An algorithm is reported for estimation and suppression of small vibration effects in image sequences. Such effects, even of sub-pixel magnitude, may critically degrade power spectrum of temporal-domain signals. The algorithm consists of the following steps: (1) We perform preliminary detection of the presence of vibration and localize its fundamental frequency by estimating and analyzing the two-dimensional signal, composed of micro-displacements caused by vibrations; (2) We approximate this two-dimensional signal by a two-dimensional periodic function, treating it basically the same way as periodic signals. This model depends on a small number of coefficients. These coefficients are determined by direct LS fitting of the data. (3) We eliminate the effects of the vibration using this model function, for each pixel separately. With this algorithm, several image sequences were processed. The vibration image motions were reconstructed with sub-pixel accuracy and were not, usually, reducible to one-dimensional sinusoidal motion. The algorithm appears to be useful for improving detection of periodic signals
in image sequences and reducing false alarms. This article continues our work on detection of periodic signals in image sequences.
Parametric studies of the gain and the power of a small scale supersonic chemical oxygen- iodine laser are presented. The laser is of 5 cm long active medium, and utilizes a simple sparger-type O2(1(Delta) ) chemical generator and a medium size pumping system. A grid nozzle is used for iodine injection and supersonic expansion. 45 W of CW laser emission at 1315 nm are obtained in the present experiments. The small size and the simple structure of the laser system and its stable operation for long periods make it a convenient tool for studying parameters important for high power supersonic iodine lasers and for comparison to model calculations. The gain and the lasing power are studied as a function of the molar flow rates of the various reagents, and conditions are found for optimal operation. Good agreement is found between the experimental results and calculations based on a simple 1D semi-empirical model, previously developed in our laboratory and modified in the present work. The model is used to predict optimal values for parameters affecting the laser performance that are difficult to examine in the present experimental system.
A simple, one-dimensional leak flow tube model was used to calculate the effect of mixing on the performance of chemical oxygen-iodine lasers (COIL). Both the maximum gain and the characteristic length of the iodine dissociation are shown to be nonmonotonic functions of the iodine flow rate, nI2. The maximum nI2 for which lasing is possible is less than 1 - 2% of the oxygen flow rate. This is in agreement with experimental data and is not explained by models assuming premixed flows. The present model was applied to calculations of the performance of supersonic COILs.
Experiments in a bubble column type reactor in a chemical oxygen-iodine laser system applying high flow rates of chlorine mixed with buffer gas have been carried out. A model which accounts for the physical processes in this system is presented. It is shown that the model can describe our system as well as other systems where buffer gas was not used.