What is Terahertz (THz)?
Terahertz radiation is part of the electromagnetic spectrum lying between microwaves and the far-IR. This region has frequencies ranging from 0.1 – 10 THz and wavelengths from 3 mm to 0.03 mm. This spectral region is often referred to as the “Terahertz gap†as these frequencies fall between electronic (measurement of field with antennas) and optical (measurement of power with optical detectors) means of generation. Historically, little study of the interactions between these wavelengths and matter has been undertaken. The reason for this was the difficulty in generating and detecting terahertz.
Recent advances in combining optical and electronic methods have allowed for generation and detection of very high signal-to-noise ratio and high data acquisition rates of 0.1 – 3 THz frequencies. Consequently, a surge of interest in and study of the terahertz region is underway.
Applications of terahertz include:
Imaging through material
Similar to x-ray images, terahertz wavelengths penetrate through most materials and can easily reveal imperfections such as voids, cracks, and density variations. Terahertz offers some advantages over x-ray including that the radiation is non-ionizing and thus is completely safe. Example imaging applications include flaw detection in the sprayed-on-foam-insulation (SOFI) for the space shuttle program, detection of threat objects in checked airline baggage and stand-off detection of threat objects in packages or on people.
Spectroscopic measurements
Time-domain pulsed terahertz energy sources contain broadband frequency content. Thus, spectroscopic determinations (fingerprints) are possible allowing the identification of objects of interest (e.g., explosives, biological agents). Using spectroscopic analysis results to generate images is an especially powerful application of terahertz. Astronomy studies have used terahertz spectroscopy for a number of years.
Advances in terahertz spectroscopic analysis includes innovations in the following areas:
- Threat material detection (e.g., explosives, weapons)
- Environmental sensing (especially gas detection)
- Biomedical applications (e.g., skin cancer detection)
- Moisture content in consumer products
Material characterization
The energies of terahertz photons allow the probing and study of low energy transitions (molecular rotations, protein folding, phonons in solid state materials, electrical circuit characteristics).
- Density
- Basis weight
- Structural integrity
- Single and multilayer thickness
- Product uniformity
- Chemical analysis
