We describe a precision sub-Doppler millimeter and submillimeter-wave Lamb-dip spectrometer with a backward-wave oscillator as the radiation source. The effect of nonlinear saturation of the spectral transitions (the Lamb-dip method) is used. The spectrometer resolution (about 5–10 kHz) and the measurement accuracy of the absolute frequencies (of the order of 1 kHz) of molecular transitions in the frequency range below 0.5 THz are discussed. The spectrometer is designed for obtaining accurate radio-astronomy and molecular-spectroscopy experimental data, in particular, when seeking variation in the proton-to-electron mass ratio as a function of time and place in the Universe. The frequency records of the Lamb dips on the spectral lines of the CO, OCS, and H2O molecules, the results of measuring the center frequencies of some transitions, and comparison with the results of other works are presented. The high measurement accuracy allows us to use the molecular-transition frequencies as the secondary frequency standards.

We study the field theoretical model of a scalar field in the presence of spacial inhomogeneities in the form of one and two finite-width mirrors (material slabs). The interaction of the scalar field with the defect is described with a position-dependent mass term. For a single-layer system we develop a rigorous calculation method and derive explicitly the propagator of the theory, the S-matrix elements and the Casimir self-energy of the slab. Detailed investigation of particular limits of self-energy is presented, and the connection to known cases is discussed. The calculation method is also found applicable to the two-mirror case. With its help we derive the corresponding Casimir energy and analyze it. For particular values of parameters of the model an obtained result recovers the Lifshitz formula. We also propose a procedure to unambiguously obtain the finite Casimir self-energy of a single slab without reference to any renormalization conditions. We hope that our approach can be applied to the calculation of Casimir self-energies in other demanded cases (such as a dielectric ball, etc).

We study the field theoretical model of a scalar field in presence of spacial inhomogeneities in form of one and two finite width mirrors (material slabs). The interaction of the scalar field with the defect is described with position-dependent mass term. Within this model we derive the interaction of two finite width mirrors, establish the correspondence of the model to the Lifshitz formula and construct limiting procedure to obtain finite self-energy of a single mirror without any normalization condition.

We present the general treatment of delta-potentials in the framework of quantum field theory. The path integral calculation technique is sketched by the example of scalar fields. Results of generalization of this approach to realistic fields are given: mean electromagnetic field for fermion system and Casimir energy for photodynamics in presence of cylindrical shell are presented.

We comment on a recent publication by Fosco, Lombardo, and Mazzitelli on Casimir energies for material slabs ("finite-width mirrors") and report a discrepancy between results obtained there for a single mirror and some previous calculations. We provide a simple consistency check which proves that the method used by Fosco et al. is not reliable when applied to approximations of piecewise constant profile of the mirror. We also present an alternative method for calculation of the Casimir energy in such systems based on earlier work of ours. Our results coincide both with perturbation theory and with some older and more recent calculations, but differ from those of Fosco et al.

We present calculations of Casimir energy (CE) in a system of quantized electromagnetic (EM) field interacting with an infinite circular cylindrical shell (which we call 'the defect'). Interaction is described in the only QFT-consistent way by Chern–Simon action concentrated on the defect, with a single coupling constant a. For the regularization of UV divergencies of the theory, we use the Pauli–Villars regularization of the free-EM action. The divergencies are extracted as a polynomial in the regularization mass M, and they renormalize the classical part of the surface action. We reveal the dependence of CE on the coupling constant a. Corresponding Casimir force is attractive for all values of a. For a → ∞, we reproduce the known results for CE for perfectly conducting cylindrical shell first obtained by DeRaad and Milton. As a future task for solving existing arguments on observational status of (rigid) self-pressure of a single object, we propose for investigation a system which we call 'Casimir drum'.

We study the field theoretical model of a real scalar field in presence of spacial inhomogeneity in form of a finite width mirror (material layer). The interaction of the scalar field with the defect is described with position-dependent mass term. We calculate the propagator of the theory, the Casimir energy and the pressure on the boundaries of the layer. We discuss the renormalization procedure for the model in dimensional regularization.

Detailed studies of the internal motions of dark clouds using spectral lines of many molecules require a laboratory frequency accuracy of the order of a few m s−1. Based on our laboratory studies of the HNCO rotational spectrum in the ground vibrational state, we have increased significantly the accuracy of frequency calculation in a wide range of quantum numbers. We have achieved an (1σ) uncertainty for rotational transitions in the K a = 0, 1 states recalculated to the Doppler velocity scale ≤2 m s−1 for all frequencies <1.1 THz. This value allows radio-astronomical measurements with an accuracy comparable to that of the highest-precision observations based on spectral lines of other molecules.

We study quantum electrodynamics coupled to the matter field on singular background, which we call defect. For defect on the infinite plane we calculated the fermion propagator and mean electromagnetic field. We show that at large distances from the defect plane, the electromagnetic field is constant what is in agreement with the classical results. The quantum corrections determining the field near the plane are calculated in the leading order of perturbation theory.

We consider the problem of modeling of interaction of thin material films with fields of quantum electrodynamics. Taking into account the basic principles of quantum electrodynamics (locality, gauge invariance, renormalizability) we construct a single model for Casimir-like phenomena arising near the film boundary on distances much larger then Compton wavelength of the electron. In this region contribution of Dirac fields fluctuations are not essential and can be neglected. In the model the film is presented by a singular background field concentrated on a 2-dimensional surface and interacting with quantum electromagnetic field. All properties of the film material are described by one dimensionless parameter. For two parallel plane films the Casimir force appears to be non-universal and dependent on material property. It can be both attractive and repulsive. In the model we study scattering of electromagnetic wave on the plane film, an interaction of plane film with point charge, homogeneously charged plane and straight line current. Here, besides usual results of classical electrodynamics the model predicts appearance of anomalous electromagnetic phenomena.

Three spectral lines of the main water molecule isotope in the ground vibrational state located near 321, 325 and 380GHz were studied at low pressures and room temperature using spectrometer with radio-acoustic detection of absorption. Self-, N2- and O2-pressure broadening and shifting parameters of these lines have been precisely measured. A number of parameters, in particular pressure shifts, were obtained for the first time. Complementary study of the 325-GHz line by resonator spectrometer at atmospheric pressure validated the low pressure experiment data and allowed measurement of the 325-GHz line intensity. Obtained results are discussed in comparison with previous experimental and theoretical data.

We study quantum electrodynamics coupled to the matter field on a singular background, which we call defect. For defect on an infinite plane we calculated the mean electromagnetic field. Quantum corrections determining the field near the plane are calculated in the leading order of perturbation theory. We analyse the normalization conditions for the parameters of the defect and calculate the photoelectric function of the charged particle from the defect.

We propose an approach for investigation of interaction of thin material films with quantum electrodynamic fields. Using main principles of quantum electrodynamics (locality, gauge invariance, renormalizability) we construct a single model for Casimir-like phenomena arising near the film boundary on distances much larger then Compton wavelength of the electron where fluctuations of Dirac fields are not essential. In this model the thin film is presented by a singular background field concentrated on a 2-dimensional surface. All properties of the film material are described by one dimensionless parameter. For two parallel plane films we calculate the photon propagator and the Casimir force, which appears to be dependent on film material and can be both attractive and repulsive. We consider also an interaction of plane film with point charge and straight line current. Here, besides usual results of classical electrodynamics the model predicts appearance of anomalous electric and magnetic fields.

Modern lasers are unable yet to cause electron–positron pair production in vacuum, however it is possible to notice considerable influence of vacuum polarization on radiation that propagates in such medium. In our work we present nonlocal theory of interaction of intensive laser radiation with electron–positron vacuum. We refuse from Heisenberg–Euler approximation and it permits us to calculate nonzero response of vacuum even for a plane wave. We show how to use the "proper time" method for calculation of corrections to the Maxwell equations. These equations are solved for the case of plane wave and their solutions are investigated.

Precise N2, O2, H2, Ar, He, and self-broadenings and shifts have been obtained for Q- and R-branch transitions in the ν1 fundamental band of ammonia from simultaneous fits of low-noise, high-resolution difference-frequency laser spectra at pressures from 0.07 to 27kPa (0.5–200Torr). Observed lineshapes exhibit significant deviations from the conventional Voigt profile, which may be attributed to Dicke narrowing and/or speed-dependent broadening. At the higher pressures, line mixing is evident and must be included in the fits. For self-broadening, line mixing is dominated by collisional tunneling transitions, whereas for the non-polar buffers, rotational relaxation among selected K states is the primary mixing mechanism.

High signal-to-noise ratio spectra of the (3-0) band P(1) and P(17) lines of CO broadened by He, Ar, Kr and SF6 were measured with a frequency-stabilized cavity ring-down spectroscopy system. For each collision-partner and both lines, multiple spectra were measured over pressures spanning nearly three decades up to 130 kPa. These data were analyzed with a multispectrum fitting procedure. Line shapes were modeled using the Hartmann-Tran (HT) profile with first-order line mixing as well as several other simplified profiles. The results show that for all considered collision partners (with the exception of SF6), the HT profile captures the measured line shapes with maximum absolute residuals that are within 0.1% of the peak absorption. In the case of SF6, which is the heaviest perturber investigated here, the maximum residuals for the HT profile are twice as large as for the other collision partners.

Modern lasers are yet unable to cause electron-positron pair production in vacuum, however it is possible to notice considerable influence of vacuum polarization on radiation that propagates in such medium. The field strength of modern lasers is not strong enough for creation of electron-positron pair in a vacuum, but the powerful laser beams generates polarization of vacuum which can be established experimentally. In the framework of QED a nonlocal theory of interaction of intensive laser radiation with electron-positron vacuum is developed. Refusing from the Heisenberg-Euler approximation it appears to be possible to calculate non-zero response of vacuum even for a plane wave. It is described by corrections to the Maxwell equations obtained by means of the proper time method. Effects generated by this correction for propagation of wave are analyzed.