Dove prism with increased throughput for implementation in a rotational-shearing interferometer

Direct determination of 2D momentum space from 2D spatial coherence of light using a modified Michelson interferometer

Momentum space distribution of photons coming out of any light emitting material/device provides critical information about their underlying physical origin. Conventional methods of determining such properties impose specific instrumentational difficulties for probing samples kept within a low temperature cryostat. There were past studies to measure a one-dimensional coherence function, which could then be used for extracting momentum space information, as well as reports of measurements of just a two-dimensional (2D) coherence function. However, all of those are associated with additional experimental complexities. So, here we propose a simpler, modified Michelson interferometer based optical setup that is kept at room temperature and placed outside the low temperature cryostat at a distance away from it. We initially measure the 2D coherence function of emitted light, which can then be used to directly estimate the 2D in-plane momentum space distribution by calculating its fast Fourier transform. We also discuss how this experimental method can overcome instrumentational difficulties encountered in the past. Similar instrumentations can also be extended for momentum space resolved astronomical studies and telecommunications involving distant light sources.

Quantifying polarization changes induced by rotating Dove prisms and K-mirrors

Dove prisms and K-mirrors are devices extensively used for rotating the wavefront of an optical field. These devices have several applications, including the measurement of orbital angular momentum, microscopy, beam steering, and pattern recognition. However, the wavefront rotation achieved through these devices is always accompanied by polarization changes in the incident field, which is an undesirable feature in many of these applications. Although the polarization changes induced by a Dove prism have been explored to quite some extent, no such study is available for a K-mirror. In this paper, we theoretically and experimentally investigate polarization changes induced in the transmitted field by a rotating K-mirror. For quantifying such polarization changes, we define a quantity, mean polarization change D, which ranges from 0 to π. We find that K-mirrors can reduce D to about 0.03π for any incident state of polarization; however, reducing D to the same extent with a Dove prism is practically unviable. Therefore, K-mirrors are better alternatives to Dove prisms in applications in which the polarization changes accompanying wavefront rotation need to be minimum.

Rotational Shearing Interferometer in Detection of the Super-Earth Exoplanets

The astronomers and the general population are fascinated with the problem of exoplanet detection. By far the largest number of detected planets are the so-called Super Earths, relatively cold planets orbiting a large, red giant star, with diameters up to 1 AU, most of them at about one hundred light-year distance from us. A rotational shearing interferometer (RSI) was proposed for exoplanet detection. Here the detection capabilities of the RSI are expanded to include the case when the interferometer is not precisely aligned on the star. The theoretical analysis is applied to the case of a Super Earth with the red giant star, displaced from the origin to the Mercury, Earth, and the Martian orbit. For errors in alignment up to the Mercury orbit, the red giant star generates a slanted radiance pattern that may be eliminated using information processing. For larger distances, analysis in the Fourier domain is feasible.

Rotationally shearing interferometer for extra-solar planet detection: preliminary results with a solar system simulator

We describe preliminary experimental results on the laboratory demonstration of a technique to detect an extrasolar planet using a rotationally shearing interferometer. We simulate a planet and a star in a laboratory solar system. It consists of two laser beams; each passed through a spatial filter, collimated and combined. We confirm the theoretical prediction that the on-axis star generates no fringes for any shear angle. The star generates a uniform wave front that is invariant to the shear angle. Additionally, we demonstrate that the off-axis planet produces straight fringes. Thus, the mere presence of fringes confirms the existence of a planet. Furthermore, we illustrate that the fringe density and their inclination increase with the shear angle in the rotational shearing interferometer. Therefore, the number of fringes and their direction may be changed from the Earth to confirm (or reject) the existence of a planet.

Bimodal Incoherent Digital Holography for Both Three-Dimensional Imaging and Quasi-Infinite-Depth-of-Field Imaging

Although three-dimensional (3D) imaging and extended depth-of-field (DOF) imaging are completely opposite techniques, both provide much more information about 3D scenes and objects than does traditional two-dimensional imaging. Therefore, these imaging techniques strongly influence a wide variety of applications, such as broadcasting, entertainment, metrology, security and biology. In the present work, we derive a generalised theory involving incoherent digital holography to describe both 3D imaging and quasi-infinite-DOF (QIDOF) imaging, which allows us to comprehensively discuss the functions of each imaging technique. On the basis of this theory, we propose and develop a bimodal incoherent digital holography system that allows both 3D imaging and QIDOF imaging. The proposed system allows imaging objects using spatially incoherent light and reconstructing 3D images or QIDOF images solely by changing the phase pattern of a spatial light modulator and without requiring mechanical adjustments or any other modifications to the setup. As a proof-of-principle experiment, we evaluate the DOF and record holograms of a reflective object with the proposed system. The experimental results show that the generalised theory is effective; our demonstration platform provides the function of 3D and QIDOF imaging.

Field rotation and polarization properties of the Porro prism

We investigate the use of the Porro prism and its application as a beam rotator. The Porro prism can reverse a light beam, and the reversed beam is rotated when the Porro prism rotates. As a result of the two total internal reflections in the Porro prism, the field polarization is changed. We present a schematic setup to realize beam rotation without polarization change and power variation. The setup includes a rotatable Porro prism accompanied by a polarized beam splitter, a quarter-wave plate, and a phase compensator. This beam rotator is useful in the measurement of the orbital angular momentum of a helical beam.

Cross-axis cascading of spectral dispersion

We demonstrate a method of cascading multiple diffractive elements for improving the purity of spectral dispersion. The cross-axis cascade was implemented in a two-stage grating spectrograph, resulting in a hundredfold reduction of stray light and a high dynamic range up to -75 dB. The technique can be used for parallel spectral measurements and processing.

Achromatic interfero-coronagraph with two common-path interferometers in tandem

To attain deeper nulling for an extended incoherent star disk a scheme for an achromatic interfero-coronagraph, incorporating two common-path interferometers in tandem, is proposed. Analytical and numerical predictions of the performance, which are in reasonably good agreement, are presented. The predicted performance improvement, by using two interferometers in tandem, is demonstrated by a preliminary experiment. A star coronagraph based on the proposed technique has the possibility to reach a 10(-10) achromatic nulling contrast for an almost 10(-2) lambda/D effective source size.

Jones matrix for image-rotation prisms

The polarization-transforming properties of rotational prisms are analyzed with polarized light by using the Jones calculus and the exact ray-trace. A general expression of the Jones matrix for a rotational prism is derived, incorporating an explicit dependence on the image-rotation angle or the wave-front-rotation angle. The Jones matrix for the Pechan, Dove, Reversion, and Delta prisms is derived where the explicit dependence on the angle of rotation of the image is given. An experiment with a rotating Dove prism is also conducted to determine the output states of polarization for incident linearly polarized light. Experimental results agree with theoretical expectations.