In this collection, the authors present a new theoretical approach free from limitations of perturbation theory for calculating atomic emission spectra in an alternating electric field. The following problems are studied for the emission spectrum of helium: dependences of the AC Stark effect, transition probabilities and spectral line intensities on the electric field parameters, reasons for the change in the emission color with increasing electric field frequency, mechanisms of a sudden increase in spectral line intensities, and their quenching in the electric field and mechanisms of the formation of spectral line profiles in the electric field. This study has real-world applications in plasma spectroscopy, gas discharge physics, laser physics, and astrophysics. Next, the authors discuss the sampling and analytical procedure for helium in forensic practice. In cases of suspected helium exposure, the analysis of helium is commonly performed by the gas chromatography (GC) with thermal conductivity detector or gas chromatography-mass spectrometry (GC/MS) in combination with head-space (HS) method. A subsequent study is presented on the description of the process of ionization of the Helium atom by using a single-active-electron (SAE) model (archetype of a system to an active electron) by an intense and high frequency laser field and by a pulse combining infrared photons and one of its harmonics. The authors mathematically solve the ESDT for an active electron system, using the most efficient numerical simulation methods, followed by a spectral analysis of the wave function for the representation of the photoelectron spectrum of the studied system. This book presents an overview of the theoretical methods which have been developed to analyze electron-atom collisions in the presence of an external laser beam. Various important aspects of the theory of multiphoton free-free transitions are explored, after which a study on the collisions of electrons with atoms in the presence of the laser field is reviewed. The way in which the dressing of the atomic states by the external radiation field can affect the dynamics of the electron-impact collisions is also discussed. The final research studies the phoxonic crystal. The modeling of this device leads to the study of the interactions between photons and phonons, while also helping in the development and improvement of integrated acousto-optics devices. The goal is to seek a maximum coupling of this interaction by way of a strong confinement of the waves in the microcavities.