JP2636066B2 - LiB 3 lower O 5 lower infrared parametric oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention provides an optical parametric effect of 0.7 to 2.2.
The present invention relates to a LiB ₃ O ₅ infrared parametric oscillator having a narrow spectrum width in a wavelength range of μm and outputting coherent light of a variable frequency.

(Summary of the Invention) The present invention relates to an infrared light parametric oscillator that generates infrared light by an optical parametric effect. As an excitation light source, Nd: YLF, Nd that oscillates at 1.047 to 1.0796 μm is used.
d: YAG, Nd: GSGG or Nd: using the second high-frequency of the solid-state laser of any of, as the nonlinear optical element
By using the LiB ₃ O ₅ crystal, a coherent light having a narrow spectrum width and a variable frequency can be output in a wavelength range of 0.7 to 2.2 μm.

(Prior Art) Conventionally, an optical parametric oscillator that oscillates coherent light having a wavelength different from that of the excitation light by injecting coherent excitation light into a nonlinear optical element based on the optical parametric effect is known. This oscillator generally includes an excitation light source, a nonlinear optical element that is excited by light emitted from the excitation light source, and a pair of reflectors disposed on the incident side and the emission side of the nonlinear optical element. .

By the way, as such an optical parametric oscillator that oscillates in the infrared region, one using an MgO: LiNbO ₃ crystal or β-BaB ₂ O ₄ crystal for a nonlinear optical element is known.

(Problems to be Solved by the Invention) However, the optical parametric oscillator that oscillates in the infrared region has the following disadvantages.

In the case of using the MgO: LiNbO ₃ crystal for the nonlinear optical element, the nonlinear optical constant (d ₃₁ ) is as large as 11.8 × 10 ^-9 esu, but the refractive index is locally increased when the excitation wavelength in the visible region is used. Due to the changing optical damage, it becomes opaque, the output decreases with time, and it becomes impossible to obtain a good beam.

In the case of using a β-BaB ₂ O ₄ crystal, although there is no optical damage, the phase matching allowable angle (Δθ) is Δθ _ext
・ It is extremely small as l0.9mrad ・ cm (where _ext is the abbreviation of external angle and l is the length of the crystal), so that a long crystal cannot be used, and it is very difficult to obtain high conversion efficiency. is there.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a LiB ₃ O ₅ infrared light that oscillates stably in the infrared region with high efficiency and high output and a narrow spectral width. It is to provide a parametric oscillator.

(Means for Solving the Problems) To achieve the above object, in the LiB ₃ O ₅ infrared parametric oscillator according to claim 1 of the present invention, Nd which oscillates laser at 1.047 to 1.0796 μm as an excitation light source: YL
Using a second harmonic of a solid-state laser of any of F, Nd: YAG, Nd: GSGG or Nd: YAP, as a nonlinear optical element, a type-
1 (θ = 90 °, φ = 0 to 12 °) or type-2 (θ = φ
= 0 ゜) LiB ₃ O ₅ crystal [However, θ and φ are z
(= B), angle part of polar coordinates measured from x (= a) axis]
Is used as a means for solving the above problem.

Further, in the LiB ₃ O ₅ infrared parametric oscillator according to the second aspect, in the LiB ₃ O ₅ infrared parametric oscillator according to the first aspect, a perfect reflection mirror is used as an incident side reflection means of the nonlinear optical element, An incident-side deflection plate having a high reflectance at the wavelength of the excitation light is disposed between the incidence side of the nonlinear optical element and the perfect reflection mirror, and the excitation light is incident on the incidence-side deflection plate. And the reflected light from the incident side deflection plate is arranged to be incident on the nonlinear optical element, and the incident side deflection plate is arranged so as to have a Brewster angle with respect to the optical axis of the resonator. Between the emission side of the element and a partial reflector as emission side reflection means,
An emission-side deflection plate having a high reflectance at the wavelength of the excitation light is arranged, and the emission-side deflection plate is arranged so that light emitted from the nonlinear optical element is incident on the emission-side deflection plate, The output side deflection plate is arranged to have a Brewster angle with respect to the optical axis.

The LiB ₃ O ₅ infrared optical parametric oscillator according to claim 3, in LiB ₃ O ₅ infrared optical parametric oscillator according to claim 2, instead of a full reflector that is disposed on the incident side of the nonlinear optical element, the diffraction The configuration uses a lattice.

(Function) In the LiB ₃ O ₅ infrared parametric oscillator of the present invention, a LiB ₃ O ₅ crystal having high performance and a larger phase matching allowable angle than the conventional nonlinear optical element is used as the nonlinear optical element,
Nd: YLF, Nd: YAG, N oscillating at 1.047 to 1.0796 μm
Oscillation by the optical parametric effect is performed by exciting the solid-state laser of either d: GSGG or Nd: YAP at the second high frequency. Therefore, the relatively long LiB ₃
By using the O ₅ crystal, it is possible to improve the efficiency, and it is possible to obtain infrared coherent light with a very stable output having a narrow spectral width. LiB ₃ O ₅
By changing the phase matching condition between the crystal and the pump light, the wavelength of the output light can be continuously changed.

(Example) Hereinafter, an embodiment of LiB ₃ O ₅ infrared optical parametric oscillator according to the present invention with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the LiB ₃ O ₅ infrared parametric oscillator according to the first aspect of the present invention.
In the figure, reference numeral 1 denotes a LiB ₃ O ₅ infrared parametric oscillator (hereinafter abbreviated as LBO infrared oscillator). The LBO infrared oscillator 1 includes an excitation light source 2, a nonlinear optical element 3 disposed on the optical axis of the excitation light source 2, and an incident side and an emission side of the nonlinear optical element 3 on the optical axis of the excitation light source 2. , A complete reflecting mirror 4 and a partial reflecting mirror 5, an oven (heating means) 6, and a plane reflecting mirror 7, respectively.

As the excitation light source 2, a second harmonic of a solid-state laser of Nd: YLF, Nd: YAG, Nd: GSGG, or Nd: YAP, which oscillates laser at 1.047 to 1.0796 μm, is used.

The excitation light source 2 transmits the emitted light through a perfect reflection mirror 4 disposed on the incident side of the nonlinear optical element 3 and enters the nonlinear optical element 3 as excitation light.

The nonlinear optical element 3 has a type-1 (θ = 90 °, φ = 0
~ 12mm) or type-2 (θ = φ = 0mm)
A LiB ₃ O ₅ crystal [where θ and φ are the angle portions of polar coordinates measured from the z (= b) and x (= a) axes] is used. this
LiB ₃ O ₅ crystal has a nonlinear optical constant (d ₃₁ , d ₃₂ ) of 2.3
× 10 ^-9 and 2.5 × 10 ^-9 esu and much smaller than the nonlinear optical constants of MgO: LiNbO ₃ and β-BaB ₂ O ₄ , but the phase matching allowable angle is Δφ _ext · l = 6.4 mrad in the type-1 cut・ C
m, Δθ _ext · l ^1/2 = 3.1 ゜ cm ^1/2 , Δθ _ext · l ^1/2 = 7.60 ゜ cm ^{1/2 for} type-2 cut, Δφ _ext · l ^1/2 = 5.0
This is much smaller than the allowable phase matching angle of the MgO: LiNbO ₃ and β-BaB ₂ O ₄ crystals of 0 ゜ cm ^1/2 . Moreover, the phase matching spectrum width is also Δλs · l in the type-2 cut.
30Å · cm (where λs is the wavelength of the signal light, which is the output light having a wavelength shorter than twice the wavelength of the pump laser light),
In addition, the crystal has a high destruction threshold of about 600 MW / cm ² and has no deliquescence and can be easily coated with an antireflection film.

The complete reflecting mirror 4 arranged on the incident side of the nonlinear optical element 3 and the partial reflecting mirror 5 arranged on the emitting side of the nonlinear optical element 3 both have high transmittance at the wavelength of the excitation laser light, and The reflecting mirror 4 has a high reflectance at both the signal light (wavelength shorter than twice the wavelength of the excitation laser light) and the idler light (wavelength longer than twice the wavelength of the excitation laser light), or at one of the wavelengths. The partial reflecting mirror 5 is a dichroic reflecting mirror having a reflectance of 50 to 98% for either signal light or idler light.

In order to obtain coherent light with the LBO infrared oscillator 1 having such a configuration, for example, a second harmonic of an Nd: YAG laser is used as the pumping light source 2 and the pumping light is emitted from the second harmonic.
In the case of the type-1 cut according to the wavelength of the output light desired for the nonlinear optical element 3, the angle is appropriately tuned around the z-axis perpendicular to the paper plane shown in FIG. In this case, the temperature of the open 6 may be controlled.

The excitation light passes through the perfect reflecting mirror 4 and enters the nonlinear optical element 3 as shown by an arrow in FIG. 1, and is converted into signal light and idler light determined by the phase matching condition by an optical parametric effect. The light reaches the partial reflection mirror 5 together with a part of the excitation light that is not phase-matched and is not converted. One of the signal light and the idler light is reflected by the partial reflecting mirror 5, whereby the signal light and the idler light are placed in a resonance state with the complete reflecting mirror 4, and finally oscillate through the partial reflecting mirror 5. The plane reflecting mirror 7 reflects only the wavelength of the excitation light.
As a result, the excitation light is removed, whereby the signal light or the idler light is transmitted and becomes the output light.

In such an LBO infrared oscillator 1, since a high-performance LiB ₃ O ₅ crystal is used as the nonlinear optical element 3,
It is possible to efficiently obtain wavelength-tunable infrared coherent light having a very stable output.

FIG. 2 is a diagram showing an embodiment of a LiB ₃ O ₅ infrared optical parametric oscillator (LBO infrared oscillator) according to claim 2 of the present invention. In FIG. 2, reference numeral 10 denotes an LBO infrared oscillator. is there.
The LBO infrared oscillator 10 includes an excitation light source 11 and the excitation light source 1
A non-linear optical element 12 on which the light emitted from 1 is incident, a perfect reflecting mirror 13 and a partial reflecting mirror 14 arranged on the incident side and the outgoing side of the non-linear optical element 12, An incident-side deflection plate 15 disposed between the mirror 13, an exit-side deflection plate 16 disposed between the exit side of the nonlinear optical element 12 and the partial reflection mirror 14, and an oven 17. Things.

The pump light source 11 and the nonlinear optical element 12 are the same as the pump light source 2 and the nonlinear optical element 3 shown in FIG. 1, respectively. Here, the excitation light source 11 is arranged so that the excitation light is incident on the incident side deflection plate 15 as described later.

Perfect reflection mirror 13 arranged on the incident side of nonlinear optical element 12
Is a mirror made of anhydrous synthetic quartz having a dielectric multilayer film 13a coated on the surface on the side of the nonlinear optical element 12 and having a reflectance of 95% or more in a wavelength range of 0.7 to 2.2 μm. A plane mirror or a spherical mirror having a reflectivity of 99% is used.

On the other hand, the partial reflecting mirror 14 arranged on the emission side of the nonlinear optical element 12 has a wavelength range of 0.7 to 1.08 or 1.08 to 2.2 μm.
It is composed of a plane mirror made of anhydrous synthetic quartz having a dielectric multilayer film 14a coated on the surface on the side of the nonlinear optical element so as to have a reflectance of 50 to 98%.

An incident-side deflecting plate 15 is arranged between the entrance side of the nonlinear optical element 12 and the perfect reflecting mirror 13, and an exit-side deflecting plate 16 is arranged between the exit side of the nonlinear optical element 12 and the partial reflecting mirror 14. Have been. These incident side deflector 15 and exit side deflector 16
Are both made of anhydrous synthetic quartz coated with a dielectric multilayer film and have a high reflectivity of 95% or more at the wavelength of the excitation light. In this example, the reflectivity is 99.9%. Is used. The incident side deflection plate 15 is arranged so that the excitation light from the excitation light source 11 is incident and reflected, and the reflected light is incident on the nonlinear optical element 12, and is arranged on the optical axis of the LBO infrared oscillator 10. in which are arranged so as to be Brewster angle theta _B against.

On the other hand, the output-side deflection plate 16 has a Brewster angle θ _B with respect to the optical axis of the LBO infrared oscillator 10 so as to output the out-of-phase-matched excitation light emitted from the nonlinear optical element 12 to the outside of the resonator of the LBO infrared oscillator 10. Therefore, both the signal and the idler light are minimized in the type-1 cut of the nonlinear optical element, and the reflection loss of the signal light is minimized in the type-2 cut of the nonlinear optical element. It should be noted that in this case, Brewster angle theta _B of the incident side and the outgoing side deflection plate 15 and 16 is about 55 degrees.

In order to obtain coherent light with the LBO infrared oscillator 10 having such a configuration, for example, a second harmonic of a Nd: YAG laser is used as the pumping light source 11, and the pumping light is emitted from the second harmonic.
In the case of type-1 cut, the nonlinear optical element 12 is appropriately angle-tuned around the z-axis (similar to the case shown in FIG. 1) perpendicular to the plane of the drawing in accordance with the desired output light wavelength (φ is Or in the case of type-2, the temperature of the oven 17 may be controlled.

The excitation light is applied to the incident-side deflecting plate 15 as shown by the arrow in FIG.
Then, the light is totally reflected and enters the nonlinear optical element 12. The excitation light incident on the nonlinear optical element 12 is
The light is converted into signal light and idler light determined by the phase matching condition by the optical parametric effect, and is further emitted together with the excitation light that is not phase-matched and is not converted. The light emitted from the nonlinear optical element 12 reaches the emission-side deflection plate 16, where the excitation light is reflected and emitted out of the system. On the other hand, in the case of the type-1 cut of the nonlinear optical element, one of the signal light and the idler is placed, and in the case of the type-2, the signal light is placed in a resonance state between the completely reflecting mirror 13 and the partially reflecting mirror 14. Finally, the light oscillates through the partial reflecting mirror 14. In this case, since the signal light and the idler light are considerably longer than the wavelength of the excitation light, they are transmitted without being reflected by the deflecting plates 15 and 16.

In such an LBO infrared oscillator 10, a high-performance LiB
_{Since the 3} O ₅ crystal is used, efficient and extremely stable high-output tunable coherent light can be obtained. In addition, since the polarizing plates 15 and 16 are provided, the reflecting mirror 1 is provided.
There is no need to transmit the excitation light to 3, 14 and the oscillation can be performed without using an expensive dichroic reflector with a low destruction threshold as an optical resonator. Not to destroy
Since there is no need to control the excitation input density so as not to exceed 200 MW / cm ² , high conversion efficiency can be obtained.

Further, in the LBO infrared oscillator 10 shown in FIG. 2, if it is desired to further narrow the spectrum width of the output light, a diffraction grating may be arranged instead of the perfect reflecting mirror 13 as described in claim 3 of the present invention. I just need.

(Experimental example 1) Using the LBO infrared oscillator 10 shown in FIG.
Oscillation tuning using a 1.8 cm long LiB ₃ O ₅ cut as a type-1 (θ = 90 °, φ = 9 °) as the nonlinear optical element 12 using a second harmonic of an Nd: YAG laser (Tuning) Then, at 20 ° C, the nonlinear optical element is continuously rotated in the range of 0.7 to 2.2 µm by simply rotating the nonlinear optical element about the z-axis, and cut into type-2 (θ = φ = 0 °). Length
Simply temperature tuning from 20 ° C. to 250 ° C. using LiB ₃ O ₅ of 1.6cm, 0.7~1.006μm and 1.130~2.2μ as output light
Variable wavelength coherent light in the range of m was obtained.

(Experimental example 2) Using the LBO infrared oscillator used in Experimental example 1 and length
Using type -2LiB ₃ O ₅ crystal of 1.6 cm, the pulse width 10 ns N
d: When excited with the second harmonic of the YAG laser and measured,
The oscillation threshold is about 180 MW / cm ² at the point where the wavelength of the signal light is 1.006 μm and the wavelength of the idler light is 1.130 μm.
A maximum energy conversion efficiency of 15% was obtained with an input twice the threshold.

(Experimental example 3) Using the LBO infrared oscillator used in Experimental example 1 and length
Perform oscillation with type -2LiB ₃ O ₅ crystal of 1.6 cm, was measured spectral width of the resulting output light 0.679μm
And about 50 ° at 2.052 μm.

Next, the spectral width of the output light was measured by arranging a diffraction grating of 2400 lines / mm in place of the perfect reflecting mirror 13.
m was about 0.2 ° and 2.052 μm was about 2 °.

From the above results, it was confirmed that the spectral width of the obtained output light was reduced by arranging a diffraction grating instead of the perfect reflecting mirror 13.

(Effects of the Invention) As described above, the LiB ₃ O ₅ infrared optical parametric oscillator according to claim 1 of the present invention is a high performance type-1 (θ = 90 °, φ = 0 to 0) as a nonlinear optical element. 12
゜) or LiB ₃ cut to type-2 (θ = φ = 0 ゜)
Since the O ₅ crystal [where θ and φ are angles of polar coordinates measured from the z (= b) and x (= a) axes] is used, an efficient and very stable high-output wavelength is used. Variable infrared coherent light can be obtained.

Further, in the LiB ₃ O ₅ infrared parametric oscillator according to the second aspect, a deflecting plate is arranged on the incident side and the emitting side of the nonlinear optical element, and the excitation light is incident on the nonlinear optical element via the incident side deflecting plate. Thus, it is not necessary to use, for example, a dichroic reflector having a low destruction threshold as an optical resonator, so that a new resonator with almost no damage can be used, and therefore, it is efficient and 0.7 to 0.7 mm Very stable and high-output wavelength-variable coherent light can be obtained in a wide wavelength range of 2.2 μm.

Since the LiB ₃ O ₅ infrared parametric oscillator according to claim 3 is one in which a diffraction grating is arranged instead of the perfect reflection mirror arranged on the incident side of the nonlinear optical element, the diffraction action of this diffraction grating The spectrum width of the obtained output light can be narrowed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram showing one embodiment of a LiB ₃ O ₅ infrared optical parametric oscillator according to claim 1 of the present invention;
FIG. 2 is a schematic diagram showing an embodiment of the LiB ₃ O ₅ infrared parametric oscillator according to the second aspect. 1,10… LiB ₃ O ₅ infrared parametric oscillator (LBO infrared oscillator), 2,11… excitation light source, 3,12 …… non-linear optical element, 4,13 …… complete reflection mirror, 5,14 …… Partial reflector, 6,17…
… Oven, 15… incident side deflector, 16… exit side deflector.

Claims (3)

(57) [Claims] An excitation light source, a nonlinear optical element excited by excitation light emitted from the excitation light source, and reflection means disposed on an incident side and an emission side of the nonlinear optical element. In an optical parametric oscillator, Nd: YL which oscillates laser at 1.047 to 1.0796 μm as the excitation light source
Using a second high frequency of a solid-state laser of F, Nd: YAG, Nd: GSGG or Nd: YAP, and using the type-1 (θ = 90 °, φ = 0 to 12 °) or type as the nonlinear optical element -2 (θ
= Phi = 0 °) LiB ₃ O ₅ crystal cut in the proviso, theta, phi is z (= b), x ( = a) polar angle portion as measured from the axis] characterized by using the LiB ₃ O ₅ infrared optical parametric oscillator. 2. A completely reflecting mirror is used as an incident side reflecting means of the nonlinear optical element, and has a high reflectance between the incident side of the nonlinear optical element and the perfect reflecting mirror at the wavelength of the excitation light. An incident-side deflecting plate is arranged, and the excitation light is arranged to be incident on the incident-side deflecting plate and reflected light from the incident-side deflecting plate is incident on the nonlinear optical element. An output having a high reflectance at the wavelength of the excitation light is disposed between the output side of the nonlinear optical element and a partial reflecting mirror as an output side reflection means, so as to have a Brewster angle with respect to the optical axis. A side deflecting plate is arranged, and the emission side deflecting plate is arranged so that light emitted from the nonlinear optical element is incident on the emission side deflecting plate. Stars arranged to be a star angle LiB ₃ O ₅ infrared optical parametric oscillator to claim 1, wherein. 3. A non-linear optical element, wherein a diffraction grating is used as an incident side reflection means, and an incident side having a high reflectance at a wavelength of the excitation light is provided between the incident side of the non-linear optical element and the diffraction grating. Arranging a deflecting plate, and arranging the excitation light to be incident on the incident side deflecting plate and reflected light from the incident side deflecting plate to be incident on the nonlinear optical element,
The incident side deflection plate is disposed at a Brewster angle with respect to the optical axis, and is disposed between the exit side of the nonlinear optical element and a partial reflection mirror as an exit side reflection unit at a wavelength of the excitation light. Disposing an output-side deflection plate having high reflectivity, and disposing the output-side deflection plate so that light emitted from the nonlinear optical element is incident on the output-side deflection plate, and setting the output-side deflection plate to 2. The LiB ₃ O ₅ infrared parametric oscillator according to claim 1, wherein the LiB ₃ O ₅ infrared optical parametric oscillator is arranged at a Brewster angle with respect to the optical axis.