Objectives Nondestructive testing of various technical specimens and optical surfaces having cylindrical or conical profile. Principle Cylindrical symmetry of conical beams is optimal for using these beams to illuminate the various cylindrical specimens. 
Figure 1. Basic element of conical beam – based profilometry. A conical beam is produced by an axicon and illuminates the cylindrical object. The reflected beam contains the information about a surface quality and profile of the object. The interference fringes are ring-like. Advantages - Conical light beam enables one to realize the longitudinally uniform illumination at a certain angle.
- Capability of optical testing of unpolished surfaces. This geometry of illumination permits one to significantly reduce the speckle noise in the field reflected and to extract, thereby, information on the macroscopic shape of the surfaces.
- High speed shape measurements.
Novelty Originality of the scheme is the non-coincidence of the cone angles 1,2 of object and reference beams and the possibility to change the cone angle of the object beam. Thus, one controls the effective wavelength λeff = λ /sin(γ1). It is realized by using two lens L1 and L2 and a movable axicon A1. Also, the profilometer sensitivity, i.e., the minimal measurable deviation of the surface profile of workpieces from the ideal cylindrical surface, can be adjusted. 
Figure 2. Conical beam – based profilometer. BS – beamsplitter, L – lens, A – axicon. This scheme has extra possibility of tuning the longitudinal resolution. It is realized by means of axicon A2 placed between the lenses L3 and L4. Tuning enables to adapt the resolution to the typical scale of inhomogeneity of tested cylindrical workpieces. 
Figure 3. 3D-profile of a cylindrical metal rod tested by a conical beam - based profilometer. Technical characteristics Sensitivity > 100nm
Processing speed 1sec/running cm Applications Machinery, wire production, optical fibers Contact Prof. V.N. Belyi
Dr. N.A. Khilo
e-mail
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