JPH05301770A - Polycrystalline transparent ceramic for laser - Google Patents

Abstract

PURPOSE:To provide the subject ceramic free from any defects in its production or its raw materials themselves, unlike single crystal, also excellent in oscillation characteristics. CONSTITUTION:The objective ceramic with garnet structure contains at least one kind among SiO2, Li2O, Na2O, MgO, and CaO and a lanthanide element plus Cr and/or Ti element(s) and also has the following characteristics: (1) the mean grain diameter of the sintered compact: 5-1000mum and (2) porosity: <=1%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to yttrium aluminum garnet (YAG), gadolinium gallium garnet (GGG), gadolinium scandium gallium garnet (gadolinium garnet), which is preferably used as a laser oscillator and has a garnet structure. GSGG) and other polycrystalline transparent ceramics for laser.

[0002]

2. Description of the Related Art Garnet type solid-state lasers represented by YAG occupy about 95% of the market, and are widely applied in various fields such as fine processing of semiconductors, cutting and heat treatment of steel materials and ceramics, and laser scalpels for medical use. Green and blue lasers whose wavelengths have been converted using SHG (second harmonic) elements are also used for writing operations in magneto-optical recording materials.

By the way, YAG added with Nd or other luminescent element as an element involved in light emission is produced by the Czochralski method or the Bridgman-Stockberger method, but all of them are single crystals. is there.

When a single crystal YAG is produced by such a method, the growing temperature is required to be about 2000 ° C. and the growing rate is 0.2 to 0.3 mm / hr, which is extremely slow. From this, it takes about one month to manufacture one single crystal, and it is difficult for the manufactured single crystal YAG to have uniform light emitting elements. Particularly, in the case of growing a single crystal only when the Nd element is added, it is not only difficult to uniformly disperse the light emitting element in the host material, but also its concentration is limited to about 1 atom%. For this reason, even if a single crystal YAG is manufactured, only a part of it can be used as a laser material. Further, since the single crystal growth technique requires an extremely expensive iridium crucible, it goes without saying that the single crystal YAG to be produced is expensive and the productivity is not sufficiently satisfactory.

[0005]

The problem to be solved by the present invention is to obtain polycrystalline transparent ceramics for lasers which have no manufacturing defects or defects of the raw material itself like single crystals and which have excellent oscillation characteristics. It is in.

[0006]

The polycrystalline transparent ceramics for laser having a garnet structure of the present invention is made of SiO ₂ , Li.
₂ O, Na ₂ O, MgO, CaO, and one or more of lanthanide element, Cr, and Ti element are contained, and the average particle diameter of the sintered body is 5 to 1000 μm and the porosity is 1% or less. This solves the above problem.

[0007]

The function of the polycrystalline transparent ceramics for laser of the present invention is
A raw material powder having an appropriate particle size such as YAG, GGG, GSGG is used, and SiO ₂ , Li ₂ O, Na ₂ O, Mg is used.
One or more of O, CaO, lanthanide element and C
By containing one or more luminescent elements or sensitizing elements of r and Ti elements and performing sintering under appropriate conditions, it is possible to obtain a transparent high-density sintered body to which a laser oscillation function is added. it can.

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 further an oxide (La) of a lanthanide element serving as a light emitting element or a sensitizing element is used. ₂ O ₃ , Ce ₂ O ₃ , 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 T
Oxides such as iO ₂ and Cr ₂ O ₃ are weighed so as to have a garnet composition. Alternatively, a wet synthetic powder having a uniform composition is used in advance by an alkoxide method or a coprecipitation method.
SiO ₂ and Li ₂ O , Na ₂ O, MgO, Ca
An appropriate amount of one or more O oxide components is added. Where Y ₂
If the purity of O 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. In order to obtain the average particle diameter and density of the sintered body within the scope of the claims, the primary particle diameter of the raw material powder is 1 μm.
It is preferable to use Al ₂ O ₃ and Y ₂ O ₃ of m or less.

Oxide components such as SiO ₂ and Li ₂ O are
As long as the amount is appropriate, the microstructure of the polycrystalline body is improved and the heterogeneous phase (YAlO ₃ or Al ₂ O remaining in the sintered body
₃ ) is eliminated, the transparency of the material (the 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 does not have an electronic structure such as d and f electrons,
There is almost no adverse effect on the laser oscillation characteristics. However, these elements replace Al ³⁺ and Y ³⁺ which are trivalent ions in the YAG ceramics, but the monovalent element L
i, Na, divalent element Mg, Ca, and tetravalent element Si
Has a valence different from that of Al or Y. Therefore, at the atomic level of a simple system, lattice defects occur at anion or cation sites in order to maintain the charge of crystals in the polycrystalline body.
This defect amount does not deteriorate the optical characteristics at a relatively small level, but if it is too large, it causes discoloration and the like due to lattice defects of the host material. Therefore, when adding these elements, by adding as little as possible and by properly combining elements having different valences (for example, adding divalent and tetravalent in equal amounts),
A host material having better optical properties can be obtained, and the addition amount of these oxides 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 blended powder and mixed in a pot mill, and the mixed powder is dried under reduced pressure or normal pressure. The powder obtained is molded 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, the temperature range is 1600 to 1850 ° C., hot press (HP) or hot isostatic press (HIP).
In the case of 1, the target sintered body can be obtained by performing an appropriate sintering time in the temperature range of 1400 to 1850 ° C. It is also possible to sinter in oxygen gas or hydrogen gas, and the desired sintered body can be obtained by combining these sintering methods.

For use as a solid-state laser, the density of the sintered body is 99.0% or more of the theoretical density (porosity is 1% or less), and the average particle diameter constituting the polycrystalline body is 5 to 5.
It must be in the range of 1000 μm. If the density of the sintered body is lower than 99.0%, the light transmittance will be extremely reduced. The relative density of the sintered body can be obtained 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 the image of the surface of the pores existing inside the sintered body with a microscope or SEM. Further, when the particle size of the sintered body is larger than 1000 μm, the light emitting element cannot be uniformly solid-dissolved, or the light emitting element is segregated at the grain boundary portion, which makes it difficult to obtain an optically homogeneous and transparent material.
On the other hand, if it is less than 5 μm, the transparency for practical use cannot be obtained.

It is desirable that the transparency of the sintered body is as high as possible because it has a close relationship with the oscillation efficiency when laser oscillation is performed. This value can be expressed 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,
The value of α in [d: sample thickness] is required to be 0.204 cm ⁻¹ , preferably 0.125 cm ⁻¹ or less. The transparency can also be expressed by the internal loss of linearly transmitted light, and when a sample having a thickness of 10 mm is irradiated with linear light, the internal loss needs to be 30% or less. This means that for samples with the same surface processing accuracy, thicknesses of 1 mm and 11 m
The difference in the linear transmittance of the sample of m is within 30%. If the absorption loss inside the base material is larger than this, the absorption loss becomes large due to the amplification of light, and not only laser oscillation does not occur, but also the base material is destroyed in some cases. The absorption loss of the base material is determined by the slope when the transmittance is plotted against the thickness of the sample in the visible wavelength range (or the background level of the transmittance with respect to the measurement wavelength) where there is no absorption of the luminescent element. It can be predicted that the laser oscillation efficiency depends on the transparency of the base material, but the value is more preferably 20% or less (α = 0.
It is important to stop the loss below 125 cm ^-1 ).
Also, regarding the absolute value of the transmittance (the surface roughness of the sample is 0.
400 mm sample with a thickness of 1 mm (limited to 1 μm or less)
In the wavelength range of up to 900 nm, it is also 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 element is the greatest advantage when producing a solid-state laser material from a sintered body, and is an important technique particularly when a large-sized large-power laser is intended. Regarding the homogeneity, 80% or more of the particles constituting the sintered body have a concentration difference within a range of ± 15% (for example, a range containing 2 atomic% of a luminescent element is within a range of 2 ± 0.3%).
Need to be in. The concentration distribution is determined by randomly analyzing about 50 particles, at least about 20 particles of the sintered body. The concentration distribution of the luminescent element or the sensitizing element in the sintered body can be easily measured by an instrument analyzer such as EDX (energy dispersive X-ray spectroscope) or IMA (ion microanalyzer) that measures a minute region.

The laser is originally a flash lamp or LD
A (laser diode) excites a light emitting element existing inside the material and continuously amplifies the light emitting element, so that a strong laser beam can be oscillated. Here, when a material having grain boundaries such as polycrystalline ceramics is excited to cause laser oscillation, the laser light amplified inside the grains is lost at the grain boundary portion (attenuation due to different phase or crystal defect). Generally, it is considered impossible to oscillate a laser in a polycrystalline body. Moreover, even if laser oscillation occurs, the optical loss at the grain boundary should be large, and it is expected that the characteristic deterioration will be remarkable compared to the single crystal material, so it is considered that all solid-state laser materials should be single crystals. The current situation is exactly the same. Although the level of crystal defects (lattice defects) inside the grain of the polycrystalline body should be lower than that of the single crystal originally (because it does not melt), it is difficult for near-perfect mass transfer to occur during the sintering process, so the texture inside the grain A crystalline or crystal structure defect is left. However, if such an inconvenience is avoided, the optical characteristics inside the grains of the polycrystalline ceramic exceed that of the single crystal, and the amplification capability of the laser becomes high. Although the optical loss at the grain boundary portion cannot be denied, it is possible to withstand practical use by reducing the loss at the grain boundary portion as much as possible. Further, the characteristics of a laser material are not only all of this transmittance but also various factors such as the uniformity of the luminescent element, the concentration of the luminescent element in the host material, and the distortion of the material. Since it is highly possible that the crystalline body is superior to the single crystalline body, there are some that are equivalent to or superior to the single crystalline body in view of the entire characteristics. For example, regarding the strain of the material, a considerable residual strain can be confirmed when observed through a polarizing plate in a single crystal, but such a strain is hardly detected in a polycrystalline body, which is an excellent feature.

The single crystal YAG containing Nd is N
Not only is the concentration distribution of d non-uniform, but its concentration can be contained only up to about 1 atom%, but in the case of polycrystalline YAG by sintering, its Nd concentration can be contained up to 10-12 atom%, Moreover, the distribution can be made extremely uniform. From this, it is considered that it can be applied to a new solid-state laser having features such as small size and high power.

[0016]

EXAMPLE As an example, a polycrystalline polycrystalline ceramics for a laser whose host material is YAG will be described.

The total amount of Al ₂ O ₃ and Y ₂ O ₃ and the lanthanide element as a luminescent element and a sensitizing element and Cr and Ti is 10
Weigh 0 g, and add SiO ₂ , Li ₂ O, Na ₂
Add a predetermined amount of each oxide of O, MgO, CaO, and put each powder and ethyl alcohol 300c into the pot mill.
c, and 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 preformed into a tablet having a diameter of 50 mm and a height of 15 mm and then rubber-pressed at a pressure of 1000 kg / cm ² .

This molded product was placed in an electric furnace and heated to 100 ° C /
After raising the temperature at hr and firing at a predetermined temperature, 100 ° C / hr
Cooled in. Diameter 6 mm, thickness 10 from the obtained sintered body
A sample of mm was prepared, and the surface roughness of both surfaces was 5 nm and the parallelism was ⅛λ.

[0020]

[Table 1] In Examples 1 to 12 shown in Table 1, the average particle diameter and porosity of the sintered body were changed by selecting the sintering temperature, the sintering time, the firing atmosphere, etc. The results of oscillation characteristics when excited by a lamp are shown.

Comparative Example Table 2 shows a single crystal containing YAG as a host material and containing 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 it was excited by an 808 nm LD (300 mW), the output was 84 mW and the output efficiency was 28.0%.

[0022]

[Table 2] [Results] As is clear from Table 1, in the polycrystalline transparent ceramics for laser of the present example, when Nd and an oxide were added, the laser output increased especially with an increase in Nd concentration. .. As shown in Examples 7 and 8, it is possible to increase the concentration of the Nd element, which cannot be added by the conventional single crystal growth technique, and it is possible to increase the output about twice as much as that of the conventional single crystal. .. In addition, Examples 10 to 12 show examples in which a lanthanide element other than Nd is added, but all of them showed considerably high level laser oscillation efficiency.

On the other hand, Comparative Examples 2 to 4 having an average particle diameter or porosity outside the scope of claims have extremely low oscillation efficiency or no oscillation. Comparative Example 5 having the average particle size and porosity within the scope of the claims and having no added element such as SiO ₂ can ensure a relatively high oscillation efficiency, but with the same average particle size and porosity. It can be seen that the oscillation efficiency is reduced as compared with Example 2 including the additive element.

Although only the case where YAG is used as the host material is shown here, the same result was obtained with other garnet structure ceramics such as GGG and GSGG.

[0025]

According to the present invention, it becomes possible to oscillate a laser by using a polycrystalline transparent ceramic having a cubic crystal structure. In terms of material characteristics, it is possible to increase the concentration of the light emitting element (particularly Nd), and it is possible to increase the size of a material in which the light emitting element is uniform and the like. Therefore, in addition to being industrially suitable for use as a laser, it is possible to downsize and increase the output of the laser, so that the application as a microchip laser has become a hot topic recently,
Furthermore, applications such as laser processing and laser fusion are expected, taking advantage of the advantages of large size, uniformization, and higher output.

Further, in consideration of economy, the precious metal crucible (iridium) and the expensive single crystal growing apparatus which are indispensable in the conventional single crystal growing technique are not required, which is advantageous. In addition, in the sintering method, the temperature required for sintering the material is lower than its melting point,
Moreover, since the sintering time is about several to several tens of hours, the amount of electric power consumed for the synthesis is remarkably small. Furthermore, since a large number of sintered bodies can be produced in one sintering furnace and efficient production can be performed with the near net shape technology while maintaining a shape close to the shape of the material used, cost, mass production and economic efficiency (effective use of rare earth resources and (Electricity cost reduction) etc.

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[Procedure amendment]

[Submission date] June 3, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

The function of the polycrystalline transparent ceramics for laser of the present invention is
A raw material powder having an appropriate particle size which constitutes YAG, GGG, GSGG is used, and SiO ₂ , Li ₂ O, Na ₂ O,
A laser oscillation function was added by containing at least one of MgO and CaO, and at least one luminescent element or sensitizing element such as a lanthanide element and Cr or Ti element and performing sintering under appropriate conditions. It is possible to obtain a transparent high density sintered body.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

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 further an oxide (La) of a lanthanide element 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 so as to have a garnet composition. Alternatively, a wet synthetic powder having a uniform composition is used in advance by an alkoxide method or a coprecipitation method. SiO ₂ and Li ₂ O , Na ₂ O, MgO, CaO
Add one or more appropriate amount of the oxide component. Where 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. In order to obtain the average particle diameter and density of the sintered body within the scope of the claims, the primary particle diameter of the raw material powder is 1 μm.
It is preferable to use Al ₂ O ₃ and Y ₂ O ₃ of m or less.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0019

[Correction method] Change

[Correction content]

This molded product was placed in an electric furnace and heated to 100 ° C /
After raising the temperature at hr and firing at a predetermined temperature, 100 ° C / hr
Cooled in. Diameter 6 mm, thickness 10 from the obtained sintered body
A sample having a size of 2 mm was prepared, and the surface roughness of both surfaces was 5 nm and the flatness was ⅛λ.

Claims (1)

[Claims] 1. SiO ₂ , Li ₂ O, Na ₂ O, Mg
One or more of O and CaO, lanthanide element and Cr, T
containing one or more of the i elements, and the average particle size of the sintered body is 5
Polycrystalline transparent ceramics for lasers having a garnet structure with a porosity of 1% or less at .about.1000 .mu.m.