Anwendungen von Pikosekunden- und Dauerstrich-Lasern mit hoher Ausgangsleistung in der stereotaktischen Neurochirurgie

Im Rahmen der vorliegenden Arbeit wurden Laserstrahlen eines Nd:YAG-Pikosekunden-Lasersystems mit einer maximalen Ausgangsleistung von 6 W und eines Nd:YAG-Dauerstrichlasers mit einer Leistung von 28 W fuer Anwendungen in der stereotaktischen Neurochirurgie verfuegbar gemacht. Hierbei galt es, die Laserstrahlen durch einen Gelenkspiegelarm hindurch in 4 m Entfernung durch das innerste Rohr einer Tumorsonde mit einem Durchmesser von 2,8 mm maximal zu transmittieren, um sie anschliessend in isotonischer Kochsalzloesung nach weiteren 3,8 cm zu fokussieren. Es wurden umfangreiche Messungen der Strahlqualitaet und der Pulsstabilitaet des Pikosekunden-Lasers durchgefuehrt. Eine Moeglichkeit zur Reduktion der in der isotonischen Kochsalzloesung entstehenden thermischen Streulinse, die eine Fokussierung verhinderte, wurde entwickelt und umgesetzt. Die neurochirurgische Einsetzbarkeit des gesamten Systems wurde in mehreren in vitro und in vivo Experimenten gezeigt

Reconstruction of hidden 3D shapes using diffuse reflections

We analyze multi-bounce propagation of light in an unknown hidden volume and demonstrate that the reflected light contains sufficient information to recover the 3D structure of the hidden scene. We formulate the forward and inverse theory of secondary and tertiary scattering reflection using ideas from energy front propagation and tomography. We show that using careful choice of approximations, such as Fresnel approximation, greatly simplifies this problem and the inversion can be achieved via a backpropagation process. We provide a theoretical analysis of the invertibility, uniqueness and choices of space-time-angle dimensions using synthetic examples. We show that a 2D streak camera can be used to discover and reconstruct hidden geometry. Using a 1D high speed time of flight camera, we show that our method can be used recover 3D shapes of objects "around the corner"

A trillion frames per second: the techniques and applications of light-in-flight photography

Cameras capable of capturing videos at a trillion frames per second allow to freeze light in motion, a very counterintuitive capability when related to our everyday experience in which light appears to travel instantaneously. By combining this capability with computational imaging techniques, new imaging opportunities emerge such as three dimensional imaging of scenes that are hidden behind a corner, the study of relativistic distortion effects, imaging through diffusive media and imaging of ultrafast optical processes such as laser ablation, supercontinuum and plasma generation. We provide an overview of the main techniques that have been developed for ultra-high speed photography with a particular focus on `light-in-flight' imaging, i.e. applications where the key element is the imaging of light itself at frame rates that allow to freeze it's motion and therefore extract information that would otherwise be blurred out and lost.Comment: Published in Reports on progress in Physic

PERISCOPE: PERIapsis Subsurface Cave Optical Explorer

The PERISCOPE study focuses primarily on lunar caves, due to the potential for being imaged in orbital scenarios. In the intervening years, from 2012-2015, scientists developed further rationales and interest in the scientific value of lunar caves. It does not appear that they are likely to be sinks for water-ice due to the relatively warm temperatures(~-20 degrees Celsius) in the caves leading to geologically-rapid migration of unbound water due to sublimation, and inevitable loss through any skylights. However, the skylights themselves reveal apparent complex layering, which may speak to a more complex multi-stage evolution of mare flood basalts than previously considered, and so their examination may provide even more insight into the lunar mare, which in turn provide a primary record of early solar system crustal formal and evolution processes. Further extrapolation of these insights can be found within the exoplanet community of researchers,who find the information useful for calibrating star formation and planetary evolution models. In addition, catalogues of lunar and martian skylights, "caves" or "atypical pit craters" have been developed, with numbers for both bodies now in the low hundreds thanks to additional high resolution surveys and revisiting the existing image databases

Time-resolved reconstruction of scene reflectance hidden by a diffuser

We use time-of-flight information in an iterative non-linear optimization algorithm to recover reflectance properties of a three-dimensional scene hidden behind a diffuser. We demonstrate reconstruction of wide-field images without relying on diffuser correlation properties

Decomposing global light transport using time of flight imaging

Global light transport is composed of direct and indirect components. In this paper, we take the first steps toward analyzing light transport using high temporal resolution information via time of flight (ToF) images. The time profile at each pixel encodes complex interactions between the incident light and the scene geometry with spatially-varying material properties. We exploit the time profile to decompose light transport into its constituent direct, subsurface scattering, and interreflection components. We show that the time profile is well modelled using a Gaussian function for the direct and interreflection components, and a decaying exponential function for the subsurface scattering component. We use our direct, subsurface scattering, and interreflection separation algorithm for four computer vision applications: recovering projective depth maps, identifying subsurface scattering objects, measuring parameters of analytical subsurface scattering models, and performing edge detection using ToF images.United States. Army Research Office (contract W911NF-07-D-0004)United States. Defense Advanced Research Projects Agency (YFA grant)Massachusetts Institute of Technology. Media Laboratory (Consortium Members)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie