Intermediate Plane Research Articles

Speckle reduction in line-scan laser projectors using binary phase codes

A Barker binary phase code of maximum length 13 has previously been used for speckle reduction in line-scan laser projectors, and a speckle contrast factor decrease down to 13% has been achieved. In this Letter, Barker-like binary phase codes of lengths longer than 13 are used at an intermediate image plane. It is shown by theoretical calculation that a much better speckle reduction with a speckle contrast factor up to 6% can be achieved by using longer binary phase codes other than the Barker code.

Isolated Management of the Aging Neck

The contour of the neck is a very important determinant of facial aesthetics. Precise knowledge of neck anatomy is essential for adequate planning and execution of this procedure. There are three anatomic and surgical planes involved in the management of the aging neck; the superficial plane (subcutaneous fat), the intermediate plane (platysma muscles and the fat between the two muscles), and the deep plane (subplatysmal fat, the anterior belly of the digastric muscles, and the submandibular glands). These planes need to be thoroughly evaluated in the preoperative assessment and dealt with according to each patient's needs. Even though this article focuses on isolated management of the aging neck, careful evaluation of the neck and its relationship to the lower third of the face is fundamental. If there is significant jowling and descent of the neck-face interface, an isolated neck-lift procedure will not address that problem and will lead to a suboptimal result. In these patients, a face and neck lift is a more appropriate operation.

CALCULATION OF MODULATION TRANSFER FUNCTION OF AN OPTICAL SYSTEM BY USING SKEW RAY TRACING

The resolution and performance of an optical system can be characterized by a quantity known as the modulation transfer function (MTF), which is a measurement of an optical system’s ability to transfer contrast from the specimen to the intermediate image plane at a specific resolution. Accordingly, this study employs skew ray tracing based on a 4 × 4 homogeneous coordinate transformation matrix and Snell’s law to develop a detailed methodology for determining the spot diagram on the image plane when light rays pass through the optical system. And the authors present calculations of the MTF of an optical system by using the spot diagram on the image plane. The numerical results of the proposed methodology are demonstrated using a symmetrical optical system.

Recording and controlling the 4D light field in a microscope using microlens arrays

By inserting a microlens array at the intermediate image plane of an optical microscope, one can record four-dimensional light fields of biological specimens in a single snapshot. Unlike a conventional photograph, light fields permit manipulation of viewpoint and focus after the snapshot has been taken, subject to the resolution of the camera and the diffraction limit of the optical system. By inserting a second microlens array and video projector into the microscope's illumination path, one can control the incident light field falling on the specimen in a similar way. In this paper, we describe a prototype system we have built that implements these ideas, and we demonstrate two applications for it: simulating exotic microscope illumination modalities and correcting for optical aberrations digitally.

Phase-shifting Gabor holography

We present a modified Gabor-like setup able to recover the complex amplitude distribution of the object wavefront from a set of inline recorded holograms. The proposed configuration is characterized by the insertion of a condenser lens and a spatial light modulator (SLM) into the classical Gabor configuration. The phase shift is introduced by the SLM that modulates the central spot (dc term) in an intermediate plane, without an additional reference beam. Experimental results validate the proposed method and produce superior results to the Gabor method.

Alternative opto-mechanical architectures for the LISA instrument

As part of the on-going LISA Mission Formulation study under ESA contract, EADS Astrium has recently suggested and investigated a variety of novel LISA payload architectures utilizing so-called "In-Field Pointing" for accommodation of seasonal constellation dynamics. Here, the annual variation in the angle between the interferometer arms of roughly ±1° is compensated by steering the lines of sight of the individual telescopes with a small actuated mirror located in an intermediate pupil plane inside the telescopes. This introduces a certain flexibility for the overall payload configuration and allows for very compact designs. In particular, it enables a "single active proof mass" mode with a true cold redundancy between a nominal and a backup GRS system on board each spacecraft, and thus enhances mission robustness.

Geometrical superresolved imaging using nonperiodic spatial masking

The resolution of every imaging system is limited either by the F-number of its optics or by the geometry of its detection array. The geometrical limitation is caused by lack of spatial sampling points as well as by the shape of every sampling pixel that generates spectral low-pass filtering. We present a novel approach to overcome the low-pass filtering that is due to the shape of the sampling pixels. The approach combines special algorithms together with spatial masking placed in the intermediate image plane and eventually allows geometrical superresolved imaging without relation to the actual shape of the pixels.

Optical Design of A Compact Imaging Spectrometer for STSAT3

A compact imaging spectrometer (COMIS) for use in the STSAT3 microsatellite is currently under development. It is scheduled to be launched into a low Sun-synchronous Earth orbit ( ${\sim}700km$ ) by the end of 2010. COMIS was inspired by the success of CHRIS, which is a small hyperspectral imager developed for the ESA microsatellite PROBA. COMIS is designed to achieve nearly equivalent imaging capabilities of CHRIS in a smaller (65 mm diameter and 4.3 kg mass) and mechanically superior (in terms of alignment and robustness) package. Its main operational goal will be the imaging of Earth's surface and atmosphere with ground sampling distances of ${\sim}30m$ at the $18{\sim}62$ spectral bands ( $4.0{\sim}1.05{\mu}m$ ). This imaging will be used for environmental monitoring, such as the in-land water quality monitoring of Paldang Lake, which is located next to Seoul, South Korea. The optics of COMIS consists of two parts: imaging telescope and dispersing relay optics. The imaging telescope, which operates at an f-ratio of 4.6, forms an image (of Earth's surface or atmosphere) onto an intermediate image plane. The dispersion relay optics disperses the image and relay it onto a CCD plane. All COMIS lenses and mirrors are spherical and are made from used silica exclusively. In addition, the optics is designed such that the optical axis of the dispersed image is parallel to the optical axis of the telescope. Previous efforts focused on manufacturing ease, alignment, assembly, testing, and improved robustness in space environments.

Speckle suppression in laser display using several partially coherent beams

An optical scheme for speckle suppression using two or three partially coherent beams in a projection system is proposed. Diffractive optical elements (DOE) placed in the intermediate image plane create several beams carrying the image to a screen. Transparent plates of different thicknesses are placed in the Fourier plane of the projective lens and used for beam decorrelation. The coherence matrix algorithm for speckle suppression is used to calculate the speckle contrast ratio. It is shown that for a small decorrelation length and using the same maximum thickness of the transparent plates, two partially coherent beams would provide better suppression than three beams with different diffraction orders. However, for a large decorrelation length, the three beam setup provides better speckle suppression for all three colors examined with a suppression coefficient close to theoretical limits. Verification of speckle suppression using three-beam decorrelation is reported.

High-fidelity numerical realization of multiple-step Fresnel propagation for the reconstruction of digital holograms

A cascaded Fresnel algorithm for the flexible reconstruction of digital holograms is proposed. Since the fast-Fourier-transform-based numerical realization of the Fresnel integral shows a dependency of its pixel resolution and its computation window size on the propagation distance different from that of the corresponding physical system, the computation window can be smaller than the actual physical diffraction field in the intermediate plane. Consequently, distortions in the final reconstruction may occur. A method is proposed to eliminate such distortion. The validity of this method is shown by both numerical simulations and experimental results.

Cystal end temperature distribution under different pumping light in solid state laser

In order to study how different pumping light profiles affect the crystal end temperature field, a classification creterion is suggested, according to which the pumping light can be classified as column light, Gaussian light and plane top light. The end temperature under different pumping power and different pumping light focus diameter are studied.It was found that the end temperature is the highest under the column pumping light, intermediate plane top pumping light and lowesl under Gaussian pumping light when the pumping light has the same power and the same focus diameter.It shows that the pumping light profile can seriously affect the crystal end temperature field. Finally the effect of the thermal effect caused by the end temperature was studied, which was found to affect the laser quality seriously. When the equivalent curvature radius of the thermal lens changes from 85 to 150mm, the far field walk-off angle and waist diameter become larger and larger and the laser works unsteadily.

ADVANCEMENTS IN ULTRASOUND MEASUREMENT ON LARGE-SCALE SOLID ROCKET MOTORS

Since 1990, many theoretical and experimental studies have been carried on to measure motor data, like the propellant regression rate in SRM or ITI behavior. Ultrasonic measurements are one of the "low cost methods" to perform such measurements. By working closely with the DGA/DE/CAEPE (Centre d’Achèvement et d’Essais des Propulseurs et Engins), the rocket motor assembly and test center for the French ballistic missiles, SNPE Materiaux Energétique (SME) has investigated the application of this technique to determine different characteristics of solid propellant in full-scale motors to be able to predict accurately their internal ballistics and performance. The first generation of ultrasound transducers was used on a full scale motor test in 1998. These measurements allowed us to assess different local phenomena, such as the front flame arrival time on the thermal insulators all along the motor or the burning rate behavior at low pressure. The ultrasonic data acquisition was recorded during the entire test but, with this type of transducers, the front flame regression has been observed on only the last 15 cm of propellant, which represents the final part of the motor test. Recent system studies carried out in SME during the last 3 years have focused on this technology. The aim of these studies was essentially to improve the actual measurement method to increase the depth of acquisition. New ultrasonic measurement methods have been developed. These new transducers, commonly called "Great Depth Transducers," are adapted to follow up the propellant flame regression on a far more important depth. On the same kind of motor, the capacity offered by the new transducers permitted us to confirm and to compare more accurately, and on a large web of the grain, the different behaviors of the burning rate between a casting point, a knit-line, or an intermediate plane. These results are quite new and give us a fresh approach which brings us to a better understanding of the local burning rate variation and its connections with the casting process. This study has been supported by CNES within its Research and Technology Program and by DGA, the French Armament Procurement Agency. EUROPROPULSION and AVIO, responsible for ballistic performance of MPS P230, have provided SME with necessary information to complete this study.

Visibility retrieval in Michelson wide-field stellar interferometry

Wide-field interferometry has become a subject of increasing interest in recent years. New methods have been suggested in order to avoid the drawbacks of the standard wide-field method (homothetic mapping), which is not applicable when the aperture is highly diluted; for this reason, imaging with non-homothetic arrays is being extensively studied (E. Pedretti, et al., Astron. Astrophys. Suppl. Ser. 147 285 (2000); S. Gillet, et al., Astron. Astrophys. 400 393 (2003)). The field of view of a pupil-plane interferometer or a densified array consists of only a few resolution elements; in order to improve these systems, we have developed a new method consisting of a Michelson pupil-plane combination scheme where a wide field of view can be achieved in one shot. This technique, called the ‘staircase mirror’ approach, has been described in a previous paper (I. Montilla, S.F. Pereira and J.J.M. Braat, Appl. Optics 44 328 (2005)) and uses a stair-shaped mirror in the intermediate image plane of each telescope in the array, allowing for simultaneous correction of the differential delay for both the on- and off-axis image positions. Experimental results have been obtained showing the simultaneous recovery of the fringes of off-axis stars with an appreciable angular separation, and with a contrast similar to that of the on-axis reference star. With this example we demonstrate an increase of the field of view by a factor of 5, with no need for extra observation time. In this article, we present a further analysis of the method. We investigate how to retrieve the visibility when a star is focused on the edge of a step of the stair-shaped mirror. Even though the optical pathlength difference correction is discontinuous, we show both numerically and analytically that the visibility can be completely recovered, so that no information is lost. Our experimental results demonstrate that the visibility can be retrieved to within a 1% error.

Advanced technology solar telescope multiple Fabry-Pérot interferometer telecentric optical design

We present four preliminary designs for a telecentric optical train supporting the Advanced Technology Solar Telescope (ATST) multiple Fabry-Perot interferometer (MFPI), which is to be used as an imaging spectrometer and imaging spectropolarimeter. The point of departure for all three designs is the F/40 telecentric image at the Coude focus of the ATST. The first design, representing the high-spectral-resolution mode of operation, produces an intermediate F/300 telecentric image within the triple etalon system and a 34-arcsec field of view (FOV). The second design, intermediate between high- and low-spectral-resolution modes of operation, produces an intermediate F/150 telecentric image at the etalons and a 1.1-arcmin FOV. The third and fourth designs each represent a low-resolution mode of operation, producing an F/82 telecentric image at the etalons and a 2-arcmin FOV. Each design results in good telecentricity and image quality. Departures from telecentricity at the intermediate image plane cause field-dependent shifts of the bandpass peak, which are negligible compared to the bandpass FWHM. The root mean square (rms) geometric spot sizes at the final image plane fit well within the area of a camera pixel, which is itself in accordance with the Nyquist criterion, half the width of the 28-µm-wide resolution element (as determined from the diffraction limit of the ATST). For each configuration, we also examine the impact that the Beckers effect (the pupil apodization caused by the angle-dependent amplitude transmittance of the MFPI) has on the image quality of the MFPI instrument.

Unified analysis and mathematical representation of film-thickness behavior of film-substrate systems

The ellipsometric function p of a film-substrate system is studied as the film thickness d is kept constant and the angle of incidence phi is changed. The generated constant-thickness contours (CTCs) are characterized by an introduced mathematical behavior indicator that represents a group of CTCs. The behavior of each group is developed and studied in the four planes phi-d, X, Z, and p, where X is the film-thickness exponential function and Z is a previously introduced intermediate plane. In the phi-d plane the film-thickness domain is identified and divided into a sequence of disconnected thickness subdomains (DTSs), depending on only N0 and N1, and their number depending on the range in which N0/N1 lies. The behavior of the CTCs in the successive planes X, Z, and p is then studied in each DTS, and the CTC's space is divided into disconnected subfamilies according to the behavior indicator. Equivalence classes that reduce the infinite number of subfamilies into a finite number are then introduced. The transformation from each plane to the next is studied with the origin of the Z plane mapped onto the point at infinity of the p plane, forming a singularity. A multiple-film-thickness inequality is derived to determine the unique solution of the film thickness. The type of reflection being internal or external at both ambient-film and film-substrate interfaces affects the analysis and is also considered. To conclude we introduce the design of polarization-preserving devices and a novel oscillating single-element ellipsometer to fully characterize zero film-substrate systems as examples of applying the knowledge developed here.

S2 Orientation of Microfibrils in Softwood Tracheids and Hardwood Fibers

In this study the soft-rot method was applied to measuring the variation of microfibril angle (mfa) in loblolly pine, black cherry, sugar maple and canelo. For loblolly pine and black cherry, measurements of the radial wall indicated a gradual decrease in mfa across the earlywood portion of the growth ring, with an abrupt decrease at the latewood zone for pine, and in contrast only a slight decrease in microfibril angle across an annual ring of black cherry. In loblolly pine microfibril angle measurements indicated that the average microfibril angle in radial sections was very similar to the average for tangential sections of the same block. The average microfibril angles in the intermediate plane, or cell corner, were statistically similar to that of the tangential and radial plane, for pine, cherry, and maple. In canelo, microfibril angles in radial sections were significantly larger than in tangential and intermediate sections. In pine latewood the microfibril angles were less than the average mfa for the entire ring, and the earlywood microfibril angles were greater than the average mfa of the entire ring, thus the average mfa for the growth ring did not represent actual measured mfa values.

Inverse Mushroom-shaped Nonmechanical Penetrating Keratoplasty Using a Femtosecond Laser

To demonstrate the feasibility of an inverse mushroom-shaped nonmechanical corneal trephination using a femtosecond laser in a noncontact manner. Experimental study. In this laboratory study, 10 polymethylmethacrylate (PMMA) blocks and 20 porcine corneas were treated with an industrial femtosecond laser source. The trephination profile consisted of (1) a 7- or 6-mm diameter cylinder from the anterior chamber, (2) an intermediate horizontal connecting plane, and (3) a concentric 5- or 4-mm diameter cylinder upwards. Applying appropriate combinations of pulse energy and spacing, trephination took less than 60 seconds. In porcine eyes, light microscopy displayed trephination edges delineated by partly confluent gas bubbles (10-40 mum) with tissue bridges in between. By TEM, the cut edges were lined by a delicate, electron-dense layer (5-40 nm). Femtosecond laser technology seems to offer a promising approach towards minimally invasive self-sealing "no-stitch keratoplasty."

Michelson wide-field stellar interferometry: principles and experimental verification

A new interferometric technique for Michelson wide-field interferometry is presented that consists of a Michelson pupil-plane combination scheme in which a wide field of view can be achieved in one shot. This technique uses a stair-shaped mirror in the intermediate image plane of each telescope in the array, allowing for simultaneous correction of the differential delay for the on-axis and off-axis image positions. Experimental results in a laboratory setup show that it is possible to recover the fringes of on-axis and off-axis stars with an angular separation of 1 arc min simultaneously and with a similar contrast. This new technique represents a considerable extension of the field of view of an interferometer without the need for extra observation time.

S2 Orientation of Microfibrils in Softwood Tracheids and Hardwood Fibers

In this study the soft-rot method was applied to measuring the variation of microfibril angle (mfa) in loblolly pine, black cherry, sugar maple and canelo. For loblolly pine and black cherry, measurements of the radial wall indicated a gradual decrease in mfa across the earlywood portion of the growth ring, with an abrupt decrease at the latewood zone for pine, and in contrast only a slight decrease in microfibril angle across an annual ring of black cherry. In loblolly pine microfibril angle measurements indicated that the average microfibril angle in radial sections was very similar to the average for tangential sections of the same block. The average microfibril angles in the intermediate plane, or cell corner, were statistically similar to that of the tangential and radial plane, for pine, cherry, and maple. In canelo, microfibril angles in radial sections were significantly larger than in tangential and intermediate sections. In pine latewood the microfibril angles were less than the average mfa for the entire ring, and the earlywood microfibril angles were greater than the average mfa of the entire ring, thus the average mfa for the growth ring did not represent actual measured mfa values.

Achromatic four-quadrant phase mask (FQPM) coronagraphy using natural beam splitter phase shifts

The four-quadrant phase mask (FQPM) is an exciting new approach to coronagraphy, a classic astronomical technique for detecting faint companions very close to bright stars. Starlight rejection is potentially very high, and inner working distances are substantially smaller than those achieved with classical Lyot coronagraphy. The key component of the original FQPM scheme is a transparent mask divided into quadrants delivering relative phase shifts alternately 0/pi/0/pi, inserted in an intermediate focal plane of the telescope. Monochromatic masks of this kind have been successfully demonstrated in laboratory and telescope tests. Fabrication of masks with achromatic pi phase shifts is challenging but of great interest for optimum astronomical sensitivity. In this paper I present a novel concept for achromatic FQPM operation that utilizes intrinsic phase relationships between transmitted and reflected beams in a dielectric beam splitter.