A.K. Chakraborty

Frequency-response characteristics of a perfect lens masked by polarizing devices

The imaging characteristics of a perfect lens partially masked by a linear polarizer can be varied continuously either by rotating an analyzer placed at the output side or by changing the state of polarization of the input beam. In this paper we study the frequency-response characteristics and the point-spread function of such a system. It is also shown that the proposed system can be adapted either for apodization or for superresolution simply by rotating the analyzer. The fact that the unpredictable phase introduced by the mask has no harmful effect on the performance of the system makes it convenient for several applications. Expressions are obtained for the optical transfer function and the point-spread function of such a system. Some specific cases are illustrated graphically, and some probable applications are discussed.

Simulation of effects of phase and amplitude coatings on the lens aperture with polarization masks

It is well known that circular symmetric phase and amplitude coatings on the lens aperture modify the imaging qualities of a lens. The present paper shows that the effects of such phase and amplitude coatings on the imaging properties of a lens can be achieved by using suitably oriented polarization masks on the lens aperture. The fact that the response of such a system can be continuously varied by changing the orientation of the polarizing devices included in the system lends it a versatility unobtainable by the use of conventional phase and amplitude coatings on the lens aperture.

Frequency Response Characteristics of a Perfect Lens Partially Masked by a Retarder

Abstract The optical frequency response of a perfect lens partially masked by a retarder has been studied. The optical transfer function (OTF) of such a system depends upon the relative orientation of the analyser, placed at the output, relative to the slow and fast axes of the mask, and also on the relative aportioning of the lens aperture by the mask. The OTF of the system also depends upon the retardation introduced by the mask. In the present paper, we have computed the OTF of the masked lens for different values of the relevant parameters with and without the analyser at the output.

Vector Wave Imagery with a Lens Masked by Polarizers

Abstract The optical transfer function (OTF) of an imaging system using polarization devices depends in general on the state of polarization of the input beam. In fact, the ‘amplitude point spread function’ (APSF) of such a system is different for different linearly polarized components of the input beam. This implies that the APSF of a system using polarizing devices behaves as a vector quantity. The nature of the final image is determined by the relative contribution of the two components of the vector APSF. The specific imaging system considered in the present study consists of a circularly symmetric polarization mask with linear polarizers having different orientations for the central circular and annular regions of an ideal lens aperture. If the light originating from an object point is in general elliptically polarized, the OTF of such a system with an analyser at the output is seen to have three additive components, which are, in fact, the Fourier coefficients of the OTF which varies periodically w...

Extraction of Difference Using a Polarization-shifted Periodic Carrier

A method is proposed for subtracting two images using a polarization-shifted periodic carrier. The method has been successfully used to find the intensity gradient of a test object in the form of a transparency. Some experimental results are presented.

Photoelastic testing using a birefringence-sensitive interferometer

Abstract An interferometric technique for photoelastic testing of small and transparent samples is proposed. By the introduction of two properly oriented polarisers in the two arms of a Twyman-Green interferometer, it has been shown that the modified interferometer is rendered sensitive to birefringent samples placed in the path of a plane polarised parallel beam of light entering the interferometer. Since the sample is placed in the common arm, unequal phases either inherent in the sample or due to deformation under stress will not be reflected in the output. During the testing procedure, the two arms of the interferometer can be left totally undisturbed. Information on the stress distribution over the sample area can be obtained from the recorded interferometric pattern - since the recorded fringe shifts are proportional to the developed stresses. The principle of the technique is discussed and experimental results are provided.

Imaging Characteristics Of A Birefringent Lens

In the present paper we discuss the imaging qualities of a birefringent lens. The transmittance of such a lens, sandwiched between two polarizers, varies radially. The fact that the nature of this radial variation of transmittance can be controlled by changing the orientations of the two polarizers relative to the optic axis of the birefringent lens, may be utilised for continuously modifying the imaging characteristics of the lens. The study of the point spread functions (PSF) of such a polarizer-birefringent lens-polarizer combination reveals that this can be utilised both for achieving apodisation and superresolntion.

A Mixed Solc Birefringent Filter

In this article, the transmission characteristics of new mixed birefringent filter have been studied. The term ‘mixed’ is used because in this filter both linear and circular birefringence are utilized for shaping its transmission function. The filter has a so called ‘lossless core’, consisting of alternate rotators and retarders, and two linear polarisers at the two ends. Because of the similarity of the proposed mixed birefringent filter with the fan type Solc filter, it has been given the name ‘Mixed Solc Birefringent Filter’ (MSBF).

A Single Element Birefringence-Sensitive Interferometer

It is shown that a cube beam splitter can serve as a single-element birefringence-sensitive interferometer. The polarization-masked beam splitter is oriented as in Gate’s Interferometer i.e., the beam splitting interface is parallel to the incident plane beam. The output consists of a pair of collinearly propagating orthogonally polarized beams which intercepts the birefringent sample placed before a linear polarizer. It is interesting to note that in the proposed method, measurement of birefringence remains unaffected by any phase non-uniformity that might be present in the sample.

A new mixed birefringent filter

Abstract Birefringent filters can be used for tuning lasers, with some advantages over prisms, gratings and tilted etalons. In this paper the transmission characteristics of a new mixed birefringent filter are investigated. The term ‘mixed’ is used because both circular birefringence and linear birefringence have been utilized in the fabrication of this filter. It has a loss-less core, formed by a cascaded system of alternate rotators and retarders, and a linear polarizer at each end. The performance of this filter is better because of the more effective suppression of side peaks. Unlike previous birefringent filters, this one may be used inside a linear resonator.