Abstract.A novel method for estimating the mixing height based on ceilometer measurements is described and tested against commonly used methods for determining mixing height. In this method an idealised backscatter profile is fitted to the observed backscatter profile. The mixing height is one of the idealised backscatter profile parameters.An extensive amount of ceilometer data and vertical soundings data from the Helsinki area in 2002 is utilized to test the applicability of the ceilometer for mixing height determination. The results, including 71 convective and 38 stable cases, show that in clear sky conditions the mixing heights determined from ceilometer based aerosol profiles and BL-height estimates based on sounding data are in a good agreement. Rejected outlier cases corresponded to very low aerosol concentrations in the mixed layer leading to a very weak aerosol backscatter signal in the lowest layer.

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Studies are reported on frequency drifts in extended-cavity diode lasers caused by external effects, such as changes in temperature and air pressure. A laser system operating at 780 nm has been constructed utilizing low expansion materials and such mechanical structures that compensate for the external effects. By placing the laser system in a pressure-proof and temperature-controlled housing, a relative frequency stability of better than 10−10 (40 kHz) is obtained for integration times of 10 μs to 10 s. The drift of the laser frequency caused by spectral aging of the diode laser is about 3 MHz/h. As a consequence of high passive stability, the variations of the laser intensity are also greatly reduced to a relative drift value of 4×10−5/h.

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Abstract-Effects of external optical feedback from a reflection grating on the linewidth of a GaAlAs semiconductor laser operating at 780 nm are investigated. Accurate linewidth measurements as a function of the laser frequency tuning have been performed by applying the self-homodyne technique with a short delay line. A realistic coupled-cavity model, which incorporates the frequency-dependent reflection from the grating, is used to explain the measured data. The agreement between the theoretical and experimental results was found to be good.Index Terms-External cavity laser, linewidth, self-homodyne method.