Showing papers on "Terahertz radiation published in 1987"

Tunneling transfer devices

Abstract: Coupled quantum wells in which charge carriers shift from well to well by means of tunneling transfer The quantum wells are created by disposing a material with lower carrier energy between layers of material with higher carrier energy The spacing between wells is thin enough to allow tunneling transfer The coupling of the wells displaces energy levels so that a system of N coupled wells has a spectrum of N energy levels Under the proper conditions, transistions from one energy level to another result in the shift of charge carriers from one well to another Because the tunneling transfer process is very fast, electronic devices capable of operating at terahertz frequencies are possible Transistors, lasers, and detectors of electromagnetic radiation employing coupled quantum wells are disclosed

Simultaneous measurement of moisture content and basis weight of paper sheet with a submillimeter laser

Abstract: A system for detecting simultaneously the moisture content and basis weight of paper is disclosed utilizing a submillimeter laser source of radiation of two different wavelengths which is subsequently scanned across the face of the paper. A plurality of detectors placed on the side of the paper opposite the laser supplies the transmittance information for each of the wavelengths to a microcomputer which in turn calculates the moisture content and the basis weight of the material. The two different wavelengths of submillimeter radiation are produced by either a pair of submillimeter lasers pumped by a continuous wave CO2 laser or by a single submillimeter laser pumped by a waveguide type continuous wave CO2 laser whose output is controlled by a piezoelectric crystal tuned resonator in order to provide the required two separate wavelengths alternating in time which are output in the single beam of the submillimeter laser.

On the mechanism and frequency limit of double‐barrier quantum‐well structures

Abstract: Two parameters are adopted to characterize the transport process in double‐barrier quantum‐well (DBQW) structures. It is shown that, in general, both coherent resonant tunneling and incoherent sequential tunneling processes are possible. However, for most high‐frequency applications, large current densities (>104 A/cm2) are required and, therefore, the sequential process is unlikely to occur. To determine the high‐frequency capability, both the adiabatic limit of the dc current‐voltage curve as well as the capacitance charging time in an embedding circuit need to be considered. We confirm that the DBQW structures with barrier thickness of 20 A or smaller can operate up to about 1 THz.

Optically pumped submillimeter gas lasers and the prospects for constructing space-qualifiable LO systems

Abstract: An optically pumped, submillimeter laser operating in the 500 micron (600 GHz) to 100 micron (3 THz) spectral range is the primary and, at present, the only available local oscillator (LO) source for laboratory and astronomical heterodyne applications for this wavelength region. A short review of the state-of-the-art of submillimeter lasers as LO sources, with an emphasis given to receiver systems designed for airborne heterodyne observations, is presented. The characteristics and prospects for constructing a space-qualifiable laser LO system will also be given.

Stark spectroscopy using tunable far-infrared radiation

Abstract: We report on an experimental demonstration of molecular Stark spectroscopy based on the use of tunable far-infrared radiation at 0.91 THz. The radiation was generated by the nonlinear mixing of the radiation from two CO2 lasers in a point-contact metal–insulator–metal diode. The technique is used to make the first reported measurement of the permanent dipole moment of 13CH3OH; μa = 0.883(25) D.

Frequency Mixing of 50 GHz Microwave and 4.25 THz FIR Light by a Josephson Point Contact

Abstract: The harmonic mixing of 50 GHz microwave and 4.25 THz far-infrared (FIR) light, the highest order mixing ever reported in this frequency range, has been achieved using a Josephson point contact made of Nb. The conditions under which the mixing was performed are described. The conversion efficiency of the incident FIR light to the beat signal is evaluated and the performance limit of the Nb Josephson point contact is also discussed.

Spectroscopy with Ultrashort Electrical Pulses

Abstract: Recently optoelectronic techniques have been used to generate and detect subpicosecond electrical pulses on coplanar transmission lines.[1,2] The frequency bandwidth of these short electrical pulses ranges up to 1 THz and covers an important part of the far infrared energy spectrum from 0 to 30 cm-1, in which can be found the gap frequencies of superconductors, magnetic excitations, and the far infrared modes of lattices and molecules. With the proper generation geometry, these pulses propagate as a single mode excitation of the transmission line, and the pulse reshaping is determined by the frequency dependent dielectric response of the transmission line materials. These features, plus the fact that the earlier observations showed that the subpicosecond pulses broadened to only 2.6 psec after propagating 8 mm on the transmission line, allow for the following spectroscopic applications of these guided wave electrical pulses. In this paper we will discuss the study of far infrared absorption in superconductors and some magnetic modes in rare-earth garnets.