My name is HIdeki Hirori. Title of my talk is “Making invisible worlds visible”. Firstly, I’d like to show you a nice picture
of Mt. Daisen. This summer, I visited the Daisen. This is me and very dark but at that time the sky was very blue, bright sunlight was coming, so thanks to the sunlight, we
could enjoy the very nice view of the nature. Of course, during the day time, thanks to
the sunlight we could see the very nice view of the mountain and nature. But under the darkness of night, our naked
eye almost doesn’t work. However, there’s still a small light, an infrared light. Some snakes can hunt and catch animals by detecting infrared radiation or
infrared light. Not only the infrared light but also microwave
light is coming from the space and it’s called cosmic background radiation and it tells us the history of the universe. So the question is “What is the difference
between visible light, infrared light, and microwave light. It’s just only wavelength. This is the chart of the lights with different wavelengths. Here is visible light, infrared light and microwave light. From left side to right side, the wavelength becomes shorter and shorter. And our naked eye can detect the wavelength of 380 nano-meters to 780 nano-meters. Infrared wavelength is a little bit longer
than the visible light. and microwave wavelength is much, much longer than the visible light and infrared light. Actually it’s from 1mm to 10 cm. So, I’d say that we are surrounded by many kinds of natural lights. It’s very convenient to see and to get information from the objects. We can see the objects by sunlight and the
microwave give us the history of the universe. Infrared light is important for the snakes. So, the humankind has started to develop or invent technology to generate artificial lights. It allows us to live a richer, more convenient life. As you know, Dr. Röntgen invented
the technology to generate X-rays and it allows us to see our bones in our body. Thomas Edison and many other researchers developed electric valves or LEDs. They are very convenient for the illumination
and it’s also used in remote controllers of electronic devices in your house And also the microwave is very convenient to warm up your cold food from your refrigerator. The radiofrequency wave is a very cool technology. Actually, it allows us to communicate with each other regardless of our physical distances. So I would emphasize from these figures that good and cool technologies have come to our ordinary life after developing new lights. But still, you can see here, there is a missing region. We call here the “terahertz region”. I’d explain why we call this region terahertz (THz) and why it’s so important. I explain the lights with different wavelengths. The typical wavelength of the THz frequency region is 0.3 mm. And the light can be also characterized by
the frequency and we can convert the wavelength to the frequency by a very simple equation,
just by dividing the speed of light by wavelength λ. In this case, the frequency of this terahertz
light is 10000….many zero. Actually, there are twelve zeros. 10(12) is expressed as “tera”. So the frequency is 1 THz. We call this region a THz light or THz wave Why is it so important? Because there
are many potential applications. For example, you can see one guy taken in visible light. If you see this guy with THz light, you can find that this guy has a knife hidden by a newspaper. This means THz is highly
transparent for clothes and paper but is not transparent for metal and water. In this case, a knife and a human body. Also, photon energy of terahertz is much, much
smaller than the X-ray, and is much more safer compared with X-ray used in a security check system. And also, it has a potential application for drug tests. As you can see, there are three kinds of chemicals packed in plastic bags. The left one is codeine used in normal medicine. The right one is sucrose. It’s like sugar. Both are not illegal ones. But the center one is cocaine which is an illegal chemical. You cannot distinguish between them in the visible region. but if you see these chemicals with Terahertz light, you can distinguish them because these chemicals have different absorption line in the THz frequency region. So when you shine the THz light onto the chemicals, the intensity of reflected THz light or transmitted light is different from each other. So we can distinguish these chemicals
by the difference in intensity of THz light. So I’d say that THz frequency
region is a fingerprint region of molecules. And the other application is medical imaging. This is a cancer tissue of human skin that was taken in the visible frequency region. The solid black line indicates the cancer region and the dashed line indicates the normal region,
not cancer region. It’s hard to distinguish between these two
regions. But by using THz lights, you can distinguish between these two regions because the THz light is strongly absorbed by water molecules. And the cancer region has less water contents
compared with normal regions, so, when you shine the THz light onto these tissues and
transmitted THz light in the cancer region is higher, so, we can also distinguish these
two regions by difference in transmitted intensity of THz light. To make these imaging applications in reality,
the important point or problem is the speed of imaging. If you use a weaker THz power generator, the imaging speed is very, very slow like this. So, if you use a much stronger THz generator, maybe the imaging speed becomes much faster. To make the THz imaging system in real application, a stronger THz generator is required. To do this, there are many researchers in all over the world that have developed THz generation techniques. This graph is showing the THz power developed
by other research groups all over the world as a function of the year. MIT and the University of Tokyo developed
very nice THz source, but there is a difficulty to overcome the field strength of 1MV/cm of
THz power. But in 2011, we could overcome the difficulty
to generate the THz pulse with1 MV/cm. It’s the world strongest THz source. Before going to my setup, I’d explain the different devices to generate the THz waves. You are very familiar with this device. And
actually I’m using a laser pointer. If you break down this laser pointer, you can see
it like this. The important point is that there are just
three components. Firstly an infrared laser is coming from the semiconductor devices and there is a crystal. As the infrared laser goes through the crystal, the wavelength of Infrared laser is converted to green laser. My actual setup is that there are many, many
optics, the mirrors and lenses. But the principle is very similar with the
laser pointer. We are using Lithium Niobate as a crystal and we are shining a laser beam
whose wavelength is 800 nm onto the Crystal. And especially we optimize the focusing condition
of laser beam. We could generate very strong THz light. We can convert the wave length of 800nm to 300 micrometers. Then, we have now very strong THz light. So we apply the strong THz light to develop a microscope to see living cells. Actually observing the living cells is the ultimate goal. And actually by using our high power THz source, we could develop the world’s fastest THz microscope with a very high spatial resolution. It’s a collaboration work with Olympus. I hope that THz power is getting higher and higher We may be able to take a larger images and pictures. and also, with a higher speed I hope that in future, it can be used in the surgical space, and also, the important point is that by using the THz light, we can detect cancer or some diseased area which cannot be detected by naked eye. Hopefully THz can detect these kinds of cancer region and help the surgery a lot. Thank you for your kind attention. [applause]