الفهرس 
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Abstract
Photothermal spectroscopy compnses a group of high-sensitivity methods used to measure optical absorption and thermal characteristics of a sample. Optical energy is absorbed and eventually converted into thermal energy by enormous number of materials (solids, liquids and gases). It is common for excited electronic states in atoms or molecules to loose their excitation energy by a series of non-radiative transitions that result in a general heating of the material. Such processes are the origins of the photothermal effects and techniques. This effect gave a chance for the development of two spectroscopic techniques, photothermal deflection and thermal lens spectroscopy, which are considered the principle techniques to measure absorption directly. Photothermal deflection spectroscopy (PDS) and thermal lensing (TL) have proved in recent years to be valuable analytical tools for measuring very small concentrations of analytes in solids, liquids and gases. Both spectroscopic techniques measure the heat deposited in the material due to absorption of photons, by optical method. In this work : 1- we have exploited the PDS and TL techniques to detect very low level concentrations of Reactive-Red pollutant in drink water.2-we reported the use of thermal lens technique as a quantitative method to study the concentration-dependence of the photodegradation of polymethyle methacrylate, (PMMA), doped with rhodamine 6G.3- we employed the transverse PDS to detect a subsurface defect of different sizes on the surface of metal. First, one of the most famous Pollutants in water is the textile red reactive dyes. Red reactive dyes are used by a wide number of industries. photothermal (PDS) and thermal lens (TL) techniques will be used for detecting the traces of one type of these dyes in water. A He-Ne laser at 632.8 nm is used as a probe beam whereas an argon ion laser beam (488-514 nm) is used as pump beam. A photothermal setup was mounted on a rigid iron table to minimize vibrations from outside. The sample (Reactive-Red) in a clear quartz cuvet is introduced in the path of the probe beam. The pump beam was coupled into the sample collinearly with the probe beam. The changes of the refractive index, induced by a modulated argon beam were measured by monitoring the change of the probe beam diameter with a photodiode detector. A low concentration of 50 ppb has been measured using PDS technique while a 5 ppb has been measured at the same laser power and chopper frequency using TL technique. The results indicated that thermal lens technique is more precise than PDS technique for measuring a very low concentrations in liquids. Second, in this part we report the use of thermal lens technique as a quantitative method to study the concentration-dependence of the photodegradation of poly methyle methacrylate, (PMMA), doped with rhodamine 6G, at different concentrations of the dye (100 ppm, 50 ppm and 25 ppm). Modulated argon ion laser beam at 488-514 nm with TEMoo mode, was used in this study as a pump beam to generate thermal lens in the sample. A He-Ne laser source was used as a probe beam, which made to pass through the sample collinearly with the pump beam. Experimental results indicated that the rate of photo degradation is directly proportional to the incident modulated laser power while it decreases with the increase of concentration of the dye molecules. In the present case we have not observed any dependence of photodegradation on modulation frequency within the range of 10-50 Hz. Third, using the transverse arrangement of PDS we were able to detect subsurface defects in Al sample. The defects were of different shapes, different sizes and different conductivities at different depths from the surface. The results showed that there is a general enhancement of the signal at the beginning and the end of the hole. This enhancement decreases as the frequency increases, and increases as the thermal conductivity of the defect decreased. These results are consistence with the assumption that heat flow is impedent at each edg.