JPH04350629A - Organic nonlinear optical crystal and nonlinear optical parts - Google Patents

Abstract

PURPOSE:To decrease the surface reflection of the org. nonlinear optical crystal to incident light or exit light of a specific wavelength. CONSTITUTION:The antireflection film of the org. nonlinear optical crystal having the antireflection film on the surface satisfies the following two requirements: 1.40<=(n)<=1.50, nd=0.25lambda+ or -0.025lambda+0.5mlambda, where (n); the refractive index of the constituting material, nd; the optical film thickness of the constituting material, (m); integer >=0, lambda; the specific wavelength. This org. nonlinear optical crystal is formed with the antireflection film on the optically smooth surface.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic nonlinear optical crystal having an antireflection film useful as a nonlinear optical component in the fields of optical communication and optical information processing.

0002

BACKGROUND OF THE INVENTION Since organic nonlinear optical crystals are materials used for optical purposes in a wide sense, it is desired that they be treated with an antireflection film to prevent light reflection on the crystal surface. In fact, it is common practice to apply an antireflection coating to nonlinear optical components using inorganic nonlinear optical crystals. 4-(N,N-dimethylamino)-3 is an example of an antireflection coating applied to an organic nonlinear optical crystal.
- There is a description that anti-reflection coating was applied to acetamidonitrobenzene (DAN) (S. Ducharm
e et al., Applied Physics Letters
, vol. 57, No. 6, 537, 1990). However, as clarified in the present invention, there is no disclosure of the refractive index of film-constituting materials, optical film thickness, etc. to the extent that processing of anti-reflection films can be carried out.

An example of an organic nonlinear optical crystal immersed in an antireflection-treated optical cell together with matching oil for adjusting the refractive index in order to reduce reflection on the crystal surface is the above-mentioned S. It is described in Ducharme et al. There is also an example of using a glass plate treated with an anti-reflection film and pasting this glass plate on an organic nonlinear optical crystal to reduce reflection on the crystal surface (Kitaoka et al., Optics, Vol. 19, No. 8).
No. 538, 1990). However, in either case, the antireflection film is not formed directly on the surface of the nonlinear optical crystal as realized in the present invention.

0004

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic nonlinear optical crystal in which surface reflection of incident light or emitted light of a specific wavelength is reduced.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the present invention has the following configuration.

An organic nonlinear optical crystal having an antireflection film on its surface, the antireflection film satisfying the following two conditions.

1.40≦n≦1.50 nd=0.25λ±0.025λ+0.5mλ where, n; refractive index of constituent material nd; optical film thickness of constituent material m; integer greater than or equal to 0 λ; specific Wavelength” The organic nonlinear optical crystal referred to in the present invention may be any organic crystal that exhibits a nonlinear optical effect. Second-order nonlinear optical effects and third-order nonlinear effects are known as nonlinear optical effects, and second-order nonlinear optical effects include first-order electro-optic effects (
Pockels effect) and second-order harmonic generation (SHG) effect, and third-order nonlinear optical effects include second-order electro-optic effect (
Kerr effect) and third harmonic generation (THG) effect.

4'-Nitrobenzylidene-3-alkanoylamino-4-methoxyaniline and 4'-nitrobenzylidene-3-halogenoalkanoylamino-4-methoxyaniline preferably used in the present invention, and at least a portion thereof The deuterium-substituted compound is 4'-nitrobenzylidene-3-acetamino-4
-methoxyaniline (MNBA), 4'-nitrobenzylidene-3-ethylcarbonylamino-4-methoxyaniline (MNBA-Et), 4'-nitrobenzylidene-3-chloroacetamino-4-methoxyaniline (M
NBA-Cl), 4'-nitrobenzylidene-3-bromoacetamino-4-methoxyaniline (MNBA-B
r), 4'-nitrobenzylidene-3-(β-chloroethyl)carbonylamino-4-methoxyaniline (MN
-NHCOR representing an alkanoylamino group or a halogenoalkanoylamino group such as BA-ClEt), where R is an alkyl having 2 or less carbon atoms, a halogenated alkyl, and a compound in which at least a portion of these is substituted with deuterium refers to Crystals of these compounds all exhibit large second-order nonlinear optical effects (Japanese Patent Application Laid-open No. 6
3-113429), the vapor pressure of the compound is low and it is possible to form an antireflection film by vapor deposition, so it is suitable for an organic nonlinear optical crystal having an antireflection film on its surface according to the present invention.

[0009] Also, as an organic crystal exhibiting a large second-order nonlinear optical effect,

0010

[Chemical formula 3]

3,9-E,E'-5a,6 represented by
, 11a,12-tetrahydro[1,4]benzoxazino[3,2-b][1,4]benzoxazine (E,
E' is an acceptor substituent) crystal (JP-A-1-45
No. 388) is also suitable for organic nonlinear optical crystals having an antireflection film on the surface according to the present invention. where E and E
' are the same acceptor substituents. Acceptor substituents include nitro, cyano, isocyanate,
Examples include aldehyde, alkoxycarbonyl such as methoxycarbonyl and ethoxycarbonyl, sulfonyl, and halogen. Nitro, aldehyde, and alkoxycarbonyl groups are preferred because the heat resistance of the crystal increases due to hydrogen bonding with the N--H group. For example, 3,9-dinitro-5a,6,11a,12-tetrahydro[1,4
] Benzoxazino[3,2-b][1,4]benzoxazine (DNBB), 3,9-dimethoxycarbonyl-5a,6,11a,12-tetrahydro[1,4]benzoxazino[3,2-b][ 1,4]benzoxazine (DMCBB).

The surface of a crystal referred to in the present invention may be any surface as long as it is a surface for the purpose of inputting or emitting light of a specific wavelength, and may be a naturally grown surface or a cleaved surface of an organic crystal, or a surface that can be cut or cleaved in any direction. It may be a polished surface. When light of a specific wavelength enters or exits approximately perpendicular to this surface,
It has the greatest anti-reflection effect. In general, organic nonlinear optical crystals have different refractive indexes depending on the plane orientation of the crystal and the polarization direction of input and output light due to the anisotropy of the crystal. It goes without saying that the antireflection film of the present invention is effective on the surface of an organic nonlinear optical crystal that has a refractive index greater than the refractive index of the antireflection film, but more preferably has a refractive index of 1.6 or more. It is a crystal surface. This is because reflected light can be reduced to less than half. More preferably, the crystal surface has a refractive index in the range of 1.7 to 2.6. This is because reflected light can be reduced to one fourth or less.

The surface of the organic nonlinear optical crystal forming the antireflection film may be a single surface or two or more surfaces. When antireflection films are formed on a plurality of surfaces, they may be antireflection films for light of the same specific wavelength, or may be antireflection films for light of different specific wavelengths.

[0014] In general, light reflection is caused by a boundary surface with discontinuous refractive index. If this boundary surface, that is, the surface of the organic nonlinear optical crystal in the present invention, is smooth compared to the wavelength of the light, part or all of the incident light will be specularly reflected. On the other hand, if the surface irregularities are at least as large as the wavelength, reflection proceeds in various directions. This kind of reflection is called diffuse reflection or diffuse reflection (Iwanami Publishing, ``Dictionary of Physical and Chemical Science'' (3rd edition, expanded edition); ``Reflection''). The antireflection film of the present invention is effective even on surfaces where diffuse reflection occurs partially due to surface irregularities, scratches, defects, etc. Therefore, the surface of the organic nonlinear optical crystal on which the antireflection film is formed does not necessarily have to be a flat surface as long as light can enter and exit, but may be a curved surface such as a spherical surface or a cylindrical surface. Further, it may be the entirety of these surfaces, or a part thereof, such as the incident end surface of an optical waveguide.

The material forming the antireflection film of the present invention has a refractive index of 1.40 to 1.50 at a specific wavelength;
Any material may be used as long as it is transparent to a specific wavelength, but a material that can be formed into a film by vacuum evaporation is desirable. This is because film formation by vacuum evaporation allows for easy adjustment of film thickness. More preferably, a dielectric film, such as SiO2, which is transparent to near-infrared light and visible light is preferable. The dielectric film is
This is because the film has high strength and is not easily scratched, and also functions as a protective film for organic nonlinear optical crystals, and is also highly transparent. SiO2 is preferable because it can be easily formed into a film by vapor deposition. In addition, it is 1.4 in the visible light wavelength region.
5, and the refractive index changes slightly depending on the wavelength and also depending on the method of producing the deposited film, but the refractive index is about 1.
．． It does not exceed 40-1.50.

The vacuum evaporation method referred to in the present invention may be any general physical vapor deposition method. For the purpose of improving the quality of the deposited film, an ion shower using oxygen ions or argon ions may be used in combination. When depositing a dielectric film with a high melting point, electron beam heating evaporation is preferably used. More preferably, it is desirable to heat the organic nonlinear optical crystal that is the deposition substrate. This is because the smoothness of the deposited film and the adhesion strength of the film are further improved. The heating temperature for organic nonlinear optical crystals must be kept at a temperature at which the organic crystal used does not melt or sublimate in vacuum.
When using organic crystals with very high heat resistance, 120~
Heating at 150°C is desirable. In the case of organic crystals with poor heat resistance, it is necessary to set the temperature to a lower temperature, but the temperature may be adjusted depending on the heat resistance of the organic crystals. When depositing SiO2 to form an antireflection film on organic crystals with low heat resistance, the temperature is preferably in the range of 60 to 120°C.

[0017] Substrate heating also has the effect of promoting the degassing of adsorbed gases, especially water vapor, present on the surface of organic crystals and improving the adhesion strength of the antireflection film.
When the temperature is 00° C. or lower, it is desirable to perform vacuum heating for at least 30 minutes before vapor deposition. Although the heating temperature before vapor deposition may be changed as necessary, it is desirable to suppress fluctuations in the substrate temperature during vapor deposition. This is because the refractive index of the deposited film becomes nonuniform, which causes the antireflection performance to vary.

[0018] The organic crystal may be heated by direct heat radiation from a hot plate placed on the back surface, or by contact with a hot plate. Heating may also be performed using a heating lamp installed on the back side or the front side. Furthermore,
Thermal radiation from the heated vapor deposition material may be used without providing a special device for heating the organic crystal. For example, when depositing SiO2 by electron beam heating, if the distance to the organic crystal that is the deposition substrate is about 25 cm, the temperature of the organic crystal increases to about 60 to 80°C. Lamp heating from the back side or the front side is desirable because the organic crystal can be heated more uniformly and there is less temperature fluctuation during deposition.

The optical film thickness as used in the present invention is the optical film thickness of the constituent material of the antireflection film at a specific wavelength, and is equal to the product of the refractive index of the constituent material and the film thickness. Since the refractive index of the constituent materials has different values depending on the wavelength of light, the optical film thickness is measured using light of the same specific wavelength at which the refractive index was measured. The optical film thickness can be easily measured based on the interference pattern of the transmission spectrum and reflection spectrum of the organic nonlinear optical crystal on which the antireflection film is formed.

[0020] When forming an antireflection film using a vapor deposition method, it is preferable to use an optical film thickness monitor because the optical film thickness at a specific wavelength can be measured on the spot during vapor deposition. It is preferable to select the film thickness monitoring light within a range of about ±20% around a specific wavelength, since this can avoid the effects of refractive index dispersion of the constituent materials.

[0021] If the optical film thickness monitor cannot use light with a wavelength approximately equal to a specific wavelength, the deviation in the optical film thickness due to the wavelength dependence of the refractive index can be calibrated using the above-mentioned interference pattern. Good. In this case, it is preferable to use a wavelength that has a simple integer ratio relationship with the specific wavelength, for example, a wavelength that is half the specific wavelength, as the film thickness monitoring light to facilitate control. Of course, if the refractive index dispersion of the constituent materials is small, it is unnecessary to particularly correct the influence of the refractive index dispersion, even if, for example, light with a wavelength half the specific wavelength is used as the monitor light.

Furthermore, when using a crystal resonator type film thickness monitor, the optical film thickness may be similarly calibrated using an interference pattern. Regardless of whether an optical or crystal resonator type film thickness monitor is used, it is easy to control the optical film thickness accuracy to an accuracy of 5%. With careful control, it is quite possible to obtain an optical film thickness accuracy of 1 to 2%.

The optical thickness of the antireflection film of the present invention is nd=
0.25λ±0.025λ+0.5mλ where,
n; refractive index nd of constituent material; optical film thickness m of constituent material; integer λ greater than or equal to 0; must be a specific wavelength. The value of m may be any natural number such as 0, 1, 2, . . . , but it is preferable that m=0 in terms of ease of obtaining a homogeneous film and productivity.

[0024] The specific wavelength referred to in the present invention refers to the wavelength of light incident on or emitted from an organic nonlinear optical crystal in vacuum. The anti-reflection coating is effective against light of this specific wavelength.

[0025] When an organic nonlinear optical crystal is used as a nonlinear optical component, it needs to have a surface with little diffuse reflection as described above. An optically smooth surface in the present invention refers to a surface with little diffuse reflection, and is a surface where the intensity of diffusely reflected light does not exceed at most half of specular reflection in the absence of an antireflection film. The optically smooth surface may be produced by the cutting and polishing described above, or by using crystal cleavage. In this case, it is possible to form an optically smooth surface with almost no diffuse reflection and surface irregularities that are equal to or less than the wavelength.

The nonlinear optical component of the present invention may be an organic nonlinear optical crystal having an antireflection coating on an optically smooth surface, even if it is used in its original form by being held in an appropriate device. Alternatively, it may be fixed in a container with appropriate strength. In order to facilitate handling, it may be adhesively fixed to a frame made of metal, plastic, or the like.

[0027] Although an optical fiber or the like may be directly bonded to the surface on which the anti-reflection film is formed in order to input and emit light, it is preferable that the anti-reflection film is directly exposed. This is because direct exposure has a greater antireflection effect.

The organic nonlinear optical crystal having the antireflection film of the present invention on its surface has reduced surface reflection for incident light and emitted light of specific wavelengths. Furthermore, when a transparent dielectric material formed by a vacuum evaporation method is used as the material constituting the antireflection film, it can also function as a surface protection film for the organic nonlinear optical crystal, which is relatively soft and easily damaged. The nonlinear optical component made of the organic nonlinear optical crystal of the present invention enables efficient use of light due to the antireflection film formed on the optically smooth surface of the organic nonlinear optical crystal, and Stray light can be prevented.

The present invention will be explained in more detail with reference to the following examples.

[0030]

【Example】

Example 1 A plate-shaped DNBB crystal was obtained by crystal growth from a methyl ethyl ketone solution. This crystal is an α-type monoclinic crystal with the following lattice constant.

Lattice constant a = 10.19A (Angstrom) b = 23.49A c = 6.86A β = 122.65°DNBBα type crystal is a biaxial crystal with two optical axes, and three principal refraction All rates are different (nX > nY > nZ
). The smallest principal refractive index nZ is at least 1.5
1 or more (measurement wavelength 1.06 μm). Therefore, D.N.
The antireflection film shown in the present invention can be formed on any surface of the BBα type crystal.

The two widest planes of the plate-like DNBBα type crystal thus obtained are {010} planes. this{
010} surface, an antireflection film against light with a wavelength of 1064 nm was formed by the following method.

The {010} plane of the obtained DNBBα type crystal was sandwiched between thin stainless steel plates having a circular opening with a diameter of 4 mm, and the plates were installed in the upper part of a vacuum evaporation apparatus having a substrate heating function using halogen lamp heating. SiO2 sintered pellets were placed at the electron beam heating position of the evaporation source at the bottom of the evaporation apparatus. At this time, the distance between the evaporation source and the DNBBα type crystal was about 80 cm.

After the vapor deposition apparatus was evacuated to 5×10 −6 Torr, the organic crystal was heated to 100° C. with a halogen lamp, and after 15 minutes, SiO 2 was heated with an electron beam to start vapor deposition. During vapor deposition, DNBB was used to make the film thickness uniform.
A hemispherical dome fitted with an α-type crystal was rotated. By measuring the change in transmittance of the monitor glass that was deposited at the same time as the DNBBα crystal using monochromatic light using an interference filter, an optical film thickness monitor can directly determine the optical film thickness. The thickness was measured. Using an interference filter with a transmitted light wavelength of 1050 nm, the film thickness monitor lamp was made monochromatic to provide a film thickness monitor light. During vapor deposition, the film was formed at a nearly constant rate, and the film was formed at a rate of about 10
A SiO2 film having an optical thickness of nd=0.25λ (λ=1064 nm) was formed on the {010} plane of the DNBB crystal in 1 minute. The electron beam heating was stopped, the inside of the vapor deposition apparatus was returned to atmospheric pressure, and the DNBBα type crystal was taken out.

[0035] Perform the same operation to create another {010
A SiO2 film having an optical thickness of 0.25λ (λ=1064 nm) was also formed on the {010} planes, and a DNBBα type crystal was obtained in which antireflection films were formed on both {010} planes.

[0036] Regarding the {010} plane of the DNBBα type crystal with antireflection films formed on both sides, a 1064 nm Nd-Y
The transmittance was measured by entering an AG laser beam perpendicularly to the incident surface. This {010} plane is a birefringent plane whose refractive index varies depending on the polarization direction. Therefore, the reflectance is also expected to have different values depending on the polarization direction. Therefore, for the measurement, a laser beam whose polarization direction was made random using a depolarization plate was used. Transmittance was 96%.

Comparative Example 1 Regarding the transmittance of the {010} plane of the DNBBα type crystal on which no antireflection film was formed, obtained by the same method as in Example 1, 1064 nm Nd-YAG laser light (randomly polarized light) was used. The transmittance was 87% as a result of measurement by entering the light perpendicularly to the incident surface.

Example 2 A single crystal of 4'-nitrobenzylidene-3-ethylcarbonylamino-4-methoxyaniline (abbreviated as MNBA-Et) was grown from a dimethylacetamide solution by the temperature drop method. This crystal is an α-type monoclinic crystal with the following lattice constant.

[0039] Lattice constant a=8.28A
b = 28.06A c = 7.65A β = 115.27゜Z = 4 The MNBA-Etα type crystal is a biaxial crystal with two optical axes, and the three principal refractive indices are all different (nX > nY
>nZ). The smallest principal refractive index nZ is at least 1.53 or more (measurement wavelength 1.06 μm). Therefore, the antireflection film shown in the present invention can be formed on any surface of the MNBAα type crystal.

{010} of this MNBA-Etα type crystal
After cutting parallel to the {010} plane to obtain a smooth surface,
Optical polishing was performed on both sides. Diamond paste was used for the abrasive particles, and buffing was performed for the finish.

After polishing, the heating temperature of the organic crystal during vapor deposition was set to 6
The wavelength was 106 in the same manner as in Example 1 except that the temperature was kept at 0°C.
Antireflection films against 4 nm light were formed on both sides.

[0042] Regarding the MNBA-Et{010} plane,
Due to the birefringence of the crystal, it is expected that the effectiveness of the antireflection coating will depend on the polarization direction. Therefore, as in Example 1, regarding the transmittance of the MNBA-Et{010} plane, using a randomly polarized 1064 nm Nd-YAG laser beam,
The transmittance was 95% when measured with the light incident perpendicular to the incident surface.
Met.

Comparative Example 2 Regarding the transmittance of the {010} plane of the MNBA-Et crystal on which no antireflection film was formed, obtained by the same method as in Example 2, 1064 nm Nd-YAG laser light (randomly polarized light) was used. ) was measured by entering the light perpendicularly to the incident plane, and the transmittance was 83%.

Example 3 A plate-shaped single crystal of 4'-nitrobenzylidene-3-acetamino-4-methoxyaniline (abbreviated as MNBA) was grown from a dimethylacetamide solution by a temperature drop method. This crystal is an α-type monoclinic crystal with the following lattice constant.

[0045] Lattice constant a=8.38A
b = 26.84A c = 7.49A β = 115.336゜Z = 4 MNBAα type crystal is a biaxial crystal with two optical axes, and all three principal refractive indices are different (nX > nY > nZ
). The smallest principal refractive index nZ is at least 1.5
3 or more (measurement wavelength 1.06 μm). Therefore, MN
The antireflection film shown in the present invention can be formed on any surface of the BAα type crystal.

[0046] In order to obtain a {010} smooth surface of this MNBAα type crystal, both sides were optically polished. Diamond paste was used for the abrasive particles, and buffing was performed for the finish.

After polishing, an antireflection film against 1064 nm light was formed on both sides in the same manner as in Example 1, except that a filter with a transmitted light wavelength of 530 nm was used as an interference filter to monochromate the film thickness monitoring light. .

Regarding the MNBA plane as well, it is expected that the effect of the antireflection film depends on the polarization direction due to the birefringence of the crystal. Therefore, as in Example 1, MNBA{010
} The transmittance of the surface was measured using a randomly polarized 1064 nm Nd-YAG laser beam incident perpendicularly to the incident surface, and the transmittance was 96.5%.

As shown in Comparative Example 3, the reflectance is reduced to one fourth or less compared to the transmittance without an antireflection film.

Comparative Example 3 Regarding the transmittance of the {010} plane of the MNBAα type crystal without an antireflection film, obtained by the same method as in Example 3, 1064 nm Nd-YAG laser light (randomly polarized light) was used. The transmittance was 83% as a result of measurement by entering the light perpendicularly to the incident surface.

Example 4 Regarding the transmittance of the {010} plane of the MNBAα type crystal obtained in the same manner as in Example 3, an interference filter with a transmitted light wavelength of 830 nm was used to monochromate the film thickness monitoring light.
An antireflection film against light with a specific wavelength of 830 nm was formed on both surfaces in the same manner as in Example 1 except that the filter was used.

[0052] MNBA{0
10} plane, the transmittance was measured by applying a semiconductor laser beam of 830 nm perpendicularly to the incident plane.

As a result of using a laser beam whose polarization direction was made random using a depolarizing plate, the transmittance was 96.5%.

When the transmittance was measured by rotating the polarization direction with respect to the incident {010} plane using a linearly polarized laser beam without using a depolarizing plate, the maximum value of the transmittance was 99%.
The minimum value was 94% in the case of the polarization direction (B) perpendicular to the polarization direction A which showed the maximum value.

Comparative Example 4 Regarding the transmittance of the {010} plane of the MNBAα type crystal on which no antireflection film was formed, obtained by the same method as in Example 4, 830 nm semiconductor laser light was applied perpendicularly to the incident plane. The transmittance was measured.

When a laser beam whose polarization direction was made random using a depolarizing plate was used, the transmittance was 82.5%.

When the transmittance was measured by rotating the polarization direction with respect to the incident {010} plane using a linearly polarized laser beam without using a depolarizing plate, the maximum value of the transmittance was 90%.
78 for the polarization direction perpendicular to the polarization direction that showed the maximum value.
It was the minimum value of %. Furthermore, the polarization direction of the incident laser beam showing the maximum and minimum transmittance was completely opposite to that in the case where the antireflection film was formed.

That is, {010
} surface has a transmittance of 99%, the transmittance without the anti-reflection film is 78%, and the {010} surface with the anti-reflection film has a transmittance of 94% in the direction (B). )
The transmittance without the antireflection film was 90%.

Example 5 Semiconductor laser excitation internal cavity type Nd3+:YVO4 Secondary nonlinear optical element with a nonlinear optical component made of DNBBα type crystal having an antireflection film inside the laser cavity: 1 neodymium (Nd3+) A polished yttrium vanadate (YVO4) crystal doped with .05 atm% is used as a laser crystal, and this laser crystal 17 is
．． It is sandwiched between two mirrors, a mirror 15 with a reflectance of 100% and a mirror 16 with a reflectance of 99.8% for light of 064 μm, and further from a semiconductor laser (output 700 mW) 12 with a Peltier element on a heat sink 11. Wavelength of 0.809μm
A semiconductor laser excitation internal cavity type Nd3+:YVO4 laser was constructed in which the laser beam 14 of et al., Laser Research, Vol. 18, No. 8, 94 (1990)).

Similar to Example 1, a DNBBα type single crystal was obtained by recrystallization from a methyl ethyl ketone solution. A DNBBα type crystal having two planes (phase matching planes) perpendicular to the phase matching direction for second harmonic generation (incident light; 1.064 μm laser beam) was obtained in the following manner.

The DNBBα type crystal was attached to a goniometer of a crystal cutter and adjusted so that a plane perpendicular to the phase matching direction at θ=40° and φ=35° could be cut. Here, θ and φ are the main refractive index axes nX, nY, n
Using Z (where nX > nY > nZ), nY
The angle between the axis (crystal b axis) orientation and the phase matching orientation is θ,
Let φ be the angle formed by the projection of the phase matching orientation onto the nX - nZ plane (crystal ac plane) and the nZ axis. The goniometer was fixed at this position and cutting was performed twice. Remove the crystal,
DN polished with diamond paste to have two optically smooth phase matching surfaces parallel to each other.
A BBα type crystal was obtained. The crystal thickness (phase matching orientation) is
It was about 0.7 mm.

The obtained polished DNBBα type crystal was
Into the 2mm diameter hole in the center of the 0mm glass disk,
It was fixed so that the phase matching surface was parallel to the disk surface.

Similar to Example 1, SiO was deposited on the two optically smooth phase matching surfaces of this crystal by electron beam evaporation.
2 was vapor-deposited to form an antireflection film against light with a wavelength of 1064 nm, and a nonlinear optical component made of organic nonlinear optical crystal DNBB was obtained.

The laser beam transmittance of the DNBB organic nonlinear optical component having this antireflection film at 1.064 μm was about 93%.

This DNBB organic nonlinear optical component 18 is attached to a goniometer and inserted between the output side mirror 16 and the laser crystal 17 inside the resonator of the Nd3+:YVO4 laser, and a laser beam 1 of 1.064 μm is generated.
Adjusted to be perpendicular to 9. FIG. 1 shows the second-order nonlinear optical element thus obtained. After optimal adjustment, a 0.532 μm green light 110 with a maximum intensity of about 410 μW was obtained.

The same DNBBα type crystal is inserted into the laser resonator without forming an antireflection film,
0.532 μm When the maximum intensity of green light was measured,
The maximum intensity was approximately 40 μW.

From these results, it was found that a nonlinear optical component made of an organic nonlinear optical crystal having an antireflection film has a high transmittance, so that the incident laser light can be used effectively and the conversion efficiency is improved.

Example 6 In order to theoretically predict the effect of the anti-reflection film according to the present invention, organic non-linear optical crystals having an anti-reflection film according to the present invention and an organic non-linear optical crystal without an anti-reflection film were prepared, respectively. (Formula 1) and (Formula 2: Comparative example)
FIG. 2 shows the results of calculating the reflectance on the surface of an organic nonlinear optical crystal when light of a specific wavelength is incident perpendicularly to the incident surface based on the following.

RAR=(nf 2 / nO −1) 2 /(nf
2/nO +1)2 (Formula 1) RAR: Reflectance of organic nonlinear optical crystal (with antireflection film according to the present invention) nf: Refractive index of antireflection film constituent material (nf = 1.4
5) nO: refractive index of organic nonlinear optical crystal Rno = (nO -1)2 / (nO +1)2
(
Equation 2) Rno: Reflectance of organic nonlinear optical crystal (without antireflection film) nO: Refractive index of organic nonlinear optical crystal. Moreover, this result can also be applied to the surface reflection of the emitted light of an organic nonlinear optical crystal. The calculation results show that the antireflection film of the present invention is effective in reducing surface reflection of organic nonlinear optical crystals, and in particular reduces reflected light by half or less on crystal surfaces with a refractive index of 1.6 or more. .7~2.
It is shown that the reflected light can be reduced to one-fourth or less for crystal surfaces in the range of 6.

[0070]

According to the present invention, it is possible to obtain an organic nonlinear optical crystal with reduced surface reflection for incident light or emitted light of a specific wavelength, and a nonlinear optical component with reduced surface reflection.

[Brief explanation of the drawing]

[Figure 1] Semiconductor laser pumped internal cavity type Nd3+:YV
DNBB with anti-reflection coating inside the O4 laser cavity
It is a drawing of a wavelength conversion element in which nonlinear optical components made of organic nonlinear optical crystals are arranged.

[Fig. 2] Shows the results of calculating how much the surface reflectance (one side) of an organic nonlinear optical crystal having an antireflection film according to the present invention is reduced depending on the refractive index of the crystal. (The value of surface reflectance in the case of complete reflection is assumed to be 1.)

[Explanation of symbols]

11: Heat sink, 12: Semiconductor laser with Peltier element, 13: Lens, 14: Semiconductor laser beam (wavelength 0.809 μm)
, 15: High reflectance mirror (reflectance 100% for wavelength 1.064 μm), 16: High reflectance mirror (reflectance 99.8% for wavelength 1.064 μm), 17: Laser crystal (Nd3+: YVO4), 18:D
NBB second-order nonlinear optical component,

Claims (7)

[Claims] 1. An organic nonlinear optical crystal having an antireflection film on its surface, wherein the antireflection film satisfies the following two conditions. 1.40≦n≦1.50 nd=0.25λ±0.025λ+0.5mλ Where, n; refractive index of constituent material nd; optical film thickness of constituent material m; integer greater than or equal to 0 λ; specific wavelength 2. The organic nonlinear optical crystal according to claim 1, wherein the antireflection film is a deposited film formed by a vacuum deposition method. 3. The organic nonlinear optical crystal according to claim 1, wherein the antireflection film is made of SiO2. 4. An organic nonlinear optical crystal having the following general formula [Chemical formula 1
] (However, R is an alkyl group having 2 or less carbon atoms, a halogenated alkyl group) 4'-nitrobenzylidene-
3-alkanoylamino-4-methoxyaniline, 4'
-Nitrobenzylidene-3-halogenoalkanoylamino-4-methoxyaniline and a compound at least partially substituted with deuterium. Nonlinear optical crystal. 5. An organic nonlinear optical crystal, 3,9-E,E'-5a,6,11a,1 represented by
2-tetrahydro[1,4]benzoxazino[3,2
-b][1,4]benzoxazine (E, E' are acceptor substituents), the organic nonlinear optical crystal according to claim 1. 6. The organic nonlinear optical crystal according to claim 1, wherein the surface is an optically smooth surface. 7. A nonlinear optical component comprising the crystal according to claim 6.