A light source device, includes an excitation light source for generating excitation light, a light condensing device, and a fluorescent cavity. The fluorescent cavity includes a chamber and a fluorescent layer, the chamber having a light window for allowing light to enter and exit and a bottom wall opposite to the light window. The fluorescent layer is provided on the surface of the bottom wall. The excitation light is concentrated by the light condensing device, and then is incident from the light window to the surface of the fluorescent layer to form a light spot and excite the fluorescent layer to generate a laser. The area of the light window is smaller than the area of the light spot, and the laser can be emitted from the light window.