Patent Publication Number: US-2023137107-A1

Title: High bandwidth energy source for improved transmission through optical fiber for intravascular lithotripsy

Description:
RELATED APPLICATION 
     This application is related to and claims priority on U.S. Provisional Patent Application Ser. No. 63/273,065 filed on Oct. 28, 2021, and entitled “HIGH BANDWIDTH ENERGY SOURCE FOR IMPROVED TRANSMISSION THROUGH OPTICAL FIBER FOR INTRAVASCULAR LITHOTRIPSY”. To the extent permissible, the contents of U.S. Provisional Application Ser. No. 63/273,065 are incorporated in their entirety herein by reference. 
    
    
     BACKGROUND 
     Vascular lesions within vessels in the body can be associated with an increased risk for major adverse events, such as myocardial infarction, embolism, deep vein thrombosis, stroke, and the like. Severe vascular lesions can be challenging to treat and achieve patency for a physician in a clinical setting. Vascular lesions may be treated using interventions such as drug therapy, balloon angioplasty, atherectomy, stent placement, vascular graft bypass, to name a few. Such interventions may not always be ideal or may require subsequent treatment to address the lesion. 
     Using optical fiber delivery of laser pulses to generate plasma-induced mechanical impulses on the lesions is one way to treat vascular lesions by fragmentation. Shaping the temporal form of the optical pulse makes it possible to reduce the peak power of the pulse below the damage threshold of the optical fiber and still transmit full energy for generating the mechanical impulse. This increases the amount of energy that can be delivered in a set time interval while minimizing the peak laser intensity to remain below the damage threshold of the optical fiber. However, nonlinear optical processes in the bulk optical fiber may still throttle back energy transmission through the fiber. Thus, nonlinear optical processes can limit the peak energy delivered and the device&#39;s ability to fracture lesions. 
     One of the principal issues encountered with using optical energy pulses to generate plasma-driven acoustic bubbles is coupling sufficient energy into an optical fiber&#39;s input end (proximal end) or other light guide to create an effective therapeutic effect at an output end (distal end) of the optical fiber. Damage to the light guide that transmits the optical energy pulse inside the body has been a critical challenge in developing this technology. The factors involved are the Laser-Induced Damage Threshold (LIDT) of the light guide interfaces and the bulk threshold of the medium itself. The LIDT for bulk fused silica is 1866 J cm −2  at 1064 nm for a 12 ns pulse. The LIDT for surfaces can be one-tenth of this or less. Surface finish quality and cleanliness significantly impact this number. Since the damage threshold for the light guide surface is much lower than that for bulk material, failures typically appear as damage on the light guide&#39;s input (proximal) end. The amount of energy transmitted through the light guide is then limited by the peak intensity of the pulse on the proximal surface. This limitation has been addressed primarily by stretching the energy pulse width temporally. This reduces peak power and surface irradiance while maintaining overall energy. 
     Additionally, recent experiments have indicated that for pulses with an approximately Gaussian temporal shape, the peak pressure generated by the optical pulse is proportional to the peak intensity of the pulse. This means that even though shorter pulses are limited to lower total energies by the damage threshold of the transmission medium, they can produce similar pressure waves to longer pulses using significantly less total optical energy. The result is that sufficiently energetic pressure waves can be created to fracture calcified lesions while remaining well below the damage threshold of the light guide. 
     Even using the technique of pulse stretching to reduce peak power at the light guide surface, the peak power remains sufficiently high to induce Stimulated Brillouin Scattering (SBS) in the light guide material itself. SBS is a nonlinear process that can occur in an optical medium at relatively low input power levels. It manifests itself by generating a backward-propagating Stokes wave that carries most of the input power once the Brillouin threshold is reached. The interaction of the input photon and the moving refractive index variations within the material creates a backward scattered phonon, the Stokes wave. This process removes energy from the input beam. In turn, the backward propagating wave creates a region of periodic index variation that behaves like a Bragg grating. This scatters more of the forward beam backward. This nonlinear process creates an exponential decrease in total transmitted energy with incremental increase input. It fundamentally throttles back the total energy transmitted as more is put in. 
     For the case where the input light frequency linewidth, Δv p , is narrow compared to the frequency linewidth of Brillouin scatter, the unsaturated Brillouin gain coefficient, G B0 , at wavelength λ is given by: 
     
       
         
           
             
               G 
               
                 B 
                 ⁢ 
                 0 
               
             
             = 
             
               
                 2 
                 ⁢ 
                 π 
                 ⁢ 
                 
                   n 
                   7 
                 
                 ⁢ 
                 
                   p 
                   12 
                   2 
                 
               
               
                 c 
                 ⁢ 
                 
                   λ 
                   2 
                 
                 ⁢ 
                 ρ 
                 ⁢ 
                 
                   V 
                   s 
                 
                 ⁢ 
                 Δ 
                 ⁢ 
                 
                   υ 
                   B 
                 
               
             
           
         
       
     
     where p 12  is the elasto-optical coefficient of the material, p is its density, n is its refractive index, V s  is the acoustic velocity of the vibrations, and Δv B  is the Brillouin frequency linewidth in the material. The Brillouin frequency linewidth in silica is around 135 MHz. At λ=1 μm, G B0 =4.5×10 −9  cm/W. If the input photon beam linewidth, Δv p , is larger than 
     
       
         
           
             
               G 
               B 
             
             = 
             
               
                 G 
                 
                   B 
                   ⁢ 
                   0 
                 
               
               ⁢ 
               
                 
                   Δ 
                   ⁢ 
                   
                     υ 
                     B 
                   
                 
                 
                   Δ 
                   ⁢ 
                   
                     υ 
                     p 
                   
                 
               
             
           
         
       
     
     This indicates directly that the one way to reduce the effects of SBS is to significantly broaden Δv p . 
     Linewidth (optical bandwidth) is a measure of spectral purity (monochromaticity). In general, pulsed solid-state lasers with short cavity lengths have characteristically narrow linewidths, on the order of tens of kHz to hundreds of MHz. It is also helpful to consider this in terms of coherence length given by: 
     
       
         
           
             
               L 
               
                 c 
                   
               
             
             = 
             
               c 
               
                 π 
                 ⁢ 
                 Δ 
                 ⁢ 
                 
                   υ 
                   p 
                 
               
             
           
         
       
     
     This range of linewidths corresponds to a coherence length from around thousands of meters down to 2 m. This is the range over which laser light can interfere with itself and contribute to SBS. The 135 MHz Brillouin frequency linewidth in silica corresponds to a coherence length around 70 cm. To reduce the Brillouin gain coefficient to the point where SBS would not impact light transmission through the fiber, the linewidth needs to be several orders of magnitude greater than the basic Brillouin frequency linewidth. That would be 13 GHz to 30 GHz, corresponding to a coherence length around 7 mm to 3 mm. Other energy sources can have bandwidths ranging from 50 μm to 69 μm, corresponding to 13.25 GHz to 18.25 GHz at 1064 nm. 
     SUMMARY 
     The present invention is directed toward a catheter system for treating a treatment site within or adjacent to a vessel wall or heart valve. In various embodiments, the catheter system includes a light guide and a light source. The light guide is configured to selectively receive light energy. The light source generates the light energy. The light source is in optical communication with the light guide. The light source can include (i) a seed source that outputs the light energy, (ii) a pre-amplifier that receives the light energy from the seed source, the pre-amplifier being in optical communication with the seed source, and (iii) an amplifier that receives the light energy from the pre-amplifier, the amplifier being in optical communication with the pre-amplifier and the light guide. 
     In some embodiments, the catheter system further includes a seed controller that controls the seed source. 
     In certain embodiments, the catheter system further includes an optical element that is configured to direct the light energy into the light guide. 
     In various embodiments, the seed source includes one of a diode laser, a programmable semiconductor laser, a gated fiber optic laser, and a low power solid-state laser. 
     In some embodiments, the seed source, the pre-amplifier, and the amplifier are free space coupled within the light source. 
     In certain embodiments, the seed source is optically coupled to the pre-amplifier with a first coupling light guide, and the pre-amplifier is optically coupled to the amplifier with a second coupling light guide. 
     In various embodiments, the pre-amplifier includes one of a fiber optic laser, a solid-state laser, a flashlamp, and a diode pumped neodymium-doped yttrium aluminum garnet rod. 
     In some embodiments, the amplifier includes one of a high gain stage that is configured to have a high energy output capability, a fiber optic laser, a diode pumped solid-state laser, and a flashlamp. 
     In certain embodiments, the amplifier includes a gain medium including one of (i) a neodymium-doped yttrium aluminum garnet rod, (ii) a neodymium-doped yttrium aluminum garnet slab, (iii) a neodymium-doped glass, and (iv) an erbium-doped yttrium lithium fluoride, the gain medium being optically coupled to one of a laser diode stack and a flashlamp. 
     In various embodiments, the light source includes a collimator that collimates the light energy output by the pre-amplifier, the collimator being in optical communication with the pre-amplifier and the amplifier. 
     The present invention is also directed toward a catheter system for treating a treatment site within or adjacent to a vessel wall or heart valve. In various embodiments, the catheter system includes a light guide and a light source. The light guide is configured to selectively receive light energy. The light source generates the light energy. The light source is in optical communication with the light guide. The light source can include (i) a seed source that outputs the light energy, (ii) a linewidth modifier that modifies a linewidth of the light energy output by the seed source, (iii) a pre-amplifier that receives the light energy from the linewidth modifier, the pre-amplifier being in optical communication with the linewidth modifier, (iv) a collimator that collimates the light energy output by the pre-amplifier, the collimator being in optical communication with the pre-amplifier, and (v) an amplifier that receives the light energy from the pre-amplifier, the amplifier being in optical communication with the collimator and the light guide. 
     In some embodiments, the seed source includes one modulated distributed feedback laser. 
     In certain embodiments, the seed source includes a plurality of modulated distributed feedback lasers. 
     In various embodiments, the plurality of modulated distributed feedback lasers are configured to have a seed offset in center wavelengths that is above and below an amplifier wavelength of the amplifier. 
     In some embodiments, the seed source is optically coupled to the linewidth modifier with a first coupling light guide. 
     In certain embodiments, a seed pulse shape of the seed source is at least partially controlled by directly modulating the seed source. 
     In various embodiments, a seed pulse shape of the seed source is at least partially controlled by an acousto-optic modulator. 
     In some embodiments, the seed source includes a diode that is configured to have a high spatial coherence and a low temporal coherence. 
     In certain embodiments, the diode is a super-luminescent diode. 
     In various embodiments, the linewidth modifier is a band-limiting filter. 
     In some embodiments, the linewidth modifier is a fiber-optic Bragg grating. 
     In certain embodiments, the seed source and the linewidth modifier work in conjunction to (i) increase a seed linewidth of the seed source, (ii) improve amplification of the light energy, and (iii) minimize Stimulated Brillouin Scattering in the light guide. 
     The present invention is further directed toward a catheter system for treating a treatment site within or adjacent to a vessel wall or heart valve. In various embodiments, the catheter system includes a light guide and a light source. The light guide is configured to selectively receive light energy. The light source generates the light energy. The light source is in optical communication with the light guide. The light source can include (i) a seed source that outputs light energy, and (ii) an amplifier that receives the light energy from the seed source, the amplifier being in optical communication with the seed source and the light guide. 
     The present invention is also directed toward a method for treating a treatment site within or adjacent to a vessel wall or a heart valve that includes providing and/or using any of the catheter systems shown and/or described herein. 
     This summary is an overview of some of the teachings of the present application and is not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details are found in the detailed description and appended claims. Other aspects will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which is not to be taken in a limiting sense. The scope herein is defined by the appended claims and their legal equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG.  1    is a simplified schematic diagram of one embodiment of a portion of a catheter system having features of the present invention; 
         FIG.  2    is a simplified schematic diagram of another embodiment of a portion of the catheter system; 
         FIG.  3    is a simplified schematic diagram of yet another embodiment of a portion of the catheter system; and 
         FIG.  4    is a simplified schematic diagram of yet another embodiment of a portion of the catheter system. 
     
    
    
     While embodiments are susceptible to various modifications and alternative forms, specifics thereof have been shown by way of example and drawings, and will be described in detail. However, it should be understood that the scope herein is not limited to the particular aspects described. On the contrary, the intention is to cover modifications, equivalents, and alternatives falling within the spirit and scope herein. 
     DESCRIPTION 
     Treatment of vascular lesions (also referred to herein as “treatment sites”) can reduce major adverse events or death in affected subjects. As referred to herein, a major adverse event is one that can occur anywhere within the body due to the presence of a vascular lesion. Major adverse events can include but are not limited to, major adverse cardiac events, major adverse events in the peripheral or central vasculature, major adverse events in the brain, major adverse events in the musculature, or major adverse events in any of the internal organs. 
     As used herein, the terms “intravascular lesion,” “vascular lesion,” and “treatment site” are used interchangeably unless otherwise noted. The intravascular lesions and/or the vascular lesions are sometimes referred to herein simply as “lesions.” Also, as used herein, the terms “focused location” and “focused spot” can be used interchangeably unless otherwise noted and can refer to any location where the light energy is focused to a small diameter than the initial diameter of the light source. 
     Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention, as illustrated in the accompanying drawings. 
     In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer&#39;s specific goals, such as compliance with application-related and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it is appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
     The catheter systems disclosed herein can include many different forms. Referring now to  FIG.  1   , a schematic cross-sectional view is shown of a catheter system  100  in accordance with various embodiments. The catheter system  100  is suitable for imparting pressure waves to induce fractures in one or more treatment sites within or adjacent to a vessel wall of a blood vessel or on or adjacent to a heart valve within a body of a patient. In the embodiment illustrated in  FIG.  1   , the catheter system  100  can include one or more of a catheter  102 , a light guide bundle  122  including one or more light guides  122 A (some embodiments described here include at least a first light guide and a second light guide), a handle assembly  128 , a source manifold  136 , a fluid pump  138  and a system console  101 . The system console  101  can include one or more of a multiplexer  123 , a light source  124 , a power source  125 , a system controller  126 , a graphic user interface  127  (also sometimes referred to herein as a “GUI”), and an optical analyzer assembly  142 . Alternatively, the catheter system  100  can include greater or fewer components than those specifically illustrated and described in relation to  FIG.  1   . 
     It is appreciated that while the catheter system  100  is generally described herein as including a light guide bundle  122 , including one or more light guides  122 A, and a light source  124 . In some alternative embodiments, the catheter system  100  can include an energy guide bundle that includes different types of energy guides and/or a different type of energy source. 
     In various embodiments, the catheter  102  is configured to move to a treatment site  106  within or adjacent to a vessel wall  108 A of a blood vessel  108  within a body  107  of a patient  109 . The treatment site  106  can include one or more vascular lesions  106 A, such as calcified vascular lesions, for example. Additionally, or in the alternative, the treatment site  106  can include vascular lesions  106 A such as fibrous vascular lesions. Still alternatively, in some implementations, the catheter  102  can be used at a treatment site  106  within or adjacent to a heart valve within the body  107  of the patient  109 . 
     The catheter  102  can include an inflatable balloon  104  (sometimes referred to herein simply as a “balloon”), a catheter shaft  110 , and a guidewire  112 . The balloon  104  can be coupled to the catheter shaft  110 . The balloon  104  can include a balloon proximal end  104 P and a balloon distal end  104 D. The catheter shaft  110  can extend from a proximal portion  114  of the catheter system  100  to a distal portion  116  of the catheter system  100 . The catheter shaft  110  can include a longitudinal axis  144 . The catheter shaft  110  can also include a guidewire lumen  118 , which is configured to move over the guidewire  112 . As utilized herein, the guidewire lumen  118  defines a conduit through which the guide wire  112  extends. The catheter shaft  110  can further include an inflation lumen (not shown) and/or various other lumens for various other purposes. In some embodiments, the catheter  102  can have a distal end opening  120  and can accommodate and be tracked over the guidewire  112  as the catheter  102  is moved and positioned at or near the treatment site  106 . In some embodiments, the balloon proximal end  104 P can be coupled to the catheter shaft  110 , and the balloon distal end  104 D can be coupled to the guidewire lumen  118 . 
     The balloon  104  includes a balloon wall  130  that defines a balloon interior  146 . The balloon  104  can be selectively inflated with a balloon fluid  132  to expand from a deflated state suitable for advancing the catheter  102  through a patient&#39;s vasculature to an inflated state (as shown in  FIG.  1   ) suitable for anchoring the catheter  102  in position relative to the treatment site  106 . Stated in another manner, when the balloon  104  is in the inflated state, the balloon wall  130  of the balloon  104  is configured to be positioned substantially adjacent to the treatment sites  106 . It is appreciated that although  FIG.  1    illustrates the balloon wall  130  of the balloon  104  is shown spaced apart from the treatment site  106  of the blood vessel  108  when in the inflated state, this is done merely for ease of illustration. It is recognized that the balloon wall  130  of the balloon  104  will typically be substantially directly adjacent to and/or abutting the treatment site  106  when the balloon  104  is in the inflated state. 
     The balloon  104  suitable for use in the catheter system  100  includes those that can be passed through the vasculature of a patient  109  when in the deflated state. In some embodiments, the balloon  104  is made from silicone. In other embodiments, the balloon  104  can be made from polydimethylsiloxane (PDMS), polyurethane, polymers such as PEBAX™ material, nylon, or any other suitable material. 
     The balloon  104  can have any suitable diameter (in the inflated state). In various embodiments, the balloon  104  can have a diameter (in the inflated state) ranging from less than one millimeter (mm) up to 25 mm. In some embodiments, the balloon  104  can have a diameter (in the inflated state) ranging from at least 1.5 mm up to 14 mm. In some embodiments, the balloons  104  can have a diameter (in the inflated state) ranging from at least two mm up to five mm. 
     In some embodiments, the balloon  104  can have a length ranging from at least three mm to 300 mm. More particularly, in some embodiments, the balloon  104  can have a length ranging from at least eight mm to 200 mm. It is appreciated that a balloon  104  having a relatively longer length can be positioned adjacent to larger treatment sites  106  and, thus, may be used for imparting pressure waves onto and inducing fractures in larger vascular lesions  106 A or multiple vascular lesions  106 A at precise locations within the treatment site  106 . It is further appreciated that a longer balloon  104  can also be positioned adjacent to multiple treatment sites  106  at any one given time. 
     The balloon  104  can be inflated to inflation pressures of between approximately one atmosphere (atm) and 70 atm. In some embodiments, the balloon  104  can be inflated to inflation pressures of from at least 20 atm to 60 atm. In other embodiments, the balloon  104  can be inflated to inflation pressures of from at least six atm to 20 atm. In still other embodiments, the balloon  104  can be inflated to inflation pressures of from at least three atm to 20 atm. In yet other embodiments, the balloon  104  can be inflated to inflation pressures of from at least two atm to ten atm. 
     The balloon  104  can have various shapes, including, but not to be limited to, a conical shape, a square shape, a rectangular shape, a spherical shape, a conical/square shape, a conical/spherical shape, an extended spherical shape, an oval shape, a tapered shape, a bone shape, a stepped diameter shape, an offset shape, or a conical offset shape. In some embodiments, the balloon  104  can include a drug-eluting coating or a drug-eluting stent structure. The drug-eluting coating or drug-eluting stent can include one or more therapeutic agents, including anti-inflammatory agents, anti-neoplastic agents, anti-angiogenic agents, and the like. 
     The balloon fluid  132  can be a liquid or a gas. Some examples of the balloon fluid  132  suitable for use can include, but are not limited to, one or more of water, saline, contrast medium, fluorocarbons, perfluorocarbons, gases, such as carbon dioxide, or any other suitable balloon fluid  132 . In some embodiments, the balloon fluid  132  can be used as a base inflation fluid. In some embodiments, the balloon fluid  132  can include a mixture of saline to contrast medium in a volume ratio of approximately 50:50. In other embodiments, the balloon fluid  132  can include a mixture of saline to contrast medium in a volume ratio of approximately 25:75. In still other embodiments, the balloon fluid  132  can include a mixture of saline to contrast medium in a volume ratio of approximately 75:25. However, it is understood that any suitable ratio of saline to contrast medium can be used. The balloon fluid  132  can be tailored based on composition, viscosity, and the like so that the rate of travel of the pressure waves are appropriately manipulated. In certain embodiments, the balloon fluid  132  suitable for use herein is biocompatible. A volume of balloon fluid  132  can be tailored by the chosen light source  124  and the type of balloon fluid  132  used. 
     In some embodiments, the contrast agents used in the contrast media can include but are not limited to iodine-based contrast agents, such as ionic or non-ionic iodine-based contrast agents. Some non-limiting examples of ionic iodine-based contrast agents include diatrizoate, metrizoate, iothalamate, and ioxaglate. Some non-limiting examples of non-ionic iodine-based contrast agents include iopamidol, iohexol, ioxilan, iopromide, iodixanol, and ioversol. In other embodiments, non-iodine-based contrast agents can be used. Suitable non-iodine-containing contrast agents can include gadolinium (III)-based contrast agents. Suitable fluorocarbon and perfluorocarbon agents can include but are not limited to agents such as perfluorocarbon dodecafluoropentane (DDFP, C5F12). 
     The balloon fluids  132  can include those that include absorptive agents that can selectively absorb light in the ultraviolet region (e.g., at least ten nanometers (nm) to 400 nm), the visible region (e.g., at least 400 nm to 780 nm), or the near-infrared region (e.g., at least 780 nm to 2.5 μm) of the electromagnetic spectrum. Suitable absorptive agents can include those with absorption maxima along the spectrum from at least ten nm to 2.5 μm. Alternatively, the balloon fluid  132  can include absorptive agents that can selectively absorb light in the mid-infrared region (e.g., at least 2.5 μm to 15 μm) or the far-infrared region (e.g., at least 15 μm to one mm) of the electromagnetic spectrum. In various embodiments, the absorptive agent can be those that have an absorption maximum matched with the emission maximum of the laser used in the catheter system  100 . By way of non-limiting examples, various lasers described herein can include neodymium:yttrium-aluminum-garnet (Nd:YAG−emission maximum=1064 nm) lasers, holmium:YAG (Ho:YAG−emission maximum=2.1 μm) lasers, or erbium:YAG (Er:YAG−emission maximum=2.94 μm) lasers. In some embodiments, the absorptive agents can be water-soluble. In other embodiments, the absorptive agents are not water-soluble. In some embodiments, the absorptive agents used in the balloon fluids  132  can be tailored to match the peak emission of the light source  124 . Various light sources  124  having emission wavelengths of at least ten nanometers to one millimeter are discussed elsewhere herein. 
     The catheter shaft  110  of the catheter  102  can be coupled to the one or more light guides  122 A of the light guide bundle  122  that are in optical communication with the light source  124 . The light guide(s)  122 A can be disposed along the catheter shaft  110  and within the balloon  104 . Each of the light guides  122 A can have a guide distal end  122 D that is at any suitable longitudinal position relative to a length of the balloon  104 . In some embodiments, each light guide  122 A can be an optical fiber, and the light source  124  can be a laser. The light source  124  can be in optical communication with the light guides  122 A at the proximal portion  114  of the catheter system  100 . More particularly, the light source  124  can selectively, simultaneously, sequentially, and/or be in optical communication with each of the light guides  122 A in any desired combination, order, and/or pattern due to the presence and operation of the handle assembly  128 . 
     In some embodiments, the catheter shaft  110  can be coupled to multiple light guides  122 A such as a first light guide, a second light guide, a third light guide, etc., which can be disposed at any suitable positions about the guidewire lumen  118  and/or the catheter shaft  110 . For example, in certain non-exclusive embodiments, two light guides  122 A can be spaced apart by approximately 180 degrees about the circumference of the guidewire lumen  118  and/or the catheter shaft  110 ; three light guides  122 A can be spaced apart by approximately 120 degrees about the circumference of the guidewire lumen  118  and/or the catheter shaft  110 , or four light guides  122 A can be spaced apart by approximately 90 degrees about the circumference of the guidewire lumen  118  and/or the catheter shaft  110 . Still alternatively, multiple light guides  122 A need not be uniformly spaced apart from one another about the circumference of the guidewire lumen  118  and/or the catheter shaft  110 . More particularly, the light guides  122 A can be disposed either uniformly or non-uniformly about the guidewire lumen  118  and/or the catheter shaft  110  to achieve the desired effect in the desired locations. 
     The catheter system  100  and/or the light guide bundle  122  can include any number of light guides  122 A in optical communication with the light source  124  at the proximal portion  114 , and with the balloon fluid  132  within the balloon interior  146  of the balloon  104  at the distal portion  116 . For example, in some embodiments, the catheter system  100  and/or the light guide bundle  122  can include from one light guide  122 A to five light guides  122 A. In other embodiments, the catheter system  100  and/or the light guide bundle  122  can include from five light guides  122 A to fifteen light guides  122 A. In yet other embodiments, the catheter system  100  and/or the light guide bundle  122  can include from ten light guides  122 A to thirty light guides  122 A. Alternatively, in still other embodiments, the catheter system  100  and/or the light guide bundle  122  can include greater than 30 light guides  122 A. 
     The light guides  122 A can have any suitable design for purposes of generating plasma and/or pressure waves in the balloon fluid  132  within the balloon interior  146 . In certain embodiments, the light guides  122 A can include an optical fiber or flexible light pipe. The light guides  122 A can be thin and flexible and can allow light signals to be sent with very little loss of strength. The light guides  122 A can include a core surrounded by a cladding about its circumference. In some embodiments, the core can be a cylindrical core or a partially cylindrical core. The core and cladding of the light guides  122 A can be formed from one or more materials, including but not limited to one or more types of glass, silica, or one or more polymers. The light guides  122 A may also include a protective coating, such as a polymer. It is appreciated that the index of refraction of the core will be greater than the index of refraction of the cladding. 
     Each light guide  122 A can guide light energy along its length from a guide proximal end  122 P to the guide distal end  122 D, having at least one optical window (not shown) that is positioned within the balloon interior  146 . 
     In various embodiments, the guide distal end  122 D can further include and/or incorporate a distal light receiver  122 R that enables light energy to be moved back into and through the light guide  122 A from the guide distal end  122 D to the guide proximal end  122 P. Stated another way, the light energy can move in a first direction  121 F along the light guide  122 A that is generally from the guide proximal end  122 P toward the guide distal end  122 D of the light guide  122 A. At least a portion of the light energy can also move in a second direction  121 S along the light guide  122 A that is substantially opposite the first direction  121 F, i.e., from the guide distal end  122 D toward the guide proximal end  122 P of the light guide  122 A. Moreover, as described in greater detail hereinbelow, the light energy emitted from the guide proximal end  122 P after being moved back through the light guide  122 A (in the second direction  121 S) can be separated and then optically detected, interrogated, and/or analyzed through use of the optical analyzer assembly  142 . 
     The light guides  122 A can assume many configurations about and/or relative to the catheter shaft  110  of the catheter  102 . In some embodiments, the light guides  122 A can run parallel to the longitudinal axis  144  of the catheter shaft  110 . In some embodiments, the light guides  122 A can be physically coupled to the catheter shaft  110 . In other embodiments, the light guides  122 A can be disposed along a length of an outer diameter of the catheter shaft  110 . In yet other embodiments, the light guides  122 A can be disposed within one or more light guide lumens within the catheter shaft  110 . 
     The light guides  122 A can also be disposed at any suitable positions about the circumference of the guidewire lumen  118  and/or the catheter shaft  110 , and the guide distal end  122 D of each of the light guides  122 A can be disposed at any suitable longitudinal position relative to the length of the balloon  104  and/or relative to the length of the guidewire lumen  118  to more effectively and precisely impart pressure waves for purposes of disrupting the vascular lesions  106 A at the treatment site  106 . 
     In certain embodiments, the light guides  122 A can include one or more photoacoustic transducers  154 , where each photoacoustic transducer  154  can be in optical communication with the light guide  122 A within which it is disposed. In some embodiments, the photoacoustic transducers  154  can be in optical communication with the guide distal end  122 D of the light guide  122 A. Additionally, in such embodiments, the photoacoustic transducers  154  can have a shape that corresponds with and/or conforms to the guide distal end  122 D of the light guide  122 A. 
     The photoacoustic transducer  154  is configured to convert light energy into an acoustic wave at or near the guide distal end  122 D of the light guide  122 A. The direction of the acoustic wave can be tailored by changing an angle of the guide distal end  122 D of the light guide  122 A. 
     In certain embodiments, the photoacoustic transducers  154  disposed at the guide distal end  122 D of the light guide  122 A can assume the same shape as the guide distal end  122 D of the light guide  122 A. For example, in certain non-exclusive embodiments, the photoacoustic transducer  154  and/or the guide distal end  122 D can have a conical shape, a convex shape, a concave shape, a bulbous shape, a square shape, a stepped shape, a half-circle shape, an ovoid shape, and the like. The light guide  122 A can further include additional photoacoustic transducers  154  disposed along one or more side surfaces of the length of the light guide  122 A. 
     In some embodiments, the light guides  122 A can further include one or more diverting features or “diverters” (not shown in  FIG.  1   ) within the light guide  122 A that are configured to direct light to exit the light guide  122 A toward a side surface which can be located at or near the guide distal end  122 D of the light guide  122 A, and toward the balloon wall  130 . A diverting feature can include any system feature that diverts light energy from the light guide  122 A away from its axial path toward a side surface of the light guide  122 A. Additionally, the light guides  122 A can each include one or more light windows disposed along the longitudinal or circumferential surfaces of each light guide  122 A and in optical communication with a diverting feature. Stated in another manner, the diverting features can be configured to direct light energy in the light guide  122 A toward a side surface that is at or near the guide distal end  122 D, where the side surface is in optical communication with a light window. The light windows can include a portion of the light guide  122 A that allows light energy to exit the light guide  122 A from within the light guide  122 A, such as a portion of the light guide  122 A lacking a cladding material on or about the light guide  122 A. 
     Examples of the diverting features suitable for use include a reflecting element, a refracting element, and a fiber diffuser. The diverting features suitable for focusing light energy away from the tip of the light guides  122 A can include but are not to be limited to, those having a convex surface, a gradient-index (GRIN) lens, and a mirror focus lens. Upon contact with the diverting feature, the light energy is diverted within the light guide  122 A to one or more of a plasma generator  133  and the photoacoustic transducer  154  that is in optical communication with a side surface of the light guide  122 A. As noted, the photoacoustic transducer  154  then converts light energy into an acoustic wave that extends away from the side surface of the light guide  122 A. 
     The source manifold  136  can be positioned at or near the proximal portion  114  of the catheter system  100 . The source manifold  136  can include one or more proximal end openings that can receive the one or more light guides  122 A of the light guide bundle  122 , the guidewire  112 , and/or an inflation conduit  140  that is coupled in fluid communication with the fluid pump  138 . The catheter system  100  can also include the fluid pump  138  that is configured to inflate the balloon  104  with the balloon fluid  132  as needed. 
     As noted above, in the embodiment illustrated in  FIG.  1   , the multiplexer  123  includes one or more of the light source  124 , the power source  125 , the system controller  126 , and the GUI  127 . Alternatively, the multiplexer  123  can include more components or fewer components than those specifically illustrated in  FIG.  1   . For example, in certain non-exclusive alternative embodiments, the multiplexer  123  can be designed without the GUI  127 . Still alternatively, one or more of the light source  124 , the power source  125 , the system controller  126 , and the GUI  127  can be provided within the catheter system  100  without the specific need for the multiplexer  123 . 
     In some embodiments, the multiplexer  123  can include a two-channel splitter design. The guide bundle  122  can include a manual positioning mechanism that is mounted on an optical breadboard and/or platen. This design enables linear positional adjustment and array tilting by rotating about a channel one light guide  122 A axis (not shown in  FIG.  1   ). The adjustment method, in other embodiments, can include at least two adjustment steps, 1) aligning the planar positions of the guide beam  124 B at Channel 1, and 2) adjusting the light guide bundle  122  to achieve the best alignment at Channel 10. 
     As illustrated in  FIG.  1   , in certain embodiments, at least a portion of the optical analyzer assembly  142  can be positioned within the multiplexer  123 . Alternatively, various components of, or the entire optical analyzer assembly  142 , can be positioned outside of, or spaced apart from, the multiplexer  123 . 
     As shown, the multiplexer  123 , and the components included therewith, is operatively coupled to the catheter  102 , the light guide bundle  122 , and the remainder of the catheter system  100 . For example, in some embodiments, as illustrated in  FIG.  1   , the multiplexer  123  can include a console connection aperture  148  (also sometimes referred to generally as a “socket”) by which the light guide bundle  122  is mechanically coupled to the multiplexer  123 . In such embodiments, the light guide bundle  122  can include a guide coupling housing  150  (also sometimes referred to generally as a “ferrule”) that houses a portion, e.g., the guide proximal end  122 P, of each of the light guides  122 A. The guide coupling housing  150  is configured to fit and be selectively retained within the console connection aperture  148  to provide the mechanical coupling between the light guide bundle  122  and the multiplexer  123 . 
     The light guide bundle  122  can also include a guide bundler  152  (or “shell”) that brings each of the individual light guides  122 A closer together so that the light guides  122 A and/or the light guide bundle  122  can be in a more compact form as it extends with the catheter  102  into the blood vessel  108  during use of the catheter system  100 . In some embodiments, the light guides  122 A leading to the plasma generator  133  can be organized into a light guide bundle  122 , including a linear block with an array of precision holes forming a multi-channel ferrule. In other embodiments, the light guide bundle  122  could include a mechanical connector array or block connector that organizes singular ferrules into one of (i) a linear array, (ii) a circular pattern, and (iii) a hexagonal pattern. 
     The light source  124  can be selectively and/or alternatively coupled in optical communication with each of the light guides  122 A, i.e., to the guide proximal end  122 P of each of the light guides  122 A, in the light guide bundle  122 . In particular, the light source  124  is configured to generate light energy in the form of a source beam  124 A, such as a pulsed source beam, that can be selectively and/or alternatively directed to and received by each of the light guides  122 A in the light guide bundle  122  as an individual guide beam  124 B. An optical element  147  can selectively and/or alternatively direct the guide beam  1248  to the light guides  122 A in the light guide bundle  122  and/or the multiplexer  123 . The optical element  147  can include a lens, a focusing lens, a coupling lens, and/or a reflector. Alternatively, the catheter system  100  can include more than one light source  124 . For example, in one non-exclusive alternative embodiment, the catheter system  100  can include a separate light source  124  for each light guide  122 A in the light guide bundle  122 . The light source  124  can be operated at low energies. 
     The light source  124  can have any suitable design. In certain embodiments, the light source  124  can be configured to provide sub-millisecond pulses of light energy from the light source  124  that are focused onto a small spot in order to couple it into the guide proximal end  122 P of the light guide  122 A. Such pulses of light energy are then directed and/or guided along the light guides  122 A to a location within the balloon interior  146  of the balloon  104 , thereby inducing plasma formation (also sometimes referred to herein as a “plasma flash”) in the balloon fluid  132  within the balloon interior  146  of the balloon  104 , such as via the plasma generator  133  that can be located at the guide distal end  122 D of the light guide  122 A. In particular, the light emitted at the guide distal end  122 D of the light guide  122 A energizes the plasma generator  133  to form the plasma within the balloon fluid  132  within the balloon interior  146 . The plasma formation causes rapid bubble formation and imparts pressure waves upon the treatment site  106 . An exemplary plasma-induced bubble  134  is illustrated in  FIG.  1   . 
     When the plasma initially forms in the balloon fluid  132  within the balloon interior  146 , it emits broad-spectrum electromagnetic radiation. This can be seen as a flash of broad-spectrum light detectable by the naked eye. A portion of the light emitted from the plasma bubble  134  can be transmitted to the distal light receiver  122 R at the guide distal end  122 D of the light guide  122 A and travel back to the guide proximal end  122 P where it can be separated, detected, and analyzed through use of the optical analyzer assembly  142 . The intensity and timing of the visible light pulse relative to the plasma generating pulse provides an indication that the plasma generator  133  functioned, its energy output, and its functional condition. Visible light flashes may occur in other locations of the light guide  122 A if the light guide  122 A is damaged or broken. Such other visible light flashes will also be coupled into the light guide  122 A and carried back to the guide proximal end  122 P. The intensity and timing of these other light pulses provide an indication of damage to or failure of the light guide  122 A or the plasma generator  133 . In such situations, the optical analyzer assembly  142  can include a safety shutdown system that can be selectively activated to shut down the operation of the catheter system  100 . 
     The configuration of the plasma generator  133  and/or the distal light receiver  122 R can, in certain embodiments, further allow ambient light that originates outside of the catheter  102  to be coupled into the guide distal end  122 D of the light guide  122 A. In one implementation, the optical analyzer assembly  142  monitors for returned ambient light energy that traverses the light guide  122 A from the guide distal end  122 D to the guide proximal end  122 P. If any ambient light energy is present and detected by the optical analyzer assembly  142  in such situations, this is an indication that the catheter  102  is located outside of the body  107  of the patient  109 , and the optical analyzer assembly  142  can be configured to lock out the light source  124  accordingly. In particular, in such situations, the safety shutdown system  283  of the optical analyzer assembly  142  can be selectively activated to shut down the operation of the catheter system  100 . 
     In various non-exclusive alternative embodiments, the sub-millisecond pulses of light energy from the light source  124  can be delivered to the treatment site  106  at a frequency of between approximately one hertz (Hz) and 5000 Hz, between approximately 30 Hz and 1000 Hz, between approximately ten Hz and 100 Hz, or between approximately one Hz and 30 Hz. Alternatively, the sub-millisecond pulses of light energy can be delivered to the treatment site  106  at a frequency that can be greater than 5000 Hz or less than one Hz or any other suitable range of frequencies. 
     It is appreciated that although the light source  124  is typically utilized to provide pulses of light energy, the light source  124  can still be described as providing a single source beam  124 A, i.e., a single pulsed source beam. 
     The light sources  124  suitable for use can include various types of light sources, including lasers, seed sources, and lamps. For example, in certain non-exclusive embodiments, the light source  124  can be an infrared laser that emits light energy in the form of pulses of infrared light. Alternatively, as noted above, the light sources  124 , as referred to herein, can include any suitable type of energy source. 
     Suitable lasers can include short pulse lasers on the sub-millisecond timescale. In some embodiments, the light source  124  can include lasers on the nanosecond (ns) timescale. The lasers can also include short pulse lasers on the picosecond (ps), femtosecond (fs), and microsecond (us) timescales. It is appreciated that there are many combinations of laser wavelengths, pulse widths, and energy levels that can be employed to achieve plasma in the balloon fluid  132  of the catheter  102 . In various non-exclusive alternative embodiments, the pulse widths can include those falling within a range, including at least ten ns to 3000 ns, at least 20 ns to 100 ns, or at least one ns to 500 ns. Alternatively, any other suitable pulse width range can be used. 
     Exemplary nanosecond lasers can include those within the UV to IR spectrum, spanning wavelengths of about ten nanometers (nm) to one millimeter (mm). In some embodiments, the light sources  124  suitable for use in the catheter system  100  can include those capable of producing light at wavelengths of from at least 750 nm to 2000 nm. In other embodiments, the light sources  124  can include those capable of producing light at wavelengths of from at least 700 nm to 3000 nm. In still other embodiments, the light sources  124  can include those capable of producing light at wavelengths of from at least 100 nm to ten micrometers (μm). Nanosecond lasers can include those having repetition rates of up to 200 kHz. In some embodiments, the laser can include a Q-switched thulium:yttrium-aluminum-garnet (Tm:YAG) laser. In other embodiments, the laser can include a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser, holmium:yttrium-aluminum-garnet (Ho:YAG) laser, erbium:yttrium-aluminum-garnet (Er:YAG) laser, excimer laser, helium-neon laser, carbon dioxide laser, as well as doped, pulsed, fiber lasers. In still further embodiments, the light source  124  can include SLEDs that have bandwidths ranging from 13.25 GHz to 18.25 GHz at 1064 nm. 
     The catheter system  100  can generate pressure waves having maximum pressures in the range of at least one megapascal (MPa) to 100 MPa. The maximum pressure generated by a particular catheter system  100  will depend on the light source  124 , the absorbing material, the bubble expansion, the propagation medium, the balloon material, and other factors. In various non-exclusive alternative embodiments, the catheter system  100  can generate pressure waves having maximum pressures in the range of at least approximately two MPa to 50 MPa, at least approximately two MPa to 30 MPa, or at least approximately 15 MPa to 25 MPa. 
     The pressure waves can be imparted upon the treatment site  106  from a distance within a range from at least approximately 0.1 millimeters (mm) to greater than approximately 25 mm, extending radially from the light guides  122 A when the catheter  102  is placed at the treatment site  106 . In various non-exclusive alternative embodiments, the pressure waves can be imparted upon the treatment site  106  from a distance within a range from at least approximately ten mm to 20 mm, at least approximately one mm to ten mm, at least approximately 1.5 mm to four mm, or at least approximately 0.1 mm to ten mm extending radially from the light guides  122 A when the catheter  102  is placed at the treatment site  106 . In other embodiments, the pressure waves can be imparted upon the treatment site  106  from another suitable distance that is different than the foregoing ranges. In some embodiments, the pressure waves can be imparted upon the treatment site  106  within a range of at least approximately two MPa to 30 MPa at a distance from at least approximately 0.1 mm to ten mm. In some embodiments, the pressure waves can be imparted upon the treatment site  106  from a range of at least approximately two MPa to 25 MPa at a distance from at least approximately 0.1 mm to ten mm. Still alternatively, other suitable pressure ranges and distances can be used. 
     The power source  125  is electrically coupled to and is configured to provide the necessary power to each of the light source  124 , the system controller  126 , the GUI  127 , the handle assembly  128 , and the optical analyzer assembly  142 . The power source  125  can have any suitable design for such purposes. 
     The system controller  126  is electrically coupled to and receives power from the power source  125 . Additionally, the system controller  126  is coupled to and is configured to control the operation of each of the light source  124 , the GUI  127 , and the optical analyzer assembly  142 . The system controller  126  can include one or more processors or circuits for purposes of controlling the operation of at least the light source  124 , the GUI  127 , and the optical analyzer assembly  142 . For example, the system controller  126  can control the light source  124  for generating pulses of light energy as desired and/or at any desired firing rate. Additionally, the system controller  126  can control and/or operate in conjunction with the optical analyzer assembly  142  to effectively provide continuous real-time monitoring of the performance, reliability, safety, and proper usage of the catheter system  100 . 
     The system controller  126  can further be configured to control the operation of other components of the catheter system  100 , such as the positioning of the catheter  102  adjacent to the treatment site  106 , the inflation of the balloon  104  with the balloon fluid  132 , etc. Further, or in the alternative, the catheter system  100  can include one or more additional controllers that can be positioned in any suitable manner for purposes of controlling the various operations of the catheter system  100 . For example, in certain embodiments, an additional controller, and/or a portion of the system controller  126  can be positioned and/or incorporated within the handle assembly  128 . 
     The GUI  127  is accessible by the user or operator of the catheter system  100 . Additionally, the GUI  127  is electrically connected to the system controller  126 . With such design, the GUI  127  can be used by the user or operator to ensure that the catheter system  100  is effectively utilized to impart pressure onto and induce fractures at the treatment site(s)  106 . The GUI  127  can provide the user or operator with information that can be used before, during, and after use of the catheter system  100 . In one embodiment, the GUI  127  can provide static visual data and/or information to the user or operator. In addition, or in the alternative, the GUI  127  can provide dynamic visual data and/or information to the user or operator, such as video data or any other data that changes over time during the use of the catheter system  100 . In various embodiments, the GUI  127  can include one or more colors, different sizes, varying brightness, etc., which may alert the user or operator. Additionally, or in the alternative, the GUI  127  can provide audio data or information to the user or operator. The specifics of the GUI  127  can vary depending upon the design requirements of the catheter system  100 , or the specific needs, specifications, and/or desires of the user or operator. 
     As shown in  FIG.  1   , the handle assembly  128  can be positioned at or near the proximal portion  114  of the catheter system  100  and/or near the source manifold  136 . In this embodiment, the handle assembly  128  is coupled to the balloon  104  and is positioned spaced apart from the balloon  104 . Alternatively, the handle assembly  128  can be positioned at another suitable location. 
     The handle assembly  128  is handled and used by the user or operator to operate, position, and control the catheter  102 . The design and specific features of the handle assembly  128  can vary to suit the design requirements of the catheter system  100 . In the embodiment illustrated in  FIG.  1   , the handle assembly  128  is separate from, but in electrical and/or fluid communication with one or more of the system controller  126 , the light source  124 , the fluid pump  138 , the GUI  127 , and the optical analyzer assembly  142 . In some embodiments, the handle assembly  128  can integrate and/or include at least a portion of the system controller  126  within an interior of the handle assembly  128 . For example, as shown, in certain such embodiments, the handle assembly  128  can include circuitry (not shown in  FIG.  1   ) that can form at least a portion of the system controller  126 . In some embodiments, the circuitry can receive electrical signals or data from the optical analyzer assembly  142 . Further, or in the alternative, the circuitry can transmit such electrical signals or otherwise provide data to the system controller  126 . 
     In one embodiment, the circuitry can include a printed circuit board (not shown) having one or more integrated circuits, or any other suitable circuitry. In an alternative embodiment, the circuitry can be omitted or can be included within the system controller  126 , which in various embodiments can be positioned outside of the handle assembly  128 , e.g., within the multiplexer  123 . It is understood that the handle assembly  128  can include fewer or additional components than those specifically illustrated and described herein. 
     As with all embodiments illustrated and described herein, various structures may be omitted from the figures for clarity and ease of understanding. Further, the figures may include certain structures that can be omitted without deviating from the intent and scope of the invention. 
       FIG.  2    is a simplified schematic diagram of another embodiment of a portion of the catheter system  200 .  FIG.  2    illustrates a non-limiting, non-exclusive example of a master oscillator and power amplifier (MOPA) configuration for the light source  224 . In some such embodiments, the MOPA configuration enables a low-power master oscillator to seed the power amplifier with an appropriate pulse to amplify. If the pulse energy is low enough that the amplifier gain is not significantly depleted during the pulse, the temporal shape of the output of the system will closely match the output of the seed laser. 
     The MOPA configuration also makes it possible to significantly increase the linewidth of the light source  224  while minimizing the nonlinear optical processes and maintaining adequate light energy transmission through the light guide  222 A. This configuration provides techniques and methods that significantly increase the linewidth of energy output by the light source  224  by enabling transmission through small diameter light guides  222 A with minimal loss. 
     As illustrated in  FIG.  2   , the catheter system  200  can include the light guide  222 A, the light source  224 , a power source  225 , a plasma generator  233 , and an optical element  247 . These components can be substantially similar in form, placement, and/or function as previously described with respect to the catheter system  100  illustrated in  FIG.  1   . The catheter system  200  can further include a seed controller  258 , a seed source  260 , a pre-amplifier  262 , and an amplifier  264 . 
     The seed controller  258  controls the operation and/or functionality of the seed source  260 . For example, the seed controller  258  can control the output of energy from the seed source  260 . The seed controller  258  can control the wavelength, center wavelength, seed pulse shape, frequency, and/or any suitable characteristic of the energy output by the seed source  260 . The seed controller  258  can directly modulate the seed source  260 . The design and specific features of the seed controller  258  can vary to suit the design requirements of the catheter system  200  and/or the seed source  260 . 
     The seed controller  258  can include one or more processors, microprocessors, and/or circuits for purposes of controlling the operation of at least the seed source  260 . The seed controller  258  can include a printed circuit board having one or more integrated circuits, an acousto-optic modulator, or any other suitable circuitry. In an alternative embodiment, the seed controller  258  can be omitted or can be included within the system controller  126  (illustrated in  FIG.  1   ), which in various embodiments can be positioned outside of the light source  124 , e.g., within the multiplexer  123 . It is understood that the seed controller  258  can include fewer or additional components than those specifically illustrated and described herein. 
     The seed source  260  outputs light energy. The seed source  260  can be in optical communication with the light guide  222 A, the optical element  247 , the pre-amplifier  262 , and the amplifier  264 . The seed source  260  can be free space coupled with the pre-amplifier  262 , and the amplifier  264  within the light source  224 . The seed source  260  can be configured to have a seed offset in center wavelengths that is above and below an amplifier wavelength of the amplifier  264 . The seed source  260  can be configured to have a seed pulse shape that is at least partially controlled by (i) directly modulating the seed source  260 , or (ii) by an acousto-optic modulator (which can be included within the seed controller  258 ). 
     The seed source  260  can have a seed linewidth that is inherent to the seed source. The seed source  260  can be programmable so that the seed linewidth is adjustable to fit the design requirements of the catheter system  200  and/or the seed source  260 . In various embodiments, the seed source  260  can be run at a low threshold to length the seed pulse shape. The seed linewidth of the seed source  260  can be adjusted so that a seed center wavelength and a seed overall linewidth is substantially matched to a pre-amplifier center wavelength of the pre-amplifier  262  and/or an amplifier center wavelength of the amplifier  264 . By substantially matching the linewidths and/or center wavelengths, the energy conversion of the light energy is improved. 
     The design and specific features of the seed source  260  can vary to suit the design requirements of the catheter system  200 , the light source  224 , the light guide  222 A, the optical element  247 , the pre-amplifier  262 , and/or the amplifier  264 . The seed source  260  can include a diode, a super-luminescent diode, a diode laser, a programmable semiconductor laser, a gated fiber optic laser, a low power solid-state laser, and/or a modulated distributed feedback laser. It is understood that the seed source  260  can include fewer or additional components than those specifically illustrated and described herein. 
     The pre-amplifier  262  receives and amplifies the light energy from the seed source  260 . In various embodiments, the pre-amplifier  262  can be in optical communication with the light guide  222 A, the optical element  247 , the seed source  260 , and/or the amplifier  264 . The pre-amplifier  262  can be powered by the power source  225 . The design and specific features of the pre-amplifier  262  can vary to suit the design requirements of the catheter system  200 , the light source  224 , the light guide  222 A, the optical element  247 , the seed source  260 , and/or the amplifier  264 . 
     The pre-amplifier  262  can include a fiber optic laser, a solid-state laser, a flashlamp, and/or a diode pumped neodymium-doped yttrium aluminum garnet rod. It is understood that the pre-amplifier  262  can include fewer or additional components than those specifically illustrated and described herein. In some embodiments, the pre-amplifier  262  can be entirely omitted from the light source  224  depending on the output energy of the seed source  260  and the design requirements of the catheter system  200 , the light source  224 , the light guide  222 A, the optical element  247 , and/or the amplifier  264 . In other embodiments, the light source  224  may include a plurality of pre-amplifiers  262 . 
     The amplifier  264  receives and amplifies the light energy from the seed source  260  and/or the pre-amplifier  262 . In various embodiments, the amplifier  264  can be in optical communication with the light guide  222 A, the optical element  247 , the seed source  260 , and/or the pre-amplifier  262 . The amplifier  264  can be powered by the power source  225 . The design and specific features of the amplifier  264  can vary to suit the design requirements of the catheter system  200 , the light source  224 , the light guide  222 A, the optical element  247 , the seed source  260 , and/or the pre-amplifier  262 . 
     The amplifier  264  can include a high gain stage that is configured to have a high energy output capability, a fiber optic laser, a diode pumped solid-state laser, a gain medium, and/or a flashlamp. The gain medium can include (i) a neodymium-doped yttrium aluminum garnet rod, (ii) a neodymium-doped yttrium aluminum garnet slab, (iii) a neodymium-doped glass, and/or (iv) an erbium-doped yttrium lithium fluoride. The gain medium can be optically coupled to one of a laser diode stack and a flashlamp (e.g., within the amplifier  264 ). It is understood that the amplifier  264  can include fewer or additional components than those specifically illustrated and described herein. The amplifier  264  can have varying amplifier bandwidths. In some embodiments, the amplifier bandwidth can vary from 1 MHz to 1000 GHz. In other embodiments, the amplifier bandwidth can be less than 1 MHz or greater than 1000 GHz. 
     The amplifier  264  can include a solid-state high-power amplifier that omits a tuned cavity. The solid-state high-power amplifier can be driven to amplify the light energy to a gain medium linewidth of the gain medium. In some embodiments, when the gain medium includes neodymium-doped yttrium aluminum garnet, the gain medium linewidth is around 0.7 nm. In other embodiments, the light energy solid-state high-power amplifier can be driven to amplify the light energy to a gain medium linewidth of greater than 0.7 nm or less than 0.7 nm. 
     In some embodiments, the amplifier  264  can be entirely omitted from the light source  224  depending on the output energy of the seed source  260  and the design requirements of the catheter system  200 , the light source  224 , the light guide  222 A, the optical element  247 , and/or the pre-amplifier  262 . In other embodiments, the light source  224  can include a plurality of amplifiers  264 . 
       FIG.  3    is a simplified schematic diagram of yet another embodiment of a portion of the catheter system  300 . As illustrated in  FIG.  3   , the catheter system  300  can include the light guide  322 A, the light source  324 , a power source  325 , a plasma generator  333 , and an optical element  347 , the seed controller  358 , the seed source  360 , the pre-amplifier  362 , and the amplifier  364 . These components can be substantially similar in form, placement, and/or function as previously described with respect to the catheter system  300  illustrated in  FIGS.  1 - 2   . In certain embodiments, the catheter system  300  can further include a plurality of coupling light guides  322 C and a collimator  366 . 
     The coupling light guides  322 C can optically couple the various components of the light source  324 . For example, as shown in  FIG.  3   , a coupling light guide  322 C can optically couple the seed source  360  to the pre-amplifier  362 , and another coupling light guide  322 C can optically couple the pre-amplifier  362  to the collimator  366 . 
     Coupling modes of the various components within the light source  324  can be mixed depending on (i) the design requirements of the catheter system  300  and/or the light source, and (ii) the energy output of the seed source  360 , the pre-amplifier  362  and the amplifier  364 . For example, free space coupling and coupling light guides  322 C can each be utilized within the light source  324  (e.g., as shown in  FIG.  3   ). 
     The design and specific features of the coupling light guide  322 C can vary to suit the design requirements of the catheter system  300 , the light source  324 , the light guide  322 A, the optical element  347 , the seed source  360 , the pre-amplifier  362 , the amplifier  364 , and/or the collimator  366 . The coupling light guide  322 C can be a fiber optic cable. 
     The collimator  366  can collimate the light energy output by the seed source  360 , the pre-amplifier  362 , and/or the amplifier  364 . The collimator  366  can be in optical communication with the light guide  322 A, the optical element  347 , the seed source  360 , the pre-amplifier  362 , and/or the amplifier  364 . The design and specific features of the collimator  366  can vary to suit the design requirements of the catheter system  300 , the light source  324 , the light guide  322 A, the optical element  347 , the seed source  360 , the pre-amplifier  362 , and/or the amplifier  364 . It is understood that the collimator  366  can include fewer or additional components than those specifically illustrated and described herein. 
       FIG.  4    is a simplified schematic diagram of yet another embodiment of a portion of the catheter system  400 . As illustrated in  FIG.  4   , the catheter system  400  can include a light guide  422 A, a plurality of coupling light guides  422 C, a light source  424 , a power source  425 , a plasma generator  433 , and an optical element  447 , a seed controller  458 , the seed source  460 , the pre-amplifier  462 , the amplifier  464 , and a collimator  466 . These components can be substantially similar in form, placement, and/or function as previously described with respect to the catheter system  400  illustrated in  FIGS.  1 - 3   . In certain embodiments, the catheter system  400  can further include a linewidth modifier  468 . 
     The linewidth modifier  468  modifies a linewidth of the light energy output by the seed source  460 . In various embodiments, the linewidth modifier  468  can be in optical communication with the light guide  422 A, the optical element  447 , the seed source  460 , the pre-amplifier  462 , and/or the amplifier  464 . The linewidth modifier  468  and the seed source  460  can work in conjunction to (i) increase a seed linewidth of the seed source  460 , (ii) improve amplification of the light energy, and (iii) minimize Stimulated Brillouin Scattering (SBS) in the light guide  422 A. 
     The design and specific features of the linewidth modifier  468  can vary to suit the design requirements of the catheter system  400 , the light guide  422 A, the light source  424 , the optical element  447 , the seed source  460 , the pre-amplifier  462 , and/or the amplifier  464 . The linewidth modifier  468  can include a band-limiting filter and/or a fiber-optic Bragg grating, as non-limiting, non-exclusive examples. It is understood that linewidth modifier  468  can include fewer or additional components than those specifically illustrated and described herein. 
     Lasers 
     The lasers suitable for use herein can include various types of lasers, including lasers and lamps. Suitable lasers can include short pulse lasers on the sub-millisecond timescale. In some embodiments, the laser can include lasers on the nanosecond (ns) timescale. The lasers can also include short pulse lasers on the picosecond (ps), femtosecond (fs), and microsecond (us) timescales. It is appreciated that there are many combinations of laser wavelengths, pulse widths, and energy levels that can be employed to achieve plasma in the balloon fluid of the catheters illustrated and/or described herein. In various embodiments, the pulse widths can include those falling within a range, including from at least 10 ns to 200 ns. In some embodiments, the pulse widths can include those falling within a range including from at least 20 ns to 100 ns. In other embodiments, the pulse widths can include those falling within a range including from at least 1 ns to 5000 ns. 
     Exemplary nanosecond lasers can include those within the UV to IR spectrum, spanning wavelengths of about 10 nanometers to 1 millimeter. In some embodiments, the lasers suitable for use in the catheter systems herein can include those capable of producing light at wavelengths of from at least 750 nm to 2000 nm. In some embodiments, the lasers can include those capable of producing light at wavelengths of from at least 700 nm to 3000 nm. In some embodiments, the lasers can include those capable of producing light at wavelengths of from at least 100 nm to 10 micrometers (μm). Nanosecond lasers can include those having repetition rates of up to 200 kHz. In some embodiments, the laser can include a Q-switched thulium:yttrium-aluminum-garnet (Tm:YAG) laser. In some embodiments, the laser can include a neodymium:yttrium-aluminum-garnet (Nd:YAG), holmium:yttrium-aluminum-garnet (Ho:YAG), erbium:yttrium-aluminum-garnet (Er:YAG), excimer laser, helium-neon laser, carbon dioxide laser, as well as doped, pulsed, fiber lasers. 
     Pressure Waves 
     The catheters illustrated and/or described herein can generate pressure waves having maximum pressures in the range of at least 1 megapascal (MPa) to 100 MPa. The maximum pressure generated by a particular catheter will depend on the laser, the absorbing material, the bubble expansion, the propagation medium, the balloon material, and other factors. Such factors can include: 
     (i) Pulse energy can be the primary factor in determining the size of the bubble generated and its ability to fracture calcified lesions. Clinical effectiveness is tied directly to mechanical energy and not the acoustic shockwave that precedes the mechanical bubble. Energy has an inverse cubic relationship with: R∝√{square root over (E/p)}. 
     (ii) Pulse width and envelope shape play lesser roles. These factors impact the overall conversion efficiency and the amplitude of the acoustic shockwave that precedes the mechanical bubble. 
     (iii) Energy delivered—delivering more energy into the region where plasma is generated on the relaxation timescale of the phenomenon improves the conversion efficiency—packing more light energy into the plasma before the bubble begins to form increases conversion efficiency and peak acoustic energy. 
     (iv) Temporal stretching of the light energy pulse is an effective way to reduce surface irradiance below the damage threshold for light guide material while maintaining total energy in the pulse, thereby maximizing bubble size. 
     In some embodiments, the catheters illustrated and/or described herein can generate pressure waves having maximum pressures in the range of at least 2 MPa to 50 MPa. In other embodiments, the catheters illustrated and/or described herein can generate pressure waves having maximum pressures in the range of at least 2 MPa to 30 MPa. In yet other embodiments, the catheters illustrated and/or described herein can generate pressure waves having maximum pressures in the range of at least 15 MPa to 25 MPa. In some embodiments, the catheters illustrated and/or described herein can generate pressure waves having peak pressures of greater than or equal to 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa, 21 MPa, 22 MPa, 23 MPa, 24 MPa, or 25 MPa, 26 MPa, 27 MPa, 28 MPa, 29 MPa, 30 MPa, 31 MPa, 32 MPa, 33 MPa, 34 MPa, 35 MPa, 36 MPa, 37 MPa, 38 MPa, 39 MPa, 40 MPa, 41 MPa, 42 MPa, 43 MPa, 44 MPa, 45 MPa, 46 MPa, 47 MPa, 48 MPa, 49 MPa, or 50 MPa. It is appreciated that the catheters illustrated and/or described herein can generate pressure waves having operating pressures or maximum pressures that can fall within a range, wherein any of the forgoing numbers can serve as the lower or upper bound of the range, provided that the lower bound of the range is a value less than the upper bound of the range. 
     Therapeutic treatment can act via a fatigue mechanism or a brute force mechanism. For a fatigue mechanism, operating pressures would be about at least 0.5 MPa to 2 MPa, or about 1 MPa. For a brute force mechanism, operating pressures would be about at least 20 MPa to 30 MPa, or about 25 MPa. Pressures between the extreme ends of these two ranges may act upon a treatment site using a combination of a fatigue mechanism and a brute force mechanism. 
     The pressure waves described herein can be imparted upon the treatment site from a distance within a range from at least 0.01 millimeters (mm) to 25 mm, extending radially from a longitudinal axis of a catheter placed at a treatment site. In some embodiments, the pressure waves can be imparted upon the treatment site from a distance within a range from at least 1 mm to 20 mm, extending radially from a longitudinal axis of a catheter placed at a treatment site. In other embodiments, the pressure waves can be imparted upon the treatment site from a distance within a range from at least 0.1 mm to 10 mm, extending radially from a longitudinal axis of a catheter placed at a treatment site. In yet other embodiments, the pressure waves can be imparted upon the treatment site from a distance within a range from at least 1.5 mm to 4 mm, extending radially from a longitudinal axis of a catheter placed at a treatment site. In some embodiments, the pressure waves can be imparted upon the treatment site from a range of at least 2 MPa to 30 MPa at a distance from 0.1 mm to 10 mm. In some embodiments, the pressure waves can be imparted upon the treatment site from a range of at least 2 MPa to 25 MPa at a distance from 0.1 mm to 10 mm. In some embodiments, the pressure waves can be imparted upon the treatment site from a distance that can be greater than or equal to 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, or 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm, or can be an amount falling within a range between, or outside the range of any of the foregoing. 
     By shaping the temporal form of the optical pulse to have a fast rise time and minimal overshoot (ideally approaching a square wave), the efficiency for generating the pressure wave can be improved, and the amount of energy that can be delivered in a given time interval can be increased while decreasing the peak laser intensity to remain below the damage threshold of the optical fiber. 
     The present technology is also directed toward methods for treating a treatment site within or adjacent to a vessel wall, with such methods utilizing the devices disclosed herein. 
     It should be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content and/or context clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense, including “and/or” unless the content or context clearly dictates otherwise. 
     It should also be noted that, as used in this specification and the appended claims, the phrase “configured” describes a system, apparatus, or other structure that is constructed or configured to perform a particular task or adopt a particular configuration. The phrase “configured” can be used interchangeably with other similar phrases such as arranged and configured, constructed and arranged, constructed, manufactured and arranged, and the like. 
     As used herein, the recitation of numerical ranges by endpoints shall include all numbers subsumed within that range, inclusive (e.g., 2 to 8 includes 2, 2.1, 2.8, 5.3, 7, 8, etc.). 
     It is recognized that the figures shown and described are not necessarily drawn to scale, and that they are provided for ease of reference and understanding, and for relative positioning of the structures. 
     The headings used herein are provided for consistency with suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not be viewed to limit or characterize the invention(s) set out in any claims that may issue from this disclosure. As an example, a description of a technology in the “Background” is not an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” or “Abstract” to be considered as a characterization of the invention(s) set forth in issued claims. 
     The embodiments described herein are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art can appreciate and understand the principles and practices. As such, aspects have been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope herein. 
     It is understood that although a number of different embodiments of the catheter systems have been illustrated and described herein, one or more features of any one embodiment can be combined with one or more features of one or more of the other embodiments, provided that such combination satisfies the intent of the present invention. 
     While a number of exemplary aspects and embodiments of the catheter systems have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, and sub-combinations as are within their true spirit and scope, and no limitations are intended to the details of construction or design herein shown.