March 1, 2012

Touchless and Non-destructive – Fiber optic terahertz screens materials and analyses substances

Fraunhofer HHI has developed a complete system for the mobile, flexible and low-cost practical use of terahertz radiation in industrial environments. This complete system is based on a chip developed by Fraunhofer HHI in combination with components and technologies originally developed for fiber optic telecommunications.

THz combines the characteristics of radio waves and infrared light

Terahertz, or THz for short, is a frequency band which until only recently was very difficult to exploit. In the electromagnetic spectrum THz is precisely situated between radio waves and infrared light and combines the characteristics of these two frequencies. This particular combination means that the radiation – which is completely safe for humans – can penetrate and analyze materials and substances, thus opening up a new range of possibilities.

Mobile and affordable – terahertz as a complete system

Terahertz sensor systems are at a premium when it comes to non-destructive investigation of the insides of materials. Only terahertz systems used to be heavy, cumbersome and complex, and a great deal of serious development went into terahertz technologies before the apparent good qualities of terahertz could be harnessed for practical uses in industrial environments at acceptable costs. With its "TeraWave Time Domain Spectrometer" complete system Fraunhofer HHI has now found a way with a system that integrates all the components and processes required for its mobile, flexible real-world usage.

A new chip from Fraunhofer HHI tones up THz for real-world usage

The control unit of the complete systems contains telecom-developed lasers which emit ultra-short light pulses on what is known as the "Telecom wavelength" of 1.5 µm. This laser light is sent via flexible standard fiber optic cable to moveable THz emitter and detector heads. What is really crucial here are the Opto-Chips built into these THz heads.

Fraunhofer HHI THz sensor systems can be flexibly integrated into fabrication workflows

For realization of the complete system, Dr. Bernd Sartorius, group manager of Terahertz Technology at Fraunhofer HHI, and his team have integrated these chips in fiber-coupled flexible emitter and detector modules. As Bernd Sartorius explains, "Our system takes terahertz out of the lab environment. Our terahertz sensors can be flexibly integrated in a huge variety of fabrication and monitoring workflows. Control and evaluation is done by the laptop."

Terahertz at work

Monitoring the production and processing of plastics is one important area of use for terahertz sensors. In the food industry mobile complete systems can be used to scan packaging and foodstuffs to monitor the quality of contents. Unlike metal detectors, this system can even detect non-metallic materials like splinters of glass in chocolate.

The new technology is also ideal for the scanning of letters and packets to detect possible bio-weapons or explosives. The photo below shows a powder-filled plastic pouch between two sections of corrugated cardboard representing part of a packet. The THz emitter and detector heads developed by Fraunhofer HHI conduct a THz spectroscopic analysis of the powder. The THz transmission spectrum on the left shows an absorption band which identifies the powder as harmless lactose.

THz irradiates packages like corrugated cardboard boxes and can make a spectroscopic analysis of the materials inside. Photo: Fraunhofer HHI
THz irradiates packages like corrugated cardboard boxes and can make a spectroscopic analysis of the materials inside. Photo: Fraunhofer HHI