1.1 Definition and properties of terahertz waves

Terahertz waves sit between microwaves and infrared light, spanning 0.1 to 10 THz. They're tricky to make and detect, creating a "terahertz gap" that's slowly being bridged by new tech. These waves are opening doors in imaging, security, and communications.

Terahertz radiation can see through many materials but gets absorbed by water. It's safer than X-rays and great for detailed images. Scientists are working hard to overcome generation and detection challenges, paving the way for exciting new applications.

Terahertz Waves: Definition and Range

Electromagnetic Spectrum Positioning

Top images from around the web for Electromagnetic Spectrum Positioning

• 

  Electromagnetic wave - Wikiversity View original

  Is this image relevant?

• 

  Electromagnetic spectrum - Wikipedia View original

  Is this image relevant?

• 

  16.5 The Electromagnetic Spectrum – University Physics Volume 2 View original

  Is this image relevant?

• 

  Electromagnetic wave - Wikiversity View original

  Is this image relevant?

• 

  Electromagnetic spectrum - Wikipedia View original

  Is this image relevant?

1 of 3

Top images from around the web for Electromagnetic Spectrum Positioning

• 

  Electromagnetic wave - Wikiversity View original

  Is this image relevant?

• 

  Electromagnetic spectrum - Wikipedia View original

  Is this image relevant?

• 

  16.5 The Electromagnetic Spectrum – University Physics Volume 2 View original

  Is this image relevant?

• 

  Electromagnetic wave - Wikiversity View original

  Is this image relevant?

• 

  Electromagnetic spectrum - Wikipedia View original

  Is this image relevant?

1 of 3

• Terahertz waves occupy the spectral region between microwaves and infrared light in the electromagnetic spectrum
• Frequency range typically spans from 0.1 THz to 10 THz
• Corresponding wavelengths fall between 3 mm and 30 μm
• Also known as submillimeter waves or far-infrared radiation
• Exhibit properties of both radio waves and light due to their unique position in the spectrum

Technological Challenges

• Terahertz gap refers to difficulties in efficiently generating and detecting radiation in this frequency range
• Challenges stem from limitations of traditional electronic and optical technologies
• Gap has historically hindered widespread application and research in this area
• Recent advancements in technology are gradually bridging this gap (quantum cascade lasers, photomixing techniques)

Properties of Terahertz Waves

Material Interaction

• Penetrate many non-conducting materials (clothing, paper, plastics, ceramics)
• Strongly absorbed by water and other polar molecules
• Limited propagation through atmosphere due to water vapor absorption
• Materials have distinct spectral fingerprints in terahertz range
• Enable non-destructive material identification and analysis (pharmaceutical quality control, art conservation)

Safety and Resolution

• Non-ionizing radiation safer for biological applications compared to X-rays
• Short wavelength allows for high-resolution imaging capabilities
• Photon energy corresponds to many molecular rotational and vibrational transitions
• Useful for spectroscopy applications (chemical analysis, material characterization)

Challenges in Terahertz Technology

Generation Difficulties

• Traditional electronic sources struggle at terahertz frequencies due to parasitic capacitances and transit time effects
• Optical sources face challenges due to lack of suitable materials with appropriate bandgaps
• Specialized techniques developed to overcome generation challenges
  • Photomixing combines two laser sources to generate terahertz radiation
  • Quantum cascade lasers engineered to emit in terahertz range
  • Free-electron lasers use relativistic electron beams for terahertz generation

Detection Complexities

• Thermal background noise significant at room temperature for terahertz frequencies
• Complicates detection processes and requires sensitive equipment
• Detection methods convert terahertz signals to measurable quantities
  • Heterodyne mixing down-converts terahertz signals to lower frequencies
  • Bolometers measure temperature changes induced by terahertz radiation
  • Electro-optic sampling uses nonlinear optical effects for detection

Atmospheric Limitations

• Atmospheric absorption, particularly by water vapor, limits propagation distance
• Restricts long-range applications and outdoor use
• Necessitates controlled environments or short-range operations for many applications
• Drives development of high-power sources and sensitive detectors to overcome attenuation

Applications of Terahertz Waves

Security and Imaging

• Security screening detects concealed weapons and explosives through clothing and packaging
• Medical imaging provides safe, high-resolution images of biological tissues
  • Cancer detection (skin cancer, breast cancer)
  • Dental diagnostics (non-invasive cavity detection)
• Quality control inspects packaged goods and pharmaceutical products non-destructively
• Art conservation analyzes paintings and historical artifacts to reveal hidden layers or authenticate works

Communications and Industry

• Wireless communications offer ultra-high bandwidth potential for short-range, high-speed data transmission
• Spectroscopy enables material identification and chemical analysis using unique molecular fingerprints
• Semiconductor industry uses terahertz waves for non-contact testing of devices and circuits
  • Fault detection in integrated circuits
  • Characterization of semiconductor materials