When a laser beam is shone on biological tissue, the tissue components absorb the light and the tissue heats up. This causes the tissue to expand and contract, creating vibrations. Different materials inside the tissue absorb different amounts of light at different wavelengths, creating individual ‘fingerprints’ in the emitted sound waves When a laser beam is shone on biological tissue, the tissue components absorb the light and the tissue heats up. This causes the tissue to expand and contract, creating vibrations. Different materials inside the tissue absorb different amounts of light at different wavelengths, creating individual ‘fingerprints’ in the emitted sound waves Health Health News, Wellbeing Tips, Diseases, Treatment and Nutrition | The Hindu