1550nm&780nm femtosecond laser for Terahertz
In recent years, the research and application of terahertz technology have shown significant technical advantages and industrial prospects in food/drug testing, security equipment, medical diagnosis, semiconductor material damage detection and many other fields. The advent of ultrafast fiber lasers has further accelerated the commercialization of terahertz technology. Compared with the complex and huge volume of lamp pumped terahertz gas lasers and the expensive price of Ti:sapphire laser, ultrafast fiber lasers are favored by the market for their advantages of high integration, small size, simple operation and easy batch operation.
What is terahertz ?
Terahertz (THz, 1012Hz) usually refers to the electromagnetic wave whose frequency is within the range of 0.1~10THz (corresponding wavelength is 3 mm ~ 30 μm). In the optical field, it is called far infrared, while in the field of electronics, it is called submillimeter wave, ultra-microwave, etc., which is between microwave and infrared light in the whole spectrum. The main characteristics of terahertz compared with other electromagnetic waves include:
(1) Low photon energy (safety), far lower than X-ray photon energy, will not produce harmful ionization to biological tissues, suitable for in vivo detection of biological tissues;
(2) High penetrability: the femtosecond pulse width and very high temporal resolution make the terahertz wave have good penetrability to many dielectric materials and non-polar materials, and can penetrate walls, ceramics, carbon plate, cloth, plastic, etc. for perspective imaging under low loss condition.
(3) Fingerprint spectroscopy: the absorption spectrum and dispersion characteristics of many organic molecules are located in this region, and the terahertz spectrum of each material contains rich physical and chemical information.
THZ radiation source is the key to whether THZ technology can be translated into real productivity. There are three kinds of terahertz sources: terahertz sources based on vacuum electronics; Photonic terahertz source; Terahertz source based on semiconductor. Among them, photonic terahertz sources mainly use ultrafast laser as terahertz excitation source.
THZ signal detection technology:
In principle, THZ signal detection technology can be divided into coherent pulse time-domain continuous wave detection technology and incoherent direct energy detection technology.
Thz-TDS system is a terahertz generation and detection system based on coherent detection technology, which can obtain the amplitude and phase information of terahertz pulse at the same time, and directly obtain the optical parameters such as the absorption coefficient, refractive index and transmittance of samples by Fourier transform the time waveform. The terahertz time domain spectrum has high detection SNR, wide detection bandwidth and high detection sensitivity, which can be widely used in the detection of a variety of samples.
Terahertz coherent detection system
The coherent detection system of terahertz consists of a beam splitting device, which divides a beam of ultra-fast pulse laser into pump light and detection light, in which the pump light excites the terahertz pulse, while the detection light sampling detects the terahertz pulse, so the detection light and the terahertz pulse have a fixed time relationship. In the detection system, the time delay of the pump light and the detection light is precisely controlled, so that the detection pulse and the terahertz pulse reach the detector or the detection crystal at different time. Since the pulse width of the detected light (femtosecond magnitude) is far less than the width of the terahertz pulse to be detected (picosecond magnitude), the time delay between the two is controlled by optical delay platform, which is equivalent to the detection pulse scanning the terahertz pulse, so as to obtain the complete waveform of the terahertz pulse.
THz-TDS technology is a new spectral measurement technology developed in the 1980s. This technique uses the wide band terahertz pulse obtained by femtosecond laser technology to reflect through or from the sample, measure the resulting terahertz electric field intensity over time, and then obtain the sample information. This measurement technique is mainly used to detect the properties and physical phenomena of the material between far-infrared and microwave.
The typical terahertz time domain spectroscopy system is mainly composed of three parts: ultra-fast fiber laser, terahertz emission and detection device and time delay control system. Such as sketches, place the sample in the light path of terahertz time-domain spectroscopy system. The time domain waveform of terahertz wave before and after the reflection of the sample was collected and converted to the frequency domain by Fourier transform. Some optical parameters related to the measured sample can be tested through the analysis and processing of the two sets of frequency-domain data, such as refractive index, absorption coefficient, etc.
Rainbow OEM series femtosecond fiber laser developed by NPI lasers can provide two wavelengths of 1550 nm and 780 nm, which is specially designed and developed for commercial terahertz system integration. Both products have passed the strict industrial test standard, with the advantages of high stability, reliability, maintenance free, easy integration, etc., and are the ideal laser source for the current terahertz commercial system.