Optical glass, optical element, optical system, cemented lens, objective lens for microscope, interchangeable lens for camera, and optical device

Abstract

An optical glass in which La3+ content: 5 to 35%, Si4+ content: 5 to 25%, Nb5+ content: 5 to 35%, Al3+ content: 5 to 35%, and total content of Ti4+, Zr4+, Nb5+, Ta5+, and Al3+ (Ti4++Zr4++Nb5++Ta5++al3+): 45 to 80%, expressed in mol% of cation.

Description

Optical glass, optical elements, optical systems, cemented lenses, objective lenses for microscopes, interchangeable lenses for cameras, and optical devices

[0001] The present invention relates to optical glass, optical elements, optical systems, cemented lenses, microscope objective lenses, interchangeable camera lenses, and optical devices. This invention claims priority to Japanese Patent Application No. 2022-158015, filed on September 30, 2022, and the contents of that application are incorporated by reference into this application in designated states where incorporation by reference of documents is permitted.

[0002] Optical glass is used in a variety of optical elements and optical devices, and for example, Patent Document 1 discloses halide glass for use in the ultraviolet to infrared region. In order to increase the degree of freedom in designing the optical systems used in optical devices, there is a demand for the development of optical glass with a high refractive index.

[0003] Japanese Patent Application Publication No. 07-081973

[0004] In one aspect of the present invention, the cation is represented by mole % as follows: ３＋ Content: 5-35%, Si ４＋ Content: 5-25%, Nb ５＋ Content: 5-35%, Al ３＋ Content: 5-35%, Ti ４＋ , Zr ４＋ , Nb ５＋ , Ta ５＋ and Al ３＋ Total content of (Ti ４＋ + Zr ４＋ +Nb ５＋ +Ta ５＋ +Al ３＋ ): 45 to 80%, it is an optical glass.

[0005] Another aspect of the present invention is an optical element using the above-mentioned optical glass.

[0006] Another aspect of the present invention is an optical system including the optical element described above.

[0007] Another aspect of the present invention is an objective lens for a microscope, which includes an optical system including the optical element described above.

[0008] Another aspect of the present invention is an interchangeable lens for a camera, which includes an optical system including the optical element described above.

[0009] Another aspect of the present invention is an optical device including an optical system including the optical element described above.

[0010] Another aspect of the present invention is a cemented lens having a first lens element and a second lens element, at least one of the first lens element and the second lens element being made of the optical glass described above.

[0011] Another aspect of the present invention is an optical system including the cemented lens described above.

[0012] Another aspect of the present invention is an objective lens for a microscope, which includes an optical system including the cemented lens described above.

[0013] Another aspect of the present invention is an interchangeable lens for a camera, which includes an optical system including the cemented lens described above.

[0014] Another aspect of the present invention is an optical device including an optical system including the above-described cemented lens.

[0015] FIG. 1 is a perspective view showing an example in which the optical device according to the present embodiment is used as an imaging device; FIG. 2 is a schematic view showing another example in which the optical device according to the present embodiment is used as an imaging device, and is a front view of the imaging device; FIG. 3 is a schematic view showing another example in which the optical device according to the present embodiment is used as an imaging device, and is a rear view of the imaging device; FIG. 4 is a block diagram showing an example of the configuration of a multiphoton microscope according to the present embodiment; FIG. 5 is a schematic view showing an example of a cemented lens according to the present embodiment; FIG. 6 is a schematic view showing the overall configuration of a gas jet type levitation furnace according to the present embodiment; FIG. 7 is an enlarged schematic view of a pedestal on a stage of the gas jet type levitation furnace according to the present embodiment; ｄ -P ｇ , Ｆ ) is a graph plotting the optical constants (ν ｄ -n ｄ ) is a graph plotting

[0016] An embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described below. The present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be practiced with appropriate modifications within the scope of its gist.

[0017] Furthermore, the expression "0 to N%" of the Q content includes cases where the Q component is not included and cases where the Q component is more than 0% and not more than N%.

[0018] The expression "not containing Q component" means that the Q component is substantially not contained, and indicates that the content of this component is at or below the impurity level. At or below the impurity level, for example, means less than 0.01%.

[0019] The expression "devitrification resistance" refers to the resistance of glass to devitrification. Here, "devitrification" refers to a phenomenon in which glass loses transparency due to crystallization or phase separation that occurs when the temperature of glass is raised to or above its glass transition temperature or when the temperature is lowered from a molten state to or below its liquidus temperature.

[0020] <Optical Glass> The optical glass according to this embodiment contains, in terms of cation mol %, La ３＋ Content: 5-35%, Si ４＋ Content: 5-25%, Nb ５＋ Content: 5-35%, Al ３＋ Content: 5-35%, Ti ４＋ , Zr ４＋ , Nb ５＋ , Ta ５＋ and Al ３＋ Total content of (Ti ４＋ + Zr ４＋ +Nb ５＋ +Ta ５＋ +Al ３＋ ): 45 to 80%, it is an optical glass.

[0021] In this specification, unless otherwise specified, the content of each component is expressed in mole percent of cation. The mole percent of cation refers to the ratio of the number of moles of the target cation to the number of moles of the total cations contained in the optical glass. More specifically, SiO２ 50 mol%, Na ２ In the case of 50 mol% O, the molar percentage of the cation is Si ４＋ is 33.3%, Na ＋ The content of each cation is not particularly limited, but may be contained in the optical glass in the form of, for example, an oxide.

[0022] The optical glass according to this embodiment is ２ O ３ and Nb ２ O ５ This is a novel optical glass that achieves a high refractive index and high transmittance by using a composition system containing the above as the main component. This composition system does not vitrify when melted in a crucible, but can be obtained by the floating melting method. However, by combining a low specific gravity with high stability against devitrification, the glass floats easily, and glass gobs with a diameter of 10 mm or more can be stably produced by the floating melting method.

[0023] First, each component of the optical glass according to this embodiment will be described.

[0024] La ３＋ is, for example, La in terms of oxide composition. ２ O ３ It is a component contained as La ３＋ has the effect of increasing the refractive index and transmittance. However, when the content of La increases, the specific gravity tends to increase. ３＋ The content of is 5 to 35%. The lower limit of this content is preferably 8%, more preferably 12%, and even more preferably 15%. The upper limit of this content is preferably 32%, more preferably 29%, and even more preferably 26%.

[0025] Si ４＋ is, for example, SiO ２ It is a component contained as Si. ４＋ is a component that can improve the stability against devitrification and at the same time maintain a low specific gravity. However, if the content of Si increases, the refractive index tends to decrease. From this viewpoint, Si ４＋The content of is 5 to 25%. The lower limit of this content is preferably 6%, more preferably 8%, and even more preferably 10%. The upper limit of this content is preferably 24%, more preferably 22%, and even more preferably 20%.

[0026] Nb ５＋ is, for example, Nb in terms of oxide composition. ２ O ５ It has the effect of increasing the refractive index and transmittance. However, as the content of this component increases, the specific gravity tends to increase. From this viewpoint, Nb ５＋ The content of is 5 to 35%. The lower limit of this content is preferably 8%, more preferably 12%, and even more preferably 16%. The upper limit of this content is preferably 32%, more preferably 29%, and even more preferably 26%.

[0027] Al ３＋ is, for example, Al in terms of oxide composition. ２ O ３ It is a component contained as Al. ３＋ is a component that can improve the stability against devitrification and at the same time maintain a low specific gravity. However, if the content of Al is increased, the refractive index tends to decrease. ３＋ The content of is 5 to 35%. The lower limit of this content is preferably 8%, more preferably 12%, and even more preferably 14%. The upper limit of this content is preferably 32%, more preferably 29%, and even more preferably 26%.

[0028] Zr ４＋ is, for example, ZrO in terms of oxide composition. ２ Zr is a component contained as ４＋ has the effect of increasing the stability against devitrification and the refractive index. ４＋ The content of is 0 to 15%. The lower limit of this content is preferably 2%, more preferably 4%, and even more preferably 6%. The upper limit of this content is preferably 14%, more preferably 12%, and even more preferably 10%.

[0029] Ti ４＋ is, for example, TiO in terms of oxide composition. ２ It is a component contained as Ti. ４＋ has the effect of increasing the refractive index while maintaining a low specific gravity. However, if the content of Ti increases, the transmittance tends to decrease. ４＋ The content of is 0 to 20%. The lower limit of this content is preferably 2%, more preferably 4%, and even more preferably 6%. The upper limit of this content is preferably 20%, more preferably 16%, and even more preferably 10%.

[0030] Ta ５＋ is, for example, Ta in terms of oxide composition. ２ O ５ It is a component contained as Ta ５＋ has the effect of improving stability against devitrification while maintaining low dispersion. However, when the content of Ta is increased, the specific gravity tends to increase. From this viewpoint, Ta ５＋ The content of is 0 to 15%. The lower limit of this content is preferably 2%, more preferably 3%, and even more preferably 5%. The upper limit of this content is preferably 12%, more preferably 10%, and even more preferably 8%.

[0031] Ti ４＋ and Zr ４＋ and Nb ５＋ and Ta ５＋ and Al ３＋ Total content of (Ti ４＋ + Zr ４＋ +Nb ５＋ +Ta ５＋ +Al ３＋ ) is 45 to 80%. The lower limit of this total content is preferably 50%, more preferably 54%, and even more preferably 56%. The upper limit of this total content is preferably 76%, more preferably 73%, and even more preferably 70%. (Ti ４＋ + Zr ４＋ +Nb ５＋ +Ta ５＋ +Al ３＋By setting the tungsten content (Tg) in this range, it is possible to achieve both a high refractive index and a high transmittance while maintaining stability against devitrification during melting.

[0032] The glass composition according to this embodiment may contain, as other optional components, Y ３＋ , B ３＋ may further contain any one of the following.

[0033] Y ３＋ For example, in terms of oxide, ２ O ３ It is a component contained as Y. ３＋ is a component that can increase the refractive index and transmittance without impairing the low dispersion. ３＋ The content of La is 0 to 15%. The lower limit of this content is preferably 2%, more preferably 4%, and even more preferably 6%. The upper limit of this content is preferably 12%, more preferably 10%, and even more preferably 8%. ３＋ and Y ３＋ It is preferable to contain both of these.

[0034] B ３＋ For example, in terms of oxide, ２ O ３ It is a component that constitutes the network-forming oxide. ３＋ Since B is a highly volatile component, if it is introduced in excess, it may cause fluctuations in the composition of the glass during production, and striae may become apparent. ３＋ It is preferable that the composition is substantially free of B. ３＋ When the component (I) is contained, the upper limit of the content is preferably 10%, more preferably 5%, and even more preferably 2%.

[0035] In addition, if necessary, suitable amounts of known clarifiers, colorants, defoamers, fluorine compounds, and other components may be added to the glass composition for the purpose of clarifying, coloring, decoloring, fine-tuning of optical constants, etc. Furthermore, other components may be added in addition to the above components, as long as the effects of the optical glass according to this embodiment can be obtained.

[0036] It is preferable to use high-purity raw materials with low impurity content. A high-purity product is one that contains 99.85 mass% or more of the component in question. The use of high-purity raw materials reduces the amount of impurities, which tends to increase the internal transmittance of the optical glass.

[0037] Next, the physical properties of the optical glass of this embodiment will be described.

[0038] From the viewpoint of the visible light transmittance of an optical system, the optical glass according to this embodiment preferably has a high internal transmittance. Taking this into consideration, the optical glass according to this embodiment has a wavelength (λ80) at which the internal transmittance per 10 mm is 80% of 420 nm or less. The upper limit of the wavelength at which λ80 is achieved is preferably 405 nm, more preferably 400 nm, and even more preferably 395 nm.

[0039] From the viewpoint of thinning the lens, the optical glass according to this embodiment has a high refractive index (refractive index (n ｄ However, in general, the refractive index (n ｄ In view of this situation, the refractive index (n ｄ ) is in the range of 1.95 to 2.15. ｄ The lower limit of the refractive index (n ｄ The upper limit of the ratio (R) is preferably 2.12, more preferably 2.08, and even more preferably 2.05.

[0040] The Abbe number (ν ｄ ) is in the range of 20 to 35. And the Abbe number (ν ｄ The lower limit of the Abbe number (ν ｄ The upper limit of the number of carbon atoms is preferably 32, more preferably 30, and even more preferably 29.

[0041] From the viewpoint of correcting aberrations in the lens, the partial dispersion ratio (P ｇ , Ｆ ) is 0.55 to 0.65. ｇ , Ｆ The lower limit of the partial dispersion ratio (P ｇ , Ｆ The upper limit of the partial dispersion ratio (P ｇ , Ｆ ) is expressed by the following formula: -0.00403 × ν ｄ +0.704<P ｇ,Ｆ <-0.00403 × ν ｄ It is preferable that the partial dispersion ratio (P ｇ , Ｆ ) is a value calculated based on the refractive index measured by the V-block method.

[0042] The optical glass according to this embodiment has a length in the major axis direction of 10 mm or more. The length in the major axis direction is preferably 11 mm or more, more preferably 12 mm or more, and even more preferably 13 mm or more. The "length in the major axis direction" here refers to the maximum value in the diameter direction of the glass gob, and in the case of a substantially spherical glass gob, refers to the diameter value.

[0043] The optical glass according to this embodiment preferably has a thickness (T) of 4 mm or more, more preferably 5 mm or more, and even more preferably 5.5 mm or more. Here, "thickness" refers to the height in the direction perpendicular to the maximum diameter (diameter (D)) of the glass gob, and in the case of a substantially spherical glass gob, refers to the diameter value.

[0044] The optical glass according to this embodiment preferably has a weight of 1.5 g or more, more preferably 2.0 g or more, and even more preferably 2.5 g or more.

[0045] When the optical glass according to the present invention is produced using a levitation furnace, it is desirable that the specific gravity thereof be 6.0 or less. In view of this situation, the optical glass according to this embodiment has a specific gravity (S ｇ ) is 4.6 to 5.6. The lower limit of the specific gravity is preferably 4.7, more preferably 4.8, and even more preferably 4.9. The upper limit of the specific gravity is preferably 5.5, more preferably 5.3, and even more preferably 5.1.

[0046] The optical glass according to this embodiment has a glass transition temperature (T ｇ ) and crystallization initiation temperature (T ｘ ) temperature difference (ΔT = T ｘ -T ｇ In view of this situation, the glass transition temperature (T ｇ ) and crystallization initiation temperature (T ｘ ) temperature difference (ΔT = T ｘ -T ｇ ) is 80°C to 200°C. The lower limit of the difference is preferably 100°C, more preferably 130°C, and even more preferably 160°C. The upper limit of the difference is preferably 190°C, more preferably 180°C, and even more preferably 170°C. ΔT can be used as an index of stability against devitrification. Generally, a high ΔT means that the stability against devitrification of the glass is high. In the present embodiment, the glass transition temperature (T ｇ ) and crystallization initiation temperature (T ｘ ) can be measured by differential thermal analysis.

[0047] From the above perspective, the optical glass according to this embodiment can be suitably used, for example, as an optical element provided in optical equipment. Examples of such optical elements include mirrors, lenses, prisms, and filters. Examples of optical systems that use the optical elements include objective lenses, condenser lenses, imaging lenses, and interchangeable lenses for cameras. These optical systems can be suitably used in various optical devices, such as imaging devices, such as interchangeable-lens cameras and non-interchangeable-lens cameras, and microscopes, such as fluorescence microscopes and multiphoton microscopes. Such optical devices are not limited to the imaging devices and microscopes described above, but also include, but are not limited to, telescopes, binoculars, laser rangefinders, projectors, and the like. Examples of these optical devices are described below.

[0048] <Imaging Device> FIG. 1 is a perspective view showing an example of an imaging device using the optical device according to this embodiment. The imaging device 1 is a so-called digital single-lens reflex camera (interchangeable lens camera), and the taking lens 103 (optical system) includes an optical element whose base material is the optical glass according to this embodiment. A lens barrel 102 is detachably attached to a lens mount (not shown) of a camera body 101. Light passing through the lens 103 of the lens barrel 102 forms an image on a sensor chip (solid-state image sensor) 104 of a multi-chip module 106 disposed on the rear side of the camera body 101. This sensor chip 104 is a bare chip such as a so-called CMOS image sensor, and the multi-chip module 106 is, for example, a COG (chip-on-glass) type module in which the sensor chip 104 is bare-chip mounted on a glass substrate 105.

[0049] 2 and 3 are schematic diagrams showing another example in which the optical device according to the present embodiment is used as an imaging device. Fig. 2 shows a front view of the imaging device CAM, and Fig. 3 shows a rear view of the imaging device CAM. The imaging device CAM is a so-called digital still camera (a camera with a non-interchangeable lens), and the taking lens WL (optical system) includes an optical element whose base material is the optical glass according to the present embodiment.

[0050] When the power button (not shown) of the imaging device CAM is pressed, the shutter (not shown) of the taking lens WL is opened, light from the subject (object) is collected by the taking lens WL, and an image is formed on the imaging element located on the image plane. The subject image formed on the imaging element is displayed on the liquid crystal monitor M1 located behind the imaging device CAM. After the photographer decides the composition of the subject image while looking at the liquid crystal monitor M1, he or she presses the release button B1 to capture the subject image with the imaging element, which is then recorded and saved in memory (not shown).

[0051] The image pickup device CAM is provided with an auxiliary light emitting unit EF that emits auxiliary light when the subject is dark, a function button B2 that is used to set various conditions for the image pickup device CAM, and the like.

[0052] Optical systems used in such digital cameras and the like are required to have higher resolution, lower chromatic aberration, and smaller size. To achieve these, it is effective to use glasses with different dispersion characteristics in the optical system. In particular, glasses with low dispersion and a high partial dispersion ratio (P ｇ , Ｆ ) is in high demand. From this perspective, the optical glass according to this embodiment is suitable as a component of such optical equipment. Note that optical equipment to which this embodiment can be applied is not limited to the imaging device described above, but also includes, for example, projectors. The optical element is also not limited to a lens, but also includes, for example, a prism.

[0053] <Microscope> Figure 4 is a block diagram showing an example of the configuration of a multiphoton microscope 2 according to this embodiment. The multiphoton microscope 2 includes an objective lens 206, a condenser lens 208, and an imaging lens 210. At least one of the objective lens 206, the condenser lens 208, and the imaging lens 210 includes an optical element whose base material is the optical glass according to this embodiment. The following description will focus on the optical system of the multiphoton microscope 2.

[0054] The pulsed laser device 201 emits ultrashort pulsed light, for example, with a near-infrared wavelength (approximately 1000 nm) and a pulse width in femtosecond units (e.g., 100 femtoseconds). The ultrashort pulsed light immediately after being emitted from the pulsed laser device 201 is generally linearly polarized in a predetermined direction.

[0055] The pulse splitting device 202 splits the ultrashort pulsed light, increases the repetition frequency of the ultrashort pulsed light, and emits it.

[0056] The beam adjusting unit 203 has functions such as a function to adjust the beam diameter of the ultrashort pulsed light incident from the pulse splitting device 202 to match the pupil diameter of the objective lens 206, a function to adjust the focusing and divergence angles of the ultrashort pulsed light in order to correct axial chromatic aberration (focus difference) between the wavelength of the light emitted from the sample S and the wavelength of the ultrashort pulsed light, and a pre-chirp function (group velocity dispersion compensation function) to impart reverse group velocity dispersion to the ultrashort pulsed light in order to correct the pulse width of the ultrashort pulsed light being widened by group velocity dispersion while passing through the optical system.

[0057] The repetition frequency of the ultrashort pulsed light emitted from the pulsed laser device 201 is increased by the pulse dividing device 202, and the above-mentioned adjustment is performed by the beam adjusting unit 203. The ultrashort pulsed light emitted from the beam adjusting unit 203 is then reflected by the dichroic mirror 204 in the direction of the dichroic mirror, passes through the dichroic mirror 205, and is collected by the objective lens 206 to be irradiated onto the sample S. At this time, the ultrashort pulsed light may be scanned over the observation surface of the sample S by using a scanning means (not shown).

[0058] For example, when observing the fluorescence of a sample S, the fluorescent dye with which the sample S is stained undergoes multiphoton excitation in the area of ​​the sample S irradiated with the ultrashort pulsed light and in its vicinity, emitting fluorescence (hereinafter referred to as "observation light") having a wavelength shorter than that of the ultrashort pulsed light, which is an infrared wavelength.

[0059] Observation light emitted from the sample S in the direction of the objective lens 206 is collimated by the objective lens 206 and is reflected by or transmitted through the dichroic mirror 205 depending on its wavelength.

[0060] The observation light reflected by the dichroic mirror 205 enters the fluorescence detection unit 207. The fluorescence detection unit 207 is composed of, for example, a barrier filter, a PMT (photomultiplier tube), etc., receives the observation light reflected by the dichroic mirror 205, and outputs an electrical signal corresponding to the amount of light. Furthermore, the fluorescence detection unit 207 detects the observation light across the observation surface of the sample S as the ultrashort pulsed light scans the observation surface of the sample S.

[0061] It is also possible to remove the dichroic mirror 205 from the optical path so that all of the observation light emitted from the sample S in the direction of the objective lens 206 is detected by the fluorescence detection unit 211. In this case, the observation light is descanned by a scanning means (not shown), transmitted through the dichroic mirror 204, collected by the collecting lens 208, passed through a pinhole 209 provided at a position approximately conjugate with the focal position of the objective lens 206, transmitted through an imaging lens 210, and incident on the fluorescence detection unit 211.

[0062] The fluorescence detection unit 211 is configured with, for example, a barrier filter, a PMT, etc., receives the observation light imaged on the light receiving surface of the fluorescence detection unit 211 by the imaging lens 210, and outputs an electrical signal according to the amount of light. Furthermore, the fluorescence detection unit 211 detects the observation light across the observation surface of the sample S as the ultrashort pulsed light scans the observation surface of the sample S.

[0063] It is also possible to remove the dichroic mirror 205 from the optical path so that all of the observation light emitted from the sample S in the direction of the objective lens 206 is detected by the fluorescence detection unit 211 .

[0064] Furthermore, observation light emitted from the sample S in the direction opposite to the objective lens 206 is reflected by the dichroic mirror 212 and enters the fluorescence detection unit 213. The fluorescence detection unit 213 is composed of, for example, a barrier filter, a PMT, etc., and receives the observation light reflected by the dichroic mirror 212 and outputs an electrical signal according to the amount of light. Furthermore, the fluorescence detection unit 213 detects the observation light across the observation surface of the sample S as the ultrashort pulsed light scans the observation surface of the sample S.

[0065] The electrical signals output from the fluorescence detection units 207, 211, and 213 are input, for example, to a computer (not shown), which can generate an observation image based on the input electrical signals, display the generated observation image, and store the data of the observation image.

[0066] <Cemented Lens> Fig. 5 is a schematic diagram showing an example of a cemented lens according to this embodiment. The cemented lens 3 is a compound lens having a first lens element 301 and a second lens element 302. At least one of the first lens element and the second lens element uses the optical glass according to this embodiment. The first lens element and the second lens element are cemented together via a cementing member 303. A known adhesive or the like can be used as the cementing member 303. Note that the term "lens element" refers to each of the lenses that make up a single lens or a cemented lens.

[0067] The cemented lens according to this embodiment is useful from the viewpoint of correcting chromatic aberration, and can be suitably used in the optical elements, optical systems, optical devices, and the like described above. Furthermore, optical systems including cemented lenses can be particularly suitably used in interchangeable lenses for cameras, optical devices, and the like. While the above-described embodiment has been described as a cemented lens using two lens elements, this is not limiting, and a cemented lens using three or more lens elements may also be used. When a cemented lens using three or more lens elements is used, it is sufficient that at least one of the three or more lens elements is formed using the optical glass according to this embodiment.

[0068] <Method for manufacturing optical glass> The optical glass according to this embodiment can be manufactured using, for example, a levitation furnace. Levitation furnaces include electrostatic, electromagnetic, sonic, magnetic, and gas jet types, and are not particularly limited, but it is preferable to use a gas jet type levitation furnace for levitation melting of oxides. Below, a manufacturing method using a gas jet type levitation furnace will be described as an example.

[0069] FIG. 6 is a schematic diagram showing the overall configuration of a gas jet levitation furnace, and FIG. 7 is an enlarged schematic diagram of a pedestal on a stage of the gas jet levitation furnace.

[0070] In the gas jet type levitation furnace 4, the raw material M is placed on a pedestal 402 on a stage 401. Then, laser light L emitted from a laser light source 403 is irradiated onto the raw material M via mirrors 404 and 405. The temperature of the raw material M heated by the irradiation of the laser light L is monitored by a radiation thermometer 406. Based on the temperature information of the raw material M monitored by the radiation thermometer 406, the output of the laser light source 403 is controlled by a computer 407. In addition, the state of the raw material M is photographed by a CCD camera 408, and the photograph is output to a monitor 409 (see FIG. 6). It should be noted that, for example, a carbon dioxide laser can be used as the laser light source.

[0071] In the gas jet levitation furnace 4, the raw material M is levitated by the gas sent to the pedestal (see FIG. 7). The flow rate of the gas sent to the pedestal is controlled by a gas flow regulator 410. For example, gas can be sprayed from a nozzle with a conical hole, and the raw material M can be levitated while being heated non-contact with a laser beam L. When the raw material M melts, it takes on a spherical or ellipsoidal shape due to its own surface tension and remains levitated in that state.

[0072] Thereafter, when the laser light L is shut off, the molten raw material is cooled, and transparent glass is obtained. The type of gas is not particularly limited, and any known gas can be used as appropriate, such as oxygen, nitrogen, carbon dioxide, argon, air, etc. The shape of the nozzle and the heating method are also not particularly limited, and any known method can be used as appropriate.

[0073] Conventionally, when optical glass is manufactured using a container such as a crucible, SiO ２ , B ２ O ３ , P ２ O ５ , GeO ２It has been necessary to enhance glass-forming ability by including a large amount of a network-forming oxide such as ZnO. Therefore, when a glass composition containing a large amount of a material that is not a network-forming oxide and a small amount of the above-mentioned network-forming oxide is used, crystallization (heterogeneous nucleation) originating from the container-melt interface occurs, often making vitrification impossible. Furthermore, glass gobs are sometimes used as materials for optical lenses in various optical instruments, and it is desirable to be able to stably produce large glass gobs.

[0074] In this regard, in this embodiment, for example, when optical glass is produced by the method using the levitation furnace described above, there is no contact between the container and the melt, so heterogeneous nucleation can be minimized. As a result, glass formation from the melt is greatly promoted, making it possible to vitrify compositions that contain little or no network-forming oxides, which are impossible to produce by crucible melting. By adopting this production method, optical glass of the composition according to this embodiment, which could not be vitrified in the past, can be produced. Furthermore, large glass gobs such as those described above can also be produced. In addition, the optical glass according to this embodiment has a high refractive index and a high Abbe number. Because the optical glass according to this embodiment has many advantages, it can be used as a high-refractive-index, low-dispersion glass material or a broadband transmission material.

[0075] Next, examples of the present invention and comparative examples will be described, but the present invention is not limited to these.

[0076] <Preparation of Optical Glass> The optical glasses according to each example and comparative example were prepared using a gas-jet levitation furnace 4 shown in FIGS. 6 and 7 according to the following procedure. First, glass raw materials selected from oxides were weighed to obtain the composition (mol % of cations) shown in each table. The glass raw materials may also be selected from hydroxides, carbonates, nitrates, and sulfates. Next, the weighed raw materials were mixed in an alumina mortar. These raw materials were uniaxially pressed at 20 MPa to form cylindrical pellets. The resulting pellets were fired in an electric furnace at 1000 to 1300°C in air for 3 to 6 hours to produce sintered bodies. The resulting sintered bodies were roughly crushed, and 50 to 4000 mg of each were placed in a pedestal nozzle. The raw materials were then melted by irradiating them from above with a carbon dioxide laser while injecting air gas. The melted raw materials formed a spherical or ellipsoidal shape due to their own surface tension and were suspended in a levitation state due to the gas pressure. The raw materials were cooled by shutting off the laser output when they were completely melted. Further annealing was performed at temperatures of 760 to 810°C for 10 hours, yielding gobs (glass spheres) for each example with diameters of 10.30 to 14.55 mm and thicknesses of 5.20 to 6.04 mm. No visible volatilization was observed during melting of the glass in each example, and no bubbles or devitrification were observed.

[0077] <Evaluation of Physical Properties> FIGS. 8 and 9 are graphs plotting the optical constants of each example.

[0078] Crystallization initiation temperature (T ｘ ), glass transition temperature (T ｇ ), and the temperature difference (ΔT) is measured. ｘ ) and glass transition temperature (T ｇ ) were measured by differential thermal analysis during the temperature rise process (temperature rise rate: 10°C / min), and T ｘ -T ｇ was defined as the temperature difference (ΔT).

[0079] Specific gravity (S ｇ ) Specific gravity of each sample (S ｇ ) was measured by Archimedes' method. The specific gravity value was rounded to three decimal places.

[0080] Diameter (D) and Thickness (T) The diameter (D) and thickness (T) of each sample were measured with an electronic caliper.

[0081] Refractive index (n ｄ ) and Abbe number (ν ｄ The samples of the examples were processed into a 90-degree prism, and the refractive index was measured by the V-block method using a refractive index measuring instrument (manufactured by Kalnew Optical Industries Co., Ltd.; "KPR-3000"), and the Abbe number and partial dispersion ratio were calculated.

[0082] In the comparative example, the refractive index was measured and the Abbe number was calculated by the prism coupling method using a prism coupler (manufactured by Metricon, model "2010 / M"). In the prism coupling method, a glass sample was polished, the polished surface was attached to a single crystal rutile prism, and the angle of total reflection when light of the measurement wavelength was incident was measured to determine the refractive index. Five measurements were taken at each of three wavelengths: 473 nm, 594.1 nm, and 656 nm, and the average value was used as the measured value. Furthermore, the obtained measured values ​​were fitted by the least squares method using the following Drude-Voigt dispersion equation, and the refractive indexes at the d-line (587.562 nm), F-line (486.133 nm), and C-line (656.273 nm) and the Abbe number (ν ｄ ) was calculated.

[0083]

[0084] (n: refractive index, m: electron mass, c: speed of light, e: elementary charge, N: number of molecules per unit volume, f: oscillator strength, λ ０ : characteristic resonance wavelength, λ: wavelength)

[0085] n ｄ indicates the refractive index of glass for light of 587.562 nm. ｄ ) was calculated using the following formula (2): Ｃ , n Ｆ , and represent the refractive index of the glass for light with wavelengths of 656.273 nm and 486.133 nm, respectively. ｄ = (n ｄ −1) / (n Ｆ -n Ｃ ) (2) The refractive index value was rounded to six decimal places.

[0086] Partial dispersion ratio (P ｇ , Ｆ ) The partial variance ratio (P ｇ , Ｆ ) is the primary variance (n Ｆ -n Ｃ ) partial variance (n ｇ -n Ｆ ) and was calculated using the following formula (3): ｇ indicates the refractive index of the glass for light with a wavelength of 435.835 nm. ｇ , Ｆ ) values ​​were rounded to four decimal places. ｇ , Ｆ = (n ｇ -n Ｆ ) / (n Ｆ -n Ｃ ) ... (3)

[0087] Internal transmittance The internal transmittance of each sample was measured using a spectrophotometer (Hitachi High-Tech Science Corporation; "Ultraviolet-Visible-Infrared Spectrophotometer UH4150") to measure the transmittance of a 4-9 mm thick parallel-polished product at wavelengths of 300 to 700 nm, and then the refractive index measurement data was used to remove and correct the contribution to transmittance due to reflectance at each wavelength, and the value was converted to the transmittance for a 10 mm thickness. Fitting was performed using the least squares method from the refractive index data in the V-block method for 10 emission lines of h, g, F', F, e, d, C', C, r, and t lines using the following dispersion curve equation.

[0088]

[0089] The refractive index value n at each wavelength λ calculated using the dispersion curve equation λ The transmittance T is calculated by taking into account the surface reflectance R of each wavelength and the multiple reflections of the incident light on the front and back surfaces, assuming that there is no internal light absorption. ｔｈ The external transmittance measured value T at a thickness of t mm was calculated by the following formula. eｘｐ and T ｔｈ Using the internal transmittance T (ｔｍｍ) was calculated.

[0090]

[0091] The internal transmittance T at the thickness t mm calculated above (ｔｍｍ) Using this, the transmittance value T (１０ｍｍ) was calculated using the following formula:

[0092]

[0093] Each table shows the composition and physical properties of each example and comparative example. Unless otherwise specified, the content of each component is based on the mole percent of cation. Furthermore, each physical property is a value for glass in an unpressed state.

[0094]

[0095]

[0096]

[0097]

[0098] From the above, it was confirmed that the optical glass of each Example combines high refractive index, high transmittance, low specific gravity, and devitrification resistance at a high level, and furthermore, when produced by the float melting method, can be made large enough to have a diameter of 10 mm or more.

[0099] 1...imaging device, 101...camera body, 102...lens barrel, 103...lens, 104...sensor chip, 105...glass substrate, 106...multi-chip module, CAM...imaging device (non-interchangeable lens camera), WL...taking lens, M1...liquid crystal monitor, EF...fill-in light emitting unit, B1...release button, B2...function button, 2...multiphoton microscope, 201...pulse laser device, 202...pulse splitting device, 203...beam adjustment unit, 204, 205, 212...dichroic mirror, 206... ..Objective lens, 207, 211, 213...Fluorescence detection unit, 208...Condenser lens, 209...Pinhole, 210...Imaging lens, S...Sample, 3...Cemented lens, 301...First lens element, 302...Second lens element, 303...Cemented member, 4...Gas levitation furnace, 401...Stage, 402...Pedestal, 403...Laser light source, 404, 405...Mirror, 406...Radiation thermometer, 407...Computer, 408...CCD camera, 409...Monitor, 410...Gas flow regulator, L...Laser light, M...Raw material

Claims

1. In terms of molar percentage of cations, La ３＋ Content: 5 - 35%, Si ４＋ Content: 5 - 25%, Nb ５＋ Content: 5 - 35%, Al ３＋ Content: 5 - 35%, Ti ４＋ , Zr ４＋ , Nb ５＋ , Ta ５＋ and Al ３＋ The total content of (Ti ４＋ + Zr ４＋ + Nb ５＋ + Ta ５＋ + Al ３＋ ): 45 - 80%, is an optical glass.

2. In terms of molar percentage of cations, Ti ４＋ Content: 0 - 20%, the optical glass according to Claim 1.

3. In terms of molar percentage of cations, La ３＋ Content: 5 - 35%, Si ４＋ Content: 5 - 25%, Nb ５＋ Content: 5 - 35%, Ti ４＋ Content: 0 - 20%, Ti ４＋ , Zr ４＋ , Nb ５＋ , Ta ５＋ and Al ３＋ The total content of (Ti ４＋ + Zr ４＋ + Nb ５＋ + Ta ５＋ + Al ３＋ ): 45 - 80%, is an optical glass.

4. In terms of molar percentage of cations, Zr ４＋ Content: 0 - 15%, the optical glass according to any one of Claims 1 to 3.

5. In terms of molar percentage of cations, Ta ５＋ Content: 0 to 15%, the optical glass according to any one of claims 1 to 3.

6. In terms of molar percentage of cations, Y ３＋ Content: 0 to 15%, the optical glass according to any one of claims 1 to 3.

7. B ３＋ The optical glass according to any one of claims 1 to 3, which does not substantially contain.

8. The wavelength (λ80) at which the internal transmittance of the optical glass is 80% per 10 mm is 420 nm or less, the optical glass according to any one of claims 1 to 3.

9. The refractive index of the optical glass with respect to the d-line is 1.95 to 2.15, the optical glass according to any one of claims 1 to 3.

10. The Abbe number of the optical glass is 20 to 35, the optical glass according to any one of claims 1 to 3.

11. The partial dispersion ratio (P ｇ , Ｆ ) of the optical glass satisfies the following formula -0.00403 × ν ｄ + 0.704 < P ｇ,Ｆ < -0.00403 × ν ｄ + 0.717... (1) The optical glass according to any one of claims 1 to 3 that satisfies.

12. The specific gravity (S ｇ ) of the optical glass is 4.6 to 5.6, the optical glass according to any one of claims 1 to 3.

13. The temperature difference (ΔT = T ｇ ) between the glass transition temperature (T ｘ ) and the crystallization start temperature (T ｘ - T ｇThe optical glass according to any one of claims 1 to 3, wherein the [condition] is 80 to 200 °C.

14. The optical glass according to any one of claims 1 to 3, wherein the length in the major axis direction of the optical glass is 10 mm or more.

15. An optical element using the optical glass according to any one of claims 1 to 3.

16. An optical system including the optical element according to claim 15.

17. An objective lens for a microscope including the optical system according to claim 16.

18. An interchangeable lens for a camera including the optical system according to claim 16.

19. An optical device including the optical system according to claim 16.

20. Having a first lens element and a second lens element, A cemented lens, wherein at least one of the first lens element and the second lens element is the optical glass according to any one of claims 1 to 3.

21. An optical system including the cemented lens according to claim 20.

22. An objective lens for a microscope including the optical system according to claim 21.

23. An interchangeable lens for a camera including the optical system according to claim 21.

24. An optical device including the optical system according to claim 21.