Laser-sustained plasma and endoscopic light source

Abstract

To provide laser sustained plasma and an endoscopy light source.SOLUTION: An illumination source includes a laser driver unit configured to emit a plasma sustaining beam. An ingress collimator receives the plasma sustaining beam and produces a collimated ingress beam. A focusing optic receives the collimated ingress beam and produces a focused sustaining beam. A sealed lamp chamber contains an ionizable medium that, once ignited, forms a high-intensity light-emitting plasma having a waist size smaller than 150 microns. The sealed lamp chamber further includes an ingress window configured to receive the focused sustaining beam, and an egress window configured to emit the high-intensity light. An ignition source is configured to ignite the ionizable medium, and an exit fiber is configured to receive and convey the high-intensity light. The-high intensity light is white light with a black body spectrum, and the exit fiber has a diameter in the range of 200-500 micrometers.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 776,006, filed on Dec. 6, 2018, entitled "Laser - sustained Plasma and Endoscopic Light Source". The entire disclosure of the above - identified application is incorporated herein by reference in its entirety.

[0002] The present invention relates to an illumination device, and more particularly to high - intensity arc lamps.

Background Art

[0003] A high - intensity arc lamp is a device that emits a high - intensity beam of electromagnetic radiation. The lamp generally includes a gas - containing chamber, such as a glass bulb, and has an anode and a cathode used to excite the gas (ionizable medium) within the chamber. A discharge occurs between the anode and the cathode, providing power to the excited (e.g., ionized) gas and maintaining the light emitted by the ionized gas during operation of the light source.

[0004] FIG. 1 shows an external view and a cross - sectional view of a prior - art low - wattage parabolic xenon lamp 100. The lamp is generally composed of metal and ceramic. Xenon, the fill gas, is inert and non - toxic. The lamp sub - assembly can be constructed by high - temperature soldering within a fixture that limits the assembly to tight dimensional tolerances. FIG. 2 shows some of such lamp sub - assemblies and fixtures after soldering.

[0005] Referring to FIGS. 1 and 2, the prior art lamp 100 has three main sub-assemblies. Namely, a cathode, an anode, and a reflector. The cathode assembly 3a includes a lamp cathode 3b, a plurality of struts holding the cathode 3b to a window flange 3c, a window 3d, and a getter 3e. The lamp cathode 3b is a small pencil-shaped component made of, for example, triated tungsten. During operation, the cathode 3b emits electrons, and those electrons move across the arc gap of the lamp and strike the anode 3g. Since the electrons are thermionically emitted from the cathode 3b, the cathode tip must maintain a high temperature and low electron emission in order to function.

[0006] The cathode support 3c firmly holds the cathode 3b in a fixed position and conducts current to the cathode 3b. The lamp window 3d may be a ground and polished single crystal sapphire (AlO2). The sapphire allows the thermal expansion of the window 3d to match the flange thermal expansion of the flange 3c, so that the hermetic seal is maintained over a wide operating temperature range. The thermal conductivity of the sapphire transports heat to the lamp flange 3c and evenly disperses the heat to avoid cracking of the window 3d. The getter 3e is wound around the cathode 3b and installed on the support. The getter 3e absorbs contaminant gases generated within the lamp during operation, preventing contaminants from contaminating the cathode 3b and transporting unwanted substances onto the reflector 3k and the window 3d, thereby extending the life of the lamp. The anode assembly 3f consists of an anode 3g, a base 3h, and a tubular portion 3i. The anode 3g is generally composed of pure tungsten and is much duller in shape than the cathode 3b. This shape is largely due to the discharge physics that spreads the arc at its positive electrical attachment point. The arc is typically somewhat conical in shape, with the tip of the cone in contact with the cathode 3b and the base of the cone on the anode 3g. The anode 3g is larger than the cathode 3b to conduct more heat. Approximately 80% of the waste heat conducted within the lamp is conducted to the outside through the anode 3g, and 20% is conducted through the cathode 3b. The anode is generally configured to have a less heat-resistant path to the lamp's heat sink, so the lamp base 3h is relatively large. The base 3h is composed of iron or other thermally conductive material to conduct the heat load from the lamp anode 3g. The tubular portion 3i is a port for evacuating the lamp 100 and filling it with xenon gas. After filling, the tubular portion 3i is sealed, for example, clamped by a hydraulic tool or cold welded, so that the lamp 100 is sealed and simultaneously disconnected from the filling and processing station. The reflector assembly 3j includes a reflector 3k and two sleeves 3l. The reflector 3k may be a nearly pure polycrystalline alumina body that has been burnished with a high-temperature material to give the reflector a mirror finish. The reflector 3k is then sealed to the sleeve 3l, and a reflective coating is applied to the burnished inner surface.

[0007] Figure 3A shows a first perspective view of a prior art cylindrical lamp 300. Two arms 345, 346 project outwardly from the shield chamber 320. The arms 345, 346 house a pair of electrodes 390, 391 that project inwardly into the shield chamber 320 and provide an electric field for the 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.

[0008] The chamber 320 has an entrance window 326 through which laser light from a laser source (not shown) can enter the chamber 320. Similarly, the chamber 320 has an exit window 328 through which high-intensity light from the activated plasma can exit the chamber 320. The light from the laser is focused onto the excited gas (plasma) to provide sustaining energy. The ionized medium may be added to or removed from the chamber by a controlled high-pressure valve 398.

[0009] Figure 3B shows a second perspective view of the cylindrical lamp 300 by rotating the view of Figure 3A vertically by 90 degrees. The controlled high-pressure valve 398 is located substantially opposite the viewing window 310. Figure 3C shows a second perspective view of the cylindrical lamp 300 by rotating the view of Figure 3B horizontally by 90 degrees. Overall, the internal profile of the chamber 320 matches the external profile of the chamber 320.

[0010] An endoscope is a typically slender, tubular, illumination optical instrument (a type of borescope) used to view deep inside the body and is used in a procedure called endoscopy. Endoscopes are used to examine internal organs such as the throat or esophagus. Specific instruments are named according to the organ they target. Examples include the cystoscope (bladder), pyeloureteroscope (kidney), bronchoscope (bronchi), arthroscope (joint), and colonoscope (colon), and laparoscope (abdomen or pelvis). These can be used for visual examination and diagnosis or for assistance in surgeries such as arthroscopy. The light source of an endoscope is typically located remotely from the light exit aperture near the object to be illuminated. Light is transmitted from the light source through an optical guide such as an optical fiber to the exit aperture.

[0011] Minimally invasive endoscopy and robotic surgery are driven by fiber optic light sources. The fibers typically range in diameter from 3.0 to 4.8 mm. However, current light sources may suffer from loss of radiance, which could be a problem in the field of endoscopy and robotic surgery practice. Also, the diameter of the fiber guiding the light is becoming unsuitable in an environment where an imaging channel and possibly an instrument actuation channel are required in the same fiber bundle. The current trend is to obtain more information from the available space, which is reducing the diameter of the fibers. For example, a smaller fiber bundle could enable procedures that are currently not possible with current methods and devices. Existing light sources do not have sufficient étendue to couple significant levels of light into fibers having a diameter smaller than 3 mm. As a result, the light is insufficient for the camera to produce a sufficiently noise-free image. Therefore, it is necessary to address one or more of the above disadvantages. SUMMARY OF THE INVENTION

[0012] Embodiments of the present invention provide a laser sustained plasma and an endoscopic light source. Briefly stated, the present invention is directed to applications where high brightness or irradiance is transmitted through a small diameter optical guide or fiber less than 1 mm, thus making more space available for imaging fibers and / or laser transmission fibers.

[0013] Other systems, methods, and features of the present invention will be apparent to or will become apparent to those of ordinary skill in the art upon examination of the following drawings and detailed description. All such additional systems, methods, and features are included herein, are within the scope of the present invention, and are intended to be protected by the accompanying claims.

Brief Description of the Drawings

[0014] The accompanying drawings, which are incorporated herein and form a part of this specification, are included to provide a further understanding of the invention. The components in the drawings are not necessarily to scale, and emphasis has instead been placed on 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.

[0015]

Figure 1

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Best Mode for Carrying Out the Invention

[0016] The following definitions are useful for interpreting the terms applied to the features of the embodiments disclosed herein and are intended only to define the elements within the present disclosure.

[0017] As used in the present disclosure, "blackbody" refers to an object that can absorb all of the electromagnetic radiation incident upon it. A blackbody maintained at a constant temperature is a perfect radiator at that temperature because the radiation reaching and leaving the blackbody must be in equilibrium. The blackbody spectrum refers to the spectrum of electromagnetic waves that a blackbody can emit.

[0018] As used in the present disclosure, collimated light is light in which the light rays are substantially parallel and thus will spread minimally as they propagate.

[0019] As used in the present disclosure, "substantially" means "almost" or within normal manufacturing tolerances. For example, a substantially flat window is intended to be flat by design but may vary from a perfectly flat state based on variations due to manufacturing.

[0020] Next, embodiments of the present invention will be referred to in detail. Examples of these embodiments are illustrated in the accompanying drawings. In the drawings and the specification, as much as possible, the same reference numerals are used to refer to the same or similar parts.

[0021] As mentioned in the background section, minimally invasive robotic surgery typically uses an optical fiber light source within a diameter range of 3.0 to 4.8 mm. The following exemplary embodiments of the present invention will describe an endoscopic light source configured to provide white light having a blackbody spectrum with a fiber diameter of 200 to 500 micrometers.

[0022] In a first embodiment of an endoscopic light source 400 as shown by FIG. 4, the combined laser source 420 may include a plurality of laser driver units 102-104. Each laser driver unit 102-104 may emit light of different wavelengths / wavelength bands and / or intensities. The light from the laser driver units 102-104 is combined in an optical conductor 401, e.g., an optical fiber, and emitted through an optical expander 105. The output optics of the combined laser source 420 may have a different configuration for alternative embodiments. Similarly, in alternative embodiments, the combined laser source 420 may include more than three drive units or less than three drive units.

[0023] The first laser driver unit 102 provides a part of the beam 405. The beam 405 is collimated through the incident collimator 106 and focused into the plasma sustaining beam 407 through, for example, the focusing optical component 107. The plasma sustaining beam 407 enters the cylindrical shield chamber of the lamp 108 through the incident window 109. For example, the lamp 108 may be a cylindrical lamp. The shield chamber of the lamp 108 contains an ionizable medium 425, such as xenon, krypton, or a mixture of xenon and krypton. Once ignited, the ionizable medium 425 forms a plasma 430 that emits high-intensity light 410. The plasma 430 is sustained by the energy from the first laser driver unit 102 through the plasma sustaining beam 407. The plasma 430 may be ignited (ionized) by an electronic ignition module 114, such as electrodes 790, 791 (FIG. 7). The electronic ignition module 114 may provide power to the electrodes 790, 791 through electrical connections at the 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, through auto-ignition by the first laser driver unit 102.

[0024] The high-intensity output light 410 exits the chamber of the lamp 108 through the output window 110 and is optically coupled to the output fiber 113. For example, the high-intensity output light 410 may be substantially white in color and collimated into a collimated beam 411 through the output collimating optics 111, and then focused onto the entrance surface of the output fiber 113 through the output focusing optics 112. For example, the collimating optics 111 may be a simple one such as a single positive lens, a multi-lens beam expander based on a combination of positive and negative lens assemblies, or a parabolic mirror, or a combination of a parabolic mirror and a combination of a positive lens and a negative lens. The light is emitted from an output surface 414, for example, an output surface located at the distal end of an endoscope close to the illumination target. The output fiber 113 has a fiber diameter 415 in the range of, for example, 200 to 500 micrometers.

[0025] The first laser driver unit 102, for example, a low-power (150 watt) 979 nm first laser driver unit 102, can generate a plasma having a plasma plume size of 150 microns or less that can be efficiently coupled within the diameter of the exit fiber 113 under a pressure ranging from 10 bar to 50 bar within xenon, krypton, or a mixed noble gas. This is not possible with standard endoscopic light sources, such as solutions with xenon short arcs or non-laser solid light sources.

[0026] The second laser driver unit 104 has a different wavelength from the first laser driver unit 102. For example, the second laser driver unit 104 may generate a 10 - 100 mW beam at 803 nm (or other wavelength), which can be mixed with the plasma sustaining beam generated by the 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 the dye for fluorescence techniques. Alternatively, the fluorescence excitation beam generated by the second laser driver unit 104 may be mixed with high-intensity light at the output of the lamp 108. For example, the beams may be mixed using a dichroic-coated mirror with an angle less than 45 degrees that reflects one wavelength and passes the other wavelength, where the two beams being mixed are orthogonal, but the mixing mirror is less than 45 degrees. Alternatively, a mix cube having the same functionality may be used. The diagonal of the cube is the mixing surface, but the facet through which the beam enters (vertically) may be coated with a specific coating to shape the characteristics of the aforementioned beam.

[0027] The first laser driver unit 102, for example a 150 W laser diode stack, is coupled to the optical conduit 401, for example through beam correction optics (not shown). The beam correction optics or shaping optics described and required herein are used to shape the enhanced diode stack light output having different divergence degrees in the horizontal and vertical planes into a more symmetric beam pattern with a substantially uniform divergence degree in all directions. The optical conduit 401 may be, for example, a 200 micrometer laser fiber, which maintains 95% of the power at, for example, a numerical aperture (NA) of 0.15, but other NA ranges, for example 90% of the power at 0.2 NA, or even 80% of the power at 0.3 NA, would be practical. The latter two examples will show lower system outputs, but would still be sufficient for some applications.

[0028] Since the first laser driver unit 102 generates a beam invisible to the human eye, a third laser driver unit 103 that generates visible light, for example a low-power red laser of less than 5 mW, may be mixed with the output of the first laser driver unit 102 and / or the second laser driver unit 104. Thus, the optical alignment of all the optical components 105, 106, 107, 111, 112 and the lamp 108 can be performed using visible light instead of using other means, for example an IR converter for visualizing the position of a 979 nm wavelength beam.

[0029] The output of the optical conduit 401 may be terminated within a fiber connector (not shown), enabling a modular approach for switching the laser driver units 102, 103, 104. The fiber connector is coupled to beam adjustment optics, for example an optical expander 105, an incident collimator 106, for example a collimating lens, and an incident focusing optic 107, for example a focusing lens. The optical expander 105 shapes the beam waist of the laser at the focus point. The NA of the incident focusing optic 107 is preferably within the range of 0.4 to 0.6.

[0030] The focused output of this laser drive system including the plasma sustaining beam 407 is delivered into the lamps 108, 208 through the entrance window 109. In a first embodiment, the lamp may be configured as a cylindrical shield cavity lamp 108 having a sapphire entrance window 109 for laser entry and a sapphire exit window 110 for high-intensity visible output light, as shown in FIG. 4. The cylindrical shield cavity lamp 108 generates an expanded beam 410 having an NA of 0.4 to 0.6. The output collimating optics 111 receives and collimates the expanded beam 410 to produce a collimated high-intensity beam 411. The output focusing optics 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.

[0031] A second exemplary embodiment of the endoscope light source 500 is shown in FIG. 5. The combined laser source 420, the lamp entrance optics 106, 107, the output focusing optics 112, and the exit fiber 113 are substantially the same as those described in the first embodiment shown in FIG. 4.

[0032] In a second exemplary embodiment 500, the lamp may be configured as a parabolic reflector cavity design lamp 208 having a sapphire entrance window 109 for laser entry and a sapphire exit window 110 for high-intensity visible light emission. The lamp entrance optical components 106, 107 focus the plasma sustaining beam 407 into the lamp focusing region 530 of the parabolic reflector cavity design lamp 208, and thus the plasma 430 excited by the plasma sustaining beam 407 is located in the lamp focusing 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 having a beam size limited by the diameter of the exit window 110 and a configurable divergence. Note that the divergence of the parabolic reflector is determined by the diameter (or aperture) of the parabolic mirror (assuming the parabolic mirror is fully filled by the expanding light) divided by the light source (plasma) point size, e.g., a point size of about 150 microns, so the divergence is approximately eight times smaller than that of a typical xenon lamp for endoscopes, whereby more light is coupled to the exit fiber 113 than in the prior art. The exit focusing optical component 112 at the output of the lamp 208 focuses the collimated light 511 into the focused output light 512, which is introduced into the exit fiber 113.

[0033] FIG. 6 is a flowchart of an exemplary embodiment of a method for generating high-intensity light coupled to a small-diameter optical guide. As would be understood by one of ordinary skill in the art in the technical field of the present invention, any of the process descriptions or blocks in the flowchart represent modules, segments, portions of code, or steps that include one or more instructions for implementing the specific logical function in that process, and alternative implementations in which functions may be executed in an order not illustrated or described, including substantially simultaneously or in a reverse order, depending on the relevant functions, are within the scope of the present invention. The method is described with reference to FIGS. 4 and 6.

[0034] As shown by block 610, a plasma sustaining beam 407 having a power of 150 W or less is generated, for example, by the first laser driver unit 102. One or more other light sources may be mixed into the plasma sustaining laser beam. For example, the output of a second laser driver unit 104 that generates a different wavelength from the first laser driver unit 102, for example, a 10 - 30 mW laser of 803 nm ± 15 nm, and / or the output of a third laser driver unit 103 that generates visible light, for example, a low power red laser. The second laser driver unit 104 preferably generates 5 - 10 mW of equivalent power.

[0035] As shown by block 620, an ionizable medium 425 is ignited within the shield chamber of the lamp 108 to form a plasma 430. For example, the ionizable medium 425 may be xenon, krypton, or a mixture of xenon and krypton, etc. The ionizable medium 425 may be ignited, for example, by the first laser driver unit 102 and / or by non - electrode ignition agents (not shown) using a pair of electrodes 790, 791 (FIG. 7) that extend into the chamber of the lamp 108. The plasma sustaining beam 407 is introduced into the shield chamber of the lamp 108 through the entrance window 109, and as shown by block 630, the plasma sustaining beam 407 provides energy for maintaining the plasma 430.

[0036] As shown by block 640, the plasma 430 is maintained within the chamber of the lamp 108 with a plasma waist size of 150 microns or less. For example, the waist size can be controlled via the power level of the first laser driver unit 102 and / or by the lamp input optics 105, 106, 107. The plasma 430 emits high-intensity light 410, such as visible light exhibiting a black box spectrum. The chamber of the lamp 108 emits the high-intensity light 410 generated by the plasma 430 through the chamber output window 110, as shown by block 650. The high-intensity light 410 may be collimated into a collimated beam 411 via the output collimating optics 111 and then focused to form a focused output light 412. The focused output light 412 is coupled to an output fiber 113 having a diameter of 500 μm or less, for example 200 - 500 micrometers, as shown by block 660.

[0037] It will be apparent to those skilled in the art that various modifications and changes 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, the present invention is intended to cover modifications and variations of the present invention provided they fall within the scope of the following claims and their equivalents.

Claims

1. An incident laser source comprising: a first laser driver unit configured to generate a first beam that results in a plasma sustaining beam; and a second laser driver unit configured to generate a second beam that results in a visible beam, wherein the second beam is mixed with the first beam to generate an output beam. An incident window configured to receive an entrance beam based on the output beam of the incident laser source; a shield chamber storing an ionizable medium that forms a high-intensity light-emitting plasma when ignited by the entrance beam; and an exit window configured to emit high-intensity light generated by the high-intensity light-emitting plasma. An exit fiber having a diameter of less than 500 micrometers, configured to receive and transmit the high-intensity light. An endoscope light source comprising the above.

2. The endoscope light source according to claim 1, wherein the shield chamber is a cylindrical shield cavity or a parabolic reflector cavity.

3. The endoscope light source according to claim 1, further comprising a third laser driver unit configured to generate a third beam that is mixed with the first beam and the second beam to generate the output beam.

4. The endoscope light source according to claim 3, wherein the third beam and the first beam have different wavelengths.

5. The endoscope light source according to claim 1, further comprising one or more electrodes within the shield chamber configured to provide an electric field for ignition of the ionizable medium within the shield chamber.

6. The endoscope light source according to claim 1, further comprising an optical expander configured to emit the output beam resulting from the mixing of the first beam and the second beam.

7. A collimator configured to collimate the output beam from the optical expander; and Focusing optics configured to focus the output beam collimated by the collimator as the plasma sustaining beam and the visible beam onto the shield chamber. The endoscope light source according to claim 6, further comprising the above.

8. The endoscope light source according to claim 1, wherein the diameter of the exit fiber is less than 200 micrometers.

9. The endoscope light source according to claim 1, further comprising a collimating optical component configured to collimate the high-intensity light emitted from the exit window.

10. The endoscope light source according to claim 9, further comprising a focusing optical component configured to focus the high-intensity light collimated by the collimating optical component onto the exit fiber.

11. The endoscope light source according to claim 10, wherein the exit fiber is used to illuminate an object in the body.

12. A method for generating high-intensity light coupled to a small-diameter optical guide, comprising: igniting an ionizable medium in a shielded lamp chamber to form a plasma; generating a plasma-maintaining laser beam by a first laser driver unit of an incident laser source; mixing the plasma-maintaining laser beam with a visible laser beam generated by a second laser driver unit of the incident laser source; providing energy to the plasma in the shielded lamp chamber by the plasma-maintaining laser beam based on aligning the plasma-maintaining laser beam with the shielded lamp chamber using the visible laser beam; maintaining the plasma in the shielded lamp chamber with a plasma waist size of 150 micrometers or less; emitting the high-intensity light generated by the plasma through an exit window of the shielded lamp chamber; coupling the high-intensity light to an exit fiber having a diameter of 500 micrometers or less. A method comprising the above steps.

13. The method according to claim 12, wherein igniting the ionizable medium in the shielded lamp chamber is performed in a cylindrical shield cavity or a parabolic reflector cavity.

14. The method according to claim 12, further comprising generating another laser beam by a third laser driver unit of the incident laser source.

15. The method according to claim 14, wherein generating the another laser beam includes generating the another laser beam having a power in the range of 10 to 30 mW.

16. The method according to claim 12, wherein generating the plasma-maintaining laser beam includes generating the plasma-maintaining laser beam having a power of 150 mW or less.

17. The method according to claim 12, wherein coupling the high-intensity light is coupling the high-intensity light to the output fiber having the diameter of 200 micrometers or less.

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