Frequency characteristics and dynamical behaviors of self-modulation in vertical-cavity surface-emitting lasers

Abstract The frequency characteristics of a VCSEL with a quarter-wave plate (QWP) and an external reflector are investigated with the translation matrix of the vectorial field. Two series of eigenmode with a shift of half the free spectrum range are linearly polarized, respectively, along the neutral axes of QWP. We also numerically explore the polarization self-modulation phenomenon by using a vectorial laser equation and considering the inhomogeneous broadening of the gain medium. If the external cavity is so short that the shift is bigger than the homogeneous broadening, two stable longitudinal modes oscillate, respectively, on the neutral axes of QWP because they consume different carriers. With a long external cavity, the competition of the modes for the common carriers causes the intensity fluctuation of the modes with a period of one round-trip time of the external cavity

laserinducedparticlejetanditsignitionapplicationinpremixedcombustiblegases

A hot particle jet is induced as a laser pulse from a free oscillated Nd:YAG laser focused on a coal target. The particle jet successfully initiates combustion in a premixed combustible gas consisting of hydrogen, oxygen, and air. The experiment reveals that the ionization of the particle jet is enhanced during the laser pulse. This characteristic is attributed to the electron cascade process and the ionization of the particles or molecules of the target. The initial free electrons, which are ablated from the coal target, are accelerated by the laser pulse through the inverse Bremsstrahlung process and then collide with the neutrals in the jet, causing the latter to be ionized

Spectral Characteristics of CN Radical (B - X) and Its Application in Determination of Rotational and Vibrational Temperatures of Plasma

The aim is to resolve the difficulties of measurement of temperature at several thousands of Celsius degrees for some unstable non-equilibrium gas flows. Based on the molecular spectroscopy theory and inherent molecular structure characteristics of the CN radical, the dependence of the spectral profile on the rotational temperature (RT), vibrational temperature (VT) and optical apparatus function are numerically explored within some certain ranges. Meanwhile, by comparing the numerically calculated spectra with the experimental spectra of the CN radical, the corresponding RT and VT of the plasma induced by the interaction of the laser pulse from an oscillated Nd:YAG laser with the coal target are determined, respectively. In addition, a short discussion on the thermodynamic state and the energy transfer process of the CN radical is also given

aninvestigationofelectromagneticwavepropagationinplasmabyshocktube

This paper presents the electromagnetic wave propagation characteristics in plasma and the attenuation coefficients of the microwave in terms of the parameters n(e), v, w, L, w(b). The phi800 mm high temperature shock tube has been used to produce a uniform plasma. In order to get the attenuation of the electromagnetic wave through the plasma behind a shock wave, the microwave transmission has been used to measure the relative change of the wave power. The working frequency is f = (2 similar to 35) GHz (w = 2pif, wave length lambda = 15 cm similar to 8 mm). The electron density in the plasma is n(e) = (3 x 10(10) similar to 1 x 10(14)) cm(-3). The collision frequency v = (1 x 10(8) similar to 6 x 10(10)) Hz. The thickness of the plasma layer L = (2 similar to 80) cm. The electron circular frequency w(b) = eB(0)/m(e), magnetic flux density B-0 = (0 similar to 0.84) T. The experimental results show that when the plasma layer is thick (such as L/lambda greater than or equal to 10), the correlation between the attenuation coefficients of the electromagnetic waves and the parameters n(e), v, w, L determined from the measurements are in good agreement with the theoretical predictions of electromagnetic wave propagations in the uniform infinite plasma. When the plasma layer is thin (such as when both L and lambda are of the same order), the theoretical results are only in a qualitative agreement with the experimental observations in the present parameter range, but the formula of the electromagnetic wave propagation theory in an uniform infinite plasma can not be used for quantitative computations of the correlation between the attenuation coefficients and the parameters n(e), v, w, L. In fact, if w < w(p), v(2) much less than w(2), the power attenuations K of the electromagnetic waves obtained from the measurements in the thin-layer plasma are much smaller than those of the theoretical predictions. On the other hand, if w > w(p), v(2) much less than w(2) (just v approximate to f), the measurements are much larger than the theoretical results. Also, we have measured the electromagnetic wave power attenuation value under the magnetic field and without a magnetic field. The result indicates that the value measured under the magnetic field shows a distinct improvement

Experimental research on ppb-level ozone detection method based on gas phase chemiluminescence technology

The "ozone hole" and ozone pollution have caused numerous environmental problems that threaten human survival. Therefore, real-time monitoring of the concentration of trace ozone components in the atmosphere is critical. In recent decades, the ethylene chemiluminescence method has become a common method for diagnosing trace ozone in the air due to its high sensitivity, low detection limit, and simple operation. However, this method requires a large amount of high-purity ethylene, which presents risks such as flammability and explosion during actual measurements. Therefore, this paper proposes a new strategy for measuring trace ozone levels at the ppb with high safety and sensitivity, based on the chemiluminescence reaction mechanism between NO and ozone. Firstly, this article designs a system for preparing quantitative ozone standard gas using the principle of plasma discharge and the ultraviolet broadband absorption concentration measurement method; Subsequently, a fluorescence measurement system with high sensitivity and low detection limit was built based on the principle of chemiluminescence and weak light detection technology; Finally, experimental investigations on the chemiluminescence laws of traditional hydrocarbons and NO chemiluminescence laws was conducted with the help of the aforementioned weak light measurement system. The results indicate that the NO chemiluminescence reaction is more prominent than hydrocarbons and is an ideal excitation gas for ozone fluorescence detection. The chemiluminescence signal of NO is approximately 17 times higher than that of C2H4, 68 times higher than that of C2H2, and much higher than that of other hydrocarbons such as CH4, C2H6. The experiment also showed that within the concentration range of 0-10 ppm and103 ppm of NO excitation gas, the measurement system has high linearity and sensitivity, drastically improving the safety and sensitivity of the measurement system. For example, when the NO concentration is 1000 ppm, the correlation linearity coefficient R2 is above 0.999, the lower limit of Allan variance detection can reach approximately 20 ppt