Figure 4

Position-dependent photo-excitation in bilaminar single-crystal system.

(a) Optical micrograph of a bilaminar single crystal and a schematic diagram of the position-dependent spot-excitation measurements using a 200 μm stripe laser beam. The size of the laser stripe is shown on the picture (blue line) with an indicator of the beam centre (green triangle). (b) (0–1) Spectral linewidth (FWHM) during the position-dependent excitation. The red dotted line indicates the normal FWHM. The spectra from both positions A and B are narrow, indicating that all of the position-dependent excitations occurred above the ASE threshold energy. (c) The excitation position-dependent integrated intensity of the (0–1) peak. We excited two different series of crystal positions, labelled as position A and position B. The red arrows indicate the observation directions of the photoluminescence measurements. The red circles and black squares mark the excitation centres of each measurement. Two dashed lines represent the positions of the parallel edges of the upper crystal. Although the measurement path of position A (red circles) crosses the upper crystal, that of position B (black squares) is separated from the upper crystal. The measurements show that the upper crystal leads to a significant enhancement of the emission intensity.