An original laser-radiation beam having a symmetrical M2 but poor beam quality is sliced in one transverse axis, by a fanned-out stack of parallel transparent plates, into a plurality of beam slices. The electrophoretic panel includes a plurality of pixels. The code is constructed from a plurality of pixels in a first data set indicating the positions of the pixels and generates a corrected data set indicating the position that each pixel would occupy if each pixel was moved at the velocity of the product until the pixel was printed. The rollers guide the chain by rolling. High sensitivity is demonstrated experimentally in detecting broadband ultrasound pulses from a 10 MHz transducer.