Optical resonators and their manufacturing methods

Abstract

To provide a liquid optical resonator that has an excellent function as a laser oscillator, and an optical resonator manufacturing method by which the liquid optical resonator can be easily manufactured.SOLUTION: An optical resonator manufacturing method of the present invention includes: a first step of forming a water-repellent film 12 on one surface 11a of a substrate 11; a second step of producing non-volatile liquid obtained by adding a fluorescent dye to ionic liquid; and a third step of discharging and arranging a droplet 13 containing the non-volatile liquid onto the water-repellent film 12, by using a droplet discharge device allowing discharge of a droplet of a predetermined size at predetermined timing.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an optical resonator and a method for manufacturing the same.

Background Art

[0002] Techniques for confining light in a resonator and performing laser oscillation have attracted attention. Although various laser media that function as laser oscillators are known, many of them are composed of solid materials. For example, a light-emitting device that uses spherical polymer particles as a solid material and enables the manifestation of whispering gallery mode oscillation has been disclosed (Patent Document 1).

[0003] The laser medium of the solid material is chemically stable but requires laborious production. In contrast, the laser medium of the liquid material is chemically unstable and can only be used in a sealed environment where the environment such as the atmospheric composition, temperature, and humidity is controlled.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid optical resonator having an excellent function as a laser oscillator and a method for manufacturing the optical resonator that enables easy production thereof.

Means for Solving the Problems

[0006] To solve the above problems, the present invention employs the following means.

[0007] (1) A method for manufacturing an optical resonator according to one aspect of the present invention comprises: a first step of forming a water-repellent film on one surface of a substrate; a second step of preparing a non-volatile liquid by adding a fluorescent dye to an ionic liquid; and a third step of using a droplet dispensing device that enables the dispensing of droplets of a predetermined size at a predetermined timing to dispensing and placing droplets containing the non-volatile liquid onto the water-repellent film.

[0008] (2) In the method for manufacturing an optical resonator described in (1) above, it is preferable that in the third step, the distance between the droplet ejection part of the droplet ejection device and the water-repellent film be 0.1 mm or more and 10.0 mm or less.

[0009] (3) In the method for manufacturing an optical resonator according to either (1) or (2) above, it is preferable to adjust the relative positional relationship between the droplet dispensing section of the droplet dispensing device and the substrate in the third step so that the droplet is positioned at a predetermined location on the water-repellent film.

[0010] (4) In the method for manufacturing an optical resonator described in either (1) or (2) above, it is preferable that in the third step, the droplet containing the non-volatile liquid further contains a volatile liquid, and the volume of the volatile liquid is 0.1 times or more and 30,000 times or less the volume of the non-volatile liquid.

[0011] (5) An optical resonator according to one aspect of the present invention comprises a substrate, a water-repellent film covering one surface of the substrate, and a droplet disposed on the water-repellent film, wherein the droplet consists of a non-volatile liquid and a fluorescent dye, and has a diameter of 1 μm or more and 30 μm or less in a plan view from the thickness direction of the water-repellent film.

[0012] (6) In the optical resonator described in (5) above, it is preferable that the contact angle between the droplet and the water-repellent film is 140° or more.

[0013] (7) In the optical resonator described in either (5) or (6) above, it is preferable that a plurality of droplets are arranged on the water-repellent film and are spaced apart at predetermined intervals. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a liquid optical resonator having excellent functions as a laser oscillator and a method for manufacturing an optical resonator that enables easy manufacture thereof.

Brief Description of the Drawings

[0015] [Figure 1] It is a cross-sectional view of an optical resonator according to an embodiment of the present invention. [Figure 2] It is a diagram for explaining the configuration of a manufacturing apparatus for an optical resonator according to an embodiment of the present invention. [Figure 3] It is an enlarged view of a portion where an optical resonator is formed in the manufacturing apparatus for the optical resonator of FIG. 2. [Figure 4] It is an enlarged view of a part of an optical resonator manufactured by the manufacturing apparatus for the optical resonator of FIG. 2. [Figure 5] As Example 1, it is an image of droplets ejected from a droplet ejection unit. [Figure 6] As Example 1, it is an image of the upper surface of an array of optical resonators. [Figure 7] As Example 1, it is an image of the side surface of an array of optical resonators. [Figure 8] It is a diagram for explaining the configuration of a microscopic fluorescence spectrometer used in Example 1. [Figure 9] It is a graph showing the emission spectrum obtained with the optical resonator of Example 1. [Figure 10] It is a graph showing the emission spectrum obtained with the optical resonator of Example 1. [Figure 11] It is a graph showing the emission spectrum obtained with the optical resonator of Example 1. [Figure 12] It is a graph showing the emission spectrum obtained with the optical resonator of Example 1. [Figure 13] It is a graph showing the emission spectrum obtained with the optical resonator of Example 1. [Figure 14]This graph shows the relationship between the drop distance of the droplet from the droplet ejection unit and the performance of the resulting optical resonator in Example 2. [Figure 15] (a) and (b) are images of the optical resonators in Examples 1 and 3. [Figure 16] This graph shows the emission spectrum obtained from the optical resonator in Example 3. [Figure 17] This graph shows the results of absorption and emission measurements of visible and ultraviolet light from the optical resonator in Example 3. [Modes for carrying out the invention]

[0016] The optical resonator and its manufacturing method according to an embodiment to which the present invention is applied will be described in detail below with reference to the drawings. Note that, for the sake of clarity, the drawings used in the following description may show enlarged versions of key features, and the dimensional ratios of each component may not be the same as those in reality. Furthermore, the materials, dimensions, etc., exemplified in the following description are merely examples, and the present invention is not limited to these; it can be implemented with appropriate modifications without altering its essence.

[0017] <First Embodiment> [Optical resonator] Figure 1 is a schematic diagram illustrating the configuration of an optical resonator 10 according to the first embodiment of the present invention. The optical resonator 10 mainly comprises a substrate 11, a water-repellent film 12 covering one surface 11a of the substrate, and a droplet 13 placed on the water-repellent film 12. Hereinafter, the substrate 11 in which the water-repellent film 12 has been formed may be referred to as a water-repellent substrate 15.

[0018] The substrate 11 is plate-shaped and is not particularly limited as long as it can form a water-repellent film 12 on at least one surface 11a. Examples of substrates 11 include silicon substrates, quartz substrates, glass substrates, sapphire substrates, mica substrates, and the like.

[0019] The shape of one surface 11a of the substrate when viewed from above is not particularly limited and may be circular, elliptical, triangular, square, rectangular, or a polygon with five or more sides. The thickness of the substrate 11 is not particularly limited and can be adjusted as appropriate according to the thickness of the water-repellent film 12, the particle size of the droplets 13, etc. The shape of one surface 11a of the substrate 11 in the thickness direction may be any shape that can form the water-repellent film 12 and may be flat or have irregularities.

[0020] The water-repellent film 12 is composed of a large number of water-repellent inorganic fine particles 14 deposited on one surface 11a of the substrate 11. The thickness of the water-repellent film 12 is not particularly limited, but is preferably 1 μm or more and 1000 μm or less, and more preferably 20 μm or more and 40 μm or less.

[0021] The arithmetic mean roughness (Ra) of the surface 12a of the water-repellent film 12 is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.5 μm or more and 2 μm or less. When the arithmetic mean roughness (Ra) of the surface 12a of the water-repellent film 12 is 0.1 μm or more, droplets 13 of a predetermined particle size can be placed on the surface 12a of the water-repellent film 12. When the arithmetic mean roughness (Ra) of the surface 12a of the water-repellent film 12 is 5 μm or less, the contact angle of the droplets 13 increases due to the lotus effect.

[0022] The arithmetic mean roughness (Ra) of the surface 12a of the water-repellent film 12 can be calculated, for example, by electrically detecting the cross-sectional curve by tracing the sample surface with a stylus-type surface roughness meter manufactured by ULVAC, and in accordance with JIS B 0601:2013 "Geometric product specifications (GPS) - Surface properties: Contour curve method - Terms, definitions and surface property parameters".

[0023] The water-repellent inorganic fine particles 14 have a core inorganic or organic fine particle (not shown) and a water-repellent coating (not shown) that covers part or all of the surface of the inorganic or organic fine particle.

[0024] The particle size of the water-repellent inorganic fine particles 14 is not particularly limited, but is appropriately adjusted according to the arithmetic mean roughness (Ra) of the surface 12a of the water-repellent film 12. The particle size of the water-repellent inorganic fine particles 14 is preferably 50 nm to 200 nm, and more preferably 80 nm to 120 nm.

[0025] The materials for inorganic nanoparticles are not particularly limited, but examples include silicon dioxide, titanium dioxide, and aluminum oxide. On the other hand, the materials for organic nanoparticles are not particularly limited, but examples include polystyrene.

[0026] The material for the water-repellent film 12 is not particularly limited, but examples include fluorine-containing compounds. Examples of fluorine-containing compounds include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, and perfluoroalkoxy fluororesins.

[0027] The droplet 13 is a substantially spherical structure made of a non-volatile liquid containing an ionic luminescent dye. In this embodiment, a substantially spherical structure means a structure whose exposed surface (outermost surface) is spherical or a curved surface that is convex in the direction of exposure.

[0028] When viewed from the droplet discharge section 103 side in a plan view (plan view from the thickness direction of the water-repellent film 12), the diameter of the droplet 13 is preferably 1 μm or more and 1 mm or less, more preferably 1 μm or more and 80 μm or less, and most preferably 1 μm or more and 30 μm or less. If the diameter of the droplet 13 is 2 μm or more, Whispering Gallery Mode (WGM) oscillation occurs internally when excitation light is irradiated. If the diameter of the droplet 13 is 1 mm or less, the droplet 13 can maintain its shape on the surface 12a of the water-repellent film 12 for a long period of time and has good adhesion to the surface 12a of the water-repellent film 12.

[0029] The contact angle θ of the droplet 13 with respect to the surface 12a of the water-repellent film 12 is preferably 140° or more, and more preferably 160° or more. When the contact angle θ of the droplet 13 is 140° or more, the contact area between the droplet 13 and the water-repellent film 12 is small, so less oscillating light leaks from the droplet 13 to the water-repellent film 12. When the droplet 13 in this case is used as a laser oscillator, the laser oscillation threshold becomes lower.

[0030] The non-volatile liquid constituting the droplet 13 is not particularly limited, as long as it is a liquid that does not volatilize at temperatures below 25°C and can form a spherical structure by surface tension when dropped onto the surface 12a of the water-repellent film 12. For example, a non-volatile liquid with a surface tension of 30 mJ / m 2 Ionic liquids with a surface tension exceeding 30 mJ / m² are preferably used, containing any of the following as cations: imidazolium, pyrrolidinium, pyridinium, piperidinium, ammonium, or phosphonium; or containing any of the following as fluorides, chlorides, bromides, iodides, tetrafluoroborates, hexafluorophosphates, hexafluoroantimonates, bistrifluoromethylsulfonylimides, trifluoromethanesulfonates, methyl sulfates, acetates, dicyandiamides, or dimethylphosphates. 2 As ionic liquids exceeding this value, for example, imidazolium tetrafluoroborate represented by the following formula (1), or glycerol are preferably used.

[0031] [ka] [However, R1 is an alkyl group having 1 to 6 carbon atoms, and R2 is an alkyl group having 2 to 10 carbon atoms.]

[0032] Among imidazolium tetrafluoroborates, 1-ethyl-3-methylimidazolium tetrafluoroborate, represented by the following formula (2), is preferred.

[0033] [ka]

[0034] The fluorescent dye (ionic luminescent dye) contained in the non-volatile liquid is not particularly limited as long as it dissolves in the non-volatile liquid and emits light of a different wavelength from the excitation light when irradiated with excitation light. As ionic luminescent dyes, organic dyes containing one of the molecular skeletons of rhodamine, coumarin, pyromethene, stilbene, fluorene, or carbazole are preferably used, for example, the compound represented by formula (3) below (Acid Red 52), the compound represented by formula (4) below (Stilbene 420), the compound represented by formula (5) below (Pyrromethene 556), and the compound represented by formula (6) below (Rhodamine 6G).

[0035] [ka]

[0036] [ka]

[0037] [ka]

[0038] [ka]

[0039] In droplet 13, the molar ratio of the ionic luminescent dye to the non-volatile liquid (ionic luminescent dye / non-volatile liquid) is preferably 0.0001 or more and 0.01 or less, and more preferably 0.001 or more and 0.002 or less. When the molar ratio is 0.0001 or more, droplet 13 becomes a uniform spherical structure, and sufficient light amplification can be achieved when irradiated with excitation light. When the molar ratio is 0.01 or less, a sufficient amount of light emission can be obtained.

[0040] Since the droplet 13 consists of a non-volatile liquid containing the above-mentioned ionic luminescent dye, its shape is maintained for several months or more at room temperature and in the atmosphere, and it can stably emit light for a long period of time at room temperature and in the atmosphere. Furthermore, because the droplet 13 consists of a non-volatile liquid, it is elastically deformable and deforms in response to slight external forces such as gas flow, causing the laser oscillation wavelength to modulate. By utilizing this characteristic, the droplet 13 can be used, for example, as a flow velocity sensor.

[0041] [Manufacturing method for optical resonators] An optical resonator according to one embodiment of the present invention can be manufactured mainly by the following first, second, and third steps.

[0042] (first step) A water-repellent film 12 is formed on one surface 11a of the substrate. The method for forming the water-repellent film 12 is not particularly limited, but for example, a slurry containing water-repellent inorganic fine particles 14 is applied or sprayed onto one surface 11a of the substrate 11 to form a coating film made of the slurry on one surface 11a of the substrate 11. Then, the coating film formed on one surface 11a of the substrate 11 is heated and dried to obtain a water-repellent substrate 15 equipped with a water-repellent film 12.

[0043] The slurry contains water-repellent inorganic fine particles 14, as well as a solvent for dispersing the water-repellent inorganic fine particles 14. The solvent is not particularly limited, and any solvent capable of dispersing or dissolving the water-repellent inorganic fine particles 14 is selected. Preferred solvents include, for example, liquefied natural gas, heptane, hexane, pentane, butane, propane, and dimethyl ether. The viscosity of the slurry is not particularly limited and is appropriately adjusted depending on the material of the substrate 11 and the method of applying the slurry.

[0044] Methods for applying the slurry include, for example, spraying, dropping, spin coating, dipping, application with a brush or similar device, and inkjet spraying. Methods for spraying the slurry include, for example, the spray method. The temperature and time for heating the coating film formed on one surface 11a of the substrate 11 are appropriately adjusted according to the type of solvent contained in the slurry.

[0045] (Second process) A non-volatile liquid is prepared by adding a fluorescent dye to an ionic liquid and dissolving it by heating and ultrasonic treatment for a predetermined time (approximately 10 minutes). The amount of fluorescent dye added is adjusted so that the content ratio of the ionic luminescent dye to the non-volatile liquid is 0.0001 or more and 0.01 or less, preferably 0.001 or more and 0.002 or less. The prepared non-volatile liquid is preferably filtered using a membrane filter (pore size approximately 0.20 μm) to remove impurities and other particles.

[0046] (Third step) Droplets made of a non-volatile liquid are ejected and placed on a water-repellent film. Figure 2 is a schematic diagram illustrating the configuration of the droplet ejection device 100 used for ejecting the droplets. The droplet ejection device 100 is a device that utilizes (applies) the principle of a so-called inkjet printer, and is configured to eject high-viscosity droplets 13 that function as laser oscillators instead of printing ink. The droplet ejection device 100 mainly comprises a liquid storage section 101, a liquid flow path 102, a droplet ejection section 103, a substrate holding section 105, and a housing 106. The droplet ejection section 13 is configured to eject high-viscosity droplets, and is configured to have a higher ejection pressure than the ink ejection section of a typical inkjet printer. The substrate holding section 105 is a substrate holding stage (XYZ motorized stage, etc.) on which the droplets 13 are dropped. In Figure 2, the configuration of each part is shown in a simplified manner, but various design changes are possible depending on the application.

[0047] In the droplet dispensing device 100 shown in Figure 2, the non-volatile liquid obtained in the second step is contained in the liquid storage section 101. The substrate 11 is held on the substrate holding section 105 so that the water-repellent film 12 faces the droplet dispensing section 103. The position of the substrate holding section 105 relative to the droplet dispensing section 103 is also adjusted. Then, droplets 13 that have reached the droplet dispensing section 103 via the liquid flow path 102 from the liquid storage section 101 are dispensed to a predetermined position on the water-repellent film 12 using the piezoelectric element 104.

[0048] Figure 3 is an enlarged view of the portion of the droplet ejection device 100 in which the optical resonator 10 is formed. By discharging droplets 13 while scanning the droplet ejection unit 103 over the substrate 11, the droplets 13 can be arranged at multiple positions on the water-repellent film 12 so that they are aligned at predetermined intervals. By adjusting the timing of scanning of the droplet ejection unit 103 and the discharge of droplets 13, an array-like arrangement as shown in Figure 3 can be achieved, and other arrangements can also be made.

[0049] Figure 4 is an enlarged view of a cross-section of a portion R of the optical resonator 10 shown in Figure 3. The distance D1 between droplets 13 placed on the water-repellent film 12 can be freely adjusted by the timing of scanning of the droplet ejection unit 103 and ejection of the droplets 13. For example, when the optical resonator 10 is used as a display, lighting, or sensor, this distance D1 is preferably 1.01 to 1000 times the diameter D2 of the droplet 13, or between 0.00001 mm and 1000 mm.

[0050] The droplet ejection device 100, with a configuration similar to that of an inkjet printer, is capable of ejecting droplets 13 of a predetermined size at a predetermined timing. While it is preferable to control the position adjustment of the substrate holding unit 105 and the amount of droplet 13 ejected by computer, it is also preferable to perform these operations manually depending on the situation. For example, the amount of droplet 13 ejected can be adjusted by controlling the magnitude and duration of the pulse voltage applied to the piezoelectric element 104 and the temperature of the droplet ejection unit 103 while observing the droplet ejection process from the side (horizontal direction).

[0051] In the droplet ejection device 100, the distance H between the droplet ejection section 103 (tip) and the surface 12a of the water-repellent film on the substrate 11 can be adjusted. By changing this distance H, the performance of the ejected droplet 13 as an optical resonator changes. The longer the distance H, the lower the laser threshold of the ejected droplet 13 becomes, and the smaller the variation, but it becomes more difficult to control the position of the droplet 13 on the water-repellent film 12. Conversely, the shorter the distance H, the higher the laser threshold of the ejected droplet 13 becomes, and the larger the variation, but the precision of the droplet 13 placement on the water-repellent film 12 can be improved. Note that changing the distance H does not affect the diameter of the ejected droplet 13.

[0052] The reason why the laser threshold of the positioned droplet 13 changes with distance H is that the velocity of the ejected droplet 13 as it falls and collides with the water-repellent film 12 changes according to the distance H. The falling velocity of the ejected droplet is highest immediately after ejection (at the start of falling), decreases due to air resistance during the fall, and becomes a nearly constant velocity (final velocity).

[0053] Therefore, the shorter the distance H, the more the droplet 13 will collide with the water-repellent film 12 at a high velocity close to its initial velocity, resulting in a strong impact. As a result, the positioned droplet 13 will not be able to maintain its spherical shape and will be crushed, increasing the laser threshold.

[0054] On the other hand, the longer the distance H, the more the droplet 13 will collide with the water-repellent film 12 at a low velocity close to its final velocity, and will not experience a very strong impact. As a result, the droplets 13 that are positioned will be able to maintain a shape close to a sphere, and the laser threshold will be reduced.

[0055] From the viewpoint of achieving both controllability of the laser threshold and controllability of the arrangement of the droplet 13, the distance H is preferably 0.1 mm or more and 10.0 mm or less, and more preferably 2.0 mm or more and 3.0 mm or less, as will be described later in the examples.

[0056] In the droplet dispensing device 100, the relative positional relationship between the droplet dispensing section 103, the substrate 11, and the water-repellent film 12 can be adjusted, so that multiple droplets 13 can be positioned at predetermined locations on the water-repellent film 12 with high precision.

[0057] As described above, according to the optical resonator manufacturing method of this embodiment, by using a droplet ejection device 100 based on the principle of an inkjet printer, droplets 13 having the function of a laser oscillator can be dropped onto predetermined positions on the water-repellent film 12 in the atmosphere. By ejecting droplets 13 while changing the position of the droplet ejection unit 103, droplets can be dropped onto multiple positions on the water-repellent film 12, and predetermined arrangements such as an array can be formed by multiple droplets 13. Therefore, according to the optical resonator manufacturing method of this embodiment, a liquid optical resonator having the function of a laser oscillator can be easily manufactured.

[0058] An optical resonator in which multiple droplets 13 are arranged in an array has a variety of potential applications. For example, it could be used as a lighting device that emits light with stable purity over a large area, a display in which the constituent materials of the droplets are adjusted to emit a predetermined color at each position in the array, or a two-dimensional sensor that detects humidity, gas flow, etc., by emitting light.

[0059] In the manufacturing method of the optical resonator of this embodiment, by adjusting the fall distance of the ejected droplet 13, the shape of the droplet 13 placed on the water-repellent film 12 can be made closer to a spherical shape, and the contact area with the water-repellent film 12 can be reduced. In this case, the amount of oscillating light leaking from the droplet 13 into the water-repellent film is reduced, and the laser threshold of the droplet 13 is lowered, so an optical resonator with excellent function as a laser oscillator can be obtained.

[0060] <Second Embodiment> The method for manufacturing an optical resonator according to the second embodiment of the present invention differs from the method for manufacturing an optical resonator according to the first embodiment only in that a volatile liquid is mixed with the non-volatile liquid produced in the second step. The optical resonator according to this embodiment is similar to the optical resonator according to the first embodiment in that it comprises a substrate, a water-repellent film covering one surface of the substrate, and a droplet placed on the water-repellent film, but the size of the droplet is different. The optical resonator and its manufacturing method according to this embodiment can achieve at least the effects of the optical resonator and its manufacturing method according to the first embodiment.

[0061] The size of the droplets ejected from the droplet ejection unit is determined by the configuration of the droplet ejection unit. The lower limit of the diameter of the ejected droplets is generally around 30 μm, and the size of the droplets that reach and are positioned on the water-repellent film is also approximately the same.

[0062] In this embodiment, the discharged droplets are a mixed liquid obtained by mixing a non-volatile liquid with a volatile liquid. Examples of volatile liquids include water, ethanol, and chloroform. The mixing of the volatile liquid may be performed simultaneously with the addition of the fluorescent dye to the ionic liquid in the second step, or it may be performed between the second and third steps.

[0063] The volume of the volatile liquid to be mixed is preferably equivalent to the difference between the lower limit of the volume of droplets that can be discharged and the volume of droplets to be placed on the water-repellent film. The volume of the volatile liquid is preferably 0.1 times or more and 30,000 times or less of the volume of the non-volatile liquid. The mixing of the volatile liquid may be carried out such that the volume ratio of the non-volatile liquid to the volatile liquid is, for example, 1:9.

[0064] As the droplets of the mixed liquid ejected from the droplet ejection unit fall onto the water-repellent film, the volatile liquid contained in the droplets evaporates. As a result, the droplets that reach and are placed on the water-repellent film consist only of non-volatile liquid, and their diameter is more than an order of magnitude smaller than the diameter of the droplet immediately after ejection. In other words, the diameter of the droplets placed on the water-repellent film in this embodiment is even smaller than the lower limit of the diameter of droplets ejected in a typical droplet ejection device (inkjet printer). Therefore, according to this embodiment, droplets of a more ideal size for a laser oscillator (diameter of 1 μm or more and 30 μm or less) can be placed on the water-repellent film. [Examples]

[0065] The effects of the present invention will be made clearer by the following examples. However, the present invention is not limited to the following examples and can be modified as appropriate without altering its essence.

[0066] (Example 1) The optical resonator of the present invention was manufactured by performing the first, second, and third steps of the above embodiment.

[0067] As the first step, a water-repellent substrate was fabricated by forming a water-repellent film on one surface of the substrate using the following procedure. First, a quartz substrate (15 mm x 15 mm) to be used as the substrate was set in a spin coater and rotated at 1000 rpm. A superhydrophobic spray was then sprayed vertically onto one main surface of the quartz substrate from a distance of 10 cm for about 10 seconds. After that, the quartz substrate was removed from the spin coater and dried at room temperature for about 24 hours. The water-repellent film on the dried quartz substrate was sprayed with the superhydrophobic spray again using the same procedure and dried to obtain a water-repellent substrate.

[0068] As the second step, a non-volatile liquid was prepared by adding a fluorescent dye to an ionic liquid using the following procedure. 1-ethyl-3-methylimidazolium tetrafluoroborate, given by formula (2) above, was used as the ionic liquid. Acid Red 52, given by formula (3) above, was used as the fluorescent dye. The content ratio of 1-ethyl-3-methylimidazolium tetrafluoroborate to Acid Red 52 was set to 1:200.

[0069] In the third step, multiple droplets were placed on the water-repellent film using the following procedure. The distance between the droplet ejection unit and the water-repellent film was set to 2 mm. A pulse voltage of 25.3 V was applied to the piezoelectric element of the droplet ejection unit, causing droplets to be ejected toward the water-repellent film. The duration of the pulse voltage was set as follows. Time width of the first pulse voltage (1st pulse width): 95 μs The duration of the next pulse voltage (2nd pulse width): 15 μs Time interval between the 1st pulse voltage and the 2nd pulse voltage: 16.7 μs Furthermore, in order to reduce the viscosity of the droplets and facilitate their discharge, the droplet discharge section was heated to bring the droplet temperature to 70°C.

[0070] Figure 5 shows images of droplets ejected from the droplet ejection unit 103 and falling. The positions of the droplets 200 μs, 300 μs, 500 μs, 700 μs, and 900 μs after ejection are shown. Closer to the droplet ejection unit 103, the falling velocity of the droplets increases as the distance from the ejection unit 103 increases. On the other hand, further away from the droplet ejection unit 103, the falling velocity of the droplets remains constant regardless of the falling distance. From these observations, it can be seen that the falling velocity of the ejected droplets is highest immediately after ejection (at the start of falling), decreases due to air resistance during the fall, and becomes almost constant (final velocity).

[0071] Figures 6 and 7 are fluorescence microscope images of droplets 13 ejected onto a water-repellent film and arranged in an array. The fluorescence microscope image in Figure 6 was obtained from the direction normal to the surface of the water-repellent film, and Figure 7 was obtained from a direction tilted 15 degrees from the same normal direction. From both directions, the droplets 13 appear circular, indicating that they are spherical.

[0072] Figure 8 is a diagram illustrating the configuration of the microfluorescence spectroscopy apparatus 200. The microfluorescence spectroscopy apparatus 200 mainly consists of an excitation light source (laser) 201, a camera 202, a beam splitter 203, a flip mirror 204, an objective lens 205, an XY stage 206, a long-pass filter 207, and a detector (spectrometer) 208.

[0073] In the microfluorescence spectrometer 200, when the excitation light source 201 emits laser light (excitation light), the laser light is reflected by the beam splitter 203, and then focused by the objective lens 205 before irradiating the droplet 13. When the droplet 13 is irradiated with laser light, the droplet 13 emits fluorescence due to the oscillation of whispering gallery modes (WGM) inside it.

[0074] The fluorescence passes through the beam splitter 203, with some of it passing through the flip mirror 204 and entering the camera 202, while other portions are reflected by the flip mirror 204 and enter the detector 208 via the long-pass filter 207. The detector 208 measures the spectrum of the received fluorescence and outputs its spectral pattern to a display device or the like.

[0075] From a set of multiple droplets, the emission spectra of five arbitrary droplets were analyzed using the micro-fluorescence spectrometer 200 shown in Figure 8. Specifically, excitation light (wavelength 355 nm, frequency 1 kHz, pulse width 7 ns) was irradiated while gradually increasing the intensity, and emission spectra were acquired at each irradiation intensity. The irradiation intensity at which laser oscillation (peak) was confirmed in the emission spectrum was defined as the laser threshold.

[0076] Figures 9-13 are graphs showing the emission spectra of the five droplets that were analyzed. In each droplet, when the excitation light intensity was set above a certain level, a peak indicating laser oscillation appeared in the emission spectrum, allowing the laser threshold to be identified. The laser threshold identified for each of the five droplets was 4.77 μJ / cm². 2 3.11 μJ / cm² 2 , 2.08 μJ / cm 2 , 11.58 μJ / cm 2 6.00 μJ / cm 2 These results are all sufficiently low compared to the laser thresholds of generally known liquid lasers. From these results, it can be seen that the droplets arranged according to the present invention have excellent functionality as laser oscillators.

[0077] (Example 2) In the same procedure as in Example 1, optical resonators were fabricated under conditions where the distance between the droplet ejection section and the water-repellent film was 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 3.0 mm, 5.0 mm, and 7.0 mm, and the laser threshold of the optical resonators fabricated under each condition was measured.

[0078] Figure 14 is a graph showing the measurement results. The horizontal axis of the graph shows the distance (mm) between the droplet ejection section and the water-repellent film, i.e., the fall distance of the ejected droplet. The vertical axis of the graph shows the laser threshold (μJ / cm²) of multiple droplets prepared under each condition. 2 The average value of the laser threshold decreases as the droplet falls further. The average value of the laser threshold decreases as the droplet falls further, and the variability from the average value also decreases. From this result, it can be inferred that droplets collide with the hydrophobic film at a lower velocity as they fall further, and because they do not receive a strong impact, the droplets placed on the hydrophobic film can maintain a shape close to a sphere.

[0079] The results show that the longer the droplet falls, the more likely it is that droplets with high performance as laser oscillators will be positioned. However, if the droplet falls too far, the variation in the direction of droplet ejection increases. As a result, it becomes difficult to eject droplets to the desired position on the water-repellent film, and it becomes impossible to arrange multiple droplets regularly in an array-like manner. Note that when the droplet falls at distances of 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, and 3.0 mm, an array-like arrangement of multiple droplets is achieved, and the diameter of each droplet was approximately the same at all fall distances. From these results, it is considered preferable that the droplet fall distance be between 2.0 mm and 3.0 mm in order to achieve both high performance as a laser oscillator for the droplets and regular arrangement of the droplets.

[0080] (Example 3) An optical resonator was manufactured according to the second embodiment described above. The volatile liquids were mixed so that the volume ratio of the non-volatile liquid to the volatile liquid was 1:9. Other conditions were the same as in Examples 1 and 2.

[0081] Figures 15(a) and (b) are images of the droplet 13A and 13B sides of the optical resonators manufactured in Examples 1 and 3, respectively. The diameter D2 of droplet 13A in Example 1 is approximately 35 μm, while the diameter D2 of droplet 13B in Example 3 is approximately 20 μm. In Example 3, droplet 13B has a volume of 1 / 10 and a diameter of 1 / 2.1 compared to its state immediately after ejection from the droplet ejection unit. It is thought that droplet 13B in Example 3 is smaller than its state immediately after ejection because volatile liquid evaporated after being ejected from the droplet ejection unit.

[0082] The droplet 13 was irradiated with excitation light (wavelength 355 nm, frequency 1 kHz, pulse width 7 ns), and the emission spectrum of the droplet 13 was analyzed. Figure 16 is a graph showing the obtained emission spectrum. The horizontal axis of the graph shows the wavelength (nm) of the excitation light, and the vertical axis shows the emission intensity. The presence of a sharp laser peak above a broad emission peak indicates that the droplet 13 functions as a laser oscillator.

[0083] Absorption and emission measurements were performed on droplet 13 using visible and ultraviolet light. Figure 17 is a graph showing the obtained fluorescence spectrum. The horizontal axis of the graph shows the wavelength (nm) of visible and ultraviolet light, and the vertical axis shows the absorption intensity and emission intensity. The peak values ​​of the absorption wavelength and the emission wavelength differ in ultraviolet light, indicating that the ionic luminescent dye emits fluorescence in response to incident light. [Explanation of symbols]

[0084] 10...optical resonator 11...Base material 11a... One side of the substrate 12. Water-repellent film 12a... Surface of the water-repellent film 13, 13A, 13B...droplet 14. Water-repellent inorganic fine particles 15. Water-repellent substrate 100...Droplet discharge device 101...Liquid containment section 102...Liquid flow path 103...Droplet discharge part 104... Piezoelectric element 105...Base material holding part 106... cabinet 200...Micro-fluorescence spectroscopy measuring device 201...Excitation light source 202...Camera 203...Beam Splitter 204...Flip mirror 205... Objective lens 206...XY Stage 207...Long-pass filter 208... Detector D1... Distance between droplets D2...Diameter of the liquid droplet H... Distance between the droplet discharge section and the water-repellent substrate

Claims

1. The first step involves forming a water-repellent film on one surface of the substrate, The second step involves preparing a non-volatile liquid by adding a fluorescent dye to an ionic liquid, The process includes a third step of using a droplet dispensing device that enables the dispensing of droplets of a predetermined size at a predetermined timing, to dispensing and positioning droplets containing the non-volatile liquid onto the water-repellent film, The amount of the fluorescent dye added is adjusted so that the molar ratio of the ionic luminescent dye to the non-volatile liquid is between 0.0001 and 0.

01. As the non-volatile liquid, an ionic liquid with a surface tension exceeding 30 mJ / m², containing any of imidazolium, pyrrolidinium, pyridinium, piperidinium, ammonium, or phosphonium as a cation, or an ionic liquid containing any of fluoride, chloride, bromide, iodide, tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, bistrifluoromethylsulfonylimide, trifluoromethanesulfonate, methyl sulfate, acetate, dicyandiamide, or dimethylphosphate, or glycerol may be used. A method for manufacturing an optical resonator, characterized in that the ionic luminescent dye used is an organic dye containing one of the molecular skeletons of rhodamine, coumarin, pyromethene, stilbene, fluorene, or carbazole.

2. The method for manufacturing an optical resonator according to claim 1, characterized in that, in the third step, the distance between the droplet ejection section of the droplet ejection device and the water-repellent film is set to 0.1 mm or more and 10.0 mm or less.

3. The method for manufacturing an optical resonator according to either claim 1 or 2, characterized in that, in the third step, the relative positional relationship between the droplet dispensing section of the droplet dispensing device and the substrate is adjusted so that the droplet is positioned at a predetermined location on the water-repellent film.

4. In the third step, The droplet containing the non-volatile liquid further contains a volatile liquid, A method for manufacturing an optical resonator according to either claim 1 or 2, characterized in that the volume of the volatile liquid is 0.1 times or more and 30,000 times or less the volume of the nonvolatile liquid.

5. Substrate and A water-repellent film covering one surface of the substrate, A liquid droplet disposed on the water-repellent film, The aforementioned droplets consist of a non-volatile liquid and a fluorescent dye, and in a plan view from the thickness direction of the water-repellent film, their diameter is 2 μm or more and 30 μm or less. The content ratio of the ionic luminescent dye to the non-volatile liquid is 0.0001 or more and 0.01 or less in molar ratio. As the non-volatile liquid, an ionic liquid with a surface tension exceeding 30 mJ / m², containing any of imidazolium, pyrrolidinium, pyridinium, piperidinium, ammonium, or phosphonium as a cation, or an ionic liquid containing any of fluoride, chloride, bromide, iodide, tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, bistrifluoromethylsulfonylimide, trifluoromethanesulfonate, methyl sulfate, acetate, dicyandiamide, or dimethylphosphate is used. An optical resonator characterized in that the ionic luminescent dye used is an organic dye containing one of the molecular skeletons of rhodamine, coumarin, pyromethene, stilbene, fluorene, or carbazole.

6. The optical resonator according to claim 5, characterized in that the contact angle between the droplet and the water-repellent film is 140° or more.

7. The optical resonator according to either 5 or 6, characterized in that a plurality of droplets are arranged on the water-repellent film and are spaced apart at predetermined intervals.

Images