Laser wavelengths used are 300-1000 nm and the pulse duration is 300 ps to 20 ns. For the material to be processed and the predetermined interval, the irradiation intensity is controlled to cause plasma formation without plasma illumination. Intensity at the laser focus is controlled by inspection. The lower limit of irradiation intensity, is at the limits of detection. The upper limit corresponds with the onset of plasma illumination. In a liquid medium, bubbles are formed with a fixed, selected radius. In an aqueous liquid medium, the irradiation intensity used is 90 GW/cm 2>. When the transparent material is a solid body, cavities are formed and/or the refractive index in the body is varied locally. Pulse duration is at least three times the time constant of plasma recombination in the material being processed. The pulse duration lies in the range 0.9-11 ns. The equipment used, has a controller relating irradiation intensity to the results of inspection. This holds the pulses uniform over time, within the range between the limits of detection and plasma illumination. The inspection unit registers bubble formation. The laser is a seeded solid laser or a microchip laser. An independent claim IS INCLUDED FOR the corresponding laser equipment.
