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We propose an alignment strategy for millimeter spectroscopy of cornea that uses imaging to screen for sufficient alignment conditions. The performance of different corneal imaging objectives, in the presence of misalignment, is evaluated. The cornea is illuminated with a TEM00 Gaussian beam at 650 GHz and the beam is swept across the cornea. Images are generated by calculating the coupling between illumination and scattered beams for each illumination beam position and angle. The cornea is displaced at intervals of 500 microns in the transverse and axial directions and with new coupling coefficient maps generated at each misaligned position. Contrast in the misaligned cases are compared to the aligned case via zero normalized spatial cross correlation. The results show a maximum normalized cross correlation of 0.92 for a two-mirror scanning system and 0.74 for a one-mirror scanning objective. The analysis suggests that imaging contrast at 650 GHz can be used to screen for misalignment that would be difficultto detect with MMW.

in this paper, a novel Frequency Selective Surface (FSS) with polarization staggered bands is proposed. The beams in orthogonal polarization of different frequency bands are divided into a group and transmitted the FSS. The rest are divided into another group and are reflected by the FSS. The FSS with polarization staggered bands is good at separation the bands with narrow transition zone, which realizes transmission and reflection of the incident waves in four different physical mechanisms. What is more, a new frequency separation scheme in quasi-optical feed system is discussed. The FSS with polarization staggered bands, which separate two bands near 90GHz and 108GHz, is fabricated and tested. The reflection coefficient of TM polarization is about 1dB, and the transmission and reflection coefficients in the other band or polarization are less than 0.6dB.

The most critical condition for performing Dynamic Nuclear Polarization (DNP) is achieving sufficiently high electronic B(1e) fields over the sample at the matched EPR frequencies, which for modern high-resolution NMR instruments fall into the millimeter wave (mmW) range. Typically, mmWs are generated by powerful gyrotrons and/or extended interaction klystrons (EIKs) sources and then focused onto the sample by dielectric lenses. However, further development of DNP methods including new DNP pulse sequences may require B(1e) fields higher than one could achieve with the current mmW technology. In order to address the challenge of significantly enhancing the mmW field at the sample, we have constructed and tested one-dimensional photonic band-gap (PBG) mmW resonator that was incorporated inside a double-tuned radiofrequency (rf) NMR saddle coil. The photonic crystal is formed by stacking ceramic discs with alternating high and low dielectric constants. The thicknesses of the discs are chosen to be λ/4 or 3λ/4, where λ is the wavelength of the incident mmW field in the corresponding dielectric material. When the mmW frequency is within the band gap of the photonic crystal, a defect created in the middle of the crystal confines the mmW energy, thus forming a resonant structure. An aluminum mirror in the middle of the defect has been used to split the structure in order to reduce its size and simplify the resonator tuning. The latter is achieved by adjusting the width of the defect by moving the aluminum mirror with respect to the dielectric stack using a gear mechanism. The 1D PBG resonator was the key element for constructing a multi-resonant integrated DNP/NMR probehead operating at 198 GHz EPR / 300 MHz (1)H / 75.5 MHz (13)C NMR frequencies. Initial tests of the multi-resonant DNP/NMR probehead were carried out using a quasioptical 200 GHz bridge and a Bruker Biospin Avance II spectrometer equipped with a standard Bruker 7 T wide-bore 89 mm magnet parked at 300.13 MHz (1)H NMR frequency. The mmW bridge built with all solid-state active components allows for the frequency tuning between ca. 190 to ca. 198 GHz with the output power up to 27 dBm (0.5 W) at 192 GHz and up to 23 dBm (0.2 W) at 197.5 GHz. Room temperature DNP experiments with a synthetic single crystal high-pressure high-temperature (HPHT) diamond (0.3×0.3×3.0 mm(3)) demonstrated dramatic 1,500–fold enhancement of (13)C natural abundance NMR signal at full incident mmW power. Significant (13)C DNP enhancement (of about 90) have been obtained at incident mmW powers of as low as

This paper presents a novel THz optical design that allows the acquisition of THz reflectivity maps of in vivo cornea without the need for a field flattening window and preliminary imaging results of in vivo rabbit cornea. The system’s intended use is to sense small changes in corneal tissue water content (CTWC) that can be precursors for a host of diseases and pathologies. Unique beam optics allows the scanning of a curved surface at normal incidence while keeping the source detector and target stationary. Basic system design principles are discussed and image sets of spherical calibration targets and corneal phantom models are presented. The presented design will enable, for the first time, non-contact THz imaging of animal and human cornea.

The Airborne Millimeter- and Submillimeter Observing System (AMSOS) is a total-power radiometer for observations of the 183.3-GHz water vapor rotational line, operated onboard a Learjet aircraft of the Swiss Air Force. The radiometer is also used to observe the 175.45-GHz ozone line in the other sideband. The neatly designed quasi optics provide a regular and narrow output beam with a half-power beam-width angle of 1.2/spl deg/ and efficient sideband switching. A /spl lambda//4-quasi-optical isolator is used for baseline reduction securing attenuation of internal reflections by more than 30 dB. A low noise temperature of the ambient-temperature-operating system (1900 K) and excellent target pointing (better than 0.1/spl deg/) provide a good duty cycle and reliable calibration. A reliable control over the radiometer's operational parameters, like system stability and system temperatures, and higher automatization were required to come up with high demands of an onboard operation. The measured spectra look typical for the region and time where they were observed.

In this paper, we show that the phenomenon of extraordinary transmission through arrays of subwavelength holes, present in the optical regime, is also present in the millimeter wave range. After presentation of the theoretical foundations of the enhanced transmission, measurements of the transmission response have been performed on different samples by using a millimeter wave quasioptical vector network analyzer in the range between 45 and 110 GHz. The prototypes have been fabricated in Aluminum plates with several thickness and different hole diameters drilled by using a laser machine. Good agreement between theory and experiment is obtained, with clear signals of the existence of resonant transmission at wavelengths close to the period of the array. Possible applications in frequency selective surfaces and near-field imaging are envisaged.

Aluminum nitride (AlN) film coatings on flexible substrates (polymeric Teflon, Mylar) have been obtained using a hybrid helicon-arc ion-plasma deposition technique with high adhesion of coatings. Studies of optical, morphological, and structural properties of AlN films have been carried out. It was found that AlN coatings on Teflon and Mylar thin-film substrates substantially suppress transmission of infrared (IR) radiation within the spectral range λ ∼ 5–20 μm at certain technological parameters and thickness of AlN. Transmission in THz regions by using quasioptics attains T ≈ 79%–95%, and losses measured in the channels within the microwave region 2 to 36 GHz are

The paper considers an optimum sectional waveguide taper (OSWT) which at a shortest length of the transition region provides nearly adiabatic propagation of the fundamental mode between circular, widely different in diameter quasioptical transmission lines of class “hollow dielectric waveguide” (HDW). Derived as a consequence of coaxial circular-horn sections, the OSWT offers all the advantages of a simple geometry and lends itself to simple fabrication techniques. The relationships among the critical geometrical parameters and the loss calculation formulae are presented. The comparison studies show that even at a few sections, the OSWT is almost as good in performance as the parabolic taper, but the OSWT is much better from a mechanical viewpoint. And compared to the ordinary linear taper, the OSWT allows essential cut in length and loss with the broadbandness kept. The HDW-based four-sectional OSWT has been fabricated and tested in a quite broad wave range 2,5-8 mm. The testing results lend a good support to the analytical formulae lying at the basis of the design software.

Enhanced millimeter wave transmission through a subwavelength slot placed into a corrugated conducting wafer, using perfect conductor model, is experimentally observed compared with the case of the single isolated slot. The corrugated wafer responds in a similar way as in the optical regime, in which a surface plasmon model is employed to describe the metal. Experimental results of the enhanced transmission and reflection of the corrugated wafer have been measured by using a quasioptical vector network analyzer. Future applications of enhanced subwavelength transmission in quasioptical devices are envisaged.

For the transverse magnetic mode, the second‐order Bragg interaction of the guided and the radiated waves is considered for a thin film dielectric waveguide with a corrugated film–cover interface. A set of four canonical equations for the deexcitation and the excitation of the guided waves are derived by employing a quasioptical technique. The governing equations are applied for the treatment of a surface‐emitting distributed feedback laser. Some design criteria are obtained for optimizing the performance of the laser. When these design criteria are used, the laser characteristics are insensitive to small changes in the physical parameters about their designed values. Numerical results are presented to illustrate the performance of the laser. The shape of the surface relief grating is found to play a vital role in determining the gain threshold and the gain margin of the laser.

Two-dimensional (2D) quasioptical elements are demonstrated as guiding structures in the THz frequency regime. A planar polyethylene lens is incorporated in a parallel metal plate structure and is shown to focus guided THz radiation to a spot comparable to that expected for a three-dimensional (3D) optical element in free space. A 2D double-slit aperture is also demonstrated to diffract the incoming THz beam as expected for 3D. The spatial resolution of the measurement techniques employed is illustrated by the sharpness of the measured diffraction pattern.

This chapter contains sections titled: A Hybrid Dielectric Slab-Beam Waveguide for the Sub-Millimeter Wave Region A Dielectric Slab Waveguide with Four Planar Power Amplifiers A 10-Element Active Lens Amplifier on a Dielectric Slab

Optical control of the propagation direction of a terahertz pulse inside an optically transparent parallel plate waveguide is demonstrated by patterned charge carrier photoexcitation of a silicon slab embedded within the waveguide. It is shown experimentally and through finite element simulations that photoexcitations with sufficient conductivity can induce a partial reflection, capable of steering the pulse inside the two-dimensional waveguide. A beamsplitter is demonstrated as proof of principle and is used to delay the arrival of the reflected terahertz pulse at the detector by several picoseconds by moving the excitation in the plane.

Compared to Millimeter waves THz frequencies can provide an almost magnitude higher resolution, which enables detection of small threats at larger distances. Here we present an active THz standoff imaging system based on commercially available BWO sources and a thermal detector. At a excitation frequency of 720GHz an almost diffraction limited resolution was achieved of about 1.6mm at 1.2m distance to the target. With signal to noise ratio of 35dB detection of metal and ceramic weapons covered by different clothing is demonstrated. A detailed system analysis is done, which led to limiting factors of the proposed system.

Investigation of behaviour of a nonlinear Fabry-Perot interferometer with a paramagnetic filling in the conditions of inhomogeneous broadening of the electron paramagnetic resonance line is of interest for different implementations in the spectroscopy, quasioptics and dynamic nuclear polarisation.

We have developed a wide-bandwidth, high-sensitivity, continual terahertz-wave sensor that utilizes a quasioptical parabolic mirror and a Schottky barrier diode and successfully applied it at up to 7THz range. This sensor utilizes a parabolic cylindrical mirror, a long-wire antenna, and a Schottky barrier diode. The antenna, placed at the focal point of the parabolic mirror, quasioptically collects the terahertz signal. This configuration eliminates the need for frequency-dependent reception readjustments of the antenna and the mirror positions, greatly improving operability.