Bc. Li et al., PULSED-LASER INDUCED MODE-MISMATCHED CROSSED-BEAM THERMAL LENS MEASUREMENTS, Review of scientific instruments, 68(7), 1997, pp. 2741-2749
In this article, an accurate Fresnel diffraction model for a pulsed la
ser induced thermal lens effect in mode-mismatched crossed-beam config
uration is presented. The effect of a lateral offset between the two b
eams is included in the model. This model is used to calculate the dif
fraction field of the probe beam at the detection plane from the very
near- to the far-field, therefore the evolution of the intensity profi
le of the probe beam from the near- to the far-field is clearly illust
rated. Numerical calculations predict and experimental results demonst
rate that the thermal lens (TL) signal maximum is obtained when the pr
obe beam propagates about a characteristic distance away from the samp
le position, while the characteristic distance is determined by the ra
dius of the excitation beam in the sample and the wavelength of the pr
obe beam. At large size mismatch of two beams and near-field detection
cases, the TL signal is approximately independent on the sample locat
ion relative to the waist of the probe beam. The theoretical and exper
imental results are of great importance to configuration optimization
of an extremely sensitive and compact TL instrument, which is the tren
d in the development of analytical instruments.