LD-PD’s photodetectors contain PIN photodiodes that utilize the photovoltaic effect to convert optical power into an electrical current. When terminated into 50Ω into an oscilloscope, the pulse width of a laser can be measured. When terminated into 50Ω into a spectrum analyzer, the frequency response of a laser can be measured. Most LD-PD's photodetectors come with their own internal bias supply consisting of long-life lithium cells. Plugging a coaxial cable into the photodetector's output connector and terminating into 50Ω at the oscilloscope or spectrum analyzer is all that is required for operation.