arXiv subjects

M. B. Roopashree

Publications and source records attributed to M. B. Roopashree.

4 recordsLinked to original sources

arXiv2010

Extrapolating Zernike Moments to Predict Future Optical Wave-fronts in Adaptive Optics Using Real Time Data Mining

We present the details of predicting atmospheric turbulence by mining Zernike moment data obtained from simulations as well as experiments. Temporally correlated optical wave-fronts were simulated such that they followed Kolmogorov phase statistics. The wave-fronts reconstructed either by modal or zonal methods can be represented in terms of Zernike moments. The servo lag error in adaptive optics is minimized by predicting Zernike moments in the near future by using the data from the immediate past. It is shown statistically that the prediction accuracy depends on the number of past phase screens used for prediction and servo lag time scales. The algorithm is optimized in terms of these parameters for real time and efficient operation of the adaptive optics system. On an average, we report more than 3% improvement in the wave-front compensation after prediction. This analysis helps in optimizing the design parameters for sensing and correction in closed loop adaptive optics systems.

astro-ph.IM↗

arXiv2010

Performance of centroiding algorithms at low light level conditions in adaptive optics

The performance metrics of different centroiding algorithms at low light level conditions were optimized in the case of a Shack Hartmann Sensor (SHS) for efficient performance of the adaptive optics system. For short exposures and low photon flux, the Hartmann spot does not have a Gaussian shape due to the photon noise which follows Poissonian statistics. The centroiding estimation error was calculated at different photon levels in the case of changing spot size and shift in the spot using Monte Carlo simulations. This analysis also proves to be helpful in optimizing the SHS specifications at low light levels.

astro-ph.IM↗

arXiv2009

Effective coherence length estimation of optical wavefronts

In adaptive optics, the measurement of spatial coherence length helps in deciding the optimum design parameters of a Shack Hartmann Sensor (SHS). Two methods of estimating the spatial coherence length of optical wavefronts are presented. The first method is based on counting the number of Hough peaks in the wavefront. The second method is based on a simple data mining technique applied on the wavefronts. Optical wavefronts with different properties are simulated and used for statistical analysis. A comparison of the performance of the two methods is presented using Monte Carlo simulations. It is shown that both these methods can become efficient tools in estimating the effective coherence length of optical wavefronts.

astro-ph.IM↗

arXiv2009

Spatial Light Modulator for wavefront correction

We present a liquid crystal method of correcting the phase of an aberrated wavefront using a spatial light modulator. A simple and efficient lab model has been demonstrated for wavefront correction. The crux of a wavefront correcting system in an adaptive optics system lies in the speed and the image quality that can be achieved. The speeds and the accuracy of wavefront representation using Zernike polynomials have been presented using a very fast method of computation.

astro-ph.IM↗