Apparatus and method for enhancing laser beam efficacy in a liquid medium

Abstract

The present disclosure generally relates to the field of laser based medical devices. Particularly, but not exclusively, the present disclosure relates to an apparatus and method for enhancing laser beam efficacy in a liquid medium. In many embodiments, laser pulses are modulated based on bubble dynamics to improve energy delivery to a target. A variety of exemplary pulse modulation scheme are described including modulating pulse power down during expansion of an index bubble and modulating pulse power up during collapse of the index bubble.

What is claimed is: 
     
         1 . A system, comprising:
 a fiber laser; and   a controller comprising a processor and memory, the memory comprising instructions that when executed by the processor cause the processor to:
 determine a pulse energy for the fiber laser; 
 identify a distance between a tip of the fiber laser and a target, wherein a liquid is located between the tip of the fiber laser and the target; 
 determine a modulation scheme based on the distance; 
 set an initial pulse power for the modulation scheme to generate an index bubble in the liquid based on the distance; and 
 initiate a pulse according to the modulation scheme via the fiber laser, wherein the modulation scheme reduces power of the pulse after initiation of the pulse at the initial pulse power. 
   
     
     
         2 . The system of  claim 1 , wherein the modulation scheme increases power of the pulse to a maximal system power level at a time estimated for the index bubble to reach maximal size. 
     
     
         3 . The system of  claim 2 , wherein the instructions, when executed by the processor, further cause the processor to estimate the time the index bubble takes to reach maximal size based on the initial pulse power and an absorption coefficient of the liquid at a wavelength of the fiber laser. 
     
     
         4 . The system of  claim 1 , wherein the instructions, when executed by the processor, further cause the processor to:
 identify an updated distance between the tip of the fiber laser and the target; and   determine an updated modulation scheme based on the updated distance.   
     
     
         5 . The system of  claim 1 , wherein the modulation scheme is configured to modulate pulse power down during expansion of the index bubble and modulate pulse power up during collapse of the index bubble. 
     
     
         6 . The system of  claim 1 , wherein the modulation scheme comprises an initial modulation frequency and the instructions, when executed by the processor, further cause the processor to determine the initial modulation frequency based on a time to collapse of the index bubble, a time for the index bubble to reach maximum size, and a time from lasing initiation to start of bubble formation. 
     
     
         7 . The system of  claim 1 , wherein the instructions, when executed by the processor, further cause the processor to set the initial pulse power for the modulation scheme to generate the index bubble in the liquid based on the distance and the pulse energy. 
     
     
         8 . The system of  claim 1 , wherein the instructions, when executed by the processor, further cause the processor to integrate the power of the pulse with respect to time and terminate the pulse when the integral of the power of the pulse with respect to time equals the pulse energy. 
     
     
         9 . The system of  claim 1 , wherein the instructions, when executed by the processor, further cause the processor to classify the target as distant target based on the distance and set the initial pulse power to a maximal system power level based on classification of the target as distant. 
     
     
         10 . The system of  claim 9 , wherein the modulation scheme is configured obtain a resonant effect by cycling at periods between 0.7 and 1.3 times a time from start to collapse of the index bubble. 
     
     
         11 . At least one non-transitory computer-readable medium comprising a set of instructions that, in response to being executed by a processor circuit, cause the processor circuit to:
 determine a pulse energy for a fiber laser;   identify a distance between a tip of the fiber laser and a target, wherein a liquid is located between the tip of the fiber laser and the target;   determine a modulation scheme based on the distance;   set an initial pulse power for the modulation scheme to generate an index bubble in the liquid based on the distance; and   initiate a pulse according to the modulation scheme via the fiber laser, wherein the modulation scheme reduces power of the pulse after initiation of the pulse at the initial pulse power.   
     
     
         12 . The at least one non-transitory computer-readable medium of  claim 11 , wherein the modulation scheme increases power of the pulse to a maximal system power level at a time estimated for the index bubble to reach maximal size. 
     
     
         13 . The at least one non-transitory computer-readable medium of  claim 12 , wherein the set of instructions, in response to execution by the processor circuit, further cause the processor circuit to estimate the time the index bubble takes to reach maximal size based on the initial pulse power and an absorption coefficient of the liquid at a wavelength of the fiber laser. 
     
     
         14 . The at least one non-transitory computer-readable medium of  claim 11 , wherein the set of instructions, in response to execution by the processor circuit, further cause the processor circuit to:
 identify an updated distance between the tip of the fiber laser and the target; and   determine an updated modulation scheme based on the updated distance.   
     
     
         15 . The at least one non-transitory computer-readable medium of  claim 11 , wherein the set of instructions, in response to execution by the processor circuit, further cause the processor circuit to set the initial pulse power for the modulation scheme to generate the index bubble in the liquid based on the distance and the pulse energy. 
     
     
         16 . The at least one non-transitory computer-readable medium of  claim 11 , wherein the set of instructions, in response to execution by the processor circuit, further cause the processor circuit to integrate the power of the pulse with respect to time and terminate the pulse when the integral of the power of the pulse with respect to time equals the pulse energy. 
     
     
         17 . A method, comprising:
 determining a pulse energy for a fiber laser;   identifying a distance between a tip of the fiber laser and a target, wherein a liquid is located between the tip of the fiber laser and the target;   determining a modulation scheme based on the distance;   setting an initial pulse power for the modulation scheme to generate an index bubble in the liquid based on the distance; and   initiating a pulse according to the modulation scheme via the fiber laser, wherein the modulation scheme reduces power of the pulse after initiation of the pulse at the initial pulse power.   
     
     
         18 . The method of  claim 17 , comprising modulating pulse power down during expansion of the index bubble and modulating pulse power up during collapse of the index bubble. 
     
     
         19 . The method of  claim 17 , comprising classifying the target as distant target based on the distance and set the initial pulse power to a maximal system power level based on classification of the target as distant. 
     
     
         20 . The method of  claim 19 , comprising cycling at periods between 0.7 and 1.3 times a time from start to collapse of the index bubble.