Tattoo Removal and Other Dermatological Treatments using Multi-Photon Processing

Abstract

A system and method for removing a portion of a tattoo using multi-photon ablation is described. A localized, multi-photon processing event is initiated within a vicinity of a pigment in order to remove it. The multi-photon event requires a relatively low energy, but very intense, pulse of light. The low amount of energy per pulse allows ablation of the material to be highly localized, with negligible thermal damage to surrounding material. The multi-photon event may be initiated by focusing a suitable electromagnetic pulse, such as a 2 mJ laser pulse having a pulse duration of 100-300 femtoseconds, into a focal volume small enough that the intensity exceeds 10 11 Watts/cm 2 . A suitably configured Ti:Sapphire solid state laser provides such pulses at 1-10 kHz. By repeating the multi-photon event along the location of a tattoo, the tattoo may be removed with minimal damage to the surrounding tissue.

1 . A method of removing a portion of a tattoo, comprising:
 locating a position of a pigment defining said portion of said tattoo on or within said patient; and   initiating, using a femtosecond laser and a computer controlled focusing element, a localized, multi-photon processing event in, or within a vicinity of said pigment.   
     
     
         2 . The method of  claim 1  wherein initiating said localized, multi-photon processing event further comprises: providing a pulse of electromagnetic radiation; and focusing said pulse to a focal volume such that an intensity of said electromagnetic radiation within said focal volume exceeds 10 11  W/cm 2 . 
     
     
         3 . The method of  claim 2  wherein said pulse of electromagnetic radiation has a temporal pulse length in a range from 100 to 300 femtoseconds in duration. 
     
     
         4 . The method of  claim 3  wherein said pulse of electromagnetic radiation has an energy that is equal to or less than 2 mJ. 
     
     
         5 . The method of  claim 3  wherein said pulse of electromagnetic radiation has a bandwidth that is equal to or greater than 100 GHz. 
     
     
         6 . The method of  claim 3  further comprising setting said focal volume of said focused pulse to substantially correspond to a thickness of said pigment. 
     
     
         7 . The method of  claim 3  wherein said focal volume is equal to or less than 500 μm in diameter. 
     
     
         8 . The method of  claim 1  further comprising repeating initiating said a localized, multi-photon processing event until said pigment is removed. 
     
     
         9 . The method of  claim 2  wherein said pulse of electromagnetic radiation has a temporal pulse length that is equal to or less than 100 femtoseconds in duration. 
     
     
         10 . The method of  claim 2  wherein said pulse of electromagnetic radiation has a temporal pulse length that is equal to or less than 200 picoseconds in duration. 
     
     
         11 . The method of  claim 2  wherein said pigment is located within a dermal layer of said patient. 
     
     
         12 . The method of  claim 11  wherein said locating said position of said pigment further comprises locating an upper surface of said patient's epidermis and wherein said focusing further comprises locating said focal volume in a range of 10 μm to 2000 μm below said upper surface. 
     
     
         13 . The method of  claim 12  wherein locating said focal volume further comprises positioning a lens relative to said upper surface of said patient's epidermis; and preventing initiation of said localized, multi-photon processing event unless said lens is located such that said focal volume will occur in said range of 10 μm to 2000 μm below said upper surface. 
     
     
         14 . The method of  claim 13  wherein said pigment is an inorganic heavy metal salt, an inorganic heavy metal oxide, an azo-organic pigment, or a polycyclic organic pigment. 
     
     
         15 . An apparatus for removing a portion of a tattoo, comprising:
 a femto-second laser;   a pigment locating device for locating a position of a pigment defining said portion of a tattoo; and   a computer for controlling the emission of a pulse of electromagnetic radiation by said femto-second laser, and to control a focusing device, containing at least one lens, so as to initiate a localized, multi-photon process in or within a vicinity of said pigment.   
     
     
         16 . The apparatus of  claim 15  wherein said pulse of electromagnetic radiation has a temporal pulse length in the range of 100 to 300 femto-seconds in duration, a bandwidth that is equal to or greater than 100 GHz; said focal volume corresponds substantially to a thickness of said pigment; and said predetermined threshold is equal to or greater than 10 11  W/cm 2 . 
     
     
         17 . The apparatus of  claim 15  further comprising a visible light beam for locating an upper surface of said patient's epidermis; and, a feedback loop that prevents initiation of said localized, multi-photon processing event unless said focusing lens is located such that said focal volume would occur in said range of 10 μm to 2000 μm below said upper surface. 
     
     
         18 . The apparatus of  claim 15  further comprising a computer processor programmed to use a signal from visible light beam to effect said feedback loop.