Quantum mechanical description of light

In changing from the classical to the quantum mechanical description of light, one of the principal results is that light is emitted or absorbed in discrete quanta known as photons, with an energy of... 

Altliough a complete treatment of optical phenomena generally requires a full quantum mechanical description of tire light field, many of tire devices of interest tliroughout optoelectronics can be described using tire wave properties of tire optical field. Several excellent treatments on tire quantum mechanical tlieory of tire electromagnetic field are listed in [9]. 

C. Curutchet, D.G. Scholes, B. Mennucci, R. Cammi. How solvent controls electronic energy transfer and light harvesting Toward a quantum-mechanical description of reaction field and screening effects. J. Phys. Chem. B 111, 13253 (2007)... 

Of course, a vector model described above has strong limitations. It can be applied only in the case of large angular momentum quantum number nlues. To have a precise (luantum mechanical description of light interaction with atoms and molecules, one should use a quantum mechanical description. Usage of monochro-... 

Expressions similar to (25) have previously been reported in the literature [14,15], where a perturbation on the form given in (17) was either simply postulated [14] or derived from a classical description of the incident X-ray pulse [15], Here, (25) has been derived from first principles, i.e., the quantum theory of light-matter interactions, with a quantum mechanical description of the incident X-ray pulse. 

In this chapter we consider classical and quantum mechanical descriptions of electromagnetic radiation. We develop expressions for the energy density and irradiance of light passing through a homogeneous medium, and we discuss the Planck black-body radiation law and linear and circular polarization. Readers anxious to get on to the interactions of light with matter can skip ahead to Chap. 4 and return to the present chapter as the need arises. 

H, He+, Li +, Be T and so on, are one-electron atoms. Each consists of only two particles, a nucleus and an electron. The quantum mechanical description of one-electron atoms is the starting point for understanding the electronic structure of atoms and of molecules. It is a problem that can be solved analytically, and it is useful to work through the details. In the case of the hydrogen atom, the nuclear mass is about 2000 times that of an electron. Thus, the proton would be expected to make small excursions about the mass center relative to any excursions of the very light electron. That is, we expect the electron to be "moving quickly" about, and in effect, orbiting the nucleus. 

In this chapter we summarize basic concepts of lasers with regard to their applications in spectroscopy. A well-founded knowledge of some subjects in laser physics, such as passive and active optical cavities and their mode spectra, amplification of light and saturation phenomena, mode competition and the frequency spectrum of laser emission, will help the reader to gain a deeper understanding of many problems in laser spectroscopy and to achieve optimum performance of an experimental setup. A more detailed treatment of laser physics and an extensive discussion of various types of lasers can be found in textbooks on lasers (see, for instance, [1.1-3, 5.1-4]). For more advanced presentations based on a quantum mechanical description of lasers, the reader is referred to [1.4,5, 5.5-7]. 

The problem, in essence, is to provide for an angular interaction by an accurate quantum mechanical description of the transition matrix for absorbance and reflectance. In other words, the field of the electromagnetic wave which penetrates the bulk metal will determine the photocurrent, provided that a correction is made for the reflected light. It has been shown that, approximately," ... 

By 1930, these paradoxes had been resolved by quantum mechanics, which superseded Newtonian mechanics. The classical wave description of light is adequate to explain phenomena such as interference and diffraction, but the emission of light from matter and the absorption of light by matter are described by the particlelike photon picture. A hallmark of quantum, as opposed to classical, thinking is not to ask What is light but instead How does light behave under particular experimental conditions Thus, wave-particle duality is not a contradiction, but rather part of the fundamental nature of light and also of matter. 

In order to better understand the emission and absorption of light by molecules, it is necessary to look at the quantum-mechanical concept of the nature of tight In this concept, light is considered to be a beam of photons whose energies are quantized. Detailed description of quantum mechanics and spectroscopy is beyond the scope of this book. Here will only be presented the major conclusions necessary for better understanding of light. 

The essential and peculiar feature of the quantum mechanical model of the atom lies in its description of electrons as waves rather than particles. It is far more inmitive to think of electrons as particles, perhaps resembling tiny marbles, than to envision them as waves. But just as we ve seen for light, experimental observations led to the idea that electrons can exhibit wave-like behavior. The first evidence of the wave nature of electrons came through diffraction experiments in 1927. Diffraction was already a well-understood phenomenon of waves, so the observation of electron diffraction strongly suggested the need for a wave-based treatment of the electron. 

The quantum-mechanical description may be illustrated by a specific example, taken from [12.9], where optical pumping on the transition (7, M) (7, M ) is achieved by linearly polarized light with a polarization vector in the jc-y-plane, perpendicular to the field direction along the z-axis (Fig. 12.5). ITie linearly polarized light may be regarded as a superposition of left- and right-hand circularly polarized components and The excited-state wave function for the excitation by light polarized in the jc-direction is... 

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