JPH05163099A - Laser crystal - Google Patents

Abstract

PURPOSE:To provide a crystal, having a wide absorption wavelength of an excited light absorption band thereof and excellent in stability of emitted laser beam output with hardly any laser damage. CONSTITUTION:The objective laser crystal is characterized by its expression as the general formula (Ba1-2xAxRx)B2O4 or (Ba1-3yR2y)B2O4 [A is potassium, rubidium or cesium; R is rare earth element or transition metallic element; (x) is a number of >0 and <=0.2; (y) is a number of >0 and <=0.2], the crystal system of the trigonal system and the space group of R3/C.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a laser crystal, in particular, it relates to α-BaB ₂ O ₄ -type crystal containing a rare earth element or a transition metal element as a laser active element, laser oscillation, is preferably used as the laser crystal for laser amplification ..

[0002]

2. Description of the ^Related Art Conventionally, Nd ^{3+ has been used} as a laser active ion.
Laser crystals containing Y ₃ Al ₅ O ₁₂ as a host crystal (hereinafter referred to as “Nd: YAG”) and YLiF ₄ as a host crystal (hereinafter referred to as “N
d: YLF ". ) Etc. The laser crystal containing Nd ³⁺ and Cr ³⁺ as laser active ions uses Ga ₃ Sc ₂ Ga ₃ O ₁₂ as a host crystal (hereinafter referred to as “Nd: Cr: GSGG”) and the like. There is.

For example, Nd: YAG is widely used as a laser crystal because it can grow large-sized and high-quality crystals (J. of Crystal Growth, 99 (1990) 841 to 844).
).

[0004]

However, the above N
Crystals such as d: YAG, Nd: YLF, and Nd: Cr: GSGG have a characteristic that the absorption wavelength of their excitation light absorption band is narrow.

By the way, a semiconductor laser is preferably used as a light source for exciting a laser crystal because it can obtain laser light of various wavelengths. However, the semiconductor laser has a property that the laser wavelength oscillated easily changes due to the influence of temperature, current, and the like. Therefore, even if the above-mentioned semiconductor laser is used to excite the crystal to cause laser oscillation, the amount of excitation light absorbed by the crystal changes due to wavelength fluctuations of the semiconductor laser, and the laser light oscillated from the crystal fluctuates, resulting in laser output. Is not stable.

The present invention has been made to solve the above-mentioned drawbacks, and an object of the present invention is to provide a wide absorption wavelength in the excitation light absorption band of a crystal, reduce laser damage, and output an oscillated laser beam. To provide a crystal having high stability.

[0007]

The laser crystal of the present invention has the general formula (Ba _1-2x A _x R _x ) B ₂ O ₄ or the general formula (Ba _1-3y R _2y ) B ₂ O ₄ (wherein , A is potassium, rubidium, and cesium, R is a rare earth element or a transition metal element, x is a number greater than 0 and less than or equal to 0.2, and y
Is a number greater than 0 and less than or equal to 0.2. ), The crystal system is a trigonal system, and the space group is R bar 3 _C.

The present invention will be described below. In the crystal of the present invention, the crystal system is a trigonal system and the space group is R bar 3 _C.
Is. That is, α-BaB which is the host crystal of the present invention
It is a crystal of the same type as ₂ O ₄ . In the above general formula, R represents a rare earth element or a transition metal element, and as the rare earth element,
Specifically, praseodymium (Pr), neodymium (N
d), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),
Examples include ytterbium (Yb). Specific examples of the transition metal element include chromium (Cr) and titanium (Ti).

In the crystal of the present invention, R is 2 or more kinds of rare earth elements, 2 or more kinds of transition metal elements, or
A rare earth element and a transition metal element can also be included. Similarly, A may contain two or more kinds of alkali metal elements. It is appropriate that x and y be 0.2 or less in order to prevent the polyphase of the crystal or the change of the crystal system. Further, from the viewpoint that the alkali metal element represented by A and the rare earth element or transition metal element represented by R are solid-solved in the crystal, x and y may be numbers exceeding 0.
However, x and y are preferably 0.001 or more from the viewpoint of obtaining a good-quality single crystal and the viewpoint of laser oscillation.

The method for producing a single crystal of the present invention will be described below with reference to an example. First, the raw materials are mixed and adjusted so that the composition of the melt is the above general formula. As a raw material,
Generally used ones such as carbonates and oxides may be appropriately used, for example, BaCO ₃ , H ₃ BO ₃ , Nd ₂ O.
₃ , Er ₂ O ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ C
Examples include O _{3 and the} like. Alternatively, a sintered body represented by the general formula A _0.5 R _0.5 B ₂ O ₄ (A is an alkali metal element and R is a rare earth element) prepared in advance from these compounds, or a rare earth element and B ₂ O ₄ And the sintered body and Ba
B ₂ O ₄ can also be used as a melting raw material.

The mixture of raw materials is, for example, 1100 to 11
It is melted by heating at 50 ° C. for 2 to 10 hours. Then, a single crystal can be grown by cooling this melt. The method for growing the single crystal is not particularly limited as long as it is a method capable of cooling the melt as described above, and a known method such as Czochralski method can be adopted.

In the crystal manufacturing method of the present invention, it is possible to grow the crystal by melt growth. Therefore, the composition of the grown crystal and that of the melt are the same, and there is no concern that the flux will be taken in as impurities. As a result, a good quality crystal can be obtained, and a crystal with less laser damage is obtained. Furthermore, this method has a growth rate of 1 to 1 as compared with the growth using flux.
It also has an advantage that high quality crystals can be obtained in a short time at 5 mm / h and 50 to 100 times faster.

[0013]

The present invention will be described in more detail with reference to the following examples. Example 1 (1) Solid Solution Confirmation Experiment As raw materials, α-BaB ₂ O ₄ , K ₂ CO ₃ , and Rb ₂ C were used.
O ₃ , Cs ₂ CO ₃ , Nd ₂ O ₃ , La ₂ O ₃ , Y ₂ O
₃ , Cr ₂ O ₃ is used, and x or y in the chemical formulas shown in Table 1 and Table 2 is 0.014, 0.028, 0.056,
0.083, 0.11, 0.17, 0.25 and 0.3
It was blended so as to be 2, and melted in a platinum crucible at 1100 ° C. for 5 hours to prepare a melt. The melt was naturally cooled to obtain crystals. The obtained crystal was heat-treated again at 1000 ° C. for 24 hours and then naturally cooled to room temperature. The crystals were analyzed by powder X-ray diffraction test. The results are shown in Tables 1 and 2.

In the table, a sample which is a single phase having an α-BaB ₂ O ₄ type crystal structure and in which neodymium (Nd) is confirmed to be in solid solution due to peak shift is indicated by ◯.
The sample in which the above crystal phase was confirmed is indicated by x.

[0015]

[Table 1]

[0016]

[Table 2]

From this result, the chemical formula (Ba _1-2x Cs _x N
In d _x ) B ₂ O ₄ and (Ba _1-3y Nd _2y ) B ₂ O ₄ , x and y are in the range of 0 to 0.25, the crystal system is a trigonal system, and the space group is R bar 3 _C. Single phase with structure (α-
It was confirmed to be a BaB ₂ O ₄ type crystal). Also,
When x and y are 0.32 or more, the crystal is α-BaB ₂ O ₄
And a crystal coexisting with other phases. Furthermore, x and y
Of more than 0.5, the crystals were almost free of α-BaB ₂ O ₄ .

(2) Growth of Single Crystal A single crystal was grown by the Czochralski method using an apparatus as shown in FIG. As a starting material, α-BaB ₂
200 g of O ₄ polycrystal and 44.1 g of a sintered body having a composition of Cs _0.5 Nd _0.5 B ₂ O ₄ were pulverized and mixed, and used. This raw material mixture was melted at 1100 ° C. in a platinum crucible, and a single crystal was grown at a pulling rate of 1 mm / h for about 40 hours. The obtained Ba _0.8 Cs _0.1 Nd _0.1 B ₂ O ₄ single crystal is a trigonal crystal system with a maximum diameter of about 30 mm and a length of about 30 mm, and the space group is R 3 bar _C (α-BaB ₂ O ₄ type crystal). ) Was a high quality single crystal (hereinafter α-Ba _0.8 Cs
_It is shown as _0.1 Nd _0.1 B ₂ O ₄ . ). The single crystal of this example was as easy as growing an α-BaB ₂ O ₄ single crystal.

(3) Evaluation of workability of crystal and measurement of transmittance α-Ba _0.8 Cs _0.1 obtained by growing the above single crystal
Nd _0.1 B ₂ O ₄ was cut into a thickness of about 1 mm. At this time, the crystal machinability was good. Next, the cut-out sample was polished to obtain a parallel plate sample, and its transmittance was measured. As a result, except that Nd ³⁺ absorption was confirmed, α-B
There is no difference from aB ₂ O ₄ and the absorption edge is α-BaB ₂ O.
_It was the same as ₄ .

(4) Evaluation of stability in air α-Ba _0.8 Cs _0.1 obtained by growing the above single crystal
Nd _0.1 B ₂ O ₄ had no change in appearance and physical properties even if left at room temperature for 2 months.

(5) Fluorescence measurement of Nd ³⁺ α-Ba _0.8 Cs _0.1 obtained by growing the above single crystal
Nd _0.1 B ₂ O ₄ was processed into 5 mm square, and the second harmonic wave of 1.06 μm, which is the fundamental wave of Nd: YAG laser, 0.5
When irradiated with light of 3 μm, as shown in FIGS. 1 and 2, the fluorescent wavelengths of Nd are 0.888 μm and 1.068 μm.
Generation of fluorescence of m was confirmed. As can be seen from FIGS. 1 and 2, the fluorescence of the laser single crystal obtained in this example is broad. Therefore, it can be seen that the corresponding absorption band of the excitation light is broad.

(6) Laser Oscillation Experiment Using the experimental arrangement as shown in FIG. 3, the semiconductor laser 1 having a wavelength of 0.8 μm is used as the excitation light source and the fundamental wavelengths of Nd ³⁺ of 1. A laser oscillation experiment of 068 μm was performed.

The crystal 2 of α-Ba _0.8 Cs _0.1 Nd _0.1 B ₂ O ₄ had a size of 5 mmφ and a thickness of 10 mm, and had both sides parallel-polished. The incident end face of the excitation light is provided with an AR (non-reflective) coat 3 of light having a wavelength of 0.8 μm (wavelength of the light from the excitation light source), and the other end face has a wavelength of 1.06.
An HR (high reflection) coat 4 was applied with light (oscillation wavelength) of μm. Then, when the light obtained by the laser oscillation is condensed by the condenser lens 6, the fundamental wavelength of Nd ³⁺ is 1.06.
A stable laser oscillation of 8 μm was confirmed.

Example 2 Cs _0.5 Nd _{0.5 of} Example 1
Ba _0.7 Nd _0.2 B ₂ O was prepared in the same manner as in Example 1 except that a sintered body of Nd and B ₂ O ₃ was used instead of B ₂ O _4.
4 single crystals were grown. As a result, the crystal system having a maximum diameter of about 30 mm and a length of about 30 mm, which is almost the same size as the crystal of Example 1, is a trigonal system and the space group is R3 bar _C (α-BaB _2).
A high quality Ba _0.7 Nd _0.2 B ₂ O ₄ single crystal (O ₄ type crystal) was obtained (hereinafter referred to as α-Ba _0.7 Nd _0.2 B ₂ O ₄ ).

The obtained single crystal was easy to grow as in Example 1, and there was no change in appearance and physical properties even if it was left at room temperature for 2 months. Next, a laser oscillation experiment was conducted on the obtained crystal.
A stable laser oscillation of the fundamental wavelength of ³⁺ of 1.068 μm was confirmed.

By optimizing the conditions, larger size,
High quality single crystals can be grown. Furthermore, in this example, as starting materials, α-BaB ₂ O ₄ polycrystal and Cs were used.
_Although a sintered body having a composition such as _0.5 Nd _0.5 B ₂ O ₄ was used, the starting materials are not limited to these, and commercially available materials such as BaCO ₃ , H ₃ BO ₃ , Cs ₂ C may be used.
O _3, Nd ₂ O ₃ reagent or the like may be used. Further, by adding a rare earth element other than Nd or a transition metal element as laser active ions in the same manner as in this example, a laser crystal capable of obtaining laser oscillation corresponding to these ions can be obtained.

[0027]

According to the present invention, a crystal having a wide absorption wavelength in the excitation light absorption band of the crystal and a high stability of the output of the laser light oscillated from the crystal can be obtained. Further, crystals can be easily grown, high quality crystals can be obtained, laser damage is small, laser oscillation is possible at room temperature, and there is no need for temperature control.

Further, the crystal of the present invention is excellent in workability,
It also has the advantage of being stable in the atmosphere. Therefore, the crystal of the present invention can be preferably used as a laser crystal for laser oscillation and laser amplification.

[Brief description of drawings]

FIG. 1 is a fluorescence spectrum of Nd ³⁺ having a wavelength of 0.888 μm.

FIG. 2 is a fluorescence spectrum of Nd ³⁺ having a wavelength of 1.068 μm.

FIG. 3 is a schematic diagram of a laser oscillator.

FIG. 4 is a schematic sectional view of a Czochralski single crystal growth apparatus.

[Explanation of symbols]

 1 Semiconductor Laser 2 Single Crystal 3 Highly Reflective Coating 4 Non-Reflective Coating 5 Condensing Lens 6 Condensing Lens 11 Lifting Shaft 12 Upper Lid 13 Crucible 14 Raw Material Melt 15 Heater 16 Crucible Stand 17 Insulation Material

Claims (3)

[Claims] 1. A general formula (Ba _1-2x A _x R _x ) B ₂ O ₄ or a general formula (Ba _1-3y R _2y ) B ₂ O ₄ (wherein A is potassium, rubidium or cesium, R is a rare earth element or a transition metal element, x is a number greater than 0 and 0.2 or less, and y is a number greater than 0 and 0.2 or less.), And the crystal system is a trigonal system. The laser crystal is characterized in that the space group is R3 bar _C. 2. The laser crystal according to claim 1, wherein the rare earth element is at least one selected from praseodymium, neodymium, samarium, europium, terbium, dysprosium, holmium, erbium, thulium and ytterbium. 3. The transition metal element is at least one selected from chromium and titanium.
The laser crystal described.