Terahertz radiation

Special waves are all around us.

These waves sit between two other types of waves. They can see through thin things like paper. They can also see through wood or plastic.

These waves can even see inside our bodies. They are safer than X-rays for doctors to use. They do not hurt our living parts. Even unpeeling tape makes these waves! They are very useful for science.

Terahertz waves are a special kind of light.

They sit in a middle spot. They are between microwaves and infrared light. Scientists call this the "terahertz gap." This gap exists because it is hard to make these waves.

These waves can do many things. They can pass through paper, wood, and plastic. They can even see through some body tissue. This makes them a safe choice for doctors. Unlike X-rays, they are non-ionizing. This means they do not damage living cells or DNA.

However, these waves have some limits. They cannot pass through metal or liquid water. They also do not travel far in our air. Gases in the sky soak them up quickly. Because of this, we cannot use them for long-distance radio.

Space scientists use them to study the stars. They look at cold dust in our galaxy. To do this, they use telescopes in space. They must go above the clouds to see clearly. Even unpeeling tape makes these waves! It happens when the sticky part pulls away.

Terahertz radiation is a very special kind of light. It sits in a middle ground between microwaves and infrared light. Scientists call this middle area the "terahertz gap." This gap exists because making these waves is a hard job. It is difficult to create and control them with normal electronics.

This radiation uses frequencies from 0.1 to 10 terahertz. One terahertz is a huge number of vibrations. It equals 1,000 gigahertz or 10 to the 12th power hertz. These waves are also called submillimeter waves in astronomy.

These waves work in a very interesting way. They can pass through many different things like paper and wood. They can also travel through plastic, ceramics, and even clothing.

However, they have some limits on what they can do. They cannot pass through metal or liquid water. They also cannot go through thick clouds or fog. The gases in our air soak up most of the energy. This means the waves only travel a few meters in air. Because of this, we cannot use them for long-distance radio.

Scientists have worked for a long time to study these waves. In the 1960s, people made the first images using terahertz radiation. In 2007, researchers at Argonne National Laboratory made a small device. This device used special crystals from the University of Tsukuba in Japan. These crystals use the Josephson effect to make waves. In 2008, engineers at Harvard University made waves at room temperature. Before this, many devices needed very cold temperatures to work. This was because the energy of the waves is quite small.

There are many important facts about how these waves behave. Terahertz radiation is non-ionizing, which is a very important trait. This means the waves do not damage living cells or DNA. Because of this, they might replace X-rays for medical images. They can see through some body tissue like fatty tissue. However, their images have lower resolution than X-rays. This means the images need to be enhanced to look clear.

They can also help detect things like epithelial cancer.

We can see how these waves connect to the wider world. They help us look at the stars and far-off galaxies. Astronomers use them to study cold dust in the Milky Way. They use big telescopes like the James Clerk Maxwell Telescope. These telescopes must be in space or on high mountains. This is because the atmosphere blocks the waves from reaching Earth. You can even find these waves in your own home. Unpeeling adhesive tape creates these waves through a process called tribocharging. It is amazing how much is happening in the invisible world.

Terahertz radiation is a specific type of electromagnetic wave. It sits in a transition region between microwaves and far infrared light. This middle ground is often called the "terahertz gap." It is called a gap because the technology to create and control these waves is still developing.

The International Telecommunication Union designates this band between 0.1 and 10 terahertz (THz). Some sources consider the upper boundary to be as high as 30 THz. One terahertz is a massive number, equaling 1,000 gigahertz or 10 to the 12th power hertz. These waves are also known as submillimeter radiation because their wavelengths range from 3 mm down to 30 micrometers.

The way these waves interact with the world is very unique. Terahertz radiation travels in a straight line, known as line of sight. It is non-ionizing, which means it does not have enough energy to damage DNA or living cells. This makes it a safer alternative to X-rays for certain uses. Like microwaves, these waves can penetrate many non-conducting materials. This includes things like clothing, paper, cardboard, wood, plastic, and ceramics. However, their penetration depth is usually less than that of microwaves. They are also blocked by metal and liquid water.

Because of how these waves behave, they have specific uses in science and industry. They can pass through thin layers of material for inspection. This allows for material characterization and relief measurement. Scientists can use them to produce high-resolution images of the interior of solid objects. In medicine, they could potentially detect epithelial cancer. This is because they can detect differences in the density and water content of tissue. While they can penetrate some body tissue, they have lower resolution than X-rays. This means the resulting images often need to be enhanced to be useful.

Creating these waves has historically been a major technical challenge. Conventional electronic devices used for radio waves cannot easily generate these frequencies. Most current devices require very low temperatures to work. This is because the energy of THz photons is very small. Low temperatures are needed to suppress environmental noise. Researchers are currently using strategies like optomechanical meta-devices to improve operation temperatures. In 2008, engineers at Harvard University achieved a breakthrough. They used a semiconductor source to create coherent terahertz radiation at room temperature. They did this through the nonlinear mixing of two modes in a mid-infrared quantum cascade laser.

There have been many different ways to produce these waves. Some methods use vacuum electronic devices like the gyrotron or the free-electron laser. Other methods use solid-state sources like resonant-tunneling diodes, which can operate up to 1.98 THz. In 2007, scientists at Argonne National Laboratory announced a compact device using superconducting crystals. These crystals use the Josephson effect. This effect occurs when an external voltage causes an alternating current to flow across junctions. This current then induces an electromagnetic field. Even simple actions can create these waves. In 2009, scientists discovered that unpeeling adhesive tape generates terahertz radiation. This happens through tribocharging, which is the buildup and discharge of static electricity.

Terahertz radiation is also vital for studying the universe. It is emitted as part of black-body radiation from anything warmer than 2 kelvin. While this emission is weak, it is very important for astronomy. It helps scientists characterize cold cosmic dust in interstellar clouds within the Milky Way. It also helps study distant starburst galaxies.

Because Earth's atmosphere strongly absorbs these waves, telescopes must be placed in special locations. They are often located at very high altitudes or in space. Notable observatories include the James Clerk Maxwell Telescope and the Herschel Space Observatory. The Atacama Large Millimeter Array is another important tool for these observations.

Finally, the study of terahertz waves connects to the very building blocks of life. The frequencies of these waves are similar to the motion of biomolecular systems. For example, 1 THz is equivalent to a timescale of one picosecond. This range is comparable to the relaxation timescales of many biological molecules. This means that radiation in this range could potentially modulate biological or neurological functions. Because the energy is low, it can achieve these effects without causing significant heating or ionization. As technology improves, the "terahertz gap" will continue to close, opening new doors in medicine, communication, and space science.