Primary aberration contribution to incoherent backscatter heterodyne lidar returns

Abstract

The optics of a coherent lidar system using incoherent backscatter is modeled in a way that allows results of the wave theory of aberrations to be applied directly. Parametric plots are obtained showing the aberration and range dependence of the effective antenna area using truncated Gaussian beams. The Rayleigh criterion is an adequate guide to the optical tolerances required for the far-field return, and in the near field returns are not necessarily degraded by aberrations. Examples are given for the range weighting of returns for various primary mirror configurations.

Investigation of spherical aberration effects on coherent lidar performance

“…From the previous theoretical treatments [8] we know that for a fixed ρ the weighting function will suffer from both peak shift and broadening effects under the influence of SA. Recalling Eq.…”

“…Due to the circular symmetry, the field on the target plane can be calculated numerically by a simple Fourier-Bessel transformation of Eq. (1) with an appropriate field curvature [8]. …”

“…In practice, most lidar designs involve lens selection for the telescope or optical transceiver, which predominantly suffers from SA due to the difficulty in manufacturing lenses with SA-corrected surfaces especially for larger aperture sizes with short focal lengths. Furthermore, Rye showed numerically [8] that for equal degrees of coma, SA and astigmatism, the SA is found as the dominant contributor to the lidar signal reduction. In this work the impact of the SA is measured by probing the lidar weighting function of the system with a rotating belt as the hard target using a 1550 nm CW beam output as shown in the schematic layout in Fig.…”

“…However, those are all theoretical treatments and focus mainly on diffraction limited system designs. A previous theoretical analysis did include the aberration effects [8], but only for a fixed degree of beam truncation at the exit aperture that is optimal for an aberration-free system. This work is dedicated to investigating the weighting function change under the influence of SA to provide an experimental counterpart of the theory proposed by Rye [8], and we will expand the analysis to include optimization of the beam truncation in the presence of SA.…”

“…A previous theoretical analysis did include the aberration effects [8], but only for a fixed degree of beam truncation at the exit aperture that is optimal for an aberration-free system. This work is dedicated to investigating the weighting function change under the influence of SA to provide an experimental counterpart of the theory proposed by Rye [8], and we will expand the analysis to include optimization of the beam truncation in the presence of SA. In practice, most lidar designs involve lens selection for the telescope or optical transceiver, which predominantly suffers from SA due to the difficulty in manufacturing lenses with SA-corrected surfaces especially for larger aperture sizes with short focal lengths.…”