Full-field optical thickness profilometry of semitransparent thin films with transmission densitometry

Abstract

A novel bidirectional thickness profilometer based on transmission densitometry was designed to measure the localized thickness of semitransparent films on a dynamic manufacturing line. The densitometer model shows that, for materials with extinction coefficients between 0.3 and 2.9?D/mm, 100-500microm measurements can be recorded with less than +/-5% error at more than 10,000 locations in real time. As a demonstration application, the thickness profiles of 75mmx100?mm regions of polymer electrolyte membrane (PEM) were determined by converting the optical density of the sample to thickness with the Beer-Lambert law. The PEM extinction coefficient was determined to be 1.4D/mm, with an average thickness error of 4.7%.

Wetting phenomena during processing of high-viscosity shear-thinning fluid

“…The quality of the downstream coated film is inspected using an imaging system that incorporates an overhead Lumenera LM135M camera. The camera is connected by a USB 2.0 cable to a computer running a specially-designed neural network program developed in MATLAB 2008a graphical user interface [24]. In addition, the contact line and the mechanism of air-bubble generation is monitored using a SZ 6145TR Olympus microscope with 45Â optical zoom equipped with a 3.2 megapixel digital Lumenera camera.…”

3D-form metrology of arbitrary optical surfaces by absorption in fluids

“…The use of transmitted light through liquids has already been used for the optical determination of surface topography [9][10][11][12][13][14][15]. In the work of Purcell et al [9], still based on interferometry, a non-absorbing liquid is used to reduce optical path differences at steep slopes by index matching with the surface materials.…”

“…On the other hand, we find in the literature the use of optical absorption to estimate depth or thickness [10][11][12][13][14][15]. Although the Lambert-Beer law is commonly used to calculate the specific absorption of substances [10][11], it can be seen the other way around, i.e., to estimate the thickness of solid films [12], or to obtain the relative profile of a surface compared to a reference surface. In this last case, a liquid with known absorption fills the space between both elements [13][14][15].…”

Topographic optical profilometry by absorption in liquids

“…The use of transmitted light through liquids is interesting for the optical determination of surface topography [9][10][11][12][13][14][15]. In the work of Purcell et al [9] a non-absorbing liquid is used to reduce the apparent surface slope by index matching with the surface materials and therefore controlling refraction.…”

“…On the other hand, the use of optical absorption to estimate depth or thickness is not new [10][11][12][13][14][15]. Although the Lambert-Beer law is commonly used to calculate the specific absorption of substances [10,11], it can be seen the other way around, i.e., used to estimate the thickness of solid films [12], or more interesting to our goal, to obtain the relative profile of a surface compared to a reference surface when a liquid with known absorption fills the space between both elements [13][14][15]. To apply this last strategy correctly a reference optical signal is necessary.…”