Investigations of the MGy dose level radiation effects on the photometric budget of a radiation-hardened CMOS-based camera.

We studied the impact of ionizing radiation at high dose levels (megagray, MGy) on the photometric budget of a radiation-resistant complementary metal oxide semi-conductor (CMOS)-based camera. This is achieved by measuring the radiation-induced degradation of each subpart, namely its illumination system, its optical system, and its CMOS image sensor. The acquired experimental results allow performing a rather realistic simulation of the radiation effects at the system level. Thanks to appropriate mitigation techniques, limited image darkening and color change are obtained at MGy dose levels. The presented results confirm the feasibility of a CMOS-based camera able to resist to MGy dose level of ionizing radiations with an acceptable degradation of the image quality, opening the way to its implementation in the most challenging harsh environments.

Shack-Hartmann multiple spots with diffractive lenses.

In this Letter we aim to bring an understanding to the apparition of multiple spots when using a Shack-Hartmann (SH) wavefront sensor behind diffractive lenses. In contrast to previous work, this phenomenon is described in terms of diffractive orders. It is illustrated with Zemax simulations, where three kinds of diffractive lenses (monofocal, bifocal, and trifocal) are set behind a microlens array. The presence of multiple spots is related to the phase jump of the diffractive profile and also to the number of steps seen through the microlens pupil. The possibility of assessing the optical quality of such lenses using SH measurements is discussed, in particular within the field of ophthalmology, where the need for precautions is underlined.

Interfaces detection after corneal refractive surgery by low coherence optical interferometry.

The detection of refractive corneal surgery by LASIK, during the storage of corneas in Eye Banks will become a challenge when the numerous operated patients will arrive at the age of cornea donation. The subtle changes of corneal structure and refraction are highly suspected to negatively influence clinical results in recipients of such corneas. In order to detect LASIK cornea interfaces we developed a low coherence interferometry technique using a broadband continuum source. Real time signal recording, without moving any optical elements and without need of a Fourier Transform operation, combined with good measurement resolution is the main asset of this interferometer. The associated numerical processing is based on a method initially used in astronomy and offers an optimal correlation signal without the necessity to image the whole cornea that is time consuming. The detection of corneal interfaces - both outer and inner surface and the buried interface corresponding to the surgical wound - is then achieved directly by the innovative combination of interferometry and this original numerical process.

Low coherence interferometry for central thickness measurement of rigid and soft contact lenses.

In this paper we propose contact lens central thickness measurement with a low coherence interferometry technique using either a SLED source or a broadband continuum generated in air-silica Microstructured Optical Fiber (MOF) pumped with a picosecond microchip laser. Each of these sources associated with the interferometer provides, at the same time, good measurement resolution and quick signal recording without moving any optical elements and without need of a Fourier Transform operation. Signal improvement is performed afterwards by a numerical treatment for optimal correlation peaks detection leading to central thickness value of several contact lenses.

Video rate depth-resolved two-dimensional imaging through turbid media by femtosecond parametric amplification.

We report two-dimensional imaging through a liquid scattering medium by noncollinear femtosecond parametric amplification in a reflection configuration. The experiment presented permits direct observation at video rate of two-dimensional images with 24-mum depth resolution and 90-mum transverse resolution for an area with a 2.5-mm diameter on the object. These resolutions are achievable through a turbid phantom with a depth near 12 scattering mean free paths in double pass.

Imaging in diffuse media with ultrafast degenerate optical parametric amplification.

We demonstrate the application of a subpicosecond optical parametric amplifier working at degeneracy to imaging in diffuse media. This optical parametric amplifier exhibits small-signal gains greater than 10(4), thereby acting as a high-gain ultrafast amplifying gate. We have used it to construct the image of a grid pattern hidden behind 20 mean free paths of a highly diffusing solution of latex microspheres with a spatial resolution of 200 microm.

Extinction measurements in diffusing mammalian tissue with heterodyne detection and a titanium:sapphire laser.

Total optical absorption in mammalian tissues is measured in the near infrared by the use of heterodyne detection and a Ti:sapphire laser. Because of the high sensitivity, directivity, and signal-to-noise ratio of the setup, we were able to detect coherent photons after attenuation by more than 9 optical densities. This method allows us to detect unscattered photons that are passing through more than 7 mm of various tissues such as brain, muscle, liver, skin, and fat selectively.