Light source device

A light source device comprising:

• a laser diode configured to emit laser light;
• a substrate directly or indirectly supporting the laser diode;
• a glass cap secured to the substrate and covering the laser diode, the glass cap comprising a front glass wall configured to transmit the laser light that is emitted from the laser diode, the front glass wall having an incident surface on which the laser light is incident and an emission surface from which the laser light exits;
• and
• a photodetector directly or indirectly supported by the substrate and located outside of the glass cap;
• wherein:
• the photodetector is configured to detect light that is reflected at the front glass wall and transmitted through the glass cap;
• the glass cap comprises a rear glass wall located on a side opposite the front glass wall with respect to the laser diode;
• and
• the photodetector is located on a rear side of the rear glass wall and is configured to detect the light transmitted through the rear glass wall.