TWI907940B - Active mirror device, light collector and laser pumping system - Google Patents

Abstract

A light collector includes two light reflectors. The two reflectors are connected at one end at an angle to form a gradually widening wedge structure, and at the other end form a gradually opening light exit port. At least one of the two reflectors is an active mirror device, including a substrate with a smooth reflective surface and a light-emitting element disposed on the smooth reflective surface. Light emitted by the light-emitting element of the light collector is reflected, amplified, and focused towards the gradually opening light exit port to pump a crystal and generate laser radiation. The gradually widening wedge structure of the light collector can be filled with a bright material to convert light of one wavelength from the light-emitting elements into emitted light of another wavelength for pumping the crystal.

Description

Active mirror device, light collector and laser pumping system

The present invention relates to a light collector for pumping a laser, and more particularly, to a gradually widened wedge-shaped light collector capable of concentrating light and outputting the light through a gradually opening light outlet, and a laser pumping system including the gradually widened wedge-shaped light collector.

Optical laser pumping is a process that uses light to pump an active medium, raising the atoms in that medium from a low energy level to a higher one. When the atoms are stimulated by surrounding photons, they emit more photons with the same properties as the surrounding photons, and then return to a lower energy level. This is the process of enhancing laser light or radiation through stimulated emission. For example, solid-state lasers typically use flash lamps or laser diodes to emit pump light to optically pump the laser crystal and produce a laser beam. Typically, the laser beam is very collimated, unlike the pump light, which is sometimes more widely scattered in space. The effectiveness of laser pumping depends on the effective concentration of the pump light within the laser crystal, allowing it to be converted into laser radiation within the crystal. However, effectively focusing the pump light is a major challenge when the light produced by the pump source is diffused in a manner similar to that emitted by a flash or light-emitting diode.

U.S. Patent Application Publication No. 2016/0322775 A1 discloses a side-pumped laser amplifier using multiple laser diode stacks, wherein a tapered wedge structure is intended to guide and concentrate light from a large input aperture (proximate to the laser diode stack) to a small output aperture (proximate to a laser dielectric). In this case, as light passes through the narrow wedge structure, most of the light either penetrates the sidewalls of the dielectric wedge and dissipates, or is reflected back and leaves through the large input aperture. Only a limited amount of light is reliably delivered to and pumps the laser crystal.

Therefore, one of the objectives of this invention is to provide a light collector that overcomes the shortcomings of conventional methods.

The light collector of this invention includes two light reflectors connected to each other at an angle, forming a wedge-shaped structure that is closed at one end, gradually widens, and forms a gradually opening light outlet at the other end. Each of the light reflectors has a surface on which reflected light is incident to generate reflected light. At least one of the light reflectors is an active mirror device, which includes a substrate having a smooth reflective surface and a plurality of light-emitting elements disposed on the smooth reflective surface of the substrate. Each light-emitting element includes a bottom reflective layer disposed on the substrate and an active layer disposed on the bottom reflective layer. The side of each active layer away from the bottom reflective layer is planar. When a current is applied, the active layer actively generates actively emitted light.

Therefore, the reflective surface of the substrate and the light-emitting elements both reflect incident light to generate reflected light. In particular, for each light-emitting element, when incident light is reflected from the bottom reflective layer and enters the active layer, enhanced reflected light is generated. That is, light is amplified whenever it passes through the active layer. The aforementioned active emitted light, the reflected light, the amplified reflected light, and any combination thereof are defined as focused light, which exits the gradually widening wedge-shaped light collector through the gradually widening light exit port.

Another objective of this invention is to provide the aforementioned active mirror device.

Another object of the present invention is to provide a laser pumping system. The laser pumping system of the present invention includes a laser crystal and at least one of the aforementioned light collectors. An aperimeter-opening exit port of the at least one light collector is adjacent to the laser crystal. Focused light exiting from the aperimeter-opening exit port of the light collector enters the laser crystal to provide laser gain.

The advantage of this invention is that the focused light is effectively concentrated into the laser crystal through the gradually opening light outlet, thereby achieving high-efficiency laser pumping.

Before this invention is described in detail, it should be noted that similar elements are represented by the same designation in the following description.

For ease of explanation, the spatial relative terms used throughout this document, such as "top," "bottom," "up," "down," "right," "left," "downward," "upward," and similar terms, refer simultaneously to the features illustrated in the diagrams. However, the features of this invention may be oriented in different ways (e.g., rotated 90 degrees or in other orientations), and the spatial relative terms used herein may be interpreted accordingly.

As shown in Figures 1 and 2, an embodiment of the light collector 1000a disclosed herein includes two light reflectors. These two light reflectors, as illustrated in Figure 1, are connected to each other at their left ends at an angle α, forming a gradually widening wedge structure to guide light towards the gradually widening light outlet 800 at the right end of the light collector 1000a. Specifically, "gradually widening" as used herein refers to a path in which light propagates gradually widening within the wedge structure. In some embodiments, the angle α ranges from greater than 0 degrees to less than 90 degrees. Specifically, these light reflectors may be connected directly or indirectly at the left end via an intermediary. The two sides of the wedge-shaped structure can be covered by two reflective layers 300a respectively, the reflective layers 300a being made of materials such as dielectric or metal.

In this embodiment, one of the two light reflectors (e.g., the lower one) is the active mirror device 200 as shown in Figures 3 and 4, while the other (e.g., the upper one) is a mirror reflector 500. The mirror reflector 500 includes a base layer 501 having a smooth surface (e.g., a downward-facing surface), such as a glass plate, and a high-reflectivity layer 300 coated on the smooth surface of the base layer 501. The materials of the high-reflectivity layer 300 and the aforementioned reflective layer 300a may include at least one of dielectric, aluminum (Al), silver (Ag), or gold (Au) thin films. In one embodiment, the active mirror device 200 is attached to a cooling plate (not shown) for heat removal from the light-emitting element 230.

Specifically, the active mirror device 200 includes a substrate (which includes a base layer 210 and a reflective layer 220 on the base layer 210) and a plurality of light-emitting elements 230 arranged in an array disposed on and bonded to the reflective layer 220. As shown in FIG3, the active mirror device 200 is equivalent to a planar light source. When powered by a power source (not shown) through appropriate wiring, the light-emitting elements 230 emit light, which is referred to below as "actively emitted light 290 (see FIG4)".

In this embodiment, the substrate 210 has high thermal conductivity to rapidly dissipate the heat emitted by the light-emitting elements 230. The reflective layer 220 has a smooth reflective surface and may be a metal film with both high thermal conductivity and high reflectivity, such as a thin film made of silver or gold. Each light-emitting element 230 may include a built-in bottom reflective layer 238 disposed on the reflective layer 220 and emitting light upwards, and an action layer 233 disposed on the bottom reflective layer 238. The side of each action layer 233 away from the bottom reflective layer is planar. In some embodiments, the action layer 233 may include, but is not limited to, a P-type semiconductor layer, an N-type semiconductor layer, and an action region formed between the P-type semiconductor layer and the N-type semiconductor layer. When an electric current is applied, the active layer 233 actively generates actively emitted light 290. The material of the active layer 233 may include conductive or semiconductor materials, such as Al, In, Ga, As, Ze, Se, P, or any combination thereof, i.e., gain media. The bottom reflective layer 238 may include a layer of gold (Au), a distributed Bragg reflector (DBR), or any combination thereof. It is worth noting that Figure 4 is a diagram not drawn to scale, which enlarges the size of the light-emitting element 230 relative to the substrate 210 for clarity; in fact, these light-emitting elements 230 are extremely thin and can range from hundreds of nanometers to several micrometers. It should be noted that in some embodiments, the substrate 210 itself has a smooth reflective surface, and the light-emitting elements are disposed and bonded to the smooth reflective surface of the substrate 210, so a reflective layer 220 is not required.

Taking the light collector 1000a shown in Figure 1 as an example, the gradually opening light outlet 800 of the light collector 1000a is located at the right end. Based on the law of reflection (that is, the angle of reflection equals the angle of incidence), when one of the light-emitting elements 230 of the active mirror device 200 located below emits light (marked as _L1 ) vertically upward, the light ray ( _L1 ) travels to the gradually opening light outlet 800 in a zigzag path. During multiple reflections, the angle of incidence and the angle of reflection of the light ray ( _L1 ) on the surfaces of the two reflectors gradually increase. When light is emitted towards the upper right (marked _L2 ), the light ( _L2 ) travels directly through the apertured light exit port 800, or is emitted from the apertured light exit port 800 after one or more reflections on the surface of the two reflectors. When light is emitted towards the upper left (marked _L3 ), the angle of incidence and the angle of reflection gradually decrease during multiple reflections until the light ( _L3 ) turns and travels to the right, eventually emitting from the apertured light exit port 800.

In this way, the light emitted from the light-emitting elements 230 will ultimately be emitted only through the gradually widening light-emitting port 800 at the right end of the light collector 1000a. Therefore, the light collector 1000a disclosed herein can be described as a unidirectional light guide and collector. Moreover, in the direction in which the light collector 1000a directs the focused light towards the gradually widening light-emitting port 800, its wedge-shaped structure is gradually widening. That is to say, the internal light will always be concentrated and travel in the direction of the gradually widening wedge-shaped structure.

Referring to Figures 1 and 4, the actively emitted light 290 from one of the light-emitting elements 230 can become the incident light 270 on the high-reflectivity layer 300 or the reflective layer 220 of the light collector 1000a. The reflective layer 220 of the active mirror device 200 reflects the incident light 270 to generate reflected light 280. In some cases, the incident light 270 is incident on one of the light-emitting elements 230 and reflected through the active layer 233. Then, since the active layer 233 is a gain medium used to generate more light, it amplifies the reflected light to form enhanced reflected light 285. Therefore, the active mirror device 200 can serve as a combination of a light emitter, a light reflector, and a light amplifier. The aforementioned active emission light 290, reflected light 280, amplified reflected light 285, and any combination thereof, i.e. focused light, are guided through the gradually opening light outlet 800 and leave the light collector 1000a.

Referring to Figure 5, in one embodiment, both light reflectors of the light collector 1000b are active mirror devices 200. That is, the mirror reflector 500 of the light collector 1000a in Figure 1 is replaced by another active mirror device 200. In this embodiment, when both light reflectors are active mirror devices 200, the amount of light emission, reflection, and amplification all increase. In other words, the intensity of the light leaving the gradually opening light outlet 800 of the light collector 1000b is multiplied.

Referring to Figure 6, in one embodiment, the light collector 1000c includes two light reflectors and a dielectric wedge 450 located between the two light reflectors. The two light reflectors of the light collector 1000c are an active mirror device 200 (located below) and a high-reflectivity layer 300 (located above) coated on the upper surface of the dielectric wedge 450. The material of the high-reflectivity layer 300 may include at least one of the following for reflecting light emitted from the active mirror device 200: aluminum (Al), silver (Ag), gold (Au), or a dielectric. The dielectric wedge 450 fills the space between the two light reflectors. The dielectric wedge 450 may be made of a light-permeable dielectric material such as glass or plastic. Furthermore, the light collector 1000c further includes an anti-reflection layer 350 coated on the bottom surface of the dielectric wedge 450 in order to minimize reflection loss between the dielectric wedge 450 and the active mirror device 200 and enhance light transmission.

Referring to Figure 7, in one embodiment, the light collector 1000d includes two light reflectors (same as those in the light collector 1000c described above), a bright wedge 460, and an anti-reflection layer 350 coated on the bottom surface of the bright wedge 460. That is, the light collector 1000d of Figure 7 can be obtained by replacing the dielectric wedge 450 of the light collector 1000c in Figure 6 with the bright wedge 460. Specifically, the bright wedge 460 includes a wedge-shaped body similar to the dielectric wedge 450 and is doped with bright light elements 600, such as fluorescent, phosphorescent dyes, or quantum dots. These bright light elements 600 convert the actively emitted light 290 of one wavelength from the active mirror device 200 into emitted light of another wavelength. Then, the emitted light of another wavelength is guided and focused toward the apertured light outlet 800. For example, the active mirror device 200 can emit blue light, while the luminescent element 600, which includes cerium-doped yttrium aluminum garnet (Ce:YAG), can be excited by blue light to produce emitted light in the yellow-orange-red spectrum. Then, the yellow-orange-red light is guided toward the apertured light outlet 800 by the light collector 1000d.

Referring to Figure 8, in one embodiment, the light collector 1000e includes two light reflectors and a light-emitting wedge 460 as described above. In this embodiment, both light reflectors are active mirror devices 200. To minimize light loss due to reflection and enhance light transmission, two anti-reflective layers 350 may be coated on the bottom and top surfaces of the light-emitting wedge 460, respectively.

Each of the concentrators 1000a, 1000b, 1000c, 1000d, and 1000e mentioned above (hereinafter referred to as "concentrator 1000") is well-suited for pumping laser crystals. Referring to Figures 9 and 10, in one embodiment, a single-sided laser pumping system 100a includes a laser crystal 700 having a rectangular cross-section, a concentrator 1000, and a cooling box 750 for heat dissipation (not shown in Figure 9). Figure 10 is a schematic cross-sectional view of Figure 9, showing the rectangular cross-section of the laser crystal 700 and further showing the cooling box 750. The laser crystal 700 and the concentrator 1000 are mounted in the cooling box 750 for heat dissipation.

The laser crystal 700 has four side surfaces, hereinafter referred to as the front, rear, top, and bottom surfaces, and is mounted in a laser cavity formed by two cavity mirrors 910 and 920. The aperipheral exit port 800 of the light collector 1000 is adjacent to one of the side surfaces of the laser crystal 700, for example, the front surface. The light collector 1000 outputs pump light (i.e., the focused light mentioned above) through the aperipheral exit port 800 into the laser crystal 700, and the laser crystal 700 in the laser cavity absorbs the pump light, generating laser radiation 930 through stimulated emission. In this embodiment, the single-sided laser pumping system 100a further includes an antireflective layer 350 coated on the front surface of the laser crystal 700 and a high-reflective layer 300 coated on the rear surface. The antireflective layer 350 is used to enhance light transmission when the pump light passes through it and enters the laser crystal 700, while the high-reflective layer 300 is used to reflect unabsorbed pump light back into the laser crystal 700 for continued use.

The laser crystal 700 can be one of the following: neodymium-doped yttrium aluminum garnet (Nd:YAG), yttrium-doped yttrium aluminum garnet (Yb:YAG), holmium-chromium-thulium tridoped yttrium aluminum garnet (Ho:Cr:Tm:YAG), yttrium neodymium vanadate-doped crystal (Nd: _YVO4 ), erbium-doped yttrium aluminum garnet (Er:YAG), chromium-fluorine-aluminum-calcium-lithium lithium garnet (Cr:LiSAF), titanium-doped sapphire crystal (Ti:sapphire), chromium crystal, erbium:yttrium-carbyl gallium garnet crystal (Cr, Er:YSGG), alexandrite crystals, erbium phosphate glass crystals (Er:glass), etc.

Laser pumping capability can be enhanced by using multiple light collectors 1000. Referring to Figure 11, a cross-sectional view for one embodiment, the dual-sided laser pumping system 100b includes a laser crystal 700 having a rectangular cross-section, two light collectors 1000, and a cooling box 750 for heat dissipation. The two light collectors 1000 are disposed on two adjacent sides of the laser crystal 700. For example, the two light collectors 1000 are arranged with their gradually opening light exit ports 800 adjacent to and facing the front and top surfaces of the laser crystal 700. The dual-sided laser pumping system 100b further includes two anti-reflective layers 350 coated on the front and top surfaces of the laser crystal 700, respectively, and two high-reflective layers 300 coated on the rear and bottom surfaces of the laser crystal 700, respectively. The anti-reflective layers 350 are used to enhance light transmission when the pump light enters the laser crystal 700, while the high-reflective layers 300 are used to reflect unabsorbed pump light back into the laser crystal 700 for continued use. Each of the light collectors 1000 outputs pump light (i.e., the focused light mentioned above) through its gradually opening light output port 800 into the laser crystal 700, and the laser crystal 700 in the laser cavity absorbs the pump light and generates laser radiation 930 by stimulated emission (Figure 9).

In another embodiment, two light collectors 1000 are aligned facing each other and disposed on two opposite sides of the laser crystal 700. For example, as shown in Figure 12, which illustrates a cross-sectional view of an embodiment, the two light collectors 1000 are arranged with their gradually opening light exit ports 800 facing the front and rear surfaces of the laser crystal 700, respectively, so that the pump light emitted by the two light collectors 1000 is guided to excite the laser crystal 700.

Referring to Figures 13, 14, and 15, cross-sectional views of some embodiments show a laser pumping system 100c including a laser crystal 700' having a circular cross-section, two light collectors 1000, and a cooling box 750 for dissipating heat from the active mirror assembly. In one embodiment, the laser pumping system 100c may further include a transparent tube 550 having a cooling liquid 560 flowing therein for removing heat from the laser crystal 700'. The laser crystal 700' may be disposed and fixed in the transparent tube 550 by, for example, a rubber ring. The gradually opening light-emitting ports 800 of the light collectors 1000 are adjacent to the laser crystal 700', and are particularly attached to a first portion and a second portion of the circumferential surface of the transparent tube 550. The first portion and the second portion may each constitute one-third (e.g., but not limited to) of the circumferential surface of the transparent tube 550, as shown in FIG. 13, or constitute half of the circumferential surface of the transparent tube 550, as shown in FIGS. 14 and 15. In one embodiment shown in FIG. 15, the light reflectors at the bottom of the light collectors 1000 are located on the same plane.

Referring to Figure 16, in a cross-sectional view of one embodiment, the multi-sided laser pumping system 100d includes a laser crystal 700' with a circular cross-section, more than two light collectors 1000, a transparent tube 550 in which a cooling liquid 560 flows to remove heat from the laser crystal 700', and a cooling box 750 for dissipating heat from the active mirror devices. The gradually opening light outlets 800 of the light collectors 1000 are attached to the circumferential surface of the transparent tube 550, and the pump light emitted by the light collectors 1000 is directed to the laser crystal 700'.

In summary, the light collector 1000 with an active mirror device 200 forming a gradually widening wedge structure effectively concentrates all light into the laser crystal 700 through the gradually widening light outlet 800, thereby achieving efficient laser pumping.

However, the above description is merely an example of the present invention and should not be used to limit the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the patent specification shall still fall within the scope of the present invention.

1000, 1000a~e: Concentrator; 100a~d: Laser pump system; 200: Active mirror device; 210: Substrate; 220: Reflective layer; 230: Light-emitting element; 233: Actual layer; 238: Bottom reflective layer; 270: Incident light; 280: Reflected light; 290: Enhanced reflected light; 300: High reflectivity layer; 300a: Reflective layer; 350: Anti-reflection layer; 450: Dielectric wedge; 460: Bright light wedge; 500: Mirror reflector; 501: Substrate layer; 550: Transparent tube; 560: Cooling liquid; 600: Bright light element; 700: Laser crystal; 750: Cooling box; 800: Gradient light outlet; 910: Cavity mirror; α: Angles _L1 , _L2 , _L3. Light

Other features and effects of the present invention will be clearly shown in the embodiments with reference to the drawings, wherein: Figure 1 is a schematic diagram illustrating an embodiment of a light collector according to the present disclosure; Figure 2 is an exploded schematic diagram illustrating that the upper of two light reflectors is exploded and moved upward; Figure 3 is a top view illustrating an embodiment of an active mirror device according to the present disclosure including an array of light-emitting elements on a reflective layer on a substrate; Figure 4 is a cross-sectional view illustrating one of the light-emitting elements according to an embodiment of the present disclosure; Figures 5 to 8 are schematic diagrams illustrating various embodiments of light collectors according to the present disclosure; Figures 9 and 10 are schematic diagrams illustrating embodiments of a laser pumping system employing a light collector according to the present disclosure. Figures 11 to 16 are cross-sectional views illustrating various other embodiments of a laser pumping system employing multiple light collectors according to this disclosure.

1000a: Concentrator; 200: Active mirror assembly; 210: Substrate; 220: Reflective layer; 230: Light-emitting element; 300: High-reflectivity layer; 500: Specular reflector; 501: Substrate; 800: Gradient light outlet; α: Angles _L1 , _L2 , _L3 : Light rays.

Claims (15)

An active mirror device includes: a substrate having a smooth reflective surface; and a plurality of light-emitting elements disposed on the smooth reflective surface of the substrate. Each light-emitting element includes a bottom reflective layer disposed on the substrate and an active layer disposed on the bottom reflective layer. The side of each active layer away from the bottom reflective layer is planar. When a current is applied, the active layer actively generates active light emission. The smooth reflective surface of the substrate reflects light incident thereon to generate reflected light, and the bottom reflective layer of each light-emitting element reflects the light incident thereon into the active layer, whereby the active layer amplifies the reflected light to generate enhanced reflected light. The active mirror device as claimed in claim 1, wherein the bottom reflective layer comprises any one of the following: a layer made of gold (Au), a dispersed Bragg reflector (DBR), and a combination thereof. The active mirror device as claimed in claim 1, wherein the active layer includes a gain medium for generating light. The active mirror device as claimed in claim 1, wherein the substrate includes a base layer and a reflective layer on the base layer having the smooth reflective surface, and the base layer has high thermal conductivity for dissipating heat from the light-emitting elements. A light collector comprising: two light reflectors connected at an angle at one end of the light collector to form a gradually widening wedge structure, and forming an apertured light exit at the other end of the light collector, each light reflector having a surface that reflects incident light to produce reflected light; wherein at least one of the light reflectors is an active mirror device as described in any one of claims 1 to 4, and focused light including the actively emitted light, the reflected light, the enhanced reflected light, and any combination thereof is guided through the apertured light exit and leaves the light collector. The light collector as described in claim 5, wherein one of the light reflectors is the active mirror device, and the other of the light reflectors is a mirror reflector comprising a base layer having a smooth surface and a highly reflective layer coated on the base layer. The light collector as described in claim 5 further comprises: a dielectric wedge made of a light-permeable dielectric material and filling the space between the two light reflectors. The light collector of claim 7 further includes an anti-reflective layer coated on one of the dielectric wedges adjacent to the active mirror device. As in claim 7, the light collector further incorporates a plurality of light-emitting elements that convert actively emitted light of one wavelength into emitted light of another different wavelength. A laser pumping system includes: a laser crystal; and at least one light collector, each comprising: two light reflectors connected at an angle at one end of the light collector to form a gradually widening wedge structure, and forming an aperimeter-opening light exit at the other end of the light collector, the aperimeter-opening light exit being adjacent to the laser crystal, each light reflector having a surface that reflects incident light to generate reflected light; wherein at least one of the two light reflectors is an active mirror device as described in any one of claims 1 to 4, and focused light including the actively emitted light, the reflected light, the enhanced reflected light, and any combination thereof is guided through the aperimeter-opening light exit to leave the light collector and enter the laser crystal. The laser pumping system of claim 10 further includes an antireflective layer coated on one surface of the laser crystal, wherein the focused light penetrates the antireflective layer into the laser crystal. The laser pumping system of claim 11 further includes a highly reflective layer coated on another surface of the laser crystal, the other surface being opposite to the surface coated with the antireflective layer, for reflecting unabsorbed focused light back into the laser crystal for continued use. The laser pumping system of claim 10, wherein the laser crystal is a laser crystal having a circular cross-section; the laser pumping system further includes a transparent tube having a cooling liquid flowing therethrough, wherein the laser crystal is disposed and fixed in the transparent tube, the cooling liquid being used to remove heat generated by the laser crystal. As in claim 13, the laser pumping system wherein the gradually opening light outlet of each light collector is attached to a portion of the circumferential surface of the transparent tube. As in claim 10, the laser pumping system wherein, for each of the light collectors, the gradually opening light outlet is arranged to face the laser crystal in such a way that the focused light emitted by the light collector is guided into the laser crystal.