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International Conference on Engineering and Emerging Technologies (ICEET)

Light Quantization with Classical Fields in Strong Laser

Huber Nieto–Chaupis

Published Dec 27, 2024• 0 citations
Publisher

Abstract

In this paper is demonstrated that quantum ef-fects can be derived in a straightforward manner from the classical radiation intensity equation. To accomplish this, it is employed the equation done by Hartemann and Kerman inside the framework of Nonlinear Compton backscattering. Thus, through mathematical procedures involving the usage of integer-order Bessel functions, it is derived expressions that are in fully agreement to the quantum mechanics formulation of coherence as the one given by Glauber by which a Gaussian profile is representing the coherent states of light. The resulting classical field of emission is interpreted from the spectrum consisting of classical radiated energy against Doppler frequency. It has yielded peaks that are been interpreted ad emitted photons.

DOI
10.1109/iceet65156.2024.10913539

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In this paper is demonstrated that quantum ef-fects can be derived in a straightforward manner from the classical radiation intensity equation. To accomplish this, it is employed the equation done by Hartemann and Kerman inside the framework of Nonlinear Compton backscattering. Thus, through mathematical procedures involving the usage of integer-order Bessel functions, it is derived expressions that are in fully agreement to the quantum mechanics formulation of coherence as the one given by Glauber by which a Gaussian profile is representing the coherent states of light. The resulting classical field of emission is interpreted from the spectrum consisting of classical radiated energy against Doppler frequency. It has yielded peaks that are been interpreted ad emitted photons.
High-order harmonic generation is a highly nonlinear phenomenon in which ultraviolet photons are generated when an atom is subjected to a high-intensity infrared laser field. This process has been extensively studied, but most of the formulations employ a semiclassical approach in which the electron is treated quantum mechanically while the driving field is treated classically. Although some recent studies follow a quantum-optical approach, the existing descriptions do not offer much insight into the physical processes taking place, and are always limited to monochromatic driving fields. In this thesis, we construct a fully quantized framework for strong-field ionization and high-harmonic generation that allows for quantization of both the driving field and the ultraviolet emission. The presented formalism extends the Strong-Field Approximation theory to a quantum-optical framework, with which we can obtain an analytical expression for the electron and the driving field after the interaction.
When an electron is accelerated, it emits radiation. In the relativistic quantum realm the elementary radiation process is the emission of a single photon, a process known as nonlinear Compton scattering in the case of an electron moving in the presence of a strong electromagnetic wave. This process is typically described within the Furry picture, where the electromagnetic wave is described as a classical background field and the electron-positron field is quantized in the presence of that background field. Equivalently one can quantize the electron-positron field in the vacuum but then the photon emission process is described as a transition from an initial state to a final state both featuring, apart from the electron (the initial state) and the electron and the photon (the final state), the same coherent state of photons appropriately related to the electromagnetic wave. Here, we consider a more general situation where the initial and the final state feature the same squeezed coherent state. Then, we specialize to the case where the coherent state corresponds to a plane-wave field and the mostly populated modes of the coherent state are also squeezed. We show that, when quantum fluctuations induced by the squeezing in the coherent field are negligible, a condition well satisfied at available squeezing levels, the squeezing effects effectively reduce to a frequency modulation of the plane-wave field corresponding to the coherent state. By means of numerical examples we show that at already available squeezing levels the emission spectrum of nonlinear Compton scattering and the total photon yield can be altered significantly. Analytical explanations of the main numerical results are also provided.
We study the general problem of matter-laser interaction within the framework of nonrelativistic quantum electrodynamics, with particular emphasis on strong laser field effects. Consequently, we formulate a well-defined approximation leading in a straightforward manner toward the conventional semiclassical mode of description. Namely, we arrive naturally to two coupled equations of motion: (i) the Schr\"odinger equation which governs the quantum dynamics of an atomic system driven by classically described radiation field (composed of an incoming laser pulse plus radiation emitted from the atom), and (ii) the classical Maxwell wave equation which describes the emission of radiation from the mentioned atomic source. Employing the formalism of adiabatic Floquet theory, we derive a simple criterion of validity of the just described semiclassical approach. It shows that the semiclassical treatment is justified in most situations. On the other hand, it turns out that the semiclassical approximation breaks down completely in certain special but realistic cases, regardless of the fact that the incoming laser pulse contains a huge number of photons. Under such special circumstances, we anticipate new effects arising due to the quantized nature of the radiation field, to be observable, for example, in harmonic generation spectra. Our considerations are illustrated more explicitly using a simple model of a two-level atom strongly driven by a laser. The quantum dynamics of this model problem is resolved within the framework of quantum electrodynamics while adopting well-defined and physically justifiable approximations. As an outcome, analytic formulas are found serving as a quantitative criterion of (non)applicability of the semiclassical approach and demonstrating the breakdown of semiclassical theory under well-defined conditions. An illustrative numerical calculation is provided.
Abstract The spontaneous emission of a quantum system driven by a high-intensity, high-frequency classical laser field is analyzed. The study is based on the accurate consideration of the quantum system interacting with vacuum-quantized field modes in the first order of perturbation theory, while the intense laser field is considered classically beyond this theory. It is demonstrated that the spectrum of the spontaneous emission can be used for analyzing the strong-field dynamics and the structure of the energy spectrum of an atomic system. In particular, it is found that in high-frequency fields (where the energy of the laser quanta is greater than the ionization potential) atoms manifest the features of the Kramers–Henneberger atom. It is also found that in the stabilization regime, the atom emits both odd and even laser radiation harmonics.
We present an analytical framework for the emergence of nonclassical radiation in strongly laser-driven quantum systems, with a focus on high-order harmonic generation (HHG). Starting from a Pauli-Fierz description, we employ a parametric factorization of the coupled light-matter wavefunction that reduces the dynamics to coupled equations for a field-driven electronic state and a quantized light mode. Within this framework, we identify a simple and predictive mechanism for nonclassicality: it originates from the nonlinear dependence of the electronic dipole response on the light-mode coordinate. An approximately constant dipole yields coherent radiation, a linear dependence produces squeezing, and higher-order nonlinearities give rise to Wigner-function negativity. We illustrate this mechanism for atomic and molecular model systems and analyze its scaling in multi-emitter configurations, indicating routes toward high-photon-number nonclassical radiation in HHG. Our results provide a transparent connection between strong-field dynamics and quantum-optical properties of emitted light, offering a basis for engineering nonclassical states in intense laser-matter interactions.