Mid-infrared detection system based on frequency conversion technique. (Image provided by SIACAS)

Shenyang Institute of Automation, Chinese Academy of Sciences (SIACAS) announced On January 25th that its Terahertz team has made important progress in infrared detection. Highly-sensitive detection of ns-pulses between 3 and 8 micrometers has been realized by using frequency conversion technique via BGSe crystal. It will help to promote cutting-edge research in the fields of biology, medicine, chemical engineering，etc. This work was published by Optica on January 20th.

Compared to traditional visible light and near-infrared (near-IR) rays, the interaction between waves and molecules can be stronger in case of mid-infrared (mid-IR). Moreover, the resonant phenomenon due to a certain wavelength within mid-IR can help to improve the signal-to-noise (SNR) ratio in spectroscopy. Consequently, mid-IR detection is important for explorations in life science, material science, environment protection, medical diagnosis, etc. Current mid-IR detectors are mainly based on thermo detection and opto-electronic detection mechanisms, and sensitivity has been the bottleneck for accurate and quantitative characterization of infinitesimal traces of substances.

Aiming at the limited sensitivity of mid-IR, researchers designed a system based on frequency conversion detection. Its working mechanism is to change weak mid-IR signals into near-IR signals effectively. Since the near-IR signals contain the information of mid-IR signals and are easy to detect,  highly-sensitive mid-IR detection can be implemented via such an indirect approach.

The Terahertz team has analyzed nonlinear crystals systematically and decided to use the BGSe crystal，which was produced by YAO Jiyong from Technical Institute of Physics and Chemistry, Chinese Academy of Sciences.

"In most cases, the BGSe crystal is used as the source, we tap into the detection funciton of the crystal and use it at the detection side."said QI Feng, researcher of SIACAS and also head of the team. "We optimized the phase-matching condition and realized effect detection of weak signals in case of a strong noise background."

The BGSe crystal .(Image provided by SIACAS)

Experimental studies have been implemented and in case of ns-pulse detection, such a system is at least 100 times more sensitive than the HgCdTe detector. AJ-level pulses have been detected successfully. The dynamic range of the system is over 110 dB and the response is quite uniform over 3-8 μm, both parameters above outperform classical detection methods. Moreover, the performance can be improved further in future.

Scientists during experiments. (Image provided by SIACAS)

Contact:

QI Feng  
Email: qifeng@sia.cn