Laser-based inspection of trivalent chromium conversion coatings on rough, cold-rolled aluminium substrates is studied from a basic physics perspective by means of angle and wavelength dependent measurements. As a result, we show that the correlation between the scattered laser light and the coating weight of the conversion layer is dominated by the phenomenon of interference. The combined experimental and numerical approach of our study is based on an appropriate layer model which was developed from a set of reference measurements of confocal microscopy, electron microscopy and X-ray photoelectron spectroscopy. The aluminium alloy AA3003 with a trivalent chromium conversion coating serves as an example. Our derived model is capable to reconstruct the reflectance of a laser beam at grazing incidence even for a pronounced surface roughness of R q ≈ 300   n m , for different coating thicknesses less than 70 n m corresponding to coating weights between zero and 0.5 g / m 2 and for laser wavelengths from 405 n m to 785 n m . In our discussion we outline the possibility to transfer the results to other aluminium alloys and/or other metallic substrates, as well as their potential for industrial applications such as 100% inline-capability, costs, velocity and ruggedness.

Optical breadboards are generally constructed in a sandwich-like plate structure: Comparatively thin upper and lower metal plates are bonded to a central honeycomb structure, so that a particularly high mechanical stability and a minimum of bending is achieved at the same time as low weight [1]. Structural dampers are mounted in the honeycomb structure to secure vibration damping. The top surface has a plurality of tapped holes for mounting equipment, that are sealed to avoid contamination of the breadboard core [2][3][4]. The entire construction is framed with bordering side elements. Some of them are used to increase the board stability against shear forces [5] or for damping treatment [6].The optical breadboard can be combined with legs containing pneumatic vibration isolators. These act as mechanical lowpass filters reducing the transmission of vibrations from the floor to the tabletop. From a fundamental viewpoint, the system properties can be described with the vibration theory for damped harmonic oscillation of a pendulum (horizontal vibrations) and of a spring (vertical vibrations) [7][8][9]. Historically, granite slabs on industrial springs that obey a low resonance frequency in the sub-5-Hz regime have been used as optical support. Thus, the stability of optical setups against a spectrum of acoustic and mechanical frequencies is secured, typically ranging from 10 to 1.000 Hz. While granite tables provide the flatness and rigidity required, their great weight and the difficulty of attaching components to the surfaces make them cumbersome to use. Still, these constructions are preferred for specific setups with extreme requirements to stiffness [10].Heavy sandboxes, decoupled from the environment by air hoses, were an interesting alternative to granite slabs for many years. These constructions have become widespread, especially in the field of holography [11] and allow the simple positioning of optical components and objects in the sand volume [12]. Because they are easy to assemble/disassemble as well as inexpensive, sandboxes can be seen as the origin of do-it-yourself (DIY) constructions for optical breadboards and tables. Further DIY-approaches combine thin, low-weight granite slabs in sandboxes. But there are also several 'cheap & easy'examples that combine a thin plate of aluminum or wood with foam materials or rubber (see e.g. reference [13]). Here, the combination of several stiff materials with different speeds of sound produces a breadboard for which a wide range of vibrations are critically damped, also referred to as composite breadboards, commercially available nowadays [14]. In recent years, 3D-printing technology entered the field of DIY-production of optical baseplates [15][16][17]. Also, the combination of 3D-printed optical elements mounted on a solid rail system [18] was proposed, according to the original invention of optical benches of A. Weinhold [19]. Other examples focus on open cage structures [20,21] according to the LINOS microbench concept [22] that, however, dispenses with the...

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We present a modular optical honeycomb breadboard based on 3D-printed building bricks and industrial aluminum extrusions for agile prototyping of (laser based) optical assemblies in many engineering processes outside the laboratory environment.