平衡探测器是直接探测太赫兹信号的器件，位于高速太赫兹时域光谱 (THz-TDS)系统末端光信号检测部分，是将光学信号转变为模拟电信号的关键器件，其性能决定了测量出的 THz信号的精确度。利用 2个低噪声光电二极管串联，直接探测出 2束激光的差值光电流，降低了探测噪声；选用增益带宽乘积为4 GHz的运算放大器对差值光电流进行两级放大，得到高动态范围的 THz信号，提高了THz信号的探测速度，并测量了 α-乳糖一水合物吸收峰，得到了和文献中相同的吸收峰。

Balanced detector, which is located at the end of high-speed Terahertz Time-Domain Spectroscopy(THz-TDS) system, is a device to detect THz signals directly. The optical signal detection part is the key device for converting the optical signal into analog electrical signal. Its performance determines the accuracy of the measured THz signal. Using two low-noise photodiodes in series, the differential photocurrent of two lasers is directly detected, and the detection noise is reduced. The operational amplifier with a gain bandwidth product of 4 GHz is utilized to perform two-stage amplification of the differential photocurrent. The THz signal with high dynamic range is obtained and the detection speed of the THz signal is improved. The absorption peaks of α-lactose monohydrate are measured, and the same absorption peaks as those in literatures are obtained.