Mixing of 28-THz CO2-laser radiation by nanometer thin film Ni-NiO-Ni diodes with difference frequencies up to 176 GHz

We report on the first successful mixing of 28 THz radiation performed with thin-film nanometer-scale Ni-NiO-Ni diodes connected to integrated bow-tie infrared antennas. Difference frequencies up to 176 GHz were measured between two CO2- laser 28 THz emissions in mixing processes up to the fifth order by addition of microwaves generated by a Gunn oscillator. The bow-tie antennas show almost perfect polarization with respect to the incident radiation. The mixing of infrared radiation with point-contact metal-oxide- metal (MOM, MIM) diodes was first reported in 1968. In the meanwhile the range of operation of these devices has been extended to the visible. The operation of these diodes in the point-contact configuration is restricted to laboratory applications because of their irreproducibility and low mechanical stability. They are currently used in absolute frequency measurements for the development of time and frequency standards and in high-resolution spectroscopy as tunable far-infrared (FIR) radiation source. Serious attempts were made to integrate the MOM diodes on a substrate in order to produce more practical devices for field applications. In the early seventies, Small et al. and Wang et al. reported the fabrication of thin-film diodes with rectification capabilities in the 10 micrometer region. Small et al. also reported on third-order frequency mixing performed with a FIR carrier frequency of approximately 1 THz with difference frequencies of about 75 GHz. Our own development of thin-film Ni-NiO-Ni diodes with integrated dipole, bow-tie and spiral antennas as detectors has been described previously. The first experiments on mixing 28 THz radiation with our Ni-NiO-Ni diodes were made at LENS (Florence, Italy). They resulted in the measurement of difference frequencies up to 85 MHz. We now report on the first successful mixing of two 28 THz (10.7 micrometer) CO2-laser transitions in the 10P branch with difference frequencies up to 176.2 GHz performed by thin-film Ni-NiO-Ni diodes.