APPARATUS FOR DYNAMIC COOLING OF BIOLOGICAL TISSUES DURING LASER SURGERY

A method for performing laser treatment of biological tissues is performed by cooling a selected portion of the biological tissue for a predetermined first time period to establish a predetermined nonequilibrium dynamic temperature gradient through the tissue so that substantially only the selected portion of the biological tissue is cooled by a predetermined minimum temperature drop. The temperature gradient is established by providing a spurt of a predetermined amount of cryogenic liquid in direct contact with the biological tissue. A superficial and deeper part of the selected portion of the biological tissue is immediately irradiated for a time period which is approximately equal to or in excess of one millisecond. The irradiation is effective to thermally treat the deeper part of the biological tissue while leaving the superficial part of the biological tissue substantially undamaged. Heat is quickly dissipated from the superficial part of the biological tissue by means of supplying the latent heat of vaporization to the cryogenic liquid. The selected portion of the biological tissue is cooled for a predetermined third time period overlapping with the second time period by providing one or more additional spurts of predetermined corresponding amounts of cryogenic liquid in direct contact with the biological tissue at the site which is being irradiated in order to maintain the selected portion of the biological tissue at or below an average selected temperature.