Stephane Bourquin

Optical coherence topography based on a two-dimensional smart detector array

A low-coherence reflectometer based on a conventional Michelson interferometer and a novel silicon detector chip with a two-dimensional array of pixels that allows parallel heterodyne detection is presented. We demonstrate acquisition of three-dimensional images with more than 100,000 voxels per scan at a sensitivity of -58 dB and a rate of 6 Hz.

Video-rate optical low-coherence reflectometry based on a linear smart detector array.

A low-coherence reflectometer based on a conventional Michelson interferometer and a novel silicon detector chip that allows parallel heterodyne detection is presented. Cross-sectional images of 64x256 pixels covering an area of 1.92 mm x 1.3 mm are acquired at video rate and with a sensitivity close to the shot-noise limit. Applications in surface profiling and thickness measurement are demonstrated.

Parallel optical coherence tomography in scattering samples using a two-dimensional smart-pixel detector array

Parallel optical coherence tomography in scattering samples is demonstrated using a 58 x 58 smart-pixel detector array. A femtosecond mode-locked Ti:Sapphire laser in combination with a free space Michelson interferometer was employed to achieve 4 mum longitudinal resolution and 9 mum transverse resolution on a 260 x 260 mum field of view. We imaged a resolution target covered by an intralipid solution with different scattering coefficients as well as onion cells

Ultrahigh resolution real time OCT imaging using a compact femtosecond Nd:Glass laser and nonlinear fiber.

Ultrahigh resolution, real time OCT imaging is demonstrated using a compact femtosecond Nd:Glass laser that is spectrally broadened in a high numerical aperture single mode fiber. A reflective grating phase delay scanner enables broad bandwidth, high-speed group delay scanning. We demonstrate in vivo, ultrahigh resolution, real time OCT imaging at 1 microm center wavelength with <5 microm axial resolution in free space (<4 microm in tissue). The light source is robust, portable, and well suited for in vivo imaging studies.

Multiple scattering in optical coherence tomography. I. Investigation and modeling

We present a new model of optical coherence tomography (OCT) taking into account multiple scattering. A theoretical analysis and experimental investigation reveals that in OCT, despite multiple scattering, the field backscattered from the sample is generally spatially coherent and that the resulting interference signal with the reference field is stationary relative to measurement time. On the basis of this result, we model an OCT signal as a sum of spatially coherent fields with random-phase arguments--constant during measurement time--caused by multiple scattering. We calculate the mean of such a random signal from classical results of statistical optics and a Monte Carlo simulation. OCT signals predicted by our model are in very good agreement with a depth scan measurement of a sample consisting of a mirror covered with an aqueous suspension of microspheres. We discuss other comprehensive OCT models based on the extended Huygens-Fresnel principle, which rest on the assumption of partially coherent interfering fields.

Multiple scattering in optical coherence tomography. II. Experimental and theoretical investigation of cross talk in wide-field optical coherence tomography

We present a comprehensive study of multiple-scattering effects in wide-field optical coherence tomography (OCT) realized with spatially coherent illumination. Imaging a sample made of a cleaved mirror embedded in an aqueous suspension of microspheres revealed that, despite temporal coherence gating, multiple scattering can induce significant coherent optical cross talk. The latter is a serious limitation to the method, since it prevents shot-noise-limited detection and diffraction-limited imaging in scattering samples. We investigate the dependence of cross talk on important system design parameters, as well as on some relevant sample properties. The agreement between theoretical and experimental results for the wide range of parameters investigated was very good, in both the lateral and the axial dimensions. This further confirms the validity of the model developed in our companion paper [J. Opt. Soc. Am. A 22, 1369-1379 (2005)].

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

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, thus permitting rapid time- and wavelength-resolved femtosecond pump-probe spectroscopy. Measurements on a thin sample of bulk GaAs are performed across 58 simultaneous wavelengths. Differential probe transmission changes as small as approximately 2 x 10(-4) can be measured over a 5-ps delay scan in only approximately 3 min. This technology can be applied to a wide range of pump-probe measurements in condensed matter, chemistry, and biology.

Real-time optically sectioned wide-field microscopy employing structured light illumination and a CMOS detector

Real-time optically sectioned microscopy is demonstrated using an AC-sensitive detection concept realized with smart CMOS image sensor and structured light illumination by a continuously moving periodic pattern. We describe two different detection systems based on CMOS image sensors for the detection and on-chip processing of the sectioned images in real time. A region-of-interest is sampled at high frame rate. The demodulated signal delivered by the detector corresponds to the depth discriminated image of the sample. The measured FWHM of the axial response depends on the spatial frequency of the projected grid illumination and is in the μm-range. The effect of using broadband incoherent illumination is discussed. The performance of these systems is demonstrated by imaging technical as well as biological samples.

Transverse priority scanning and microscopy for high-resolution optical coherence tomography

We demonstrate methods for achieving high resolution imaging using alternate scanning techniques in optical coherence tomography and optical coherence microscopy. These techniques enable high transverse resolutions and overcome depth of field limitations. Cellular level resolutions in human tissue may be achieved.

A semi-analytical model accounting for multiple scattering in optical coherence tomography

We present a semi-analytical model of optical coherence tomography (OCT) taking into account multiple scattering. The model rests on the assumptions that the measured portion of the backscattered sample field is spatially coherent and that the sample is motionless relative to measurement time. This allows modeling an OCT signal as a sum of spatially coherent fields with random phase arguments-constant during measurement time-caused by multiple scattering. We calculate the mean OCT signal from classical results of statistical optics and a Monte Carlo simulation. Our model is shown to be in very good agreement with a whole range of experimental data gathered in a comprehensive study of cross-talk in wide-field OCT realized with spatially coherent illumination. The study consists of depth scan measurements of a mirror covered with an aqueous suspension of microspheres. We investigate the dependence of cross-talk on important optical system parameters, as well as on some relevant sample properties. We discuss the more complex OCT models based on the extended Huygens-Fresnel principle, which rest on different assumptions since they assume partially coherent interfering fields.