We present a deformable mirror based remote focusing method for three-dimensional imaging in high-resolution microscopy systems. The method relies on predefined mirror mode arrays that are obtained during initial mirror training step with a low complexity wavefront-sensing module. The imaging plane can be refocused over distances over a hundred times greater than the original depth of field of the objective lens along the optical axis at millisecond rates. We will demonstrate the combination of the remote focusing method with spatiotemporally focused two-photon excitation applied to three-dimensional imaging of biological samples.
A common-path interferometric profilometer using a Savart plate as a lateral shearer has been successfully tested
under harsh environmental conditions to measure the shape of a surface, detecting defects and characterizing
surface properties. The whole profile is obtained from a single image and its depth sensitivity is easily scalable,
making this technique suitable for many different applications. Although this system has been successfully used
for surface inspection and defect detection, some behaviors cannot be explained by the usual simple model for
fringe formation, which, amongst other things, considers normal incidence of the incoming rays into the Savart
plate. These deviations from the ideal case are more noticeable for high resolutions from short distances. This
paper studies the formation of the fringe pattern, which is crucial for understanding the behavior of the system
and proper calibration.
We propose a common-path two-wavelength interferometric system based on a single optical element, a Savart plate, that is able to obtain single-shot profile measurements with submicron precision from safe working distances (beyond 100 mm). These characteristics make this sensor ideal for surface inspection in on-line applications. For the illumination branch, two lasers with close wavelengths are combined and then passed through a rotating holographic diffuser for drastic speckle reduction. In the acquisition branch, the interferometric signals of both wavelengths are captured simultaneously by a camera, and their phase signals are combined to extend the measurement range.
We propose a common-path two-wavelength intereferometric system based on a single optical element, a Savart
Plate, able to obtain profile measurements at frame rate. To improve precision up to the sub-micron levels from
safe working distances (beyond 100 mm), we use a speckle reduction system based on a rotating holographic
diffuser. The interferometric signals of the two wavelengths are obtained simultaneously and their phase signals
are combined to extend the measurement range.
The system's common-path interferometry nature, and the possibility of acquiring a distance profile in a
single frame, make it ideal for surface inspection in industrial environments.
Conoscopic Holography proved to be a very adequate solution for in-situ optical measurement in industrial
inspection and quality control systems, offering high-precision with a wide range of standoff distances, while
being quite insensitive to the harsh environmental conditions often encountered in industry, as it is a common-path
technique.
With the aim of extending their applicability, we have already addressed, with good results, several issues
that improve sensors based on this technology which include: the use of phase information to obtain one-shot
profile measurements at frame rate with higher precision; new signal processing techniques; and speckle reduction
to diminish measurement errors. However, the undesirable effect of using the phase information is that it reduces
the maximum steep that can be measured without ambiguity, which becomes an issue when working with high
precisions.
In this article we present our ongoing work towards using the concepts of multiple-wavelength interferometry
to extend the measurement range, something that, to our knowledge, has not been done for this technology
before.
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