To a one--dimensional laser bar code scanner

by analyzing the longitudinal profile characteristics of the laser beam

and using convolution and Laplace transform

we obtain the exact expression of the Gaussian filtering effect which is generated when the laser beam scans the bar code images. And then we use the expression of the Gaussian filtering effect to design a Bessel filter

which can eliminate the Gaussian filtering effect and enhance the waveform edge. MATLAB is used to simulate the designed Bessel filter

the result shows that the filter improved the edge with no enhance of noise. That could be some reference value to improve the one--dimensional bar code signal.