Synthetic-aperture chirp confocal imaging.

An imaging system that combines synthetic-aperture imaging, holography, and an optical chirp with confocal imaging is described and analyzed. Comparisons are made with synthetic-aperture radar systems. Adaptation of several synthetic-aperture radar techniques to the optical counterparts is suggested.

Ultrafast, cross-correlated harmonic imaging through scattering media.

A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of objects obscured by a highly scattering medium when no ballistic component is evident in the scattered light and imaging is performed with any portion of the scattered light pulse. We present a time-gated, inherently low-pass spatially filtered imaging method that minimizes signal-averaging requirements and greatly facilitates imaging under severe scattering (turbid) conditions.

Investigation of ultrafast time gating by spatial filtering.

With a spatial-filtering method of gating, we explore image formation through scattering media using first-arriving light. Gating times of a few femtoseconds and less are produced, and the resolution at these extremely short gating times is investigated.

Spatially partially incoherent and broad spectrum holographic stereo vision.

We suggest a technique that allows reconstruction of three-dimensional objects with spatially incoherent broad-spectrum illuminating light sources. The reconstruction is obtained by the realization of a holographically recorded parallax-based stereo vision. Experimental results demonstrate the suggested technique.

Physician asthma management practices in Canada.

OBJECTIVES: To establish national baseline information on asthma management practices of physicians, to compare the reported practices with the Canadian Consensus recommendations and to identify results potentially useful for interventions that improve physician asthma management practices. DESIGN: National, stratified cross-sectional survey. SETTINGS: The 10 provinces and two territories of Canada, from 1996 to 1997. PARTICIPANTS: Questionnaires were sent to 4489 physicians stratified by province/territory and specialty group (family/general practice, respirology, internal medicine, pediatrics and allergy/immunology); 2605 responses were received. OUTCOME MEASURES: Methods for the diagnosis, treatment, education and follow-up of patients with asthma ('asthma management practices'). RESULTS: Significant variations existed among the five specialty groups in asthma management practices. A low use of objective measures of airflow limitation to assist with diagnosis was found among some respondents (mostly family physicians). Up to 40% of physicians regarded the daily fixed dosing (three or four times a day) of inhaled, short acting beta2-agonist as 'first-line therapy' for moderate to severe asthma. A minority of physicians reported using written action plans for patients or referring them to other health professionals for asthma education. Insufficient time during appointments and a perceived lack of appropriate educational materials were frequently cited as reasons for not providing asthma education. The perceived knowledge of the Canadian Consensus recommendations varied among physicians but was lowest among nonspecialists. CONCLUSIONS: The survey showed variations in certain aspects of the management of asthma by physicians. The findings will help to target specific areas for future physician education programs and other behavioural change strategies.

Volume reflection holographic confocal imaging.

The Denisyuk volume reflection hologram is produced with spatially incoherent light to form an image-plane hologram. The image formed in readout combines the properties of volume holography and confocal image formation.

Spectral holography for coherence-gated imaging.

A spectral-holography application called spectral-decomposition holography forms a recorded image according to optical path length. In this method all wavelength components of a broad-spectrum source simultaneously backlight a nonscattering binary-phase object. A spectral hologram is thus recorded. Subsequent computer processing recovers temporally discriminated images.

Realization of time gating by use of spatial filtering.

A method for simulating conventional time gating in low-coherence optical imaging processes in highly scattering media is given. The method uses monochromatic instead of broadband light, and spatial filtering is substituted for time gating. The process enables the study of imaging techniques in scattering media to be carried out in an easy and highly controllable way. Experimental results are given.

Electronic channel fringe holography for depth and delay measurements.

Electronic spectral holography in the form developed by Shih [Ph.D. dissertation, University Microfilms, Ann Arbor, Mich. (1995)] is adapted to various applications, including optical coherence tomography in scattering media, contouring of surfaces, and optical fiber mode examination.

Ensemble-averaged Shack-Hartmann wave-front sensing for imaging through turbid media.

A technique is described for ensemble-averaging the light wave emerging from a turbid medium, enabling the recovery of optical information that is otherwise lost in a speckle pattern. The technique recovers both an amplitude and a phase function for a wave that has been corrupted by severe scattering, without the use of holography. With the phase estimated, an ensemble-averaged field is constructed that can be backprojected to form an image of the object obscured by the scattering medium. Experimental results suggest that the technique can resolve two object points whose signals are unresolved on the exit surface of a diffuser.

Time-gated ensemble-averaged imaging through highly scattering media.

A previously described ensemble-averaged imaging method [Opt. Lett. 21, 1691 (1996)] is extended by its combination with holographically implemented time-gated imaging. This combined method is shown to extend the effectiveness of the ensemble-averaged method by permitting imaging through thicker diffusers. Experimental results are presented.

High-resolution optical chirped pulse gating.

We describe a system for achieving high-resolution range gating using optically chirped pulses. The technique converts signals from the time domain into signals in the frequency domain through a nonlinear, sum-frequency generation process. The technique is based on similar methods used in microwave radar. We draw analogies between our method and conventional and time-lens imaging processes, and present experimental results demonstrating the method.

Direct three-dimensional image transmission through single-mode fibers with monochromatic light.

Direct three-dimensional image transmission through one single-mode or multimode fiber is demonstrated. Image transmission is carried out with a grating interferometer under monochromatic, spatially incoherent illumination.

Ensemble-averaged imaging through highly scattering media.

A method for imaging through highly scattering media is described that consists of forming a multiplicity of holograms and performing an extensive averaging process. This process produces an estimate of the phase distribution across the exiting surface of the medium. This information is combined with the available magnitude data to form an ensemble-averaged wave front that can be backprojected to form an image of absorbers within or behind the scattering medium.

Coherence confocal-imaging system for enhanced depth discrimination in transmitted light.

A system for image-plane holography that uses a spectrally and spatially broad radiation source is analyzed and shown to provide depth discrimination in excess of that offered by conventional confocal imaging. The enhanced depth discrimination is a consequence of two factors: the simultaneous reduction of both the spatial and the temporal coherence of the source, and the special property of certain grating interferometers of presenting a spectrally dispersed light beam to the object while forming achromatic fringes at the hologram-recording plane.

Resolution-enhanced detection of moving objects embedded within scattering media using time-gated speckle methods.

The holographic first-arriving-light method in combination with the speckle differencing method is used to provide resolution-enhanced detection of moving objects embedded in scattering media. Results show that the first-arriving-light technique provides significant resolution improvements over standard speckle differencing.

Analysis of direct three-dimensional image transmission through optical fibers by the use of coherence methods.

The use of a grating interferometer under spatially incoherent illumination for direct three-dimensional image transmission through optical fibers is analyzed. The issues of resolution, image depth, and signal-to-noise ratio are addressed. Experimental results are presented.

Detection of moving objects embedded within scattering media by use of speckle methods.

Speckle-pattern subtraction methods are used for the detection of moving objects embedded in scattering media. Results show that the ability to detect small nonstationary objects is greatly enhanced.

Spatial filtering of first-arriving light.

The effect of combining low-pass spatial filtering with the first-arriving-light method for imaging through a scattering medium was investigated. The modification is highly effective for media having a significant specular transmission component but is essentially ineffective for media without a specular component.

Stretch, time lenses, and incoherent time imaging.

The stretch, or time-lens, concept is developed further. Alternative formulations that lead to invariant systems are described, as well as methods for synthesizing the time equivalent of spatially and temporally incoherent systems.