Staffan Schedin

Simultaneous three-dimensional dynamic deformation measurements with pulsed digital holography

The three deformation components x, y, z of a vibrating object are measured simultaneously by use of digital holography with a double-pulse ruby laser source. The object is illuminated from three different directions, each optically path matched with three reference beams such that three independent digital holograms are formed and added incoherently in one single CCD image. The optical phase difference between the two recordings taken for each hologram is quantitatively evaluated by the Fourier-transform method so that a set of three phase maps is obtained, representing the deformation along three sensitivity vectors. The total object deformation is obtained as a vector resultant from the data of the three phase maps. To give the full three-dimensional (3-D) description, the shape of the object is measured by the two-wavelength contouring method. Experiments are performed with a cylinder as the test object, transiently and harmonically excited. The 3-D deformation and shape measurement results are presented graphically.

Aberration compensation in digital holographic reconstruction of microscopic objects

Abstract We present a digital method for the compensation of the aberrations appearing when a lensless hologram of a microscopic object is reconstructed. The digital hologram of the microscopic object is recorded on a relatively low resolution device (CCD sensor). An expansion of the hologram by interpolation of the recorded intensity is performed in order to increase the number of pixels. For digital reconstruction of the wavefronts the expanded hologram is multiplied by the reference wave followed by simulation of the diffraction using the Rayleigh-Sommerfeld propagation relation. Experimental results are presented.

The unfolding of the P pili quaternary structure by stretching is reversible, not plastic

P pili are protein filaments expressed by uropathogenic Escherichia coli that mediate binding to glycolipids on epithelial cell surfaces, which is a prerequisite for bacterial infection. When a bacterium, attached to a cell surface, is exposed to external forces, the pili, which are composed of ∼103 PapA protein subunits arranged in a helical conformation, can elongate by unfolding to a linear conformation. This property is considered important for the ability of a bacterium to withstand shear forces caused by urine flow. It has hitherto been assumed that this elongation is plastic, thus constituting a permanent conformational deformation. We demonstrate, using optical tweezers, that this is not the case; the unfolding of the helical structure to a linear conformation is fully reversible. It is surmised that this reversibility helps the bacteria regain close contact to the host cells after exposure to significant shear forces, which is believed to facilitate their colonization.

Helicobacter pylori adhesion to carbohydrates.

Adherence of bacterial pathogens to host tissues contributes to colonization and virulence and typically involves specific interactions between bacterial proteins called adhesins and cognate oligosaccharide (glycan) or protein motifs in the host that are used as receptors. A given pathogen may have multiple adhesins, each specific for a different set of receptors and, potentially, with different roles in infection and disease. This chapter provides strategies for identifying and analyzing host glycan receptors and the bacterial adhesins that exploit them as receptors, with particular reference to adherence of the gastric pathogen Helicobacter pylori.

Tomographic reconstruction of transient acoustic fields recorded by pulsed TV holography

Pulsed TV holography combined with computerized tomography (CT) are used to evaluate the three-dimensional distribution of transient acoustic fields in air. Experiments are performed with an electrical discharge between two electrodes as the sound source. Holograms from several directions of the acoustic field are recorded directly onto a CCD detector by use of a double-pulsed ruby laser as the light source. Phase maps, representing projections of the acoustic field, are evaluated quantitatively from the recorded holograms. The projections are used for the CT reconstruction to evaluate the pressure-field distribution in any cross section of the measured volume of air.

Highly Sensitive Pulsed Digital Holography for Built-in Defect Analysis with a Laser Excitation.

A highly sensitive method is presented for noninvasive defect analysis on thin structures with a Q-switched double-pulsed ruby laser with frequency doubling (347 nm). In our research we feature an all-optical arrangement, where a focused laser pulse derived from the same ruby laser (694 nm) acts as a built-in synchronous excitation source for digital holographic interferometry. The recordings are made with a CCD camera for capturing two holograms (two states of the specimen) corresponding to the two UV laser pulses with a short time separation (10-50 mus). Subtraction of the phase distribution in two digital holograms gives a fringe phase map that shows the change in deformation of the specimen between the recordings. The advantage of the proposed method is two fold. First, the use of a shorter wavelength results in a higher sensitivity. Second, owing to the induced synchronous built-in optical excitation, the specimen is not subjected to any external physical excitation devices. Experimental results are presented on identification and evaluation of defects in thin metal sheets.

Pulsed digital holography for deformation measurements on biological tissues

Digital holograms are recorded of biological tissues by use of a Q-switched double-pulsed ruby laser. An image-plane digital holography setup is used with a CCD camera for capturing two holograms with a short time separation (20-800 micros). Subtraction of the phase distribution in two digital holograms yield a fringe phase map that shows the change in deformation of the tissue surface between the recordings. Experiments are performed on tissue from a pig that was excited by a short-shock pulse and on a human hand that was excited by sinusoidal stimulation. Results when the object is imaged through an endoscope are also presented. The technique could be an approach for measuring parameters like elasticity on biological tissues.

Lensless digital-holographic interferometry for the measurement of large objects

A method for the recording of digital holograms of large objects on electronic sensors is presented. An aperture is located between the object and the charge coupled device (CCD) sensor. A reference point source is located close to the aperture. The distance between the aperture and the CCD, its size and the location of the point source are chosen in order to permit the sensor to record the spatial frequencies of the interference pattern between the reference and the object light going through the aperture. The reconstruction is done digitally by performing a Fourier transform of the recorded intensity and filtering in the Fourier plane in order to get the complex amplitude of the object wavefront in the plane of the aperture. The imaging of the object in a plane is done by simulation of the propagation wavefront.

Pulsed digital holography combined with laser vibrometry for 3D measurements of vibrating objects

Abstract An optoelectronic system is presented that is used to measure the 3D vector components of a vibrating object. The complete determination of the vibration occurs by combination of three different measurements. 1. A 3D system based on digital holography for the measurement of the 3D deformation vector along the directions x, y and z is used. Pulses from a ruby laser are used to record holograms on CCD sensors, which are later digitally reconstructed. 2. The shape of the object is determined. A ruby laser emitting two pulses with different wavelengths is used. The shape is obtained by subtraction of the phases of the wavefronts recorded at the two different wavelengths. 3. For the absolute measurement of a vibration using double exposure holographic techniques, it is necessary to have a reference point where the absolute vibration is known. This measurement is done by using a 3D laser vibrometer.

Short coherence digital holography for 3D microscopy

Summary An optical system based on short coherence digital holography suitable for 3D microscopic investigations is described. An interferometer is built by using a short coherence laser (coherence length 50 micrometers). The sample is located in one arm of the interferometer, and the other arm is used as reference. The interference occurs only when the path lengths of the reference and measurement arms are matched within the coherence length of the laser. This interference pattern (hologram) is recorded on a CCD faceplate. The reference mirror position is shifted and, a sequence of holograms is recorded. These are then reconstructed numerically by using the wave propagation relation. The reconstruction contains the 3D information of the object. Experimental results showing the difference between a white light image and a short coherence hologram are presented.