Characteristics of the Beam-Steerable Difference-Frequency Generation of Terahertz Radiation
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Characteristics of the Beam-Steerable Difference-Frequency Generation of Terahertz Radiation Ken-ichiro Maki & Takayuki Shibuya & Chiko Otani & Koji Suizu & Kodo Kawase
Received: 25 February 2010 / Accepted: 29 November 2010 / Published online: 14 December 2010 # Springer Science+Business Media, LLC 2010
Abstract We have investigated the characteristics of a terahertz (THz) beam steering method based on a combination of difference-frequency generation (DFG) with the principle of the phased array antenna. In the DFG of THz radiation from a nonlinear optical crystal pumped by optical beams, the phase front of the THz radiation is indirectly tilted by adjusting the relative incidence angle between the pump beams to the crystal. A magnification of the steering angle with a factor of 193 is demonstrated as the most important effect provided by the method. The effect allows the use of a high-speed optical deflector for adjusting the incidence angle, accelerating the steering more than a hundred times compared with mechanical methods. The phase mismatching between the THz radiation and the pump beams as well as the refraction at the crystal surface limit the steering angle of the THz radiation to 56°, full width at half maximum. Keywords Beam steering . Difference-frequency generation . Phased array antenna . Phase matching
1 Introduction Developments of sources, detectors, and spectrometers in terahertz (THz) frequency region have been remarkable in the recent time [1]. The qualities of the THz radiation such as transmission through a large number of materials are particularly useful in imaging [2]. The THz imaging has a great potential in achieving non-destructive inspection used in industry, transportation and medicine. The measurement speed of the THz imaging needs to be, however, further improved for the practical use. Quick measurements enable us to inspect numerous and large objects such as products and constructions, expanding the range of applications. The typical THz imaging scheme involves mechanical movement. The K. Maki (*) : C. Otani Terahertz Sensing and Imaging Laboratory, Advanced Science Institute, RIKEN, 519-1399 AramakiAoba, Aoba-ku, Sendai, Miyagi 980-0845, Japan e-mail: [email protected] T. Shibuya : K. Suizu : K. Kawase Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan
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J Infrared Milli Terahz Waves (2011) 32:603–617
transmittance or reflectance at every spot in an object is collected to obtain its entire image, which is acquired by moving the object on which a fixed THz beam is focused . On the other hand, moving the beam focus on a fixed object can increase the scanning speed, and an electrical beam steering can accelerate the measurement. Besides imaging, the THz beam steering can also impact the field of wireless communications [3]. Raising the carrier frequency up to the THz region leads to expanding the bandwidth of communications, by increasing the data transfer rate. The THz wireless communication may allow us to transmit large amounts of data such as high definition
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