Responsivity is defined as the produced photocurrent (in Amperes) per Watt of incident radiation. It is a function of wavelength. Hence, the spectral response of the photodiode should be as high as possible at the wavelength of the laser to be measured. The spectral responsivities of the FPD series are shown in the figure. Ophir offers several fast photodiodes models with Silicon photodiodes having spectral response from 320 nm to 1100 nm, UV enhanced Silicon with extended response from 193 nm to 1100 nm, and InGaAs photodiodes which are sensitive from 900 nm to 1700 nm.