Compact 1.64 THz source based on a dual-wavelength diode end-pumped Nd:YLF laser with a nearly semiconfocal cavity
We describe a compact dual-wavelength (1.047 and 1.053 μm) diode end-pumped Q-switched Nd:YLE laser source which has a number of applications in demand. In order to achieve its dual-wavelength operation it is suggested for the first time to use essentially nonmonotonous dependences of the threshold pump powers at these wavelengths on the cavity length in the region of the cavity semiconfocal configuration under a radius of the pump beam smaller than the radius of the zero Gaussian mode. Here we demonstrate one of the most interesting applications for this laser: difference frequency generation in a GaSe crystal at a frequency of 1.64 THz. A superconducting hot-electron bolometer is used to detect the THz power generated and to measure its pulse characteristics.
These proceedings have been written in an attempt to communicate the major purpose of the NATO Advanced ResearchWorkshop (ARW), 2013, that is, to bring to light the possibilities of performance, based on the actual level, of the everpromising THz (terahertz) technology, a kind of Araba Fenice, not yet known tomost technical operators, especially its appeal in security applications. To achieve this, the ARWhas invited highly experienced scientists with expertise in THz science and technology and its application areas. We begin with the consideration that the risk of mass murder due to terroristic attacks is on the rise, thus posing a threat for security in the civil and military world. To counter this problem, we look at one of the most appealing, newly emerging, technologies that is based on the THz detection of explosives and other forms of threats. However, operational difficulties (both for THz sensors and sources), especially regarding size, complexity of use, overall cost, and the need of very low temperatures for sensors, strongly limit the application of this technology. To find solutions to these and related issues, we invited expert scientists to present review papers on the most advanced sensors and sources based on THz technology, especially for security system applications. The ARW has been conferred the major task of describing the most advanced technologies, in terms of identifying their operational strengths and weaknesses, forecasting the best technological solutions to overcome the actual operational limits, and suggesting to the NATO SPS (Science for Peace and Security) Division the most reliable ways to proceed for future developments. To achieve a broad evaluation of the above aspects, a questionnaire on various key points with regard to the actual performance and possible future developments in the field of THz science, technology, and applications has been discussed.
We report on the development of a highly sensitive optical receiver for heterodyne IR spectroscopy at the communication wavelength of 1.5 μm (200 THz) by use of a superconducting hot-electron bolometer. The results are important for the resolution of narrow spectral molecular lines in the near-IR range for the study of astronomical objects, as well as for quantum optical tomography and fiber-optic sensing. Receiver configuration as well as fiber-to-detector light coupling designs are discussed. Light absorption of the superconducting detectors was enhanced by nano-optical antennas, which were coupled to optical fibers. An intermediate frequency (IF) bandwidth of about 3 GHz was found in agreement with measurements at 300 GHz, and a noise figure of about 25 dB was obtained that was only 10 dB above the quantum limit.
A thorough spectral study of the intrinsic single-photon detection efficiency in superconducting TaN and NbN nanowires with different widths has been performed. The experiment shows that the cut-off of the intrinsic detection efficiency at near-infrared wavelengths is most likely controlled by the local suppression of the barrier for vortex nucleation around the absorption site. Beyond the cut-off quasi-particle diffusion in combination with spontaneous, thermally activated vortex crossing explains the detection process. For both materials, the reciprocal cut-off wavelength scales linearly with the wire width where the scaling factor agrees with the hot-spot detection model.
The development of terahertz imaging instruments for security systems is on the cutting edge of terahertz technology. We are developing a THz imaging system based on a superconducting integrated receiver (SIR). An SIR is a new type of heterodyne receiver based on an SIS mixer integrated with a flux-flow oscillator (FFO) and a harmonic mixer which is used for phase-locking the FFO. Employing an SIR in an imaging system means building an entirely new instrument with many advantages compared to traditional systems. In this project we propose a prototype THz imaging system using an 1 pixel SIR and 2D scanner. At a local oscillator frequency of 500 GHz the best noise equivalent temperature difference (NETD) of the SIR is 10 mK at an integration time of 1 s and a detection bandwidth of 4 GHz. The scanner consists of two rotating flat mirrors placed in front of the antenna consisting of a spherical primary reflector and an aspherical secondary reflector. The diameter of the primary reflector is 0.3 m. The operating frequency of the imaging system is 600 GHz, the frame rate is 0.1 FPS, the scanning area is 0.5 × 0.5 m2, the image resolution is 50 × 50 pixels, the distance from an object to the scanner was 3 m. We have obtained THz images with a spatial resolution of 8 mm and a NETD of less than 2 K.
We demonstrate coherent dynamics of quantized magnetic fluxes in a superconducting loop with a weak link, a nanobridge patterned from the same thin NbN film as the loop. The bridge is a short, rounded shape constriction, close to 10 nm long and 20–30 nm wide, having minimal width at its center. It superposes neighboring fluxoid states of the loop. Quantum state control and coherent oscillations in the driven time evolution of the tunnel-junctionless system are achieved. Decoherence and energy relaxation in the system are studied using a combination of microwave spectroscopy and direct time-domain techniques. The effective flux noise behavior suggests inductance fluctuations as a possible cause of the decoherence.
The problem of designing stabilizing resonator (SR) for a 4-mm wavelengths range coaxial magnetron with low level of output power has been considered. The recommendations for choosen the coaxial resonator external to internal diameter relations depending on technical project requirements are developed.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.