Use of a field lens for improving the overlap function of a lidar system employing an optical fiber in the receiver assembly.

This paper presents a method to compute the overlap function of a lidar system in which a step-index optical fiber (or a bundle of such fibers) is used to carry the light collected by the telescope to the photoreceiver and a field lens is placed between the telescope and the optical fiber to increase the receiver field of view (FOV). The use of field lenses is a classical way to increase the FOV of radiometric systems (such as the receiving part of a lidar) when there is no numerical aperture (NA) limitation after the lens. However, when such a limitation exists, as in the case studied here, it will place a limit on the maximum attainable FOV. In the case of lidars, which have range-resolution capabilities, the limited FOV has an effect on the fraction of power coming from scattering volumes at different ranges that actually reaches the photodetector. This fraction is a function (the so-called overlap function) of the range of the scattering volume and its behavior has an impact on the accuracy of the retrievals. The application of the method developed in this paper shows that, in spite of the fiber NA limit, in practical situations the goal is attained of making the overlap function steeper and reaching higher values by using a field lens.

[1]  A. Ansmann,et al.  Independent measurement of extinction and backscatter profiles in cirrus clouds by using a combined Raman elastic-backscatter lidar. , 1992, Applied optics.

[2]  K. Sassen,et al.  Lidar crossover function and misalignment effects. , 1982, Applied optics.

[3]  A. Papayannis,et al.  Analysis of the receiver response for a noncoaxial lidar system with fiber-optic output. , 2002, Applied optics.

[4]  J R Jenness,et al.  Design of a lidar receiver with fiber-optic output. , 1997, Applied optics.

[5]  Y Sasano,et al.  Geometrical form factor in the laser radar equation: an experimental determination. , 1979, Applied optics.

[6]  Empfangsleistung in Abhängigkeit von der Zielentfernung bei optischen Kurzstrecken-Radargeräten. , 1974, Applied optics.

[7]  J Harms,et al.  Lidar return signals for coaxial and noncoaxial systems with central obstruction. , 1979, Applied optics.

[8]  Shunxing Hu,et al.  Geometrical form factor determination with Raman backscattering signals. , 2005, Optics letters.

[9]  A. Ansmann,et al.  Experimental determination of the lidar overlap profile with Raman lidar. , 2002, Applied optics.

[10]  David D. Turner,et al.  Full-Time, Eye-Safe Cloud and Aerosol Lidar Observation at Atmospheric Radiation Measurement Program Sites: Instruments and Data Analysis , 2013 .

[11]  W Lahmann,et al.  Geometrical compression of lidar return signals. , 1978, Applied optics.

[12]  J. Langerholc,et al.  Geometrical form factors for the lidar function. , 1978, Applied optics.

[13]  F. Marenco,et al.  A lidar for water vapour measurements in daytime at Lampedusa, Italy , 2003 .

[14]  Herwig Kogelnik,et al.  Laser beams and resonators , 1966 .

[15]  Volker Freudenthaler,et al.  The telecover test: A quality assurance tool for the optical part of a lidar system , 2008 .

[16]  Adolfo Comeron,et al.  Spatial filtering efficiency of monostatic biaxial lidar: analysis and applications. , 2002, Applied optics.