A line source consisting of a laser, a fiber-like waveguide, phosphors, and a holed cavity was suggested. In this study, the line source can emit the light through the phosphor with small source width at various wavelengths which is difficult to realize with the laser. Also, this line source is effective in emitting uniform light over the entire length. When the phosphor is included inside a fiber, it absorbs the laser beam and emits fluorescence. The light emitted from the phosphor escapes the fiber since it does not satisfy total internal reflection condition. At first, we performed the simulation with the simple structure where the phosphor was uniformly distributed over the rod. The simulation demonstrated the effect of a holed cavity on the uniformity and energy efficiency. In the simulation, when mean free path was 400 mm, energy efficiency was 81.7% and the variation of the irradiance was 6.92%. Energy loss seemed to be occur primarily on the both sides of mirror. To reduce the lateral width of line source, the core-clad structure was introduced with phosphor evenly distributed inside the core. In this structure, the size of the line source width gets smaller than that of the non-core structure because the illumination light only emits at the core which diameter is very small. The diameters of the core and the clad are 0.5 mm and 5.0 mm, respectively. The mean free path of phosphor was 35 mm and energy efficiency was 72.4% with illuminance variation of 4.55%.
Another important things in implementing this structure are the location of a hole and the aiming angle of the laser. In fact, the entrance hole was off-centered about 0.2 mm and the aiming angle of the laser was 10° away from the center. It considerably influenced the uniformity of irradiance. If the entrance hole is at the center of clad, it has higher chance to interact with phosphors near hole and causes irradiance irregularities.
Therefore, the simulations demonstrate that a holed cavity line source can provide energy efficiency of above 70% and illuminance variation of less than 5%. Especially, the core-clad structure is useful for realizing a thin line source.
Thesis Advisor: Prof. Young-Gu Ju