Fiber orientation measurement using polarization imaging.

In this paper, we present a new technique to determine the orientation of hair fiber, a key parameter in the evaluation of visual appearance of hair. Using polarization imaging and image analysis tools, we are able to measure the orientation of hair fiber for each pixel in the image. A theoretical analysis of the optical set-up is presented. Experimental data on a single fiber, hair tress, and complete head are given. Application to shampoo and conditioner is also demonstrated.

New luster formula for the characterization of hair tresses using polarization imaging.

Hair luster is one of the most important parameters of visual appearance perceived by consumers. Current luster formulae (TRI, Reich-Robbins, ...) are optimized for goniophotometric measurements. They are based on a mathematical decomposition of reflected light into specular and diffused light and the meaurement of the shine peak width on the fitted angular distributions. In this expose, we are describing a polarization imaging system measuring luster of hair tresses with an innovative algorithm. Using polarization imaging allows to physically separating the specular light from the diffused light for each pixel of the imaged tress. Angular distributions of the specular and diffused light are obtained in a few seconds. Where conventional methods calculate the shine peak width on the angular distribution, the imaging system imitates the human eye and calculates the shine width directly on the image. The new formula combines different measured parameters to objectively quantify luster. It was designed to exhibit a higher correlation with visual perception along with a higher sensitivity. Results obtained with conventional formulae are compared on different hair tresses, treated and untreated. The new formula is found to be consistent for a whole range of hair colors, from light to dark.

Low-noise photorefractive amplification and detection of very weak signal beams.

We present theoretical and experimental analyses of the signal-to-noise ratio (SNR) of photorefractive two-wave mixing detection that uses BaTiO(3). The influence of beam fanning is taken into account in the detection process. Different known methods to enhance the SNR of the detection are theoretically and experimentally compared. A 10-fold improvement of the SNR is obtained, and the detection of a 1-pW signal intensity for a SNR of 50 is achieved for two of them.

Low-noise preamplifier for multistage photorefractive image amplification.

We present a two-beam coupling configuration in photorefractive BaTiO(3) that provides a low-noise amplification of the signal to be detected. A two-wave mixing gain of 100 is reached, in conjunction with very low beam fanning background in the signal direction. The extensions of this configuration to photorefractive heterodyne detection and to multistage image amplif ication are theoretically and experimentally studied.

Enhancement of the signal-to-background ratio in photorefractive two-wave mixing by mutually incoherent two-beam coupling.

We present and experimentally demonstrate a new method for enhancing the signal-to-background ratio of two-wave mixing in photorefractive crystals. The method uses a mutually incoherent third beam to suppress the fanning in a dark ring-shaped region in which the amplified signal is located. A 20-fold improvement of the signal-to-background ratio is measured in BaTiO(3) at lambda = 514 nm. The extension of this principle to wide-field-of-view heterodyne detection is discussed.