170 research outputs found
VIDES AIZSARDZĪBAS MĀCĪBU PRAKSES LABORATORIJA TOP ZEMNIEKU SAIMNIECĪBĀ “ALEKSANDRI” (z/s A)
Laboratorija bijušās Rundānu muižas teritorijā - vietā, kurā jaunieši iepazīsies ar daudziem Latgales pakalnu, purvu vides aizsardzības un izmantošanas praktiskiem un teorētiskiem darbiem. Izmitināšana, ēdināšana, atpūta ar rundāniešu pamestības noskaņu pārvarēšanu. Iesākums krievvalodīgo zonas atdzimšanai...Laboratorijas ideju pamatā ir profesoru G.Novika, A.Ūbeļa, M.Oša u.c. koncepcijas par vidi kā antropogēnu procesu kompleksu, kopu, ieskaitot tajos etniskos un reliģiskos faktorus. Izmantotas etnoekoloģiskās “Eko - Ludzas” zinātniskās grupas atziņas. Ora et labora! - no latīņu valodas var iztulkot, ka oratoram ir jāstrādā, ka vides aizsardzībai nepieciešama trīsvienība Dievs - Daba - Darbs.Laboratorijas vieta Rundānu pagasts - vēsturē reti minēts, jo atrodas pa vidu starp Zilupi, Dagdu, Rēzekni, Ludzu, Nirzu. Z/s A izvietota Latgales augstienes ūdensšķirtnē. Vides tīrības etalons. Te savu tecējumu sāk Sarjanka - Daugavas pieteka. Rundānu strauts aiznes ūdeņus uz Veļikajas upi. Te pēdējā laikā seno latgaļu pilskalnu aizsardzības līnija
Sub-Hz line width diode lasers by stabilization to vibrationally and thermally compensated ULE Fabry-Perot cavities
We achieved a 0.5 Hz optical beat note line width with ~ 0.1 Hz/s frequency
drift at 972 nm between two external cavity diode lasers independently
stabilized to two vertically mounted Fabry-Perot (FP) reference cavities.
Vertical FP reference cavities are suspended in mid-plane such that the
influence of vertical vibrations to the mirror separation is significantly
suppressed. This makes the setup virtually immune for vertical vibrations that
are more difficult to isolate than the horizontal vibrations. To compensate for
thermal drifts the FP spacers are made from Ultra-Low-Expansion (ULE) glass
which possesses a zero linear expansion coefficient. A new design using Peltier
elements in vacuum allows operation at an optimal temperature where the
quadratic temperature expansion of the ULE could be eliminated as well. The
measured linear drift of such ULE FP cavity of 63 mHz/s was due to material
aging and the residual frequency fluctuations were less than 40 Hz during 16
hours of measurement. Some part of the temperature-caused drift is attributed
to the thermal expansion of the mirror coatings. High-frequency thermal
fluctuations that cause vibrations of the mirror surfaces limit the stability
of a well designed reference cavity. By comparing two similar laser systems we
obtain an Allan instability of 2*10-15 between 0.1 and 10 s averaging time,
which is close to the theoretical thermal noise limit.Comment: submitted to Applied Physics
Compact solid-state laser source for 1S-2S spectroscopy in atomic hydrogen
We demonstrate a novel compact solid-state laser source for high-resolution
two-photon spectroscopy of the transition in atomic hydrogen. The
source emits up to 20 mW at 243 nm and consists of a 972 nm diode laser, a
tapered amplifier, and two doubling stages. The diode laser is actively
stabilized to a high-finesse cavity. We compare the new source to the stable
486 nm dye laser used in previous experiments and record 1S-2S spectra using
both systems. With the solid-state laser system we demonstrate a resolution of
the hydrogen spectrometer of 6 \times 10^{11} which is promising for a number
of high-precision measurements in hydrogen-like systems
Frequency-modulation spectroscopy with blue diode lasers
Frequency-modulation spectroscopy provides ultrasensitive absorption measurements. The technique is especially adaptable to diode lasers, which can be modulated easily, and has been used extensively in the near-infrared and infrared spectral regions. The availability of blue diode lasers now means that the accessible wavelength region can be increased. We successfully demonstrate wavelength-modulation spectroscopy and two-tone frequency-modulation spectroscopy for the weak second resonance line of potassium at 404.8 nm and for the transition at 405.8 nm in lead, starting from the thermally populated 6p(2) P-3(2) metastable level, information on the modulation parameters is obtained with a fitting procedure. Experimental signal-to-noise ratios: at different absorption levels are compared with theoretical signal-to-noise ratios and show good agreement. Detection sensitivities of 2 x 10(-6) and 5 x 10(-6) for wavelength and two-tone frequency-modulation spectroscopy, respectively, for a 120-Hz bandwidth are demonstrated. (C) 2000 Optical Society of America
Cascade coherence transfer and magneto-optical resonances at 455 nm excitation of Cesium
We present and experimental and theoretical study of nonlinear
magneto-optical resonances observed in the fluorescence to the ground state
from the 7P_{3/2} state of cesium, which was populated directly by laser
radiation at 455 nm, and from the 6P_{1/2} and 6P_{3/2} states, which were
populated via cascade transitions that started from the 7P_{3/2} state and
passed through various intermediate states. The laser-induced fluorescence
(LIF) was observed as the magnetic field was scanned through zero. Signals were
recorded for the two orthogonal, linearly polarized components of the LIF. We
compared the measured signals with the results of calculations from a model
that was based on the optical Bloch equations and averaged over the Doppler
profile. This model was adapted from a model that had been developed for D_1
and D_2 excitation of alkali metal atoms. The calculations agree quite well
with the measurements, especially when taking into account the fact that some
experimental parameters were only estimated in the model.Comment: small changes to text of previous version; 12 pages, 8 figure
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