JPH11212128A - Wavelength converting element, production thereof and solid laser device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert the wavelength of incident light with high efficiency while generating the phenomenon of QPM through a constant dielectric composed of crystal, which is not a ferroelectric, by forming the crystal, which has a positive polarity in prescribed direction, so as to form polysynthetic twin structure periodically alternating positive polarity and negative polarity for specified width. SOLUTION: A crystal 10 having the positive polarity in the prescribed direction is formed so as to form the polysynthetic twin structure periodically alternating the positive polarity and negative polarity for width (d) expressed by the equality of d=mλ/(n2 ω-nω). Then, laser light, which is amplified on the xy plane of the crystal 10 and made incident vertically to polarity direction, is defined as incident light. In the equality, (m) is a degree, n2 ω is a refractive index at the time the wavelength of λ/2, and nω is a refractive index at the time of the wavelength of λ. When the laser light is amplified on the xy plane of the crystal 10 of the polysynthetic twin structure and made incident to the crystal 10 vertically to the polarity direction, this laser can be emitted while converting its wavelength by half.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength conversion element made of twin crystal quartz and a method for manufacturing the same. More specifically, by combining with a solid-state infrared laser such as a YAG laser capable of high output, a wavelength conversion element for converting the wavelength of the solid-state laser to a wavelength from green to blue or ultraviolet region, a method for manufacturing the same, and a method for manufacturing the same. And a solid-state laser device using the same.

[0002]

2. Description of the Related Art A wavelength conversion element of this kind is made of a nonlinear optical crystal. This nonlinear optical phenomenon is a phenomenon caused by the interaction between the electromagnetic field of a strong laser beam and the medium. The response of the medium is not proportional to the strong light, and nonlinearity appears. The efficiency of wavelength conversion of incident light is estimated by the magnitude of the nonlinear constant. For this reason, a search for a material having a large nonlinear constant has been widely performed worldwide. On the other hand, since the refractive index of the nonlinear optical crystal has wavelength dispersion, the speed of the fundamental wave is not equal to the speed of the second harmonic, so that a phase difference appears in the second harmonic with respect to the fundamental wave. For this reason, in the crystal, the second light generated along the optical path
The composite wave of the harmonic becomes a periodic function. Therefore, a distance x having a phase difference of π exists between the second harmonic generated at the crystal end and the second harmonic generated at a certain distance x from the crystal end. The length of the distance x is called a coherent length.

[0003] When the coherent length is exceeded, the intensity of the combined harmonic decreases, and increases and decreases repeatedly in this cycle. Using this phenomenon, Armstrong (Armstron
g) et al. proposed that the efficiency of the second harmonic could be increased by inverting the sign of the nonlinear optical constant in each cycle and inverting the phase of the second harmonic. That is, by stacking crystals whose polarization direction is inverted so that the sign of the nonlinear optical constant is inverted at the coherent length, the intensity of the second harmonic from the coherent length can be increased. The dimension of the coherent length is about 10 μm. In addition, to create a crystal in which the sign of the nonlinear optical constant is inverted at such a period,
It was actually considered impossible. However, Li
After it became clear that it was possible to create polarizations in which the C ⁺ directions of 180 ° crystals of ferroelectric oxide single crystals such as NbO ₃ , LiTaO ₃ , KTP, etc. could be changed at this period, it became active. It is being studied. Such wavelength conversion in which the polarization directions are rotated by 180 degrees is performed by quasi-phase matching (QPM).
This is called wavelength conversion by g). The features of this QPM include:
The phase matching wavelength can be set freely by setting the period length, the phase matching wavelength range can be expanded by creating multiple periods, the temperature tolerance required for phase matching can be more than doubled, It can be used in the form of a wave path, and the use of a non-linear optical constant d ₍₃₃₎ .

Heretofore, as a wavelength conversion element of this kind, a right-handed crystal and a left-handed crystal are alternately stacked as a wavelength conversion element of this kind due to the difference in the rotation of the helical axis in the C-axis direction of the ordinary derivative crystal. Proposed a nonlinear optical element typified by a lithium tetraborate single crystal (JP-A-9-197455).

[0005]

The applicant of the present invention in Japanese Patent Application Laid-Open No. 9-197455 suggested that this nonlinear optical element can be applied to a paraelectric crystal as well. Thus, it was impossible to alternately stack right-handed crystals and left-handed crystals due to the difference in the rotation of the helical axis in the C-axis direction. SUMMARY OF THE INVENTION It is an object of the present invention to provide a wavelength conversion element capable of efficiently converting the wavelength of incident light by causing a QPM phenomenon by a paraelectric made of quartz that is not a ferroelectric, a method of manufacturing the same, and a method of using the same. To provide a solid-state laser device.

[0006]

The invention according to claim 1 is
As shown in FIG. 1, a crystal 1 having a positive polarity in a predetermined direction.
0 has a width d represented by the following formula (1), and is formed so as to form a fragment twin structure in which positive and negative polarities alternate alternately.
A wavelength conversion element characterized in that laser light having an amplitude in the xy plane of 0 and incident perpendicular to the polarity direction is incident light. d = mλ / (n ₂ ω−nω) (1) where m is the order, n ₂ ω is the refractive index at the wavelength of λ / 2,
nω is the refractive index at the wavelength of λ. When a laser beam having an amplitude in the xy plane of the crystal and perpendicular to the polarity direction is incident on the quartz crystal 10 having the fragment twin structure, the wavelength of the laser beam is converted into half and emitted.

The invention according to claim 2 comprises a step of polishing the surface of the crystal 10 having a positive polarity in a predetermined direction as shown in FIG. 3, and a step of polishing the surface of the polished crystal 10 with NiCr.
The step of forming the film or the Ni film 11 is performed so that the width d ₁ of the removed portion 11a of the film and the width d ₂ of the film 11b of the remaining portion of the film have values represented by the following formula (2). N above
a step of patterning the iCr film or the Ni film 11 in a stripe pattern parallel to the above-mentioned polarity direction;
0 to a temperature lower than the phase transition temperature of the crystal to form a twin crystal structure of the crystal, and a striped NiC remaining on the surface of the crystal 10 having the twin structure of the crystal.
and a step of removing the r film or the Ni film 11b. d ₁ = d ₂ = mλ / (n ₂ ω−nω) (2) where m is the order, n ₂ ω is the refractive index at the wavelength of λ / 2,
nω is the refractive index at the wavelength of λ. NiCr on the surface
By heat-treating the crystal 10 having the film or the Ni film 11 patterned at a temperature lower than the phase transition temperature of the crystal, positive and negative polarities alternate periodically with the widths d ₁ and d ₂ .
The wavelength conversion element 15 of the present invention can be easily manufactured.
Note that m in the order of the above equations (1) and (2) is an odd number (usually 1). This is the width d (same for d ₁ and d ₂ )
Is always an odd multiple of λ / (n ₂ ω−nω), a second harmonic (SHG) is generated.

Further, the invention according to claim 3 is shown in FIGS.
A solid-state laser device using the wavelength conversion element 15 according to claim 1 as shown in FIG. For example, by combining the wavelength conversion element 15 according to claim 1 with an infrared solid-state laser 16 such as a YAG laser capable of high output,
6 can be converted to wavelengths from green to blue or ultraviolet.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. Quartz used for the wavelength conversion element of the present invention is an ordinary derivative that is not a strong derivative, but has nonlinearity due to its piezoelectricity. Quartz crystal can perform wavelength conversion in a wide range from green to blue or ultraviolet region and is excellent in moisture resistance as compared with lithium tetraborate single crystal or the like. Further, quartz is transparent to light having a wavelength from green to blue or ultraviolet, is resistant to optical damage, and has the characteristics that a high-quality crystal can be easily grown. To manufacture this wavelength conversion element, a crystal having a positive polarity in a predetermined direction is prepared. The crystal is an AT cut crystal (φ = + 35 ゜ 18 ′) and a BT cut crystal (φ = −) shown in FIG.
49 ゜ 8 '), CT cut quartz (φ = + 37 ゜ 40'),
There are DT cut quartz (φ = −52 ゜ 30 ′), ET cut quartz (φ = + 66 ゜), etc., and the Z cut quartz shown in FIG. 1 whose cut plane is parallel to the xy plane, and the cut plane is in the xz plane. Although there is a parallel Y-cut crystal, any crystal may be used. This crystal has a width d expressed by the above-described formula (1) using a photolithography method or an electron beam method.
At (= d ₁ = d ₂ ), it is formed so as to form a piece twin structure in which the positive and negative directions of the polar axis alternate.

Next, a method of manufacturing a quartz crystal having a piece twin structure by photolithography will be described. As shown in FIG. 3, after polishing the surface of the quartz crystal 10, a NiCr film or Ni film 1 having a thickness of about 0.1 μm to 1 μm is formed on the surface.
1 is formed by vapor deposition or the like (FIG. 3A). A photoresist resin is applied on this film to form a photoresist film 12. Next, a photomask 1 on which the pattern to be transferred is baked
Set 3 on this crystal. This pattern is formed in a stripe shape such that a portion to be exposed having a width d _{1 and} a portion to be masked having a width d ₂ are alternately arranged. Here, d ₁ and d ₂ are equal. d ₁ and d ₂ are widths derived from the above-described equation (2). Next, ultraviolet light 1 is applied from above the mask 13.
Irradiation No. 4 ((b)). Only the resist film 12 under the white portion of the mask is exposed by the irradiation of the ultraviolet rays 14.
The resist film portion exposed with a solvent such as ethanol is removed, and the other portion 12a is left (FIG. (C)). Then, the NiCr film or Ni film 11 not covered with the resist film is removed by etching with an acidic aqueous solution such as HCl or an alkaline aqueous solution such as NaOH, and the remaining resist film 12a is also removed. As a result, the striped pattern in which the removed portions 11a of the film having the width d ₁ and the remaining portions 11b of the film having the width d ₂ are alternately formed is a crystal 1
0 (see (d)). Subsequently, heat treatment is performed at a temperature of 500 to 580 ° C. lower than the phase transition temperature of the quartz for about 10 minutes. By this heat treatment, the remaining portion 11b of the film is formed.
The crystal immediately below the polarity from positive (x ⁺⁾ negative ^- changes (x). It is considered that this change in polarity occurs due to the difference between the coefficient of thermal expansion of the film and the coefficient of thermal expansion of quartz (FIG. (E)). Finally, the remaining portion 11b of the film is removed to obtain the wavelength conversion element 15 of the present invention.

FIG. 1 shows an example of a Z-cut quartz crystal 10 having a polarity in the x-axis direction. A wavelength conversion element 15 is made by making the quartz crystal 10 a fragment twin structure having alternating positive and negative polarities. The incident light of this wavelength conversion element has amplitude on the xy plane of the crystal 10 and is incident perpendicularly to the x-axis. FIG. 2 shows an example of an AT-cut quartz crystal 10 having a polarity in a direction perpendicular to the x-axis. The wavelength conversion element 15 is made by forming the quartz crystal 10 into a fragment twin structure having alternating positive and negative polarities. The incident light of the wavelength conversion element 15 has an amplitude on the xy plane of the crystal 10 and is incident parallel to the x-axis. When a laser beam having an amplitude in the xy plane of the quartz crystal and perpendicular to the polarity direction is incident on the wavelength conversion element 15 formed of the quartz crystal 10 having the fragment twin structure, the above-described QPM phenomenon occurs. The wavelength of the laser light can be converted into half and emitted.

The laser used in combination with the wavelength conversion element of the present invention is 1064 nm to 300 nm such as a Nd: YAG laser, a dye (dye) laser, a Ti-sapphire laser, or the like.
nm wavelength lasers. As shown in FIG.
Two wavelength conversion elements 1 after Nd: YAG laser 16
By arranging 5 and 15, light having a wavelength of a fourth harmonic (266 nm) having high coherence, which is 1/4 of the wavelength of 1064 nm of the Nd: YAG laser, can be generated. As shown in FIG. 5, by disposing the third harmonic generation unit 17 and one wavelength conversion element 15 in this order at the subsequent stage of the Nd: YAG laser 16, 1/6 of the wavelength of the Nd: YAG laser of 1064 nm is provided. That is, light having a wavelength of the sixth harmonic (177 nm) having high coherence can be generated. These fourth harmonics (266 nm) and sixth harmonics (1
The light having a wavelength of 77 nm is emitted from a KrF excimer laser (24
8 nm).

[0013]

Next, an embodiment of the present invention will be described. <Example 1> A wavelength conversion element using this laser light (wavelength: 1064 nm) as incident light was manufactured in combination with an Nd: YAG laser. First, 3mm x 3mm x 0.5m as crystal
AT with polarity in the direction perpendicular to the x-axis of m shown in FIG.
Cut quartz was used. The NiCr film 11 is patterned into stripes parallel to the polarity direction by the photolithography method shown in FIG. 3, and then heat-treated at 550 ° C. for 10 minutes, so that the positive and negative polarities alternate periodically with a width d. A crystal 10 having a crystal structure was produced, and the remaining NiCr film 11b was removed to obtain a wavelength conversion element 15. The width d of the wavelength conversion element 15 is m = 1, λ = 1066 nm, and the refractive index nω = 1.
By substituting 5305 and the refractive index n ₂ ω = 1.5468 into the above-mentioned equation (1), d = about 65.3 μm was obtained. One wavelength conversion element is arranged at the subsequent stage of the Nd: YAG laser, and the laser light emitted from the Nd: YAG laser is adjusted so as to oscillate in the xy plane of the crystal and become parallel to the x-axis. The light was incident on the wavelength conversion element. Laser light frequency 10Hz, power 100mJ
When, green light having a wavelength of 532 nm was obtained from the wavelength conversion element with a power of 5 mJ.

Embodiment 2 A wavelength conversion element 15 suitable for the solid-state laser device shown in FIG. 5 was manufactured. The width d of the wavelength conversion element 15 is m = 1, λ = 355 nm, and the refractive index nω =
By substituting 1.567 and the refractive index n ₂ ω = 1.68 into the above equation (1), d = about 3.14 μm was obtained. Except for the value of the width d, a wavelength conversion element was obtained in the same manner as in Example 1. After arranging the third harmonic generation unit 17 and one wavelength conversion element 15 in this order at the subsequent stage of the Nd: YAG laser 16, a laser beam having a frequency of 10 Hz and a power of 500 mJ is incident on the wavelength conversion element 15. An ultraviolet laser beam having a wavelength of 177.5 nm was obtained from the wavelength conversion element 15 with a power of 1 mJ.

[0015]

As described above, the crystal which has conventionally been considered impossible to convert the wavelength is made into a twin twin structure of the present invention.
The wavelength of the incident light can be converted with high efficiency. For example, if the incident light is a laser beam having a wavelength of 1064 nm of an Nd: YAG laser, the laser beam can be converted into the wavelengths of the fourth harmonic (266 nm) and the sixth harmonic (177 nm) by the wavelength conversion element of the present invention. These converted wavelengths are shorter than the KrF excimer laser (248 nm).

Accordingly, a laser beam of an infrared laser, for which a high-power device has already been developed, is incident on the wavelength conversion element of the present invention, and light of a fourth or sixth harmonic wavelength is emitted from this wavelength conversion element. If it can be produced, laser light in the ultraviolet region or a region close thereto can be easily obtained. This laser light is used for marking, lithography, various semiconductor processes,
It can be expected to be applied to various fields such as medicine.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a wavelength conversion element of the present invention.

FIG. 2 is a configuration diagram of another wavelength conversion element of the present invention.

FIG. 3 is a diagram showing a manufacturing process of the wavelength conversion element.

FIG. 4 is a configuration diagram of a solid-state laser device using the wavelength conversion element.

FIG. 5 is a configuration diagram of another solid-state laser device using the wavelength conversion element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Quartz 11 NiCr film or Ni film 11a Removal part of film 11b Remaining part of film 15 Wavelength conversion element

Claims (3)

[Claims] A quartz crystal having a positive polarity in a predetermined direction.
Is formed so as to form a fragment twin structure in which positive and negative polarities alternate periodically with a width (d) represented by the following formula (1), and oscillates in the xy plane of the crystal (10). A wavelength conversion element, wherein a laser beam incident perpendicularly to a polarity direction is used as incident light. d = mλ / (n ₂ ω−nω) (1) where m is the order, n ₂ ω is the refractive index at the wavelength of λ / 2,
nω is the refractive index at the wavelength of λ. 2. A step of polishing a surface of a crystal (10) having a polarity in a predetermined direction; and a step of polishing a NiCr film or a Ni film (1) on the surface of the polished crystal (10).
Forming a 1), the width (d ₁ ) of the removed portion (11a) of the film and the remaining portion (11b) of the film
Patterning the NiCr film or Ni film (11) into stripes parallel to the polarity direction such that the width (d ₂ ) of the film has a value represented by the following equation (2): Heat-treating the crystal-patterned crystal (10) at a temperature lower than the phase transition temperature of the crystal to create a fragment twin structure of the crystal, and a crystal (10 And b) removing the striped NiCr film or Ni film (11b) remaining on the surface of the wavelength conversion element. d ₁ = d ₂ = mλ / (n ₂ ω−nω) (2) where m is the order, n ₂ ω is the refractive index at the wavelength of λ / 2,
nω is the refractive index at the wavelength of λ. 3. A solid-state laser device using the wavelength conversion element (15) according to claim 1.