Determination of the optical characteristics of turbid media by the laser optoacoustic method

Abstract

Hydrogenated diamond-like carbon (DLC) films were deposited on Si (100) wafers by a plasma enhanced chemical vapour deposition technique using CH 4 plus Ar as the feedstock. The friction and wear properties of the resulting films under different relative humidities, ranging from 5% to 100%, in a nitrogen environment, were measured using a ball-on-disc tribometer, with Si 3 N 4 balls as the counterparts. The friction surfaces of the films and Si 3 N 4 balls were observed on a scanning electron microscope, and investigated by x-ray photoelectron spectroscopy. The results showed that the friction coefficient increased continuously from 0.025 to 0.09 with increase in relative humidity from 5% to 100%, while the wear rate of the films sharply decreased and reached a minimum at a relative humidity of 40%, then it increased with further increase of the relative humidity. The interruption of the transferred carbon-rich layer on the Si 3 N 4 ball, and the friction-induced oxidation of the films at higher relative humidity were proposed as the main reasons for the increase in the friction coefficient. Moreover, the oxidation and hydrolysis of the Si 3 N 4 ball at higher relative humidity, leading to the formation of a tribochemical film, which mainly consists of silica gel, on the friction surface, are also thought to influence the friction and wear behaviour of the hydrogenated DLC films.

<title>Laser pulse propagation in turbid media: Monte Carlo simulation and comparison with experiment</title>

“…Behind the maxima the curves decay exponentially with the degree of (-L2 PaPc(i _ g)), where Lm 5 the sample thickness. This is in agreement with [9]. It should be noted here that the lower point of the curves is above the zero level because about some hundred photons reach the forward detector.…”

“…The total intensity consists of the scattered light and the incident light. The position of the maximum Zmax depends on the properties of the medium and it is situated at the depth of 1 12 [9]. It takes place not only for continuous radiation but also for quasi-stationary pulses, which duration exceeds the photon lifetime in the medium (ttac/nY', where c is speed of light in vacuum, n is refractive index ofthe medium, or the propagation time Lmn/c (if 1.…”

Optoacoustic spectroscopy for real-time monitoring of strongly light-absorbing solutions in applications to analytical chemistry

“…Thus, the measured values of μ a are limited from below. In our previous papers, we demonstrated that the minimum value of light absorption that can be readily measured with the OA technique using a tabletop setup and conventional mJ nanosecond lasers is of an order of μ a  ∼ 0.05 [47]. However, the smaller is light absorption, the larger should be the depth ($\sim {\mu }_a^{-1}$) of the sample cell.…”

Determination of optical parameters of pulp suspensions by time-resolved detection of photoacoustic signals and total diffuse reflectance measurements

“…To split out the absorption and reduced scattering coefficients from the effective attenuation coefficient, we can measure either the amplitude of photoacoustic generation in the medium [2] or the photon transport mean path [6]. However, the former method necessitates measuring several physical and system parameters (which are usually unknown), while the latter poses very high requirements for the transducer (ultra-wide bandwidth) and the detection channel (very fast sampling frequency).…”