JP5147064B2 - Method for producing organic optical single crystal - Google Patents

Description

  The present invention relates to a method for producing an organic optical single crystal with improved generation time of terahertz waves generated from the organic optical single crystal, and the produced organic optical single crystal.

  Organic optical crystals include stilbazolium derivatives, in particular DAST (4-dimethylamino-N-methyl-4-stilbazolium tosylate) crystals which are stilbazolium derivatives, DASC (4-dimethylamino-N-methyl-4-stilbazolium) -P-chlorobenzenesulfonate) crystal, MC-PTS (merocyanine-p-toluenesulfonic acid) crystal, MMONS (3-methyl-methoxy-4'-nitrostilbene) crystal, DAD ((-) 4- (4'-) Dimethylaminophenyl) -3- (2′-hydroxypropylamino) cyclobutene-3,4-dione) crystals, and LAP (L-arginine phosphate mono-hydrate) crystals, pNA (4-nitroaniline), MNA (2 -Methyl-nitroaniline) and other organic crystals It is known and has high nonlinearity as compared with inorganic optical crystal, the wavelength conversion element for the threshold is high photodamage, application to optical elements is expected.

  Among these organic optical crystals, DAST crystal, DASC crystal, and MC-PTS crystal, which are stilbazolium cation derivatives, are used as organic nonlinear optical crystals by utilizing the nonlinear optical effect and electro-optical effect, Expected to be applied to terahertz wave detection elements, high-sensitivity electric field sensors, etc., various research and development have been conducted.

  To date, various proposals have been made in terms of crystal growth in terms of crystal growth speed and growth environment in the DAST crystal. For example, in order to provide a uniform crystal free of defects, a crystal having uniform electro-optical characteristics over the entire crystal by growing a natural nucleus on a tilted substrate and then combining with a specific gravity difference solvent cleaning method (Patent Document 1), when a solute is precipitated from a supersaturated solution, a magnetic field application method (Patent Document 2) in which a magnetic field is applied to grow into a highly oriented crystal structure, and a terahertz wave generator In addition, as a crystal whose terahertz wave output is not attenuated, there is a method in which a linear defect does not exist on an internal cleavage plane for forming a crystal while stirring an organic optical crystal material solution in a supersaturated state (Patent Document 3). .

  In general, a frequency region (0.1 to 100 THz) including a submillimeter wave to a far infrared region is collectively referred to as a terahertz electromagnetic wave region, and is located at a boundary between a light wave and a radio wave. This terahertz wave is not only used in the information and communication field as an electromagnetic wave, but also has properties such as energy of 1/1 million of that of X-rays, is safe for the human body, penetrates paper and plastic materials, and does not penetrate metal. Because of its nature, it reacts sensitively to the difference in the water content of drugs and compounds that need to be inspected easily and without contact with non-contact, non-destructive materials, analysis tools for biomolecules and various compounds, malignant tumors Its application is wide-ranging, such as early detection of defects, defect inspection of internal structure of semiconductor LSI, and physical property evaluation of wafers.

  The terahertz wave generator generates two electromagnetic waves having different wavelengths in a two-wavelength parametric oscillator by a laser irradiated from a laser irradiator, and the two electromagnetic waves are incident on a difference frequency generating element through a condenser lens, A configuration in which an electromagnetic wave (terahertz wave) corresponding to a difference frequency between the two electromagnetic waves is generated from a difference frequency generating element is generally used, and the organic nonlinear optical crystal is used as the difference frequency generating element.

The organic nonlinear optical crystal is irradiated with the laser irradiated from the laser irradiator. Conventional organic nonlinear optical crystals are damaged in the crystal when the beam density of two-wavelength light is 1.1 GW / cm ² or less. There was a problem that the generation time of the terahertz wave was shortened. So far, in the DAST crystal, the crystal whose incident laser peak power density is 2.8 GW / cm ² is considered to have the most laser durability (Patent Document 3), and the stable generation time of the terahertz wave is as follows. It was not confirmed.

  The damage threshold of a crystal is generally indicated by the beam density of a laser that irradiates the crystal. It is understood that the higher the beam density of the laser irradiating the crystal, the more likely the crystal will be damaged, and the lower the beam density, the less likely the crystal will be damaged. According to this, the generation time of the terahertz wave is long when laser irradiation with a low peak power value is performed, and the generation time is short when laser irradiation with a high peak power value is performed.

  At present, various studies have been made on the production of crystals with good characteristics during crystal growth as described above. However, studies from the viewpoint of improving the generation time of terahertz waves for single crystals after crystal growth are still in progress. Was not.

As a conventional method for producing an organic single crystal, a method in which a polycrystal of an organic material is made into a single crystal by placing it in an atmosphere maintained at a constant temperature below the melting point (Patent Document 4), an organic compound is made of polycrystal or amorphous A method for growing a nonlinear optical element (Patent Document 5), which is processed at a temperature lower than the melting point after being refined, has been proposed. There is no indication that a terahertz wave is stably generated from an organic optical crystal grown as a single crystal and the generation time is improved.
JP 2004-107104 A JP 2004-205531 A JP 2007-232936 A JP-A-4-349200 JP 7-168221 A

  It is an object of the present invention to establish a method for producing an organic optical single crystal capable of stably generating terahertz waves generated from the organic optical single crystal, and to provide the produced organic optical single crystal. To do.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have been able to stably generate a terahertz wave generated from an organic optical single crystal by annealing the organic optical single crystal. It came to invent the manufacturing method of an optical single crystal, and the manufactured organic optical single crystal.

  Conventionally, annealing treatment has been applied to various metal materials as a method of reducing various lattice defects scattered in the crystal and removing residual stress existing in the crystal, and also to silicon single crystals and various inorganic crystals. It's being used. Particularly in the case of organic optical crystals, as described in Patent Documents 3 and 4, the annealing treatment has been used to single-crystal polycrystals and amorphous ones. Also, it has been used as a method for reducing various lattice defects in organic thin film crystals.

  However, organic optical bulk single crystals have very close melting and decomposition temperatures, are very weak in mechanical and thermal strength, and are difficult to handle near the melting point. Since the crystal size is large and there is a risk of fluctuations in the transfer of heat due to annealing, it has been considered in the art that the annealing process of organic optical bulk single crystals is impossible.

It was known that the generation time of terahertz waves generated from an organic optical crystal when the organic optical crystal was irradiated with a laser was not stable and decayed with time. It has not yet been elucidated. Therefore, the present inventors analyzed the laser-irradiated crystal using a polarizing microscope, a phase contrast microscope, a structural analysis, NMR, etc., and the cause was the thermal decomposition of the molecules and the uniform orientation of the molecules inside the crystal by laser irradiation. It has been found that various defects such as turbulence in sex occur and cause damage.
And it came to invent the manufacturing method of the crystal | crystallization which can improve the generation | occurrence | production time of the terahertz wave which generate | occur | produces from the organic optical single crystal by annealing with respect to the grown bulk single crystal.

That is, the present invention
[1] A method for producing an organic optical single crystal in which the generation time of terahertz waves generated from the organic optical single crystal is improved by annealing the organic optical single crystal.
[2] The method for producing an organic optical single crystal according to the above [1], wherein the annealing treatment is performed in an inert gas at a temperature not higher than a melting point of the organic optical single crystal and not lower than a temperature at which a degree of freedom of crystal molecules is increased.
[3] The method for producing an organic optical single crystal according to the above [1] or [2], wherein the annealing treatment is maintained at an annealing temperature for a time sufficient to remove defects in the crystal and then gradually cooled.
[4] The method for producing an organic optical single crystal according to any one of [1] to [3], wherein the annealing treatment is performed under a condition where a magnetic field is applied.
[5] The method for producing an organic optical single crystal according to any one of [1] to [4], wherein the organic optical single crystal is a crystal made of a stilbazolium derivative.
[6] Any one of the above [1] to [5], wherein the organic optical single crystal is at least one crystal selected from any of DAST, DASC, and MC-PTS crystals that are stilbazolium cation derivatives A method for producing an organic optical single crystal according to 1.
[7] An organic optical single crystal produced by the production method described in any one of [1] to [6] above.

  By annealing the organic optical single crystal, it is possible to provide an organic optical single crystal with improved generation time of terahertz waves generated from the organic optical single crystal.

The present invention is described in detail below.
The organic optical single crystal targeted by the present invention includes a stilbazolium derivative crystal represented by the following formula 1. The stilbazolium derivatives, -X, -Y and Z ^- combined in various derivatives have been configured. MMONS (3-methyl-methoxy-4′-nitrostilbene) crystal, DAD ((−) 4- (4′-dimethylaminophenyl) -3- (2′-hydroxypropylamino) cyclobutene-3,4-dione ) Crystals and various organic nonlinear optical crystals such as LAP (L-arginine phosphate mono-hydrate) crystals, pNA (4-nitroaniline), and MNA (2-methyl-nitroaniline) crystals.

Among them, a crystal composed of a stilbazolium derivative represented by the following formula 1 useful as an organic nonlinear optical crystal can be used.

  In particular, among the stilbazolium derivative crystals, DAST (4-dimethylamino-N-methyl-4-stilbazolium tosylate) crystal in which X = 9, Y = i, and Z = b, X = 9, Y DASC (4-Dimethylamino-N-methyl-4-stilbazolium-p-chlorobenzenesulfonate) crystal in which Z = c, MC-PTS (merocyanine- in which X = 1, Y = I, Z = b) The use of a single crystal of (p-toluenesulfonic acid) is most preferable because an organic nonlinear optical crystal useful for improving the generation time of terahertz waves can be obtained.

  In the present invention, any laser can be used for generating terahertz waves (THz waves) as long as it can generate terahertz waves when irradiated on an organic optical single crystal. For example, laser light sources include Nd; YAG lasers with wavelengths of 1475 nm and 1493 nm and a pulse width of 15 ns / pulse, and Nd; YAG / SHG lasers with a wavelength of 532 nm and a pulse width of 10 ns / pulse. .

  The annealing method in the present invention may be any apparatus as long as it is an apparatus capable of annealing an organic optical single crystal. For example, an annealing process can be performed as follows using an incubator. The organic optical single crystals are arranged on, for example, a ceramic floor made of a heat-resistant material for preventing deformation due to heating, and placed in an incubator. The inside of the incubator is evacuated and then replaced with an inert gas, and the temperature is raised to an arbitrary set temperature which is an annealing temperature. After raising the temperature, the temperature is kept for an arbitrary annealing time, and then gradually cooled to room temperature.

The annealing treatment temperature in the present invention is generally sufficient to remove defects in the crystal, and the temperature varies depending on the substance. Depending on the size, physical properties, and annealing time of the organic optical crystal, the temperature is experimentally set within the range below the melting point of the organic optical single crystal and the temperature at which the degree of freedom of crystal molecules is increased. Preferably, it is set to a temperature in the range of 10 ° C. to 60 ° C. lower than the melting point of the organic optical single crystal. Moreover, what is necessary is just to heat up by this arbitrary temperature increase rate to this preset temperature. For example, the temperature can be raised at a rate of 1 ° C./min. In the case of the DAST crystal, the melting point is 259.7 ° C. according to the differential scanning calorimeter (DSC), so that it is 249.7 ° C. to 199.7 ° C., preferably 240 ° C. to 200 ° C., particularly preferably 225 Annealing can be performed at a temperature of 215 ° C to 215 ° C.
In the case of a DASC crystal, it is desirable to experimentally set the annealing temperature based on the melting point measured with a differential scanning calorimeter (DSC) or the like, or the literature value (281 ° C.).

  The atmosphere for annealing may be a non-oxidizing atmosphere. It is good to carry out in an inert gas atmosphere. Examples of the inert gas include argon, nitrogen, and helium. Preferably, the treatment is performed in an argon gas atmosphere.

  When the annealing treatment is performed, it is also preferable to improve the generation time of the terahertz wave under the condition that a magnetic field is applied. By improving the orientation of the crystal by the action of the magnetic field, an effect of preventing the attenuation of the THz wave output caused by the phase defect considered to be one of the causes of the attenuation of the THz wave output can be obtained. As a magnetic field to be applied, a horizontal unidirectional magnetic field is applied, but it is a magnetic field of 0.01T to 10T (Tesla), and is preferably a magnetic field generated by a superconducting magnet. As for the orientation direction of the DAST crystal by the magnetic field, the a-axis of the DAST crystal is oriented parallel to the magnetic field direction. In addition, the magnetic field strength at which an increase in the orientation rate in the DAST crystal can be expected is about 0.05T to 0.2T. For this reason, the orientation of the DAST crystal is grown after the single crystal is grown by setting the magnetic field direction to be at least 0.05 T and the magnetic field direction and the DAST crystal a-axis being parallel. The rate increases.

The annealing treatment time is determined in accordance with the size and physical properties of the organic optical single crystal to be treated, and also in accordance with the annealing temperature, but is generally sufficient for removing defects in the crystal, Since the time varies depending on the substance, the time may be set experimentally. In the case of the DAST crystal of the following formula 2, the melting point is 259.7 ° C. according to the differential scanning calorimeter (DSC), and is 2 hours to 140 hours depending on the annealing treatment temperature. The annealing time is preferably 10 hours to 20 hours, and particularly preferably annealed at 220 ° C. for 12 hours.

The present inventors examined the optimum annealing temperature range in relation to time within the temperature range where the annealing temperature is below the melting point of the organic optical single crystal and up to 60 ° C.
The DAST crystal powder was observed over a temperature range of 210 ° C. to 240 ° C., and the heat retention time at each heating temperature was changed as shown in Table 1 to observe the change in crystal state. As a result, annealing temperature adaptability is “Yes” when the crystal state is maintained, annealing temperature adaptability “limit point” when crystal surface is liquefied (decomposition and melting), and crystal liquefaction (decomposition and melting) Annealing temperature adaptability was set to “none”.

  When the crystal surface is liquefied, or the crystal is liquefied (decomposed and melted), the NMR measurement results show that a chemical shift has occurred, and it is a decomposition product that does not hold the DAST skeleton, or by thermal decomposition. Since it is a carbide, the nonlinear optical effect and electro-optical effect as the DAST crystal are lost. FIG. 1 shows the annealing effect temperature range. The state change limit point curve indicates the temperature at which the DAST crystal starts to liquefy and the heat retention time until the change occurs. According to this result, in the case of the DAST crystal, it can be said that it is the temperature range / time in which annealing can be performed within the range below the state change limit point curve shown in FIG. Further, by drawing an approximate curve based on the melting point of DAST and the experimental data in Table 1, the heat retention time up to 200 ° C. which is the annealing effect temperature range in the DAST crystal can be estimated.

  After heating and keeping at the annealing temperature, it is gradually cooled to room temperature at an arbitrary rate. The method of slow cooling (sometimes referred to as cooling) is not particularly limited as long as the effect of improving the generation time of the terahertz wave generated from the organic optical single crystal of the present invention is not impaired. For example, it is not preferable that a partial temperature (an improved degree of freedom of crystal molecules) is lowered in the annealed crystal because the above effect may be impaired. If these are taken into consideration, the cooling method may be either linear or stepwise. It is preferable to experimentally set the optimum conditions so that the entire crystal can enjoy the above-mentioned effects uniformly in consideration of the characteristics of the compound constituting the heated and heat-retained crystal and heat conduction depending on the crystal size. . As a preferable example of the cooling method, from an industrial viewpoint, since the temperature control step can be omitted, it is possible to naturally cool the whole apparatus that can be annealed in a non-oxidizing atmosphere after heat treatment in a room temperature environment. For example, only crystals that have been heated and kept at the annealing temperature can be naturally cooled in a room temperature environment, and if precise temperature control is possible using equipment, the temperature is lowered at a rate of 0.05 ° C./min or higher. Can be mentioned.

  The target crystal that can be used in the production method of the present invention may be a crystal produced by any growth method. For example, for a DAST crystal, any growth method such as a natural nucleus growth method, a seed crystal growth method, a slope method, a magnetic field application method, or a solution stirring method may be used. In particular, it is preferable to use a method that does not depend on a growth method with improved crystal growth rate or growth environment. Organic optical crystals that do not depend on the improved crystal growth method have various lattice defects inside the crystal and have inferior terahertz wave generation time. A crystal can be grown by a simple means without providing a special control means having a large degree.

  Examples of the inferior terahertz wave generation time include crystals by a natural nucleus growth method. Formation of the organic optical single crystal by the natural nucleus growth method is performed as follows. First, an organic substance constituting the organic optical single crystal is dissolved in methanol or the like as a solvent, and then a nucleus growth material is immersed in this solution. Then, the solution temperature is lowered so that the organic matter becomes supersaturated. Then, an organic substance is deposited on the nucleus growth material and grows to obtain an organic optical single crystal. According to the present invention, even if the terahertz wave generation time is inferior, the terahertz wave generation time can be improved.

The terahertz wave generation time in the organic optical crystal was determined by the terahertz wave output as follows. In the terahertz wave output obtained when laser irradiation under certain conditions is performed, the value calculated by dividing each output value using the maximum terahertz wave output observed during the measurement is within 5 minutes from the start of irradiation. This was targeted as a crystal in which the generation of terahertz waves was stable for a crystal that was not continuously attenuated to 0.5 or less for 20 seconds or longer.
Also, in the terahertz wave output obtained when laser irradiation under certain conditions is performed, the value calculated by dividing each output value using the maximum terahertz wave output observed during the measurement is within 5 minutes from the start of irradiation. In addition, a crystal that continuously attenuates to 20 seconds or more and 0.5 or less was a crystal in which the generation of terahertz waves was not stable.
Here, the measurement time required for once splitting the region of 0.1 THz to 10 THz is 5 minutes, and the laser irradiation time is set to 5 minutes in order to evaluate a crystal capable of one or more measurements from the viewpoint of practicality. .

The irradiation laser conditions after annealing are shown below.
・ Pulse width of incident laser: 15ns
Beam density: 0.48, 0.62, and 1.5 GW / cm ²
Laser wavelength: 1475 nm and 1493 nm
The THz output was detected by a pyroelectric element (DTGS (Deuteriated triglycine sulfate)).

  The present invention also relates to an organic optical single crystal with improved terahertz wave generation time obtained by any one of the manufacturing methods described above. The organic optical single crystal in which the generation time of the terahertz wave is improved can be used not only for the generation of terahertz but also as various electro-optical elements. For example, it can be used as an electro-optical element for terahertz wave detection, high-sensitivity electric field sensor, high-speed optical modulator, electric field probe, electro-optical sampling, two-dimensional electric field mapping, or spatial electric field detection.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. The DAST crystal, which is a representative example of the organic optical single crystal of the present invention, will be described below.

[Example 1]
It was confirmed whether there was an annealing effect at 215 ° C. to 225 ° C. within the state change limit point curve range of the “annealing effect temperature range” in FIG. The manufacturing method of the DAST crystal used is shown below.

(Single crystal growth)
The DAST single crystal was grown by a natural nucleus generation method. 400 g of methanol was added to 17.7 g of commercially available DAST powder (purity 99.9% or more, manufactured by Daiichi Chemicals) to prepare a DAST growth solution. Next, this solution was heated to 55.0 ° C. while being stirred, and maintained at 55.0 ° C. for 10 hours to completely dissolve the DAST powder. Thereafter, 280 ml of the prepared solution was dispensed to obtain a crystal growth solution. The adjusted crystal growth solution was again heated to 55.0 ° C. and maintained at 55.0 ° C. for 10 hours. Next, the solution was lowered to 44.8 ° C. while being stirred, and then maintained for 30 minutes, and seed crystals attached to the support were introduced. After the seed crystal is charged, the temperature is quickly lowered to 43.3 ° C., and the seed crystal attached to the support is grown for 40 days while lowering the solution temperature at a rate of 0.1 ° C./day. After growing naturally occurring crystals during the same period, the crystals on the bottom of the container were collected. Next, the collected bulk crystals were washed with acetone for 20 seconds and with ethyl acetate for 5 minutes or more.

The size of each DAST single crystal obtained is shown in Table 2.

The sample numbers cont-1, 225-1, 220-1, 220-2, 215-1 and 215-2 were annealed by the following method and conditions.
EYELA VACUUM OVEN VOS-201SD was used as an incubator. DAST crystals are arranged on a Si wafer as a heat-resistant floor plate, put into an incubator, the inside of the incubator is evacuated once, and then argon gas as an inert gas is filled into the apparatus. The annealing temperature was raised to 215 ° C., 220 ° C., and 225 ° C. at a rate of 1 ° C./min. Annealing treatment was performed for 12 hours as the holding time, and then the crystals were cooled to room temperature by natural slow cooling.

FIG. 2 shows the results of a terahertz wave (THz wave) generation test. The beam density applied to the crystal to generate THz waves is 480 MW / cm ² . Table 3 shows the time during which the THz wave is stably generated in each sample at 0.5 or more.

  As shown in FIG. 2, in the case of the sample number cont-1 without annealing, the output value continuously decreased to 0.5 or less in 576 seconds, whereas at 215 ° C., 220 ° C. and 225 ° C. The crystals that were annealed for 12 hours (sample numbers 225-1, 220-1, 220-2, 215-1, and 215-2) stably generated THz waves of 0.5 or more for 1200 seconds or more. From this, it can be understood that the effect of annealing can be obtained as long as it is within the state change limit point curve range of the annealing effect temperature range.

[Example 2]
It was confirmed whether the crystals produced by various growth methods also have an annealing effect. The manufacturing method of the DAST crystal used is shown below.
(Growth of J-1, J-2, J-3 single crystals)
Sample numbers J-1, J-2, and J-3 single crystals were grown in the same manner as the single crystal of Example 1.

(Growth of JS-1 and JS-2 single crystals)
(Preparation of seed crystal)
A DAST single crystal was obtained by growing a seed crystal. The DAST seed crystal was prepared by adding 400 g of methanol to 10.4 g of commercially available DAST powder (purity: 99.0% or more, manufactured by Daiichi Chemicals Co., Ltd.) to prepare a DAST solution. Next, this solution was heated to 55.0 ° C. while being stirred, and maintained at 55.0 ° C. for 10 hours to completely dissolve the DAST powder. Thereafter, 40 mL of the prepared solution was dispensed to prepare a seed crystal solution. The prepared seed crystal solution was heated again to 55.0 ° C., maintained at 55.0 ° C. for 10 hours, and then lowered to 23.3 ° C. to precipitate seed crystals.
(Single crystal growth)
For growth of the DAST single crystal, 400 g of methanol was added to 17.7 g of the DAST powder to prepare a DAST growth solution. Next, this solution was heated to 55.0 ° C. while being stirred, and maintained at 55.0 ° C. for 10 hours to completely dissolve the DAST powder. Thereafter, 280 mL of the prepared solution was dispensed to obtain a crystal growth solution. The adjusted crystal growth solution was again heated to 55.0 ° C. and maintained at 55.0 ° C. for 10 hours. Next, the solution was lowered to 44.8 ° C. while being stirred, and then maintained for 30 minutes, and seed crystals attached to the support were introduced. After the seed crystal was charged, the temperature was quickly lowered to 43.3 ° C., and a bulk single crystal was grown for 40 days while lowering the solution temperature at a rate of 0.1 ° C./day.

(Growth of JP-1, JP-2, JP-3 single crystals)
(Preparation of seed crystal)
The seed crystal was grown under the same conditions as the seed crystal production in the above (Growth of JS-1 and JS-2 single crystals).
(Single crystal growth)
In the growth of the DAST single crystal, the bulk single crystal was grown under the same conditions as the growth of the single crystal in the above (JS-1, JS-2 single crystal growth). Thereafter, the (001) plane and the (00-1) plane were polished so that the crystal thickness was uniform.

The size of each DAST bulk single crystal obtained is shown in Table 4.

Samples J-1, J-2, J-3, JS-1, JS-2, JP-1, JP-2, and JP-3 were annealed to the DAST crystal by the following method and conditions. It was.
EYELA VACUUM OVEN VOS-201SD was used as an incubator. DAST crystals are arranged on a Si wafer as a heat-resistant floor plate, put into an incubator, the inside of the incubator is evacuated once, and then argon gas as an inert gas is filled into the apparatus. The annealing temperature was raised to 220 ° C. at a rate of 1 ° C./min, an annealing treatment was performed for 12 hours as a holding time, and then the crystals were cooled to room temperature by natural slow cooling.

FIG. 3 shows the THz wave generation test results before and after annealing of J-1, J-2, and J-3 single crystals. Fig. 4 shows the THz wave generation test results before and after annealing of JS-1 and JS-2 single crystals. Fig. 5 shows the generation of THz waves before and after annealing of JP-1, JP-2 and JP-3 single crystals. The test results are shown. The beam density applied to the crystal to generate THz waves is 622 MW / cm ² . The portion of the crystal irradiated with the laser for the THz wave generation test is a portion whose internal permeability of the crystal is confirmed to be good by a microscope. In addition, for crystals whose internal damage has been caused by laser in the prior evaluation, there is concern about attenuation of THz wave output due to internal damage, and the internal transparency of the crystal is comparable before and after the occurrence of damage, and laser irradiation This is a site that has not been damaged. Table 5 shows the time during which THz waves are stably generated in each sample at 0.5 or more.
The generation time of THz waves is improved by annealing even in crystals grown by various manufacturing methods. From this, it was understood that the effect of annealing can be obtained in a crystal grown by any manufacturing method.

[Example 3]
A confirmation test of beam density dependence and annealing effect for stable THz wave generation was performed. The production of the DAST single crystal was grown under the same conditions as in Example 1.
The size of each DAST bulk single crystal obtained is shown in Table 6.

  As in Example 1, annealing of sample numbers C-1, C-2, and C-3 to the DAST crystal was performed at a rate of 1 ° C./min up to an annealing temperature of 220 ° C., and an annealing treatment for 12 hours as a holding time. After that, the crystals were cooled to room temperature by natural slow cooling.

The generation of terahertz waves due to beam density dependence was confirmed. In order to confirm the relationship between the beam density shown in the above [0008] and the THz wave generation time, the beam density dependency for confirming stable THz wave generation in the DAST crystal was verified.
As a condition, C-1 and C-2 is a DAST crystal stably 0.5 or more THz wave within 300 seconds in the laser irradiation is set to an output of less than the laser output 1.5 GW / cm ² can no longer be generated Alternatively, a laser having a laser output of 1.5 GW / cm ² was applied to C-3, which is a DAST crystal that stably generated a THz wave of 0.5 or more for 300 seconds or more. Moreover, the part of the crystal irradiated with the laser for the THz wave generation test is a part where the internal permeability of the crystal is confirmed to be good by a microscope. In addition, for crystals whose internal damage has been caused by laser in the prior evaluation, there is concern about attenuation of THz wave output due to internal damage, and the internal transparency of the crystal is comparable before and after the occurrence of damage, and laser irradiation This is a site that has not been damaged. If the THz wave generation time is shortened as the beam density is higher, the time during which the THz wave is stably generated becomes faster or stable when the laser output of 1.5 GW / cm ² is irradiated according to the above condition method. This is because it can be presumed that the time during which the THz wave is stably generated becomes early even in the crystal where the wave is generated. The results are shown in Table 7.

FIG. 6 shows the THz wave generation test result of the crystal due to the difference in beam density. Condition 7 in Table 7 is the time required for the output value / maximum output value to become 0.5 or less when the beam density is less than 1.5 GW / cm ² , and condition B is the output value when the beam density is 1.5 GW / cm ² . / The time until the maximum output value becomes 0.5 or less. Sample No. C-3 is a DAST crystal in which a THz wave of 0.5 or more was stably generated in 300 seconds or more in laser irradiation set to a laser output of less than 1.5 GW / cm ^{2 as} described above. In FIG.
Looking at the beam density dependency of THz wave generation in each crystal, the time during which THz waves are generated is shortened by increasing the beam density in any crystal. That is, this indicates that it is difficult to stably generate THz waves when the beam density is increased in any DAST crystal.

To DAST crystals A-1, A-2, and A-3, in which a THz wave of 0.5 or more can no longer be stably generated within 300 seconds by laser irradiation set to an output of less than 1.5 GW / cm ² On the other hand, in the same manner as in Example 1, the temperature was raised to an annealing temperature of 220 ° C. at a rate of 1 ° C./min, an annealing treatment for 12 hours was performed, and then the crystals were cooled to room temperature by natural slow cooling. Thereafter, a durability test by laser irradiation of 1.5 GW / cm ² was performed.

The THz wave generation test by laser irradiation is as follows. The DAST crystal placed on the DAST crystal rotation jig is irradiated with a two-wavelength laser beam through a lens and mirror system, and the DLATGS output is monitored every second using an A / D converter to check the THz wave generation status. confirmed. Before annealing treatment and the beam density 1.5 GW / cm less than ² of the two-wavelength light, after annealing was beam density 1.5 GW / cm ² of the two-wavelength light. The two-wavelength laser was irradiated with laser light set to wavelengths λ ₁ = 1475 nm, λ ₂ = 1493 nm, pulse width 15 ns / pulse, and repetition frequency 50 Hz. Moreover, the part of the crystal irradiated with the laser for the THz wave generation test is a part where the internal permeability of the crystal is confirmed to be good by a microscope. In addition, for crystals whose internal damage has been caused by laser in the prior evaluation, there is concern about attenuation of THz wave output due to internal damage, and the internal transparency of the crystal is comparable before and after the occurrence of damage, and laser irradiation This is a site that has not been damaged.

The results of the THz wave generation test are shown in Table 8 and FIG. Before annealing, none of the three samples stably generated a THz wave of 300 seconds or more, but all three samples were crystals that generated a stable THz wave of 300 seconds or more by the annealing treatment.

According to the present invention, it is possible to improve the generation time of the terahertz wave generated from the organic optical single crystal by annealing the organic optical single crystal. And the organic optical single crystal which improved the generation | occurrence | production time of the terahertz wave by the manufacturing method can be obtained easily, and it can utilize effectively as what was stabilized for terahertz wave generation.

Annealing effect temperature range diagram of the crystal of the present invention Results of terahertz generation test of crystals of the present invention Terahertz generation test result 1 before and after annealing of the crystal of the present invention 1 Terahertz generation test result 2 before and after annealing of the crystal of the present invention 2 Terahertz generation test result 3 before and after annealing of the crystal of the present invention 3 Damage density beam density test results Terahertz generation test result before and after annealing of the crystal of the present invention 4

Claims (6)

  An organic optical single crystal composed of a stilbazolium derivative is generated from the organic optical single crystal by annealing in an inert gas at a temperature below the melting point of the organic optical single crystal and above the temperature at which the degree of freedom of crystal molecules is increased A method for producing an organic optical single crystal, wherein the generation time of a terahertz wave is improved as compared with that before the annealing treatment.   The method for producing an organic optical single crystal according to claim 1, wherein the annealing treatment is held at an annealing temperature for a sufficient time to remove defects in the crystal and then slowly cooled.   The method for producing an organic optical single crystal according to claim 1, wherein the annealing treatment is performed under a condition where a magnetic field is applied. The method for producing an organic optical single crystal according to claim 1, wherein the stilbazolium derivative is a stilbazolium derivative represented by the following formula 1.
  The method for producing an organic optical single crystal according to any one of claims 1 to 4, wherein the organic optical single crystal is at least one of DAST and DASC which are stilbazolium cation derivatives.   The method for producing an organic optical single crystal according to claim 5, wherein the organic optical single crystal is a DAST crystal.