Submillimeter Wave Region Research Articles

AN OPEN RESONATOR FOR PHYSICAL STUDIES

The excitation efficency of the TEM01q oscillation of an two-mirror hemispherical open resonator (OR) is studied. The resonator is excited by the TE01 wave of a circular waveguide joined in the middle of the OR plane mirror. Given the waveguide optimum size, the TEM01q mode excitation efficiency reaches 78%. Analysis of the resonant system spectrum in the 4-mm wave region shows that this waveguide-OR system offers a single mode resonance curve across almost a 10-GHz tuning range. The TEM0110 mode field distribution with and without the circular waveguide in the middle of the OR plane mirror is available due to the small scatterer method. It is shown that the considered open system is suitable for measuring electromagnetic characteristics of high-loss substances and metamaterials in the short-wave end of the millimeter (mm) region as well as in the submillimeter (submm) wave region.

Microfabrication of millimeter wave vacuum electron devices by two-step deep-etch x-ray lithography

The circuits for millimeter wave vacuum electron devices with all circuit elements including an electron beam tunnel are microfabricated by two-step deep-etch x-ray lithography (x-ray LIGA). The discrepancies of eigenfrequency between experiment and simulation are within 1.1% in a coupled-cavity structure and 1.4% in a folded waveguide structure when the operating frequency is about 100GHz. Furthermore, a measured tolerance of below 2μm, and a measured surface roughness of 20–70nm, of LIGA-fabricated circuits implies the two-step LIGA microfabrication has potential applications up to the submillimeter wave region.

Millimetre-wave spectroscopy and ab initio calculations for fluorophosphaethyne (FCP)

The semistable FCP molecule has been produced in the gas phase by a high temperature reaction between phosphine and trichlorofluoromethane. Its rotational spectrum has been observed in the millimetre- and submillimetre-wave regions, from 80 to 650 GHz, for the ground and various vibrationally excited states of F12CP, and for the ground state of F13CP. All the excited states that lie below 1200 cm−1, which are 1000, 0110, 0200, 0220, 0310, 0330, and 1110, have been investigated for the most abundant isotopologue. The analysis of the spectra has been performed taking simultaneously into account the strong Fermi resonance that couples the states v 1, v 2, v 3 with v 1 − 1, v 2 + 2, v 3, and l-type resonances between different sublevels of a given bending state, in order to obtain directly deperturbed rotational parameters. CCSD(T) calculations with a series of correlation consistent basis sets have been also performed, which provided a reliable estimate of the quartic force field of fluorophosphaethyne. Effects due to truncation of the basis and to core correlation have been accounted for. The theoretical force field has been partly refined by a least-squares fit to the available vibrational and rotational experimental data. A mixed experimental–theoretical equilibrium structure has been finally calculated combining experimental ground-state rotational constants of F12CP and F13CP with computed zero-point contributions. The best estimate of the equilibrium structure of fluorophosphaethyne can be established as re (F−C) = 1.2759 ± 0.0004 Å and re (C−P) = 1.5445 ± 0.0002 Å.

Microwave spectrum of P 14N and P 15N: Spectroscopic constants and molecular structure

In the present work the J+1← J, with J=1–3, 6, 7, 10–16, rotational transitions of P 14N and the J+1← J, with J=1, 2, 7, 8, 10–14, rotational transitions of P 15N have been observed in the millimeter- and submillimeter-wave region. These measurements allowed us to improve the ground state rotational parameters of P 14N as well as provide those of P 15N for the first time. The present measurements have been combined with rotational and vibrorotational transitions available in the literature to yield the Dunham coefficients. The equilibrium structure has also been determined to a high accuracy. The experimental investigation has been supported by highly accurate ab initio computations.

The Lamb-dip spectrum of the J + 1 ← J ( J = 0, 1, 3–8) transitions of H 13CN: The nuclear hyperfine structure due to H, 13C, and 14N

The pure rotational J + 1 ← J transitions, with J = 0, 1, 3–8, of H 13CN have been observed in the millimeter- and submillimeter-wave region using the Lamb-dip technique to resolve the hyperfine structure due to H, 13C, and 14N. The present observations allow us to provide for the first time the spin–rotation constant of 13C and the spin–spin interaction constant S 12 (between H and 13C) as well as to remarkably improve the quadrupole coupling and spin–rotation constants of 14N. In addition, a good empirical estimation of C I (H), based on ab initio calculations, has also been provided. Furthermore, our frequencies together with previous data permit to determine the most accurate ground state rotational parameters known up to now.

テラヘルツ・遠赤外分光 ＶＩ．サブミリ波・テラヘルツ帯における天文観測

The submillimeter-wave and terahertz region, whose wavelength is from 1mm to 0.1mm, is a frontier not only in spectroscopy but also in astronomy, but it will rapidly develop in the near future. In this article, the astronomical application in this wavelength region is reviewd both from technical and scientific points of view. As for the detection technique, we particularly focus on the heterodyne detection.

Transmission and reflection characteristics of slightly irregular wire-grids with finite conductivity for arbitrary angles of incidence and grid rotation

In the first half of this paper, an efficient method to calculate transmission and reflection characteristics of wire-grids consisting of periodic arrays of cylindrical conductors for arbitrary directions of incidence is presented by extending exact theory of wire-grids proposed by Yasumoto et al. In the latter half of this paper, an approximate calculation method for wire-grids with slight random irregularity in their spacings between wires is proposed by treating the irregularity as a small perturbation to the theory for regular grids. A comparison with preliminary measurements for actual wire-grids in millimeter- and submillimeter-wave regions demonstrated that this method is effectively applicable to wire-grids whose irregularity is not too much.

The millimeter- and submillimeter-wave spectrum of the trans–gauche conformer of diethyl ether

The results of a first investigation of the rotational spectrum of the trans–gauche conformer of diethyl ether are reported. Two spectrometers have been used to measure the spectrum in the millimeter-wave and submillimeter-wave regions and a total of 1090 absorption line frequencies in the range 108–366 GHz were obtained and analyzed. Of these lines, 902 were measured with a spectrometer employing the fast scan submillimeter spectroscopic technique (FASSST) at Ohio State and the remaining 188 were measured with the phase-lock two-loop system (PLL) in Warsaw. The spectrum was fit to within experimental accuracy with the use of the A-reduced Watson Hamiltonian. Based on relative intensity measurements, the percentage of diethyl ether at room temperature in the trans–gauche conformer was found to be 30.5(13)%, in good agreement with prior spectroscopic values and an ab initio determination based on an energy difference of 5.40 kJ mol −1 (452 cm −1) between the excited trans–gauche and ground trans–trans conformers. This work also stimulated a critical evaluation of the data acquisition and calibration procedure of the FAAAST spectrometer, the results of which will be discussed.

Frequency dependence of penetration depth for epitaxial NbN thin films at 0.1–1.1 THz

To enable the design of fully epitaxial NbN–SIS mixers, we estimated the penetration depth of epitaxial NbN thin films in the submillimeter wave region. Tunnel junctions with sizes of 40 × 3, 20 × 3, and 10 × 3 μm 2 were fabricated to observe Fiske steps. X-ray analysis showed that all the NbN and MgO layers that formed the tunnel junction were epitaxially grown. Based on the harmonic Fiske steps, the penetration depth of the epitaxial NbN films was estimated in the frequency range from 0.1 to 1.1 THz. Using the Mattis–Bardeen theory, we found that the measured penetration depths in the submillimeter wave region were larger than the calculated results. This result indicates that it is important to design fully epitaxial NbN–SIS mixers based on the measurement results of penetration depth.

Laboratory and radio-astronomical spectroscopy of the hyperfine structure of N2D$\mathsf{^+}$

We present the first laboratory measurements of the hyperfine structure of the J = 1 ← 0 rotational transition of N 2 D + , a good tracer of the dense regions of molecular cloud cores, and the spectra of unresolved high J transitions recorded in the 308-463 GHz region. Together with a high sensitivity radio-astronomical spectrum of the N 2 D + J = 1 → 0 rotational transition in a quiescent cloud core, we determined with high precision the frequencies of the seven hyperfine components and the molecular spectroscopic constants, allowing us to make predictions on the N 2 D + frequencies of higher J transitions occurring in the submillimeter-wave region.

Difference spectra measurement of squid rhodopsin in the submillimeter wave region.

Theoretical studies by computer simulation have shown that vibrational modes, which depend on the subdomain motions of proteins, are located in the submillimeter wave region (i.e., 10-100 cm(-1)], 0.3-3 THz). We have successfully observed, by measuring the difference spectrum between squid rhodopsin and metarhodopsin to avoid water absorption, that squid rhodopsin shows its absorption features in this region. Our experimental results show that a native protein in solution indicates not only an absorbent property in this region but also an actual change of absorption with changes in protein conformation.

Electromagnetic bandgap antennas and components for microwave and (sub)millimeter wave applications

This paper reviews the primary application areas of electromagnetic bandgap (EBG) technology at microwave and (sub)millimeter wave frequencies. Examples of EBG configurations in the microwave region include array antennas, high precision GPS, mobile telephony, wearable antennas and diplexing antennas. In the submillimeter wave region a 500 GHz dipole configuration and a novel heterodyne mixer is shown for the first time. Some emphasis is also placed on EBG waveguides and filters. As most fundamental components will be available in EBG technology, a fully integrated receiver could be developed in order to take full advantage of this technology. True integration of passive and active components can now begin to materialise using EBG technology.

Submillimeter-wave spectrum of carbonyl sulfide: rare isotopic species

Rotational spectra of four rare isotopic species of OCS were observed in the 110–690GHz region with a source-modulated submillimeter-wave spectrometer. Spectral lines of 18O13CS, O13C36S, 18OC36S, and 18O13C34S were measured in their natural abundances, 21.4, 1.51, 0.29, and 0.95ppm, respectively. The rotational constants and centrifugal distortion constants were precisely determined from observed line frequencies by least squares methods. In order to facilitate sensitivity examination in the submillimeter-wave region, transition frequencies and peak absorption coefficients were calculated and tabulated for the spectral lines of the four species up to the 1000GHz region.

Pyrolysis of ortho-cyanotoluene and PCl 3 mixtures: the millimeter and submillimeter-wave spectrum of NCCCCP

The unstable NCCCCP molecule has been detected in the pyrolysis products of phosphorus trichloride and ortho-cyanotoluene mixtures. Its rotational spectrum has been investigated in the millimeter and submillimeter-wave regions for the ground and various vibrationally excited states which approximately lie below 400 cm −1, namely ( v 8, v 9)=(0,1),(0,2),(0,3),(0,4),(1,0), and (1,1). Transitions up to J=241←240 were measured for the ground state, making a precise evaluation of the sextic centrifugal distortion constant possible. The l-type resonances between the different sublevels of the bending states have been taken into account in the analysis of the spectra, which yielded accurate determinations of the x L(99) and x L(89) anharmonicity constants.

Accurate quartic and sextic centrifugal distortion constants of [formula omitted

1-Phosphapropyne has been produced in the gas phase by pyrolysis of a mixture of ethane and phosphorus trichloride. The ground state rotational spectra of the most abundant isotopomer and of the isotopic variants 13 CH 3 CP and CH 3 13 CP have been investigated in the millimeter and submillimeter wave regions obtaining very accurate values of the quartic centrifugal distortion constants D J and D JK and of the sextic distortion constants H JK and H KJ .

Rotational spectrum of [formula omitted] and [formula omitted]: completely resolved nuclear hyperfine structures due to [formula omitted] and [formula omitted

The pure rotational spectrum of 13 C 17 O has been observed in the millimeter- and submillimeter-wave region using the Lamb-dip technique in order to increase the instrumental resolving power and so to resolve both the hyperfine structure due to 17 O and that due to 13 C . In this way very accurate values of the rotational and centrifugal distortion constants, the 17 O nuclear electric quadrupole coupling constant and the 17 O and 13 C spin–rotation constants have been obtained. In addition, the J=1←0 and J=2←1 transitions of 13 C 18 O have been recorded using the Lamb-dip technique. The resolved hyperfine structure of these transitions allowed us to determine the rotational and 13 C spin–rotation constants. The experimental determination of all these parameters has been supported by ab initio computations.

Operating properties of thin‐film slot antennas at 2.5‐THz submillimeter wave band

AbstractWith a view to the design and fabrication of slot array antennas operating in the submillimeter wave region above 2.5 THz, the operating characteristics of a thin‐film slot antenna on a dielectric substrate are studied with emphasis on the radiation pattern. It is found that unlike the thin‐film slot antenna in the frequency region below 700 GHz, the thin‐film slot antenna itself is likely to be operated at the free‐space wavelength, but the antenna is not that in free space and is influenced by the dielectric constant and absorption coefficient of the substrate and the substrate thickness. It is also found that the coplanar waveguide is operating at a mean wavelength derived from the average dielectric constant of free space and the dielectric substrate, like that in the frequency region below 700 GHz. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(11): 8–15, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10053

A low-cost fabrication technique for symmetrical and asymmetrical layer-by-layer photonic crystals at submillimeter-wave frequencies

This paper presents a rapid, versatile, and practical technique for the manufacture of layer-by-layer photonic crystals in the millimeter- and submillimeter-wave regions. Mechanical machining is used to derive a rugged layer-by-layer structure from high-resistivity silicon wafers. Unlike traditional anisotropic etching techniques, this method does not rely on any particular crystal orientation of the substrate and allows greater flexibility in the photonic crystal design. Automatic alignment of alternating layers is achieved via careful placement of the separation cuts. Using this ability, two configurations of photonic crystals are realized and their RF characteristics are measured and presented. Firstly, a symmetrical photonic crystal is studied as an initial demonstration of the technique. This is followed by an asymmetrical example, where a different frequency response is observed for the two orthogonal polarizations of the incident radiation. Two measurement techniques are used to characterize the photonic crystals and the merits of each are discussed. Theoretical predictions are seen to agree well with the measured behavior.

Relation between generated power and critical current density of flux-flow oscillators in submillimeter wave region

Height of current steps I S in current–voltage characteristics and radiation power P are studied experimentally of flux-flow Josephson oscillators (FFOs) with 1< J CF<12 kA/cm 2, where J CF is the critical current density of FFOs. It has been found I S, which is proportional to the generated power in the FFO, is almost proportional to J CF. In addition, P coupled to a superconductor–insulator–superconductor detector vertically stacked on the FFO increases with J CF, i.e. from P=6 nW for J CF=1 kA/cm 2 up to P=360 nW for J CF=12 kA/cm 2. These experimental results suggest the advantage of high- J CF FFOs.

A millimeter-wave six-port reflectometer based on the sampled-transmission line architecture

This letter presents a proof-of-concept implementation of a millimeter-wave reflectometer for measuring complex reflection coefficients. The reflectometer is based on the six-port architecture and consists of a single section of WR-10 rectangular waveguide and a set of three Schottky power detectors. Design considerations as well as measurements in the 75 to 110 GHz range are described and discussed. Because of its simple architecture, the reflectometer is amenable to scaling for measurements well into the submillimeter-wave region of the spectrum.