Nonlinear optical materials convert terahertz radiation into infrared light

May 09, 2014
Figure 1: A crystal of lithium niobate with an alternating stacking structure that gives the material nonlinear optical properties. Credit: Kouji Nawata, RIKEN Center for Advanced Photonics

Terahertz radiation, part of the frequency spectrum of light between microwaves and infrared, can pass through many materials and is potentially useful for applications such as airport security scanning. Commercial use of the technology, however, has been held back by the difficulty in detecting terahertz signals. Kouji Nawata and colleagues from the Tera-Photonics Research Team at the RIKEN Center for Advanced Photonics have now developed a system that can upconvert terahertz radiation to higher-frequency infrared light for more efficient detection.

"Conventional terahertz detectors are thermal sensors that convert terahertz energy into heat," explains Nawata. "This can cause the sensitivity of these detectors to become worse in hot environments."

Optical detection after frequency conversion represents an attractive solution. Nawata's team achieved this goal by taking advantage of the unusual properties of nonlinear optical materials, which have an optical response that is dependent on . These materials are useful because they provide a way of making two beams of interact indirectly, where a high-intensity beam of light sets the optical properties of the crystal and thus influences the propagation of a second, lower-intensity pulse. An example of such a nonlinear optical process is difference frequency generation (DFG), which creates a third beam of light with a frequency that is roughly equal to the difference of the two incident beams.

Using their nonlinear optical material in a DFG configuration, the researchers were able to take a 1.6-terahertz pulse and combine it with a high-intensity laser beam to generate a near-infrared signal. They demonstrated that the intensity of the DFG was proportional to the incoming , proving the scheme to be a useful way of measuring the strength of the incoming terahertz pulse. The approach was also sensitive, detecting pulses of terahertz light with a miniscule 25 femtojoules of energy.

The real advantage of this technique, however, is its flexibility. Nawata and his colleagues engineered their nonlinear material (Fig. 1) by stacking layers of lithium niobate such that the atomic crystal orientation was alternated between layers. They were able to optimize detection for a specific frequency of terahertz light by changing the periodicity of this stacking or by altering the angle between the light propagation and the stacking directions.

"One potential application that we would like to develop is terahertz wireless communication," says Nawata. "This technology could enable speeds a thousand times faster than present gigahertz-class communication, and the concept could easily be combined with fiber optics technologies."

Explore further: Technologies for the optical characterization of materials at terahertz frequencies

More information: Nawata, K., Notake, T., Ishizuki, H., Qi, F., Takida, Y., Fan, S., Hayashi, S., Taira, T. & Minamide, H. "Effective terahertz-to-near-infrared photon conversion in slant-stripe-type periodically poled LiNbO3." Applied Physics Letters 104, 091125 (2014). DOI: 10.1063/1.4868096

add to favorites email to friend print save as pdf

Related Stories

Organic crystals put laser focus on magnetism

Jul 27, 2012

( -- In the first successful experiment of its type at SLAC's Linac Coherent Light Source, scientists used terahertz frequencies of light to change the magnetic state of a sample and then measured ...

Ultra-thin light detectors

Mar 27, 2014

A new, extremely thin kind of light detectors was created at Vienna University of Technology. Two very different technologies were combined for the first time: metamaterials and quantum cascade structures.

Laser-induced damage in focus

Jan 17, 2014

The transformation of infrared light to a different wavelength, such as visible light, is important in many applications. Some of the most efficient semiconductor lasers operate in the infrared region of ...

High power laser sources at exotic wavelengths

Apr 14, 2014

High power laser sources at exotic wavelengths may be a step closer as researchers in China report a fibre optic parametric oscillator with record breaking efficiency. The research team believe this could ...

Recommended for you

New filter could advance terahertz data transmission

13 hours ago

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

14 hours ago

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

A new X-ray microscope for nanoscale imaging

16 hours ago

Delivering the capability to image nanostructures and chemical reactions down to nanometer resolution requires a new class of x-ray microscope that can perform precision microscopy experiments using ultra-bright ...

Top-precision optical atomic clock starts ticking

Feb 26, 2015

A state-of-the-art optical atomic clock, collaboratively developed by scientists from the University of Warsaw, Jagiellonian University, and Nicolaus Copernicus University, is now "ticking away" at the National ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.