Cross-talk between different modes has always been an intrinsic issue of a modal wavefront sensor. Efforts have been put to reduce the effect of these inter-modal cross-talk either by varying the detector aperture or by changing the mode of intensity measurement at the detector. Since the modal wavefront sensor considers the incident wavefront as a linear combination of some orthogonal basis set, say the Zernike polynomials, the presence of cross-talk between the different modes of these basis set greatly affects the sensor output. As a result the measure of the modal content of the various orthogonal modes in the incident wavefront are affected, leading to inaccuracy in measurements. In this work we present a new method of measurement of the orthogonal modes present in an incident wavefront. The proposed method can be considered as a modified version of the modal wavefront sensing technique proposed by Neil et al, having advantages in terms of cross-talk reduction between modes and linearity enhancement, in the process of measurement of various orthogonal modes present in the incident wavefront. In this paper we also present some of our simulation results in support of our proposed sensing technique.
A modal wavefront sensor is known for its quick detection, flexibility and simplicity in the measurement of the various aberration modes (in the form of an orthogonal basis set such as the Zernike modes) present in the wavefront of an incident beam. But the output of these type of sensor suffers from inter-modal crosstalk that may arise due to the coexistence of a large number of aberration modes in the incident beam. This leads to degradation of the quality of the sensor output, resulting in inaccuracy in the measurement of aberration modes. Booth et al. provided an optimized expression of the sensor output that reduced the inter-modal cross-talk and improved the linear response of the sensor to a great extent. However, the issue of cross-talk still persists and the sensor for a particular mode is still vulnerable to the presence of other modes. In the present work, we present an analytical study of the influence of inter-modal cross-talk on the output of a holographic modal wavefront sensor for various aberration modes. Theoretical, simulation and experimental results are presented for better visualization of the cross-talk effect.
Liquid Crystal Spatial Light Modulators (LCSLM) are of great importance in various scientific applications such as adaptive optics, optical microscopy, optical trapping etc., due to their capability to dynamically reconfigure the amplitude, phase and polarization profiles of the incoming beam. Here LCSLMs are basically used to display computer generated holograms which give rise to diffraction orders. Recently we have observed that the fluctuations in both the diffracted and undiffracted beam, which may cause great disturbances in the applications, have a close relationship with the power on-off instants of the LCSLM. Thus there exists some link between the heat dissipation from the LCSLM panel and the beam fluctuations. In this paper we provide a detailed investigation on the cause and nature of the beam fluctuations in the LCSLM.