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A sensitive technique for the detection of temperature changes in the bulk of a transparent material due to absorption of any laser beam is the thermal-lensing technique. So far to our knowledge the thermal-lensing models will yield zero signal, if one probes the temperature changes in the space where the laser beam focuses. We developed a model that uses a low power c.w. laser to detect the absorption changes in the focal volume of a Q-switched laser beam. The change in the absorption from pulse to pulse will be detected as a change in the far field intensity profile of the c.w. beam; taking in account the aberrant nature of the induced thermal-lens, an expression for the above profile is given; the far field fractional axial intensity is derived without any high order terms elimination, which allows for an accurate and sensitive measurement of the absorption coefficient for one and n-photon absorption processes.
thermal-lensing, temperature change, Q-switched laser, c.w. laser, fractional axial intensity, absorption coefficient
University of Arkansas, Fayetteville, AR