Product Introduction

The Terahertz Toolbox provides the main accessories for the Terahertz Time Domain Spectrometer (THz TDS) system, as well as corresponding control software for the hardware in the system. We can also provide design solutions for building the system.

1、 THz TDS based on photoconductive antenna

If your laboratory already has femtosecond lasers, including femtosecond fiber lasers and titanium sapphire femtosecond lasers, the pulse width requirement is on the order of 100fs. You can build a terahertz time-domain spectrometer system at a low cost.

To build a conventional THz TDS based on photoconductive antenna, the system requires the following fs laser:

Yichi Optoelectronics provides customers with all the accessories to build their own THz TDS.

The following is the optical path diagram of a terahertz time-domain spectrometer based on a photoconductive antenna. The system mainly includes: 1) a pair of photoconductive antennas; 2) A linear stepper motor; 3) Signal generator (applying bias voltage to the antenna); 4) Lock In Amplifier By adding some optical beam splitters and conventional optical components such as reflectors, the optical path can be constructed.

Notes to be noted:

In general, the inverse ratio of the transmission of the beam splitter in the antenna TDS system is 1:1, and the intensity of the transmitted and reflected light is the same. The specific bias voltage applied to the antenna and the required light intensity of the antenna depend on the antenna specifications of different manufacturers (depending on the electrode structure of the optical waveguide antenna). The antenna of Batop in Germany generally has a bias voltage of 10V, and the excitation light and detection light power are both 10-15mW.

2. Ensure that the optical path difference between the generated light path and the detection light path is within the compensation range of the stepper motor. Starting from the BS beam splitter, the transmitted light passes through the BS beam splitter and reaches the THz Detector detection antenna to generate an optical path; The reflected light passes through the BS beam splitter and reaches the THzDetector detection antenna as the detection light path. During the scanning process of a stepper motor, the peak of the terahertz time-domain spectrum is located when the optical path length and the detection optical path length are equal.

3. The most important thing in building an optical path is to align the beam with the antenna. When adjusting the optical path, a multimeter can be used to measure the resistance of the antenna. When the LT GaAs substrate is irradiated with laser, a large number of photo generated carriers are generated between the antenna electrodes, and the antenna resistance will also decrease significantly. By observing the resistance changes on the multimeter in real time, it is easy to determine whether the beam is accurately irradiated in the middle of the antenna electrodes.

THz TDS Optical Path Diagram

Terahertz time-domain spectrometer based on photoconductive antennaThe main hardware of the system includes:

1. Electronic box set, including pulse voltage generator and phase-locked detection device;

2. THz photoconductive antenna with collimated TPX terahertz lens;

3. Linear stepper motor;

4. Equipped with spectrometer software, it can achieve fast/slow scanning, imaging, angle scanning, etc. THz spectrum calculation and analysis, such as calculating the refractive index of materials.

1. Photoconductive antenna:

Set of fiber-coupled antennas setup in a transmissionconfiguration

2. Signal generator&lock-in amplifier (Lock in)

Data acqusition systems with BNC ports for emitter and detectorantenna

(The BNC interface on the right is connected to the generating antenna, and a bias voltage is applied to the generating antenna. The BNC interface on the left is connected to the detecting antenna to collect THz time-domain signals.)

3. Linear stepper motor:

Zaber linear stage typically used as delay linein THz spectrometer.

4. Control software T3DS

Front panel of the T3DS software displaying the results of areference measurement

Imaging measurement of TDTS software

2、 THz TDS based on zinc telluride crystal

The following is the optical path diagram of an optically pumped terahertz (OPTP) detection system based on zinc telluride crystal ZnTe. The main part is still a terahertz time-domain spectrometer system, which mainly includes: 1) a pair of zinc telluride crystals; 2) Two linear stepper motors; 3) Optical chopper (modulation signal); 4) By adding some optical beam splitters, reflectors, off-axis parabolic mirrors, polarizing spectrometers, balanced photodetectors, etc. to the lock-in amplifier, an optical path can be constructed.

Precautions to be taken

In the figure below, there are two beam splitters and three paths of light. The emitted light after passing through BS2 is the excitation light that excites ZnTe to produce THz radiation. The light intensity generally ranges from 30-60mW depending on the size of the light spot. The transmitted light after passing through BS2 is the probe light, and the intensity is generally 1/10 of the excitation light. All other light intensities are reserved for the pump light transmitted through BS1 to pump and excite the sample.

2. It is necessary to adjust 1/4 of the probe to change the detection light to circular polarization, that is, the light intensity entering the two holes of the balanced detector is equal, and the differential signal is zero (the principle of free space electro-optic sampling is not repeated here, please refer to the EOD of the free space electro-optic sampling detector)

3. After generating zinc telluride crystals, due to the transmission of excitation light, a terahertz window plate such as Teflon or polytetrafluoroethylene is required HDPE、 Or plastic foam sheet can block the excitation light (the mentioned material is basically transparent to terahertz).

4. It is also necessary to pay attention to the issue of equal optical path points. Due to the addition of pump light, the two paths of light from the BS1 beam splitter to the sample need to meet the equal optical path point conditions mentioned above.

Other accessories required for terahertz time-domain spectrometer system

crystal（ZnTe、DAST、DSTMS、OH1、LiNbO3）

Photoconductive antenna（monopole、Antenna array）

Terahertz near-field probe

Off-axis parabolic mirror

Optical Chopper

THz pulse electro-optic sampling detector

THz yuanpiece（THz polarizer，THz lens，THz filter、THz waveplate、THz prism、THz beam splitterEtc.)