Patent Publication Number: US-2023164902-A1

Title: Laser sustained plasma and endoscopy light source

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/704,029, filed on Dec. 5, 2019, and entitled “LASER SUSTAINED PLASMA AND ENDOSCOPY LIGHT SOURCE,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/776,006, filed on Dec. 6, 2018, entitled “LASER SUSTAINED PLASMA AND ENDOSCOPY LIGHT SOURCE.” The contents of each of these applications is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to illumination devices, and more particularly, is related to high-intensity arc lamps. 
     BACKGROUND 
     High intensity arc lamps are devices that emit a high intensity beam of electromagnetic radiation. The lamps generally include a gas containing chamber, for example, a glass bulb, with an anode and cathode that are used to excite the gas (ionizable medium) within the chamber. An electrical discharge is generated between the anode and cathode to provide power to the excited (e.g. ionized) gas to sustain the light emitted by the ionized gas during operation of the light source. 
       FIG.  1    shows a pictorial view and a cross section of a low-wattage parabolic Xenon lamp  100 . The lamp is generally constructed of metal and ceramic. The fill gas, Xenon, is inert and nontoxic. The lamp subassemblies may be constructed with high-temperature brazes in fixtures that constrain the assemblies to tight dimensional tolerances.  FIG.  2    shows some of these lamp subassemblies and fixtures after brazing. 
     Referring to  FIG.  1    and  FIG.  2   , there are three main subassemblies in the lamp  100 : cathode; anode; and reflector. A cathode assembly  3   a  contains a lamp cathode  3   b,  a plurality of struts holding the cathode  3   b  to a window flange  3   c,  a window  3   d,  and getters  3   e.  The lamp cathode  3   b  is a small, pencil-shaped part made, for example, from thoriated tungsten. During operation, the cathode  3   b  emits electrons that migrate across a lamp arc gap and strike an anode  3   g.  The electrons are emitted thermionically from the cathode  3   b,  so the cathode tip must maintain a high temperature and low-electron-emission to function. 
     The cathode struts  3   c  hold the cathode  3   b  rigidly in place and conduct current to the cathode  3   b.  The lamp window  3   d  may be ground and polished single-crystal sapphire (AlO2). Sapphire allows thermal expansion of the window  3   d  to match the flange thermal expansion of the flange  3   c  so that a hermetic seal is maintained over a wide operating temperature range. The thermal conductivity of sapphire transports heat to the flange  3   c  of the lamp and distributes the heat evenly to avoid cracking the window  3   d.  The getters  3   e  are wrapped around the cathode  3   b  and placed on the struts. The getters  3   e  absorb contaminant gases that evolve in the lamp during operation and extend lamp life by preventing the contaminants from poisoning the cathode  3   b  and transporting unwanted materials onto a reflector  3   k  and window  3   d.  The anode assembly  3   f  is composed of the anode  3   g,  a base  3   h,  and tabulation  3   i.  The anode  3   g  is generally constructed from pure tungsten and is much blunter in shape than the cathode  3   b.  This shape is mostly the result of the discharge physics that causes the arc to spread at its positive electrical attachment point. The arc is typically somewhat conical in shape, with the point of the cone touching the cathode  3   b  and the base of the cone resting on the anode  3   g.  The anode  3   g  is larger than the cathode  3   b,  to conduct more heat. About 80% of the conducted waste heat in the lamp is conducted out through the anode  3   g,  and 20% is conducted through the cathode  3   b.  The anode is generally configured to have a lower thermal resistance path to the lamp heat sinks, so the lamp base  3   h  is relatively massive. The base  3   h  is constructed of iron or other thermally conductive material to conduct heat loads from the lamp anode  3   g.  The tabulation  3   i  is the port for evacuating the lamp  100  and filling it with Xenon gas. After filling, the tabulation  3   i  is sealed, for example, pinched or cold-welded with a hydraulic tool, so the lamp  100  is simultaneously sealed and cut off from a filling and processing station. The reflector assembly  3 j includes the reflector  3   k  and two sleeves  3   l.  The reflector  3   k  may be a nearly pure polycrystalline alumina body that is glazed with a high temperature material to give the reflector a specular surface. The reflector  3   k  is then sealed to its sleeves  3   l  and a reflective coating is applied to the glazed inner surface. 
       FIG.  3 A  shows a first perspective of a cylindrical lamp  300 . Two arms  345 ,  346  protrude outward from the sealed chamber  320 . The arms  345 ,  346  house a pair of electrodes  390 ,  391 , which protrude inward into the sealed chamber  320 , and provide an electric field for ignition of the ionizable medium within the chamber  320 . Electrical connections for the electrodes  390 ,  391  are provided at the ends of the arms  345 ,  346 . 
     The chamber  320  has an ingress window  326  where laser light from a laser source (not shown) may enter the chamber  320 . Similarly the chamber  320  has an egress window  328  where high intensity light from energized plasma may exit the chamber  320 . Light from the laser is focused on the excited gas (plasma) to provide sustaining energy. The ionized media may be added to or removed from the chamber with a controlled high pressure valve  398 . 
       FIG.  3 B  shows a second perspective of the cylindrical lamp  300 , by rotating the view of  FIG.  3 A  ninety degrees vertically. A controlled high pressure valve  398  is located substantially opposite the viewing window  310 .  FIG.  3 C  shows a second perspective of the cylindrical lamp  300 , by rotating the view of  FIG.  3 B  ninety degrees horizontally. In general, the interior profile of the chamber  320  matches the exterior profile of the chamber  320 . 
     An endoscope is an illuminated optical, typically slender and tubular instrument (a type of borescope) used to look deep into the body and used in procedures called an endoscopy. It is used to examine the internal organs like the throat or esophagus. Specialized instruments are named after their target organ. Examples include the cystoscope (bladder), nephroscope (kidney), bronchoscope (bronchus), arthroscope (joints) and colonoscope (colon), and laparoscope (abdomen or pelvis). They can be used to examine visually and diagnose, or assist in surgery such as an arthroscopy. Endoscope light generating sources are typically located remotely from a light emitting aperture near the illumination target. Light is conveyed from the light source to the emitting aperture via a light guide, such as an optical fiber. 
     Minimally invasive endoscopic and robotic surgeries are driven by fiber optic light sources. The fibers are typically in the range of  3 . 0  to  4 . 8 mm in diameter. However, present light sources may experience a loss of radiance that may be problematic for example, in the fields of endoscopic and robotic surgery practice. Furthermore, the diameter of the fibers guiding the light is more and more prohibitive in an environment where there is a need for imaging channels and in some cases tool actuation channels in the same fiber bundle. The present trend is to seek more information out of the available space which is driving the diameter of the fibers down. For example, smaller fiber bundles may enable procedures that are currently not possible with current methods and devices. Existing light sources don&#39;t have sufficient etendue to couple significant levels of light in a fiber having a diameter smaller than 3 mm. This results in insufficient light for cameras to render a sufficiently noise free image. Therefore, there is a need to address one or more of the above mentioned shortcomings. 
     SUMMARY 
     Embodiments of the present invention provide a laser sustained plasma and endoscopy light source. Briefly described, the present invention is directed to applications where high brightness or irradiance is delivered through small diameter light guides or fibers less than  1 mm so more space is available for imaging fibers and/or laser delivery fibers. 
     Other systems, methods and features of the present invention will be or become apparent to one having ordinary skill in the art upon examining the following drawings and detailed description. It is intended that all such additional systems, methods, and features be included in this description, be within the scope of the present invention and protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG.  1    is a schematic diagram of a high intensity lamp in exploded view. 
         FIG.  2    is a schematic diagram of the high intensity lamp of  FIG.  1    in cross-section view. 
         FIG.  3 A  is a schematic diagram of a cylindrical laser driven sealed beam lamp. 
         FIG.  3 B  is a schematic diagram of the cylindrical laser driven sealed beam lamp of  FIG.  3 A  from a second view. 
         FIG.  3 C  is a schematic diagram of the cylindrical laser driven sealed beam lamp of  FIG.  3 A  from a third view. 
         FIG.  4    is a schematic diagram of an exemplary first embodiment of lamp having a cylindrical plasma lamp chamber. 
         FIG.  5    is a schematic diagram of an exemplary second embodiment of lamp having a parabolic plasma lamp chamber. 
         FIG.  6    is a flowchart of an exemplary embodiment of a method for producing high intensity light coupled to a small diameter light guide. 
         FIG.  7    is a schematic diagram detail of lamp electrodes for the first embodiment of  FIG.  4   . 
     
    
    
     DETAILED DESCRIPTION 
     The following definitions are useful for interpreting terms applied to features of the embodiments disclosed herein, and are meant only to define elements within the disclosure. 
     As used within this disclosure, “black body” refers to an object capable of absorbing all the electromagnetic radiation falling on it. A black body maintained at a constant temperature is a full radiator at that temperature because the radiation reaching and leaving it must be in equilibrium. A black body spectrum refers to the spectrum of electromagnetic waves a black body is able to emit. 
     As used within this disclosure, collimated light is light whose rays are substantially parallel, and therefore will spread minimally as it propagates. 
     As used within this disclosure, “substantially” means “very nearly,” or within normal manufacturing tolerances. For example, a substantially flat window, while intended to be flat by design, may vary from being entirely flat based on variances due to manufacturing. 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     As mentioned in the Background section, minimally invasive and robotic surgeries typically use fiber optic light sources in the  3 . 0  to  4 . 8 mm diameter range. The following exemplary embodiments of the present invention describe an endoscopic light source configured to provide white light with a black body spectrum into a  200 - 500  micrometer fiber diameter. 
     Under a first embodiment of an endoscopic light source  400  as shown by  FIG.  4   , a combination laser source  420  may include a plurality of laser driver units  102 - 104 . Each laser driver unit  102 - 104  may emit a different wavelength/waveband and/or intensity of light. The light from the laser driver units  102 - 104  is combined in a light conduit  401 , for example an optical fiber and emitted via an optical expander  105 . Egress optics for the combination laser source  420  may be configured differently for alternative embodiments. Similarly, in alternative embodiments the combination laser source  420  may include more than three driver units or less than three driver units. 
     A first laser driver unit  102  provides a portion of the beam  405 . The beam  405  is collimated via an ingress collimator  106  and focused into a plasma sustaining beam  407 , for example, via focusing optics  107 . The plasma sustaining beam  407  enters a sealed cylindrical chamber of a lamp  108  via an ingress window  109 . For example, the lamp  108  may be a cylindrical lamp. The sealed chamber of the lamp  108  contains an ionizable media  425 , for example, Xenon, Krypton or a mix of Xenon and Krypton. The ionizable media  425 , once ignited, forms a plasma  430  that emits a high intensity light  410 . The plasma  430  is sustained by the energy from the first laser driver unit  102  via the plasma sustaining beam  407 . The plasma  430  may be ignited (ionized) by an electronic ignition module  114 , for example, electrodes  790 ,  791  ( FIG.  7   ). The electronic ignition module  114  may provide electrical power to the electrodes  790 ,  791  via electrical connections in arms  745 ,  746  ( FIG.  7   ) of the lamp  108 . Alternatively, the electronic ignition module  114  may be omitted, and the plasma may be ignited without electrodes, for example via auto-ignition by the first laser driver unit  102 . 
     The high intensity egress light  410  exits the chamber of the lamp  108  via an egress window  110  and is optically coupled to an exit fiber  113 . For example, the high intensity egress light  410  may be substantially white in color and may be collimated into a collimated beam  411  via egress collimating optics  111 , and then focused into an ingress surface  413  of the exit fiber  113  via egress focusing optics  112 . For example, the collimating optics  111  may be as simple as a single positive lens, a multi lens beam expander based on positive and negative lens assembly or a parabolic mirror or combination of parabolic mirror and a combination of positive and negative lenses. The light is emitted at an egress surface  414 , for example, the egress surface located at a far end of an endoscope near an illumination target. The exit fiber  113  has a fiber diameter  415  in the range of, for example, 200-500 micrometers. 
     The first laser driver unit  102 , for example, a low power (150 Watt) 979 nm first laser driver unit  102 , may generate a plasma in a Xenon, Krypton or mixed noble gas under pressures within the lamp  108  ranging from 10 bar to 50 bar with a plasma waist size of 150 microns or less that may be efficiently coupled into the diameter of the exit fiber  113 , which is not possible with the standard endoscope light sources, for example a xenon short arc solution or non-laser solid state light sources. 
     A second laser driver unit  104  having a wavelength different from the first laser driver unit  102 . For example the second laser driver unit  104  may produce an 803 nm (or other wavelength) 10-100 mW beam that may be mixed with the plasma sustaining beam produced by first laser driver unit  102  for fluorescence based diagnostics. The light from the second laser driver unit  104  is preferably mixed with visible light at the output of the lamp  108  to excite dyes for fluorescence techniques. Alternatively, the fluorescence exciting beam produced by the second laser driver unit  104  may be mixed with the high intensity light at the output of the lamp  108 . For example, the beams may be mixed using a dichroic coated mirror under 45 degrees that reflects one wavelength and passes the other wavelength, where the two beams to be mixed are orthogonal while the mixing mirror is under 45 degrees. Alternatively a mix cube may be used with the same functionality. The diagonal of the cube is the mixing surface while the facets where the beams enter (orthogonally) may be coated with specific coatings to shape the properties of said beams. 
     The first laser driver unit  102 , for example a 150 W laser diode stack is coupled, for example through beam correction optics (not shown) into a light conduit  401 . Beam correction optics or shaping optics as described and needed here are used to shape the elevated diode stack light output having a different divergence in the horizontal and vertical plane into a more symmetrical beam pattern with mostly equal divergence in all directions. The light conduit  401  may be for example a 200 micrometer laser fiber keeping, for example, 95% of the power in a numerical aperture (NA) of 0.15 but other NA ranges may be practical, for example, 90% of power in a 0.2 NA or even 80% of power in a 0.3 NA. The latter two examples will exhibit lower system output but that may still be sufficient for some applications. 
     Since the first laser driver unit  102  produces a beam that is not visible to the human eye, a third laser driver unit  103  producing visible light, for example, a low power red laser under 5 mW may be mixed with the output of the first laser driver unit  102  and/ or the second laser driver unit  104  so the optical alignment of all optical components  105 ,  106 ,  107 ,  111 ,  112  and the lamp  108  can be performed using visible light instead of using other means, for example, IR convertors to visualize the location of the  979  nm wavelength beam. 
     The output of the light conduit  401  may be terminated into a fiber connector (not shown) allowing for a modular approach to change out the laser drive unit(s)  102 ,  103 ,  104 . The fiber connector is coupled to beam conditioning optics, for example, the optical expander  105 , the ingress collimator  106 , for example a collimating lens, and the ingress focusing optics  107 , for example a focusing lens. The optical expander  105  shapes the beam waist of the laser in the focusing point. The NA of the ingress focusing optics  107  is preferably in the 0.4-0.6 range. 
     The focused output of this laser drive system including the plasma sustaining beam  407  is delivered into the lamp  108 ,  208  via the ingress window  109 . Under the first embodiment, the lamp may be configured as a cylindrical sealed cavity lamp  108 , as shown in  FIG.  4    with a sapphire ingress window  109  for laser entry and a sapphire egress window  110  for high intensity visible egress light. The cylindrical sealed cavity lamp  108  generates an expanding beam  410  with a NA of 0.4-0.6. Egress collimating optics  111  receives and collimates the expanding beam  410  to produce a collimated high intensity beam  411 , and an egress focusing optic  112  at the output of the lamp  108  focuses the collimated light  411  into a focused output light  412  which is introduced into the exit fiber  113 . 
     A second exemplary embodiment of an endoscopic light source  500  is shown in  FIG.  5   . The combination laser source  420 , the lamp ingress optics  106 ,  107 , the egress focusing optic  112  and the exit fiber  113  are substantially as described in the first embodiment shown by  FIG.  4   . 
     Under the second exemplary embodiment  500 , the lamp may be configured as a parabolic reflector cavity design lamp  208  with a sapphire ingress window  109  for laser entry and a sapphire egress window  110  for high intensity visible egress light. The lamp ingress optics  106 ,  107  focus the plasma sustaining beam  407  to a lamp focal region  530  of the parabolic reflector cavity design lamp  208 , so the plasma  430  energized by the plasma sustaining beam  407  is located at the lamp focal region  530 . The parabolic reflector cavity design lamp  208  reflects the high intensity light generated by the plasma  430  to produce a collimated beam  511  with a beam size limited by a diameter the egress window  110  and a configurable divergence. It should be noted that since the divergence of a parabolic reflector is determined by the diameter (or aperture) of the parabolic mirror (assuming the parabolic mirror is fully filled by the expanded light) divided by the light source (plasma) point size using, for example, a point size on the order of 150 micron, the divergence is about eight times smaller than a typical xenon lamp for endoscopy, thereby coupling more light into the exit fiber  113  than previous techniques. The egress focusing optic  112  at the output of the lamp  208  focuses the collimated beam  511  into a focused output light  512  which is introduced into the exit fiber  113 . 
       FIG.  6    is a flowchart of an exemplary embodiment of a method for producing high intensity light coupled to a small diameter light guide. It should be noted that any process descriptions or blocks in flowcharts should be understood as representing modules, segments, portions of code, or steps that include one or more instructions for implementing specific logical functions in the process, and alternative implementations are included within the scope of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention. The method is described with reference to  FIG.  4    and  FIG.  6   . 
     A plasma sustaining beam  407  having a power at or below 150 W is generated, for example, by a first laser driver unit  102  as shown by block  610 . One or more other light sources may be mixed into the plasma sustaining laser beam, for example, an output of a second laser driver unit  104  producing a wavelength different from the first laser driver unit  102 , for example, an 803 nm 10-30 mW laser ±15 nm, and/or an output of a third laser driver unit  103  producing visible light, for example, a low power red laser. The second laser driver unit  104  preferably produces 5-10 mW of equivalent power. 
     An ionizable medium  425  is ignited within a sealed chamber of a lamp  108  to form a plasma  430 , as shown by block  620 . For example, the ionizable medium  425  may be Xenon, Krypton, or a mixture of Xenon and Krypton, among others. The ionizable medium  425  may be ignited, for example, with a pair of electrodes  790 ,  791  ( FIG.  7   ) extending into the chamber of the lamp  108 , by the first laser driver unit  102 , and/or by non-electrode ignition agents (not shown). The plasma sustaining beam  407  is introduced into the sealed chamber of the lamp  108  via an ingress window  109 , and the plasma sustaining beam  407  provides energy to sustain the plasma  430  as shown by block  630 . 
     The plasma  430  is sustained within the chamber of the lamp  108  with a plasma waist size of 150 microns or below as shown by block  640 . For example, the waist size may be controlled via the power level of the first laser driver unit  102 , and/or by the lamp ingress optics  105 ,  106 ,  107 . The plasma  430  emits a high intensity light  410 , for example, a visible light exhibiting a black box spectra. The chamber of the lamp  108  emits the high intensity light  410  generated by the plasma  430  through a chamber egress window  110  as shown by block  650 . The high intensity light  410  may be collimated into a collimated beam  411  via egress collimating optics  111 , and then focused to form a focused output light  412 . The focused output light  412  is coupled into an exit fiber  113  having a diameter of 500 μm or less as shown by block  660 , for example, 200-500 micrometers. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.