Advanced Materials Research Vols. 760-762

Abstract: A Haken-Lorentz equation with self-feedback light field as well as its stability condition were gained through a series of mathematic process, and the stability judgements of the equation under 6 groups of parameters were gained using the stability condition, then a MATLAB simulation was carried out on the equation and the movement orbits of the equation were gained. It shows that when the stability condition gives a stable judgement, the movement orbit in the mathematic simulation is a single helix ends in a stable point, which shows that the simulation results are stable too; when the stability condition gives an unstable judgement, the movement orbits in the mathematic simulation are two chaotic helixes, which shows that the simulation results are unstable too. The judgements which result from the stability condition are consistent with the MATLAB simulation judgements, which shows that this stability condition can be a criterion of the Haken-Lorentz equation with self-feedback light field in some parameter ranges.

Abstract: In order to make a numerical simulation of the chaos in standing wave lasers, a dynamic equation that is feasible to mathematical evaluation is required. There is a summation symbol in the well known Haken laser equation, and it results in a tremendously heavy quantity of evaluation. In order to simplify the evaluation, the light field in the Haken laser equation was expanded in the standing wave form. Two macroscopic variables were brought in to eliminate the summation symbol in terms of single mode and homogeneously broadening. Therefore, a simplified Maxwell-Bloch equation was gained. Then by normalizing, a new equation was obtained. This equation is in a simple form. Its every variable has unambiguous meaning and every coefficient is only related to gain or dissipation and is easy to obtain. Moreover, the equation is used in two MATLAB numerical simulations of a CO₂ laser and a chaotic attractor is obtained. So the equation could be a mathematical model in numerical simulations of standing wave laser chaos.

Abstract: At present, the research on the minimum resolvable contrast is limited to the simple imaging system, or the imaging devices, and mainly limited to the method of measurement in the laboratory, the research on minimum resolvable contrast of the telescope has not developed. Based on the imaging process of the telescope and the detecting SNR, noise equivalent contrast is put forward, then combined with the system MTF, the model on minimum resolvable contrast of the telescope is build. At last, the model is simulated on the computer, the simulation results indicated that the minimum resolvable contrast can evaluate the telescope ability more comprehensive, the atmosphere, the aberration and the motion can affect the ability seriously. The model can give a scientific basis for the optimization design of the system and the development of practical work.

Abstract: This paper reports experimental and simulation studies on degradation of optical power of low power LEDs due to current stress and temperature variation. The goal of this study was to study the effect of aging and ambient temperature on optical output power of light emitting diodes and to determine the effective lifespan of LED under stress condition. The LED samples were stressed at four levels of operating current 20mA, 30mA, 40mA, and 45mA with stress time up to 1000h. We find that degradation rate increases with increasing operating current. When LEDs are overstressed by driving at higher current the optical power degraded with stress time. A Mathematical model is developed to predict the behavior of LED at different operating current. Simulations are carried out with this model using MATLAB. Using degradation pattern at higher operating current the lifespan of LEDs was predicted at normal operating current.

Abstract: The paper demonstrates the effect of lens inner structure on radiation pattern and light extraction efficiency of LED and the application to artificial light in compact greenhouse. A commercial software package of Trace Pro and one-factor at-a-time method are used to simulate the lens with different inner structure. The optimum parameters of lens inner structure design for the maximum light extraction efficiency and the best uniform luminous are described by the corner radius of curvature, lens width, and lens height, respectively. In comparison with a commercial artificial light of LED matrix used in agriculture, the high-power LED module with proposed lens inner structure exhibit good improvement in uniformity of illumination and light extraction. This study may provide a practical guideline for design and fabrication of a high-performance lens used in various compact agricultural applications.

Abstract: The authors have investigated the edge emission of microcavities which are formed by low-molecular organic light emitting diodes sandwiched between dielectric mirrors and the metal cathode. The edge emission relative to the surface emission is found to significantly depend on the layer number of alternating high and low refractive index films in dielectric mirrors. The enhancement of cavity devices can reach a factor of ~3.0 compared with noncavity devices. Spectra of organic film pumped by edge emission of microcavity devices have been observed, a mechanism of achievement of an amplified spontaneous emission has been discussed theoretically.

Abstract: Methamphetamine hydrochloride crystal (trade name Methedrine) that is one of the illegal drugs used as a stimulant to the nervous system has been considered to be detected by T-ray via the terahertz time-domain spectroscopy (THz-TDS). In this research, we simulated the THz spectra of Methedrine by molecular dynamics methods for the first time. The terahertz spectra at temperatures 78.4K, 200K, 294K and 400K in the frequency range of 10-100cm^-1 were investigated, which exhibited the variation of spectra position and intensity with increasing temperature. Firstly, we used DL_POLY simulation package to obtain the instantaneous values of the dipole moment. Subsequently, the intensities of THz vibrational modes were obtained by the Fourier transform of the autocorrelation function of the dipole moment. The results showed our theoretical calculation by molecular dynamics simulations got a good consistency with available experimental spectroscopy. These are useful to determine the best conditions of temperature at which the terahertz time-domain spectroscopy of Methedrine results a highly informative spectrum.

Abstract: Oxygen plays a fundamental role in nature and industrial process, the fast on-line oxygen concentration detection is of great significance. Tunable diode laser absorption spectroscopy (TDLAS) is capable high selective, high sensitive, non-intrusive, this technique exploits the diode laser tunable and narrow bandwidth characteristics, by selecting one absorption line of the target gas to avoid interference from other gas and realize oxygen concentration fast on-line detection. In this paper, we use vertical cavity surface-emitting laser (VCSEL) as the light source, adopting the wavelength modulation spectroscopy and the harmonic detection technology to measure the second harmonic signal and realize oxygen concentration fast on-line detection. The detection concentration range between 0.1% to 40% and detection accuracy is 0.1%.

Abstract: Retracted paper: The conventional material for the optical fiber communication laser diode is based on InGaAsP, which might be substituted by a potential candidate, InGaAlN. The new active region material, InN, is introduced regarding to its crystal growth and characterization, including the structural, optical and electrical properties. This material is promising for providing good performance of temperature stability of the wavelength. In addition, it is environmentally friendly.