Numerical Simulation of Fiber Laser Operated in Passively QSwitched and Mode-Locked Regimes

The aim of this chapter is to highlight the role of simulation methods as tools for analysis of low and medium average power fiber laser operated in passively Q-switched and/or mode-locking regimes into the design of various applications such as materials micro-processing of sensor applications. The chapter’s purpose consists in making available to specialists in the field of lasers, electro-optics and even nano-photonics improved procedures for designing high-accuracy remote sensors dedicated to large range of laboratory, industrial and military applications. The reason that this chapter deals with passive optical Q-switching and mode-locking techniques tailored for fiber lasers is the high percentage of sensing devices operating in this regime. Numerical simulation results obtained for this class of laser emitters can be used for other types of lasers, such as optical fiber lasers. There are briefly presented the two main mathematical methods used to analyze solid laser oscillators in passive optical Q-switching regime: the coupled rate equations approach and the iterative approach. The validation of the presented numerical simulation methods is done by comparison with experimental results

Optimization of Cosmic Radiation Detection in Saline Environment

Following the interaction of a neutrino with saline environment, the Cherenkov cone will be generated. The electromagnetic effect of the Cherenkov cone is perpendicular to the cone generator and it has the energy directly proportional to the neutrino energy. In the saline environment, neutrinos with very high energies (noise – 115 dBm) can be determined. Investigation of these neutrinos will lead to the construction of a Cherenkov detector. The construction of a Cherenkov detector involves the design and the construction of a very large number of detection elements and of cascade amplifiers. Another necessary condition is to know exactly the distribution of the dielectric parameters of the saline environment. In order to know the distribution of the dielectric parameters of the saline environment, it is necessary to make a map of their distribution. Under these conditions, the number of detection elements will be optimized and also the optimal position of the future Cherenkov detector will be determined. In this chapter, we will present the methodology of calculating the detection elements and a method to determine the dielectric parameters. Measurements of attenuation of the propagation of electromagnetic waves in this environment will be presented. We will detail how to optimize a Cherenkov detector

Numerical Simulation Methods Applied at Fiber Grating Sensors Design

The paper presents the results obtained in simulation of fiber Bragg grating (FBG) and long-period grating (LPG) sensors and their applications. The optical properties of FBG and LPG are firstly analyzed and, consequently, the basics of simulation models are provided. Coupled-mode theory and the transfer matrix methods are the two techniques used for the simulation of FBG and LPG. The numerical simulations are performed for an improved design of these types of fiber sensors, designs dedicated to specified applications. The different FBG types, i.e. the normal, chirped, apodized, according to different laws and tilted cases, are analyzed. Also, various LPG configurations are numerically simulated. The two main categories of sensing applications, for temperature and for mechanical stress/strain evaluation, are simulated for each type of fiber grating sensor. The chapter is intended to be a synthesis of already obtained results to which some results of research in development are added

Stable One-Dimensional Periodic Wave in Kerr-Type and Quadratic Nonlinear Media

We present the propagation of optical beams and the properties of one-dimensional (1D) spatial solitons (“bright” and “dark”) in saturated Kerr-type and quadratic nonlinear media. Special attention is paid to the recent advances of the theory of soliton stability. We show that the stabilization of bright periodic waves occurs above a certain threshold power level and the dark periodic waves can be destabilized by the saturation of the nonlinear response, while the dark quadratic waves turn out to be metastable in the broad range of material parameters. The propagation of (1+1) a dimension-optical field on saturated Kerr media using nonlinear Schrödinger equations is described. A model for the envelope one-dimensional evolution equation is built up using the Laplace transform

Ultrabroadband THz spectroscopy of disordered materials

We perform THz spectroscopic investigations of the dielectric function of disordered materials in the THz region. Specifically, we consider amorphous materials and perform ultrabroadband THz spectroscopy of chalcogenide glasses where we observe the transition from universal scaling of the absorption at low frequencies to medium-range order and local order at higher frequencies

Ultrabroadband terahertz spectroscopy of chalcogenide glasses

Chalcogenide glasses are receiving a lot of attention due to their unique optical properties. In this paper we study the optical properties of As2S3 and GaLaS glasses in a broad terahertz (THz) frequency range (0.2-18 THz). Complex dispersion behavior with drastic changes of refractive index and absorption coefficient is found for both glasses. We observe the breakdown of the universal power-law dependence of the absorption coefficient due to atomic vibrations observed at low THz frequencies in disordered materials, and see the transition to localized vibrational dynamics for the As2S3 compound at higher frequencies. In addition, As2S3 displays two transparency regions, at 7-8 THz and 12.2 THz, of potential interest for future nonlinear applications in the THz rang

Satellite thermal infrared anomalies associatedwith strong earthquakes in the Vrancea area ofRomania

Thermal anomalies which are known to be significantprecursors of strong earthquakes can be evidencedby spectral thermal infrared (TIR) bands recordedby sensors on board of NOAA-AVHRR and Terra/Aqua-MODIS satellite. In order to locate relevant thermal anomalousvariations prior to some strong even moderate earthquakesrecorded in Vrancea tectonic active zone in Romania,satellite derived geophysical parameters have beenused: land surface temperature (LST), outgoing long-waveradiation (OLR) and mean air temperature (AT). Spatiotemporalvariations of LST, OLR, and AT before and afterthree strong earthquakes in Vrancea area (Mw = 7.4, 4March 1977; Mw = 7.1, 30 August 1986; Mw = 6.9, 30 May1990) and a moderate earthquake (Mw = 5.9, 27 October2004) have been analyzed. Anomalous spatio-temporalpatterns of these parameters developed a few days up tofew weeks before the earthquakes disappeared after themain shocks. Significant increases in land surface temperature,outgoing long-wave radiation, and mean air temperaturecan be assigned to energy exchange mechanismduring earthquake preparatory events. Such preseismicanomalies can be considered to be associated with thethermodynamic, degassing and ionization geochemicalprocesses which seem to be activated due to the increasedstress in the ground, and microfracturing of the rocks especiallyalong area’s active faults