STEP HEIGHT DETERMINATION BY A FOCUSED GAUSSIAN-BEAM

The interaction of a focused laser beam with a step on a conducting su rface is investigated by a vector method. The 2-D problem is solved by using a model of fictitious current filaments, while 3-D problems are treated by using a model of fictitious dipoles as the sources of the scattered field. Computer simulations indicate a difference between th e two polarization components (TE and TM), but with the samples invest igated in this work, these differences are too small for practical mea surements. The scattered field distribution is found to be strongly de pendent on the step height relative to the observation plane and on it s position relative to the beam waist. Thus, measurements of the inten sity distribution in the observation plane can provide information abo ut these parameters with high sensitivity, Experimental investigation confirms that the height of a step in the range lambda/10 to lambda/4 can be measured with an accuracy of 5%, including its sign (up or down ). The position of the step with respect to the beam can be estimated with an accuracy of about 1/100 of spot size.