JP2023104418A - Nonlinear optical crystal, manufacturing method therefor, wavelength conversion element using the same, and ultraviolet laser device using the same - Google Patents

Abstract

To provide a nonlinear optical crystal capable of generating light in the deep ultraviolet region, a manufacturing method therefor, a wavelength conversion element using the same, and an ultraviolet laser device using the same.SOLUTION: A nonlinear optical crystal of the present invention comprises at least an Ln element, Ga element, M element, Q element and oxygen, where Ln represents an element selected from a group consisting of yttrium (Y) and lanthanides, M represents germanium (Ge) and/or silicon (Si), and Q represents sulfur (S) and/or selenium (Se), and is a crystal having a crystal structure identical to La3Ga3Ge2S3O10.SELECTED DRAWING: Figure 1

Description

Application for application of Article 30, Paragraph 2 of the Patent Law is filed Published on October 8, 2021 Angewandte Chemie International Edition, https://onlinelibrary. wiley. com/doi/abs/10.1002/ange. 202112692

The present invention relates to a nonlinear optical crystal, a manufacturing method thereof, a wavelength conversion element using the same, and an ultraviolet laser device using the same.

Ultraviolet (UV) lasers with high output and high convergence are important technologies in various industrial and medical fields such as high-precision microfabrication, ablative photolysis, and inspection of semiconductor masks. Laser light sources with a wavelength of 300 nm or less that are currently required are excimer lasers using halides of rare gases (XeCl, ArF, KrF, etc.), but these have various drawbacks. For example, the volume of the device is very large, gas discharge at high voltage, regular maintenance is required. On the other hand, all-solid-state ultraviolet lasers using nonlinear optical (NLO) crystals are small and maintenance-free, and are attracting attention as light sources to replace excimer lasers.

Ultraviolet NLO crystal can convert the frequency of infrared laser (1064 nm for Nd:YAG laser) into laser in the ultraviolet frequency region by the second harmonic generation (SHG) phenomenon, which is a nonlinear optical phenomenon, and emits a high laser beam. plays an important role in the quality and output of So far, boric acid-based ultraviolet NLO crystals typified by β-BaB ₂ O ₄ , LiB ₃ O ₅ and CsLiB ₆ O ₁₀ have been put into practical use (see, for example, Non-Patent Documents 1 to 3).

However, it is very difficult to obtain NLO materials for UV applications with properties suitable for practical use in the near-UV or deep-UV regions. The requirements for nonlinear optical crystals for ultraviolet applications are:
(i) large nonlinear optical constants (d _ij >d ₃₆ (KDP)=0.39 pm/V);
(ii) moderately high birefringence (d _n ~0.07-.10 @ 1064 nm);
(iii) a wide UV light transmission window or short absorption edge and large bandgap;
(iv) chemical and thermal stability,
(v) ease of growing large single crystals; None of the crystals in Non-Patent Documents 1 to 3 satisfy all of these conditions, and the search for new substances continues.

C. Chen et al., Sci. Sin. B, 1985, 28, 235-243 S. Lin et al. App. Phys. , Vol. 67, No. 2, 1990, 634-638 Y. Mori et al., Appl. Phys. Lett. , 1995, 67, 1818-1820

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a nonlinear optical crystal capable of generating light in the deep ultraviolet region, a method for manufacturing the same, a wavelength conversion element using the same, and an ultraviolet laser device using the same.

The nonlinear optical crystal according to the present invention includes at least Ln element, Ga element, M element, Q element and oxygen (where Ln is an element selected from the group consisting of yttrium (Y) and lanthanides, M is germanium (Ge) and/or silicon (Si), Q _is sulfur (S) and _/ or selenium (Se)) and has the _same crystal structure _{as La3Ga3Ge2S3O10} It consists of crystals, thereby solving the above problems.
A crystal having the same crystal structure as the La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ may belong to the hexagonal system.
A crystal having the same crystal structure as said La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ has P-62c symmetry and lattice constants a, b and c are
a=1.01701±0.05 nm
b=1.01701±0.05 nm
c=0.75198±0.05 nm
may be satisfied.
The crystal is represented by _LnaGabMcQdOe , where a+ _b + _c +d+ _e =1, and the parameters a, b, c, d and e are _:
0.1≦a≦0.18,
0.1≤b≤0.18,
0.05≦c≦0.13,
0.1≦d≦0.18, and
0.43≤e≤0.55
may be satisfied.
Said parameters a, b, c, d and e are
0.14≦a≦0.15,
0.14≦b≦0.15,
0.09≦c≦0.10,
0.14≦d≦0.15, and
0.47≤e≤0.48
may be satisfied.
The lanthanoids include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium. (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
It may have a bandgap in the range of 4.6 eV or more and 5.0 eV or less.
The nonlinear optical constants d ₂₂ and −d ₁₆ at a wavelength of 1.064 μm may satisfy the range of 0.5 pm/V or more and 0.7 pm/V or less.
The birefringence at a wavelength of 1.064 μm may satisfy the range of 0.1 to 0.15.
The absorption edge may be 255 nm or less.
The method for producing a nonlinear optical crystal according to the present invention includes at least Ln element, Ga element, M element, Q element and oxygen (wherein Ln is an element selected from the group consisting of yttrium (Y) and lanthanides, M is germanium (Ge) and/or silicon (Si), and Q is sulfur (S) and/or selenium (Se)). , thereby solving the above problem.
The heating may be liquid phase growth of the raw material mixture by a flux method.
The heating may heat the raw material mixture in a temperature range of 800° C. or higher and 1000° C. or lower.
A wavelength conversion element according to the present invention comprises the above nonlinear optical crystal, thereby solving the above problems.
An ultraviolet laser device according to the present invention includes a laser light output unit that emits fundamental wave light, and a wavelength conversion unit that converts the fundamental wave light into ultraviolet laser light having a wavelength shorter than the wavelength of the fundamental wave light. A part includes at least the wavelength conversion element described above, thereby solving the problem described above.

The nonlinear optical crystal according to the present invention includes at least Ln element, Ga element, M element, Q element and oxygen (where Ln is an element selected from the group consisting of yttrium (Y) and lanthanides, M is germanium (Ge) and/or silicon (Si ₎ , Q _is sulfur (S) and/or selenium (Se)) and has the _same crystal structure _{as La3Ga3Ge2S3O10} made of crystals. Such a crystal has a large nonlinear optical constant, large birefringence, a short absorption edge, a large bandgap, and excellent chemical and thermal stability. , can be applied to the wavelength conversion element. Furthermore, it is possible to provide an ultraviolet laser device using such a wavelength conversion element.

The method for producing a nonlinear optical crystal of the present invention is obtained by heating in vacuum a raw material mixture containing the elements constituting the nonlinear optical crystal. This is advantageous because it does not require any special technique or equipment.

A diagram showing a model of a crystal represented by La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ FIG. 2 is a diagram showing powder X-ray diffraction using CuKα rays calculated from the crystal structure of a crystal represented by La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ . Schematic diagram showing an ultraviolet laser device using a wavelength conversion element made of the nonlinear optical crystal of the present invention. Schematic diagram showing another ultraviolet laser device using a wavelength conversion element made of the nonlinear optical crystal of the present invention. Figures showing the XRD patterns of the samples of Examples 2 to 5 TG curve and DTA curve of the sample of Example 1. Figure showing the diffusion/absorption spectrum of the sample of Example 1 FIG. 2 shows the grain size dependence of the SHG intensity of the sample of Example 1. A diagram showing the appearance of the sample of Example 6 Figure showing the EDX spectrum of the sample of Example 6

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same number is given to the same element, and the description is omitted.
(Embodiment 1)
Embodiment 1 describes a nonlinear optical crystal and a method for manufacturing the same according to the present invention.

The nonlinear optical crystal of the present invention includes at least Ln element, Ga element, M element, Q element and oxygen (where Ln is an element selected from the group consisting of yttrium (Y) and lanthanides, M is germanium (Ge) and/or silicon (Si), Q _is sulfur (S) and _/ or selenium (Se)) and has the _same crystal structure _{as La3Ga3Ge2S3O10} made of crystals. Such a crystal has a large nonlinear optical constant, a large birefringence, a short absorption edge, a large bandgap, excellent chemical and thermal stability, exhibits a nonlinear optical effect, and can be applied to a wavelength conversion device.

The crystal represented by La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ is a crystal that has not been reported before the present invention, which was newly synthesized by the present inventors and confirmed to be a novel crystal by crystal structure analysis. .

FIG. 1 is a diagram showing a model of a crystal represented by La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ .

According to the single crystal structure analysis performed on the La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal synthesized by the present inventors as an exemplary crystal represented by La _{3 Ga} 3 Ge ₂ S ₃ O ₁₀ , La ₃ The Ga ₃ Ge ₂ S ₃ O ₁₀ crystal belongs to the hexagonal crystal system, belongs to the P-62c space group (190th space group of the International Tables for Crystallography), and occupies the crystal parameters and atomic coordinate positions shown in Table 1.

In Table 1, the lattice constants a, b, and c indicate the lengths of the unit cell axes, and α, β, and γ indicate the angles between the unit cell axes. Atomic coordinates indicate the position of each atom in a unit cell with a value between 0 and 1 in units of the unit cell. In this crystal, there are atoms of La, Ga, Ge, S, O, La is present in one type of site La1, Ga is present in two types of sites Ga1 and Ga2, and Ge is present in two types. Analytical results were obtained which are present at positions Ga1 and Ga2. Further, an analysis result was obtained that S exists in one type of seat S1, and O exists in three types of seats from O1 to O3.

FIG. 1 shows a side view (a), a top view (b), and a local coordination environment (c) of a La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal. As shown in FIG. 1(a), the La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal has triangular prisms and lone dimers composed of GaO and (Ga/Ge)S ₂ O ₂ .

Specifically, Ga atoms and Ge atoms are randomly distributed at Wyckoff positions 4f and 6g at a ratio of 3:2, and as shown in FIGS. A tick Ga/Ge coordination environment coexists.

A homoleptic coordination environment has a large concentration ratio of O atoms to S atoms, and oxygen anions are the only ligands. Since the O atom concentration is higher than the S atom concentration, it can have a large bandgap. Moreover, since it has a homoleptic coordination environment, it can improve the ultraviolet light transmittance.

A heteroleptic coordination environment, on the other hand, has both oxygen and sulfur anions as ligands. In such a coordination environment, nonlinear optical constants and optical anisotropy can be improved by increasing local strain as well as polarizability derived from sulfur anions. Thus, the crystal of the present invention functions as a nonlinear optical crystal that satisfies the above requirements (i) to (iii) by coexistence of homoleptic and heteroleptic Ga/Ge coordination environments. .

As shown in FIG. 1(C), a Ga atom and a Ge atom (referred to as (Ga/Ge)1) at Wyckoff position 4f are tetrahedrally coordinated with four O atoms, and two (Ga/ Ge) _1O4 tetrahedra form _{lone dimers (Ga/Ge)12O7 .} On the other hand, the Ga and Ge atoms at Wyckoff position 6f (referred to as (Ga/Ge)2) are tetrahedrally coordinated with two S and two O atoms, resulting in three (Ga/Ge)S _{The 2} O ₂ tetrahedron shares vertices with two O atoms to form the ring structure (Ga/Ge) 2 S ₆ O ₃ in the ab plane. The (Ga/Ge) _1O4 and ₍ Ga/Ge) _2S2O2 tetrahedra are separated from each _other by _LaS2O6 antisquare prisms and are plane-sharing with three O atoms along the c-axis. are doing.

A crystal having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ can be identified by X-ray diffraction or neutron diffraction. As a substance showing the same X-ray diffraction result as the La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal shown in the present invention, there is a crystal shown by Ln ₃ Ga ₃ M ₂ Q ₃ O ₁₀ . wherein Ln is an element selected from the group consisting of Y and lanthanides, M is Ge and/or Si, and Q is S and/or Se. Lanthanide elements are illustratively lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Of course, crystals having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ also include La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystals themselves.

Furthermore, there are crystals in which lattice constants and atomic positions are changed by replacing constituent elements with other elements in La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystals. Here, the constituent element is replaced with another element, for example, part or all of La in the La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal is selected from the group consisting of Y other than La and lanthanoids Some or all of Ge is replaced with Si, and some or all of S is replaced with Se. These substitutions are made so that the overall charge in the crystal is neutral. A La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal has the same crystal structure as a result of these element substitutions. Substitution of elements changes the nonlinear characteristics, chemical stability, and thermal stability of the nonlinear optical crystal, so it is preferable to place them in a range in which the crystal structure is maintained, and to select them appropriately according to the application.

A crystal having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ is given by the crystal structure, the sites occupied by the atoms, and their coordinates, although the lattice constant changes due to the replacement of the constituents with other elements. The atomic positions that are bound do not change so much that the chemical bonds between the backbone atoms are broken. In the present invention, the chemical bond length of Ga-O and La-O calculated from the lattice constant and atomic coordinates obtained by Rietveld analysis of the results of X-ray diffraction and neutron diffraction in the space group of P-62c (distance between adjacent atoms) is within ±5% of the chemical bond length calculated from the lattice constant and atomic coordinates of the La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal shown in Table 1, the same crystal It is determined whether or not the crystal has the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ by defining the structure. This criterion is because, according to experiments, if the length of chemical bonds in the La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal changes by more than ±5%, the chemical bonds are broken and the crystal becomes a different crystal.

FIG. 2 is a diagram showing powder X-ray diffraction using CuKα rays calculated from the crystal structure of a crystal represented by La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ .

As a simple determination method for crystals having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ , the lattice constant calculated from the X-ray diffraction results measured for a new substance and the crystal structure data in Table 1 are used. The same crystal structure can be identified when the calculated diffraction peak positions (2θ) match for the main peaks.

For example, when the substance to be compared is obtained as a powder, it can be easily determined whether the crystal has the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ by comparing the substance to be compared with FIG. can make a definitive judgment. As the main peaks of the crystal having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ , it is preferable to determine about 10 peaks with high diffraction intensity. From this point of view, Table 1 is important as it serves as a reference for identifying crystals having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ .

Crystals having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ preferably belong to the hexagonal system. This stabilizes the crystal and can exhibit a large nonlinear optical effect.

Crystals having a crystal structure identical to La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ preferably have a symmetry of P-62c, with lattice constants a, b and c of
a=1.01701±0.05 nm
b=1.01701±0.05 nm
c=0.75198±0.05 nm
meet. This stabilizes the crystal, resulting in a large nonlinear optical constant and a large nonlinear optical effect.

A crystal having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ is Lna _{Ga b} Mc _{Q d} O _e (where a + b + c + d + e = 1, and the M and Q elements are as described above). ) and the parameters a, b, c, d and e are preferably
0.1≦a≦0.18,
0.1≤b≤0.18,
0.05≦c≦0.13,
0.1≦d≦0.18, and
0.43≤e≤0.55
meet. A nonlinear optical crystal composed of a crystal that satisfies such parameters exhibits an excellent nonlinear optical effect because the above crystal is stabilized.

In particular, parameters a, b, c, d and e are
0.14≦a≦0.15,
0.14≦b≦0.15,
0.09≦c≦0.10,
0.14≦d≦0.15, and
0.47≤e≤0.48
A crystal that satisfies is preferable because it has a stable crystal structure, exhibits a high nonlinear optical effect, and has a large nonlinear optical constant and a large birefringence.

Since the nonlinear optical crystal of the present invention has a homoleptic coordination environment and a heteroleptic coordination environment as described above, it can transmit ultraviolet light while maintaining a large nonlinear optical constant and phase matching. Excellent in nature.

The nonlinear optical crystal of the present invention more preferably has a bandgap in the range of 4.6 eV or more and 5.0 eV or less by selecting composition and elements. As a result, since the absorption edge is 255 nm or less, it has a wide ultraviolet transmission window, which is advantageous for generating light in the deep ultraviolet region. The absorption edge is not particularly limited as long as it is 255 nm or less, but may be 220 nm or more.

The nonlinear optical crystal of the present invention more preferably satisfies the range of 0.5 pm/V or more and 0.7 pm/V or less for nonlinear optical constants d22 and -d16 at a wavelength of 1.064 μm. Typical crystals that satisfy these band gaps, absorption edges and nonlinear optical constants are La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystals in which Ln is La and M is Ge, Ln is Pr and M is Ge. is _{a Pr 3} Ga ₃ Ge ₂ S ₃ O ₁₀ crystal _where Ln is Nd and M _is Ge _.

Unlike β-BaB ₂ O ₄ , LiB ₃ O ₅ and the like, the nonlinear optical crystal of the present invention does not have deliquescence and is easy to handle. Moreover, it is stable without decomposition even at high temperatures up to at least 800° C., and functions as a nonlinear optical crystal that satisfies the above requirement (iv).

The nonlinear optical crystal of the present invention may be polycrystalline powder or single crystal. A polycrystalline powder can be used as a raw material powder for producing a single crystal. Also, if it is a single crystal, it functions as a wavelength conversion element, as will be described later.

A method for manufacturing such a nonlinear optical crystal of the present invention will be described.
When the nonlinear optical crystal of the present invention is a polycrystalline powder, at least Ln element, Ga element, M element, Q element and oxygen (Ln is an element selected from the group consisting of yttrium (Y) and lanthanides). , M is germanium (Ge) and/or silicon (Si), and Q is sulfur (S) and/or selenium (Se)). .

As starting materials for the raw material mixture, an element or compound containing Ln (Ln is an element selected from the group consisting of yttrium (Y) and lanthanides), an element or compound containing Ga, an element or compound containing M, Compounds (M is germanium (Ge) and/or silicon (Si)), elements or compounds containing Q (Q is sulfur (S) and/or selenium (Se)) may be used.

The element containing Ln may be the metal of Ln. The compound containing Ln is a single substance or a mixture of two or more selected from silicides, oxides, carbonates, nitrides, oxynitrides, chlorides, fluorides, sulfides, selenides, and oxyfluorides. It's okay.

The element containing Ga may be Ga metal. The compound containing Ga is a single substance or a mixture of two or more selected from silicides, oxides, carbonates, nitrides, oxynitrides, chlorides, fluorides, sulfides, selenides, and oxyfluorides. It's okay.

The element containing M may be an M metal. The compound containing M is a single substance or a mixture of two or more selected from silicides, oxides, carbonates, nitrides, oxynitrides, chlorides, fluorides, sulfides, selenides, and oxyfluorides. It can be.

A simple substance containing Q may be a simple substance of the Q element. The Q-containing compounds may be Ln, Ga, or M sulfides and/or selenides. When a sulfide or selenide is selected as the Ln-containing compound, the Ga-containing compound, or the M-containing compound, these can be omitted.

Oxygen in the raw material mixture may be introduced by using an oxide, oxynitride, or oxyfluoride containing oxygen as a compound. From the viewpoint of suppressing impurities, the compound containing Ln is preferably an oxide of Ln, the compound containing Ga is preferably an oxide of Ga, and the compound containing M is preferably , M, and for Q, the Q element alone, or the sulfides or selenides of Ln, Ga, and M.

Vacuum sealing is preferably carried out so that the degree of vacuum is in the range of 0.001 Pa or more and 100 Pa or less. As a result, a nonlinear optical crystal with good purity is obtained. Preferably, the vacuum sealing is performed so that the degree of vacuum is in the range of 1.0 Pa or more and 10 Pa or less.

The temperature for heating the raw material mixture is not particularly limited as long as the raw material mixture melts and reacts with each other. Within this range, the reaction is promoted and the nonlinear optical crystal of the present invention is obtained. More preferably, the heating temperature is in the temperature range of 800°C or higher and 1000°C or lower.

The heating time of the raw material mixture is not particularly limited, but may be, for example, 5 hours or more and 48 hours or less. Within this range, the reaction proceeds. Preferably, the time is 18 hours or more and 30 hours or less.

When the nonlinear optical crystal of the present invention is a single crystal, liquid phase growth by a flux method may be employed when the above raw material mixture is sealed in a vacuum and heated. A metal halide salt can be used as the flux. Such metal halide salts include alkali metal halides such as lithium, sodium and potassium, and alkaline earth metal halides such as beryllium, magnesium, calcium, strontium and barium. Halides include fluorides, chlorides, bromides, iodides and the like, with chlorides being preferred.

Also in the case of manufacturing a single crystal, the above-described conditions can be adopted for the vacuum degree of vacuum sealing, the heating temperature, and the heating time. Moreover, a temperature range of 1° C./minute or more and 10 minutes or less can be adopted as the temperature increase rate during heating. After heating, it is preferable to slowly cool down to a temperature range of 450° C. or higher and 650° C. or lower at a temperature drop rate in the range of 0.01° C./min or higher and 5° C./min or lower. This can promote the growth of single crystals. In this way, since block-shaped single crystals can be grown by adopting the existing flux method, it is possible to increase the size and satisfy the above requirement (v).

(Embodiment 2)
Embodiment 2 describes an ultraviolet laser device using the nonlinear optical crystal described in Embodiment 1. FIG.
An ultraviolet laser device of the present invention includes a laser light output section that emits fundamental wave light, and a wavelength conversion section that converts the fundamental wave light from the laser light output section into ultraviolet laser light having a wavelength shorter than the wavelength of the fundamental wave light. . This wavelength conversion section includes at least a wavelength conversion element made of the nonlinear optical crystal described in the first embodiment. The laser light output unit is not particularly limited as long as it emits laser light having a wavelength from visible light to infrared light. of light sources can be used.

FIG. 3 is a schematic diagram showing an ultraviolet laser device using a wavelength conversion element made of the nonlinear optical crystal of the present invention.

FIG. 3 illustrates an ultraviolet laser device that emits ultraviolet light with a wavelength of 266 nm from laser light with a wavelength of 1064 nm. In the ultraviolet laser device 300, the laser light output unit 310 includes an Nd:YAG laser 311 that outputs laser light (fundamental wave light) having a wavelength of 1064 nm.

The wavelength conversion section 320 includes wavelength conversion elements 321 and 322 made of the nonlinear optical crystal described in the first embodiment. Since the nonlinear optical crystal is the single crystal of the nonlinear optical crystal described in the first embodiment, the description thereof is omitted. Here, for the sake of simplicity, the case where both the wavelength conversion elements 321 and 322 are made of the nonlinear optical crystal described in Embodiment 1 will be described. For example, boric acid-based ultraviolet NLO crystals typified by β-BaB ₂ O ₄ , LiB ₃ O ₅ , and CsLiB ₆ O ₁₀ typified by Non-Patent Documents 1 to 3 may be used.

The laser light (fundamental wave light) emitted by the laser light output section 310 enters the wavelength conversion element 321 of the wavelength conversion section 320 . In FIG. 3, the fundamental wave is configured to enter the wavelength converter 320 via an optical amplifier that amplifies the fundamental wave. For example, such optical amplifiers can be ytterbium (Yb) doped fiber optical amplifiers, which have high gain in this wavelength band.

The wavelength conversion unit 320 includes a wavelength conversion element 321 and a wavelength conversion element 322. The wavelength conversion element 321 converts the wavelength λ1=1064 nm (angular frequency ω) of the fundamental wave to λ1/2=532 nm (angular frequency 2ω). The wavelength conversion element 322 converts λ1/2=532 nm into λ1/4=266 nm (angular frequency 4ω) to generate the fourth harmonic. Thus, the ultraviolet laser device 300 can output high-output ultraviolet light (ultraviolet laser light) with a wavelength of 266 nm.

Although a wave plate is shown between the wavelength conversion element 321 and the wavelength conversion element 322 in FIG. 3, it is not essential. By using the wave plate, the plane of polarization of the second harmonic light wavelength-converted by the wavelength conversion element 321 and the plane of polarization of the fundamental wave remaining without being wavelength-converted by the wavelength conversion element 321 can be made the same plane. Conversion efficiency in the conversion element 322 can be improved.

After the wavelength conversion unit 320, the fourth harmonic (i.e., ultraviolet light) wavelength-converted by the wavelength conversion element 322 and the remaining fundamental and second harmonics are converted into optical elements such as prisms, dichroic mirrors, and beam splitters. (not shown) may be used to separate. Of course, optical adjustment using an optical lens such as a condensing lens may be performed on the optical path of the laser light as required.

FIG. 4 is a schematic diagram showing another ultraviolet laser device using a wavelength conversion element made of the nonlinear optical crystal of the present invention.

FIG. 4 illustrates an ultraviolet laser device that emits deep ultraviolet light of 193 nm from laser light of 1064 nm. In the ultraviolet laser device 400, the laser light output unit 410 includes an Nd:YAG laser 311 that outputs laser light (fundamental wave light) having a wavelength of 1064 nm, and a Ti: sapphire laser 422 that outputs laser light having a wavelength of 704 nm. Prepare.

The wavelength conversion section 420 includes a wavelength conversion element 421 made of β-BaB ₂ O ₄ in addition to the wavelength conversion elements 321 and 322 made of the nonlinear optical crystal described in the first embodiment.

3, the wavelength conversion element 321 converts the wavelength λ1=1064 nm (angular frequency ω) of the fundamental wave to λ1/2=532 nm (angular frequency 2ω), and converts the second harmonic wave The wavelength conversion element 322 wavelength-converts λ1/2=532 nm into λ1/4=266 nm (angular frequency 4ω) to generate the fourth harmonic. Here, the second harmonic wave from the wavelength conversion element 321 is split by an optical element such as a beam splitter to excite a Ti:sapphire laser 411 to excite laser light with a wavelength of 704 nm.

The laser light from the Ti:sapphire laser 411 and the fourth harmonic (light having a wavelength of 266 nm) from the wavelength conversion element 322 enter the wavelength conversion element 421 . Since the wavelength conversion element 421 is made of β-BaB ₂ O ₄ , the laser light of 704 nm and the fourth harmonic wave of 266 nm are sum-frequency generated and converted into light having a wavelength of 193 nm. Thus, the ultraviolet laser device 400 can output high-output deep ultraviolet light (ultraviolet laser light) with a wavelength of 193 nm.

The ultraviolet laser device shown in FIGS. 3 and 4 is merely an example, and when a 1.5 μm band is used as the wavelength at the laser light output section, a wavelength conversion element using the nonlinear optical crystal of the present invention is provided. The wavelength conversion section may be appropriately combined with a wavelength conversion element capable of second harmonic generation, sum frequency generation, difference frequency generation, parametric oscillation, or the like, and such modifications will be understood by those skilled in the art.

The present invention will now be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples.

[Raw materials used for synthesis]
The raw material powders used in the synthesis are lanthanum sulfide powder ( _La2S3 , _manufactured by Alfa Aesar, purity 99%), lanthanum oxide powder ( _{La2O3 ,} manufactured by Rare Metallic Co., Ltd., purity 99.9%), and gallium oxide. Powder (Ga ₂ O ₃ , manufactured by Rare Metallic Co., Ltd., purity 99.9%), germanium oxide powder (GeO ₂ , manufactured by Rare Metallic Co., Ltd., purity 99.9%), germanium powder (manufactured by Kojundo Chemical Co., Ltd., 99.99%), sulfur powder (Kojundo Chemical Co., Ltd., 99.99%), cerium oxide powder (Ce ₂ O ₃ , Rare Metallic Co., Ltd., purity 99.9%), praseodymium oxide powder (Pr ₆ O ₁₁ , manufactured by Rare Metallic Co., Ltd., purity 99.9%), and neodymium oxide powder (Nd ₂ O ₃ , manufactured by Rare Metallic Co., Ltd., purity 99.9%). These raw material powders were stored in an argon-filled glove box.

Barium chloride (BaCl ₂ , manufactured by Rare Metallic Co., Ltd., purity 99.9%) and sodium chloride (NaCl, manufactured by Rare Metallic Co., Ltd., purity 99.99%) were used as fluxes. These chlorides were heated overnight at 260° C. in a dry oven before use.

[Examples 1 to 5: Polycrystalline powder]
In Examples 1 to 5, polycrystalline powders of the nonlinear optical crystal of the present invention were synthesized. Raw material powders were weighed so as to have the design composition shown in Table 2. The weighed raw material powders were thoroughly mixed with an agate mortar and pestle to form pellets. This was placed in a quartz tube, evacuated to a degree of vacuum (1 Pa), and the quartz tube was sealed. The vacuum-sealed quartz tube was placed in a quartz tube furnace and fired under the conditions shown in Table 2.

Synchrotron radiation X-ray diffraction (SXRD) measurement was performed on the obtained sample of Example 1. The measurement was carried out at room temperature (25° C.) using a one-dimensional detector mounted on the NIMS BL15XU beamline at SPring-8. A synchrotron radiation X-ray was monochromatized to a wavelength of 0.65298 Å, and a sample was loaded into a glass capillary tube (inner diameter 0.2 mm). Diffraction data were collected in steps of 0.003° over the range 2-60° and analyzed by the Rietveld method using the RIETAN-FP program. The results were as shown in FIG. 2 and Table 1. From this, it can be concluded that the sample of Example 1 is a La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystal that belongs to the hexagonal system and belongs to the space group P-62c (the 190th space group of the International Tables for Crystallography). Do you get it.

The obtained samples of Examples 2 to 5 were pulverized using an agate mortar and subjected to powder X-ray diffraction measurement using the Kα line of Cu (MiniFlex-600 diffraction system manufactured by Rigaku Co., Ltd. was used). The results are shown in FIG. 5 and Table 3.

In order to examine the thermal stability of the obtained samples of Examples 1 to 5, thermogravimetric analysis (TGA) was performed using a thermal analysis apparatus (TG-DTA8122 system manufactured by Rigaku Corporation). Fill the sample in an alumina crucible, heat the sample to 1000 ° C. at a temperature increase rate of 10 ° C./min while oxygen flow (1.0 L / min), and cool to room temperature at a temperature decrease rate of 10 ° C. / min. Mass change was investigated. The results are shown in FIG.

In order to examine the reflection characteristics of the samples obtained in Examples 1 to 5, an ultraviolet-visible spectrophotometer equipped with an integrating sphere (manufactured by Shimadzu Corporation, UV-2600) was used in the diffuse reflection mode at wavelengths from 220 nm. UV-vis-NIR spectra in the range of 1200 nm were measured. A deuterium lamp was used as the ultraviolet light source, and a halogen lamp was used as the visible and near-infrared light source. The recorded reflectance spectra were converted to absorption data by the Kubelka-Munk function. The results are shown in FIG. The absorption edge and bandgap were obtained from the spectrum. Table 3 shows the results.

The samples of Examples 1-5 were investigated for second harmonic generation (SHG) by the Kurtz-Perry method using laser light (λ=1064 nm) from a Q-switched Nd:YAG laser. Samples of Examples 1-5 were ground and sieved to particle size ranges (38-55 μm, 55-88 μm, 88-105 μm, 105-155 μm, 155-200 μm). KH ₂ PO ₄ (KDP) was used as a benchmark material. The results are shown in FIG.

Also, the nonlinear optical constant and birefringence were calculated. For the calculation, the electronic structure was first subjected to GGA (Generalized Gradient Approximation)-PBE (Perdew-Burke-Emzerhof) method (JP Perdew et al., Phys. Rev. Lett. 1996, 77, 3865). I got it by calculation and went. The first-principles calculation was performed on a computer installed with CASTEP (CAmbridge Serial Total Energy Package) software (SJ Clark et al., Z. Kristallogr., 2005, 220, 567) as a package program. Based on the obtained electronic structure, the birefringence is calculated from the real part of the dielectric function, and the nonlinear optical constant is calculated using Length-gauge formalism (C. Aversa et al., Phys. Rev. B 1995, 52, 14636). bottom. Table 3 shows the results.

The above results will be summarized and explained.
FIG. 5 shows the XRD patterns of the samples of Examples 2-5.

Both XRD patterns were found to match the XRD pattern shown in FIG. Thus, the sample of Example 2 is La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystals, and the samples of Examples 3-5 have the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ . It was found that the main component was crystals. Considering the impurity peak, the amount of the main component was 80% by mass or more.

6 shows the TG and DTA curves of the sample of Example 1. FIG.

The TG curve of Example 1 did not change up to 800°C, but upon further heating to 1200°C showed a sharp weight gain of about 3.5% at 950°C via a small step of about 880°C. These behaviors were confirmed by X-ray diffraction analysis (not shown) after TG measurement, and found to be caused by decomposition of the oxysulfide phase. Since the TG curves of Examples 2 to 5 showed similar behavior, it was shown that the samples of Examples 1 to 5 have excellent thermal stability without decomposition even at high temperatures up to at least 800°C.

7 is a diagram showing the diffusion/absorption spectrum of the sample of Example 1. FIG.

According to FIG. 7, the absorption edge of the sample of Example 1 was 250 nm and the bandgap was 4.7 eV. As shown in Table 3, the absorption edges of the samples of Examples 3-5 were also below 330 nm and had bandgaps greater than 3.5 eV. In particular, it was confirmed that the crystal of the present invention has a large bandgap of 4.6 eV or more and 5.0 eV or less by adjusting the composition.

FIG. 8 is a diagram showing the particle size dependence of the SHG intensity of the sample of Example 1. FIG.

According to FIG. 8, the SHG intensity of the sample of Example 1 increased with increasing grain size and reached a plateau in the grain size range of 125 μm and above. Although not shown, the SHG intensities of the samples of Examples 2 to 5 showed similar behavior. This behavior indicates that the type I phase-matching condition is satisfied in La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ crystals, and the samples of Examples 1-5 are nonlinear optical crystals and second harmonic It was shown that waves are generated. It should be noted that in the sample of Example 1, the SHG intensity in the grain size range of 150 μm to 200 μm is 2.0 times that of the benchmark KDP, which is an excellent nonlinear optical crystal and can be used as a wavelength conversion element. Found it to work.

The calculated values of nonlinear optical constants d22 and -d16 showed good agreement with the SHG intensity (2.0×KDP). The birefringence values were confirmed to be consistent with the phase matching of the oxysulfide phase.

[Examples 6 to 10: single crystals]
In Examples 6 to 10, single crystals of the nonlinear optical crystal of the present invention were synthesized. Raw material powders were weighed in an argon-filled glove box so as to have the designed composition shown in Table 4, and filled in an alumina crucible. An alumina crucible was flame-sealed in a quartz tube with a degree of vacuum of 1 Pa. The alumina crucible was placed in a muffle furnace, heated to 850°C at a temperature increase rate of 5°C/min, held at 850°C for 24 hours, and then cooled to 550°C at a temperature decrease rate of 0.08°C/min. After that, the muffle furnace was turned off and allowed to cool to room temperature. The product was ultrasonically cleaned, de-fluxed and vacuum filtered.

The appearance of the obtained samples of Examples 6 to 10 was observed. The results are shown in FIG. Further, the samples of Examples 6 to 10 were subjected to composition analysis using a desktop microscope (TM3000, manufactured by Hitachi High-Tech Co., Ltd.) equipped with an energy dispersive X-ray spectrometer (EDX, manufactured by Oxford Instruments, SwiftED3000). . The results are shown in FIG.

9 is a diagram showing the appearance of the sample of Example 6. FIG.

According to FIG. 9, the sample of Example 6 was a colorless and transparent block crystal with a size of 0.5×0.5×0.8 mm ³ . Although not shown, the samples of Examples 7 to 10 were similarly colorless and transparent block crystals and had similar sizes.

10 shows the EDX spectrum of the sample of Example 6. FIG.

According to FIG. 10, the sample of Example 6 has a molar ratio of La/Ga/Ge/S of 3.00/2.91/2.08/3.01 and the chemistry obtained by single crystal structure analysis. It was found to be a La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ single crystal having a good match to the composition and having the same crystal structure as La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ as shown in Table 5. The sample of Example 7 is similarly La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ single crystal, the sample of Example 8 is Ce ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ single crystal, and the sample of Example 9 is Pr ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ single crystal and the sample of Example 10 was Nd ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ single crystal.

As described above, it has been found that block-shaped single crystals can be obtained using the flux method. Since such a single crystal also has a nonlinear optical effect, it can be applied to a wavelength conversion element that oscillates second harmonics. In particular, depending on the composition, the absorption edge is 255 nm or less, so that an ultraviolet laser device that emits deep ultraviolet light can be provided.

Unlike conventional nonlinear optical crystals, the nonlinear optical crystal of the present invention has a large nonlinear optical constant, large birefringence, a wide ultraviolet light transmission window, a short absorption edge, a large bandgap, chemical and thermal stability, and a second harmonic. It enables wave generation and functions as a wavelength conversion element. Furthermore, by using such a wavelength conversion element, an ultraviolet laser device can be provided.

300, 400 UV laser device 310, 410 Laser light output section 311 Nd: YAG laser 320, 420 Wavelength conversion section 321, 322, 421 Wavelength conversion element 411 Ti: Sapphire laser

Claims (15)

At least Ln element, Ga element, M element, Q element and oxygen (where Ln is an element selected from the group consisting of yttrium (Y) and lanthanides, M is germanium (Ge) and/or silicon ( Si ₎ , Q is sulfur (S) and/or _selenium (Se)), and comprises a crystal having _the same crystal _structure as _{La3Ga3Ge2S3O10} . _{2. The nonlinear optical crystal according to claim 1, wherein the crystal having the same crystal structure as La3Ga3Ge2S3O 10 belongs to the hexagonal} system. A crystal having the same crystal structure as said La ₃ Ga ₃ Ge ₂ S ₃ O ₁₀ has P-62c symmetry and lattice constants a, b and c are
a=1.01701±0.05 nm
b=1.01701±0.05 nm
c=0.75198±0.05 nm
3. The nonlinear optical crystal according to claim 1, which satisfies: The crystal is represented by _LnaGabMcQdOe , where a+ _b + _c +d+ _e =1, and the parameters a, b, c, d and e are _:
0.1≦a≦0.18,
0.1≤b≤0.18,
0.05≦c≦0.13,
0.1≦d≦0.18, and
0.43≤e≤0.55
The nonlinear optical crystal according to any one of claims 1 to 3, which satisfies Said parameters a, b, c, d and e are
0.14≦a≦0.15,
0.14≦b≦0.15,
0.09≦c≦0.10,
0.14≦d≦0.15, and
0.47≤e≤0.48
5. The nonlinear optical crystal according to claim 4, satisfying: The lanthanoids include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium. (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and at least one selected from the group consisting of lutetium (Lu), according to any one of claims 1 to 5 nonlinear optical crystal. 7. The nonlinear optical crystal according to claim 1, having a bandgap in the range of 4.6 eV or more and 5.0 eV or less. 8. The nonlinear optical crystal according to claim 1, wherein nonlinear optical constants _d22 and _-d16 at a wavelength of 1.064 μm satisfy the range of 0.5 pm/V or more and 0.7 pm/V or less. 9. The nonlinear optical crystal according to claim 1, wherein the birefringence at a wavelength of 1.064 μm satisfies the range of 0.1 to 0.15. 10. The nonlinear optical crystal according to claim 1, wherein the absorption edge is 255 nm or less. At least Ln element, Ga element, M element, Q element and oxygen (where Ln is an element selected from the group consisting of yttrium (Y) and lanthanides, M is germanium (Ge) and/or silicon ( Si) and Q is sulfur (S) and/or selenium (Se)). A method for manufacturing a nonlinear optical crystal. 12. The manufacturing method according to claim 11, wherein said heating is liquid phase growth of said raw material mixture by a flux method. The manufacturing method according to claim 11 or 12, wherein the heating heats the raw material mixture in a temperature range of 800°C or higher and 1000°C or lower. A wavelength conversion element comprising the nonlinear optical crystal according to any one of claims 1 to 10. a laser light output unit that emits fundamental wave light;
a wavelength conversion unit that converts the fundamental wave light into ultraviolet laser light having a wavelength shorter than the wavelength of the fundamental wave light,
An ultraviolet laser device, wherein the wavelength conversion section comprises at least the wavelength conversion element according to claim 14 .