Patent Application
20140217336
The present invention relates to a laser oscillation device having a gain medium to be excited typically by sunlight and a solar-pumped amplifier as well as light-amplifying glass.
In recent years, there have been research and development activities for effective use of natural energy in order to solve energy problems. Particularly, solar photovoltaic power generation or solar thermal power generation utilizing solar energy has reached a level of practical use. On the other hand, as a new method of use of solar energy, it has been proposed to convert the energy of sunlight to laser light and to refine a metal by means of such laser light (Patent Documents 1 and 2). As a laser medium, crystals or ceramics of e.g. Nd-doped YAG have been used.
Further, Nd-doped YAG crystals or YAG ceramics show highly efficient light-amplifying characteristics when they are excited by a laser diode with an excitation wavelength of 808 nm (Non-patent Document 1).
With e.g. a laser diode, highly efficient amplifying characteristics are obtainable by excitation with a specific wavelength having a large absorption coefficient.
However, in a case where light having a wide wavelength range such as sunlight was used as excitation light, there was a problem that light with a continuous wavelength could not be efficiently absorbed by e.g. YAG crystals or YAG ceramics having fine structures for absorption as shown in Non-patent Document 1.
Further, in order to increase the gain, it is necessary to increase a size, and for this purpose, it was necessary to take a measure to prevent thermal cracking of YAG crystals or YAG ceramics.
Further, YAG crystals had a problem that it took a long time for their preparation, and their mass production was impossible.
It is an object of the present invention to provide a solar-pumped laser oscillation device, a solar-pumped amplifier and light-amplifying glass which are capable of solving such problems.
The present invention provides a solar-pumped laser oscillation device (hereinafter sometimes referred to as the laser oscillation device of the present invention) wherein the gain medium is Nd-containing B2O3—Bi2O3 glass.
Further, it provides the above solar-pumped laser oscillation device, wherein the Nd-containing B2O3—Bi2O3 glass is glass having Nd2O3 added to a matrix glass comprising from 20 to 65 mol % of B2O3 and from 10 to 48 mol % of Bi2O3.
Further, it provides the above solar-pumped laser oscillation device, wherein the matrix glass contains at most 60 mol % of TeO2.
Further, it provides the above solar-pumped laser oscillation device, wherein the matrix glass contains no SiO2.
Further, it provides the above solar-pumped laser oscillation device, wherein the proportion of Nd2O3 added, is from 0.003 to 0.025 by molar ratio to the matrix glass.
Further, it provides the above solar-pumped laser oscillation device, wherein the Nd-containing B2O3—Bi2O3 glass contains Yb.
Further, it provides the above solar-pumped laser oscillation device, wherein the proportion of Yb2O3 added, is from 0.001 to 0.025 by molar ratio to the glass matrix.
Further, it provides a solar-pumped amplifier (hereinafter sometimes referred to as the amplifier of the present invention) wherein a gain medium made of Nd-containing B2O3—Bi2O3 glass is excited by sunlight to conduct amplification of light entered the gain medium.
Further, it provides the above solar-pumped amplifier, wherein the Nd-containing B2O3—Bi2O3 glass is glass having Nd2O3 added to a matrix glass comprising from 20 to 65 mol % of B2O3 and from 10 to 48 mol % of Bi2O3.
Further, it provides the above solar-pumped amplifier, wherein the matrix glass contains at most 60 mol % of TeO2.
Further, it provides the above solar-pumped amplifier, wherein the matrix glass contains no SiO2.
Further, it provides the above solar-pumped amplifier, wherein the proportion of Nd2O3 added, is from 0.003 to 0.025 by molar ratio to the matrix glass.
Further, it provides the above solar-pumped amplifier, wherein the Nd-containing B2O3—Bi2O3 glass contains Yb.
Further, it provides the above solar-pumped amplifier, wherein the proportion of Yb2O3 added, is from 0.001 to 0.025 by molar ratio to the glass matrix.
Further, it provides light-amplifying glass (hereinafter sometimes referred to as the glass of the present invention) having Nd2O3 added to a matrix glass comprising from 20 to 65 mol % of B2O3 and from 10 to 48 mol % of Bi2O3, wherein the proportion of Nd2O3 added, is from 0.003 to 0.025 by molar ratio to the matrix glass.
Further, it provides the above light-amplifying glass, wherein the matrix glass contains at most 60 mol % of TeO2.
Further, it provides the above light-amplifying glass, wherein the matrix glass contains no SiO2.
Further, it provides the above light-amplifying glass, which contains Yb.
Further, it provides the above light-amplifying glass, wherein the proportion of Yb2O3 added, is from 0.001 to 0.025 by molar ratio to the glass matrix.
According to the present invention, it becomes possible to efficiently absorb light even if the gain medium or light-amplifying glass is excited by continuous light. As a result, a large gain is obtainable, and laser light is obtainable with high efficiency.
Further, it becomes possible to reduce the size of the gain medium or light-amplifying glass, and the proportion of the surface area to the volume increases to facilitate heat dissipation.
Further, the glass can be formed by melting a raw material by heating, followed by casting the molten glass, and therefore, the gain medium or light-amplifying glass can easily be prepared, and its mass production is possible.
In the laser oscillation device of the present invention, typically Nd-containing B2O3—Bi2O3 glass as a gain medium is disposed between a mirror (reflection mirror) with a reflectance of at least 90% and a mirror (output mirror) with a reflectance of at most 50%, which constitute a resonator, and introduction of light such as sunlight into the gain medium is conducted by e.g. a lens or mirror. The introduction of sunlight into the gain medium may be conducted by collection of light in two stages, as the case requires. Further, the excitation light is typically continuous light such as sunlight and is usually applied to the gain medium from its side surface by means of a lens, but may not be so limited. As the lens in such a case, a Fresnel lens may, for example, be used. Further, in this specification, for example “excited by sunlight” includes a case where excited by e.g. continuous light without being limited to sunlight.
In the amplifier of the present invention, typically, continuous light such as sunlight as the excitation light is introduced to the gain medium by means of e.g. a lens or mirror, and at that time, collection of light may be conducted in two stages as the case requires. Further, usually at the same time as introduction of the excitation light, light (signal light) with a wavelength to be amplified, is introduced to the gain medium, but the manner of introduction of light may not be so limited.
The shape of the gain medium is not particularly limited, and it may, for example, be a rod-form or a plate-form. A rod-form gain medium may, for example, have a size of e.g. 3 mm in diameter and 80 mm in length, and a plate-form gain medium may, for example, have a size of e.g. 30 mm square and 3 mm in thickness. Further, the gain medium may have a structure such that the glass of the present invention constitutes a core, and the core is covered with a clad material having a refractive index lower than the core.
In the gain medium of the laser oscillation device and the amplifier of the present invention (hereinafter sometimes referred to as the gain medium of the present invention) as well as in the glass of the present invention, light amplification is carried out by utilizing stimulated emission from 4F3/2 level to 4I11/2 level of Nd3+.
Such light amplification is suitable for amplification of light with a wavelength of from 1.0 to 1.2 μm.
Further, by adding Yb2O3 together with Nd2O3, an energy shift from 4F3/2 level of Nd3+ to 2F5/2 of Yb3+ takes place, whereby larger light amplification is carried out.
Such light amplification is suitable for amplification of light with a wavelength of from 0.9 to 1.2 μm. Further, by permitting laser light and continuous light such as sunlight to enter the laser oscillation device or the amplifier of the present invention, or the glass of the present invention, it is possible to amplify the intensity of the laser light. The gain medium and the glass of the present invention (hereinafter sometimes referred to as the gain medium, etc. of the present invention) are preferably capable of absorbing light of from 1.2 eV (wavelength: 1033 nm) to 3 eV (wavelength: 413 nm) with good efficiency. Such ones are capable of efficiently exciting even continuous light such as sunlight.
From such a viewpoint, it is preferred that in the gain medium, etc. of the present invention, when excited with light of 2.33 eV (wavelength: 532 nm), the product of the emission lifetime and the emission intensity at a wavelength of 1064 nm (photon energy=1.165 eV) is large. Specifically, the after-described index Y for quasi-emission-efficiency is preferably at least 140 eV·ms, more preferably at least 180 eV·ms.
Further, it is preferred that in the gain medium, etc. of the present invention, when excited with light of 2.33 eV, the sum of the product of the emission lifetime and the emission intensity at a wavelength of 977 nm (photon energy=1.269 eV) and the product of the emission lifetime and the emission intensity at a wavelength of 1064 nm (photon energy=1.165 eV) is large. Specifically, the after-described index Y′ for quasi-emission-efficiency is preferably at least 380 eV·ms, more preferably at least 770 eV·ms, further preferably at least 1,100 eV·ms.
Y and Y′ are indices for quasi-emission-efficiency. Y is an index for quasi-emission-efficiency by Nd and is preferably at least 140 eV·ms, and Y′ is an index for quasi-emission-efficiency by Nd and Yb and is preferably at least 770 eV·ms.
The gain medium, etc. of the present invention are glass containing, as the main component, B2O3 as a glass network former, whereby they are stable as glass, and they contain Bi2O3 as another main component, whereby the after-described concentration quenching is less likely to occur. Further, as they contain both B2O3 and Bi2O3, they are thermally stable.
Further, as compared with a case where the gain medium or glass constituting the gain medium is a SiO2 type glass, they are excellent in the melting properties at a high temperature at the time of preparing glass.
In this specification, the content of each component in glass is represented by mol percentage as a rule, and in the following, “mol %” is referred to simply as “%”.
The gain medium, etc. of the present invention are glass having Nd added to a matrix glass comprising B2O3—Bi2O3. The matrix glass is preferably one which may be easily vitrified, and typically comprises from 20 to 65% of B2O3 and from 10 to 48% of Bi2O3. Further, in a case where the gain medium, etc. of the present invention contain Yb, the gain medium, etc. of the present invention are glass having Nd and Yb added to a matrix glass comprising B2O3—Bi2O3. Here, the proportions of Nd and Yb added are, as added as Nd2O3 and Yb2O3, respectively, represented by molar ratios to the matrix glass, of a value calculated as Nd2O3 and a value calculated as Yb2O3.
Now, the compositions of this typical matrix glass and the glass of the present invention will be described.
B2O3 is a network former and a component to facilitate glass formation by preventing crystallization during the preparation of glass and is essential. If it is less than 20%, vitrification tends to be difficult. It is preferably at least 25%, more preferably at least 30%, particularly preferably at least 33%. If it exceeds 65%, the emission intensity tends to be low. It is preferably at most 60%, more preferably at most 50%, particularly preferably at most 45%.
Bi2O3 is an essential component. If its content is less than 10%, vitrification tends to be difficult, or, if the amount of Nd added is increased, the emission intensity tends to be low due to non-radiative relaxation, i.e. concentration quenching is likely to occur. It is preferably at least 15%, more preferably at least 20%, particularly preferably at least 25%, most preferably at least 30%. If it exceeds 48%, vitrification tends to be difficult. It is preferably at most 45%, more preferably at most 42%, particularly preferably at most 40%.
In a case where it is desired to prevent the concentration quenching from occurring or to further increase the emission intensity, TeO2 may be contained, although it is not essential to contain it. The content of TeO2 in such a case is preferably from 5 to 60 mol %. If it is less than 5%, the above-mentioned object tends to be hardly accomplished, and it is more preferably at least 10%, typically at least 15%. If it exceeds 60%, glass is likely to be devitrified, and it is more preferably at most 50%, typically at most 35%.
The above-mentioned typical matrix glass of the gain medium of the present invention or the matrix glass of the glass of the present invention is composed essentially of such three components. However, other components may be contained within a range not to impair the object of the present invention. Even in such a case, the total content of the above three components is preferably at least 70%, more preferably at least 80%, particularly preferably at least 85%, typically at least 90%.
Now, such other components will be exemplified.
SiO2 may be contained as a network former in order to stabilize glass. In a case where SiO2 is contained, if it is less than 1%, its effect is small. It is preferably at least 2%, more preferably at least 5%. If it exceeds 15%, the melting temperature tends to increase. It is preferably at most 10%, more preferably at most 8%. No SiO2 should better be contained e.g. in a case where it is desired to improve the melting properties.
La2O3 has an effect to prevent concentration quenching from occurring or an effect to increase the emission intensity and may be contained in an amount of up to 4%. If it exceeds 4%, devitrification is likely to occur. It is more preferably at most 3%. In a case where La2O3 is contained, its content is preferably at least 0.5%, more preferably at least 1%, particularly preferably at least 2%.
In a case where it is desired to let the energy of excitation light be absorbed and to let energy transfer to Nd occur, Er2O3, Tm2O3, Yb2O3, Sm2O3, Ho2O3, CrO, etc. may be added. Especially when Yb2O3 is added together with Nd2O3, energy transfer from excited Nd to Yb takes place, whereby an intensive emission of Yb is obtainable.
Further, in order to facilitate vitrification, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, ZrO2, ZnO, GeO2, TiO2, In2O3, P2O5, Nb2O5, Ta2O5, etc. may be contained.
Now, the content of Nd will be described. Here, the content of Nd is, as Nd is added as Nd2O3 to the matrix glass, represented by molar ratio calculated as Nd2O3 to the matrix glass.
If Nd2O3 is less than 0.003, no adequate amplification is obtainable or is likely to be obtainable. It is preferably at least 0.005, more preferably at least 0.01. In a case where a small one is used as the gain medium or the glass of the present invention, the proportion of Nd2O3 added is preferably at least 0.005, more preferably at least 0.01. Further, if it exceeds 0.025, vitrification becomes difficult or is likely to become difficult. It is preferably at most 0.02. In a case where it is desired to prevent an influence of concentration quenching, the proportion of Nd2O3 added is preferably at most 0.02, more preferably at most 0.01.
Now, in a case where Yb is added, the content of Yb will be described. Here, the content of Yb is, as Yb is added as Yb2O3 to the matrix glass, represented by molar ratio calculated as Yb2O3 to the matrix glass.
In a case where Yb2O3 is added, its proportion is preferably from 0.001 to 0.025. If it is less than 0.001, no adequate amplification is obtainable or is likely to be obtainable. It is preferably at least 0.005, more preferably at least 0.008. In a case where a small one is used as the gain medium, etc. of the present invention, the proportion of Yb2O3 added is preferably at least 0.005, more preferably at least 0.008. Further, if it exceeds 0.025, vitrification becomes difficult or is likely to become difficult. It is preferably at most 0.02. In a case where it is desired to prevent an influence of concentration quenching, the proportion of Yb2O3 added is preferably at most 0.02, more preferably at most 0.01.
The method for preparing the glass of the present invention or the glass for the gain medium of the present invention is not particularly limited, and it may be prepared, for example, by a melting method wherein raw material is compounded, mixed and put in a gold crucible, an alumina crucible, a quartz crucible or a iridium crucible, and melted in air at from 800 to 1,300° C., and the obtained melt is cast in a prescribed mold. Otherwise, it may be prepared by a method other than the melting method, such as a sol-gel method or a vapor deposition method.
Glass in each of Examples 1 to 13 and Examples 15 to 22 was prepared by a melting method to have a composition shown in columns for from B2O3 to Nd2O3 or Yb2O3 in Tables 1 to 3, wherein the proportions of Nd2O3 and Yb2O3 added are ones having their molar ratios to the matrix glass multiplied by 100, and the contents of other components are represented by mol %. Examples 1 to 10 and 15 to 21 are working examples of the present invention, Examples 11 and 12 are comparative examples wherein glass was not obtained due to devitrification, and Examples 13 and 22 are also comparative examples.
Further, at the time of excitation with light having a wavelength of 532 nm (photon energy: 2.33 eV, the same applies hereinafter), area E of emission intensity within a range of from a wavelength of 990 nm (1.25 eV) to a wavelength of 1180 nm (1.05 eV), emission intensity E (977) at a wavelength of 977 nm (1.269 eV), emission intensity E (1064) at a wavelength of 1064 nm (1.165 eV), emission lifetime τ(977) at a wavelength of 977 nm, and emission lifetime τ(1064) (unit: ms) at a wavelength of 1064 nm, are shown in Tables 1 to 3.
Here, area E of emission intensity is represented by a relative value when E of Nd-containing YAG ceramics (tradename: transparent YAG ceramics) manufactured by Konoshima Chemical Co., Ltd. in Example 14 is regarded to be 1, and E (977) and E (1064) are represented by relative values when E (1064) in Example 2 is regarded to be 1.
Further, absorbance A (532) (unit: /cm) at a peak of a wavelength of 532 (2.33 eV), peak value A (unit: /cm) of absorbance in a range of from 1.2 eV (wavelength: 1033 nm) to 3 eV (wavelength: 411 nm), and absorbance area A′ (unit: eV/cm) in a range of from 1.2 eV to 3 eV, as well as Y=E×τ(1064)×A′/A(532) and Y′={E(1064)×τ(1064)+E (977)×τ(977)}×A′/A (532) as indices for a product of the emission intensity and the emission lifetime, are shown in Tables 1 to 3.
In Examples 1 to 4, the matrix glass is the same, but the proportion of Nd2O3 added is different. It is evident that the absorption of light increases as the proportion of Nd2O3 added increases.
Further, it is evident that in Examples 1 to 10 as working examples of the present invention, Y as an index for quasi-emission-efficiency is at least 140 eV·ms, while in Example 13 as a comparative example, Y is a value as small as 15 eV·ms.
Further, when Examples 1, 2, 15 and 3 wherein Yb2O3 is not contained, are compared with Examples 19, 16 to 18, 20 and 21 wherein Yb2O3 is added, it is evident that by the addition of Yb2O3, Y′ as an index for quasi-emission-efficiency is increased to at least 778 eV·ms.
Further, with respect to glass in Example 22 wherein Yb2O3 is contained, but Nd2O3 is not contained, the emission intensity was measured, whereby no emission was observed. This indicates that the cause for the increase of Y′ in Examples 16 to 21 is attributable to an energy shift from 4F3/2 level of Nd3+ to 2F5/2 level of Yb3+ by the addition of Yb2O3 together with Nd2O3.
Further,
The absorption peak of the glass of the present invention is 13.5/cm, while the absorption peak in
Further, in the absorption spectrum in
Further,
The present invention is useful for amplification of light using solar energy as an excitation light source. Further, it is useful for a laser device to convert sunlight to laser light. Further, it is useful for an amplifier for light having a wavelength of from 1.0 to 1.2 μm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-223073 | Oct 2011 | JP | national |
This application is a continuation of PCT Application No. PCT/JP2012/071882, filed on Aug. 29, 2012, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-223073 filed on Oct. 7, 2011. The contents of those applications are incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2012/071882 | Aug 2012 | US |
| Child | 14246613 | US |
