KR100961555B1 - Fabrication method of ferroelectric single domain of RbTiOAsO4 single crystals - Google Patents

Abstract

The present invention relates to a method of ferroelectric single domain of rubidium titanyl arsenate (RbTiOAsO ₄ , hereafter referred to as "RTA") single crystal.

According to the present invention, after the RTA crystals are grown by the fluxing method including the upper seed immersion method, the strain generated during the crystal growth and the phase transition process is controlled by controlling the temperature of the process of lowering the temperature from the temperature at which the crystal growth is completed to room temperature and Relaxation can produce RTA single crystals with a single domain throughout the crystal.

Since the RTA single crystal manufactured as described above has a single division structure in the entire crystal, all parts are applicable to the optical element, and the efficiency can be greatly improved economically.

Single domain, rubidium titanyl arsenate, ferroelectric, flux

Description

Method of ferroelectric single domain of rubidium titanyl arsenate single crystals {Fabrication method of ferroelectric single domain of RbTiOAsO4 single crystals}

The present invention relates to a ferroelectric single domain method of rubidium titanyl arsenate (RbTiOAsO ₄ , hereinafter referred to as "RTA") single crystal, and more particularly, to prepare an RTA single crystal by a flux method. However, the present invention relates to a method of ferroelectric single branching of RTA single crystals to have a single branching structure in the entire crystal by gradient of the process of lowering the temperature from the crystal growth temperature to room temperature after growth is completed.

Rubidium titanyl arsenate (RTA) single crystal is a nonlinear optical crystal, has ferroelectric properties, and has a nonlinear optical coefficient value (d ₃₃ = 15.8 pm / V) similar to KTiOPO ₄ (KTP) in inorganic crystals, thus making it a second harmonic BACKGROUND ART A spotlight as a wavelength conversion element including a second harmonic generation, an optical parametric oscillation, and the like.

In particular, since RTA single crystals can be quasi-phase-matched, the RTA single crystal has an advantage of making a highly efficient small wavelength conversion device. The most widely used method for spherical phase matching is to apply an external electric field in the polar direction of the ferroelectric so that the direction of polarization crosses by 180 ° with a spatially constant period.

The periodic polarization reversal method as described above has the advantage of simple manufacturing process and easy reproducibility, but in order for the ferroelectric to have a value as a device, the nonlinear optical coefficient value must be large in the polarization direction, and a single domain structure is required. Should have

Representative ferroelectric crystals capable of implementing such a periodic polarization inversion structure include LiNbO ₃ (LN), KNbO ₃ (KN), KTiOPO ₄ (KTP), and RbTiOAsO ₄ (RTA).

LN has the largest nonlinear optical coefficient value among the ferroelectrics exemplified above, but the laser damage threshold due to the photorefractive effect of changing the refractive index of the exposed part when the strong laser light is incident at room temperature To prevent this problem, wavelength conversion must be performed at a temperature of 100 ℃ or higher, and it is difficult to fabricate a device having a thickness of 0.5 mm or more, and KN can make the device thickness of 1 mm or more, but it is multidomain at room temperature. Because it exists in a) structure, the process of making it into a single division is essential. Nevertheless, even after the periodic polarization inversion structure is made, there is a disadvantage that the multiband structure is regenerated due to the unstable branch structure and thus cannot be used as a permanent device.

In the case of KTP, the laser light damage threshold energy value has a large advantage, but the electrical conductivity is large in the spontaneous polarization direction, so that a large current flows when the electric field is applied to fabricate the phase-matched device, thereby damaging the crystal. For this reason, RTA, which has high optical damage threshold energy value and small electrical conductivity at room temperature and similar nonlinear optical coefficient value to KTP, is very suitable as a quasi-phase matching device.

However, RTA crystals grown by the conventional high temperature flux growth method have been problematic in that they have a multi-band structure in most temperature ranges including room temperature. As an example, growth with a top-seeded solution growth method that improves the disadvantages of conventional flux methods such as polycrystal growth by spontaneous nucleation or poor crystal quality due to solvent incorporation into a single crystal Higher quality single crystals with larger apertures can be obtained than conventional methods (J. Nordborg et al., Journal of Crystal Growth , Vol. 224, pp256, 2001), but grown RTA crystals are translucent in most temperature ranges including room temperature. It exists in a multi-band structure. This is also common in all RTA single crystals grown by flux.

When light is incident on the RTA of the multi-band structure, optical scattering occurs severely in the domain wall, which is an interface between the domain and the domain, resulting in low light transmittance and the inability to fabricate a periodic polarization inversion device. There is no application value as a device material. Therefore, only a portion of the grown RTA crystals are cut and processed to utilize the optical wavelength conversion device.

There are two main reasons for the RTA decision to show multi-band structure at room temperature.

First, since the stress induced from the interface between seed crystal and grown crystal is spread throughout the crystal during RTA crystal growth, the closer the seed crystal is, the larger the magnitude of strain per unit volume. The further away, the smaller the amount of strain per unit volume. Thus, the strain inherent in the crystallization process accumulates as the temperature is lowered from the crystal growth temperature to room temperature, resulting in a multi-band structure.

RTA is particularly pyroelectric and piezoelectric, so rapid temperature changes cause mechanical polarization or distortion, such as electrical polarization due to charge imbalances inside the RTA crystals. ), The higher the temperature drop rate, the more cracking may occur in the crystal. That is, the magnitude of the deformation force generated in the RTA crystal also depends on how the rate of temperature drop is controlled. Therefore, in order to manufacture a single region of RTA, it is necessary to solve the inherent strain force by adjusting the temperature reduction rate, temperature increase rate, and constant temperature holding time in the process of lowering the temperature from the crystal growth temperature to room temperature.

Second, unlike KTP crystals whose crystal growth temperature is less than the phase-ferroelectric phase transition temperature, RTA has a crystal growth temperature range between 860 ° C. and 810 ° C., which is higher than 745 ° C. which is the ferroelectric-phase dielectric phase transition temperature. In other words, it belongs to the phase dielectric at the temperature at which the crystal is grown, but it becomes a ferroelectric phase after passing the phase transition temperature in the process of lowering the temperature, so that a multi-band structure within the RTA is likely due to the deformation force due to the structural phase transition. Moreover, it is important to lower the temperature slowly because the sudden drop in temperature in the phase transition temperature range can cause a multi-band structure in the RTA crystal.

Therefore, the present inventors have diligently developed RTA single crystals having a single division structure in the entire crystal. As a result, the RTA was grown by ablating method, and then the temperature gradient from the temperature at which the crystal growth was completed to the room temperature was reduced. It was confirmed that the decentralization is possible to complete the present invention.

After all, the main object of the present invention is to provide a ferroelectric single domain method of rubidium titanyl arsenate (RTA) single crystal.

Another object of the present invention is to provide an RTA single crystal having a single branching structure in the whole crystal prepared by the above method.

In order to achieve the above object, the present invention is to prepare a rubidium titanyl arsenate (RTA) single crystal by a flux method including a conventional top-seeded solution growth method, so as to have a single branch structure in the entire RTA single crystal After crystal growth is completed, a method of ferroelectric single branching of RTA single crystals is provided by reducing the temperature of the crystals to room temperature.

The present invention also provides an RTA single crystal having a single branching structure throughout the crystals produced by the above method.

In the ferroelectric single division method of rubidium titanyl arsenate (RTA) single crystal according to the present invention, after the RTA crystals are grown by a fluxing method including an upper seed immersion method, the temperature of the crystal growth is lowered from room temperature to room temperature. Through regulation, the strain generated during crystal growth and phase transition can be solved and relaxed to prepare RTA single crystals having a single domain throughout the crystal.

Since the RTA single crystal manufactured as described above has a single domain in the entire crystal, all parts can be applied as an optical device, and economical efficiency can be greatly improved.

Hereinafter, the present invention will be described in detail.

The present invention is to prepare a rubidium titanyl arsenate (RTA) single crystal by using a flux growth method, but after the growth is completed by gradient the temperature of the process of lowering the temperature from the crystal growth temperature to room temperature, the single fraction in the whole crystal It provides a method of ferroelectric single division of RTA single crystal to have a structure.

Specifically, the method of mono-distributing the rubidium titanyl arsenate (RTA) single crystal of the present invention, using a flux method to prepare a RTA single crystal,

(a) after the growth of the seed crystals is fixed and the temperature is fixed between 760 ~ 850 ℃ that is above the RTA single crystal phase transition temperature, and maintained for 12 to 24 hours (S100);

(b) at 800 to 700 ° C. near the phase transition temperature, dropping the temperature by 0.1 to 5 ° C. per hour (S200);

(c) maintaining 12 to 24 hours at 700 ° C. (S300); And

(d) In the temperature range of 700 ~ 350 ℃, the temperature is lowered to 30 ~ 200 ℃ per hour, and then again raised to 10 ~ 100 ℃ per hour and maintained at a constant temperature (700 ~ 600 ℃) for 12 to 24 hours, lowering and raising the temperature Repeating the process 3 to 100 times, the process of lowering the temperature to 10 ~ 60 ℃ per hour to room temperature (S400); ferroelectric single determination of the RTA single crystal having a single division structure throughout the crystal, characterized in that consisting of domain) method.

The present invention also provides an RTA single crystal prepared by the above method and having a single branching structure throughout the crystal.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

In the method of mono-distributing rubidium titanyl arsenate (RTA) single crystal according to the present invention, a process of completing crystal growth in a conventional manner at a temperature range of 810 to 860 ° C. using a flux method and lowering the temperature of the crystal to room temperature By giving a temperature gradient at, we have a single domain structure throughout the crystal.

Figure 1 shows the temperature gradient process of the ferroelectric single branching method for producing a single crystal RTA single crystal in the crystal according to the present invention.

As shown in Figure 1, after the seed crystal growth is completed, the temperature is lowered to 50 ℃ per hour to 800 ℃ to maintain the temperature for 24 hours at 800 ℃ (S100). Through the process (S100) to solve the strain generated from the interface between the seed crystal and the grown crystal in the crystal growth process.

Next, the temperature is lowered to 1 ° C. per hour between 760 ° C. and 730 ° C. near the phase dielectric-ferroelectric phase transition temperature, thereby suppressing generation of a multi-zone structure (S200).

In addition, by maintaining the temperature at 700 ℃ for 24 hours to solve the strain generated in the crystal passing the phase transition temperature (S300). In addition, between S100 and S200 and between S200 and S300 is preferably lowered to 5 ° C per hour.

Finally, the temperature is lowered to room temperature after repeating three rounds of temperature drop and raise between 700 ° C. and 300 ° C., but the temperature reduction rate is 30 ° C. per hour, and the temperature increase rate is 60 ° C. per hour (S400). In the process of repeatedly lowering and raising the temperature, it is preferable to maintain the temperature at 700 ° C. for 24 hours (S410, S420) and 600 ° C. for 24 hours (S430), in order to relieve and relax the deformation force generated in the process. .

RTA single crystal prepared by the above process can obtain a single portion of the whole crystal.

Figure 1 shows a method of ferroelectric single branching of rubidium titanyl arsenate (RTA) single crystals according to the present invention.

Claims (6)

In the method of mono-distributing rubidium titanyl arsenate (TbTiOAsO ₄ , RTA) single crystal, The RTA single crystal is prepared by using a flux method, (a) after the crystal growth is completed, after fixing the temperature between 760 ~ 850 ℃ RTA single crystal phase transition temperature or more, and maintained for 12 to 24 hours (S100); (b) at 800 to 700 ° C. near the phase transition temperature, dropping the temperature by 0.1 to 5 ° C. per hour (S200); (c) maintaining 12 to 24 hours at 700 ° C. (S300); And (d) In the temperature range of 700 ~ 350 ℃, the temperature is lowered to 30 ~ 200 ℃ per hour, and then again raised to 10 ~ 100 ℃ per hour and maintained at a constant temperature (700 ~ 600 ℃) for 12 to 24 hours, lowering and raising the temperature Repeating the process 3 to 100 times, the process of lowering the temperature to 10 ~ 60 ℃ per hour to room temperature (S400); ferroelectric single domain of the RTA single crystal having a single division structure in the whole crystal, characterized in that consisting of ) Way. The method of claim 1, The process of (a) lowers the temperature to 50 ° C. per hour after crystal growth is completed and maintains the temperature at 800 ° C. for 24 hours, thereby relieving strain generated from the interface between seed crystals and grown crystals during crystal growth. Ferroelectric single segmentation method characterized in that the giving. The method of claim 1, The process (b) is a ferroelectric single demarcation method characterized in that the temperature is lowered to 1 ℃ per hour between 760 ℃ and 730 ℃ near the phase dielectric-ferroelectric phase transition temperature, suppressing the generation of multi-band structure. The method of claim 1, The (c) process is maintained for 24 hours at 700 ℃ ferroelectric single division method characterized in that to solve the strain generated in the crystal passed the phase transition temperature. The method of claim 1, The process (d) is lowered to 30 ° C. per hour between 700 ° C. and 300 ° C. and then again raised to 60 ° C. per hour, and maintained at 700 to 600 ° C. for 24 hours, after repeating the process of lowering and raising the temperature three times, at room temperature. Until the temperature down to 30 ℃ per hour to reduce the deformation force generated in the process characterized in that the ferroelectric single division method. An RTA single crystal prepared by the method of claim 1 and having a single branching structure throughout the crystal.

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