The spatial resolution of a conventional imaging laser radar system is constrained by the diffraction limit of the telescope’s aperture. We investigate a technique known as synthetic-aperture imaging laser radar (SAIL), which employs aperture synthesis with coherent laser radar to overcome the diffraction limit and achieve fine-resolution, long-range, two-dimensional imaging with modest aperture diameters. We detail our laboratory-scale SAIL testbed, digital signal-processing techniques, and image results. In particular, we report what we believe to be the first optical synthetic-aperture image of a fixed, diffusely scattering target with a moving aperture. A number of fine-resolution, well-focused SAIL images are shown, including both retroreflecting and diffuse scattering targets, with a comparison of resolution between real-aperture imaging and synthetic-aperture imaging. A general digital signal-processing solution to the laser waveform instability problem is described and demonstrated, involving both new algorithms and hardware elements. These algorithms are primarily data driven, without a priori knowledge of waveform and sensor position, representing a crucial step in developing a robust imaging system.

Optical apertures

In the past, we have used Quelltech solutions for flatness measurement in a wide variety of projects. Here you can find a small excerpt of these projects:

In laser scanning, the optical measurement method used by QuellTech, a surface is continuously scanned with a laser line. The diffuse reflections of the laser line are recorded by a sensor. From the profile data recorded in this way, a computer can record a 3D point cloud of a scanned surface. Laser scanning as an optical measuring method is therefore particularly well suited for checking the surface flatness of starting material, profiles, rails and strip material.

Laser apertureprojector

Steven M. Beck, Joseph R. Buck, Walter F. Buell, Richard P. Dickinson, David A. Kozlowski, Nicholas J. Marechal, and Timothy J. Wright

Optical chromatic confocal metrology uses the effect of different refraction of different wavelengths in glass. Measurements with white light and laser interferometry uses the scattering behavior of reflected light to determine a surface structure.

Irisaperture

The tactile scanning step method, on the other hand, performs the flatness measurement with the aid of a contacting measuring head. This measurement is very well suited for very small measuring distances where maximum precision is required. Since the probe head usually has a spherical shape with a certain diameter, it cannot plunge into any small valley of a few µm.

In the real world, flatnesses of a few nanometers can be achieved, e.g. for highly polished flat glass surfaces. For metallic measuring objects, which are manufactured in large quantities using the usual production methods, flatness tolerances of a few µm to a few tenths of a mm are common.

Steven M. Beck, Joseph R. Buck, Walter F. Buell, Richard P. Dickinson, David A. Kozlowski, Nicholas J. Marechal, and Timothy J. Wright

NewportAperture

We would like to help you evaluate your specific measurement task. By performing an initial free test measurement of your application, we can make an early assessment of feasibility.

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LenoxlaserOrifice

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QuellTech uses the laser scanning measurement method. Laser profiles with up to 4096 points per profile are recorded. Accuracies of up to 1-2 µm can be achieved.

When measuring a flatness by the tactile 3-D coordinate measuring method, it is necessary that a tactile contact of the surface with a measuring head is required.

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Flatness is the difference between the highest and lowest points of a surface located between two ideal flat (planar) surfaces. The distance between the two planar surfaces defines the flatness tolerance.

AdjustableAperture

Laser Aperturemachine

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The QuellTech Q6 Laser Scanner product series has a proven track record in demanding industrial applications that require high levels of precision, process stability and high travel speeds.

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Measuring the flatness of surfaces is of great importance in various applications. Some examples are the testing of sealing surfaces between two bodies, such as the cylinder head gasket in automobiles. Measuring flatness is also an important factor in the production of preliminary products in the metal industry, such as the production of axis guides for measuring systems, or in the production of wafers in the semiconductor industry.

Numericalaperture

The QuellTech Q5 laser scanner series combines advantages of small form factors with high resolution and fast scan rate. The Q5 is suitable for measurement applications with limited space and rugged environmental requirements.

If you have any questions about flatness measurement or would like advice from QuellTech on this topic, we would be happy to help.

In contrast to tactile measuring methods, it is possible to record several million measuring points in a few seconds on an area of e.g. 50 x 100 mm: Flatness measurement in highest precision. This high number of measuring points enables a precise and complete recording of the flatness in a short time. The advantage over tactile measurement is that a laser light can penetrate the smallest surface structures.

Zhiwei Sun, Peipei Hou, Ya’nan Zhi, Jianfeng Sun, Yu Zhou, Qian Xu, Zhiyong Lu, and Liren Liu Appl. Opt. 53(9) 1846-1855 (2014)

The spatial resolution of a conventional imaging laser radar system is constrained by the diffraction limit of the telescope’s aperture. We investigate a technique known as synthetic-aperture imaging laser radar (SAIL), which employs aperture synthesis with coherent laser radar to overcome the diffraction limit and achieve fine-resolution, long-range, two-dimensional imaging with modest aperture diameters. We detail our laboratory-scale SAIL testbed, digital signal-processing techniques, and image results. In particular, we report what we believe to be the first optical synthetic-aperture image of a fixed, diffusely scattering target with a moving aperture. A number of fine-resolution, well-focused SAIL images are shown, including both retroreflecting and diffuse scattering targets, with a comparison of resolution between real-aperture imaging and synthetic-aperture imaging. A general digital signal-processing solution to the laser waveform instability problem is described and demonstrated, involving both new algorithms and hardware elements. These algorithms are primarily data driven, without a priori knowledge of waveform and sensor position, representing a crucial step in developing a robust imaging system.

A surface is flat if it has no structures in its surface over its entire length and width. These structures can look as follows:

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Furthermore, the laser scanning method can also be used to measure coplanarity. For example, one laser scanner scans the top surface of a target and a second laser scanner simultaneously scans the same bottom surface of the target. In this way, the parallelism of these two surfaces to each other can be calculated.