The near-field effect in a system of two-level dipole particles

We have solved a self-consistent problem on interaction of two dipole atoms located at an arbitrary distance from each other with the field of a quasiresonance light wave, whose intensity is sufficient for the system to manifest nonlinear properties. The atoms are considered as two-level systems described by means of Bloch optical equations, while the field inside of the system includes both Coulomb and retarded parts. We consider a situation where atoms are identical and the distance between them is much smaller than the length of an outer light wave. The distribution of an electric field both inside of a small object and outside of it is found numerically. It is shown that the amplitude of the electric field in a wave zone depends substantially on the frequency of the external field and interatomic distance, while the field distribution differs from the field pattern of an electric dipole. At definite values of the external field intensity an optical multistability is a feature of the system under investigation. We have elucidated the conditions under which the multistability is manifested in the present system. The results obtained are considered as the near-field effect in the optics of small objects, which makes it possible to investigate the structure of small objects by means of optical radiation. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 375–378, May–June, 2000. The present work was supported by the Russian Foundation for Fundamental Research (grant 98-02-16035) and by a grant from the Federal Purpose-Oriented Program “Integration.”     

Dependences of HTS tape critical parameters on fluences under irradiation with heavy ions and high energy electrons

Experimental data on the study of modifications of two types of the YBCO(123)-based composite tape under irradiation with electrons with the energy of 23 MeV and ¹³²Xe²⁷⁺ (167 MeV), ⁸⁴Kr¹⁷⁺ (107 MeV), and ⁴⁰Ar⁸⁺ (48 MeV) ions in a wide range of irradiation doses are presented. It is shown that no changes in the HTS transition temperature and critical current occurred under electron irradiation up to the dose D ≈ 10⁻⁴ disp/a (displacements per atom). The threshold dose of irradiation with ¹³²Xe²⁷⁺ ions, at which superconductivity disappears, is determined. In comparison with the initial value, the critical current of ⁴⁰Ar⁸⁺ ions is found to increase by ≈18% in the zero magnetic field at T = 77 K. This effect can be explained by the pinning centers for Abrikosov vortices induced by relatively small ion irradiation doses. High doses of heavy ions lead to partial or complete amorphization of a superconductor, which results first in a decrease in the critical current and transition temperature and then in a total disappearance of superconductivity. X-ray diffraction is used to study the changes in the crystal structure of the YBCO(123) superconductor under ion irradiation.     

Reduction of quantum noise in optical interferometers using squeezed light

We study the photon counting noise in optical interferometers used for gravitational wave detection. In order to reduce quantum noise a squeezed vacuum state is injected into the usually unused input port. Here, we specifically investigate the so-called “dark port case,” when the beam splitter is oriented close to 90° to the incoming laser beam, such that nearly all photons go to one output port of the interferometer, and only a small fraction of photons is seen in the other port (“dark port”). For this case it had been suggested that signal amplification is possible without concurrent noise amplification [R. Barak and Y. Ben-Aryeh, J. Opt. Soc. Am. B 25, 361 (2008)]. We show that by injection of a squeezed vacuum state into the second input port, counting noise is reduced for large values of the squeezing factor, however the signal is not amplified. Signal strength only depends on the intensity of the laser beam.     

Pulsed broadly tunable room-temperature Cr2+:CdS laser

We report the spectroscopic characteristics and laser properties of Cr²⁺:CdS. The emission lifetime of the exited state, ⁵E, of Cr²⁺ in CdS host was measured to be 0.93 μs at room temperature and 7.3 μs at liquid nitrogen temperature. The measured values of peak absorption and emission cross sections were found to be 1.4×10⁻¹⁸ and 1.1×10⁻¹⁸ cm² respectively. Room-temperature pulsed-laser operation was obtained under pumping by the 1.94 μm output of a Tm:YAP laser. The output of the free-running Cr²⁺:CdS laser was centered at ∼2.6 μm, and an absorbed energy slope efficiency of 38.8% was demonstrated. The passive crystal losses were measured to be less than 0.049 cm⁻¹ at the lasing wavelength. With an intracavity prism, the Cr²⁺:CdS laser was tuned from 2.18 to 3.32 μm.