown by the LHPG method. (b) The corresponding SEM end face image. The  hexagonal shape is apparent. (c) The drawing of the YAG atomic structure viewed from  crystal orientation.
(a) Polished end face and side view images of DCF. The core, inner cladding, and outer-cladding diameters are , , and , respectively. (b) The major composition line-scan profiles measured by EPMA. (c) Left: HRTEM image of the core region with the imaging electron beam along the  direction; center: a computer simulated image ( and ) that optimally fits the experimental one; right: atomic column positions of Y, Al, and O. The scale bars of all images represent 5 Å.
 zone axis HRTEM image of core/inner-cladding interface with several nanocrystals located in the inner-cladding, as marked by the arrows.
(a) HRTEM image of core/inner-cladding interface. The inset is the corresponding FFT pattern. (b) Schematic representation of the FFT pattern with the YAG reciprocal lattice revealing the orientation relationship between the nanocrystal and the YAG core.
(a) Highly magnified HRTEM image of the core/inner-cladding interface showing a  nanocrystal with a local orientation relationship to the YAG  core. The inset is the corresponding FFT pattern. (b) Schematic representation of the FFT pattern and YAG reciprocal lattice.
(a) A highly magnified HRTEM image at the core/inner-cladding interface. (b) The reciprocal space diffraction is obtained by the FFT of a selected area in the HRTEM image of (a). The data is then filtered to obtain the and diffractions, containing information of the lattice spacing in the vertical and lateral directions, respectively. (c) and (d) show the distribution of the strain components away from the interface. The solid squares are measured values, and the solid lines are the curve fitted results, indicating that an average strain layer gives rise to a uniform zero strain to the reference core region and high single crystallinity of the DCF core. The error bars represent standard deviations of triplicate measurements.
NIR spectra with a 3 dB bandwidth of over 240 nm generated from the DCF. The inset is the ASE measured output power as a function of the pump power, showing a maximum output power up to milliwatt order.
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