Abstract: An additive manufacturing apparatus includes a laser and a detection system. The laser emits a laser beam to heat a powder bed to form a melt pool, and the melt pool emits light proportional to a temperature of the melt pool. The detection system includes a spectral disperser and one of a) two or more on-axis sensors or b) a line scanner. The two or more on-axis sensors or the line scanner are/is located along an axis of the emitted light, the detection system receives the emitted light from the melt pool, and an intensity of the emitted light detected by the a) two or more on-axis sensors or the b) line scanner is compared with a blackbody spectral map at a particular wavelength of the emitted light to determine a temperature of the melt pool.