a laser system is described which concurrently directs highly equivalent diffracted beams derived from an initial laser beam to both sides of a substrate . the diffracted beams may be generated with sufficient energy to soften spots on the surfaces of the substrate to form texture bumps as are used on substrates for magnetic disks . the diffracted beams are generated by a multichannel acousto - optic modulator having at least two channels . the crystal in the mcaom has at least two mounting faces oriented so that the acoustic transducers mounted thereon generate acoustic fields which intersect the incident laser beam at a common angle , i . e ., the bragg angle . energizing any of the transducers causes a corresponding first order beam to be diffracted out . preferably the diffracted beams are generated by alternating driving signals to transducers to produce two beams with pulse intensity greater than 50 % of that of the incident beam which can be directed to opposite sides of a substrate for extremely uniform texturing .