Resonance aperture

The FONAR method (field-focussed nuclear magnetic resonance) exploits shaped magnetic fields and rf pulses to produce a resonance aperture the size of a pixel [Daml]. 

Fig. 5.1.1 [Dam4] Resonance aperture for FONAR imaging, (a) Contour plot of the magnetic field 6j(z, r). (b) Definition of the coordinate system in the magnet, (c) 3D representation of the sensitive region.

Resonant Sound Absorbers. Two other types of sound-absorbing treatments, resonant panel absorbers and resonant cavity absorbers (Helmholtz resonators), are used in special appHcations, usually to absorb low frequency sounds in a narrow range of frequencies. Resonant panel absorbers consist of thin plywood or other membrane-like materials installed over a sealed airspace. These absorbers are tuned to specific frequencies, which are a function of the mass of the membrane and the depth of the airspace behind it. Resonant cavity absorbers consist of a volume of air with a restricted aperture to the sound field. They are tuned to specific frequencies, which are a function of the volume of the cavity and the size and geometry of the aperture. 

For large telescope apertures, Na LGS offer improve sampling of the atmospheric turbulence due to their much higher altitude. Single beam systems are now being developed for and deployed on 8-10 m class telescopes. Since resonant backscattering from the mesospheric Na layer is the method chosen for most LGS projects, we will concentrate mostly on this technique. 

The upgrade of a frequency-domain fluorescence lifetime imaging microscope (FLIM) to a prismless objective-based total internal reflection-FLIM (TIR-FLIM) system is described. By off-axis coupling of the intensity-modulated laser from a fiber and using a high numerical aperture oil objective, TIR-FLIM can be readily achieved. The usefulness of the technique is demonstrated by a fluorescence resonance energy transfer study of Annexin A4 relocation and two-dimensional crystal formation near the plasma membrane of cultured mammalian cells. Possible future applications and comparison to other techniques are discussed. 

However, a series of factors introduce losses in the system namely, the reflectivities of the mirrors (RiandR2) on the figure, which reflect only a fraction, Ri and R2, of the intensity. Additional losses can be produced by absorption in the windows of the cell that contains the active medium (if this is the case), diffraction by apertures, and scattering due to particles or imperfect surfaces. All of those losses can be included in a loss factor per trip, expressed as e. Thus, considering both amplification and intensity decrease per round trip, the intensity after a single round trip through a resonator of length d is... 

A standing wave (SW) microwave linear accelerator consists of a linear array of resonant cavities that are energized by a common source of microwave power. These cavities are nearly isolated by webs with small-diameter apertures, and the high-energy electron beam passes through these apertures. However, they are coupled through intermediate cavities, which stabilize the microwave phase relationship between the accelerating cavities. 

Emergency In vivo Tooth Dosimeter Oral Dosimeter. Tooth enamel is only material that records the accumulated radiation exposure dose in the past in a human body. An equipment for rapid dosimetry of teeth without their extraction was fabricated upon demand by Chernobyl medical doctors to judge whether immediate medical care such as spinal transplantation is necessary.97 A portable test apparatus of in vivo human tooth dosimeter consists of a resonator cavity with an aperture and a permanent magnet of Nd-B-Fe alloy (Neomax). The sensitivity is not sufficient due to the low Q factor and non-uniform magnetic field at the tooth. 

Metal nanostructures (such as particles and apertures) can permit local resonances in the optical properties. These local resonances are referred to as localized surface plasmons (LSPs). The simplest version of the LSP resonance comes for a spherical nanoparticle, where the electromagnetic phase-retardation can be neglected in the quasi-static approximation, so that the electric field inside the particle is uniform and given by the usual electrostatic solution [3] ... 

The peaks in the white light transmission correspond to the wavelengths that match the conditions of SPP resonance in each structure. The amount of transmitted light at the peaks far exceeded what was expected from the simple aperture theory [12]. 

Lezec HJ, Thio T (2004) Diffracted evanescent wave model for enhanced and suppressed optical transmission through subwavelength hole arrays. Opt Express 12 3629-3651 Flammer PD, Schick IC, Collins RT, Hollingsworth RE (2007) Interference and resonant cavity effects explain enhanced transmission through subwavelength apertures in thin metal films. Opt Express 15 7984-7993... 

Similar contributions are present for dipole emission. Emission to the far field is enhanced the most when the dipole is located near the measurement plane, and especially, near the aperture rims where LSP resonances occur. As the dipole moves away from the substrate, the emission decays exponentially. The excitation and emission enhancement characteristics of nano ertures will next be discussed in more detail. 

As already mentioned for aperture arrays, the periodicity of the structure can lead to significant local field enhancement by resonantly exciting surface plasmons. To translate this resonance effect to an isolated aperture, the metal surface surrounding the ajjerture can be structured in a periodic maiuier in order to efficiency excite the SPP. Most designs use concentric grooves around a central nanoajjerture, which is called bull s eye aperture (56, 70, 71). 

Yuan H. X., Xu B. X., Wang H. F., ChcmgT. C. (2006). Field enhancement of nano-sized metal aperture with and without surrounding corrugations through resonant surface plasmons. Jpn. J. Appl. Phys. 45 787-791. 

We have chosen to develop the quasioptical theory needed for understanding the spectrometer by considering first the properties of lenses and reflectors. In the analysis of resonators, a very fruitful approach is to unfold the multiple reflections of the resonator into a series of lenses in circular apertures spaced by the mirror separation for a confocal resonator (Kogelnik and Li, 1966). The semiconfocal resonator is a special case of the confocal resonator. We use a flat mirror, which images the curved mirror at minus the mirror separation. In such a resonator, it is impossible... 

---