Terahertz signal detection technology: In principle, terahertz signal detection technology can be divided into coherent pulse time domain continuous wave detection technology and incoherent direct energy detection technology. The THz-TDS system is a terahertz generation and detection system based on coherent detection technology. It can obtain the amplitude and phase information of the terahertz pulse at the same time. Through the Fourier transform of the time waveform, the absorption coefficient, refractive index and transmission of the sample can be directly obtained Rate and other optical parameters. Terahertz time-domain spectroscopy has a high detection signal-to-noise ratio and a wide detection bandwidth, high detection sensitivity, and can be widely used in the detection of a variety of samples.
The terahertz coherent detection system includes a beam splitting device, which divides a beam of ultrafast pulse laser pointer into pump light and probe light. The pump light is excited to generate terahertz pulses, and the probe light samples to detect terahertz pulses, thus detecting Light and terahertz pulses themselves have a fixed time relationship. In the detection system, the delay of the pump light and the probe light in the time domain is precisely controlled.
Therefore, the detection pulse and the terahertz pulse reach the detector or the detection crystal at different times. Since the pulse width of the detection light (in the order of femtoseconds) is much smaller than the width of the terahertz pulse to be detected (in the order of picoseconds), the optical delay stage controls the time delay between the two, which is equivalent to scanning the terahertz of the detection pulse Pulse to get the complete waveform of the terahertz pulse.
THz-TDS technology is a new type of spectrum measurement technology developed in the 1980s. This technology uses a wide-band terahertz pulse obtained based on femtosecond laser technology to pass through or reflect from the sample, and measure the change of the resulting terahertz electric field intensity over time to obtain sample information. This measurement technique is mainly suitable for detecting the properties and physical phenomena of materials between far infrared and microwave.
A typical terahertz time-domain spectroscopy system is mainly composed of three parts: ultrafast fiber green laser pointer, terahertz emission and detection device, and time delay control system. As shown in the schematic diagram, the sample is placed in the optical path of the terahertz time-domain spectroscopy system, the time-domain waveform of the terahertz wave before and after the sample reflection is collected and Fourier transform is used to transform it into the frequency domain, and the two sets of frequency domain data are analyzed Processing can get some optical parameters related to the tested sample, such as refractive index, absorption coefficient, etc.