We describe a new two‐frequency lidar for measuring Na temperature profiles that uses a stabilized cw single‐mode dye laser oscillator (rms frequency jitter < 1 MHz) followed by a pulsed‐dye power amplifier (140 MHz FWHM linewidth) which is pumped by an injection‐locked Nd: YAG laser. The laser oscillator is tuned to the two operating frequencies by observing the Doppler‐free structure of the Na D2 fluorescence spectrum in a vapor cell. The lidar technique and our initial observations of the temperature profile between 82 and 102 km at Ft. Collins, CO (40.6°N,105°W) are described. Absolute temperature accuracies at the Na layer peak of better than ±3 K with a vertical resolution of 1 km and an integration period of approximately 5 min were achieved.
In this work, sensitivity to strain and temperature of a sensor relying on modal interferometry in hollow-core photonic crystal fibers is studied. The sensing structure is simply a piece of hollow-core fiber connected in both ends to standard single mode fiber. An interference pattern that is associated to the interference of light that propagates in the hollow core fundamental mode with light that propagates in other modes is observed. The phase of this interference pattern changes with the measurand interaction, which is the basis for considering this structure for sensing. The phase recovery is performed using a white light interferometric technique. Resolutions of +/- 1.4 microepsilon and +/- 0.2 degrees C were achieved for strain and temperature, respectively. It was also found that the fiber structure is not sensitive to curvature.
The principle and practice of narrow-band light detection and ranging (lidar) for temperature measurements are discussed, with emphasis on a new two-frequency technique for measuring mesospheric Na temperature and density profiles. The uniqueness of this narrow-band lidar lies in the transmitter whose line-shape function can be measured directly. The frequency of the laser output can be monitored simultaneously during data acquisition with Doppler-free fluorescence spectroscopy by using a laboratory Na cell. These measurement techniques along with the procedures for data analysis are described in detail. At present the absolute temperature accuracy at the Na layer peak is +/-3 K (+/-4 K) with a vertical resolution of 1 km and an integration period of 5 min (2.5 min). Potential applications and furtherimprovements in this lidar technique are also discussed.
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