A resonance model, describing an LC circuit interaction with a bipole, is established for the determination of the effective parameters of metamaterials. The dynamic descriptions of both an LC circuit and a bipole are harmonic oscillators. Their interplay will induce a frequency shift, meaning that the most efficient receiving frequency (resonance frequency) of an LC circuit (or split ring) resonator is not the LC intrinsic frequency (ΩLC=1/LC) or the atomic vibration frequency. The relationship between the susceptibilities (χ(2),χ(3)) and the frequencies, including the atomic vibration frequency (Ω0), the LC intrinsic frequency (ΩLC), and the practical emission field frequency (Ω), is obtained. Compared with the other second-order harmonics, the extra DC current is much stronger, regardless of whether the system reaches resonance or not. The third-order harmonics are more likely to approach the resonance states compared with the second-order effect. Once the combined frequency is located at the resonance frequency, it is most likely to create a negative χ(3), and with the increase of the LC intrinsic frequency, a negative χ(3) can be obtained without satisfying the resonance condition.
The transient nonlinear Schrodinger equation in which the frequency is a function of time is established to describe the fast-varying field in the process of supercontinuum generation. It is solved with two methods and validated by comparing its simulation results with those of reported experiments. Based on the simulations of this extended equation, it is also demonstrated that the second-order differential of the field to longitude (z) can be ignored in the supercontinuum generation, and the additive item caused by the relationship between frequency and time will induce a homogeneous frequency shift.
A noninvasive optical technique, which is based on a combination of reflectance spectroscopy and gas in scattering media absorption spectroscopy, is demonstrated. It has the potential to improve diagnostics of middle ear infections. An ear phantom prepared with a tissue cavity, which was covered with scattering material, was used for spectroscopic measurements. Diffuse reflectance spectra of the phantom eardrum were measured with a reflectance probe. The presence of oxygen and water vapor as well as gas exchange in the phantom cavity were studied with a specially designed fiber-optic probe for backscattering detection geometry. The results suggest that this method can be developed for improved clinical detection of middle ear infection.
We present a noninvasive method to study fruit ripening. The method is based on the combination of reflectance and fluorescence spectroscopies, as well as gas in scattering media absorption spectroscopy (GASMAS). Chlorophyll and oxygen are two of the most important constituents in the fruit ripening process. Reflectance and fluorescence spectroscopies were used to quantify the changes of chlorophyll and other chromophores. GASMAS, based on tunable diode laser absorption spectroscopy, was used to measure free molecular oxygen in the fruit tissue at 760 nm, based on the fact that the free gases have much narrower spectral imprints than those of solid materials. The fruit maturation and ripening processes can be followed by studying the changes of chlorophyll and oxygen contents with these three techniques.