1：Experimental Design and Method Selection:

The study involved the fabrication of AlGaN-based UV-B band lasers with varying dislocation densities and the characterization of their optical properties. The variable stripe lengths (VSL) method was used to measure the optical gain and internal loss.

2：Sample Selection and Data Sources:

Samples were grown using metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates with sputtered and high-temperature annealed AlN templates. The dislocation density was determined from the dark spot density measured via cathodoluminescence (CL) mapping.

3：List of Experimental Equipment and Materials:

A fourth-harmonic yttrium aluminum garnet laser (YAG) with a wavelength of 266 nm was used as the optical pumping source. Ni masks were used for high measurement accuracy.

4：Experimental Procedures and Operational Workflow:

The samples were characterized at room temperature. The optically pumped laser's threshold power density, optical gain, and internal loss were measured after device processing. The VSL method was employed with excitation lengths varied from 50 to 250 μm.

5：Data Analysis Methods:

The net modal gain was calculated based on the dependence of the excitation length on the emission intensity obtained via VSL measurement. The internal loss was estimated by setting the gain on the low-energy side of the peak wavelength of the gain spectrum to approximately zero.