Detection of x rays with a fiber-optic interferometric sensor.

A fiber-optic Mach-Zehnder interferometer was used for x-ray detection. A single-mode, polarization-preserving silica fiber is exposed to a high-flux x-ray beam (x-ray tube for diagnostic radiology, 30 kV, 16.8-keV average energy, 17-40-mA anodic current), modulated at f = 9 Hz by a chopper with steel blades. The energy absorbed produces a modulated temperature rise that induces a phase shift in the propagation of a He-Ne laser beam with respect to the unirradiated arm of the interferometer. We measured the linearity of the temperature rise with the energy released to the fiber and the linearity of the peak amplitude at frequency f in the power spectrum of the interferometric signal with the anodic current of the x-ray tube. A possible application of this technique to synchrotron radiation monitoring is discussed.

Investigation of the optothermal properties of a new polymeric blend: polymethyl-methacrylate-poly (ethylene-co-vinylacetate).

A new polymeric blend, polymethyl methacrylate-poly (ethylene-co-vinylacetate) (PMMA-EVA) has been produced recently in our laboratories. The optothermal characterization of PMMA-EVA was carried out by measuring the ultraviolet photoacoustic spectra of PMMA, EVA, and PMMA-EVA (25 degrees C, 220-350 nm), of a PMMA-EVA blend (250-750 nm) at two temperatures (19 degrees C and 65 degrees C), and by measuring the scattering coefficient (at 514.5 nm) of PMMA-EVA versus the temperature in the range 38-86 degrees C. Our measurements show that, in the explored thermal range, the blend undergoes a phase transition when its optical properties change drastically. The peculiar optical and thermal properties observed appear attractive for possible applications as temperature-controlled optical devices.

Quantitative measurements of porphyrin pigments in tissues via photoacoustic spectroscopy.

We investigated the possibility of using photoacoustic spectroscopy as an analytical technique for the quantitative measurement of injected porphyrins in tissues. Samples of liver excised from treated (i.e., injected 24 h in advance with 100 mg/kg Photofrin II) mice and control mice were lyophilized and reduced to powder; then, about 16-mg powder samples were compacted to equal volumes inside the photoacoustic cell. Amplitude and phase spectra were measured in the range 280-760 nm. From these data we computed the photoacoustic absorbance spectra; they were suitably normalized in order to account for differences in hemoglobin concentration among the livers of different mice. The absorbance difference spectra (treated minus control) were computed in the region of wavelengths above 450 nm, where porphyrins and hemoglobin exhibit major differences. Finally, by estimating the value of the thermal diffusion length of the powdered sample and those of the extinction coefficients of the most relevant Photofrin II components in the spectral region considered, we were able to evaluate the local drug concentration and determined a value (260 micrograms/g of wet tissue) that is in the range expected for the dose of Photofrin II injected.

Quantitative photoacoustic spectroscopy of cataractous human lenses.

Quantitative photoacoustic spectra of the nuclei of cataractous human lenses with various degrees of colouration and opacification were measured in the spectral range 250-600 nm. The lens nuclei were obtained from 20 cataractous patients through extracapsular cataract extraction. These measurements yield the light loss per unit path length in the nucleus of cataractous lenses.

Absorptance enhancement for laser metal processing: application to steel samples.

We describe a reliable technique that noticeably increases the absorptance of a metal surface without any change in its chemical and physical properties, obtained through a chemically induced enhancement of the surface roughness. The main advantages of this method are low cost, easy handling, and low tolerances. A set of optical and mechanical measurements was performed to gain a detailed knowledge of the technique.