Outline of R&D Project

 
In our CREST project, we achieved in 2011 a record electric field intensity in the terahertz (THz) region1), as large as 1 MV/cm, and opened up the field of terahertz nonlinear optics. In addition, we realized a high-speed (video rate2)) THz microscope system with a spatial resolution of 1/30 of the wavelength and successfully observed living cells with high resolution in real time. Subsequently, we expanded our research field toward a THz imaging system based on the semiconductor terahertz technology. Through these development activities, we have established the guideline for the proof of concept (POC) in the ACCEL project.
In our ACCEL project, we will improve the output power of semiconductor-based THz emitters and the sensitivity of semiconductor-based THz detectors. By arraying and modularizing THz emitters and detectors, we will construct a basic THz imaging system including optics, control system, and analysis software. The system will facilitate the development of a THz body scanner for security inspection and a THz non-destructive inspection equipment for industrial production, both of which are expected to become important steps in the realization of a safe and secure society.
1） Terahertz region
Frequency band of light wave between 300 GHz (GHz = 109 Hz) and 3 THz (THz = 1012 Hz), which corresponds to 1 mm and 100 μm in wavelength.
2） Video-rate
Frame rate of the conventional video system ranging from 20 Hz to 50 Hz which is valuable for real-time observation.

Developing a high-intensity terahertz pulse light source that allows observation of living cells

Terahertz (THz) light is the electromagnetic wave range at the boundary between radio waves and light. It has
been called an unexplored electromagnetic region because of the diffi culty with which it is generated, controlled, and
detected. However, recent technological innovations have triggered higher expectations for its commercialization.
In the CREST project, we have developed the world’s highest intensity THz pulse light source, with a peak electric
field of 1 MV/cm or more, using 100 femtoseconds pulsed lasers and lithium niobate crystals. We are able to
amplify the number of free electrons responsible for electrical conduction in the semiconductor some 1000 times by
simply irradiating the semiconductor with this THz light for a mere trillionth of a second. In addition, we were able
to discover a variety of extremely non-linear optical responses. Moreover, by developing a novel THz near fi eld
microscopic apparatus that takes advantage of the characteristics of this light source, we have achieved real-time
observation with video rates and spatial resolutions of less than a hundredth of the wavelength limit, succeeding in
the observation of living cells as well.

Construction of a high-resolution, high-speed, safe terahertz imaging system

In addition to the development of the THz light source and detector, issues to be addressed in the ACCEL project
include systemization. While the THz light source has seen rapid development, the output levels are still insuffi cient.
We will expand light-laser-excitation terahertz technology into terahertz-semiconductor technology, constructing a
basic imaging system using semiconductor sources and detectors. With the increases in output power and imaging
speed gained by making arrays and modules of semiconductor light sources and with the sensitivity improvement
gained by adding phase detection technology to detectors, we will use conversion to arrays and modules for highspeed
imaging and construct a basic terahertz imaging system composed of a light source, detector, optimized lowloss
optical system, control system, and analysis software to make possible equipment such as body scanners and
non-destructive inspection systems that are even higher-resolution, faster, and safer than the existing technologies.
This will enhance the security of public places such as transport facilities and improve the safety of products
manufactured at factories or other locations, leading to a safer and more secure society.