Publications by Theo Lasser | EPFL Graph Search

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We present a phase-shifting quantitative phase imaging technique providing high temporal and spatial phase stability and high acquisition speed. A piezoelectric microfabricated phase modulator allows tunable modulation frequencies up to the kHz range. Afte ...

Super-resolution optical fluctuation imaging (SOFI) allows one to perform sub-diffraction fluorescence microscopy of living cells. By analyzing the acquired image sequence with an advanced correlation method, i.e. a high-order cross-cumulant analysis, super-resolution in all three spatial dimensions can be achieved. Here we introduce a software tool for a simple qualitative comparison of SOFI images under simulated conditions considering parameters of the microscope setup and essential properties of the bio

For Fourier domain optical coherence tomography any sample movement during camera integration causes blurring of interference fringes and as such reduction of sensitivity for flow detection. The proposed method overcomes this problem by phase-matching a re ...

A novel imaging method employing the different kinetics of the energetic states of fluorescent markers is presented, where the contrast depends on the triplet kinetics. An attractive feature of triplet states is their long lifetime, rendering them highly sensitive to the immediate environment of their fluorescent host molecules. They typically have a lifetime of the order of ~10us to 10ms, which is 3-6 orders of magnitude longer than the lifetimes of fluorescent singlet states. The concept exploits characte

A method and a microscopy imaging apparatus for generating an optically sectioned image of a specimen are provided. The method comprises the steps of:illuminating the specimen with a modulating, spatially periodic illumination pattern; imaging said specimen on a conjugate image plane; acquiring a plurality of signals at respective positions on said image plane, each signal corresponding to the incident light intensity at that position and having an oscillatory component caused by the modulation of the illum

Visualization of data concerns most scientists. The use of color is required in order to display multidimensional information. In addition, color encoding a univariate image can improve the interpretation significantly. However up to 10% of the adult male ...

NOVELTY - The method involves generating colored images, where a common complementary metal-oxide semiconductor sensor (7) has multiple sensor elements. A light with different wavelengths is supplied separately for recording color images. A radiation with ...

We used Optical Coherence Microscopy (OCM) to monitor structural and functional changes due to ischemic stroke in small animals brains in vivo. To obtain lateral resolution of 2.2 μm over the range of 600 μm we used extended focus configuration of OCM inst ...

A new femtosecond pump-probe spectroscopy technique is demonstrated that permits the high-speed, parallel acquisition of pump-probe measurements at multiple wavelengths. This is made possible by use of a novel, two-dimensional smart pixel detector array that performs amplitude demodulation in real time on each pixel. This detector array can not only achieve sensitivities comparable with lock-in amplification but also simultaneously performs demodulation of probe transmission signals at multiple wavelengths,

Based on spectral interferometry and wavelength multiplexing, we demonstrate that a combination of these methods could lead to a 3D imaging system. This system has the advantage of a one-dimensional geometry transmission channel and a limited scanning need. This kind of imaging system could, of course, be of a great interest in small size endoscope with 3D imaging capability and a small channel cross-section (less than 1 mm). Theoretical analysis as well as experimental proof of principle is presented in th

Surface molecules, distributed in diverse patterns and clusters on cell membranes, influence vital functions of living cells. It is therefore important to understand their molecular surface organisation under different physiological and pathological condit ...

With fluorescence correlation spectroscopy (FCS), the diffusion and concentration of proteins (wheat germ agglutinin) in a nanofluidic system are measured on a single molecule level. By increasing the ionic concentration, the Debye length of the electrical double layer (EDL) decreases altering the strongly enhanced surface interactions of charged proteins in nanochannels. A theoretical model of the transport of charged mole- cules in nanofluidics facilitates the design of future nanochannel applications.

Fluorescence fluctuation spectroscopy based on an evanescent field excitation scheme leads to an alternative concept for single molecule detection with interesting experimental features. This concept is described and analyzed regarding the total fluorescence process including excitation, fluorescence emission and collection close to a dielectric interface. The realized experimental scheme showed superior performance of this concept with substantially enhanced molecular brightness when compared to the classi

A simple method for the calibration of optical path difference modulation in low-coherence interferometry is presented. Spectrally filtering a part of the detected interference signal results in a high-coherence signal that encodes the scan imperfections and permits their correction. The method is self-referenced in the sense that no secondary high-coherence light source is necessary. Using a spectrometer setup for spectral filtering allows for flexibility in both the choice of calibration wavelength and th

We address the problem of high-resolution reconstruction in frequency-domain optical-coherence tomography (FDOCT). The traditional method employed uses the inverse discrete Fourier transform, which is limited in resolution due to the Heisenberg uncertainty ...

The invention relates to a solid immersion lens (SIL) for a microscope, comprising a lens system with a predetermined numerical aperture. The refractive index of the material of the solid immersion lens is selected in such a way that the numerical aperture ...

The identification and accurate location of centers of brain activity are vital both in neuro-surgery and brain research. This study aimed to provide a non-invasive, non-contact, accurate, rapid and user-friendly means of producing functional images intrao ...

Fourier Domain Optical Coherence Tomography (FDOCT) is a high speed biomedical imaging modality which extracts the sample structure in depth. The axial resolution is given by the coherence length of the employed light source. The lateral resolution on the other hand is determined by the numerical aperture (NA) of the objective. The parallel detection of the depth information has the drawback of loosing transverse resolution along the optical axis, limiting the depth of field (DOF) and the use of FDOCT in th

The invention describes a method and a microscopy system for imaging and analysing stochastically and independently blinking point-like emitters. A multiple-order cumulants analysis in conjunction with an established blinking model enables the extraction o ...

We present the results on two-photon total-internal-reflection fluorescence correlation spectroscopy. The combination of liquid crystal spatial light modulator, providing radial polarization, with ultrafast laser (picosecond Nd:GdVO4 laser) allowed us to take the advantage of nonlinear optical contrast mechanisms to suppress the side-lobe energy specific for radial polarization and reduce the effective excited volume twice compared to one-photon evanescent wave excitation in fluorescence correlation spectro

Theo Lasser

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High-speed phase-shifting common-path quantitative phase imaging with a piezoelectric actuator

SOFI Simulation Tool: A Software Package for Simulating and Testing Super-Resolution Optical Fluctuation Imaging

Resonant Doppler flow imaging and optical vivisection of retinal blood vessels

Triplet imaging contrast by modulated excitation

Optically sectioned image generating method for microscopy imaging apparatus involves combining measured characteristics of signals from respective positions of conjugate image plane to generate optically sectioned image of specimen

How to display data by color schemes compatible with red-green color perception deficiencies

Method for recording color images and laser direct imaging signals of object, involves generating colored images, where common complementary metal-oxide semiconductor sensor has multiple sensor elements

Imaging of the stroke-related changes in the vascular system of the mouse brain with the use of extended focus Optical Coherence Microscopy

High-speed femtosecond pump probe spectroscopy with a smart pixel detector array

Multiplexed 3D imaging using wavelength encoded spectral interferometry: a proof of principle

Quantifying protein densities on cell membranes using super-resolution optical fluctuation imaging

Diffusion of Single Molecules in Nanochannels

Single molecule detection at surfaces

Self-referenced method for optical path difference calibration in low-coherence interferometry

Zero-crossing approach to high-resolution reconstruction in frequency-domain optical-coherence tomography

Solid immersion lens used in a microscope with a lens system is made of a material having a refractive index that is selected so that the numerical aperture of the lens system

Laser Doppler imaging for intraoperative human brain mapping

Fourier Domain Optical Coherence Microscopy with Extended Depth of Field

Cumulant microscopy

High volume confinement in two-photon fluorescence correlation spectroscopy with radially polarized light