JP2003034595A - Method of manufacturing lithium tetraborate single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical conversion element which operates stably over a long period of time, exhibits a long service life, has excellent workability, is compact lightweight, and low-cost. SOLUTION: When conducting a manufacturing method for single crystalline lithium tetraborate where molten polycrystalline lithium tetraborate (Li2 B4 O7 ) is pulled up in a prescribed orientation by a Czochralski method, a single crystalline Li2 B4 O7 is manufactured under the following conditions in which the temperature gradient between the surface of a molten liquid and 10 mm right over the surface is 30 deg.C-200 deg.C/cm, the temperature gradient above 10 mm is 5 deg.C-50 deg.C/cm, the pulling up speed is 0.1 mm-2 mm/h, the refractive index variation is <=10<-5> /mm, and the dislocation density is about <=1×10<3> pieces/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] TECHNICAL FIELD The present invention relates to a single crystal tetraborate
Titanium (single crystal Li_Two B_Four O₇ Or single crystal LBO)
The present invention relates to a method for manufacturing an optical conversion element using the method. [0002] 2. Description of the Related Art The single crystal LBO of the present invention is used as an optical conversion element.
As the optical device used as the second harmonic, the fourth harmonic,
Wavelength conversion element that generates the fifth harmonic, etc., and this wavelength conversion
Laser devices using devices, optical parametric oscillation
Device, prism using wavelength conversion element,
Polarizing device used, optical waveguide element using single crystal LBO, single crystal
Equipment using crystalline LBO as a nonlinear optical conversion element
It has been known. The use of laser light having a short wavelength reduces the recording density.
It has the advantage that it can be made larger. Therefore, record
Data recording on media, reading data from recording media
Light source that emits short-wavelength laser light is required as the light source
Have been. Also, laser light with a short wavelength is used for material processing.
When used, fine processing becomes possible. More medical light
Source, VLSI lithography light source, etc.
There is a need for a light source that emits the light. [0004] SUMMARY OF THE INVENTION However, 500
There is a suitable light source that emits light of sub-nm wavelength
do not do. For example, a semiconductor laser has a wavelength of about 400 nm.
It has been known that laser light can be emitted up to
There is a problem that power is very low. Short wavelength high power laser
An excimer laser is known. Excimale
Was reported by Basov et al. In the Soviet Union in 1970.
To excite liquid xenon (Xe) with an electron beam
Method for the first time, and in 1976,
Therefore, it oscillated successfully. Discharge excitation method
Shima laser is an ultraviolet pulse repetition oscillation laser.
ArF (193 nm), KrF (248 nm), XeC
Optical resonance of ultraviolet light emitted by compounds such as 1 (308 nm)
Increased by a filter and extracted as laser light.
You. Excimer lasers are used for ablation of polymer materials.
Engineering, surface modification, marking, thin film production, pharmaceutical manufacturing,
It is expected to be applied to isotope separation. But
Excimer laser, for example, has a repetition of several hundred pps (p
pulse per second)
10^-210 every second^-9Only pulse light for a second is generated,
The laser emission time is significantly shorter than the interval.
Therefore, there is a problem in the processing and deposition process in the application field.
You. Excimer lasers have a short medium gas life.
Difficulties in downsizing the laser device and poor maintainability
High operating cost, use toxic gas
Etc. Currently stable at normal temperature for a long time
And practical applications such as semiconductor lasers that emit light in the ultraviolet range
Has not been achieved. Therefore, the second harmonic generation (SHG: second)
ary harmonic-wave generation)
Research on devices has recently been active. SHG element is incident light
Generates light of half the wavelength of
Generation of light in the ultraviolet range from laser light in the infrared range
The industrial value for various application fields is extremely large
No. In particular, optical information processing for high-density information recording / reproduction
Field, display, optical measurement, processing, medical, LSI manufacturing
In any field, small, light, long-life and highly stable visible light
Or ultraviolet light is needed. For use as a wavelength conversion element such as an SHG element
Examples of the crystal used include, for example, JP-A-3-65.
No. 597, KTP (KTiOPO
_Four )It has been known. However, waves using KTP
The length conversion element has a KTP transmittance with respect to the wavelength of the laser incident light.
Bright area is wide from 0.25 to 4.5 µm, but 1 µm or less
There is a disadvantage that phase matching is not performed below. That
As a result, the wavelength conversion element using KTP
When YAG laser light is used, the frequency is twice as high as the frequency of the light.
Only light having a wave number (1/2 wavelength) can be generated. But
However, recently, higher harmonics, such as the fourth harmonic
It is desired to generate light such as waves and fifth harmonics.
You. In addition, the wavelength conversion element using KTP requires a large crystal.
And the refractive index changes inside the crystal. Accordingly
Even a KTP element cut out of a single crystal has a refractive index of
Since the phase matching angle is different because of the difference, the wavelength with high accuracy
With the disadvantage that it is difficult to realize a conversion element
I have. In addition, KTP has a so-called “nest” in the crystal.
Because it is difficult to provide large quantities of high quality KTP
Has the disadvantage of For use as a wavelength conversion element such as an SHG element
Other crystals that have been used include, for example,
BBO (β-B) disclosed in
aB _Two O_Four )It has been known. However, BBO
Has higher laser damage resistance than KTP, but is soluble in water
Deliquescence, there are difficulties in handling, and large
There is a disadvantage that it is difficult to make a crystal. An object of the present invention is to operate stably for a long time.
, Long life, good workability, small size, light weight, low price
It is an object of the present invention to provide a method for manufacturing an optical conversion element. [0009] According to the present invention, there is provided a method for melting molten metal.
Polycrystalline lithium tetraborate (Li_Two B_Four O₇ )
Pull up by Czochralski method in the pulling direction of
In the method for producing crystalline lithium tetraborate, the melt surface
And a temperature gradient between 10 mm immediately above the melt and 30 ° C./cm
00 ° C / cm, the temperature gradient above 5 ° C / cm
50 ° C./cm, lifting speed 0.1 mm / hour to 2 m
m / h, pull up, change in refractive index is 10^-Five/ Mm or less
Bottom and dislocation density of about 1 × 10^Three Pieces / cm^Two below
Single crystal Li _Two B_Four O₇ Manufacturing a single bond
A method for producing crystalline lithium tetraborate is provided. [0010] DETAILED DESCRIPTION OF THE INVENTION The above and other objects of the present invention and
And features are described in the preferred embodiment below with reference to the accompanying drawings.
It becomes clearer from the description. [0011] The inventor of the present application is a single-crystal lithium tetraborate.
(Single crystal Li_Two B_Four O₇ Or abbreviated as single crystal LBO)
As a result, the single-crystal LBO has a wavelength of the laser incident light.
Large transparent area, large laser damage resistance, good
Quality large crystals are easy to produce, excellent in processability, deliquescent
An excellent optical conversion element with low performance and easy handling
Utility value. Hereinafter, the single crystal LB of the present invention
O and this single crystal LBO were used for an optical conversion element.
Various preferred embodiments (EMBODIMENTS) for the cases are detailed below.
It will be described in detail. [0012] The "single crystal LBO of the present invention (or
In the case of single crystal LBO of the embodiment, it is manufactured by the following method.
Single-crystal LBO, and "normal single-crystal LBO"
Conventional single crystal LBO used for SAW devices, etc.
Say Unless otherwise specified as "single crystal LBO", both
means. [0013]Basics of single crystal LBO Hereinafter, the single crystal L mainly as the optical conversion element of the present invention will be described.
The basic matter of BO will be described. [0014]Production method A preferred method for producing a single-crystal LBO of the present invention (growing method)
State. According to the Czochralski method (CZ method) shown in FIG.
Using a single crystal LBO pulling device 110
The single crystal LBO of the present invention is manufactured from LBO. Raising
The apparatus 110 is a platinum crucible in which polycrystalline LBO is melted.
It has a pot 101. Li_Two B_Four O₇ Is low among oxides
Since it has a melting point, it can be grown in a platinum crucible. Platinum crucible 10
1 is surrounded by a platinum crucible through heat insulating materials 102 and 103.
Heater 1 for melting polycrystalline LBO in tub 101
04, for example, a resistance heater is provided. Platinum crucible
On the upper part of the pot 101, two heat insulating walls 105 and 106 are provided.
Pulling shaft 10 to which the seed crystal is attached
7 penetrates the heat insulating walls 105 and 106. This pull
Using a lifting device 110 to convert an optical transducer
Grow single-crystal LBO with characteristics according to its use as a child
After that, depending on the purpose of use, the single crystal LBO is
On the other hand, processing such as cutting at a predetermined angle is performed. Simple connection
An example of the conditions for growing crystalline LBO will be described. Predetermined molar ratio
Is filled in the platinum crucible 101 and the heater 1
After melting at 04, single crystal L
Raise BO. At this time, the surface of the melt and the
temperature gradient between 30 ° C./cm to 200 ° C./cm,
Preferably 50 to 150 ° C./cm, temperature above
The temperature gradient is 5 ° C / cm to 50 ° C / cm, preferably 10 ° C / cm.
Up to 40 ° C / cm and pull up the straight body of single crystal LBO
0.1mm / hour to 2mm / hour
And preferably 0.3 to 1 mm / hour. Atmosphere between the surface of the melt and 10 mm immediately above the melt
Of the temperature gradient of 30 ° C / cm to 200 ° C / cm
State. Pull up if the temperature gradient is less than 30 ° C / cm
LBO is easily polycrystallized. Temperature gradient is 2
If it is higher than 00 ° C / cm, it will be pulled up due to thermal strain.
Dislocations are likely to occur in the obtained single crystal LBO. The temperature of the atmosphere above 10 mm just above the melt
The reason for setting the gradient to 5 ° C./cm to 50 ° C./cm will be described.
By reducing the temperature gradient, the thermal expansion
Cracks can be suppressed. The lifting speed is 0.1 mm / hour to 2 mm
/ Reason for time. Lifting speed from this value
If it is increased, the normal LBO bond used for surface acoustic wave
Like crystals, white turbidity, or "nests,"
It will be cool. Regarding a normal LBO manufacturing method and its characteristics
Will be described later. In the method for growing a single crystal LBO according to the present invention,
A single crystal of 1 inch or more can be grown. Example
According to this, a single crystal having a diameter of 4 inches could be grown. [0019]Dislocation density As will be shown later in various experimental results, a conventional single crystal LBO
But an optical conversion element that is superior to KTP, BBO, etc.
It was found to work with offspring. However, more hope
Considering from the viewpoint of a better optical conversion element,
Single crystal LBO used as substrate material for SAW devices
Incorporation of dislocations and impurities that was not a problem when
And other defects absorb and scatter the laser light, causing wavelength conversion.
The wavelength conversion efficiency of the device is not so high (the
Quality is not high). Of course, with normal single crystal LBO
Also show higher optical properties than KTP and BBO,
Higher nonlinear optical constants were desired. The single bond of the present invention manufactured under the above manufacturing conditions
Crystal LBO has a low dislocation density. As a result of the research, the dislocation density
Using the small single crystal LBO of the present invention as an optical conversion element
Then, the laser light is absorbed by the ordinary single crystal LBO,
Minimal scattering, so that optical properties can be properly exhibited
Was found. That is, the primary dislocation density
When a bright single crystal LBO is used for the wavelength conversion element,
Absorption and scattering are reduced, and conversion efficiency is increased (emission
Light beam quality is increased). More than
Single crystal of the present invention from polycrystalline LBO by growing method and conditions
When LBO is grown, the dislocation density becomes 1 × 10^Three Pieces / cm^Two
It becomes a small value as follows. When the refractive index fluctuation is measured, 10
^-Five/ Mm or less. The method for measuring dislocation density
Observation of etch pits by etching and X-ray topography
Observation is performed by the method. Used for optical wavelength conversion element
The dislocation density of the single crystal LBO of the present invention is 0 to 1 × 10^Two
Pieces / cm^Two The following is preferred. Note that the SAW device base
The dislocation density of ordinary single-crystal LBO used for plate materials, etc. is 1
× 10^Three Pieces / cm^Two Larger, cloudy, so-called "nest"
Is often present. Of course, such a single crystal L
Even if BO is used, it can be used as an optical conversion element from BBO and KTP.
It turned out that all the functions were above. [0021]Optical properties According to the study of the present inventor, as shown in FIG.
At a specific angle with respect to the optical axis (c-axis) of the BO,
When laser light is applied, wavelength conversion can be performed.
I found that. The phase matching angle is used as a reference for the angle.
Degree θm is used. Angle of fundamental wave to optical axis
When incident at θm, the phase was matched in the same direction as the fundamental wave
A second harmonic is generated. This angle θm is defined as a phase matching angle.
To tell. Single crystal LBO is a negative uniaxial crystal. And
The phase matching condition is a type I crystal. Therefore, the figure
As shown in FIG. 2, the phase matching conditions include a phase matching angle.
It has been found that only θm needs to be considered. [0022]Characteristic 1. Since the single crystal LBO has a uniform composition, the upper part of the crystal
And the lower part does not cause composition deviation. 2. Single-crystal LBO is another known material that constitutes a wavelength conversion element.
Low deliquescence, stable, and easy to handle
Are better. By the way, if the deliquescence is large,
It is necessary to house the replacement element in a closed container and control humidity.
As a result, the configuration of the device becomes complicated and the size becomes large.
However, single crystal LBOs do not have that problem. 3. Single crystal LBO has the same crystal hardness as quartz.
It also has good workability such as polishing and cutting. 4. Single crystal LBO is another crystal constituting the wavelength conversion element.
The production cost is also lower than that of. 5. Since single crystal LBO is a paraelectric substance, polarization processing is not required.
It is important. Moreover, quasi-phase matching (QP
M: a phenomenon similar to Quasi-phase Matching
The wavelength of the emitted light can be converted with high efficiency. What
In this case, C⁺Rotating the shaft 180 degrees
Wavelength conversion by quasi-phase matching (QPM)
Call. The feature of this QPM is that the phase is set by setting the cycle length.
That is, the matching wavelength can be freely set. Also, single crystal
LBO uses twins to create multiple periods.
As a result, the phase matching wavelength range can be expanded. More simple
Crystal LBO has more than twice the allowable temperature range required for phase matching
growing. Furthermore, single-crystal LBO is bulk
Can also be used in the form of an optical waveguide. Furthermore, single crystal LBO
Can use a nonlinear optical constant d (33).
These QPMs are C ⁺ Rotate the axis 180 degrees
It can be applied only to ferroelectrics because
Although it was thought, the research of the inventor
It has been found that the present invention can be applied to the single crystal LBO of the present invention.
The above features make single crystal LBO practical as an optical conversion element.
Is especially important for [0023]Applications of single crystal LBO 1. Wavelength conversion element The present inventor has described the optical characteristics of the single crystal LBO of the present invention.
As a result of research, wavelength conversion equal to or higher than KTP or BBO
I found that it was possible. In particular, use single crystal LBO
For example, by using a wavelength conversion element
As a typical example, an Nd: YAG laser (wavelength 1064 n
m), the fourth harmonic (266 nm) with high coherence,
Succeeded in generating light of the fifth harmonic (213 nm) wavelength
did. Producing light of wavelength 4 or 5
If possible, use infrared lasers for which high-power devices have already been developed.
Laser in the UV or near UV range
The light can be easily created. Therefore,
In addition to fine processing, marking, lithography
, Various semiconductor processes, medical care, etc.
Application becomes possible. The present inventor has proposed that a single crystal LBO is
Wavelength of incident light when used as a replacement element (device)
Is wider than other crystals and wavelength conversion
They have found that they are practically suitable as devices. Transparent
If the area is not wide, only for a specific wavelength of light
Although it cannot be used as a wavelength conversion element,
Such a wavelength conversion element is a wavelength conversion element for a wide range of light.
Can be used as Single crystal LBO is converted to wavelength
When used in a resonator, the nonlinear optical constant is small, but high quality
It is easy to make a type crystal (currently, a single crystal L with a diameter of 4 inches)
BO can be created), and by making it a large crystal,
The conversion efficiency can be increased. The laser output is
The efficiency increases in proportion to the square of the strength and the square of the length of the crystal.
You. The present inventors have used single crystal LBO as a wavelength conversion element.
Laser damage threshold is higher than that of other crystals.
Remarkably large and practically suitable as a wavelength conversion element.
I found something. Low laser damage resistance threshold
And the energy of a small laser can damage the crystal.
And the durability as a wavelength conversion element becomes a problem.
Become. In the wavelength conversion element according to the present invention, laser damage-resistant
High threshold enables higher power laser output
In addition, it has excellent durability. 2. Various laser devices The wavelength conversion method using the single crystal LBO according to the present invention
By transmitting laser light through the single crystal LBO,
The wavelength of the laser light is converted using single crystal LBO.
Two or more laser beams simultaneously to the wavelength conversion element
And the sum frequency or difference frequency of those laser light wavelengths
It is also possible to configure a laser device that obtains a wave laser beam.
I found that. 3. Optical parametric oscillator The inventor of the present invention has proposed an optical parameter using single crystal LBO as a wavelength conversion element.
It has also been found that metric oscillation can be performed. Hereinafter, a single crystal LBO is used as an optical conversion element.
Single crystal LBO tool suitable for each optical device used
A concrete example (EXAMPLE) related to the device for that application
This will be described in detail. [0027]First embodiment As a first embodiment of the present invention, a second harmonic element (wavelength conversion
Single crystal Li used as element)_Two B_Four O₇ (Single crystal LB
O) will be described.Production (growth) of the single crystal LBO of the present embodiment Using the lifting device 110 shown in FIG.
(Stoichiometric) polycrystalline LB with a purity of 99.99% by weight
O, 1300g, platinum crucible 90mm in diameter and 100mm in height
Fill the pot 101 and tie it by Choco-Larsky (CZ) method
Crystal LBO was grown. FIG. 2 shows the phase matching angle of single crystal LBO.
It is a graph which shows the definition of a degree. The contents of this diagram are described above.
Was. [0028]Processing of single crystal LBO of this embodiment As shown in FIG. 3, the cut surface 3 with respect to the optical axis (C axis)
Cut the single crystal LBO so that the angle of 2 is 45 degrees
Then, the cut surface 32, which is the input / output surface, is optically polished,
× 15 mm × 10 mm single crystal LBO optical conversion element 30A
It was created. This optical conversion element 30A is a laser beam or the like.
When the coherent light i of
For second harmonic generation (SHG) that emits light of wavelength o
It functions as an optical conversion element (wavelength conversion element). But
Thus, the single crystal LBO of the present invention is
When the incident light of nm (0.532 μm) enters,
Emits light with a wavelength of 266 nm (0.266 μm)
Used as wavelength converter 30A for second harmonic (SHG)
it can. [0029]Refractive index fluctuation of single crystal LBO of this embodiment Single-crystal LB of this embodiment using a Mach-Zender interferometer
When the refractive index variation of O was measured,^-6/ Mm
Was. [0030]Experimental example 1 As an experimental example 1, the wavelength conversion element 30A is
48 from Lametric Oscillator (Spectra Physics)
A laser beam in the range of 6 to 1265 nm
Of the second harmonic in the range of 243 to 633 nm
(Coherent) light was obtained. Interference fringes at the transmitted wavefront
No disturbance was observed.Phase matching angle FIG. 4 is a direction orthogonal to the 45-degree cut surface 32 shown in FIG.
Laser beam incident angle to 0 degree, plus the c-axis direction,
The single crystal LBO is rotated with the (110) direction minus.
Each time it is generated from the optical parametric oscillator.
Injection of laser light when phase-matched at the wavelength of laser light
Shows the angle. From this angle of incidence,
The phase matching angle θm can be obtained. Figure 4 shows the actual
By satisfying the phase matching condition for the single crystal LBO of the experimental example,
When coherent light of a certain wavelength is incident,
This indicates that light of half the wavelength is emitted. below
In the experimental examples and examples, YAG laser
Using coherent light with a wavelength of 1064 nm
Many cases, but limited to 1064 nm incident coherent light
Instead, the single-crystal LBO of this experimental example has a range of the range illustrated in FIG.
With the ability to emit light of half the wavelength of the incident light
It was confirmed that there was. KTP, BBO, etc. are usually
Coherent light of wavelength 1064 nm from YAG laser
Is known to be able to convert to half the wavelength.
According to this experimental example using the light single crystal LBO, the wavelength 10
Coherent light of any wavelength is not limited to 64 nm coherent light.
It is verified that rent light can be converted to light of half wavelength
Was. Moreover, it can be converted to the shortest wavelength of 209 nm.
Verified. An apparatus using the following single crystal LBO,
For example, in wavelength converters and laser devices,
In the embodiment, the single-crystal LBO under the preferable conditions described above is used.
As an example, various single crystal LBOs of the present invention
Can be used. As illustrated in FIG.
When a crystal is irradiated with laser light from
The laser light travels while refracting in the crystal according to the refractive index.
The phase matching angle θm is determined by, for example,
Generates second harmonic when used as wavelength conversion element for
This is the angle between the refracted laser light and the c-axis at the time. FIG.
As is clear from the graph illustrated in FIG.
m laser light is incident on the surface 32 of the single crystal LBO
Is about plus 19 degrees. That is, wavelength 1
Fundamental wave of YAG laser emitting 064 nm laser light
Is incident, the incident angle is approximately plus 19 degrees and the phase is
Align. Since the refractive index of single crystal LBO is about 1.6,
The folding angle is about 12 degrees. Therefore, the angle with the c-axis,
That is, the phase matching angle is obtained as about 33 degrees. As well
By such a method, the phase matching angle for each wavelength can be determined. Table 1 shows the relationship between each wavelength and the phase matching angle.
You. [0032] [Table 1] The contents of Table 1 are based on the single crystal LBO of the present invention.
Wavelength is converted to half the wavelength of light
Shows the refractive index and phase matching angle of the single crystal LBO at that time.
You. The incident wavelength is the power from the optical parametric oscillator.
Light was used. Furthermore, the wavelength of 1064.0 nm
Light from YAG laser is also used, and light of 532.0 nm is used.
Uses the KTP as the SHG to convert the light of the YAG laser into half.
The wavelength of the minute was used. The phase matching method
Angular phase matching using birefringence and refractive index
There is a temperature phase matching method using temperature dependency. Rice cake
It is also possible to apply the latter phase matching method. [0034]Contents of Table 1 and Fig. 4 The graph of FIG. 4 shows that the incident light 1064 nm described above is
Not only wavelength conversion to 532 nm
According to the research of the investigators, the single crystal LBO of this example was used.
Fig. 4 shows the incident angle for other incident light.
Into the single crystal LBO of this example
The light of half the wavelength of the incident light is
This indicates that light can be emitted from the crystal LBO. Conventionally, incident
Research on wavelength conversion for incident light other than light 1064 nm
Not done. Table 1 is a specific example of the graph illustrated in FIG.
Some of the numerical values are illustrated. However, in Table 1
In this case, instead of the incident angle in FIG.
I have. Thus, the single crystal LB at several wavelengths
By measuring the refractive index of O and adapting the process
Thus, the Sellmeier equation is obtained. In addition, Se
Solving the llmeier equation at each wavelength
To calculate the phase matching angle
There is also. FIG. 5 shows wavelength conversion of the above-mentioned single crystal LBO.
532nm incident wavelength half the wavelength
Phase matching angle when converting to emission wavelength of 266 nm
FIG. 7 is a diagram geometrically showing a relationship between θm and an incident angle.
You. [0036]Wavelength conversion function Not only single crystal LBO, but also KTP and BBO are SHG
Function. However, as described later, the single crystal L
BO is the sum of two different wavelengths of coherent light or
By taking the difference (hereinafter collectively called sum frequency mixing)
1) of the wavelength 1064 nm of the light emitted from the YAG laser.
3 or 1/5 wavelength can be emitted, but KP
T does not have such a wavelength conversion function. BBO is 2
The sum or difference of two different wavelengths of coherent light
As with the single crystal LBO, the output light of the YAG laser
Emits 1/3 or 1/5 wavelength of 1064nm
But the walk-off angle is large.
In this case, large crystals cannot be used and conversion efficiency cannot be increased.
No. In contrast, the single crystal LB having a low dislocation density of the present invention
When O is used, incident light of a predetermined wavelength can be obtained with high conversion efficiency.
1/3 or 1/5 of the light emitted from the light source. Teens
Specifically, the wavelength of the light emitted from the YAG laser is 1064 nm.
1/3 or 1/5 wavelength can be emitted stably
You. [0037]Laser damage resistance The laser resistance of the wavelength conversion element made of the single crystal LBO of the present embodiment
The optical damage was measured by the following measurement method.
2, several tens of GW / cm^Two ~ 100 GW / cm
^Two And the laser light damage resistance of the single crystal LBO of this embodiment is
It was confirmed that it was 5 times or more of BBO. Laser light resistance
Damage gradually increases the power of the laser irradiating the crystal.
Comb and visually confirm that the crystal has been damaged,
Measure the force and use the laser beam
Measure the diameter and calculate the output per unit area by calculation.
And by [0038] [Table 2][0039]Transparency The wavelength conversion element 30 using the single crystal LBO of this embodiment
Investigation of the transparent region for the wavelength of the emitted laser light
As shown in Table 2, a wave of 170 nm to 3500 nm was used.
Ensure that it is transparent to long light and that the transparent area is large.
It has been certified. [0040]Handling, processing, etc. Wavelength conversion element 30A made of single-crystal LBO of this embodiment
Means that the deliquescent is very small and the polishing is
It was confirmed to be good and excellent in handleability. [0041]Single crystal size When we examined the possibility of large crystals, we found that the diameter was 4 inches
It was confirmed that the above single crystal LBO could be produced.
Was. [0042]Deterioration resistance Wavelength conversion element 30A made of single-crystal LBO of this embodiment
Is less susceptible to ultraviolet light than BBO,
Life is long. [0043]Reference Example 1 Comparison between the single-crystal LBO of this embodiment and a normal single-crystal LBO
investigated. Normal single crystal LBO is pulled up as shown in FIG.
Single crystal LBO was grown using the apparatus 110. However,
The growth condition was changed from the growth condition of the first embodiment. Reference Example 1
Then, the temperature gradient between the surface of the melt and 10 mm immediately above the melt is 2
50 ° C / cm, and the temperature gradient above 70 ° C / cm
cm and the pulling speed when pulling up the straight body of the single crystal
The degree was 2.5 mm / hour. That is, in Reference Example 1,
Means that the temperature gradient is larger than the pulling condition of the first embodiment.
Increased pulling speed. Other than the above conditions,
The single crystal LBO of Reference Example 1 was grown in the same manner as in Example 1.
Done. Thereafter, the single-crystal LBO is used in the same manner as in the present embodiment.
As shown in FIG. 3, cut the single crystal LBO
Was polished optically. Crystal size is almost the same
It is. YAG laser is added to such a normal single crystal LBO.
The second harmonic of the wavelength 532 nm emitted light is incident
At this time, as in the case of the single crystal LBO of this embodiment, the laser having a half wavelength
Laser light is recognized, and a normal single crystal LBO is also used in this embodiment.
It has a light wavelength conversion function like crystal LBO.
understood. However, ordinary single-crystal LBO has cloudiness.
And the intensity of the emitted light is the single crystal LBO of this embodiment.
The intensity of the emitted light. Normal single crystal LBO
Fluctuation of refractive index inside crystal of Mach-Zender interference
The refractive index fluctuation was about 10^-Four/ Mm
Was. Variation of the refractive index of the single crystal LBO of the present embodiment, 10^-6/
The variation is larger than mm. As described above, according to the present embodiment, the predetermined
A predetermined plane with respect to the optical axis to satisfy the phase matching angle
Single crystal lithium tetraborate (Li_Two B
_Four O ₇ ) At a predetermined incident angle on the light incident surface at a wavelength of 1000
nm or less of coherent light, and the wave of the incident light
It is possible to emit light having a wavelength of about half the length. [0045]Second embodiment As a second embodiment of the present invention, a single crystal LBO is used as a second harmonic.
An example in which the device is used as a wavelength conversion element will be described. [0046]Manufacturing method of single crystal LBO of the present embodiment Using the lifting device 110 shown in FIG.
Single crystal LBO was grown. That is, the purity of the specified molar ratio
99.99% polycrystalline LBO, 1300 g 90 m diameter
m, a platinum crucible 101 having a height of 100 mm.
After being melted with a heater, the diameter of 2
The single-crystal LBO was lifted. In the second embodiment
The pulling condition is a temperature between the surface of the melt and 10 mm immediately above the melt.
The temperature gradient is 80 ° C / cm and the temperature gradient above it is 3 ° C / cm.
At 0 ° C / cm, pull up the straight body of single crystal LBO
The lifting speed was 0.5 mm / hour. like this
The dislocation density of the single crystal LBO grown in
5 × 10 / cm^Two So
Was. The dislocation density is sufficiently small. [0047]processing To evaluate the second harmonic characteristics of this single crystal LBO
Then, the single-crystal LBO of the present example was replaced with a phase matching angle θm ≒ 17.
° so that the entrance and exit surfaces of the single crystal
Polished. The size of the crystal is 10 mm in diameter and 2 in length.
It was 5 mm. An output of 100 mJ and a wavelength of 53
Irradiate 2nm laser light, observe and evaluate transmitted light
Was. As a result, this light has a wavelength of 266, which is the fourth harmonic.
nm of the single crystal LBO obtained in this embodiment.
Was confirmed to be a material having excellent wavelength conversion characteristics.
Also, the wave from the laser beam incident output and the laser beam output
As a result of calculating the long conversion efficiency, it was about 15%.
Was. [0048]Reference Example 2 As Reference Example 2, a normal single bond used for SAW elements, etc.
Single-crystal LBO was manufactured according to the manufacturing conditions for single-crystal LBO.
That is, using the lifting device 110 shown in FIG.
Crystal LBO was grown. However, the growth conditions of the second embodiment and
Changed the training conditions. That is, in Reference Example 2, the melt table
The temperature gradient between the surface and 10mm just above the melt is 250 ° C / c
m, the temperature gradient above it is 70 ° C./cm,
2.5m pulling speed when pulling the straight body of the crystal
m / hour. That is, in Reference Example 1, the second embodiment
Increase the temperature gradient for the pulling conditions of
Speed increased. Except for the above conditions, Example 2
Similarly, a single crystal LBO of the reference example was grown. Etchin
Of the single crystal LBO of Reference Example 2
Has a dislocation density of 2 × 10^Four Pieces / cm^Two And a single crystal LB
Opacity was observed in O. Therefore, as shown in Reference Example 2,
A single crystal LBO manufactured under the following conditions
As low quality. To evaluate the second harmonic characteristics
Next, the single crystal LBO of the comparative example was cut in the same manner as in the second example.
Then, the input / output surface of the single crystal was optically polished. Crystal size
The same is true. An output of 100 mJ, wave
Irradiate a laser beam with a length of 532 nm, observe the transmitted light,
evaluated. As a result, light having a wavelength of 266 nm was observed.
However, the wavelength conversion efficiency was low. Calculation of wavelength conversion efficiency
Was about 9%, and the single crystal LB according to Reference Example 2 was obtained.
O is inferior in conversion efficiency to the single crystal LBO of this embodiment.
Was confirmed. In other words, the single crystal L of the present embodiment
BO has high conversion efficiency when used as an optical conversion element
It is shown that. [0049]Third embodiment As a third embodiment of the present invention, a single-crystal LBO is replaced by a fifth harmonic.
The case where it is used for a wavelength conversion element for use will be described. [0050]Production of single crystal LBO of this example Using the lifting device 110 shown in FIG.
(Stoichiometric) polycrystalline LB with a purity of 99.99% by weight
O, 1300g, platinum crucible 90mm in diameter and 100mm in height
The pot 101 was filled, and a single crystal LBO was grown by the CZ method.
The lifting conditions are the same as in the first embodiment or the second embodiment.
It may be the same as the one.Processing of single crystal LBO of this embodiment The grown single-crystal LBO was placed on the (110) plane and the (001) plane.
(110) plane, which is the entrance / exit surface, is optically polished.
And a wave composed of a single crystal LBO of 15 mm x 15 mm x 30 mm
The length conversion element 30B was created. [0051]Experimental example 2 Laser light of fundamental wave ω (incident wavelength λ2 = 1064 nm)
(Output 1J) and an optical parametric oscillator (Spectra P
4 times the frequency of the basic laser light generated by Hysics
Number, 4ω (wavelength λ1 = 266 nm of 1/4 of incident wavelength)
Wavelength conversion simultaneously with the auxiliary laser light (output 250mJ)
When the light enters the element 30B, a mixture of the two lights (sum
Wave), the frequency of which is five times the incident wavelength λ2 = 1064 nm.
Wave number: 5 ω (1/5 wavelength 213 nm) light (output 15
0 mJ). That is, single crystal LBO was used.
From the wavelength conversion element 30B, 1064 nm / 5 ≒ 213n
Light having a wavelength of m was generated. Experiment of phase matching angle at this time
It was about 79 degrees when determined in the same manner as in Example 1. sum
The shortest wavelength due to the frequency is 209 nm, and the phase at that time
The alignment angle was about 90 degrees. Phase matching with each incident wavelength
The relationship with the angle is shown in Table 3 below. [0052] [Table 3] When obtaining outgoing light having a wavelength x = 209 nm,
The wavelength of the first coherent light is arbitrary w (n
m), for example, 981 (nm), and the second core
The wavelength of the coherent light is 1 / [(1 / x)-(1 /
w)] (nm), for example, 266 (nm). Sa
Furthermore, single crystal Li_Two B_Four O₇ Of the first wavelength on the entrance surface of
1 coherent light and approximately 1/1 of the first coherent light.
A second coherent light having a wavelength of 2 or almost 1/4
Incident at a predetermined angle, and at least the first coherent
Of the wavelength of approximately 1/3 or approximately 1/5 of the wavelength of the
It is possible to emit a coherent light. Positions shown in Table 3
The phase matching angle was measured with the refractive index of single crystal LBO being 1.6.
It is not strictly accurate because it was calculated. why
Then, the refractive index of the crystal varies with temperature, incident wavelength, etc.
It is because it becomes. However, the values in the table above are
Values within the range of ± 10 degrees from the values in the table above.
It is believed that there is an accurate phase matching angle. Of course,
If the folding ratio can be determined accurately, the method shown in Experimental Example 1 can be used.
Thus, an accurate phase matching angle can be easily obtained.
As the phase matching method, angle phase matching using birefringence
Phase matching using temperature dependence of refractive index and refractive index
Was. Of course, the temperature phase matching method for the latter single crystal LBO
It is also possible to apply. Simple at some wavelength
Measure the refractive index of crystalline LBO and adapt the operating process.
Then, the Sellmeier equation is obtained. S
solve each of the wavelengths by solving the
There is also a method for calculating the phase matching angle.
You. [0054]Reference Example 3 The ordinary single crystal LBO described in Reference Example 1 or Reference Example 2
Used for 1/5 wavelength conversion. As a result, the single crystal of the present example
As with LBO, the phase matching angle is about 79 degrees, and the sum frequency
Is 209 nm, and the output at that time is 5
It was 0 to 120 mJ. Normal single-crystal LBO is cloudy
Intervening, bending by the Mach-Zender interferometer
The measurement result of the folding ratio change is 10^-Four/ Mm. Cloudy
And the refractive index fluctuation is 10^-6/ Mm single crystal LB of this example
Stable 5th harmonic when converted to 1/5 wavelength using O
was gotten. That is, even if a normal single crystal LBO is used
Although the fifth harmonic is obtained, the single crystal LBO of this embodiment is used.
Is more stable, and the 5th harmonic with higher conversion efficiency is obtained.
Is shown. [0055]Comparative Example 1 The wavelength conversion element 30B of the single crystal LBO of the present invention is KTP.
Except for the configuration, the conversion wavelength was the same as in Experimental Example 2.
Characteristics, laser damage resistance, transparent area, deliquescence, good quality large size
The possibility of crystallization was investigated. Table 2 shows the results. This result
From the results, the single crystal LBO of the present invention was used for the wavelength conversion element 30B.
The superiority when using was confirmed. [0056]Comparative Example 2 The single crystal LBO of the present invention is converted from the wavelength conversion element 30B by BBO.
Except for the configuration, the conversion wavelength was the same as in Experimental Example 1 above.
Characteristics, laser damage resistance, transparent area, deliquescence, good quality large size
The possibility of crystallization was investigated. Table 2 shows the results. This result
From the results, the wavelength conversion element 30 using the single crystal LBO of the present invention
The superiority of B was confirmed. BBO grows by flux method
It is easy to take in impurities, and the yield is low.
The single crystal LBO of the invention has a high yield. Also, BBO is ultraviolet
When irradiated with light, the color center is generated due to the deterioration of the crystal.
There is a problem that the single crystal LBO of the present invention
The wavelength conversion element 30B has no such problem. [0057]Comparative Example 3 The single crystal LBO of the present invention is converted to a wavelength conversion element 30B by KDP.
Except for the configuration, the conversion wavelength was the same as in Experimental Example 1 above.
Characteristics, laser damage resistance, transparent area, deliquescence, good quality large size
The possibility of crystallization was investigated. Table 2 shows the results. The result
As a result, the superiority of the single crystal LBO of the present invention was confirmed. As described above, according to this embodiment, the sum frequency
Utilizing the mixing phenomenon, for example, the wavelength x = 209 nm
When obtaining outgoing light, the wavelength of the first coherent light
Is any w (nm), for example, 981 (nm)
Therefore, the wavelength of the second coherent light is 1 / [(1 /
x)-(1 / w)] (nm), for example, 266 (n
m). In addition, the single crystal Li_Two B_Four O₇ Incident surface
A first coherent light having a first wavelength and a first coherent
Second light having a wavelength of about 1/2 or about 1/4 of the
Incident at a predetermined angle with the helical light, at least
The wavelength of the first coherent light is approximately 1/3 or approximately
It can emit coherent light of 1/5 wavelength
You. Preferably, it is cut at a predetermined plane with respect to the optical axis,
Break rate change is 10^-Five/ Mm or less and / or dislocation density
Degree is about 1 × 10^Three Pieces / cm^Two The following single crystal lithic tetraborate
Um (Li_Two B_Four O₇ ) Is used. [0059]Fourth embodiment In this embodiment, the single-crystal LBO is quadrupled as described above.
Or a single crystal that has five times the wavelength conversion function
LBO is used as a wavelength conversion element to detect light in the infrared region.
This is an example of realizing a laser device that emits light in the ultraviolet region.
This is shown with reference to FIG. Laser device 10 shown in FIG.
0 is a coherent light having a wavelength of 1064 nm (in the infrared region).
Nd: YAG, a solid-state laser that emits
Emits coherent light of wavelength 266 nm with laser 10
Composed of the secondary light source 20 and the single crystal LBO of the present invention
It has a length conversion element 30 </ b> B and a half mirror 40. The secondary light source 20 is, for example, an Nd: YAG laser.
Laser light with a wavelength of 1064 nm emitted from the laser
Long conversion element, for example, to convert light to half the wavelength of incident light
Wavelength change using β-BaB2 O4 (BBO) single crystal
The wavelength of the exchange element is converted twice, or the single element for SHG of the present invention is used.
After passing twice through the wavelength conversion element made of crystalline LBO,
1/4 wavelength of 1064 nm long, 266 nm laser light
And output. In the first optical path, Nd: YAG laser
Laser light with a wavelength of 1064 nm emitted from the laser 10
Transmits through the half mirror 40 and enters the wavelength conversion element 30B
I do. In the second optical path, the wavelength 266 from the secondary light source 20
nm laser light is reflected by the half mirror 40 and N
d: wavelength conversion together with laser light from YAG laser 10
The light enters the element 30B. That is, the first optical path and the second optical path
Laser light applied to the wavelength conversion element 30A from the optical path of
Is passed through the wavelength conversion element 30B to be summed.
And the wavelength 106 of the laser light from the Nd: YAG laser 10.
About 1/5 wavelength of 4nm, short wavelength laser light of 213nm
Will be converted to As described above, the laser device 100 operates at room temperature.
Solid-state laser that emits light in the infrared region at a wavelength of 1064 nm
The Nd: YAG laser 10 and the wavelength 1064n
a secondary light source 20 that emits light having a wavelength of 1/4 of m, and a single crystal
The wavelength conversion element 30B using LBO allows the infrared
From the wavelength of 1064 nm,
That is, a short-wavelength laser beam in the ultraviolet region of 213 nm is emitted.
Can be fired. The Nd: YAG laser 10 is transparent.
Light and insulator crystal, impurity ions N
d. Nd: YAG laser 10 at room temperature
Continuous infrared light, wavelength 1.05 to 1.12 μm
Among them, in particular, light of 1.064 μm is strongly oscillated. As described above, single-crystal LBOs are
High transparency over a range of wavelengths, laser beam loss
Less scratches. In addition, high quality large crystals can be easily manufactured.
You. Furthermore, single crystal LBO has excellent workability and deliquescence.
Small and excellent in handling. Single crystal LBO has a long life
Is also long. The aforementioned Nd: YAG laser 10 and this Nd:
d: secondary light source 20 using light from YAG laser 10
A wavelength conversion element 30B using the single crystal LBO described above;
Laser device 10 according to the present invention, comprising a laser mirror 40
0 is a small size, stable operation and long life.
And at room temperature, high energy, short wavelength ultraviolet light
Line, in the example described above, laser light having a wavelength of 213 nm was obtained.
It is. This laser device 100 is replaced with an excimer laser
I can do it. That is, such a laser device 100
Printing, plate making, optical measurement, lithography of super LSI, etc.
Application to the field can be expected. [0063]Fifth embodiment As a fifth embodiment of the present invention, the single crystal LBO of the present invention
Another laser device used as a wavelength converter for quintuple harmonics
Is described.Production method Using the lifting device 110 shown in FIG.
Crystal LBO was grown. The growth direction is good for raising the c-axis.
There are many bubbles, and they are perpendicular to the c-axis (100),
In the (110) direction, the presence of bubbles was small.processing From the grown crystal, a (100), (001) plane sample (approximately
30 mm * 30 mm * 40 mm). [0064]Operation experiment FIG. 7 shows a laser similar to the laser shown in FIG.
An experiment was conducted with the device, and first, an Nd: YAG laser (not shown)
The fundamental wave (ω) of the second harmonic and the fourth harmonic generation unit 42
And the wavelength using the single crystal LBO of the present invention.
The wavelength conversion element 30C is caused to enter the conversion element 30C,
A fifth harmonic was generated. The conditions at this time are 10 Hz, 10 Hz
Fundamental wave output of Nd: YAG laser in nsec: 400m
J, fourth harmonic: 110 mJ was injected at a phase matching angle of 79 degrees.
And a 5th harmonic output of 70 mJ was obtained. Next, the crystal is
1) While rotating in the direction, the optical parametric oscillator 4
1 to gradually change the wavelength of 1064 nm to single crystal LBO
The conversion wavelength was measured while applying. (100) surface sample
Under almost vertical incidence conditions, the shortest wavelength is 209 nm.
Was. As described above, the wavelength conversion of the single crystal LBO of the present invention is performed.
The laser device used for the element 30C has a wide wavelength range.
A laser beam that changed immediately was confirmed. [0065]Sixth embodiment As a sixth embodiment of the present invention, the single crystal LBO of the present invention
Still another laser used as a wavelength conversion element for five harmonics
The device will be described.Production method Using the lifting device 110 shown in FIG.
Crystal LBO was grown. The growth direction is good for raising the c-axis.
There are many bubbles, and they are perpendicular to the c-axis (100),
In the (110) direction, the presence of bubbles was small.processing Cut out from grown crystal and tilt 79 degrees from (001) plane
A single crystal LBO was prepared with the resulting surface as a light incident surface. That simple
The dimensions of the crystals were 20 mm × 20 mm × 45 mm. [0066]Operation experiment As shown in FIG.
Arranged between filters 60 and 62 as conversion element 30D
And a YAG rod 50, a Q switch 52, a mirror 54,
55 from the YAG laser 10a composed of 55
Output the main wave and convert through SHG crystals 56 and 58
Light was incident on the light incident surface of the element 30D. SHG crystal 5
6, 58 are, for example, single crystal LBO or BBO, etc.
Be composed. Stage single crystal sample 30D cut at 79 degrees
And rotated in the c-axis direction shown in FIG.
The generation of the fifth harmonic (5ω) was confirmed at a degree of ± 10 degrees. Its out
The maximum intensity of the power light is YAG laser (1.5 J, 10H
Using Z), the value was 120 mJ. [0067] As described above, according to the present invention, the long
It operates stably for a long time, has a long service life, is rich in workability,
A small, lightweight, low-cost optical conversion element is provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a single crystal lithium tetraborate (L) of the present invention.
FIG. 3 is a cross-sectional view showing a lifting device for manufacturing (i ₂ B ₄ O ₇ , LBO). FIG. 2 is a schematic diagram showing a definition of a phase matching angle in a single crystal LBO. FIG. 3 is a diagram showing a relationship between a cut surface of a single crystal LBO and a phase matching angle according to one embodiment of the present invention. FIG. 4 is a diagram showing a single crystal LBO according to an embodiment of the present invention.
FIG. 6 is a diagram showing a relationship between an incident angle of a laser beam and a fundamental wave when phase matching is performed in FIG. FIG. 5 is a diagram showing a relationship between a phase matching angle and an incident light angle when a single crystal LBO according to one embodiment of the present invention is used as a second harmonic wavelength conversion element. FIG. 6 shows a single crystal L according to a third embodiment of the present invention.
It is a block diagram which shows the laser apparatus which used BO as a wavelength conversion element for 5th harmonics. FIG. 7 shows a single crystal L according to a fourth embodiment of the present invention.
FIG. 11 is a configuration diagram of another laser device using BO as a fifth harmonic wavelength conversion element. FIG. 8 shows a single crystal L according to a fifth embodiment of the present invention.
FIG. 2 is a configuration diagram of a single-pass laser device using BO as a wavelength conversion element. [Description of Signs] 1 ... Platinum crucible, 2,3,5,6 ... Insulation material, 4 ... Heater

   ────────────────────────────────────────────────── ─── Continuation of front page    F term (reference) 2K002 AB12 CA02 FA11 HA20                 4G077 AA02 BD07 CF10 EA01 ED02                       EH07 EH09 HA01 PF55 PJ02

Claims (1)

Claims: 1. A molten polycrystalline lithium tetraborate (Li)
₂ B ₄ O ₇ ) in a predetermined pulling direction by the Czochralski method to produce single crystal lithium tetraborate, wherein the temperature gradient between the surface of the melt and 10 mm immediately above the melt is 30 ° C. /
cm to 200 ° C / cm, temperature gradient above 5 ° C
/ Cm to 50 ° C / cm, pulling rate 0.1 mm / hour to 2 mm / hour, pulling, refractive index variation ^10-5 / mm or less, and dislocation density about 1 × 10 ³ / cm ² or less. A method for producing single-crystal lithium tetraborate, comprising producing single-crystal Li ₂ B ₄ O ₇ described above.