Biomedical subjects

Asher A Friesem

Publications and source records attributed to Asher A Friesem.

13 recordsLinked to original sources

PubMed2006

Planar configuration for image projection.

A flat panel, compact virtual image projection display is presented. It is based on a light- guided optical configuration that includes three linear holographic gratings recorded on one planar transparent substrate so as to obtain a magnified virtual image for a small input display. The principles of the projection display, unique design, and procedures for experimentally recording an actual planar configuration are presented, along with evaluation results. The results reveal that a field of view of +/-8 degrees can be readily achieved at a distance of 36 cm, making such planar configurations attractive for head-up displays.

Journal Article↗

PubMed2005

Structure and mechanical properties of the soft zone separating bulk dentin and enamel in crowns of human teeth: insight into tooth function.

The 200-300 microm soft zone of dentin, found beneath enamel in crowns of human teeth, is thought to fulfill important roles in tooth function, but little is known about its structure-mechanical relations. Scanning electron microscopy images of fracture surfaces showed that near the dentino-enamel junction (DEJ), a porous reticulate matrix of intertubular-dentin contains tubules with no peritubular lining. Peritubular-dentin however is found at some distance from the DEJ, and it gradually thickens with increasing depth into the bulk dentin. Concurrently, tighter packing of the collagen fibers is observed with a gradual increase in mineral deposits on and between the fibers. This structurally graded zone is known to be softer when tested for micro-hardness. It undergoes greater strain compared to bulk dentin, when measured using Moiré interferometry. We investigated the deformation and stiffness of this zone by means of non-contact laser-speckle interferometry (ESPI), and nanometer-scale deformations were tracked during compression-testing performed in water. We report a significantly reduced stiffness of this zone compared to bulk dentin, with mid-buccal regions of teeth averaging 3.5 GPa compared with 9.7 GPa in mid-lingual regions. Our results support and expand upon the hypothesis that the durability of the whole tooth relies upon a bucco-lingual asymmetric matching of stiffness by means of an interphase: a cushioning soft layer between enamel and bulk dentin.

Biomechanical Phenomena↗

PubMed2005

Temporal shaping of entangled photons.

We experimentally demonstrate shaping of the two-photon wave function of entangled-photon pairs, utilizing coherent pulse-shaping techniques. By performing spectral-phase manipulations we tailor the second-order correlation function of the photons exactly like a coherent ultrashort pulse. To observe the shaping we perform sum-frequency generation with an ultrahigh flux of entangled photons. At the appropriate conditions, sum-frequency generation performs as a coincidence detector with an ultrashort response time (approximately 100 fs), enabling a direct observation of the two-photon wave function. This property also enables us to demonstrate background-free, high-visibility two-photon interference oscillations.

Journal Article↗

PubMed2005

Nonlinear interactions with an ultrahigh flux of broadband entangled photons.

We experimentally demonstrate sum-frequency generation with entangled photon pairs, generating as many as 40,000 photons per second, visible even to the naked eye. The nonclassical nature of the interaction is exhibited by a linear intensity dependence of the nonlinear process. The key element in our scheme is the generation of an ultrahigh flux of entangled photons while maintaining their nonclassical properties. This is made possible by generating the down-converted photons as broadband as possible, orders of magnitude wider than the pump. This approach can be applied to other nonlinear interactions, and may become useful for various quantum-measurement tasks.

Journal Article↗

PubMed2005

Effective grating theory for resonance domain surface-relief diffraction gratings.

An effective grating model, which generalizes effective-medium theory to the case of resonance domain surface-relief gratings, is presented. In addition to the zero order, it takes into account the first diffraction order, which obeys the Bragg condition. Modeling the surface-relief grating as an effective grating with two diffraction orders provides closed-form analytical relationships between efficiency and grating parameters. The aspect ratio, the grating period, and the required incidence angle that would lead to high diffraction efficiencies are predicted for TE and TM polarization and verified by rigorous numerical calculations.

Journal Article↗

PubMed2004

Two photon absorption and coherent control with broadband down-converted light.

We experimentally demonstrate two-photon absorption with broadband down-converted light (squeezed vacuum). Although incoherent and exhibiting the statistics of a thermal noise, broadband down-converted light can induce two-photon absorption with the same sharp temporal behavior as femtosecond pulses, while exhibiting the high spectral resolution of the narrow band pump laser. Using pulse-shaping methods, we coherently control two-photon absorption in rubidium, demonstrating spectral and temporal resolutions that are 3-5 orders of magnitude below the actual bandwidth and temporal duration of the light itself. Such properties can be exploited in various applications such as spread-spectrum optical communications, tomography, and nonlinear microscopy.

Journal Article↗

PubMed2004

Efficient mode transformations of degenerate Laguerre-Gaussian beams.

We present an approach for efficient conversion of a single-high-order-mode distribution from a laser to a nearly Gaussian distribution and vice versa. It is based on dividing the high-order mode distribution into equal parts that are then combined together coherently. We implement our approach with several optical arrangements that include a combination of discrete elements and some with single interferometric elements. These arrangements are analyzed and experimentally evaluated for converting the TEM01 mode distribution with Mx(2) = 3 to a nearly Gaussian beam with Mx(2) = 1.045 or Mx(2) = 1.15. The basic principle, design, and experimental results obtained with several conversion arrangements are presented. The results reveal that conversion efficiency is typically greater than 90%, compared with theoretical ones. In addition, some arrangement is exploited for converting the fundamental Gaussian-beam distribution into the TEM01 mode distribution.

Journal Article↗

PubMed2002

Formation of a planar coarse wavelength-division multiplexer and demultiplexer with reflection volume phase gratings.

A compact configuration for a coarse wavelength-division multiplexer (CWDM) and a coarse wavelength-division demultiplexer (CWDDM) that are based on reflection volume phase gratings is formed. The design and calculated results for four-channel CWDM and CWDDM configurations in the region near 800 nm are presented. Theoretical predictions are experimentally verified with a four-channel CWDDM whose channels are centered at 775, 800, 825, and 850 nm.

Journal Article↗

PubMed2002

Laser operation with two orthogonally polarized transverse modes.

Laser resonator configurations, which enable laser operation with two orthogonally polarized transverse modes, are presented. The intensity distributions of these two modes can be chosen to be complementary, so the gain medium can be exploited more efficiently than with a single mode, leading to improved output power. Moreover, the two modes can be combined and efficiently transformed into a single high-quality beam. Basic principles and experimental results with Nd:YAG lasers are presented.

Journal Article↗

PubMed2002

Compact red-green-blue beam illuminator and expander.

A compact multicolor beam illuminator and a compact multicolor beam expander are presented. The illuminator performs the dual task of demultiplexing a narrow red-green-blue (RGB) input beam into three separate beams, each of a different color, and expanding them to yield three separate magnified plane waves. The beam expander expands a narrow RGB input beam into a single magnified RGB plane wave. The design and recording procedures, along with experimental results for a beam illuminator and a beam expander with a magnification of approximately 3, are presented.

Journal Article↗

PubMed2002

Compact beam expander with linear gratings.

Novel compact beam expanders that could be useful for applications such as providing light to flat panel displays are presented. They are based on a planar configuration in which three spatially linear gratings are recorded on one transparent substrate, so as to expand a narrow incoming beam in two dimensions. We present the design and recording procedures along with results, showing a relatively uniform intensity of the wide output beam. Such expanders can serve for illuminating flat panel displays.

Models, Theoretical↗

PubMed2002

Compact wavelength division multiplexers and demultiplexers.

Compact devices for wavelength division multiplexing and demultiplexing, believed to be novel, are presented. These devices are based on planar optics configurations, comprising multiplexed diffractive optical elements. The principle, design, and recording of these planar devices are described, including the fact that the recording is done at a single wavelength in the green region. Experimental procedures and results for planar devices that can handle three wavelengths in the visible as well as in the near infrared are presented.

Journal Article↗

PubMedDate not supplied

Phase shifting speckle interferometry for determination of strain and Young's modulus of mineralized biological materials: a study of tooth dentin compression in water.

Mineralized biological materials have complex hierarchical graded structures. It is therefore difficult to understand the relations between their structure and mechanical properties. We report the use of electronic speckle pattern-correlation interferometry (ESPI) combined with a mechanical compression apparatus to measure the strain and Young's modulus of root dentin compressed under water. We describe the optomechanical instrumentation, experimental techniques and procedures needed to measure cubes as small as 1 x 1 x 2 mm. Calibration of the method is performed using aluminum, which shows that the measurements are accurate within 3% of the compression modulus reported for standard aluminum 6061. Our results reveal that the compression moduli of root dentin from the buccal and lingual sides of the root are quite different from the moduli of the interproximal sides. Root dentin from interproximal locations is found to have an average modulus of 21.3 GPa, which is about 40% stiffer than root dentin from the buccal and lingual locations, found to have a modulus of 15.0 GPa. Our approach can be used to map deformations on irregular surfaces, and measure strain on wet samples of varying sizes. This can be extended to the study of other biological materials including bone and synthetic biomaterials.

Compressive Strength↗