Light emitting unit and light source device

Abstract

To provide a light emitting unit and a light source device capable of reducing a discharge start voltage.SOLUTION: A light emitting unit includes a light emitting body and a voltage application circuit. The light emitting body includes a container in which a laser beam for maintaining plasma is incident and light from the plasma is emitted, a first electrode including a first discharge portion, and a second electrode including a second discharge portion. The end of the first discharge portion has a shape that becomes thinner as it approaches the second discharge portion, and the end face of the second discharge portion extends along a plane perpendicular to the extending direction of the first discharge portion. The voltage application circuit controls the potential difference between the first electrode and the second electrode by adjusting at least the voltage applied to the first electrode.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] One aspect of the present disclosure relates to a light-emitting unit and a light source device. [Background technology]

[0002] A laser excitation light source is a light source in which a discharge gas is sealed in a container, plasma generated in the discharge gas is maintained by irradiation with laser light, and light from the plasma is output as output light (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 10032620 [Patent Document 2] US Publication No. 2010 / 0164380 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned laser excitation light source, the discharge gas is sometimes filled at high pressure in order to achieve high efficiency and high output. However, when the pressure of the discharge gas is high, the discharge start voltage increases according to Paschen's law, making it difficult to generate plasma in the discharge gas.

[0005] An object of one aspect of the present disclosure is to provide a light-emitting unit and a light source device capable of reducing a discharge start voltage. [Means for solving the problem]

[0006] A light-emitting unit according to one aspect of the present disclosure comprises a light-emitting envelope and a voltage application circuit, the light-emitting envelope being a container filled with a discharge gas, the container being configured so that laser light for maintaining plasma generated in the discharge gas can be incident on the container and light from the plasma can be emitted from the container, a first electrode including a rod-shaped first discharge section arranged in the container, and a second electrode including a rod-shaped second discharge section arranged in the container so as to face the first discharge section in the extension direction of the first discharge section, the end of the first discharge section on the second discharge section side having a shape that becomes thinner as it approaches the second discharge section, and the end face of the second discharge section on the first discharge section side extends along a plane perpendicular to the extension direction, and the voltage application circuit is configured to control the potential difference between the first electrode and the second electrode by adjusting at least a voltage applied to the first electrode.

[0007] In this light-emitting unit, the end of the first discharge section on the second discharge section side has a shape that becomes thinner as it approaches the second discharge section, and the end face of the second discharge section on the first discharge section side extends along a plane perpendicular to the extension direction of the first discharge section. This makes it possible to increase the electric field strength (electric field density) in the vicinity of the end of the first discharge section. Then, the voltage application circuit adjusts the voltage applied to the first electrode, thereby controlling the potential difference between the first electrode and the second electrode. In this way, by applying a voltage to the first electrode whose electric field strength is increased in the vicinity of the end, it is possible to make discharge occur more easily and reduce the discharge start voltage.

[0008] The voltage application circuit may be configured to apply a negative voltage pulse to the first electrode as a trigger voltage for generating plasma between the first electrode and the second electrode, making it easier for discharge to occur.

[0009] The voltage application circuit may be configured to apply a positive voltage pulse to the second electrode in accordance with the timing of applying a negative voltage pulse to the first electrode. In this case, the absolute value of the peak voltage of each of the negative voltage pulse applied to the first electrode and the positive voltage pulse applied to the second electrode can be reduced compared to the case where a negative voltage pulse is applied only to the first electrode. As a result, for example, noise generated when generating a negative voltage pulse and a positive voltage pulse can be reduced.

[0010] The end of the first discharge portion may have a tapered surface, and the taper angle of the tapered surface may be 120 degrees or less. In this case, the electric field strength in the vicinity of the end of the first discharge portion can be further increased, making it easier for discharge to occur.

[0011] The taper angle may be equal to or less than 45 degrees. In this case, the electric field strength in the vicinity of the end of the first discharge portion can be further increased, making it easier for discharge to occur.

[0012] The container may include a housing that contains a discharge gas and has a first opening through which a first light, which is a laser light, enters and a second opening through which a second light, which is light from the plasma, exits, a first window that hermetically seals the first opening and transmits the first light, and a second window that hermetically seals the second opening and transmits the second light, and the housing may be made of a light-shielding material that blocks the first light and the second light. In this case, a material with high strength can be selected as the light-shielding material, so that the pressure of the discharge gas can be increased. As a result, high efficiency and high output can be achieved.

[0013] The housing may be made of a metal material, in which case the pressure of the discharge gas can be further increased.

[0014] The first electrode may be fixed to the housing via an insulating member and electrically isolated from the housing, in which case a voltage independent of the potential of the housing can be applied to the first electrode.

[0015] The housing may be made of an insulating material, in which case the components held by the housing can be easily electrically separated from each other.

[0016] The second electrode may be electrically connected to the housing, in which case the second electrode can be at ground potential by being connected to the housing, making it possible to omit wiring for the ground potential.

[0017] The first electrode may be fixed to the housing via a first insulating member and electrically isolated from the housing, and the second electrode may be fixed to the housing via a second insulating member and electrically isolated from the housing, in which case a voltage can be applied to the first electrode and the second electrode separately.

[0018] According to an aspect of the present disclosure, there is provided a light source device including the light emitting unit and a light introducing portion that causes laser light to enter the container. With this light source device, it is possible to reduce the discharge start voltage for the above-mentioned reasons. Effect of the Invention

[0019] According to one aspect of the present disclosure, it is possible to provide a light-emitting unit and a light source device capable of reducing the discharge start voltage. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a cross-sectional view of a laser excitation light source according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a perspective view of the luminous envelope according to the embodiment. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a partially enlarged view of FIG. [Figure 7]Fig. 7(a) is a diagram showing an example of an electric field distribution occurring in the first comparative example, and Fig. 7(b) is a diagram showing an example of an electric field distribution occurring in the configuration of Fig. 6. [Figure 8] FIG. 8 is a diagram showing an example of an electric field distribution generated in the second comparative example. [Figure 9] FIG. 9 is a diagram showing an example of an electric field distribution generated in the first modified example. [Figure 10] FIG. 10 is a diagram showing an example of an electric field distribution generated in the configuration of FIG. [Figure 11] Fig. 11(a) is a diagram for explaining a voltage application method of the third comparative example, and Fig. 11(b) is a diagram for explaining a voltage application method of the third comparative example. [Figure 12] Fig. 12(a) is a diagram for explaining a voltage application method of the third comparative example, and Fig. 12(b) is a diagram for explaining a voltage application method of the third comparative example. [Figure 13] Fig. 13(a) is a diagram for explaining a voltage application method according to an embodiment, and Fig. 13(b) is a diagram for explaining a voltage application method according to an embodiment. [Figure 14] FIG. 14 is a cross-sectional view of a luminous envelope according to a second modified example. [Figure 15] FIG. 15 is a diagram for explaining a voltage application method according to the second modified example. [Figure 16] Fig. 16(a) is a diagram showing a voltage application circuit according to an embodiment, and Fig. 16(b) is a diagram showing a voltage application circuit according to a second modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are designated by the same reference numerals, and duplicated description will be omitted. [Laser excitation light source configuration]

[0022] As shown in FIG. 1 to FIG. 5, the laser excitation light source (light emitting unit, light source device) 1 includes a light emitting envelope 2, a laser light source 3, a mirror 4, an optical system 5, and a case (lamp house) 6. The light emitting envelope 2, the laser light source 3, the mirror 4, and the optical system 5 are housed in the case 6. A discharge gas G1 is sealed in the light emitting envelope 2. The discharge gas G1 is, for example, xenon gas. In the laser excitation light source 1, plasma is generated in the discharge gas G1. A first light L1, which is a laser beam for maintaining the plasma, is incident on the light emitting envelope 2, and a second light L2, which is light from the plasma, is emitted from the light emitting envelope 2 as output light. The first light has a wavelength of, for example, about 800 nm to 1100 nm. The second light L2 is, for example, light in the mid-infrared region, and has a wavelength of about 2 μm to 20 μm. Details of the light emitting envelope 2 will be described later.

[0023] The laser light source 3 is, for example, a laser diode, and outputs a first light L1 which is a laser beam. The mirror 4 reflects the first light L1 from the laser light source 3 toward the optical system 5. The optical system 5 includes one or more lenses. The optical system 5 focuses the first light L1 from the mirror 4 and guides it to the light-emitting envelope 2. The laser light source 3, the mirror 4, and the optical system 5 form a light introduction section R which causes the first light L1 to enter a first opening 11 along a first optical axis A1. The first opening 11 and the first optical axis A1 will be described later.

[0024] The case 6 has a main body 61 and a cover member 62. A storage space S1 is formed in the main body 61, and the laser light source 3, the mirror 4, and the optical system 5 are arranged in the storage space S1. A recess 61a is formed in the main body 61, and an opening of the recess 61a is closed by the cover member 62 to form a storage space S2. The light-emitting envelope 2 is arranged in the storage space S2. The main body 61 has a pair of walls 611 that define the recess 61a, and each wall 611 has an opening 611a through which the second light L2 emitted from the light-emitting envelope 2 passes. The second light L2 is emitted to the outside through the opening 611a.

[0025] The main body 61 has a wall 612 that separates the storage space S1 from the recess 61a, and the storage space S1 and the storage space S2 are separated by the wall 612. An opening 612a is formed in the wall 612. A part of the optical system 5 is disposed in the opening 612a, and the first light L1 enters the light-emitting envelope 2 through the opening 612a.

[0026] A flow path 63 is formed in the cover member 62. A gas G2 flows through the flow path 63. The gas G2 is, for example, an inert gas such as nitrogen. The flow path 63 is connected to the outside via an opening 63a, and the gas G2 is supplied to the flow path 63 from an external gas supply device (not shown) via the opening 63a. The flow path 63 is connected to the storage space S2 of the main body 61 via an opening 63b, and the gas G2 flows from the flow path 63 into the storage space S2 via the opening 63b.

[0027] The gas G2 passes between the walls 611, 612 of the main body 61 and the luminous envelope 2 and / or between the cover member 62 and the luminous envelope 2, and is discharged to the outside through the ventilation hole 613a. The ventilation hole 613a is a through hole formed in the wall 613 of the main body 61 so as to communicate with the storage space S2. The wall 613 has a pair of tapered surfaces 613b formed at the boundary between the wall 613 and the pair of walls 611. The pair of tapered surfaces 613b are inclined so as to approach each other as they approach the ventilation hole 613a. Each of the tapered surfaces 613b is connected to the ventilation hole 613a. The tapered surfaces 613b guide the gas G2 toward the ventilation hole 613a. A through hole 612b is formed in the wall 612 of the main body 61, and a portion of the gas G2 that has flowed from the flow passage 63 into the storage space S2 passes through the through hole 612b and flows into the storage space S1. [Composition of the luminous envelope]

[0028] The luminous envelope 2 includes a housing 10, a first window portion 20, two second windows 30, a first electrode 40, and a second electrode 50.

[0029] The housing 10 is made of a metal material and is formed in a substantially box-like shape, and contains a discharge gas G1. More specifically, a sealed internal space S3 is formed in the housing 10, and the internal space S3 is filled with the discharge gas G1. An example of a metal material constituting the housing 10 is stainless steel. In this case, the housing 10 has a light-shielding property against the first light L1 and the second light L2. That is, the housing 10 is made of a light-shielding material that does not transmit the first light L1 and the second light L2.

[0030] The housing 10 is formed with a first opening 11 and two second openings 12. The first light L1 is incident on the first opening 11 along the first optical axis A1. The first opening 11 is formed in a circular shape, for example, when viewed from a direction parallel to the first optical axis A1 (hereinafter also referred to as the Z-axis direction). In this example, the first optical axis A1 passes through the center of the first opening 11 when viewed from the Z-axis direction. The first opening 11 includes an inner portion 11a, a middle portion 11b, and an outer portion 11c. The inner portion 11a opens to the internal space S3. The outer portion 11c opens to the outside. The middle portion 11b is connected to the inner portion 11a and the outer portion 11c. Each of the inner portion 11a, the middle portion 11b, and the outer portion 11c has, for example, a cylindrical shape. The diameter (outer shape) of the intermediate portion 11b is larger than the diameter (outer shape) of the inner portion 11a, and the diameter (outer shape) of the outer portion 11c is larger than the diameter (outer shape) of the intermediate portion 11b. A part of the optical system 5 is disposed in the outer portion 11c.

[0031] From each second opening 12, the second light L2 is emitted along the second optical axis A2. Each second opening 12 is formed in a circular shape when viewed from a direction parallel to the second optical axis A2 (hereinafter also referred to as the Y-axis direction), for example. In this example, the second optical axis A2 passes through the center of the second opening 12 when viewed from the Y-axis direction. Each second opening 12 includes an inner portion 12a, a middle portion 12b, and an outer portion 12c. The inner portion 12a opens to the internal space S3. The outer portion 12c opens to the outside. The middle portion 12b is connected to the inner portion 12a and the outer portion 12c. Each of the inner portion 12a, the middle portion 12b, and the outer portion 12c has, for example, a cylindrical shape. The diameter (outer shape) of the intermediate portion 12b is larger than the diameter (outer shape) of the inner portion 12a, and the diameter (outer shape) of the outer portion 12c is larger than the diameter (outer shape) of the intermediate portion 12b.

[0032] The first optical axis A1 intersects with the second optical axis A2 in the internal space S3. That is, the first opening 11 and the second opening 12 are arranged so that the first optical axis A1 and the second optical axis A2 intersect with each other. An intersection C of the first optical axis A1 and the second optical axis A2 is located in the internal space S3. In this example, the first optical axis A1 intersects with the second optical axis A2 perpendicularly, but the first optical axis A1 may intersect with the second optical axis A2 at an angle other than a right angle. The first optical axis A1 is not parallel to the second optical axis A2. The first optical axis A1 does not pass through the second opening 12, and the second optical axis A2 does not pass through the first opening 11.

[0033] The first window portion 20 hermetically seals the first opening 11. The first window portion 20 has a first window member 21 and a first frame member 22. The first window member 21 is formed in a circular flat plate shape, for example, from a light-transmitting material that transmits the first light L1. In this example, the first window member 21 is formed from sapphire and transmits light with a wavelength of 5 μm or less.

[0034] The first frame member 22 is formed in a frame shape from, for example, Kovar metal. The first frame member 22 is formed in a generally cylindrical shape. The first frame member 22 has a cylindrical first portion 22a and a cylindrical second portion 22b formed integrally with the first portion 22a. The outer shape of the second portion 22b is larger than the outer shape of the first portion 22a.

[0035] The first window member 21 is disposed in the first portion 22a. Specifically, a circular ring-shaped protrusion 22c that protrudes inward is formed at the boundary between the inner surface of the first portion 22a and the inner surface of the second portion 22b, and the first window member 21 is disposed in the first portion 22a in a state of contacting the protrusion 22c. In this state, the side surface 21a of the first window member 21 is in contact with the inner surface of the first portion 22a.

[0036] The side surface 21a of the first window member 21 is airtightly joined to the inner surface of the first portion 22a around the entire periphery by a joining material (first joining material) 23. This provides an airtight seal between the first window member 21 and the first frame member 22. The joining material 23 is, for example, a metal brazing material, more specifically, a silver brazing material doped with titanium. The silver brazing material doped with titanium is, for example, a brazing material composed of 70% silver, 28% copper, and 2% Ti, and is, for example, TB-608T by Tokyo Blaze Co., Ltd.

[0037] A circular ring-shaped flange portion 22d protruding outward is formed on the outer surface of the second portion 22b. The first frame member 22 is fixed to the housing 10 with the flange portion 22d disposed within the intermediate portion 11b of the first opening 11. In this state, a part of the first portion 22a of the first frame member 22 protrudes from the first opening 11. The first window member 21 is disposed to face the intersection C of the first optical axis A1 and the second optical axis A2. In this example, the light entrance surface and the light exit surface of the first window member 21 are flat surfaces extending perpendicular to the Z-axis direction.

[0038] The first frame member 22 is fixed airtight to the housing by laser welding. More specifically, the first frame member 22 is airtightly joined to the housing 10 by irradiating a laser from the outside to the contact portion between the flange portion 22d and the inner surface of the middle portion 11b of the first opening 11 and welding the entire circumference. In Figs. 4 and 5, the welding portion is indicated by the symbol W. As a result, the first frame member 22 and the housing 10 are airtightly sealed. In this way, the first window member 21 is airtightly joined to the first frame member 22 by the bonding material 23, and is airtightly fixed to the housing 10 via the first frame member 22. By interposing the first frame member 22 between the first window member 21 and the housing 10, defects caused by the difference in thermal expansion coefficient between the first window member 21 and the housing 10 can be suppressed.

[0039] Each second window portion 30 hermetically seals the second opening 12. Each second window portion 30 has a second window member 31 and a second frame member 32. The second window member 31 is formed, for example, in a circular flat plate shape from a translucent material that transmits the second light L2. In this example, the second window member 31 is formed from diamond and transmits light with a wavelength of 20 μm or less.

[0040] The second frame member 32 is formed in a frame shape from, for example, Kovar metal. The second frame member 32 is formed in a generally cylindrical shape. The second frame member 32 has a cylindrical first portion 32a and a cylindrical second portion 32b formed integrally with the first portion 32a. The outer shape of the second portion 32b is larger than the outer shape of the first portion 32a.

[0041] The second window member 31 is disposed in the first portion 32a. Specifically, the first portion 32a has an arrangement portion 32c therein, and the second window member 31 is disposed in the arrangement portion 32c. In this state, a part of the side surface 31a of the second window member 31 opposite to the intersection point C is in contact with the inner surface of the first portion 32a. The space in the second frame member 32 further includes an intermediate portion 32d connected to the arrangement portion 32c and an outer portion 32e connected to the intermediate portion 32d. The intermediate portion 32d has a truncated cone shape whose diameter (outer shape) increases toward the outside. The outer portion 32e is formed in a cylindrical shape having a diameter (outer shape) larger than that of the intermediate portion 32d.

[0042] The side surface 31a of the second window member 31 is airtightly joined to the inner surface of the first portion 32a around the entire periphery by a joining material (second joining material) 33. This provides an airtight seal between the second window member 31 and the second frame member 32. The joining material 33 is, for example, a metal brazing material, and more specifically, a silver brazing material doped with titanium.

[0043] A circular ring-shaped flange portion 32f protruding outward is formed on the outer surface of the second portion 32b. The second frame member 32 is fixed to the housing 10 with the flange portion 32f disposed within the intermediate portion 12b of the second opening 12. In this state, a part of the first portion 32a of the second frame member 32 protrudes from the second opening 12. The second window member 31 is disposed to face the intersection C of the first optical axis A1 and the second optical axis A2. In this example, the light entrance surface and the light exit surface of the second window member 31 are flat surfaces extending perpendicular to the Y-axis direction.

[0044] The second frame member 32 is fixed airtight to the housing by laser welding. More specifically, the second frame member 32 is airtightly joined to the housing 10 by irradiating a laser from the outside to the contact portion between the flange portion 32f and the inner surface of the middle portion 12b of the second opening 12 and welding the entire circumference. This causes the second frame member 32 and the housing 10 to be airtightly sealed. In this way, the second window member 31 is airtightly joined to the second frame member 32 by the bonding material 33, and is airtightly fixed to the housing 10 via the second frame member 32. By interposing the second frame member 32 between the second window member 31 and the housing 10, it is possible to suppress defects caused by the difference in thermal expansion coefficient between the second window member 31 and the housing 10.

[0045] The first electrode 40 extends along the X-axis direction (a predetermined direction) perpendicular to both the Y-axis direction and the Z-axis direction. The first electrode 40 faces the second electrode 50 across an intersection C between the first optical axis A1 and the second optical axis A2. In the X-axis direction, the distance between the intersection C and the tip of the first electrode 40 is equal to the distance between the intersection C and the tip of the second electrode 50. The first electrode 40 is formed of a metal material such as tungsten. The first electrode 40 is fixed to the housing 10 via a first insulating member 7 at the base end side and is electrically separated from the housing 10. The first electrode 40 is formed in a generally rod-like shape. The first electrode 40 has a first support portion (first portion) 41 on the base end side and a first discharge portion (second portion) 42 located on the tip side closer to the second electrode 50 than the first support portion 41. The first discharge portion 42 has a smaller diameter than the first support portion 41 and has a pointed shape. A tapered portion 42s is formed at the boundary between the first support portion 41 and the first discharge portion 42. The tapered portion 42s has a surface that is inclined so that the diameter increases toward the first support portion 41. The tapered portion 42s is disposed in a positional relationship such that it forms a recess with respect to a surface 71a of a main body portion 71 described later. The first support portion 41 is an intermediate portion (part) of the first electrode 40 in the X-axis direction. An end portion 41a on the base end side opposite to the first discharge portion 42 in the first support portion 41 is formed thicker than the portion other than the end portion 41a. The first discharge portion 42 is formed in a rod shape and is disposed inside the housing 10 (i.e., inside the internal space S3).

[0046] The first insulating member 7 has a main body 71 and a cylindrical portion 72. The first insulating member 7 is made of an insulating material such as alumina (aluminum oxide) or ceramic. The main body 71 is formed, for example, in a cylindrical shape and holds the first support portion 41 of the first electrode 40. The main body 71 has a surface 71a perpendicular to the X-axis direction. The surface 71a is a surface exposed to the internal space S3. An insertion hole 71b penetrating the main body 71 along the X-axis direction is formed in the surface 71a, and the first support portion 41 is disposed and fixed in the insertion hole 71b. The cylindrical portion 72 is formed in a cylindrical shape so as to extend from the surface 71a of the main body 71 along the X-axis direction, and surrounds a part of the first discharge portion 42 on the first support portion 41 side (base end side).

[0047] The end 41a of the first support portion 41 is airtightly joined to the inner surface of the insertion hole 71b around the entire periphery by the bonding material 43. This provides an airtight seal between the first electrode 40 and the first insulating member 7. The bonding material 43 is, for example, a metal brazing material, and more specifically, a silver brazing material doped with titanium.

[0048] The surface 71a of the main body 71 is roughened. In this embodiment, recesses 73 are formed on the surface 71a, thereby roughening the surface 71a. When viewed from the X-axis direction, the recesses 73 extend in a circular ring shape so as to surround the first discharge portion 42. The recesses 73 are disposed so as to be spaced apart from each of the first electrode 40 and the cylindrical portion 72. The shape of the recesses 73 in a cross section parallel to the X-axis direction is, for example, rectangular.

[0049] The first insulating member 7 is fixed airtight to the housing 10 via the connecting member 8. A circular ring-shaped flange portion 74 protruding outward is formed on the outer surface of the main body portion 71 of the first insulating member 7. The connecting member 8 is made of a metal material such as stainless steel. The connecting member 8 has a cylindrical first portion 81 and a circular flat plate-shaped second portion 82 extending radially inward from a first end portion 81a of the first portion 81. The tip of the second portion 82 is in contact with the outer surface of the main body portion 71. The flange portion 74 is in contact with the first portion 81 and the second portion 82.

[0050] The second portion 82 of the connection member 8 is air-tightly joined over its entire periphery to the outer surface of the main body 71 of the first insulating member 7 by a bonding material 83. This provides an air-tight seal between the connection member 8 and the first insulating member 7. The bonding material 83 is, for example, a metal brazing material, and more specifically, a silver brazing material doped with titanium.

[0051] The connection member 8 is fixed airtight to the housing 10 by laser welding. More specifically, the housing 10 has a third opening 13 formed therein. The cylindrical portion 72 of the first insulating member 7 is disposed in the third opening 13 in a state spaced apart from the third opening 13. The connection member 8 is disposed so that the second end 81b of the first portion 81 contacts the edge of the third opening 13. The connection member 8 is airtightly joined to the housing 10 by irradiating a laser from the outside to the contact portion between the first portion 81 and the edge of the third opening 13 and welding the contact portion over the entire circumference. This results in an airtight seal between the connection member 8 and the housing 10. In this manner, the first insulating member 7 is airtightly joined to the connection member 8 and is airtightly fixed to the housing 10 via the connection member 8. In this state, the first electrode 40 extends so as to penetrate the third opening 13. The third opening 13 is airtightly sealed by the first electrode 40, the first insulating member 7, and the connection member 8. The connection member 8 can also be considered to constitute a part of the housing 10.

[0052] The second electrode 50 extends along the X-axis direction. The tip of the second electrode 50 faces the first electrode 40 across the intersection C of the first optical axis A1 and the second optical axis A2. The second electrode 50 is made of a metal material such as tungsten. The second electrode 50 is electrically connected to the housing 10. The second electrode 50 is generally formed in a rod shape having a larger diameter than the first electrode 40. The second electrode 50 has a second support portion 51 on the base end side and a second discharge portion 52 located on the tip side closer to the first electrode 40 than the second support portion 51. The second support portion 51 is an intermediate portion (part) of the second electrode 50 in the X-axis direction. The second discharge portion 52 is formed in a rod shape and is disposed inside the housing 10 (i.e., inside the internal space S3).

[0053] The housing 10 is formed with a fourth opening 14. The second support portion 51 of the second electrode 50 is disposed in the fourth opening 14 such that the outer surface of the second support portion 51 contacts the inner surface of the fourth opening 14. The second support portion 51 is airtightly joined to the inner surface of the fourth opening 14 over the entire periphery by a joining material 53. This provides an airtight seal between the second electrode 50 and the housing 10. The joining material 53 is, for example, a metal brazing material, more specifically, a silver brazing material doped with titanium.

[0054] The housing 10 has an enclosure hole 15 for enclosing a discharge gas G1 in the internal space S3. An enclosure tube 16 is connected to the enclosure hole 15. The enclosure tube 16 is made of a metal material such as copper. An end 16a of the enclosure tube 16 opposite the enclosure hole 15 is sealed. A protective member 17 is attached to the enclosure tube 16 so as to cover the sealed end 16a. The protective member 17 is made of a resin material such as rubber.

[0055] The outer surface of the sealing tube 16 is joined to the inner surface of the sealing hole 15 over the entire circumference by the joining material 18. This provides an airtight seal between the sealing tube 16 and the housing 10. The joining material 18 is, for example, a metal brazing material, more specifically, a silver brazing material doped with titanium. When the discharge gas G1 is sealed, for example, the discharge gas G1 is introduced into the internal space S3 through the sealing tube 16, and then the sealing tube 16 is crushed and pressed (cut off) to seal the end 16a of the sealing tube 16. Thereafter, a protective member 17 is attached to the sealing tube 16. Such a direct sealing method is advantageous in the following respects compared to the trapping method using liquid nitrogen. That is, in the trapping method, when the light-emitting sealing body is placed in liquid nitrogen, the window member may be distorted. In the direct sealing method, such a situation can be suppressed. In addition, in the trapping method, there is a risk of variation in the sealing pressure, but in the direct sealing method, such variation can be suppressed. The trapping method is sometimes used when sealing a discharge gas inside a glass bulb.

[0056] In the luminous envelope 2, an internal space S3 is defined by the housing 10, the first window portion 20, and the second window portion 30. In the luminous envelope 2, an internal space S3 is also defined by the first electrode 40, the second electrode 50, the first insulating member 7, the connection member 8, and the sealing tube 16. The entire internal space S3 is filled with the discharge gas G1. That is, the internal space S3 is filled with the discharge gas G1. The discharge gas G1 is in contact with the first window member 21 and the first frame member 22, and the second window member 31 and the second frame member 32. The sealing pressure (maximum sealing pressure) of the discharge gas G1 is, for example, about 5 MPa (50 atmospheres). The luminous envelope 2 can withstand an internal pressure of 15 MPa or more. In the luminous envelope 2, the housing 10, the first window portion 20, and the second window portion 30 form a container 100 in which the discharge gas G1 is sealed. The container 100 is configured so that the first light L1 can enter the container 100 and the second light L2 can exit the container 100. As described above, in this example, the first light L1 enters the container 100 through the first window 20, and the second light L2 exits the container 100 to the outside through the second window 30. The first discharge unit 42 of the first electrode 40 and the second discharge unit 52 of the second electrode 50 are disposed within the container 100. [Example of operation of laser excitation light source]

[0057] The laser excitation light source 1 includes a voltage application circuit VC (FIG. 13(a)) disposed in the case 6. The voltage application circuit (voltage application unit) VC is configured to adjust the voltage applied to the first electrode 40 to control the potential difference between the first electrode 40 and the second electrode 50. As an example, the voltage application circuit VC applies a negative voltage pulse to the first electrode 40 with the second electrode 50 at ground potential. This causes electrons to be emitted from the first electrode 40 toward the second electrode 50. As a result, an arc discharge occurs, and plasma is generated between the first electrode 40 and the second electrode 50 (at the intersection C). The first light L1 from the light introduction unit R is irradiated to this plasma through the first window member 21. This maintains the generated plasma. The second light L2, which is light from the plasma, is emitted to the outside as output light through the second window member 31. In the laser excitation light source 1, the second light L2 is emitted from the two second window members 31 toward both sides in the Y-axis direction. The voltage application circuit VC may apply a positive voltage pulse as a trigger voltage for generating plasma to the first electrode 40. In this case, electrons are emitted from the second electrode 50 toward the first electrode 40. [Detailed configuration of the first electrode and the second electrode]

[0058] As shown in FIG. 6, the first discharge portion 42 of the first electrode 40 faces the second discharge portion 52 of the second electrode 50 in the X-axis direction. The end portion 42a of the first discharge portion 42 on the second discharge portion 52 side has a tapered shape (pointed shape) that becomes thinner as it approaches the second discharge portion 52. The end portion 42a of the first discharge portion 42 is pointed toward the second discharge portion 52. The end portion 42a has an end face 42b, a tapered face 42c, and a cylindrical face 42d. The end face 42b is curved so as to be convex toward the second discharge portion 52 side. The tapered face 42c is a truncated cone-shaped face inclined with respect to the X-axis direction so as to taper toward the second discharge portion 52, and is continuous with the end face 42b. The cylindrical face 42d is a cylindrical face that extends along the X-axis direction so as to surround the center line of the first discharge portion 42, and is continuous with the tapered face 42c.

[0059] The taper angle of the tapered surface 42c is 45 degrees or less. In this example, the taper angle is 30 degrees. The taper angle of the tapered surface 42c is the angle between two straight lines along both edges of the tapered surface 42c when viewed from a direction perpendicular to the X-axis direction.

[0060] The end 52a of the second discharge part 52 on the first discharge part 42 side has an end face 52b and a cylindrical surface 52c. The end face 52b faces the end face 42b and the tapered surface 42c of the first discharge part 42 in the X-axis direction. The distance between the end faces 42b, 52b in the X-axis direction is, for example, about 0.7 mm. The end face 52b extends along a plane perpendicular to the X-axis direction. In this example, the end face 52b is a flat surface perpendicular to the X-axis direction. The cylindrical surface 52c is a cylindrical surface extending along the X-axis direction so as to surround the center line of the second discharge part 52, and is continuous with the end face 52b.

[0061] Advantages of the shapes of the first electrode 40 and the second electrode 50 described above will be described with reference to Fig. 7(a) and Fig. 7(b). In Fig. 7(a), the electric field distribution is shown by equipotential lines. Between the equipotential lines, the closer the equipotential line is to the first electrode 140, the lower the potential. This also applies to Fig. 7(b) and Figs. 8 to 10 described later. In the first comparative example shown in Fig. 7(a), the end 142a of the first discharge portion 142 of the first electrode 140 and the end 152a of the second discharge portion 152 of the second electrode 150 are each pointed. In the first comparative example, as shown in Fig. 7(a), an electric field distribution occurs that is symmetrical with respect to a plane that passes through the intersection point C and is perpendicular to the X-axis direction.

[0062] In contrast, in the configuration of the embodiment, an electric field distribution as shown in Fig. 7(b) occurs. Compared to the first comparative example, the electric field strength (electric field density) is increased in the vicinity of the end 42a of the first discharge section 42. This is because the end face 52b of the second discharge section 52 extends along a plane perpendicular to the X-axis direction. That is, in the embodiment, the electric field distribution is compressed in the vicinity of the end 42a of the first discharge section 42, and the electric field density is increased.

[0063] Fig. 8 is a diagram showing an example of an electric field distribution occurring in the second comparative example. Fig. 8 shows only the vicinity of the upper half of the first electrode 140 and the second electrode 150, but a similar electric field distribution occurs in the vicinity of the lower half. This is also the case with Figs. 9 and 10. In the second comparative example, the end 142a of the first discharge portion 142 of the first electrode 140 and the end 152a of the second discharge portion 152 of the second electrode 150 are each pointed. The taper angle of the tapered surface 142c of the end 142a and the tapered surface 152c of the end 152a is 90 degrees.

[0064] Fig. 9 is a diagram showing an example of an electric field distribution generated in the first modified example. In the first modified example, the taper angle of the tapered surface 42c of the first discharge section 42 is 90 degrees. The first modified example is otherwise configured similarly to the above embodiment. From Figs. 8 and 9, it can be seen that the electric field density in the vicinity of the end 42a (end surface 42b) of the first electrode 40 is increased in the first modified example compared to the second comparative example.

[0065] Fig. 10 is a diagram showing an example of an electric field distribution generated in the configuration of the embodiment. As described above, in the embodiment, the taper angle of the tapered surface 42c of the first discharge section 42 is 30 degrees. From Figs. 8 and 10, it can be seen that in the embodiment, the electric field density in the vicinity of the end 42a (end surface 42b) of the first electrode 40 is increased compared to the second comparative example. Also, from Figs. 9 and 10, it can be seen that in the embodiment, the electric field density in the vicinity of the end 42a of the first electrode 40 is increased compared to the first modified example. [Details of voltage application method]

[0066] 11(a) to 12(b) are diagrams for explaining a voltage application method of the third comparative example. In Fig. 11(a) and Fig. 12(a), a container 200 is shown in a simplified form. The laser excitation light source 101 of the third comparative example includes a first electrode 240, a second electrode 250, and a voltage application circuit VC that applies a voltage to the first electrode 240 and the second electrode 250. Each of an end 242a of the first electrode 240 and an end 252a of the second electrode 250 is pointed.

[0067] 11(a) and 11(b), in the third comparative example, the voltage application circuit VC applies a positive voltage pulse PP rising toward the positive side to the first electrode 240 as a trigger voltage for generating plasma between the first electrode 240 and the second electrode 250. This is expected to cause electrons to be emitted from the second electrode 250 toward the first electrode 240, generating a discharge.

[0068] However, in the third comparative example, the application of a positive voltage pulse PP to the first electrode 240 pulls out electrons from the second electrode 250 in a subordinate manner. Therefore, the efficiency is low, and discharge may not occur between the first electrode 240 and the second electrode 250 as intended. In this case, as shown in FIG. 12(a) and FIG. 12(b), discharge may occur not by the first pulse P1, which is a positive voltage pulse, but by the second pulse P2, which is a negative voltage pulse following the first pulse P1. In the discharge by the second pulse P2, electrons are emitted from the first electrode 240 toward the second electrode 250. The second pulse P2 is a pulse that occurs due to the ringing phenomenon when no discharge occurs due to the first pulse P1. The absolute value of the peak voltage of the second pulse P2 is smaller than the absolute value of the peak voltage of the first pulse P1. Therefore, the efficiency of discharge by the second pulse P2 is lower than the efficiency of discharge by the first pulse P1.

[0069] 13(a) and 13(b) are diagrams for explaining a voltage application method of the embodiment. In FIG. 13(a), the container 100 is shown in a simplified form. This also applies to FIG. 15 described later. The laser excitation light source 1 of the embodiment includes a voltage application circuit VC electrically connected to the first electrode 40 and the second electrode 50. The voltage application circuit VC controls the potential difference between the first electrode 40 and the second electrode 50 by adjusting the voltage applied to the first electrode 40. As described above, in the laser excitation light source 1, the end 42a of the first discharge unit 42 has a shape that becomes thinner as it approaches the second discharge unit 52, and the end surface 52b of the second discharge unit 52 extends along a plane perpendicular to the X-axis direction.

[0070] In the embodiment, the voltage application circuit VC applies a negative voltage pulse PN rising toward the negative side to the first electrode 40 as a trigger voltage for generating plasma between the first electrode 40 and the second electrode 50. This causes electrons to be emitted from the first electrode 40 toward the second electrode 50, and a discharge occurs. In the voltage application method of the embodiment, the efficiency of the discharge can be increased compared to the case where a discharge is generated by the second pulse P2 caused by the ringing phenomenon as in the above-mentioned third comparative example. As a result, the discharge start voltage can be reduced. [Action and Effects]

[0071] As described above, in the laser excitation light source 1, the end 42a of the first discharge section 42 has a shape that becomes thinner as it approaches the second discharge section 52, and the end surface 52b of the second discharge section 52 extends along a plane perpendicular to the X-axis direction (extension direction of the first discharge section 42). This makes it possible to increase the electric field strength (electric field density) in the vicinity of the end 42a of the first discharge section 42. Then, the voltage application circuit VC adjusts the voltage applied to the first electrode 40 to control the potential difference between the first electrode 40 and the second electrode 50. In this way, by applying a voltage to the first electrode 40 whose electric field strength is increased in the vicinity of the end 42a, it is possible to make discharge occur more easily and reduce the discharge start voltage. In addition, since it is possible to widen the gap between the first electrode 40 and the second electrode 50, it is possible to ease the accuracy required for the positions of the first electrode 40 and the second electrode 50. In addition, it is possible to prevent the tips of the first electrode 40 and the second electrode 50 from melting due to heat.

[0072] The voltage application circuit VC applies a negative voltage pulse to the first electrode 40 as a trigger voltage for generating plasma between the first electrode 40 and the second electrode 50. This makes it easier for discharge to occur, as described above.

[0073] The taper angle of the tapered surface 42c of the end 42a of the first discharge part 42 is 120 degrees or less. This makes it possible to further increase the electric field strength in the vicinity of the end 42a of the first discharge part 42, making it easier for discharge to occur.

[0074] The taper angle of the tapered surface 42c is equal to or less than 45 degrees, which can further increase the electric field strength in the vicinity of the end 42a of the first discharge section 42, making it easier for discharge to occur.

[0075] The housing 10 constituting the container 100 is made of a light-shielding material that does not transmit the first light L1 and the second light L2. This allows a material with high strength to be selected as the light-shielding material, and therefore the pressure of the discharge gas G1 can be increased. As a result, high efficiency and high output can be achieved.

[0076] The housing 10 is made of a metal material, which allows the pressure of the discharge gas G1 to be further increased.

[0077] The first electrode 40 is fixed to the housing 10 via a first insulating member 7 and is electrically isolated from the housing 10. This makes it possible to apply a voltage to the first electrode 40 that is independent of the potential of the housing 10 (ground potential).

[0078] The second electrode 50 is electrically connected to the housing 10. This allows the second electrode 50 to be at ground potential by being connected to the housing 10, making it possible to omit wiring for the ground potential. [Variations]

[0079] In the luminous envelope 2 of the second modification shown in FIG. 14, the second electrode 50 is fixed to the housing 10 via the second insulating member 7A and is electrically isolated from the housing 10. The second insulating member 7A is hermetically fixed to the housing 10 via the connection member 8A. The second insulating member 7A is configured and connected in the same manner as the first insulating member 7, and the connection member 8A is configured and connected in the same manner as the connection member 8. In the second modification, since the second electrode 50 is electrically isolated from the housing 10, a voltage can be applied to the first electrode 40 and the second electrode 50 individually.

[0080] 15, the voltage application circuit VC may apply a positive voltage pulse PP to the second electrode 50 in accordance with the timing of applying a negative voltage pulse PN to the first electrode 40. The timing at which the positive voltage pulse PP applied to the second electrode 50 reaches its peak may coincide with the timing at which the negative voltage pulse PN applied to the first electrode 40 reaches its peak. In other words, the voltage application circuit VC may apply a positive voltage pulse PP having a phase opposite to that of the negative voltage pulse PN applied to the first electrode 40 to the second electrode 50. In this case, a potential difference is generated between the first electrode 40 and the second electrode 50 by the negative voltage pulse PN and the positive voltage pulse PP.

[0081] FIG. 16(b) shows an example of a voltage application circuit VC for realizing such a voltage application method. FIG. 16(a) shows an example of a voltage application circuit VC for realizing the voltage application method of the above embodiment. In the example of FIG. 16(a), the voltage application circuit VC includes a transformer T including a primary coil C1 and a secondary coil C2. The voltage applied to the primary coil C1 is transferred to the secondary coil C2 while being stepped up, and a negative voltage pulse PN is applied to the first electrode 40. The second electrode 50 is grounded. On the other hand, in the example of FIG. 16(b), the secondary coil C2 is grounded at the middle portion and divided into two parts. As a result, the secondary coil C2 is configured to be able to output voltages of both polarities. The voltage applied to the primary coil C1 is boosted and transmitted to the secondary coil C2, so that a negative voltage pulse PN having a peak voltage half that of the negative voltage pulse PN in the example of Fig. 16(a) is applied to the first electrode 40, and a positive voltage pulse PP having a peak voltage, in absolute value, half that of the negative voltage pulse PN in the example of Fig. 16(a), is applied to the second electrode 50. The potential difference generated between the first electrode 40 and the second electrode 50 in the example of Fig. 16(b) is the same as the potential difference generated in the example of Fig. 16(a).

[0082] 16(b), the absolute value of the peak voltage of each of the negative voltage pulse PN applied to the first electrode 40 and the positive voltage pulse PP applied to the second electrode 50 can be reduced compared to the case of applying a negative voltage pulse PN only to the first electrode 40 as in the example of Fig. 16(a). As a result, for example, noise generated when generating the negative voltage pulse PN and the positive voltage pulse PP can be reduced.

[0083] The present disclosure is not limited to the above-mentioned embodiment and modified examples. For example, the material and shape of each component are not limited to the above-mentioned material and shape, and various materials and shapes can be adopted. In the present disclosure, "A and / or B" means "at least one of A and B." The taper angle of the tapered surface 42c of the end portion 42a of the first discharge portion 42 may be 90 degrees or less, or may be 30 degrees or less.

[0084] In the above embodiment, the container 100 is configured by the housing 10, the first window 20, and the second window 30, but the container 100 may be, for example, a glass housing (glass bulb) entirely made of quartz. In this case, the first light L1 and the second light L2 enter or exit by passing through the glass housing. The first discharge unit 42 of the first electrode 40 and the second discharge unit 52 of the second electrode 50 are disposed in the glass housing.

[0085] When a glass housing is used for the laser excitation light source, the pair of electrodes are generally formed in the same shape. In contrast, in the above-mentioned laser excitation light source 1, the first electrode 40 and the second electrode 50 are formed in different shapes. A xenon lamp is an example of a light source in which a pair of electrodes is arranged in a glass housing. In a xenon lamp, light is generated from thermoelectrons generated by discharge in xenon gas. Since the electron supply characteristic is important, the pair of electrodes may be formed from different materials. For example, the cathode is formed from thorium-containing tungsten or bismuth, and the anode is formed from pure tungsten. In a xenon lamp, discharge is continuously generated, but in the laser excitation light source 1, it is sufficient that plasma is generated at the start of discharge, and the first electrode 40 and the second electrode 50 do not function when the discharge is maintained. Therefore, the first electrode 40 and the second electrode 50 are formed from a pure metal (for example, tungsten) that has high heat resistance and is unlikely to release substances.

[0086] In the above embodiment, two second openings 12 are formed, but only one second opening 12 may be formed, or three or more second openings 12 may be formed. The material constituting the housing 10 does not necessarily have to be a metal material, and may be an insulating material, for example, ceramic, etc. Each of the first window member 21 and the second window member 31 may be formed of diamond or sapphire, or may be formed of magnesium fluoride or quartz. The first window member 21 and / or the second window member 31 may be formed of Kovar glass.

[0087] The laser light source 3 does not have to be provided inside the laser excitation light source 1. For example, the laser excitation light source 1 may include an optical fiber that guides light from an externally disposed light source to the mirror 4, instead of the laser light source 3. In this case, the optical fiber, the mirror 4, and the optical system 5 configure a light introducing section R that causes the first light L1 to enter the first opening 11 along the first optical axis A1.

[0088] The first light L1 may be incident closer to the second electrode 50 than to the first electrode 40. That is, in the X-axis direction, the distance between the intersection C and the first electrode 40 may be longer than the distance between the intersection C and the second electrode 50. In this case, the end surface 52b of the second electrode 50 is a flat surface and is less likely to melt than the pointed end portion 42a of the first electrode 40, which is thermally advantageous.

Claims

1. A light-emitting envelope and a voltage application circuit are provided. The luminous envelope is a vessel in which a discharge gas is sealed, the vessel being configured so that a laser beam for maintaining plasma generated in the discharge gas can be incident on the vessel and light from the plasma can be emitted from the vessel; A first electrode including a rod-shaped first discharge portion disposed in the container; a second electrode including a rod-shaped second discharge portion disposed in the container so as to face the first discharge portion in the extension direction of the first discharge portion; The end of the first discharge portion on the second discharge portion side has a shape that becomes thinner as it approaches the second discharge portion, An end surface of the second discharge portion on the side of the first discharge portion extends along a plane perpendicular to the extending direction, the voltage application circuit is configured to adjust a voltage applied to at least the first electrode, thereby controlling a potential difference between the first electrode and the second electrode; The voltage application circuit is configured to apply a negative voltage pulse to the first electrode as a trigger voltage for generating the plasma between the first electrode and the second electrode.

2. The light-emitting unit according to claim 1 , wherein the voltage application circuit is configured to apply a positive voltage pulse to the second electrode in synchronization with the application of the negative voltage pulse to the first electrode.

3. The end of the first discharge portion has a tapered surface, The light-emitting unit according to claim 1 , wherein the taper angle of the tapered surface is 120 degrees or less.

4. The light-emitting unit according to claim 3 , wherein the taper angle is equal to or less than 45 degrees.

5. The container comprises: a housing that contains the discharge gas and has a first opening through which the first light, which is the laser light, enters and a second opening through which the second light, which is light from the plasma, exits; a first window portion that hermetically seals the first opening and transmits the first light; a second window portion that hermetically seals the second opening and transmits the second light, 5. The light-emitting unit according to claim 1, wherein the housing is made of a light-shielding material that blocks the first light and the second light.

6. The light-emitting unit according to claim 5 , wherein the housing is made of a metal material.

7. The light-emitting unit according to claim 5 , wherein the housing is made of an insulating material.

8. The light-emitting unit according to claim 6 , wherein the first electrode is fixed to the housing via an insulating member and is electrically isolated from the housing.

9. The light-emitting unit according to claim 8 , wherein the second electrode is electrically connected to the housing.

10. The light-emitting unit described in claim 6, wherein the first electrode is fixed to the housing via a first insulating member and is electrically isolated from the housing, and the second electrode is fixed to the housing via a second insulating member and is electrically isolated from the housing.

11. A light-emitting unit according to any one of claims 1 to 10, a light introducing section that allows the laser light to enter the container.

Images