M.B. van der Mark

Clinical optical tomography and NIR spectroscopy for breast cancer detection

The results of the first set of clinical trials with the Philips optical mammography prototype system are summarized. This optical mammo prototype is designed to image the interior of the female breast with the help of near-infrared (NIR) laser light transmission measurements. This study is expected to lead to optical tomography systems for breast cancer detection. This paper presents information on the design of the optical mammo system, the clinical measurements and the imaging results from an initial group of ten patients, and discussions about ongoing research on optical tomography.

Tomographic image reconstruction from optical projections in light-diffusing media

The recent developments in light generation and detection techniques have opened new possibilities for optical medical imaging, tomography, and diagnosis at tissue penetration depths of ~10 cm. However, because light scattering and diffusion in biological tissue are rather strong, the reconstruction of object images from optical projections needs special attention. We describe a simple reconstruction method for diffuse optical imaging, based on a modified backprojection approach for medical tomography. Specifically, we have modified the standard backprojection method commonly used in x-ray tomographic imaging to include the effects of both the diffusion and the scattering of light and the associated nonlinearities in projection image formation. These modifications are based primarily on the deconvolution of the broadened image by a spatially variant point-spread function that is dependent on the scattering of light in tissue. The spatial dependence of the deconvolution and nonlinearity corrections for the curved propagating ray paths in heterogeneous tissue are handled semiempirically by coordinate transformations. We have applied this method to both theoretical and experimental projections taken by parallel- and fan-beam tomography geometries. The experimental objects were biomedical phantoms with multiple objects, including in vitro animal tissue. The overall results presented demonstrate that image-resolution improvements by nearly an order of magnitude can be obtained. We believe that the tomographic method presented here can provide a basis for rapid, real-time medical monitoring by the use of optical projections. It is expected that such optical tomography techniques can be combined with the optical tissue diagnosis methods based on spectroscopic molecular signatures to result in a versatile optical diagnosis and imaging technology.

High-density near-field optical recording with a solid immersion lens, conventional actuator, and a robust air gap servo

We present a near-field optical recording system with a solid immersion lens (SIL) in a conventional biaxial actuator. We manufactured a super-hemispherical aplanatic SIL with a numerical aperture (NA) of NA = 1.9. Our system utilizes a gap error signal (GES) and a digital servo system to drive a conventional actuator in order to maintain a constant air gap of 25 nm between the SIL and a spinning optical disc.

Ultrafast polarization switching of lead zirconate titanate thin films

An experimental setup for ultrafast switching measurements is described. The instrumental time resolution was measured to be <or=100 ps. An analysis of the test circuit showed that it could be considered as an LRC network having a nonlinear ferroelectric capacitor. The switching and the nonswitching ferroelectric charges were shown to determine the RC and LC network time constants, respectively, and the overall experimental resolution. Experiments on PZT (lead zirconate titanate) films demonstrated switching within 360 ps as well as switching time distributions extending to more than 2 mu m. It is argued that the extended switching times can be related to a ceramic-like morphology of the films and that they are caused by the time needed for charge redistribution within the films. The fast switching is observed in films with an epitaxial relationship within columnar grains. It can be explained by 180 degrees and 90 degrees domain configurations needing only charge redistribution at the film-electrode interphases during switching. Two switching mechanisms might explain the fast switching. One is based on a high nucleation rate and propagation of domains across the film thickness. The other assumes a simultaneous reorientation of the ferroelectric dipoles (bulk switching).<<ETX>>

Low-leakage-current metal–insulator–semiconductor–insulator–metal photodetector on silicon with a SiO2 barrier-enhancement layer

We show that the leakage current through a metal–semiconductor–metal photodetector can be reduced by placing a thin interfacial silicon dioxide layer between the Schottky metal and the silicon substrate. We measure a factor 5.2 reduction in leakage-current density to 18 μA/cm2 at 5 V, a weaker increase in dark current with bias, and a factor 3.5 improvement in photoresponsivity to 0.39 A/W. We do not observe any noticeable reduction in device speed using this interfacial oxide.

Noncontact calibration of optical fiber cladding diameter using exact scattering theory

A new, contactless and nondestructive method for measuring the diameter of an optical fiber is described which has 10 nm sensitivity. In this method, polarized laser light is backscattered from the fiber, perpendicular to its axis. The measured intensity shows excellent agreement with calculations from an exact scattering theory, and reveals both the refractive index and diameter of the fiber. The high sensitivity of this method results from the intrinsic interferometric properties of the fiber itself, and depends on the wavelength of the coherent light source only. If the fibers circumference is circular, the high sensitivity of this method leads to an absolute calibration accuracy of 10 nm of the fiber diameter. >

Breast imaging using optical tomography

Due to its nonionizing nature, optical mammography could be a very attractive alternative to X-ray screening. The authors have developed a cw optical tomography apparatus with which three-dimensional images of breasts can be obtained in vivo, and it is now being used for clinical research in the Academic Hospital in Maastricht. It measures the attenuation coefficient of breast tissue. The magnitude of the reduced scattering coefficient in breast tissue is approximately 1 mm/sup -1/ and varies less than the absorption coefficient. The subject has to lie down on the machine and let one of her breasts hang freely in a cup containing a fluid. The fluid matches the mean optical properties of the breast, and is kept at approximately 31 /spl deg/C for comfort. The cup has a conical shape with a maximum diameter of 130 mm. On the boundary of the cup 255 optical fibers are mounted that lead to one detector each. Interleaved, 255 fibers are mounted that can be selected sequentially to receive the light of one of three diode lasers that are operating at different wavelengths, namely 658 nm, 786 nm, and 919 nm. All detectors measure simultaneously.

Observation of the optical analogue of the quantised conductance of a point contact

Abstract The light power transmitted by a diffusively illuminated slit of finite thickness is observed to depend stepwise on the slit width. The steps have equal height and a width of one half the wavelength of the monochromatic light used. This novel diffraction phenomenon is the analogue of the quantization of the conductance of a point contact in a two-dimensional electron gas. In contrast to the electronic case, absorption at the walls of the slit plays an important role in determining the shape of the steps, as we show from a model calculation.

Blue zero field MAMMOS recording

Recently, M. Sekine et al. (Techn. Digest ODS, pp 61, 2001) showed the first experimental results on a new MAMMOS magneto optical super resolution media type, which they call zero-field MAMMOS, that in contrast to the earlier developed AC MAMMOS type can be read-out without the need for any external modulating expansion field. These media were designed for use in a system with a DVD-like optical light path, employing a 650 nm laser and an NA of 0.6. Philips and Hitachi Maxell have, in joint effort, made and tested the first zero field MAMMOS media for use in a first-surface MO (magneto optical) recorder using a blue-violet laser with a wavelength of 405 nm and an NA of 0.7. In this paper we present the first recording results on these media, recorded with an actuated recording head that operates at 15 /spl mu/m from the storage layer of the disc. This distance is an order of magnitude smaller than the free working distance of the Blu-Ray Disc system.