A. C. Boccara

Thermo-optical spectroscopy : Detection by the mirage effect

A new thermo‐optical method based on the sensitive detection of thermal gradients adjacent to heated sample surfaces is described. Room‐ and low‐temperature experiments were performed using this technique, and its advantages over different methods are discussed.

Measuring the transmission matrix in optics: an approach to the study and control of light propagation in disordered media.

We introduce a method to experimentally measure the monochromatic transmission matrix of a complex medium in optics. This method is based on a spatial phase modulator together with a full-field interferometric measurement on a camera. We determine the transmission matrix of a thick random scattering sample. We show that this matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. This method might give important insight into the mesoscopic properties of a complex medium.

Thermal-light full-field optical coherence tomography.

We have built a high-resolution optical coherence tomography (OCT) system, based on a Linnik-type interference microscope, illuminated by a white-light thermal lamp. The extremely short coherence length of the illumination source and the large aperture of the objectives permit resolution close to 1 microm in three dimensions. A parallel detection scheme with a CCD camera provides cross-section (x-y) image acquisition without scanning at a rate of up to 50 Hz. To our knowledge, our system has the highest resolution demonstrated to date for OCT imaging. With identical resolution in three dimensions, realistic volume rendering of structures inside biological tissues is possible.

Ultrasonic tagging of photon paths in scattering media:?parallel speckle modulation processing

Tagging of photon trajectories in scattering media is possible by application of a localized ultrasonic field to the sample and by measurement of the induced speckle modulation. Instead of using a single optical detector, which integrates the signal of many speckle grains, we propose a more efficient detection scheme that uses a CCD camera and parallel lock-in detection to record the full modulation of the speckle. The advantage of this multiplex detection is demonstrated, as well as the imaging capabilities of the process for biological tissues.

Infrared-reflection-mode near-field microscopy using an apertureless probe with a resolution of λ/600

We report a near-field optical microscopy experiment at lambda = 10.6 microm, using an apertureless metallic tip functioning simultaneously in the atomic force microscopy tapping mode. The 17-nm optical resolution (lambda/600) that we achieved confirms the validity and the potential of this concept for numerous applications.

Polarization effects in apertureless scanning near-field optical microscopy: an experimental study.

Strong electric-field enhancements at the apex of a tungsten tip illuminated by an external light source were recently predicted theoretically. We present an experimental study of the dependence of this effect on the polarization angle of the incident light. It is shown that the intensity of the light scattered by the tungsten tip of an apertureless scanning near-field optical microscope is 2 orders of magnitude higher when the incident light is p polarized than when it is s polarized. This experimental result is in good agreement with theoretical predictions and provides an easy way to test the quality of the tips.

Three-dimensional cellular-level imaging using full-field optical coherence tomography

An ultrahigh-resolution full-field optical coherence tomography (OCT) system has been developed for cellular-level imaging of biological media. The system is based on a Linnik interference microscope illuminated with a tungsten halogen lamp, associated with a high-resolution CCD camera. En face tomographic images are produced in real time, with the best spatial resolution ever achieved in OCT (0.7 microm x 0.9 microm, axial x transverse). A shot-noise limited detection sensitivity of 80 dB can be reached with an acquisition time per image of 1 s. Images of animal ophthalmic biopsies and vegetal tissues are shown.

Sensitive in situ trace-gas detection by photothermal deflection spectroscopy

We present a sensitive (5ppb for ethylene, 10−7 cm−1) and simple photothermal scheme for the detection of trace gases and measuring weak absorption in gas‐phase samples. We also demonstrate the feasibility of this scheme for performing in situ measurements in the absence of sample cells or containers, thus eliminating the drawbacks of sampling and sampling techniques. Factors limiting our detectivity are discussed, and a comparison to the thermal lens effect is made.

Full-field birefringence imaging by thermal-light polarization-sensitive optical coherence tomography. II. Instrument and results

We describe an instrument for measuring the magnitude of birefringence of tomographic images and the principal directions of axes that use thermal-light polarization-sensitive optical coherence tomography. The instrument permits full-field measurements with an axial resolution of 1.5 microm and a transverse resolution limited by diffraction. We obtained a sensitivity of 84 dB, limited by shot noise, when we integrated the signal for 1 s. We verified the validity of the measurement by measuring the birefringence of a variable phase shifter. We present typical results obtained with optical samples.

Controlling light through optical disordered media: transmission matrix approach

We experimentally measure the monochromatic transmission matrix (TM) of an optical multiple scattering medium using a spatial light modulator together with a phase-shifting interferometry measurement method. The TM contains all the information needed to shape the scattered output field at will or to detect an image through the medium. We confront theory and experiment for these applications and study the effect of noise on the reconstruction method. We also extracted from the TM information about the statistical properties of the medium and the light transport within it. In particular, we are able to isolate the contributions of the memory effect and measure its attenuation length.