Transcranial infrared laser stimulation (TILS) is a neural type of photobiomodulation that can elevate neuronal metabolism by exciting cytochrome c oxidase (CCO). Veterans with PTSD will receive prefrontal TILS interventions once-per-week for six weeks. They will also receive an additional sham intervention (laser power = 0) that will be randomly assigned into the first two sessions. Broadband near-infrared spectroscopy (bbNIRS) will be used to directly assess the CCO changes during every TILS/sham session.