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In many relevant industrial applications, UV-vis online process monitoring is hampered by light scattering and opacity of the samples, whereas diluted and filtered samples are rarely available. Pulsed laser photoacoustic (PA) spectroscopy allows the measurement of both high and low absorptions without any need for sample preparation. An optimized detection geometry for absorption measurements in opaque liquids is described. The proposed PA sensor was realized by using two orthogonal detectors based on piezoelectric poly(vinylidene fluoride) (PVDF). Laser-induced pressure waves were sensed perpendicularly to (side-on mode) and along the axis of the laser beam (forward mode). Pressure waves generated by a single laser pulse, optical transmission and absorption, as well as the speed of sound in liquid samples were determined simultaneously using time-resolved detection. Evaluation of the PA signal permits the determination of absorption coefficients ranging from 0.1 to 1000 [cm.sup.-1]. The influence of absorbing or scattering compounds on the signal was investigated in dye solutions and suspensions of Ti[O.sub.2] particles.

It has been known for some time that correlated detection of pairs of photons generated by parametric down-conversion can eliminate several sources of error that occur in single-beam measurements. In the correlated photon measurements, the down-converted photons are separated into two beams with one photon of a pair in each beam. The absolute detection efficiency of a detector in one beam can be determined from the count rate of a detector in the other beam and the coincidence rate for the two detectors. These ideas can be used to measure the optical absorbance of a sample placed in front of one of the detectors. Errors due to sway light and dark counts are substantially reduced and fluctuations in pump intensity largely eliminated.

The absorbance of Cu atoms sputtered from a Cu cathode in a laboratory-modified radio frequency glow discharge atomizer for atomic absorption spectrometry was measured at different regions within the atomizer chamber for different discharge parameters. The results show that not only the discharge gas flow rate and pressure but also the applied rf power and the degree of extension of the negative glow have significant effects on the atomization and on the distribution of sputtered atoms within the atomizer chamber. The influence of various diameters and thicknesses of the sampling orifice (anode) on the plasma atomization characteristics and the sample weight loss rates has been examined. By increasing the diameter of the sampling orifice, a larger area of the cathode surface (Cu) was allowed to be sputtered, thereby generating a larger number of atoms (higher absorbance) in the analysis volume, where the sputtered atoms were studied by atomic absorption spectrometry. The absorbance of Cu atoms was inversely related to the thickness of the sampling orifice disk because the distance of the investigated region of the atomizer chamber from the cathode surface increases with increasing thickness of the sampling orifice disk. The rate of sample weight loss was inversely related to the diameter of the sampling orifice at orifice diameters higher than or equal to 4 mm. The rate of sample weight loss as a function of the thickness of the sampling orifice disk indicated that the transport efficiency of the sputtered atoms into the atomizer chamber was higher when a sampling disk having a thickness of 2 mm was used. Changing the location of the discharge gas inlet port resulted in a large increase in the atomic absorption signal. A larger increase in the atomic absorption signal of the sputtered Cu atoms was observed for the modified rf atomizer having the discharge gas inlet port on the body of the sampling orifice disk than for the unmodified rf atomizer having the discharge gas inlet port on the top of the atomizer chamber.

The quantum yield of E113Q mutant of the E113 in the UV-absorbing visual pigments of vertebrates is found to be lower than the normal animals. This demonstrates the role of E113 residue in the photoisomerization of the unprotonated chromophores for effective absorption of light by the retinal cells.

A new method is described for measuring the electron transport and recombination in dye-sensitized mesoporous materials in which the charge density is detected directly by quasi-continuous wave (cw) optical absorption measurements while simultaneously electronically measuring the conductivity through in-plane devices. The results have shown that at room temperature the recombination is weakly influenced by the charge transport and is mainly affected by the recombination reaction and the cation density.