Marija Strojnik Scholl

Ray trace through a corner-cube retroreflector with complex reflection coefficients

A vector formulation is used to derive an analytical expression for the complex reflectivity of a corner-cube retroreflector, with use of the complex reflection coefficients for the s and p polarization. This expression shows that the corner-cube retroreflector modifies the incoming electric field according to the angle of incidence and the ray path through the retroreflector. The change in the electric field depends on the errors in the surface finish, the coating nonuniformity, and the nonhomogeneity in the index of refraction in the case of the solid corner-cube retroreflector. The main point is that the corner-cube retroreflector conjugates the incident beam only in the case of a plane wave with a constant amplitude incident upon a perfect corner-cube retroreflector.

Signal generated by an extra-solar-system planet detected by a rotating rotationally shearing interferometer

An infrared rotating rotationallly shearing interferometer can be used for detection of a potential planet orbiting around a nearby star. An expression is derived for the signal generated by a star and its faint companion, and this signal is detected by a rotationally shearing interferometer. It is shown that the planet’s signal can be detected, despite the presence of a much larger star signal, because the planet produces a faint modulation superimposed upon the large star signal when the aperture rotates. In the particular case of a rotating rotationally shearing interferometer, the argument of the cosine term is shown to depend only on the planet’s and the observational parameters. However, the amplitude of the modulation term in the interferometric signal is shown to be proportional to the star’s intensity.

Thermal contrast detected with a quantum detector

We evaluate the thermal contrast detected by a quantum detector in a focal plane of an infrared instrument. The detected thermal contrast is shown to consist of two terms. The term corresponding to the temperature dependence of emissivity, previously neglected, is evaluated and shown to be a significant contributing factor. For the case of a metal mirror as a source of stray light, ghost images, and narcissus, the error is estimated to be about 20%. The term in the detected contrast associated with the radiative emission is shown to be proportional to temperature to the power of 2, rather than 3, published previously.

Thermal contrast detected with a thermal detector

We show that the thermal contrast detected in a wavelength interval with a thermal detector consists of two terms. The first term agrees with the previously published results. The second term represents the contribution of the temperature-dependent emissivity. Neglecting this term results in approximately 20% error for traditional room temperature applications. For the case of remote crop-monitoring, the contribution of the emissivity changes to the detected thermal contrast is even more important: the infection of the vegetation results in the modification of its emissivity, its temperature and its change of emissivity with temperature.

Image-plane incidence for a baffled infrared telescope

The on-axis image plane incidence of an extended object (sometimes also called irradiance), radiating as a Lambertian radiator is derived for an optical system with a central obscuration. It is then extended to off-axis image points to obtain a generalized form of image incidence for an extended source. A specific example is provided by the conceptual design proposed for the next generation US IR telescope facility, called SIRTF. An incidence error of 1% is obtained for a telescope with a large baffle around a small secondary mirror. The small error is attributed to the unusually small diameter of the secondary mirror.

Cancellation of star light generated by a nearby star-planet system upon detection with a rotationally-shearing interferometer

Abstract We derive the analytical expression for the star–planet incidance detected with a (variable angle) rotationally-shearing interferometer, with the absence of star-related quantities. The rotationally-shearing interferometer detects only the tilted wave front incident from a planet. The partial polarization of two rotated beams diminishes the signal amplitude by a factor proportional to the cosine-square of the shearing angle. The polarization considerations favor the small-angle implementation of the rotationally-shearing interferometer.

Using the y, y-bar diagram to control stray light noise in IR systems

Abstract Stray light in an (infrared) optical system is the radiation that is incident on the detector, but does not originate from the conjugate object point. Cool stops are usually placed at strategic locations to decrease the amount of stray light noise incident into the detector plane. Contrary to the present practice, the stray light control is improved when the telescope and instrument subsystems are analyzed as a single optical system. We describe an approach to the stray light management and control that may be performed simultaneously with the first order optical system design using the y,y-bar diagram.

Design parameters for a two-mirror telescope for stray-light sensitive infrared applications

Abstract Established telescope designs used in the infrared-wavelength region are not responsive to the specific imaging requirements of this wavelength interval. A Gregorian telescope using off-axis mirror segments, and a real focus for the cold stop placement is proposed for the detection of faint IR sources. Exact ray trace equations are given for a general ray propagating through two coupled confocal spheroids. Relationship between the spheroid mirror parameters and object, and image distances are presented in a graphical form to facilitate the first order telescope design.

Relief optical microelements fabricated with dichromated gelatin

Relief microlenses and micromirrors are fabricated in dichromated gelatin layers. Microelements typically have diameters of approximately a few hundred micrometers and have focal distances ranging from 4 to 15 mm.

Recursive exact ray trace equations through the foci of the tilted off-axis confocal prolate spheroids

Simple, exact ray trace equations are derived for a general ray propagating through the foci of tilted, coupled, confocal spheroids. In this off-axis optical system, there does not necessarily exist a (real) ray for which the paraxial approximation applies.