Electromagnetically induced transparency (EIT) is observed in a three-level multi-V-type system in cesium vapor at room temperature. The absorption and dispersion properties are measured under the condition that the coupling frequency is exactly resonance with transition 6S<sub>1/2</sub>(F=4) to 6P<sub>3/2</sub>(F'=3) while the probe frequency is scanned across the transitions from the 6S<sub>1/2</sub>(F=4) to all structures of the 6P<sub>3/2</sub>. The effects of the intensity of the pumping beam on EIT signal are investigated. The simple theory model was presented and the results of the experiment
agree with the simple theoretical analysis.
A cost-effective multiplexing fiber-optic remote monitoring system, which laboratory prototype, has been demonstrated. This monitoring system will help personnel to measure a spatial distribution of methane or other gases in a wide area. And the fundamentals of the remote detection are based on Frequency-Modulation Spectroscopy (FMS) technique and harmonic detection technique. By utilizing fiber-optic splitter, a component of telecommunications industry, the remote monitoring system is feasible employing single laser source to get multicenter measurement in the near infrared region. The system described here performs sufficient sensibility, considerably increased reliability and marketability over the presently available system. It results in a large potential for applying extensively to various strategic points within the environment, such as solid-waste landfill sites and mines as well as urban and residential areas and otherwise.
A systematic investigation is carried out on the optimization of diffraction efficiency (DE) of only methylene blue sensitized gelatin (MBG) holograms. The influence of the following factors on DE are studied: the concentration of methylene blue (Cm), the concentration of ammonium dichromate solution (Ca), swelling temperature (Ts), exposure (E) and the relative humidity of air (RH). This study shows that under the condition of Cm-0.009%; Ca- 5%; Ts within 35 - 45 degree(s)C; E-150 mJ/cm<SUP>2</SUP>; RH within 45 - 65%, an optimum DE of over 80%, even 90% can be achieved in MBG holograms. In our experiments we find that a moderate DE(35%) is obtained without dichromate solution in post- processing. In order to know the role which the condition of bathing the plate in a dichromate solution plays and the photo-chemical mechanism of forming the interference pattern in the films, the X-ray spectra are made, the Cr<SUP>3+</SUP> ligands are not found; this means that the quantity of Cr<SUP>3+</SUP> ligands is too small to measure, even if its is existing in the processed film. These results can not be interpreted with the normal photo-chemical mechanism of forming the holograms.