A pulsed Er:YAG laser with resonant in-band diode pumping was demonstrated. Laser pulses with 6.6 mJ energy and 50 ns pulse duration were generated. With an intra-cavity etalon a broad wavelength tuning range from 1643.47 to 1646.78 nm was obtained. A stable dual-wavelength operation was observed by fine tuning of the etalons. The separation of the two wavelengths was 0.78 nm. One of them was located within a methane absorption line and the other was off the line. The frequency stability of the narrow linewidth Er:YAG laser was less than 40 MHz. It is a very compact laser source for methane differential absorption lidar.
We report on the development of compact and frequency-stable Er:YAG laser systems emitting in the eye-safe spectral region. Resonant cw diode pumping provides 4.5 W output power in cw operation and 2.2 mJ in Q-switched operation with pulse duration of about 140 ns. The application of intra-cavity etalons allows for wavelength tuning from 1645.22 to 1646.33 nm while the frequency stability accounts for less than 50 MHz. The potential of the erbium laser sources in terms of methane detection was evaluated under laboratory conditions by absorption measurements employing a multi-pass absorption cell. The experimental investigations were accompanied by theoretical studies on the influence of pressure broadening on the absorption behavior of methane.
The northern waters of the South China Sea are rich in natural gas hydrate resources. The source of gas is a crucial factor controlling the formation of natural gas hydrates. Gas sources that form natural gas hydrates can be related to three categories: pyrolysis genesis, biological genesis, and inorganic genesis. A series of large- and medium-sized Mesozoic and Cenozoic sedimentary basins have developed in the northern South China Sea. These basins are rich in organic matter and there are multiple sets of source rocks buried deeply, which are the main gas sources for hydrate accumulation. The Chaoshan Depression is the largest Mesozoic residual depression in the northern South China Sea. Analysis of geochemical and geological samples show that there is a significant oil and gas leakage activity on the seabed. Seismic data and drilling confirmed the existence of natural gas hydrates in Chaoshan Depression. The natural gas hydrate accumulation pattern of Chaoshan Depression is a leak- type accumulation, which has the characteristics of unique structure, abundant Mesozoic gas source, and development of faulting system.
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