27 research outputs found
Spontaneous magnetostriction in the Gd-Y system: analysis of phase transformations
The transformations of magnetic and lattice subsystems states of Gd₁₀₀₋xYx (x=0, 5.5, 7.5, 10.2) alloys have been studied at temperatures 5-370 K in magnetic fields up to 4 kOe. The temperature dependences of elastic modules, thermal expansion, low field magnetization and magnetic anisotropy parameters were obtained. The linear spontaneous striction ΔL(T)/L=xh² was analized, and the effective order parameters η and magnetostrictive parameters ξ were evaluated for the four magnetic phases (canted ferromagnetic, deforming ferromagnetic helix, ferromagnetic helix, and the ferromagnetic cone, respectively): ξcf=2.2×10⁻⁵, ξdh=- 5.3×10⁻⁵, ξfh=7.1×10⁻⁵, ξfc=1.4×10⁻³
Atom focusing by far-detuned and resonant standing wave fields: Thin lens regime
The focusing of atoms interacting with both far-detuned and resonant standing
wave fields in the thin lens regime is considered. The thin lens approximation
is discussed quantitatively from a quantum perspective. Exact quantum
expressions for the Fourier components of the density (that include all
spherical aberration) are used to study the focusing numerically. The following
lens parameters and density profiles are calculated as functions of the pulsed
field area : the position of the focal plane, peak atomic density,
atomic density pattern at the focus, focal spot size, depth of focus, and
background density. The lens parameters are compared to asymptotic, analytical
results derived from a scalar diffraction theory for which spherical aberration
is small but non-negligible (). Within the diffraction theory
analytical expressions show that the focused atoms in the far detuned case have
an approximately constant background density
while the peak density behaves as , the focal distance or
time as , the focal spot size as
, and the depth of focus as .
Focusing by the resonant standing wave field leads to a new effect, a Rabi-
like oscillation of the atom density. For the far-detuned lens, chromatic
aberration is studied with the exact Fourier results. Similarly, the
degradation of the focus that results from angular divergence in beams or
thermal velocity distributions in traps is studied quantitatively with the
exact Fourier method and understood analytically using the asymptotic results.
Overall, we show that strong thin lens focusing is possible with modest laser
powers and with currently achievable atomic beam characteristics.Comment: 21 pages, 11 figure
OPTICAL TIME SCALE
The production of a time scale based on the use of an oscillation period of a highly stable laser is first reported. The new time standard allows to transfer frequency characteristics of a highly stable laser in the frequency range from 0 to 1014 Hz with no losses in accuracy. Radio-frequency oscillators were synchronized with the aid of fast-response systems of phase offset lock at division of laser frequencies
SUPERNARROW RESONANCES IN METHANE ON E-LINE OF THE P(7) TRANSITION OF THE ν3 BAND AND THEIR APPLICATION IN OPTICAL FREQUENCY STANDARDS
This paper reports on the obtaining of supernarrow resonances in methane on the E-line of the P(7) transition of the ν3 band with a relative width of about 10-11 and on the use of such resonances for frequency stabilization of a He-Ne laser at 3.39 µm. The new results are presented of investigations on production of lasers with a limiting narrow line. The prospects of the development of works on optical frequency standards are discussed