Photonic Crystal Surface Emitting Laser Diode (PCSEL) is a surface-emitting semiconductor laser with a photonic crystal structure that features a narrow spot beam pattern (narrow beam spread angle, circular shape) and a narrow spectral linewidth. The photonic crystal is an optical nanostructure having a periodic refractive index distribution with dimensions nearly equal to the light wavelengths. In this product, light is amplified and diffracted by the photonic crystal mounted in the vicinity of a light amplification layer called an active layer, and the amplified light is output as a laser beam in a direction perpendicular to the surface. Even with a large area, this laser allows a stable resonance action and so delivers a high quality beam with a narrow radiant angle.