Radiant intensity | EPFL Graph Search

In radiometry, radiant intensity is the radiant flux emitted, reflected, transmitted or received, per unit solid angle, and spectral intensity is the radiant intensity per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. These are directional quantities. The SI unit of radiant intensity is the watt per steradian (), while that of spectral intensity in frequency is the watt per steradian per hertz () and that of spectral intensity in wavelength is the watt per steradian per metre ()—commonly the watt per steradian per nanometre (). Radiant intensity is distinct from irradiance and radiant exitance, which are often called intensity in branches of physics other than radiometry. In radio-frequency engineering, radiant intensity is sometimes called radiation intensity. Mathematical definitions Radiant intensity Radiant intensity, denoted Ie,Ω ("e" for "energetic", to avoid confusion with photometric qu

Second harmonic scattering of water in a biological context

Tereza Schönfeldová

Water is one of the most abundant molecules in the universe. It forms a hydrogen bond network with unique structure and dynamics. Hydrogen bonding is highly relevant to many biological processes including membrane formation, protein folding, adsorption, and lubrication. However, the underlying molecular interactions within water and between water and membranes are difficult to study and hence not fully understood. In this thesis, we utilize second harmonic scattering (SHS) to investigate inhomogeneities in bulk water, probe structural changes in lipid bilayer membranes, and detect and characterize protein-membrane interactions. Firstly, we explore the structure of bulk water in comparison to a common model liquid, carbon tetrachloride. Combining SHS measurements and molecular dynamics simulations, we report on the nanoscale inhomogeneities in bulk water that occur on femtosecond timescales. We attribute the rise in the coherent second harmonic (SH) intensity to charge density fluctuations with enhanced nanoscale polarizabilities around transient voids. Even though the transient voids also exist in carbon tetrachloride, they do not show polarizability fluctuations and the SH response of carbon tetrachloride thus corresponds to that of a model isotropic liquid. Then, we study the structure of water around large unilamellar vesicles (LUVs), which serve as a model for cell membranes. We focus on the role of water during the lipid melting phase transition. Using SHS, differential scanning calorimetry, and temperature-dependent zeta-potential measurements, we investigate the structural changes of hydration shells around the vesicle membrane. We use lipids with phosphoserine, phosphocholine, and phosphate headgroups and observe different hydration behavior upon the lipid melting transition depending on the membrane composition. Next, we characterize the interface of membranes composed of lipids containing phosphocholine and phosphate headgroups in solutions with different CaCl2 concentrations. We observe that the SH intensity is decreasing with the addition of CaCl2, which we attribute to the formation of a condensed layer of Na+ counterions on the inner leaflet of the LUVs. Additionally, we extract the vesicle surface potential and second-order surface susceptibility from SHS data for membranes with different content of lipids with phosphate headgroups, and observe composition dependent behaviour which suggests structural membrane reorganization. We continue by exploring protein-membrane interactions using water as a contrast agent. We study a pore-forming toxin, perfringolysin O (PFO), known for selective insertion into cholesterol-rich membranes. Combining SHS measurements and cryo-electron microscopy, we compare the interaction between PFO and LUV membranes with a high and low cholesterol content. By obtaining a sub-picomolar insertion constant of PFO, we show that SHS can be used to determine protein-membrane binding constants in concentration ranges not accessible by conventional methods.Finally, we investigate the interaction of protein aerolysin and its mutants with lipid membranes. We observe changes in surface charge in the cap region of membrane-bound aerolysin at different pH of the surrounding solution. By combining SHS with single-channel measurements, we obtain the membrane binding constant of wild-type aerolysin and its mutants, and we dissect their pore-forming mechanism.

EPFL2022

Learning of physical systems: from inference to control

Babak Rahmani

To characterize a physical system to behave as desired, either its underlying governing rulesmust be known a priori or the system itself be accurately measured. The complexity of fullmeasurements of the system scales with its size. When exposed to real-world conditions, suchas perturbations or time-varying settings, the system calibrated for a fixed working conditionmight require non-trivial re-calibration, a process that could be prohibitively expensive, inefficientand impractical for real-world use cases.In this thesis, a learning procedure for solving highly ill-posed problems of modeling a system'sforward and backward response functions is proposed. In particular, deep neural networksare used to infer the input of a system from partial measurements of its outputs or to obtain adesired target output from a physical system.I showcase the applicability of the proposed methods for inference and control in opticalmultimode fibers. Amplitude/phase-encoded input of a multimode fiber is reconstructedfrom intensity-only measurements of the outputs. Conversely, the required input of the fiberfor projecting a desired output is obtained using intensity-only measurements of the output.Next, the stochastic neural network of the retina in Salamander is modeled by a probabilisticneural network. The model is used to optimize the input stimuli so as to find the simplestspatiotemporal patterns that elicit the same neuronal spike responses as those elicited byhigh-dimensional stimuli.As demonstrated in this thesis, application of data-driven methods for characterization ofcomplex large-scale real-world systems has proved useful in simplifying the measurement apparatus,end-to-end optimization of the system and automatic compensation of perturbation.

EPFL2022

Limitations of Proximity Lithography Printing

Krishnaparvathy Puthankovilakam

Photolithography is one of the earliest technologies used to transfer patterns to a substrate. It is also known as optical lithography since it uses light to transfer the pattern. The main exposure techniques exist in the industry are projection printing, contact printing, and proximity printing. Projection printing technology uses optical elements between mask and wafer to project the feature on the mask to the wafer. This is very expensive and delivers the highest resolution. In contact printing, the mask and wafer are in contact with each other and in proximity printing, the mask is kept at some proximity distance away from the wafer. Proximity printing is an easy and cost effective printing technique because the damage to the mask will be less and also no optical elements between mask and wafer are used. The main drawback of the proximity printing is the diffraction effect caused by the proximity gap between mask and wafer, which limits the resolution. The main objective of this thesis is to study the limitations of proximity printing and to increase its resolution. To study the limitations, different types of design strategies and verification methods are used in the thesis. First is the simulation technique which is performed with GenISys Layout LAB. This is specially designed for proximity printing. The software gives the aerial image and final resist pattern as output. The most interesting and important aspect is the second verification technique which is the experimental setup. A measurement setup has been built to study the light propagation from different masks and to study the aerial image at different proximity gaps. The setup is known as High Resolution Interference Microscopy (HRIM). The setup is basically a Mach- Zehnder interferometer having different light sources, sample plane and reference arm which are used according to the samples. The final verification is achieved using the mask aligner. Both the simulation and experiments are carried out using a special illumination optics called MO exposure optics from Süss MicroOptics. The thesis mainly focuses on the rule based optical proximity correction a technique which is a simple method for mass production. Correction structures are designed for one dimensional and two dimensional features in amplitude masks. Adding lines near the edge to improve the edge slope will be discussed as the one dimensional correction. The different intensity cutting planes and the comparison between simulation and experimental results will be discussed along with that. A unified correction structure is designed to solve corner rounding problem and will be studied as the two dimensional study. The structure is defined to print different line widths at single proximity gap on single exposure. Usually, all the structures in the amplitude mask are studied with their aerial image intensities at different proximity gaps. But, here the study extends to phase evaluation also. The measurement technique can measure both intensity and phase evolution from the mask structures. Phase evolution from amplitude correction features will be discussed and how the phase modulates the intensity patterns is also studied. The role of fundamental principles like phase singularities, phase shifts are also discussed to find its effects on proximity printing structures. The study also leads to the intensity and phase propagation from phase shifting mask (PSM) . The structure evaluated is a group of corners in PSM.

EPFL2017

Second harmonic scattering of water in a biological context

Tereza Schönfeldová

EPFL2022

Limitations of Proximity Lithography Printing

Krishnaparvathy Puthankovilakam

EPFL2017