JPH05100273A - Higher harmonics generation device - Google Patents

Abstract

PURPOSE:To provide highly stable high-efficiency higher harmonics generation by suppressing an increase in the number of components and obtaining plural higher harmonics by using a light source for a single fundamental wave, and increasing phase matching length without increasing the absorption by a nonlinear optical material. CONSTITUTION:The fundamental wave 20 resonates in monolithic resonators 18, 19 through a triangular ring-shaped resonance path and when it is propagated in the direction of a crystal axis (a), part of it is converted into 2nd higher harmonics 21, 22 having 430nm wavelength and projected from spherical mirrors 25, 26. When the output of an LD 13 is 100mW at 860nm wavelength, a beam splitter 16 splits the light into beams of 50nW and the 2nd higher harmonics of 5mW at 430nm wavelength are outputted from the two monolithic resonators 18, 19, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic generator for converting a fundamental wave emitted from a light source such as a semiconductor laser into a harmonic within a monolithic resonator.

[0002]

2. Description of the Related Art In recent years, various devices have been proposed for obtaining a second harmonic wave or a third harmonic wave whose wavelength is converted by passing a fundamental wave emitted from a semiconductor laser or the like through a nonlinear optical material. In these devices, a nonlinear optical material is arranged in a resonator composed of a plurality of reflecting surfaces, and a fundamental wave is confined in the resonator to be amplified so that harmonics are efficiently generated. As the resonator, a reflection film is provided on the end surface of the nonlinear optical material, and a monolithic resonator that resonates inside the resonator and a plurality of mirrors are arranged to form the resonator. An external resonator in which a material is arranged is known. Recently, in order to downsize the device and improve the conversion efficiency to higher harmonics, the mainstream is shifting from the external resonator type to the monolithic type that resonates the fundamental wave inside the nonlinear optical material. I am doing it.

FIG. 3 shows a second harmonic generation device using a monolithic resonator as an example of a conventional harmonic generation device. The second harmonic generation device 1 includes a semiconductor laser (hereinafter referred to as LD) 2, a collimator lens 3,
It is composed of a mode matching lens 4 and a nonlinear optical material 5 made of KNbO ₃ crystal or the like. LD2
Emits the fundamental wave 6 having a wavelength of 860 nm, for example.

The left and right two surfaces of the nonlinear optical material 5 in the figure are polished into spherical shapes. Of these, the surface on the left side of the drawing is the incident surface of the fundamental wave 6, and a spherical mirror 8 that partially transmits the fundamental wave 6 is formed on this surface. The surface on the right side of the drawing is the exit surface of the second harmonic wave 7, and the fundamental wave 6 is formed on this surface.
A spherical mirror 9 that is highly reflective and highly transmissive to the second harmonic 7 is formed. Further, the lower surface of the nonlinear optical material 5 in the figure constitutes a plane mirror 10 that totally reflects both the fundamental wave 6 and the second harmonic wave 7.

In the above structure, the fundamental wave 6 having a wavelength of 860 nm emitted from the LD 2 is collimated by the collimator lens 3, passes through the mode matching lens 4, and passes from the point A of the spherical mirror 8 of the nonlinear optical material 5. Incident. At this time, the fundamental wave 6 is incident at a specific angle θ with respect to the crystal axis a so that the fundamental wave 6 incident on the point A travels in parallel with the crystal axis a of the nonlinear material 5. The fundamental wave 6 resonates in a ring shape at points A, B, and C in the ring resonator constituted by the two spherical mirrors 8 and 9 and the plane mirror 10 and is amplified.

When the fundamental wave 6 passes through the nonlinear optical material 5 in the direction of the crystal axis a, a part of the fundamental wave 6 has a wavelength of 43.
It is converted into the second harmonic wave 7 of 0 nm and emitted from the point B of the spherical mirror 9. In order to meet the phase matching condition and stabilize the conversion efficiency to harmonics, the nonlinear optical material 5
Is temperature controlled by the Peltier element 11 and the like. By using such a harmonic generator, the fundamental wave can be efficiently converted into a harmonic.

[0007]

However, in the above-mentioned conventional second harmonic generator, when a plurality of second harmonics are used, a plurality of light sources such as LDs are used and the second harmonics are set one by one. It was necessary to create a wave generator, and as a result, the number of parts increased and the device could not be downsized. Also, 100
The LD having an output of about mW is expensive as hundreds of thousands of yen, which is a major obstacle to cost reduction.

Further, it is preferable to make the phase matching length (optical path length along the crystal axis a direction) long in order to increase the conversion efficiency. However, when the phase matching length is made long by a single monolithic resonator, The second harmonic output does not increase significantly due to absorption of the nonlinear optical material, and the substantial increase in the phase matching length is small due to the non-uniform temperature distribution in the nonlinear optical material. 2nd harmonic generation could not be performed.

Therefore, an object of the present invention is to provide two or more monolithic resonators for a light source of a single fundamental wave, thereby enabling miniaturization when a plurality of harmonic outputs are required, It is an object of the present invention to provide a harmonic generation device capable of increasing a phase matching length without increasing absorption by a nonlinear optical material and generating a harmonic output with high efficiency and high stability.

[0010]

In order to achieve the above object, a harmonic generator of the present invention is a monolithic type device including a non-linear optical material that causes a fundamental wave to ring-resonate in a triangular shape between two facing curved surfaces and one plane. In a harmonic generator including a resonator, n monolithic resonators (n is an integer of 2 or more) are provided for a single fundamental wave light source, and a plurality of harmonics are generated from the single fundamental wave light source. The feature is that the wave is output.

In the present invention, as shown in FIG. 1 of the embodiment, on the optical axis between a single fundamental wave light source and any one of n monolithic resonators arranged in parallel. N has a beam splitter and each of the divided fundamental waves is incident on one monolithic resonator,
You may make it output the harmonic of a book.

Further, as shown in FIG. 2 of the embodiment, it has n monolithic resonators arranged in series, and a fundamental wave from a single fundamental wave light source is used as a first monolithic resonance. The second to n-th monolithic resonators are made to sequentially enter the fundamental waves emitted from the preceding monolithic resonators to output n harmonics. Good. In this case, since the fundamental wave resonates in one monolithic resonator and its spectral line width is sufficiently narrowed, highly efficient wavelength conversion is performed in the next monolithic resonator, and a single monolithic resonator is used. As compared with the case where a monolithic resonator is used, there is an effect that a higher output harmonic can be obtained as a whole.

[0013]

In the harmonic generator of the present invention, two or more monolithic resonators are provided in parallel or in series to generate a plurality of harmonics with a small number of parts.
Also, it is possible to increase the phase matching length without increasing absorption by the nonlinear optical material, and to perform high-efficiency and highly stable harmonic generation.

[0014]

【Example】

(Embodiment 1) FIG. 1 shows an embodiment in which the present invention is applied to a second harmonic generator. The present invention is not limited to the second harmonic generation device, and can be applied to the third harmonic generation device and the like.

The second harmonic generator 12 includes an LD 13 as a laser light source, a collimator lens 14, a mode matching lens 15, a beam splitter 16, a plane mirror 17, a first monolithic resonator 18 and a second monolithic resonator 19. , Peltier elements 29 and 30 are sequentially arranged.

In this embodiment, the LD 13 has a wavelength of 860n.
m, single longitudinal, single transverse mode, which emits the fundamental wave 20 with little astigmatism is used. As the light source, light emitted from a solid-state laser medium such as YAG or YLF excited by an LD can be used. The collimator lens 14 receives the fundamental wave 20 emitted from the LD 13.
Into a parallel beam, and the mode matching lens 15
This beam is focused to play a role of matching the resonance mode in the monolithic resonators 18 and 19 with the incident beam.
The beam splitter 16 serves to divide the incident fundamental wave from the LD 13 into two. The plane mirror 17 reflects 99.9% of the fundamental wave 20 and makes the fundamental wave 20 incident on the resonator 19.

For the monolithic resonators 18 and 19, KNbO ₃ crystal is used as the nonlinear optical material in this embodiment.

The end faces of the monolithic resonators 18 and 19 located on the incident side of the fundamental wave 20 are formed in a spherical shape, and reflective films for reflecting the fundamental wave 20 by 93% are deposited on these faces. The spherical mirrors 23 and 24 are formed. Further, each of the end faces of the resonators 18 and 19 located on the emission side of the second harmonics 21 and 22 is also formed into a spherical shape, and the surface of the fundamental wave 20 is reflected by 99.9%.
Reflective films that transmit 90% of the second harmonics 21 and 22 are vapor-deposited to form spherical mirrors 25 and 26, respectively. Further, the lower surface of the non-linear optical material in the figure is cut into a flat surface along the crystal axis a and polished to obtain a fundamental wave 20, a second harmonic wave 21, 2,
2 are plane mirrors 27 and 28 that totally reflect both.

The non-linear optical materials forming the monolithic resonators 18 and 19 are both 7.0 m in length in the crystal axis a direction.
m, the radius of curvature of the spherical surface is 5.0 mm. When the second harmonic generator 12 is used to emit the fundamental wave 20 having a wavelength of 860 nm from the LD 13, the fundamental wave 20
Are collimated into parallel beams by the collimator lens 14 and then condensed by the mode matching lens 15. After that, the fundamental wave 20 is divided into two by the beam splitter 16, and one of the fundamental waves goes straight and is incident on the resonator 18.
The other is reflected by the plane mirror 17 and enters the other resonator 19.

The fundamental wave 20 that has entered the monolithic resonator 18 from the point A of the spherical mirror 23 propagates in the nonlinear optical material along the crystal axis a and faces the spherical mirror 25.
Is reflected at the point B of the plane mirror 27 toward the point C of the plane mirror 27, is reflected at the point C of the plane mirror 27 and returns to the point A of the spherical mirror 23, is reflected at the point A and propagates again along the crystal axis a. ,
Traveling wave type resonance is performed by overlapping with the original light. Similarly, the fundamental wave 20 incident on the other resonator 19 also has three points A ₁ , B _{1 of} the spherical mirrors 24, 26 and the plane mirror 28.
It is reflected at C ₁ .

As described above, the fundamental wave 20 resonates and is amplified in the monolithic resonators 18 and 19 along the triangular ring-shaped resonance path. When the fundamental wave 20 amplified in this way propagates through the nonlinear optical material in the direction of the crystal axis a, a part of the fundamental wave 20 has second wavelengths 21 and 2 having a wavelength of 430 nm.
The second harmonics 21 and 22 converted to 2 are emitted from the spherical mirrors 25 and 26, respectively, and a plurality of second harmonics can be generated.

In this embodiment, the output of the LD 13 has a wavelength of 860n.
When the m is 100 mW, the beam splitter 16 splits the beam into 50 mW beams, and the two monolithic resonators 18 and 19 each output a wavelength of 430 nm.
The second harmonic of 5 mW was output at.

Therefore, when the harmonic generator 12 of the present invention is used as a harmonic light source to construct a device that requires a plurality of harmonic light sources, a device with a small number of parts can be obtained.

(Embodiment 2) FIG. 2 shows another embodiment in which the present invention is applied to a second harmonic generation device. Also in this embodiment, the second harmonic generation device has the LD 13 and the two monolithic resonators 18 and 19 as in the first embodiment.
It is composed of The same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. As shown in this embodiment, the monolithic resonators 18 and 19 are connected to the fundamental wave 20.
A plurality of second harmonics are arranged by serially arranging with respect to the fundamental wave with a plane mirror 31 and a mode matching lens 15 provided with a film of high transmission and high reflection of the second harmonic. It is possible to obtain

In the present embodiment, the fundamental wave after passing through the first monolithic resonator 18 resonates and the spectral line width is sufficiently narrowed, and the second monolithic resonator 19 is obtained.
The wavelength conversion is performed with high efficiency. Therefore, higher output harmonics are emitted in total as compared with the case where a single monolithic resonator is used.

In this embodiment, the output of the LD 13 has a wavelength of 860n.
When the m is 100 mW, the monolithic resonator 18
Outputs a 10 mW second harmonic at a wavelength of 430 nm, and outputs a 5 mW second harmonic to the monolithic resonator 19 for a 50 mW fundamental wave input, for a total of 15 mW second harmonic. was gotten.

[0027]

As described above, according to the present invention,
Two monolithic resonators for a single fundamental wave light source
It is possible to obtain a plurality of harmonics by suppressing the increase in the number of parts by providing more than one in parallel or in series. Further, when the resonators are arranged in series with respect to the fundamental wave, the spectrum line width of the fundamental wave is narrowed by the first resonator, and therefore, the harmonics after the second resonator are It also has the effect of improving the efficiency of generation.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a second harmonic generation device of the present invention.

FIG. 2 is a side view showing another embodiment of the second harmonic generation device of the present invention.

FIG. 3 is a side view showing an example of a conventional second harmonic generator.

[Explanation of symbols]

 12 Second Harmonic Generator 13 LD 14 Collimator Lens 15 Mode Matching Lens 16 Beam Splitter 17 Planar Mirror 18 Monolithic Resonator 19 Monolithic Resonator 20 Fundamental Wave 21 Second Harmonic 23 Spherical Mirror 24 Spherical Mirror 25 Spherical Mirror 26 Spherical mirror 27 Planar mirror 28 Planar mirror 29 Peltier element 30 Peltier element 31 Planar mirror

Claims (3)

[Claims] 1. A harmonic generator comprising a monolithic resonator including a non-linear optical material that causes a fundamental wave to ring-resonate in a triangular shape between two facing curved surfaces and one plane, with respect to a single fundamental wave light source. A harmonic generator, wherein n monolithic resonators (n is an integer of 2 or more) are provided so that a plurality of harmonics are output from a single fundamental wave light source. 2. A beam splitter provided on the optical axis between the light source of the single fundamental wave and any one of the n monolithic resonators, each of the divided fundamental waves being 1 The harmonic generator according to claim 1, wherein the harmonic generator is incident on two monolithic resonators. 3. A fundamental wave from a light source of the single fundamental wave is made incident on a first monolithic resonator, and the second to nth monolithic resonators are sequentially connected to the preceding monolithic resonators. The harmonic generation device according to claim 1, wherein the fundamental wave emitted from the device is incident.