JP2007232936A - Organic optical crystal, differential frequency generating element, terahertz wave generating apparatus, linear defect generation preventing method of organic optical crystal and manufacturing method of organic optical crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic optical crystal wherein terahertz wave output is not attenuated when the organic optical crystal is used for a terahertz wave generating apparatus. <P>SOLUTION: The organic optical crystal is characterized in that no linear defect exists on a cleavage surface of an inner part of the crystal. The linear defect is different from dislocation. The linear defect exists in the crystal and does not exist on the surface of the crystal. For example, as shown in a microphotograph of Fig. 1, a cleavage surface of a DAST (4-dimethylamino-N-methyl-4-stilbazolium tosylate) crystal has a cleavage surface in a direction parallel to an axis (a) and parallel to a (001) plane and the linear defect exists here. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic optical crystal, a difference frequency generator, a terahertz wave generator, a method for preventing the occurrence of linear defects in an organic optical crystal, and a method for manufacturing an organic optical crystal.

  Organic optical crystals are used in various optical devices such as laser irradiation devices by taking advantage of their optical characteristics. One type of organic optical crystal is an organic nonlinear optical crystal that exhibits a nonlinear optical effect or the like. Organic nonlinear optical crystals are expected to be applied to terahertz wave generators, terahertz wave detectors, high-sensitivity electric field sensors, etc. by utilizing their nonlinear optical effects and electro-optic effects, and various research and development have been conducted. Yes. Among these, the application of the organic nonlinear optical crystal to the terahertz wave generator is approaching the realization stage, and the expectation is great. 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. As a terahertz wave generator, for example, an apparatus that realizes stable broadband terahertz wave generation has been developed (Patent Document 1).

  Examples of the organic nonlinear optical crystal include DAST (4-dimethylamino-N-methyl-4-stilbazolium tosylate) crystal and DASC (4-dimethylamino-N-methyl-4-stilbazolium p-chlorobenzenesulfonate). ) 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. Among these, the DAST crystal and the DASC crystal have been studied for application as the difference frequency generation element of the terahertz wave generator, and the application of the DAST crystal is particularly expected. Organic nonlinear optical crystals such as DAST crystals are manufactured by, for example, a natural nucleus growth method or a seed crystal growth method. The natural nucleus growth method is a method in which a crystal material solution is supersaturated to naturally generate crystal nuclei and grow them. In the seed crystal growth method, the crystal obtained by the natural nucleus growth method is used as a seed crystal, and the seed crystal is attached to a seed rod tip and charged into a supersaturated crystal material solution. The seed crystal is further grown by increasing the degree of supersaturation by lowering. According to the seed crystal method, a large crystal used for an electronic component or the like can be manufactured. Further, as a method for producing an organic nonlinear optical crystal excellent in crystallinity by suppressing generation of miscellaneous crystals, there is a method of stirring the solution by rotating a container containing a crystal material solution (Patent Document 2). ).

JP 2004-219967 A JP 2001-247400 A

  However, in a terahertz wave generator using an organic nonlinear optical crystal as a difference frequency generator, there is a problem that the terahertz wave output attenuates with time. Therefore, terahertz wave generators using organic nonlinear optical crystals, particularly DAST crystals and DASC crystals, are expected to have high performance, but have not yet been put into practical use due to the problem of attenuation of the terahertz wave output. Is the current situation. Such a problem is a problem that may occur in the entire organic optical crystal including the organic nonlinear optical crystal.

  Accordingly, the present invention provides an organic optical crystal whose terahertz wave output is not attenuated when used in a terahertz wave generator, a difference frequency generator using the same, a terahertz wave generator, and a method for preventing the occurrence of linear defects in an organic optical crystal. Another object is to provide a method for producing an organic optical crystal.

  In order to achieve the above object, the present inventors conducted a series of studies focusing on elucidating the cause of the attenuation of the terahertz wave output. First, the organic optical crystal in which the terahertz wave output was attenuated was observed in detail. As a result, the inside of the crystal was found to be damaged, and it was estimated that this damage was caused by the laser of the two-wavelength parametric oscillator. Damage to the optical element using an inorganic crystal due to laser is generally caused by damage to the surface portion, and an organic nonlinear optical crystal such as DAST used as a difference frequency generating element is a thin plate having a thickness of less than 1 mm. Since most of them were, the internal damage of the organic optical crystal was a phenomenon beyond the expectation of those skilled in the art. As a result of further research, it was found that in some or all of the inside of the crystal, there was an organic optical crystal having a linear defect on the cleavage plane, and the organic optical crystal having the linear defect inside the crystal. Has been found to be used in a terahertz wave generating device as a difference frequency generating element, causing damage inside the organic optical crystal and attenuating the terahertz wave output. The present inventors also found that the linear defects can be prevented by forming the crystals while stirring the crystal material solution in the production of the organic optical crystal. And based on these knowledge, it reached | attained this invention. That is, the present invention is an organic optical crystal, a difference frequency generating element, a terahertz wave generating device, a method for preventing the formation of linear defects in an organic optical crystal, and a method for manufacturing an organic optical crystal, as described below.

  The organic optical crystal of the present invention is characterized in that no linear defect exists on the cleavage plane inside the crystal.

  The difference frequency generation element of the present invention is a difference frequency generation element that generates an electromagnetic wave having a wavelength corresponding to the difference frequency of the two electromagnetic waves by incidence of two electromagnetic waves having different wavelengths, and the organic optical crystal of the present invention is It is characterized by including.

  The terahertz wave generation device of the present invention includes an excitation laser irradiator, a two-wavelength optical parametric oscillator, a condensing lens, and a difference frequency generation element, and the wavelength in the two-wavelength parametric oscillator varies depending on the laser irradiated from the laser irradiator. Two electromagnetic waves are generated, the two electromagnetic waves are incident on the difference frequency generation element through the condenser lens, and an electromagnetic wave corresponding to the difference frequency of the two electromagnetic waves is generated from the difference frequency generation element. In the generator, the difference frequency generation element is the difference frequency generation element of the present invention.

  The method for preventing the occurrence of linear defects in an organic optical crystal according to the present invention is a method for preventing the occurrence of linear defects on a cleavage plane inside the crystal in the process of forming the organic optical crystal, the method for forming the organic optical crystal Is a method of forming the crystal by supersaturating the solution in a solution in which the organic optical crystal material is dissolved, and forming the crystal while the solution is stirred to generate the linear defects. It is characterized by preventing.

  The first method for producing an organic optical crystal of the present invention is characterized in that the organic optical crystal is formed while preventing the occurrence of linear defects by the method for preventing the generation of linear defects in the organic optical crystal of the present invention. .

  The second method for producing an organic optical crystal of the present invention is obtained by a crystal forming step of forming the crystal by bringing the solution into a supersaturated state in a solution in which the organic optical crystal material is dissolved, and the crystal forming step. It is a manufacturing method having a determination step of observing the inside of the crystal and determining the presence or absence of a linear defect on a cleavage plane inside the crystal, and a selection step of selecting a crystal without the linear defect.

  In the terahertz wave generating apparatus of the present invention using the organic optical crystal or the difference frequency generating element of the present invention, the terahertz wave output is not attenuated. Therefore, the present invention makes it possible to put the terahertz wave generator into practical use. In addition, according to the organic optical crystal linear defect generation preventing method or manufacturing method of the present invention, it is possible to obtain an organic optical crystal with no attenuation of the terahertz wave output.

  In the present invention, the linear defect is a defect different from a dislocation. The linear defect is a defect that exists inside the crystal and does not exist on the crystal surface. And the said linear defect is a defect which exists on the cleavage plane of a crystal | crystallization. For example, the cleavage plane of the DAST crystal has a cleavage plane in the direction parallel to the a-axis and in the direction parallel to the (001) plane, where the linear defect exists.

  In the present invention, the organic optical crystal is preferably an organic nonlinear optical crystal. Examples of the organic nonlinear optical crystal include a single crystal of a stilbazolium derivative, an MMONS crystal, a DAD crystal, and a LAP crystal. Among these, a single crystal of a stilbazolium derivative is preferable. Examples of the stilbazolium single crystal include DAST crystal and DASC crystal. Among these, DAST crystal is preferable. In the present invention, the organic optical crystal is preferably a single crystal.

  In the organic optical crystal linear defect generation preventing method and production method of the present invention, the stirring is not particularly limited, stirring by a stirring blade, stirring by a stirring bar, stirring by moving a container holding the solution, There are stirring and the like combining these. Examples of the stirring blade include a propeller for stirring. An example of the stirring bar is a magnetic stirrer. Examples of the movement of the container include a rotational movement, a reciprocating movement, a swinging movement, and a movement combining these.

  In the second method for producing an organic optical crystal of the present invention, in addition to or instead of the selection step, a cutting step of cutting out the portion having no linear defect from the crystal having the linear defect may be provided. Good.

  Next, the present invention will be described in detail with examples. However, this invention is not restrict | limited at all by the following description.

  The organic optical crystal of the present invention is characterized by having no linear defect on the cleavage plane inside the crystal. The linear defect has the following characteristics.

(1) The linear defect exists only in the organic nonlinear optical crystal and does not exist on the crystal surface. Further, the place where the linear defect exists is a cleavage plane of the crystal. Except for these conditions, the linear defect is not recognized as being location dependent and may occur at any location.
(2) The linear defects are all linear, and there are no bent defects. The linear defect is a defect different from a dislocation because it occurs in the middle of the crystal and is interrupted in the middle. The length of the linear defect varies, but the average length is, for example, in the range of 100 μm to 6 mm, in the range of 100 μm to 5 mm, in the range of 100 μm to 4 mm, in the range of 100 μm to 3 mm, or in the range of 100 μm to 2 mm. Range.
(3) Depending on the observation direction, the linear defect may be observed as a planar defect instead of a linear defect. In the present invention, such planar defects are also referred to as “linear defects”. In the present invention, the “linear defect” may also be defined as “a defect of at least one of a linear defect and a planar defect on a cleavage plane inside a crystal”.
(4) The linear defect may occur regardless of the type of supersaturation method in crystal formation. For example, the linear defect may occur in any of a temperature drop method and a solvent evaporation method. The linear defects are not dependent on the type of solvent used in crystal formation, and may occur regardless of the type of solvent.
(5) The linear defect does not occur due to the influence of water existing in the surrounding atmosphere after the crystal is taken out from the solution. For example, since DAST crystals have deliquescence, the influence of water is considered as the cause of the occurrence of the linear defects. On the other hand, in some cases, the occurrence of the linear defect was not observed in the DAST crystal left for several months in a humid atmosphere.
(6) The linear defects are unrelated to the deterioration of the crystal over time. That is, some organic optical crystals immediately after crystal formation have the linear defects.

  Next, a method for observing the linear defects in the organic optical crystal will be described. The observation method is not particularly limited, and examples thereof include observation by the following microscope and observation by an X-ray diffraction topography method. These observation methods can be applied to observation of the determination step in the second method for producing an organic optical crystal of the present invention.

  First, the observation method using the microscope will be described. This observation method is performed using a stereomicroscope, a polarization microscope, a reflection microscope, or the like, and is a method by which the linear defect can be easily observed. The magnification at the time of observation is not particularly limited and is, for example, 10 times or more, and a magnification of 100 times or more is preferable from the viewpoint of performing detailed observation. In the observation, it is preferable to clean the crystal surface to be observed in advance in order to distinguish the crystal surface structure, crystal surface defects, crystal surface deposits, and the like from the linear defects. However, the as-grown organic optical crystal has irregularities due to the growth step on its surface. In rare cases, there is a crystal whose surface growth step runs in a direction parallel to the a-axis. In such a crystal, it may be difficult to distinguish the linear defect from the growth step only by the transmission image. The combined use of images is useful for observing linear defects more reliably. Therefore, in order to observe the linear defect clearly distinguishing from the structure of the crystal surface and the like, it is preferable to use a reflection microscope capable of observing both the reflected image and the transmitted image. For example, using the reflection microscope, first, while observing the crystal surface reflection image, focus on the surface of the crystal on the objective lens side, and then change the light source position so that the crystal transmission image can be observed. . At this point, a crystal transmission image focused on the surface on the objective lens side is observed, so that structures and deposits on the crystal surface on the objective lens side can be clearly observed, and crystal internal defects and the opposite surface are observed. The structure is not observed, or is observed as a slightly blurred image. From this state, when the focus is gradually moved into the crystal, if there is a linear defect in the observation range, the linear defect can be observed. An example of observing linear defects inside the DAST crystal by this technique is shown in the micrograph of FIG. In the figure, the arrow direction is the a-axis direction, and a portion surrounded by a dotted circle indicates one of the linear defects. As shown in the figure, in the DAST crystal, the linear defect is observed as a thin straight line when viewed from the (001) plane or the (00-1) plane, but shows a slight spread in the depth direction. Depending on the viewing direction, it is observed as a planar defect. In the DAST crystal, the linear defects have a distribution in the depth direction, and not all the linear defects are present within the crystal at the same distance from the crystal surface. When the depth of focus is changed during microscopic observation, one image of a linear defect that has been observed sharply until then is gradually blurred, but at the same time, another linear defect is gradually sharpened in an adjacent region. There are many examples of becoming observed. Further, when a polarizing microscope is used as an observation microscope, more detailed linear defects can be observed. For example, when a DAST crystal is observed with a transmission microscope that does not use polarized light such as a stereomicroscope, it is assumed that there is a crystal in which no linear defect is observed at all. There is a crystal in which fine linear defects are observed in a specific orientation by observing the crystal while using a polarizing microscope and rotating the crystal with respect to the polarization direction. This indicates that there is an orientation in which a linear defect is easily detected depending on the polarization direction of the illumination light. Moreover, the following method is mentioned as a method of suppressing the oversight of a linear defect and raising observation accuracy. The DAST crystal is observed as a red crystal in the transmission microscope image. This indicates that the R component is particularly strong among the three components of red (R), green (G), and blue (B) constituting the full-color observation image. Therefore, the linear defect that is hardly detected in the R component and is detected only in the G component or the B component is buried in the bright R component, and it may be difficult to recognize the linear defect under a full-color observation image. Therefore, as a method of preventing this oversight, an optical filter that cuts only the R component is provided between the white light source of the microscope and the crystal, or between the crystal and the eyepiece, thereby detecting the G component and the B component. It becomes possible to make it easy to see the straight line defect.

  Next, a method for observing linear defects by the X-ray diffraction topography method will be described. The observation method by the X-ray diffraction topography method is a method of diffracting X-rays at a specific index plane of a crystal to detect a crystal structure and imaging it. The image thus obtained is called a “topograph image”. From the topographic image, it is possible to observe the state of the location where the disorder is generated in the molecular orientation such as the crystal boundary such as the sector boundary, the growth stripe, and the dislocation existing inside the crystal as the change in contrast, Linear defects can also be observed. Observation by the X-ray diffraction topograph method can be carried out using an X-ray diffraction topograph measurement device. The result of observing the DAST crystal by X-ray diffraction topography is shown in the photograph of FIG. In the same figure, (A) is a DAST crystal without the linear defect, and (B) is a DAST crystal with the linear defect. Further, in the figure, the position surrounded by the solid circle is the initial generation nucleus position, the area surrounded by the dotted ellipse is the area where the linear defect exists, and the arrow direction is the a-axis direction. . In this observation, since the DAST crystal has a strong X-ray diffraction intensity from the (130) plane, a topographic image of the (130) plane was measured. As shown in the figure, the linear defect was not observed in the DAST crystal of FIG. 9A, but the linear defect was clearly observed as a contrast change in the DAST crystal of FIG. . This observation result coincided with the observation result using a reflection microscope capable of observing both a transmission image and a reflection image.

  Next, the method for preventing the occurrence of linear defects in the organic optical crystal of the present invention, the first production method, and the second production method will be described.

  The crystal formation method in the method for preventing the occurrence of linear defects in the organic optical crystal of the present invention, the first production method and the second production method is not particularly limited, and for example, a natural nucleus growth method or a seed crystal growth method is adopted. it can. As described above, the natural nucleus growth method is a method in which a crystal material solution is supersaturated to naturally generate crystal nuclei and grow them. In the seed crystal growth method, the crystal obtained by the natural nucleus growth method is used as a seed crystal, and the seed crystal is attached to a seed rod tip and charged into a supersaturated crystal material solution. The seed crystal is further grown by increasing the degree of supersaturation by lowering. The crystal material solution is not particularly limited, and is appropriately determined depending on the type of crystal. For example, in the case of a DAST crystal, a solution in which DAST is dissolved in an organic solvent such as methanol, ethanol, acetonitrile or the like can be used as the crystal material solution. The organic solvent is preferably methanol, but may be a mixed solvent in which two or more solvents are mixed, such as a solvent in which methanol and acetonitrile are mixed. In the crystal formation method of the present invention, a method for realizing the supersaturated state is not particularly limited. For example, after the crystal material solution is maintained at a saturated or unsaturated temperature, the temperature is lowered to remove the solution. Examples thereof include a temperature drop method for making a supersaturated state, and a solvent evaporation method for making a supersaturated state by evaporating the solvent of the crystal material solution. The temperature drop speed in the temperature drop method is not particularly limited, and may be continuously lowered at a predetermined speed, may be lowered while changing the speed, or may be lowered stepwise instead of continuously. May be. In the solvent evaporation method, the evaporation method of the solvent is not particularly limited, and may be natural evaporation, for example.

  Next, in the organic optical crystal linear defect generation preventing method and the first production method of the present invention, crystals are formed in a state where the crystal material solution is stirred. In the second production method of the present invention, it is preferable to form crystals while the crystal material solution is stirred. FIG. 5 shows an example of an apparatus capable of forming crystals while stirring the crystal material solution.

  As shown in the figure, this apparatus has a crystal forming vessel 2, a thermostatic bath 5, a stirring device 3, and a temperature control device 6 as main components. The crystal formation container 2 is not particularly limited, but is preferably a container formed of a material resistant to the crystal material solution. For example, a wide-mouth bottle made of Teflon (registered trademark) can be used. The crystal material container 1 is placed in the crystal forming container 2. The thermostat 5 contains a liquid (heat medium) 4, and thereby the temperature of the thermostat 5 is kept constant. For example, water is used as the liquid 1, but an oil-based heat medium such as silicone oil is used in a temperature range exceeding 100 ° C. The stirring device 3 includes a controller 33 disposed outside the thermostat 5, a magnetic stirrer 32 and a stirrer 31 disposed at the bottom of the thermostat 5. On the magnetic stirrer 32, the crystal forming container 2 is disposed, and the stirrer 31 is disposed on the bottom of the crystal forming container 2. In the stirring device 3, the stirring bar 31 is rotated by the rotation of the magnetic field in the magnetic stirrer 32, and as a result, the crystal material solution 1 in the crystal forming container 2 is stirred. The rotation of the stirrer 31 can be adjusted by the controller 33 that is electrically connected to the magnetic stirrer 32. The temperature control device 6 includes a control unit 61, a temperature sensor 62, a heater 63 and a cooler 64. The temperature sensor 62 is electrically connected to the control unit 61, measures the temperature of the liquid 4 in the thermostatic chamber 5, and transmits the result to the control unit 61 as an electrical signal. The heater 63 and the cooler 64 are electrically connected to the control unit 61, and the heater 63 and the cooler 64 are switched on and off by an electric signal from the control unit 61. A predetermined temperature program can be set in the control unit 61, and the heater 63 and the cooler 64 are turned on or off while monitoring the temperature of the liquid 4 in the thermostatic chamber 5 by the temperature sensor 62. Thus, the temperature program is executed.

  Crystal formation using this apparatus is performed, for example, as follows. That is, first, the crystal material solution 1 is brought into a stirring state by rotating the stirring bar 31 of the stirring device 3. The degree of stirring is not particularly limited, but if the stirring is too strong, miscellaneous crystals may be formed. If the stirring is too weak, the occurrence of the linear defects may not be effectively prevented. To do. On the other hand, the liquid 4 in the thermostat 5 is heated by the temperature control device 6 so that the crystal material solution 1 in the crystal formation vessel 2 is saturated or non-saturated and held for a certain period of time. The reason for maintaining the constant time in this way is to make the particle state constant in the crystal material solution 1. The particle state can also be confirmed by measuring the electrical conductivity of the crystal material solution 1. Then, a crystal is formed by lowering the temperature of the crystal material solution 1 to a supersaturated state by the temperature control device 6 while the crystal material solution 1 is stirred. The temperature drop condition is not particularly limited. In the formation of the crystal, crystal nuclei may be naturally generated and grown, or a seed crystal may be prepared in advance and the crystal may be grown using this as a nucleus. Thus, if the crystal is formed while the crystal material solution 1 is stirred, the occurrence of the linear defects can be effectively prevented.

  In this example, a temperature drop method is used to bring the crystal material solution 1 into a supersaturated state, but the present invention is not limited to this. For example, in the apparatus of this example, the crystal material solution 1 is saturated or unsaturated, the top of the crystal formation container 2 is opened, and the crystal material solution 1 is stirred with the stirrer, The liquid 4 in the thermostatic chamber 5 may be heated using the temperature control device 6 to evaporate the solvent of the crystal material solution 1 to be supersaturated to form crystals. In the present invention, crystals may be formed by combining the temperature drop method and the solvent evaporation method.

  Moreover, in this example, although the magnetic stirrer 32 and the stirring bar 31 were used as the stirring apparatus 3, this invention is not limited to this, For example, stirring using stirring blades, such as a propeller, may be sufficient, It may be agitation in which the crystal forming container 2 is moved (for example, rotational movement, reciprocating movement, swinging movement, and a combination thereof). Further, in the stirring by rotating the stirring bar, the stirring blade or the container, it is preferable to reverse the rotation direction every predetermined time. This is because the effect of stirring can be further improved by inversion.

  Next, in the second method for producing an organic optical crystal of the present invention, the crystal formation step and the inside of the crystal obtained in the crystal formation step are observed, and linear defects on the cleavage plane inside the crystal are observed. It is a manufacturing method which has the determination process which determines the presence or absence, and the selection process which selects the crystal | crystallization without the said linear defect. As described above, the observation in the determination step can be performed by observation using a microscope or observation by an X-ray diffraction topograph method. In addition, as described above, in the second manufacturing method, in addition to or instead of the selection step, a cutting step of cutting out the portion having no linear defect from the crystal having the linear defect is provided. Also good. That is, in the organic optical crystal obtained by the conventional crystal forming method, there is a case where the linear defect exists only in a partial region of the crystal and does not exist in other regions. An example of such a DAST crystal is shown in the photograph of FIG. FIGS. 1A and 1B show one DAST crystal broken by laser irradiation into two, but the linear defect exists only in a partial region of the crystal, and the others. In the region surrounded by the dotted line, the linear defect does not exist. In such a case, the organic optical crystal of the present invention can be obtained by cutting out a portion having no linear defect. The crystal cutting method is not particularly limited, and examples thereof include laser cutting and cutting using a knife such as a knife. Further, by forming a crystal while stirring the crystal material solution, the linear defect can be prevented. However, even if the linear defect occurs, a portion without the linear defect is cut out and It can be used as the organic optical crystal of the invention.

  Next, examples of the present invention will be described together with comparative examples.

In this example, the DAST crystal without the linear defects was irradiated with a laser to evaluate the damage inside. Further, as Comparative Example 1, the laser was irradiated to the three DAST crystals having the linear defects, and the damage inside thereof was similarly evaluated. That is, first, using a reflection microscope capable of observing both a transmission image and a reflection image, as described above, the inside of the DAST crystal was observed, and the DAST crystal without the linear defects was used as the crystal of this example. Three DAST crystals (A, B, and C) having linear defects were used as the crystals of Comparative Example 1. Next, the crystals of this example and comparative example 1 were irradiated with laser. In addition, with respect to the crystals (A, B, and C) of Comparative Example 1, a laser was irradiated to a portion where the linear defect was present. The laser irradiation conditions are a wavelength of 1550 nm, a repetition frequency of 10 Hz, and a laser irradiation time of 10 minutes. The peak power density of the laser is 0.38 GW / cm ² at the time of the first irradiation, and then 2 to 7 times the first peak power density as the number of irradiations increases in the second to seventh irradiations. It was. Laser irradiation was repeated until the crystal was damaged by laser irradiation, and the peak power density at which the damage occurred was examined. The results are shown in Table 1 below. In Table 1 below, “◯” indicates no damage, “×” indicates occurrence of damage, and “−” indicates that measurement was not performed.

(Table 1)
Laser peak power density (GW / cm ² )
0.38 0.76 1.1 1.5 1.9 2.3 2.8
Example 1-○ ○ ○ ○ ○ ○
Comparative Example 1 Crystal A × − − − − − −
Crystal B ○ ○ × − − − −
Crystal C ○ ○ × − − − −

As shown in Table 1, in this example, which is a crystal having no linear defects, no damage occurred even when irradiated with a laser having a peak power of 2.8 GW / cm ² . In contrast, as shown in Table 1, the crystal A of Comparative Example 1 was damaged by laser irradiation with a peak power density of 0.38 GW / cm ² , and the peak power density of Crystal B and Crystal C was 1 Damage occurred by laser irradiation of 1 GW / cm ² .

  In this example, a DAST crystal was formed using the apparatus having the configuration shown in FIG. 5 while stirring the crystal material solution. That is, DAST was dissolved in methanol at a concentration of 4.2 wt% to prepare a crystal material solution 1, which was placed in the crystal formation vessel 2. And the said stirring element 31 was rotated on the conditions of rotation speed 30-400 rpm, and the said solution 1 was stirred. In this state, first, the temperature of the solution is set to 55 ° C. by the temperature controller 6 and held in this state for 10 hours, and then the temperature of the solution is increased to 42 ° C. at a rate of 1 ° C./hour. The DAST crystal (3 mm square, 1 mm thickness) was formed by being lowered and supersaturated. About the obtained DAST crystal, the inside of the crystal was observed using a reflection microscope capable of observing both a transmission image and a reflection image as described above. This result is shown in the photomicrograph of FIG. As shown in FIG. 4, the linear defects were not observed in the DAST crystal obtained in this example.

  The organic optical crystal of the present invention can be preferably used, for example, as a difference frequency generation element of a terahertz wave generator, but can also be applied to a terahertz wave detection element, a high-sensitivity electric field sensor, and the like, and its application field is not limited. It can be applied in a wide range of fields.

It is a photograph of an example of the DAST crystal which has the said linear defect. FIG. 2 (A) is a photograph showing an example of the organic optical crystal (DAST crystal) of the present invention, and FIG. 2 (B) is a photograph of the DAST crystal having the linear defect. FIGS. 3A and 3B are photographs showing an example of a DAST crystal in which the linear defect exists in a part thereof and the linear defect does not exist in another part. FIG. 4 is a photograph of a DAST crystal obtained in another example of the present invention. FIG. 5 is a configuration diagram showing an example of the configuration of the crystal forming apparatus used in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal material solution 2 Crystal formation container 3 Stirrer 4 Liquid (heat medium)
5 Thermostatic bath 6 Temperature control device 31 Stirrer 32 Magnetic stirrer 33 Controller 61 Control unit 62 Temperature sensor 63 Heater 64 Cooler

Claims (22)

An organic optical crystal, characterized in that no linear defect exists on a cleavage plane inside the crystal. The organic optical crystal according to claim 1, wherein the linear defect is a defect different from a dislocation. The organic optical crystal according to claim 1, wherein the linear defect is a defect that exists in the crystal and does not exist on the crystal surface. The organic optical according to any one of claims 1 to 3, wherein the organic optical crystal is at least one crystal selected from the group consisting of an organic nonlinear optical crystal, a single crystal of a stilbazolium derivative, a DAST crystal, and a DASC crystal. crystal. 5. The organic optical crystal is a DAST crystal or a DASC crystal, and the linear defect is a linear defect extending in a direction parallel to the a-axis direction of the DAST crystal or DASC crystal. The organic optical crystal described. A difference frequency generating element for generating an electromagnetic wave having a wavelength corresponding to a difference frequency between the two electromagnetic waves by incidence of two electromagnetic waves having different wavelengths, wherein the organic optical crystal according to any one of claims 1 to 5 is used. A difference frequency generating element comprising: An excitation laser irradiator, a two-wavelength optical parametric oscillator, a condensing lens, and a difference frequency generating element, and the laser irradiated from the laser irradiator generates two electromagnetic waves having different wavelengths in the two-wavelength parametric oscillator; A terahertz wave generating device in which two electromagnetic waves are incident on the difference frequency generation element through the condenser lens, and an electromagnetic wave corresponding to the difference frequency of the two electromagnetic waves is generated from the difference anti-frequency generation element. A terahertz wave generating device, wherein the frequency generating element is the difference frequency generating element according to claim 6. An organic optical crystal linear defect generation preventing method for preventing the generation of linear defects on a cleavage plane inside the crystal in the process of forming the organic optical crystal, wherein the organic optical crystal forming method includes the organic optical crystal In a solution in which a material is dissolved, the crystal is formed by supersaturating the solution, and the crystal is formed while the solution is stirred to prevent the occurrence of the linear defects. A method for preventing the occurrence of linear defects in organic optical crystals. The linear defect of an organic optical crystal according to claim 8, wherein the stirring is at least one selected from the group consisting of stirring by a stirring blade, stirring by a stirring bar, and stirring by moving a container holding the solution. Occurrence prevention method. The method for preventing the occurrence of linear defects in an organic optical crystal according to claim 8 or 9, wherein the linear defects are defects different from dislocations. The method for preventing the occurrence of a linear defect in an organic optical crystal according to any one of claims 8 to 10, wherein the linear defect is a defect that exists inside the crystal and does not exist on the crystal surface. 12. The organic optical according to claim 8, wherein the organic optical crystal is at least one crystal selected from the group consisting of an organic nonlinear optical crystal, a single crystal of a stilbazolium derivative, a DAST crystal, and a DASC crystal. A method for preventing the occurrence of linear defects in crystals. The organic optical crystal is a DAST crystal or a DASC crystal, and the linear defect is a linear defect extending in a direction parallel to the a-axis direction of the DAST crystal or DASC crystal. A method for preventing the occurrence of linear defects in the organic optical crystal as described. A method for producing an organic optical crystal, wherein the organic optical crystal is formed while preventing the occurrence of linear defects by the method according to any one of claims 8 to 13. Production method. A method for producing an organic optical crystal, comprising: a solution in which the organic optical crystal material is dissolved; a crystal forming step in which the solution is supersaturated to form the crystal; and an inside of the crystal obtained in the crystal forming step And determining the presence or absence of a linear defect on the cleavage plane inside the crystal, and a method for producing an organic optical crystal comprising a selection process for selecting a crystal without the linear defect. The method for producing an organic optical crystal according to claim 15, further comprising, in place of or in place of the selection step, a step of cutting out a portion having no linear defect from the crystal having the linear defect. The method for producing an organic optical crystal according to claim 15 or 16, wherein, in the crystal forming step, crystals are formed while the solution is stirred. The method for producing an organic optical crystal according to claim 17, wherein the stirring is at least one selected from the group consisting of stirring by a stirring blade, stirring by a stirring bar, and stirring by moving a container holding the solution. The method for producing an organic optical crystal according to any one of claims 15 to 18, wherein the linear defect is a defect different from a dislocation. 20. The method for producing an organic optical crystal according to any one of claims 15 to 19, wherein the linear defect is a defect that exists inside the crystal and does not exist on the crystal surface. The organic optical crystal according to any one of claims 15 to 20, wherein the organic optical crystal is at least one crystal selected from the group consisting of an organic nonlinear optical crystal, a single crystal of a stilbazolium derivative, a DAST crystal, and a DASC crystal. Crystal production method. The organic optical crystal is a DAST crystal or a DASC crystal, and the linear defect is a linear defect extending in a direction parallel to the a-axis direction of the DAST crystal or DASC crystal. The manufacturing method of the organic optical crystal of description.

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