In this work we investigate the performance of a monostatic coherent lidar system in which the transmit beam is under the influence of primary phase aberrations: spherical aberration (SA) and astigmatism. The experimental investigation is realized by probing the spatial weighting function of the lidar system using different optical transceiver configurations. A rotating belt is used as a hard target. Our study shows that the lidar weighting function suffers from both spatial broadening and shift in peak position in the presence of aberration. It is to our knowledge the first experimental demonstration of these tendencies. Furthermore, our numerical and experimental results show good agreement.
We also demonstrate how the truncation of the transmit beam affects the system performance. It is both
experimentally and numerically proven that aberration effects have profound impact on the antenna effciency, the optimum truncation of the transmit beam and the spatial sensitivity of a CW coherent lidar system. Under strong degree of aberration, the spatial confinement is significantly degraded. However for SA, the degradation of the spatial confinement can be reduced by tuning the truncation of the transmit beam, which results from the novel finding in this work, namely, that the optimum truncation ratio depends on the degree of SA.
We consider the dynamical properties of speckles observed through a second static diffuser arising from a linear or
angularly displaced first diffuser. Analytical expressions are obtained for general situations where both the space
between the displaced and the static diffuser and the space between the static diffuser and the plane of observation
consist of an optical system that can be characterized by a complex-valued ABCD-matrix (e.g. simple and complex
imaging systems, free space propagation in both the near- and far-field, and Fourier transform systems). The use of the
complex ABCD-method means that diffraction due to inherent apertures is included. One of the diffusers is assumed to
give rise to fully developed speckle, i.e. the scattered phase is assumed to be delta-correlated, whereas the second and
dynamic diffuser has a finite lateral scale. The illumination of the displaced diffuser is assumed to be Gaussian but the
derived expressions are not restricted to a plane incident beam. The results are applicable for speckle-based systems for
determining mechanical displacements, especially for long-range systems, and for analyzing systems for measuring
biological activity beyond a diffuse layer, e.g. blood flow measurements through human skin.
The possibility to "dress up" the speckles and thereby providing them with a fine structure will be discussed. As these
speckles arise from scattering off solid targets, the dynamics of the speckles and their inherent fine structure might vary,
providing information on different aspects of the surface displacement. This is achieved by illuminating the object with
structured light, and observing the speckle field as it passes an optical system. In this way, simultaneous measurement of
displacement (e.g. 2-D) and rotation can be performed. The application of this concept with a system based on spatial
filtering velocimetry and ordinary speckle correlation will be discussed.
The trend in human-machine interface technology is heading towards optical solutions for tracking and
movement detection. Especially, interactive touch screens and pads, in which the movement of the user's
fingertips is detected and tracked, are of great commercial interest. The applications range from mobile phones
to laptops and PDA´s. However, the dynamics of scattered light from live tissue must be taken into account
when designing optical sensor systems for tracking e.g. fingertips in touch-applications. Especially, when using
coherent light sources, the statistics of the speckle-pattern originating from the scattering structure is of critical
importance for the sensor performance and has to be understood in details. We investigate theoretically and
experimentally the characteristics of the dynamics of backscattered speckle pattern generated by a human
fingertip and address the effects of an intermediate optically flat interface, between the fingertip and the
illuminating light source.
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