Diatom algae realize highly intriguing processes of biosynthesis of siliceous structures in living cells under moderate conditions. Investigation of diatom physiology is complicated by frustule (siliceous exoskeleton). Frustules consist of valves and girdle bands which are adhered to each other by means of organic substances. Removal of the frustule from the lipid membrane of diatom cells would open new possibilities for study of silicon metabolism in diatoms. We found that submillimeter laser irradiation produced by a free-electron laser causes splitting of diatom frustules without destruction of cell content. This finding opens the way to direct study of diatom cell membrane and to isolation of cell organelles, including silica deposition vesicles. We suppose that the dissection action of the submillimeter irradiation results from unusual ultrasonic waves produced by the short (30-100 ps) but high-power (1 MW) terahertz laser impulses at 5.6 MHz frequency.