响应率（英语：responsivity）是指探测系统的输入-输出增益。对输入信号具有线性响应的系统，响应率是唯一的确定值，而对非线性系统，响应率是特定位置曲线的斜率（导数）。

Responsivity measures the input–output gain of a detector system. In the specific case of a photodetector, responsivity measures the electrical output per optical input.

The responsivity of a photodetector is usually expressed in units of either amperes or volts per watt of incident radiant power. For a system that responds linearly to its input, there is a unique responsivity. For nonlinear systems, the responsivity is the local slope. Many common photodetectors respond linearly as a function of the incident power.