An approach for aligning a light source on a slider involves filtering light emerging from the air bearing surface of a (ABS) of a heat assisted magnetic recording (HAMR) slider. A first portion of the emerging light is emitted by a near field transducer in response to optical excitation and has a component having a first polarization state. A second portion of the emerging light including stray light has polarization states different from the first polarization state. The polarizing filter substantially transmits light having the first polarization state and substantially rejects light having a polarization state orthogonal to the first polarization state. Alignment coordinates for the light source are determined based on the light transmitted through the polarizing filter.