DETERMINATION OF THE LONGITUDINAL PROFILE OF A FOCUSED NDYAG GAUSSIAN-BEAM FROM 2ND-HARMONIC GENERATION IN A THIN KTP CRYSTAL

We present an original experiment describing a focused Gaussian laser beam by using second-harmonic generation (SHG) in a thin strip of a no nlinear optical material, in this case KTP doubling of an Nd:YAG laser at 1.064 mum. The dependence of the SHG efficiency on the fundamental beam radius allows the determination of beam parameters by harmonic-p ower measurements. The characterization of a telescope shows the good precision of this method in radii in the range of 10-100 mum. The aver age accuracy is 4% for the radius determination and 1.5% for the beam- waist localization.