An improvement of an optical method for in situ measurement of the intrinsic stress in thin films is described. The method presented is based on the well-known beam bending technique using the deflection of a laser beam that reflects itself on a sample. The first new development lies in the evaluation of the bending plate equation. The second uses image processing to determine the deformation of the sample. The method has been applied to pure chromium films on glass substrates to validate the stress measurements. The reproducibility of stress measurement is of about 8%. Results show the great adaptability of the technique to any kind of stress evolution during the physical vapor deposition process and give additional information about the evolution of stress versus film thickness, in comparison with ex situ techniques. Finally, a correlation between stress measurement and microstructure has been carried out.
An improvement of methods for estimating the rotational temperature from the partially resolved 391.44 nm emission band of N2
+
(B 2
u
+
- X 2
g
+
) has been developed by numerically studying this band as a function both of the temperature and of the instrumental function of the detection system. We give a simple tabulation for which one can obtain, without calculation, the rotational temperature in the range 300-900 K from measurements of the band profile considered and the experimental function. The accuracy of the temperature evaluation is better than to within 10%. The approach is validated in the range 340 - 410 K, using measurements of the 391.44 nm band in a pure N2
dc magnetron discharge.
This paper describes a control system developed for acquisition of sequences of multi-exposed images, the goal being acquisition of quantitative information from flow visualizations obtained by laser tomography. The basic equipment consist of a camera equipped with a light intensifier and an electronic shutter. The video signal of the camera is digitized by an IBM personal-computer-compatible frame-grabber. The control system is designed to synchronize the activity of the different equipments of the process: camera, shutter, frame-grabber and flow generator. Different parameters can be defined: number of images to be acquired, number of expositions, each exposure and shut-down time, delay between flow generation and image acquisition. These process parameters are transmitted through a serial line by a program developed in the Windows environment. For one frame, exposure and shut-down times can be defined with a precision of 1 mu s. These different times are generated by a sequencer obtained with programmable logical devices. The system is not specific to fluid mechanics; it can be used for quite a lot of problems that show rapid changes.
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