JP3463941B2 - Polycrystalline transparent ceramics for laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to yttrium aluminum garnet (YAG) and gadolinium gallium garnet (GGG) which are suitably used as a laser oscillation element and have a garnet structure. ), And polycrystalline transparent ceramics for laser such as gadolinium, scandium, gallium, garnet (GSGG). [0002] Garnet-structured solid-state lasers represented by YAG occupy about 95% of the market, and are applied to a wide variety of applications such as fine processing of semiconductors, cutting and heat treatment of steel materials and ceramics, and laser scalpels for medical use. In recent years, green and blue lasers whose wavelength has been converted using an SHG (second harmonic) element have been used for writing operations on magneto-optical recording materials. [0003] Incidentally, YAG to which Nd and other light-emitting elements are added as elements involved in light emission is manufactured by the Czochralski method, the Bridgman-Stockberger method, etc., but all of them are single crystals. is there. [0004] When a single crystal YAG is produced by such a method, the growth temperature needs to be about 2000 ° C, and the growth rate is extremely slow at 0.2 to 0.3 mm / hr. From this, it takes about one month to manufacture one single crystal, and it is difficult for the manufactured single crystal YAG to have a uniform light emitting element. In particular, when a single crystal is grown only with the addition of the Nd element, it is not only difficult to uniformly disperse the light emitting element in the host material, but also the concentration is limited to about 1 atomic%. For this reason, even if a single crystal YAG is manufactured, only a part can be used as a laser material. In addition, since the single crystal growing technique requires an extremely expensive iridium crucible, the produced single crystal YAG is not only expensive but also unsatisfactory in terms of productivity. SUMMARY OF THE INVENTION The problem to be solved by the present invention is to provide a polycrystalline transparent ceramic for a laser which is free from the drawbacks in manufacturing and the raw material itself as in a single crystal and has excellent oscillation characteristics. Is to get [0006] The polycrystalline transparent ceramics for laser of the present invention comprises SiO ₂ , Li ₂ O, Na ₂ O,
Sintered with MgO, and one or two or more of the CaO, lanthanide element as a light emitting element, Cr element, one or porosity containing a two or more than 1% of the garnet structure in the Ti element And the average particle diameter of the particles constituting the sintered body is 5 to 1000 μm, and
Regarding the contained luminescent elements, 80% or more of the whole particles are ±
It is characterized in that the density difference is within the range of 15% and the internal loss of the linearly transmitted light is 30% / cm or less. The polycrystalline transparent ceramic for laser of the present invention is
A raw material powder having an appropriate particle size constituting YAG, GGG, GSGG is used, and SiO ₂ , Li ₂ O, Na ₂ O,
A laser oscillation function is added by sintering under appropriate conditions, containing one or more of MgO and CaO, and one or more luminous elements or sensitizing elements of lanthanide elements and Cr and Ti elements. A transparent high-density sintered body can be obtained. In the case of YAG, first, Y ₂ O ₃ and Al ₂ O ₃ having a purity of 99% by weight, preferably 99.9% by weight or more are used, and a lanthanide element oxide (La) serving as a light emitting element or a sensitizing element is used. ₂ O ₃ , CeO ₂ , Pr ₆ O ₁₁ , Nd ₂ O
₃ , Pm ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd
₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂
O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ ) and Ti
Oxides such as O ₂ and Cr ₂ O ₃ are weighed to have a garnet composition. Alternatively, a wet synthetic powder having a uniform composition in advance by an alkoxide method, a coprecipitation method, or the like is used. In addition to this, SiO ₂ , Li ₂ O , Na ₂ O, MgO, CaO
At least one oxide component is added in an appropriate amount. Here, Y ₂ O
_If the purity of ₃ and Al ₂ O ₃ is less than 99% by weight, it becomes difficult to obtain a good laser material due to the action of impurities. Further, in order to obtain the average particle diameter and density of the sintered body as claimed in the claims, the primary particle diameter of the raw material powder must be 1 μm.
It is preferred to use m ₂ or less of Al ₂ O ₃ and Y ₂ O ₃ . Oxide components such as SiO ₂ and Li ₂ O are:
As long as the amount is appropriate, the microstructure of the polycrystalline body can be improved and the heterophase (YAlO ₃ or Al ₂ O remaining in the sintered body can be improved).
₃ ), the transparency of the material (transparency of the host material) is improved, and as a result, the oscillation efficiency of the laser is improved. On the other hand, even when these oxides are added, the cation in the oxide has no electronic structure such as d or f electron,
There is almost no adverse effect on the laser oscillation characteristics. However, these elements replace the trivalent ions Al ³⁺ and Y ³⁺ in the YAG ceramics, but the monovalent element L 3
i, Na, divalent element Mg and Ca, and tetravalent element Si
Have different valences from Al and Y, respectively. For this reason, at the atomic level of a simple system, lattice defects occur at anion or cation sites in order to maintain the charge of the crystals in the polycrystal.
If the defect amount is relatively small, the optical characteristics are not deteriorated, but if it is too large, discoloration or the like due to lattice defects of the host material occurs. Therefore, when these elements are added, they should be added as little as possible, and elements having different valences should be properly combined (for example, divalent and tetravalent are added in equal amounts).
A host material having better optical characteristics can be obtained, and the amount of these oxides added is preferably in the range of 0.005 to 1.0% by weight. An organic solvent such as alcohol or distilled water is added to the compounded powder, mixed in a pot mill, and the mixed powder is dried under reduced pressure or normal pressure. The obtained powder is formed by a uniaxial press or a cold isostatic press (CIP) and then sintered. The means for sintering is not particularly limited, but in the case of vacuum sintering, a temperature range of 1600 to 1850 ° C., hot press (HP) or hot isostatic press (HIP)
In the case of (1), the desired sintered body is obtained by performing an appropriate sintering time treatment in a temperature range of 1400 to 1850 ° C. It is also possible to perform sintering in oxygen gas or hydrogen gas, and a desired sintered body can be obtained by combining those sintering methods. For use as a solid-state laser, the sintered body has a density of 99.0% or more (1% or less in porosity) of the theoretical density and an average particle diameter of the polycrystal of 5 to 5.
It needs to be in the range of 1000 μm. If the density of the sintered body is lower than 99.0%, the light transmittance is extremely reduced. The relative density of the sintered body can be determined by comparing the densities of a single crystal and a polycrystal having the same chemical composition measured by the Gakushin method or the X-ray method. As another method, it is also required to analyze an image obtained by observing the surface of pores existing inside the sintered body with a microscope, an SEM, or the like. Also, if the particle size of the sintered body is larger than 1000 μm, the light emitting element cannot be uniformly dissolved, or the light emitting element segregates at the grain boundary, and it is difficult to be optically uniform and transparent,
On the other hand, if it is smaller than 5 μm, transparency sufficient for practical use cannot be obtained. The transparency of the sintered body is preferably as high as possible because it has a close relationship with the oscillation efficiency when laser oscillation is performed. This value can be represented by a light absorption coefficient. That is, Lambert-Beer's law, log (I _o /
I) = αd [where I _o : incident light intensity, I: transmitted light intensity (intensity of light transmitted through the sample), α: light absorption coefficient,
d: sample thickness] must be 0.204 cm ^-1 , preferably 0.125 cm ^-1 or less. The transparency can also be represented by the internal loss of linearly transmitted light. When a sample having a thickness of 10 mm is irradiated with linear light, the internal loss must be 30% or less. This means that the thickness of 1 mm and 11 m
m means that the difference in the linear transmittance is within 30%. If the absorption loss inside the base material is larger than this, the absorption loss increases due to the amplification of light, causing not only laser oscillation but also destruction of the base material in some cases. The absorption loss of the base material is determined by a slope when the transmittance is plotted with respect to the thickness of the sample in a visible wavelength region where the light emitting element is not absorbed (or a background level of the transmittance with respect to the measurement wavelength). Although it is possible to predict that the laser oscillation efficiency tends to depend on the transparency of the base material, it is more preferable that the value be 20% or less (α = 0.
It is important to keep the loss at 125 cm ^-1 or less.
In addition, the absolute value of the transmittance (when the surface roughness of the sample is 0.
400 mm sample with a thickness of 1 mm
In the wavelength range of ９００900 nm, it is necessary that the linear transmittance of the portion excluding the absorption of the light-emitting element and the like is 75% or more. On the other hand, the uniformity of the light-emitting elements is the greatest advantage when a solid-state laser material is manufactured from a sintered body, and is an important technique particularly when a large-sized high-power laser is intended. Regarding the uniformity, 80% or more of each particle constituting the sintered body has a concentration difference of ± 15% (for example, a range containing 2 at% luminescent element is 2 ± 0.3%).
It is necessary to be in. The concentration distribution is determined by randomly analyzing about 50, at least about 20 particles of the sintered body. The concentration distribution of the light-emitting element and the sensitizing element in the sintered body can be easily measured by an instrument analyzer such as EDX (energy dispersive X-ray spectrometer) or IMA (ion microanalyzer) which measures a small area. A laser is originally a flash lamp or an LD.
A (laser diode) excites a light-emitting element existing in the material and continuously amplifies the light-emitting element, so that a strong laser beam can oscillate. Here, when a material having grain boundaries such as polycrystalline ceramics is excited and laser oscillation is performed, laser light amplified inside the grains is lost at the grain boundaries (attenuation due to heterophase, crystal defects, etc.). Generally, it is generally considered impossible to perform laser oscillation in a polycrystalline body. Even if the laser oscillates, the light loss at the grain boundary should be large, and the property deterioration is expected to be remarkable compared to the single crystal material. The current situation is exactly the same. Although the level of crystal defects (lattice defects) in a polycrystal should be originally lower than that of a single crystal (because it does not melt), near-perfect mass transfer hardly occurs during the sintering process, so that Or crystal structure defects. However, if such inconveniences are avoided, the optical characteristics inside the particles of the polycrystalline ceramics are higher than that of the single crystal, and the laser amplifying ability is increased. Although the light loss at the grain boundary cannot be denied, the loss at the grain boundary is reduced as much as possible, so that it can withstand practical use. In addition, the characteristics of a laser material include not only the transmittance but also various factors such as the uniformity of the light emitting element, the concentration of the light emitting element in the host material, and the distortion of the material. Since a crystal is more likely to be superior to a single crystal, there are some which are equivalent or superior to a single crystal in view of the overall characteristics. For example, regarding the distortion of a material, a single crystal has a remarkable residual distortion when observed through a polarizing plate, but a polycrystal has such excellent characteristics that such a distortion can hardly be detected. Further, the single crystal YAG containing Nd is
Not only is the concentration distribution of d non-uniform, but its concentration can only be up to about 1 atomic%, but in the case of polycrystalline YAG by sintering, its Nd concentration can be up to 10-12 atomic%, Moreover, the distribution can be extremely uniform. From this, it is considered that application to a new type of solid-state laser having features such as small size and high power is also possible. EXAMPLES As examples, polycrystalline transparent ceramics for lasers whose host material is YAG will be described. Al ₂ O ₃ , Y ₂ O ₃ , a lanthanide element as a light emitting element and a sensitizing element, and a total amount of Cr and Ti are 10
0 g was weighed, and further added thereto were SiO ₂ , Li ₂ O, Na ₂
A predetermined amount of each oxide of O, MgO and CaO is added, and each powder and ethyl alcohol 300c are put into a pot mill.
c. Further, 500 g of alumina balls were added and mixed for 24 hours. The mixed powder was dried under a reduced pressure of 500 mmHg, and the dried powder was lightly mixed in a mortar. This powder was preliminarily formed into a tablet having a diameter of 50 mm and a height of 15 mm, and then subjected to a rubber press under a pressure of 1000 kg / cm ² . The molded body was placed in an electric furnace at 100 ° C. /
After heating at a predetermined temperature and firing at a predetermined temperature, 100 ° C / hr
And cooled. From the obtained sintered body, diameter 6mm, thickness 10
mm sample was prepared, the surface roughness of both surfaces was finished to 5 nm, and the flatness was finished to 1 / 8λ. [Table 1] In Examples 1 to 12 shown in Table 1, the average particle size and porosity of the sintered body were changed by selecting the sintering temperature, sintering time, sintering atmosphere, and the like. The result of the oscillation characteristic when excited by a lamp is shown. Comparative Example Table 2 shows a single crystal in which the host material is YAG and contains 1 atomic% of a light emitting element and a polycrystalline YAG having a composition outside the scope of the claims. Comparative Example 1 was a 1 atom% Nd YAG single crystal grown by the conventional Czochralski method, and when excited with an 808 nm LD (300 mW), the output was 84 mW and the output efficiency was 28.0%. [Table 2] [Results] As is evident from Table 1, the laser output of the polycrystalline transparent ceramics for laser of the present example was increased when Nd and oxides were added, particularly as the Nd concentration increased. . As shown in Examples 7 and 8, the Nd element, which cannot be added by the conventional single crystal growing technique, can be increased in concentration, and the output can be increased about twice that of the conventional single crystal. . Examples 10 to 12 show examples in which a lanthanide element other than Nd was added, and all of them showed a considerably high level of laser oscillation efficiency. On the other hand, Comparative Examples 2 to 4 having an average particle diameter or porosity outside the scope of the claims have extremely low oscillation efficiency or do not oscillate. Comparative Example 5, which has the average particle diameter and porosity of the claims and does not include an additive element such as SiO ₂ , can secure a relatively high oscillation efficiency, but has the same average particle diameter and porosity. It can be seen that the oscillation efficiency is lower than that of Example 2 including the additional element. Although only the case where YAG is used as the host material is shown here, similar results were obtained with other ceramics having a garnet structure such as GGG and GSGG. According to the present invention, a laser can be oscillated by using a polycrystalline transparent ceramic having a cubic crystal structure. In terms of material characteristics, the material has characteristics such as an increase in the size of a material in which a light-emitting element capable of increasing the concentration of a light-emitting element (in particular, Nd) becomes uniform. For this reason, in addition to being industrially suitable for use as a normal laser, it is also possible to reduce the size and increase the output of the laser.
In addition, applications such as laser processing and laser fusion are expected, taking advantage of the advantages of achieving large size, uniformity, and high output. Even in consideration of economy, there is no need for a noble metal crucible (iridium) or an expensive single crystal growing apparatus which is indispensable for the conventional single crystal growing technique. In addition, in the sintering method, the temperature required for sintering the material is lower than its melting point,
Also, since the sintering time is about several to several tens of hours, the amount of electric power consumed for the synthesis is extremely small. Furthermore, since a large number of sintered bodies can be manufactured in one sintering furnace, and it can be manufactured efficiently using the near-net shape technology while keeping the shape close to the shape using the material, cost, mass production, economical efficiency (effective use of rare earth resources and There are advantages such as power cost reduction).

   ────────────────────────────────────────────────── ─── Continuation of front page       (56) References JP-A-3-218963 (JP, A)                 JP-A-2-283661 (JP, A)                 JP-A-2-92817 (JP, A)                 JP-A-4-175265 (JP, A)                 JP-A-3-252355 (JP, A)                 JP-A-50-127908 (JP, A)

Claims (1)

(57) [Claims 1] SiO ₂ , Li ₂ O, Na ₂ O, Mg
Sintering having a garnet structure with a porosity of 1% or less containing one or two or more of O and CaO and one or two or more of lanthanide elements, Cr elements and Ti elements as light emitting elements And the average particle diameter of the particles constituting the sintered body is 5 to 1000 μm, and 80% or more of all the particles of the luminescent elements contained in the constituent particles are ± 15.
%, And the internal loss of linearly transmitted light is not more than 30% / cm.