Time-ordering in Heisenberg’s equation of motion as related to spontaneous radiation

Despite many years of research into Raman phenomena, the problem of how to include both spontaneous and stimulated Raman scattering into a unified set of partial differential equations persists. The issue is solved by formulating the quantum dynamics in the Heisenberg picture with a rigorous accounting for both time- and normal-ordering of the operators. It is shown how this can be done in a simple, straightforward way. Firstly, the technique is applied to a two-level Raman system, and comparison of analytical and numerical results verifies the approach. A connection to a fully time-dependent Langevin operator method is made for the spontaneous initiation of stimulated Raman scattering. Secondly, the technique is demonstrated for the much-studied two-level atom both in vacuum and in a lossy dielectric medium. It is shown to be fully consistent with accepted theories: using the rotating wave approximation, the Einstein A coefficient for the rate of spontaneous emission from a two-level atom can be derived in a manner parallel to the Weisskopf–Wigner approximation. The Lamb frequency shift is also calculated. It is shown throughout that field operators corresponding to spontaneous radiative terms do not commute with atomic/molecular operators. The approach may prove useful in many areas, including modeling the propagation of next-generation high-energy, high-intensity ultrafast laser pulses as well as spontaneous radiative processes in lossy media.

Generation of ultrashort pulses in the THz frequency range

There are results for the spontaneous coherent super-radiative undulator emission in the terahertz frequency range from a short (as compared to the wavelength of the radiated wave) dense electron bunch. If the group velocity of the wave is close to the bunch velocity, this is a process of spontaneous radiation followed by amplification of a single wave cycle. Despite the Coulomb repulsion of electrons inside the bunch, its compactness is provided by the compression of the bunch under the action of its own radiation fields. As a result, formation of an ultra-short (several cycles long) powerful wave packet occurs when the bunch moves through several undulator periods with high (∼20% in optimized systems) efficiency of extraction of the electron energy and high intensity (∼ 100 MV/m) of the peak wave field.

Spatial distribution and time evolution of metal-containing plasma of a low-current atmospheric pressure discharge with magnesium cathode

The spatial intensity distribution and temporal dynamics of the plasma generated by an atmospheric pressure discharge with magnesium cathode in an argon flow are investigated in a coaxial geometry discharge system. The repetition rate of unipolar pulses was 56 kHz and the pulse duration was 12 μs. The steady-state amplitude of the discharge current was 100 mA at a voltage of about 130 V. Under this operating mode, a local melting of the active cathode surface took place. The evaporated magnesium atoms were captured by the working gas flow and formed a green glow plume around the positive discharge column outside the anode nozzle. The image of the plasma formation was projected onto the entrance slit of the monochromator. The spatial distribution of the radiation intensity and evolution in time of its selected monochromatic components were measured. The radiation spectrum contained groups of ion and magnesium atom lines with wavelengths of 285.21 nm (singlet resonant Mg I); 383.08, 383.36, 383.9 nm (triplet Mg I); 517.3, 517.5, 518.1 nm (triplet Mg I). The results of this work are promising with regard to studying open-type spontaneous radiation sources, as well as the generation of combined gas-metal plasma flows at atmospheric pressure.

An inhibited laser

Traditional lasers function using resonant cavities, in which the round-trip optical path is exactly equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. By taking advantage of the resonant cavity enhancement, the narrowest sub-10-mHz-linewidth laser and a 10^-16-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, never has a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity where the atomic resonance is exactly between two adjacent cavity resonances been proven. Herein, we present the first demonstration of the inhibited stimulated emission, which is termed an inhibited laser. Compared with traditional superradiant AOCs exhibiting superiority for the high suppression of cavity noise in lasers, the effect of cavity pulling on the inhibited laser's frequency can be further suppressed by a factor of (2F/π)^2. This study of the inhibited laser will guide further development of superradiant AOCs with better stability, and may lead to new searches in the cavity quantum electrodynamics (QED) field.

Oblique-mode breakdown in hypersonic and high-enthalpy boundary layers over a blunt cone

The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities. In this work, the oblique-mode breakdown, as one of the most available transition mechanisms, is studied using the nonlinear parabolized stability equations (NPSE) with consideration of the thermal-chemical non-equilibrium effects. The flow over a blunt cone is computed at a free-stream Mach-number of 15. The rope-like structures and the spontaneous radiation of sound waves are observed in the schlieren-like picture. It is also illustrated that the disturbances of the species mass and vibrational temperature near the wall are mainly generated by the product term of the wall-normal velocity disturbance and the mean-flow gradient. In comparison to the CPG flow, the TCNE effects destabilize the second mode and push upstream the N factor envelope. The higher growth rate of the oblique wave leads to stronger growth of the streamwise vortices and harmonic waves.

Novel CSL bounds from the noise-induced radiation emission from atoms

We study spontaneous radiation emission from matter, as predicted by the Continuous Spontaneous Localization (CSL) collapse model. We show that, in an appropriate range of energies of the emitted radiation, the largest contribution comes from the atomic nuclei. Specifically, we show that in the energy range $$E\sim 10\,-\,10^{5}$$ E ∼ 10 - 10 5 keV the contribution to the radiation emission from the atomic nuclei grows quadratically with the atomic number of the atom, overtaking the contribution from the electrons, which grows only linearly. This theoretical prediction is then compared with the data from a dedicated experiment performed at the extremely low background environment of the Gran Sasso underground National Laboratory, where the radiation emitted form a sample of Germanium was measured.As a result, we obtain the strongest bounds on the CSL parameters for $$r_C\le 10^{-6}$$ r C ≤ 10 - 6 m, improving the previous ones by more than an order of magnitude.

A biophysical model of the recognition process of skin response patterns to optical activation

This paper presents a biophysical model of the recognition process of glow patterns (response) of the skin in the area of biologically active zones to external optical activation. The model was developed to increase the efficiency of the process of identifying the causes of differences in glow patterns. The structures of glow patterns are described and their differences are described. A rationale for the use of forced radiation of skin cells in current studies is given (recognition of weak signals of spontaneous radiation is technically difficult). Forced radiation of biological objects appears as a result of excitation of the biological environment by an external action and is much higher than spontaneous radiation. Spontaneous optical radiation of skin cells under certain conditions is one of the characteristic features of the skin. This radiation can be caused by a field form of intercellular interaction, which causes biochemiluminescence in the form of spontaneous weak signals ensuring intercellular communication. The model uses a biotechnical system related to the human physical state, its characteristics, type of meridian and external conditions. We have identified subsystems (biological and technical), the main elements of the system, determined the links between them, necessary and sufficient for drawing conclusions, formulated the main requirements for the system, determined the initial data. The results of the preliminary experimental investigations with the use of the developed model are presented in which some dependence of the luminescence patterns on the meridian type is revealed. It is noted that final conclusions on the causes of skin glow patterns differences in certain points of biologically active zones will be made when more extensive statistical data is collected using the developed model.

Universal lasing condition

Usually, the cavity is considered an intrinsic part of laser design to enable coherent emission. For different types of cavities, it is assumed that the light coherence is achieved by different ways. We show that regardless of the type of cavity, the lasing condition is universal and is determined by the ratio of the width of the atomic spectrum to the product of the number of atoms and the spontaneous radiation rate in the laser structure. We demonstrate that cavity does not play a crucial role in lasing since it merely decreases the threshold by increasing the photon emission rate thanks to the Purcell effect. A threshold reduction can be achieved in a cavity-free structure by tuning the local density of states of the electromagnetic field. This paves the way for the design of laser devices based on cavity-free systems.