Counting Terahertz Photons

Scientists at the University of Tokyo and the Japan Science and Technology Corporation have been able to detect single photons in the terahertz region of the electromagnetic spectrum for the first time. Previously, such photons, with energies around 4 millielectronvolts, could not be seen singly.

Terahertz radiation, essentially in the far-infrared, is a potentially important telecommunications carrier. Not only detection but microscopy at ultra-low terahertz light levels can be performed.

By scanning a quantum-dot probe (highly sensitive to terahertz light) across the face of a sample, the sample can be imaged with a spatial resolution of 50 microns; the radiation itself has a wavelength of 132 microns. This is even more remarkable when you consider that the power emitted from the surface being imaged is at the level of 10^-19 watts (0.1 attowatt).

Currently photon-counting microscopy glimpses a few electrons at a time oscillating at terahertz frequencies in semiconductor devices at high magnetic fields.

According to Kenji Ikushima (ikushima@thz.c.u-tokyo.ac.jp), the extraordinarily high-sensitivity of the photon counting approach will soon facilitate the study of a molecule shaking, rattling and rolling at terahertz rates. Photon-counting microscopy in this spectral range will facilitate the study of a few molecules at a time oscillating at terahertz frequencies in semiconductor devices at high magnetic fields.

Ikushima et al., Applied Physics Letters, 10 April 2006
The Komiyama Lab at the University of Tokyo