Probing depth enhancements of spectral domain optical coherence tomography using axicons for the inspection of additively manufactured polymer parts

In the past decade, advances in optical coherence tomography (OCT) have diversified its application beyond its origins in imaging applications for the life sciences. The non-destructive nature of OCT along with its subsurface imaging capability makes it a promising tool for many industrial applications, from dimensional measurement to the inspection and characterization of materials. One such application area is in the production of additively manufactured polymer parts where OCT can provide both qualitative and quantitative feedback relating to component specification and quality. Nonetheless, one major limitation of OCT is its limited depth of focus when conventional objective lenses are used. To overcome this limitation, we used an axicon lens to achieve longer depth of focus without any degradation in the resolution. This will also simplify the measurement process and speeds up the acquisition which is very beneficial in high throughput manufacturing scenarios. We demonstrate the superior performance of axicon lens by imaging dispersed set of particles in an optical phantom, clearly showing the axicon maintaining lateral resolution over a significant depth, compared with the use of a conventional OCT. We further demonstrate the suitability of this approach for use in manufacturing applications by presenting the results of a measurement of a 3D printed microfluidic device, validated against commercial X-ray computed tomography (XCT).