Marija Strojnik

Risley prisms to control wave-front tilt and displacement in a vectorial shearing interferometer

A pair of thin prisms is used to deviate a light beam without changing the image orientation in a vectorial shearing interferometer. The relative angle between prisms determines the displacement of the wave front and its tilt. The direction of the beam displacement is controlled by means of changing the relative angle between prisms. This system is employed to control the displacement of a sheared wave front as a vector quantity and to introduce a controlled amount of tilt in what we believe is a novel interferometric shearing system. The predicted performance of this wave-front director is confirmed experimentally.

FRINGE ANALYSIS AND PHASE RECONSTRUCTION FROM MODULATED INTENSITY PATTERNS

A novel method of determining phase from a modulated intensity pattern is described. A line integral of the gradient of the phase is used to reconstruct the phase, eliminating the necessity for complex methods of phase unwrapping. The new algorithm can be used with any technique that experimentally or theoretically yields the cosine and sine or the tangent of the phase. This phase-reconstruction process works effectively even in the regions of high-intensity gradients and is insensitive to the profile of the illuminating beams and to the shape of the domain boundaries.

Vectorial shearing interferometer

The vectorial shearing interferometer is based on the Mach-Zehnder configuration; it incorporates a displacement shearing system composed of a pair of wedge prisms that modify the optical path difference and the tilt of the sheared wave front with respect to that of the reference wave front. Variable shear and tilt can be implemented along any direction by choice of displacements Delta x and Delta y. The number of fringes and their orientation can be controlled with the vectorial shear. Knowledge of the prescribed displacements in the x and the y directions permits one to obtain a phase gradient in any direction.

Phase-shifted interferometry without phase unwrapping: reconstruction of a decentered wave front

We apply the method of the line integration of the phase gradient to determine unambiguously the phase from several phase-shifted interferograms (intensity fringe patterns) without phase unwrapping. The ambiguities introduced owing to the multiple values of the arctangent function and to the necessity to invoke a priori knowledge in the regions of high-intensity gradients are avoided. A decentered wave front with circular boundaries is reconstructed from high-fringe-density interferograms with an error of less than 0.1 percent, thus demonstrating the feasibility of testing the off-axis optical elements with approximate reference components.

Design of a diluted aperture by use of the practical cutoff frequency

We analyze the imaging performance of a number of diluted-aperture configurations, using the modulation transfer function. We select a single figure of merit, the practical cutoff frequency, rather than the traditional cutoff frequency, as the more useful frequency for the detection of details. Using this new parameter, we compare the performance of a number of published aperture configurations. On the basis of this analysis a new configuration is proposed for the Polar Stratospheric Telescope primary.

Optimal wavelength selection for noncontact reflection photoplethysmography

In this work, we obtain backscattered signals from human forehead for wavelengths from 380 to 980 nm. The results reveal bands with strong pulsatile signals that carry useful information. We describe those bands as the most suitable wavelengths in the visible and NIR regions from which heart and respiratory rate parameters can be derived using long distance non-contact reflection photoplethysmography analysis. The latter results show the feasibility of a novel technique for remotely detection of vital signs in humans. This technique, which may include morphological analysis or maps of tissue oxygenation, is a further step to real non-invasive remote monitoring of patients.

Remote temperature sensor employing erbium-doped silica fiber

Abstract We present experimental results demonstrating the performance of the erbium-doped silica fiber as a remote temperature sensor in the temperature interval 26–60 °C. It uses the fluorescence intensity ratio with energy levels 2H11/2 and 4S3/2. With the measured fluorescence data and incorporating a fiber optic link, its temperature resolution is better than 0.06 °C, and the sensitivity is 0.06 °C −1 .

Erbium-doped optical fiber fluorescence temperature sensor with enhanced sensitivity, a high signal-to-noise ratio, and a power ratio in the 520–530- and 550–560-nm bands

We analyze and predict the performance of a fiber-optic temperature sensor from the measured fluorescence spectrum to optimize its design. We apply this analysis to an erbium-doped silica fiber by employing the power-ratio technique. We develop expressions for the signal-to-noise ratio in a band to optimize sensor performance in each spectral channel. We improve the signal-to-noise ratio by a factor of 5 for each channel, compared with earlier results. We evaluate the analytical expression for the sensor sensitivity and predict it to be approximately 0.02 degrees C(-1) for the temperature interval from room temperature to above 200 degrees C, increasing from 0.01 degrees C(-1) at the edges of the interval to 0.03 degrees C(-1) at the center, at 100-130 degrees C. The sensitivity again increases at temperatures higher than 300 degrees C, delineating its useful temperature intervals.

Simulations and experimental results with a vectorial shearing interferometer

We describe the fundamental principle of operation of a vec- torial shearing interferometer, featuring variable shear and tilt. They may be implemented along an arbitrary direction, in our experimental setup, by controlling the relative angle between a pair of wedge prisms. We show the simulated interferometric patterns of primary aberrations. We compare them with those exhibited by spherical and aspherical optical elements obtained experimentally. The number and orientation of fringes is controllable with the shear direction and its magnitude. The vectorial shearing interferometer is shown to be effective in testing optical ele- ments and in aligning optical systems.

Simulated interferometric patterns generated by a nearby star–planet system and detected by a rotational shearing interferometer

Simulated interferometric patterns of the wave fronts generated by a star–planet system and detected with a rotational shearing interferometer are derived analytically and presented graphically. They are identical to the patterns generated solely by a planet because of the insensitivity of the rotational shearing interferometer to the detection of a rotationally symmetric wave front. The variable shearing angle is shown to control the number of fringes and their orientation. For small shearing angles the phase difference in the argument of the cosine function reduces to the derivative of the wave front multiplied by the shearing angle. The analytical expression for the intensity detected with a rotational shearing interferometer demonstrates that the rotational shearing interferometer does not see the on-axis star.