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Cell disintegration by laser-induced transient microbubbles and its simultaneous monitoring by interferometry.

Selective retina treatment (SRT) is a novel short pulsed laser therapy of several retinal diseases associated with a decreased metabolism at the retinal pigment epithelium (RPE). The range of laser pulse energies is small, in which the desired selective RPE disintegration is achieved without adverse effects to the neural retina. Thus, a real-time dosimetry control is required. We investigated a noninvasive interferometric technique able to monitor microbubble formation around the intracellular melanin granula, which is the origin of the desired RPE damage. A porcine ex vivo RPE model was irradiated by single pulses (350 ns1.7 mus) of a neodymium: yttrium lithium fluoride laser (527 nm). The specimen was simultaneously probed by a Michelson interferometer (helium neon-laser: 633 nm) and by a hydrophone. Cell viability assays (Calcein-AM) were performed after irradiation. At threshold radiant exposure for cell death (ED(50)=129+/-5 mJ cm2 for 350 ns; ED50=180+/-5 mJ cm2 for 1.7 mus), the interferometric transients changed due to microbubble formation. No major differences in the bubble dynamics were observed between both pulse durations. An algorithm to determine cell death from the interferometric transients showed less than 10% false positive or false negative results for the applied laser expositions compared to the viability assay. Interferometry is a reliable noncontact technique to monitor RPE disintegration and may serve as real-time dosimetry control during SRT.

Animals↗
PubMed1999

Topography of the lunar poles from radar interferometry: a survey of cold trap locations.

Detailed topographic maps of the lunar poles have been obtained by Earth-based radar interferometry with the 3.5-centimeter wavelength Goldstone Solar System Radar. The interferometer provided maps 300 kilometers by 1000 kilometers of both polar regions at 150-meter spatial resolution and 50-meter height resolution. Using ray tracing, these digital elevation models were used to locate regions that are in permanent shadow from solar illumination and may harbor ice deposits. Estimates of the total extent of shadowed areas poleward of 87.5 degrees latitude are 1030 and 2550 square kilometers for the north and south poles, respectively.

Ice↗
PubMed1995

Electronic speckle pattern interferometry of the vibrating larynx.

Laser holography is a technique that creates a three-dimensional image of a static object. This technique can be applied to the analysis of vibrating structures. Electronic speckle pattern interferometry uses a laser for illumination of the vibrating object and solid state detectors and digital hardware technology for capturing and processing the image in real time. This was performed on a human cadaver larynx and is the first time an interferogram of vibrating vocal cords has ever been obtained. Dark and bright interference fringes are seen that represent the vibratory motion of the vocal folds. These are presented in still photos as well as real-time on videotape. This method can provide advantages over current techniques of laryngeal study: it is sensitive to motion in the vertical dimension, and the digital data can be quantitatively analyzed. Application of this technique to study the larynx should eventually be a valuable clinical tool and provide quantitative research data.

Adult↗
PubMed1983

Conformational response of the glycocalyx to ionic strength and interaction with modified glass surfaces: study of live red cells by interferometry.

We have measured separation distances between live human red blood cells and simple or modified glass surfaces, using the finite aperture technique of microscope interferometry. In general, separation increases as the ionic strength falls, in isotonic solutions. Restriction on movement parallel to the glass in all except the most dilute salt solutions, coupled with the absence of Brownian motion, indicates direct molecular contact with the substratum. Thus increased separation must be due to swelling of the glycocalyx under electrostatic forces. However, at approximately less than to 2mM adherent cells show a separation greater than 100 nm, execute Brownian motion and the restriction on lateral motion is less evident. This suggests that secondary minimum adhesion by long-range forces with little or no direct molecular connection occurs at extreme dilution only. Treatment of cells with trypsin reduces separation by up to 40 nm, but the extent to which this reflects reduced double-layer repulsion due to loss of surface charge, as opposed to the reduced opportunity for swelling in a trimmed-down glycocalyx, is unclear. Adhesion at a separation approximately 100 nm in 1 mM buffer after trypsinization supports the view that adhesion can occur without very long glycoprotein connections, but does not prove it. Adhesion to unwettable methylated glass and completely wettable unmethylated glass, with an identical ionic strength dependence of the separation, shows that hydrophilicity is not an absolute requirement. Red cells interact closely at all ionic strengths with glass made polycationic with poly-L-lysine, owing to electrostatic attraction. The interference technique also shows that adherent cells can be spaced from the glass by an intervening layer of previously absorbed serum albumin.

Cell Adhesion↗
PubMed2005

Two improved algorithms with which to obtain contoured windows for fringe patterns generated by electronic speckle-pattern interferometry.

Fringe patterns generated by electronic speckle-pattern interferometry are full of high-spatial-frequency and high-contrast speckle noise. Filtering with contoured windows has proved to be an efficient approach to filtering out speckle noise while retaining the fringe patterns. Furthermore, with contoured windows the contoured correlation fringe pattern method can be used to derive smooth, normalized, consistent fringes. Contoured windows previously were determined by fringe orientation only, and this process generated accumulated errors. We propose two new algorithms with which to obtain the contoured windows according to the fringe intensity slope and the distance ratio to neighboring skeletons. These new techniques can determine contoured windows more precisely.

Algorithms↗
PubMed2006

Surface plasmon resonance sensor based on polarization interferometry and angle modulation.

A surface plasmon resonance (SPR) sensing technique based on polarization interferometry and angle modulation is presented. Its sensitivity is not a direct function of variation of reflection intensity, nor of phase shift. Rather, it is a function of the complex reflection coefficient. A three times standard deviation detection limit of 5.1 x 10(-7) refractive index units in a 2 Hz bandwidth is obtained with our experimental setup. A theoretical analysis shows that this technique can provide a wide linear measurement range. Moreover, the sensitivity is insensitive to the thickness of gold films over approximately 5 nm. This SPR sensing technique is suitable for physical, chemical, and biological research.

Computer-Aided Design↗
PubMed2006

Three-wavelength electronic speckle pattern interferometry with the Fourier-transform method for simultaneous measurement of microstructure-scale deformations in three dimensions.

We present the simultaneous measurement of three-dimensional deformations by electronic speckle pattern interferometry using five object beams and three colors. Each color, corresponding to an orthogonal direction of displacement, is separated through dichroic filtering before being recorded by a separate CCD camera. Carrier fringes are introduced by tilting the beam path in one arm of each of the three interferometers. The measured deformation modulates these carrier fringes and is extracted using the Fourier-transform method to achieve high displacement sensitivity. The field of view is on the order of a millimeter, making the system suitable for study of microstructural deformations. We compare experimental results with calculated values to validate out-of-plane and in-plane deformation measurements and demonstrate sensitivity on the order of 10 nm.

Algorithms↗
PubMed1999

Pupil-size effects in fiber optic stellar interferometry.

The effects of finite telescope pupil sizes on the measurement of fringe visibility in fiber optic stellar interferometry are described. It is shown theoretically that the measured fringe visibility is equal to the cross correlation of the magnitude of the source's mutual coherence function with the cross correlation of the telescopes' effective pupil functions. If the telescopes' effective pupil diameters are not small compared with the width of the source's mutual coherence function, then the measured fringe visibility will be correspondingly distorted. The theoretical results are verified experimentally in a fiber optic Mach-Zehnder interferometer.

Extraterrestrial Environment↗
PubMed2001

Phase-map measurements by interferometry with sinusoidal phase modulation and four integrating buckets.

Phase-shifting interferometry based on the integrating-bucket technique with sinusoidal phase modulation is studied theoretically and demonstrated experimentally to obtain phase maps from double-beam interferometers. The method uses four frames obtained by integration of the time-varying intensity in an interference pattern during the four quarters of the modulation period. An optimum sinusoidal phase modulation is found to minimize the effect of the additive noise. The absolute accuracy of the phase measurements is discussed. Possible applications of the method are demonstrated with two interference microscopes with which the phase modulation is achieved by sinusoidal oscillation of a mirror attached to a piezoelectric transducer and by sinusoidal birefringence modulation with a photoelastic modulator. In both experimental arrangements, phase images can be produced in real time at a rate of several hertz. Noise measurements are reported and compared with theory.

Algorithms↗
PubMed2002

Determination of particle size by using the angular distribution of backscattered light as measured with low-coherence interferometry.

We employ a novel interferometer to measure the angular distribution of light backscattered by a turbid medium. Through comparison of the measured data with the predictions of Mie theory, we are able to determine the size of the scatterers comprising the medium with subwavelength precision. As the technique is based on low-coherence interferometry, we are able to examine the evolution of the angular distribution of scattered light as it propagates into the medium. The effects of multiple scattering as a function of penetration depth in the medium are analyzed. We also present various considerations for extending this technique to determining structural information in biological tissues, such as the effects of a distribution of particle sizes and the need to average out speckle contributions.

Interferometry↗
PubMed2007

Blind phase shift estimation in phase-shifting interferometry.

A blind phase shift estimation algorithm that allows simultaneous calculation of phases and phase shifts from three or more interferograms is presented. In phase-shifting interferometry, the phase shift errors introduce specific correlations between the calculated background intensity distribution and the fringe component. These correlations can be measured with a cross-power spectrum. By minimization of an objective function based on this cross-power spectrum, the actual phase shifts are estimated and used for phase recovery. The validity of this algorithm is verified by both the numerical simulation and the experiment results.

Algorithms↗
PubMed1989

Holographic interferometry applied to the case of large deformations.

This investigation in holographic interferometry concerns an approach to a systematic quasi-compensation by appropriate optical modifications at the reconstruction in order that the fringes of interference become visible in the case of large unknown object deformations. The relevant relations are established by using the aberration theory for the image formation in combination with elementary intrinsic differential geometry.

Algorithms↗
PubMed2003

Instantaneous quadrature low-coherence interferometry with 3 x 3 fiber-optic couplers.

We describe fiber-based quadrature low-coherence interferometers that exploit the inherent phase shifts of 3 x 3 and higher-order fiber-optic couplers. We present a framework based on conservation of energy to account for the interferometric shifts in 3 x 3 interferometers, and we demonstrate that the resulting interferometers provide the entire complex interferometric signal instantaneously in homodyne and heterodyne systems. In heterodyne detection we demonstrate the capability for extraction of the magnitude and sign of Doppler shifts from the complex data. In homodyne detection we show the detection of subwavelength sample motion. N x N (N > 2) low-coherence interferometer topologies will be useful in Doppler optical coherence tomography (OCT), optical coherence microscopy, Fourier-domain OCT, optical frequency domain reflectometry, and phase-referenced interferometry.

Equipment Design↗
PubMed2003

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

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 the maximum scan range. To demonstrate the method's usefulness, it is combined with a recently published digital spectral shaping technique to measure the thickness of a pellicle beam splitter with a white-light source.

Calibration↗
PubMed2005

Time-resolved measurements from speckle interferometry.

We present time-resolved measurements by speckle interferometry of the light scattered by a liquid medium. Measurements were performed by use of reflectance geometry and are compared with results obtained in the same conditions with a femtosecond laser and a streak camera. The setup was also tested in vivo on the forearm of a human volunteer to demonstrate the potential utility of such a setup for biomedical applications.

Equipment Design↗
PubMed2005

Development of a femtosecond micromachining workstation by use of spectral interferometry.

A workstation that permits real-time measurement of ablation depth while micromachining with femtosecond laser pulses is demonstrated. This method incorporates the unamplified pulse train that is available in a chirped-pulse amplification system as the probe in an arrangement that uses spectral interferometry to measure the ablation depth while cutting with the amplified pulse in thin metal films.

Equipment Design↗
PubMed2005

Common-path phase-shift interferometry surface plasmon resonance imaging system.

Surface plasmon resonance (SPR) and common-path phase-shift interferometry (PSI) techniques are integrated in a biosensing imaging system for measuring the two-dimensional spatial phase variation caused by biomolecular interactions on a sensing chip without the need for additional labeling. The common-path PSI technique has the advantage of long-term stability, even when it is subjected to external disturbances. Hence the system meets the requirements of the real-time kinetic studies involved in biomolecular interaction analysis. The proposed SPR-PSI imaging system demonstrates a detection limit of a 2 x 10(-7) refractive-index change, a long-term phase stability of 2.5 x 10(-4) pi rms for 4 h, and a spatial phase resolution of 10(-3) pi with a lateral resolution of 100 microm.

Biosensing Techniques↗