Laser selective cutting by impulsive heat deposition in the IR wavelength range for direct-drive ablation

Inventors

Miller, R. J. Dwayne

Assignees

Light Matter Interaction Inc

Abstract

The present invention provides a method of laser processing of materials, specifically laser induced ablation processes for laser removal of material particularly important in medical and dental applications in which the laser removal of material should be done in such a way as to not damage any of the surrounding soft or hard biomaterial. The ablation process is achieved by impulsive heat deposition (IHD) by direct and specific excitation of short lived vibrations or phonons of the material in such a way as to not generate highly reactive and damaging ions through multiphoton absorption. The heat deposition and ensuing ablation process under prescribed time and wavelength conditions for laser irradiation is achieved faster than heat transfer to surrounding tissue by either acoustic or thermal expansion or thermal diffusion that otherwise would lead to excess heat related damage. The result is that all the deposited laser energy is optimally channelled into the ablation process in which the inertially confined stresses from both photomechanical expansion forces and thermally driven phase transitions and associated volume changes constructively interfere to drive the most efficient ablation process possible with minimal damage to surrounding areas by either ionizing radiation or heat effects. By choosing a specific range of wavelengths, spatial and temporal shaping of infrared laser pulses, the energy can be optimally deposited in a manner that further increases the efficiency of the ablation process with respect to minimizing collateral damage.

Core Innovation

The invention relates to a method of laser processing and laser surgery in which a pulsed laser wavelength is selected so that the laser pulses are absorbed by at least one component of the material or by at least one component of tissue to be processed. The pulsed laser is adjusted so that each laser pulse absorbed in an irradiated volume produces superheated temperatures above a vaporization point of the identified component, and most of the energy contained in each laser pulse is converted to ablation out of the volume.

The invention further requires selecting a pulse duration time that satisfies impulsive heat deposition requirements by making the pulse duration shorter than a time required for thermal diffusion out of the irradiated volume and shorter than a time required for thermally driven expansion of the irradiated volume. At the same time, the pulse duration is made long enough and the pulse energy is made low enough so that the peak intensity of each laser pulse is below a threshold for ionization driven ablation to occur in the material or tissue.

For tissue surgery, the invention is grounded in identifying tissue components to be processed and selecting a wavelength such that the laser pulses are absorbed by those tissue components to produce superheated temperatures above a vaporization point. Additional aspects include selecting water absorption lines, including OH symmetric stretching and OH bending motions in a spectral region, and shaping the laser pulses to have a substantially flat-top spatial profile.

Claims Coverage

The document includes two independent claims: one for a general method of laser processing of a material and one for a method of laser surgery on tissue. Across these independent claims, the inventive coverage centers on wavelength selection for absorption, superheating above a vaporization point, impulsive heat deposition via pulse-duration timing relative to thermal diffusion and thermally driven expansion, and suppressing ionization driven ablation by keeping peak intensity below a threshold so residual energy does not substantially damage surrounding regions.

Across the independent claims, the claimed laser processing/surgery is defined by wavelength selection to achieve absorption by a targeted component, production of superheated temperatures above a vaporization point, pulse durations arranged for impulsive heat deposition relative to thermal diffusion and thermally driven expansion, peak intensity below a threshold for ionization driven ablation, and residual energy that does not substantially damage surrounding regions, while irradiating the target volume to achieve ablation.

Stated Advantages

Documented Applications