Modular THz time-domain spectrometer | SIMTRUM Photonics Store

Working Principle

The working principle of THZ-TDS can be divided into two main parts: excitation (producing THz pulses) and detection (measuring THz pulses). The entire process is based on ultrafast laser pulse technology and usually involves the following steps:

1. Excitation (generate THz pulse)

Laser source: The THz-TDS system uses ultrafast laser pulses (usually femtosecond laser pulses) as the excitation source.

Photoelectric effect: When a laser pulse is irradiated onto a semiconductor material such as germanium (Ge), germanium phosphide (GaAs) or gallium arsenide (InGaAs), the photoelectric effect is excited. The laser pulse causes electrons in the semiconductor material to be excited, resulting in a brief pulse of electric current (THz radiation).

THz wave generation: This current pulse generates THz waves (THz radiation) through acceleration inside the material. Due to the broad spectrum nature of the laser pulse, these THz waves usually contain broadband information from low to high frequency, so they can provide comprehensive frequency information for subsequent spectral analysis.

2. Detection (measuring THz pulse)

Detectors: THZ-TDS utilizes photodetectors (usually also photodiodes based on materials such as GaAs, InGaAs, etc.) to detect electrical signals caused by THz radiation. When the detector receives the THz pulse, it can generate the corresponding electrical signal.

Electric field sampling: The detector usually measures the change in the electric field of the THz pulse when it is received. In order to obtain the complete THz waveform in time domain, the system captures the amplitude and phase information of THz wave by precisely controlling the time delay between the detection pulse and the excitation pulse, so as to realize the complete time domain measurement of THz wave.

3. Data processing

Fourier Transform: By obtaining the complete waveform of the THz wave in the time domain, the THZ-TDS system uses Fourier Transform to convert the time domain signal into the frequency domain signal. At this time, the resulting spectrum contains the frequency component of the THz wave, which can provide detailed spectral characteristics of the material or substance in this frequency band.

Analysis and interpretation: The absorption characteristics, refractive index, optical constant and other information of the material can be extracted from the frequency domain spectrum. Thus, THz-TDS can be used to study the electromagnetic properties of materials (e.g., dielectric constant, optical transmission properties, etc.).