WO2004083497A1

WO2004083497A1 - Process for producing fluoride single crystal and wavelength transforming device

Info

Publication number: WO2004083497A1
Application number: PCT/JP2004/003762
Authority: WO
Inventors: Takayo Ogawa; Satoshi Wada; Kiyoshi Shimamura; Noboru Ichinose; Nao Kurimura
Original assignee: Riken
Priority date: 2003-03-20
Filing date: 2004-03-19
Publication date: 2004-09-30
Also published as: JPWO2004083497A1

Abstract

A process for producing a fluoride single crystal, which fluoride single crystal is employable as a constituent of a light source capable of easily and stably generating ultraviolet rays of short wave and high spatial resolution, especially deep-ultraviolet of 300 nm or less wavelength and vacuum ultraviolet of 200 nm or less wavelength; and a wavelength transforming device. In particular, a process for producing a fluoride single crystal through crystal growth according to the Czochralski method, which process comprises using any of CF4 gas, Ar gas, a mixture of CF4 gas and Ar gas and N2 gas as an ambient gas during crystal growth. Pseudo phase matching is brought about by polarization inversion.

Description

Method for producing single crystal fluoride and wavelength conversion element

Technical Field Ryoaki Motoaki is related to a method for producing a single crystal of fluoride and a wavelength conversion element.

The present invention relates to a method for producing a single crystal of fluoride by a Czochralski method (hereinafter referred to as “Cz method” as appropriate) and a wavelength conversion element comprising a single crystal of fluoride. .

BACKGROUND ART With the development of nanoscience and semiconductor miniaturization technology in recent years, there is a strong demand for the development of a light source capable of generating ultraviolet light having a short wavelength and high spatial efficiency. Against this background, single crystal fluoride materials have high transmissivity, and have been greatly expected as lasers and optical materials, particularly lasers and optical materials in the ultraviolet region. However, it has been recognized that it has been extremely difficult to produce a fluoride single crystal that can be used as a laser or an optical material, that is, a high-quality fluoride single crystal without a light scatterer. In addition, during the growth of single crystal fluorides, the raw materials are refined and refined, and the crystals are grown. Researchers have been aware that the process must be performed in the toxic gas HF (hydrofluoric acid), and researchers have been relatively reluctant to manufacture fluoride single crystals. There have been few detailed reports on the growth of single crystal halides.

In addition, ordinary Balta crystals did not satisfy the phase matching conditions, and were not used for wavelength conversion devices. By the way, a technique called quasi-phase matching using polarization reversal has been conventionally known as a wavelength conversion technique. This quasi-phase matching is achieved by creating a periodic structure of the polarization by inverting the polarization of the crystal (for example, “Laser Research, Vol. 28, No. 9; ρ600-603 ( 2 0 0 0 years).. "; L i N b 0 ₃ E pin Takisharu growth and ultra-precision machining technology using waveguide S HG device" refer to Kawaguchi Ryusei Ho force M) wavelength using such quasi phase matching the conversion element, L i N b 0 ₃ or L i T a 0 ₃ such as ferroelectric oxide crystals have been known mainly.

However, these L i N b Omicron ₃ or L i T a Ο ₃ such ferroelectric oxide crystals have a wavelength 3 0 0 nm absorption edge in the vicinity, the wavelength range is the wavelength 3 0 that can be applied as the wavelength conversion element The wavelength conversion is limited to 0 nm or more, and wavelength conversion using quasi-phase matching cannot be performed in the deep ultraviolet region with a wavelength of 300 nm or less or the vacuum ultraviolet region with a wavelength of 200 nm or less. . In recent years, CLBO crystals have been energetically studied as wavelength conversion devices to shorten the wavelength of all-solid-state coherent light sources. That is, since the CLBO crystal has large birefringence, it is possible to perform wavelength conversion by phase matching using this birefringence, and to shorten the wavelength.

However, in wavelength conversion by phase matching utilizing the birefringence of the CLBO crystal, there was a problem that the wavelength was limited to 195 nm due to its refractive index dispersion. That is, in the prior art, there is no light source capable of easily and stably generating deep ultraviolet light having a wavelength of 300 nm or less or vacuum ultraviolet light having a wavelength of 200 nm or less, and a proposal for such a light source is strongly desired. Had been rare. The present invention has been made in view of the above-mentioned demands for the conventional technology, and has as its object the purpose of the present invention is to use ultraviolet light having a short wavelength and high spatial resolution, in particular, a deep ultraviolet light having a wavelength of 300 nm or less. #Provide a method for manufacturing a fluoride single crystal and a wavelength conversion element that can be used to construct a light source that can easily and stably generate vacuum ultraviolet light with a wavelength of 200 nm or less and a spring. To do. Disclosure of the invention

In order to achieve the above object, a method for producing a single crystal of fluoride according to the present invention is a method for producing a single crystal of fluoride, which is produced by growing a crystal by the Tyzo-Kralski method. Further, as the atmosphere gas during crystal growth, any one of CF ₄ gas, Ar gas, a mixed gas of Ar gas and CF ₄ gas, or N ₂ gas is used. Further, the method for producing a single crystal of fluoride according to the present invention is a method for producing a single crystal of fluoride produced by growing a crystal by the Czochralski method, wherein the inside of the furnace is set to a high vacuum before the start of crystal growth. It is.

A method of manufacturing a fluoride single crystal according to the present invention, the vacuum degree in the furnace prior to crystal growth start, is obtained as is 1 0- ³ torr or more.

Further, the method for producing a single crystal of fluoride according to the present invention is a method for producing a single crystal of fluoride produced by growing a crystal by the Cjochralski method. A heating source and a heat insulating material composed of graphite are used.

In addition, the method for producing a single crystal of fluoride according to the present invention is a method for producing a single crystal of fluoride produced by growing a crystal by the Cjochralski method. Using a heating source and a heat insulating material composed of alite, the growth conditions were a crystal rotation speed of 5 rpm to 25 rpm, a crystal pulling rate of 0.1 mmZh to 5 mmZh, and vacuum is not less 1 0- ³ torr or more, but the growth atmosphere was CF _4, a r gas, a r gas and CF ₄ mixed gas or N ₂ gas with the gas-les, such that if the deviation is there. The method for producing a single crystal of fluoride according to the present invention is described in the method for producing a single crystal of fluoride produced by growing a crystal by the Tyochralski method. A service composed of ait Heat source and with a heat insulating material, growing conditions, the crystal rotation speed is 10 r pm, pulling rate of the crystal is the 1 mm / h, the degree of vacuum prior to growth initiation is 10- ⁵ torr, the growth atmosphere it is obtained as is CF _4.

A method of manufacturing a fluoride single crystal according to the present invention, in Monore ratio and Ba F ₂ and Mg F ₂ as a raw material "1: 1" used in a proportion of, so as to produce a B aMgF ₄ as fluoride single crystal It was made.

Further, the wavelength conversion element according to the present invention is a wavelength conversion element made of a fluoride single crystal that has a predetermined transmittance, undergoes polarization inversion, and converts the wavelength by quasi-phase age.

The wavelength conversion element according to the present invention, which was one of the fluoride single crystal _{B aMgF 4, B a S r} F 4, B a S r F 4, B a Z nF 4 or B aMn F ₄ is there.

Further, a wavelength conversion element according to the present invention is one wherein the above-mentioned fluoride single crystal is produced by the method for producing a fluoride single crystal according to the present invention.

Further, in the wavelength conversion element according to the present invention, the above-mentioned fluoride single crystal is BaMg F ₄ produced by the method for producing a fluoride single crystal according to the present invention.

Further, the wavelength conversion element according to the present invention achieves a quasi-phase matching by forming a periodic structure of polarization by reversing the polarization of the fluoride single crystal produced by the method for producing a single crystal fluoride according to the present invention. is there. Using the wavelength conversion element according to the present invention, the wavelength 1 / zm at which the most stable light source can be obtained The laser light of solid-state lasers and near-infrared semiconductor lasers can be wavelength-converted by quasi-phase matching to generate deep ultraviolet light with a wavelength of 300 nm or less and vacuum ultraviolet light with a wavelength of 200 nm or less. it can.

In other words, according to the present invention, a deep ultraviolet region having a wavelength of 300 nm or less or a vacuum ultraviolet region having a wavelength of 200 nm or less, which could not be used until now, was obtained by using a quasi-phase matching method. It can be generated by wavelength conversion, and an all-solid-state coherent light source can be achieved. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of a manufacturing apparatus for performing a method for manufacturing a single crystal of fluoride according to an example of an embodiment of the present invention.

Figure 2 is a graph showing transmittance measurement results of the produced B a M g F ₄ single crystal by the present invention.

FIG. 3 is a graph showing an example in which no polarization inversion has occurred in the crystal. Figure 4 is a graph showing experimental results relating to the polarization inversion produced by the present invention B a M g F ₄ single crystals.

Figure 5 is a schematic illustration of use les were ultraviolet light source as a wavelength conversion element manufactured B a M g F ₄ single crystal by the present invention. Explanation of reference numerals

1 0 Furnace using the Czochralski ^ method (Cz furnace) 12

14 Heater

16 crucible

18 shaft

18a lower end

20 Computer

22 Vacuum pump

24 gas .taliner

Single crystal of 30 B aMg F ₄

100 titanium sapphire laser

102 KTP crystal

104 KTP crystal

BEST MODE FOR CARRYING OUT THE INVENTION 106 B aMgF ₄ Single Crystal

Hereinafter, an example of an embodiment of a method for producing a fluoride single crystal and a wavelength conversion element according to the present invention will be described in detail with reference to the accompanying drawings. First, FIG. 1 shows a schematic diagram of a manufacturing apparatus for performing a method for manufacturing a fluoride single crystal according to an example of an embodiment of the present invention.

That is, in the method for producing a single crystal of fluoride according to the present invention, the fluorine In FIG. 1, reference numeral 10 denotes a furnace (Cz furnace) by the Tiyo-Kranoreskey method.

The Cz furnace 10 includes a vacuum chamber 12, a heater 14 including a heating source and a heat insulating material disposed in the vacuum chamber 12, a crucible 16 heated by the heater 14, The lower end 18a has a shaft 18 which can fix the seed crystal and pull it upward while rotating.

Further, a computer 20 is connected to the Cz furnace 10 and various controls including temperature control of the heater 14 are performed by the computer 20, such as a rotation speed and a lifting speed of the shaft 18. The control of the crystal growth conditions is performed. Further, a vacuum pump 22 composed of a rotary pump, a diffusion pump, and the like is connected to the _CZ furnace 10, and the inside of the vacuum chamber 12 is maintained at a desired vacuum degree by the vacuum pump 22. You.

Further, a gas cleaner 24 filled with NaOH is connected to the vacuum pump 22, and the gas exhausted from the vacuum pump 22 by the gas cleaner 24 (as described later) In the embodiment, CF ₄ gas is introduced into the C z furnace 10 as an atmosphere gas at the time of crystal growth by the C z method. Here, the heater 14 is made of high-purity graphite, and the crucible 16 is made of platinum. Further, the heater 14 is heated by a high-frequency fe-heating method. In the above configuration, a case where BaMgF ₄ is produced as a fluoride single crystal by the method for producing a fluoride single crystal according to the present invention using the production apparatus shown in FIG. 1 will be described.

In this embodiment, the degree of vacuum in the Cz furnace 10 before the start of crystal growth is set at 10 to ⁵ torr. In this embodiment, CF ₄ gas (purity: 4N (99.99%)) is introduced into the Cz furnace 10 in order to grow a BaMg F ₄ single crystal in a CF ₄ atmosphere. .

In these conditions, B a F ₂ and with Mg F ₂ Toomo Le ratio as a raw material in the crucible 16 "1: 1" placed at the rate of heating by the heater 14 (heating ag: 900 ° C) and To dissolve. A seed crystal is fixed to the lower end 18 a of the shaft 18.

Then, the shaft 18 is inserted into the crucible 16 from the upper part of the crucible 16, and the seed crystal fixed to the lower end part 18 a of the shaft 18 is brought into contact with the liquid surface in which B a F ₂ and M g F ₂ are dissolved, A single crystal 30 of BaMg F ₄ is formed by gradually pulling up while rotating the shaft 18.

To summarize the growth conditions of B AMG F ₄ single crystal in this embodiment, is as follows.

• Crystal rotation speed (shaft 18 rotation speed) 10 rpm

■ Crystal pulling speed (shaft 18 pulling speed) lmm / h

And growth before the start of the degree of vacuum of 10- ⁵ torr

'' Growth atmosphere CF ₄ Here, in the method for producing a fluoride single crystal according to the present invention, in order to suppress the generation of a cloudy substance due to the reaction of a small amount of water in the Cz furnace 10 and the raw material with the powder raw material, the method becomes a source of water and oxygen. In order to remove any substances from the Cz furnace 10, the heater 14, which constitutes the heat source and the heat insulator, is made of high-purity graphite.

In order to improve the efficiency of water removal, for example, it was grown in a high vacuum of 10- ⁵ torr.

Further, as the atmosphere gas for crystal growth, CF ₄ gas of high purity, for example, 4N (99.955) purity was used.

When the crystal was grown under the growth conditions as described above, a transparent BaMg F _{4 with} a diameter of about 20 mm and a length of about 8 Omm free from the adhesion of cloudy substances and cracks and inclusions was obtained as a fluoride single crystal. A single crystal could be produced.

The B AMG F ₄ single crystal was cut to "16 mm (vertical) X 32 mm (lateral) X 2. 5 mm (thickness)", using what was mirror polished as a sample was subjected to transmission measurements.

Fig. 2 shows the results of the transmittance measurement. As shown in Fig. 2, the transmittance was high at about 200% at a wavelength of 200 ηm and about 50% at a wavelength of 140 nm, even in the deep ultraviolet region. However, in this transmittance measurement, loss due to reflection from the crystal surface is not taken into account.

In other words, by removing water during the crystal growth stage, And a transparent material could be produced. Next, an experiment for confirming the polarization reversal in this sample was performed using the above-described sample.

An experiment to confirm this polarization inversion was performed by applying a voltage to both surfaces of the sample and observing the current flowing through the sample at that time.

Here, when no polarization reversal occurs in the crystal, the crystal acts as a capacitor when a voltage is applied to the crystal, and a current flows only when the voltage changes.

On the other hand, when polarization reversal occurs in the crystal, current flows due to the movement of ions even after the voltage applied to the crystal is kept constant.

The graph shown in Fig. 3 (where the horizontal axis is time and the vertical axis is current) shows an example in which no polarization inversion occurs in the crystal, and as the voltage applied to the crystal increases, When the current force S is generated and the voltage for imprinting tf on the crystal becomes steady, the current stops flowing (see the two peaks in the graph in Fig. 1).

On the other hand, the graph shown in Fig. 4 (the horizontal axis is time and the vertical axis is current) shows the experimental results of the sample described above. It can be seen that the decrease of the value occurs exponentially little by little. The inversion of the polarization can be confirmed by;? In the tail of this current change. That is, the present invention according to the fluoride single crystals have been B a M g F ₄ single crystal produced by the method is to create a periodic structure of polarization to form a polarization inversion, to achieve quasi phase matching Can be Accordingly, B a M g F ₄ single crystal, it is possible to constitute a wavelength conversion element performs wavelength conversion by quasi phase matching using the polarization inversion. Next, an ultraviolet light source using the above-described sample as a wavelength conversion element will be described with reference to FIG.

Fig. 5 is a schematic diagram illustrating the structure of this ultraviolet light source. KTP crystal 102, which is a non-linear crystal as a wavelength conversion element that enters and converts it to its second harmonic (wavelength 471 nm), and laser light (wavelength 471 ηm) emitted from KTP crystal 102 The KTP crystal 104, which is a non-linear crystal as a wavelength conversion element that converts the laser light of 942 nm wavelength emitted from the sapphire laser 100 into a third harmonic (wavelength 314 nm), The laser beam (wavelength 314 nm) emitted from the crystal 104 is incident and a second harmonic (wavelength 157 nm) with a wavelength of 314 nm is emitted. It is configured to include a B AMG F ₄ single crystal 106 as a wavelength conversion element for converting the wavelength 157 nm).

Here, the BaMg F ₄ single crystal 106 is manufactured by the method for manufacturing a single crystal fluoride according to the present invention as described above.

In other words, in this ultraviolet light source, the laser light having a wavelength of 942 nm emitted from the titanium sapphire laser 100 is doubled by the wavelength conversion using the KTP crystal 102. Of converting the wavelength 471 nm, in the same manner to the incident laser light of the resulting wavelength 314 nm is converted to the third harmonic at a wavelength conversion using a KTP crystal 102 to B a M g F ₄ single crystal 10 6 By converting the wavelength, an all-solid-state deep ultraviolet laser with a wavelength of 157 nm has been realized. That is, the single crystal of fluoride produced according to the present invention has a high transmittance even in the deep ultraviolet region of about 80 ° at a wavelength of 180 nm and about 50% at a wavelength of 140 nm, and is easily and reversibly polarized. By using these fluoride single crystals as a wavelength conversion element, a wavelength conversion element capable of performing wavelength conversion by quasi-phase matching in a wavelength region of a wavelength of 300 nm or less can be configured.

As a result, it becomes possible to realize an all-solid coherent light source capable of generating light with a wavelength of 300 nm or less. The above-described embodiment may be modified as shown in (1) to (7) described below.

(1) In the above-described embodiments, the example of producing the B aMgF ₄ as fluoride single crystals showed a example in which the wavelength conversion element by B a M g F _4, limited to these Of course, it is not something that can be done.

That is, by changing the raw material appropriately, as the fluoride single crystal according to the present invention, for _{example, B a S r F 4,} B a Z n F 4 or B a Mn F ₄ can be produced like, also The wavelength conversion element is, for example, Ba Sr F ₄ , Ba ZnF ₄ or Ba It can be constituted by M n F _4.

(2) In the above embodiment, the crystal rotation speed (the rotation speed of the shaft 18) was set to 10 rpm, but it is needless to say that the present invention is not limited to this. That is, the crystal rotation speed (the rotation speed of the shaft 18) may be appropriately set, for example, between 5 rpm and 25 rpm.

(3) In the embodiment described above, the crystal pulling speed (the pulling speed of the shaft 18) is lmm / h, but it is needless to say that the present invention is not limited to these.

RRB

That is, the crystal pulling speed (shaft 18 pulling speed) is, for example, 0.1 ImmZl! It may be set appropriately between 5 mm / h and 5 mm / h.

(4) In the embodiment described above, the same _four gases are used. _{Although the} crystal was grown in _four atmospheres, it is a matter of course that the present invention is not limited to these. That is, as the atmosphere gas, for example, Ar gas, a mixed gas of Ar gas and CF ₄ gas (mixing ratio: “1: 1” in molecular weight) or N ₂ gas can be appropriately selected.

Also, the purity of the above-mentioned various atmosphere gases is not limited to 4N (99.99%).

That is, the purity of the atmosphere gas may be appropriately set, for example, between 3N (99.9%) and 9N (9.99.9999999%).

(5) In the above-described embodiment has been set degree of vacuum before the growth starts 10_ ^5-to 1-r, it is of course not limited to these, for example, 10 One ³ torr or more, preferably, 10 one ³ torr ~ l. It may be ¹¹ torr.

(6) In the above-described embodiment, the heater 14 is heated by the high-frequency heating method. However, it is needless to say that the heater 14 is heated by the resistance heating method. Good.

(7) The above embodiments and the modifications shown in (1) to (6) above may be used in appropriate combination. Industrial applicability

Since the present invention is configured as described above, it can easily and stably generate ultraviolet light having a short wavelength and high spatial performance, in particular, deep ultraviolet light having a wavelength of 300 nm or less and vacuum ultraviolet light having a wavelength of 200 nm or less. The present invention has an excellent effect that a method of manufacturing a fluoride single crystal and a wavelength conversion element that can be used to construct a light source capable of performing the method can be used.

Claims

The scope of the claims

1. In a method for producing a single crystal of fluoride produced by growing a crystal by the Chiyoklarski method,

Either CF ₄ gas, Ar gas, a mixed gas of Ar gas and CF ₄ gas, or N ₂ gas is used as the atmosphere gas for crystal growth

A method for producing a fluoride single crystal.

2. In a method for producing a fluoride single crystal produced by growing a crystal by the Chiyoklarski method,

High vacuum inside furnace before crystal growth starts

A method for producing a fluoride single crystal.

3. In the method for producing a fluoride single crystal according to claim 2,

The degree of vacuum in the furnace before starting crystal growth is 10 ³ torr or more

A method for producing a fluoride single crystal.

4. In a method for producing a single crystal of fluoride produced by growing a crystal by the Czochralski method,

Heat source and heat insulator composed of high-purity graphite are used as heat and heat insulator in the Chiyoklarski method. A method for producing a fluoride single crystal.

5. In a method for producing a single crystal of fluoride produced by growing a crystal by the Czochralski method,

As the heating source and heat insulating material in the Chiyoklarsky method, a heating source and heat insulating material composed of high-purity dalaphite were used.

The growth conditions are

The crystal rotation speed is 5 r pn! ~ 25 rpm,

The crystal pulling speed is 0.1 mmZh to 5 mm / h,

The degree of vacuum before the start of the growth is not less 1 0- ³ torr or more,

The growth atmosphere is CF ₄ , Ar gas, a mixed gas of Ar gas and CF ₄ gas, or N ₂ gas

A method for producing a fluoride single crystal.

6. In a method for producing a single crystal of fluoride produced by growing a crystal by the Czochralski method,

As the power and heat insulator in the Chiyoklarski method, a heat source composed of high-purity graphite and a heat insulator are used.

The growth conditions are

The crystal rotation speed is 10 rpm,

The crystal pulling speed is 1 mmZh, The degree of vacuum before the start of the growth is 10- ⁵ torr,

Growth atmosphere at the CF ₄

A method for producing a fluoride single crystal.

7. The method for producing a fluoride single crystal according to claim 6,

And Ba F ₂ and MgF ₂ in a molar ratio as the starting material: used in a proportion of "1 1", to produce the B AMG F ₄ as fluoride single crystal

A method for producing a fluoride single crystal.

8. It is made of a single crystal of fluoride that has a predetermined transmittance, is polarization-inverted, and performs wavelength conversion by quasi-phase matching.

Wavelength conversion element.

9. The wavelength conversion element according to claim 8,

The fluoride single crystal, is either _{B aMgF 4, B a S r} F 4, B a S r F 4, B a Z n F 4 or B aMnF ₄

Wavelength conversion element.

10. The wavelength conversion element according to claim 9,

The single crystal fluoride is manufactured by the method for manufacturing a single crystal fluoride according to any one of claims 1, 2, 3, 4, 5, and 6. Was

Wavelength conversion element.

11. The wavelength conversion element according to claim 8,

The fluoride single crystal is a B a M g F ₄ A manufactured by the manufacturing method of the fluoride single crystal according to claim 7

Wavelength conversion element.

1 2. It is manufactured by the method for manufacturing a single crystal fluoride according to any one of claims 1, 2, 3, 4, 5, 6, or 7. A quasi-phase matching was achieved by creating a periodic structure of polarization by reversing the polarization of a fluoride single crystal.

Wavelength conversion element.