Applied Physics B

, Volume 80, Issue 4–5, pp 527–534 | Cite as

Fresnel diffraction model for mode-mismatched thermal lens with top-hat beam excitation



A theoretical model, based on the Fresnel diffraction integral, is developed to describe the thermal lens (TL) signal in a mode-mismatched collinear configuration, which is optimized for a near field detection scheme and excitation by a cw modulated laser beam with a top-hat profile. The TL amplitudes obtained with both top-hat and Gaussian beam excitations are numerically computed and compared, and the dependence of the TL amplitude on the experimental parameters is discussed. Numerical results show that the top-hat beam TL instrument is more sensitive than the Gaussian beam TL instrument, with a potential doubling of the sensitivity. The use of the top-hat beam excitation with TL detection is a significant improvement because a top-hat beam can be easily obtained with a low-cost, wide-spectral emission white-light source. The use of incoherent light sources as the excitation sources would substantially expand the applicability of the TL technique to the general area of chemical analysis.


42.25.Fx 78.20.Nv 


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  1. 1.Institute of Optics and ElectronicsChinese Academy of SciencesShuangliu, Chengdu, SichuanChina

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