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Optical coherence tomography for process control of laser micromachining
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Image of FIG. 1.
FIG. 1.

High resolution Schwarzschild configuration of the -laser optical processing system with OCT add on.

Image of FIG. 2.
FIG. 2.

(a) Configuration and (b) photographic views of the customized Michelson interferometer at the backside of the sample alignment system.

Image of FIG. 3.
FIG. 3.

SEM image of line grating at the end face of a multimode optical fiber.

Image of FIG. 4.
FIG. 4.

(a) Surface image of the fiber end face (cf. Fig. 3) showing an area of . Thin white line indicates where the B-scan was obtained. (b) In this image, the scan area was reduced to consisting of A-scans. In both images, the damaged area is clearly visible. (c) B-scans show the different ablation depth for the coating (left), cladding (middle) and the fused silica core (right), separated by the dotted lines.

Image of FIG. 5.
FIG. 5.

Three step manufacturing of a simple “stepped pyramid.” Between each step the sample was released from its holder and the microscopic image was taken. After realignment, the next step was applied. This example shows the reliability of the OCT alignment capabilities. After the ablation, the measured depth via A-scan in the middle of the structure was (a) , (b) , (c) .

Image of FIG. 6.
FIG. 6.

Comparison between reflected-light microscope and surface OCT images. (a) 500× magnification of the microstructure and (b) matchable OCT presentation with A-scans. The debris around the structure is resolved in both images. Furthermore the OCT image contains grayscale encoded height information. By increasing the magnification to 1000× (c) and reducing the scan area from to (d) the roughness of the surface becomes visible.

Image of FIG. 7.
FIG. 7.

Surface OCT images of the phase mask with the size of (a) and (b). Defect (circle) smaller than can be also seen in the upper right of (b). Both images consist of A-scans. For comparison images were also taken with a reflected-light microscope (c) and a SEM (d).

Image of FIG. 8.
FIG. 8.

Parabolic fit to the OCT data for two different surface points of the phase mask (red dots and blue diamonds). (a) Overview of the parabolic fit to the found OCT peak. (b) Enlargement of the peak to show the different position of the two vertexes. The difference of these two points is step height of two pixel structures.


Generic image for table
Table I.

Comparison of depth measurements by OCT and a commercial confocal microscope.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Optical coherence tomography for process control of laser micromachining