JP2014126567A - Infrared solid-state laser oscillation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared solid-state laser oscillation device achieving high output with low costs.SOLUTION: A bending reflector 1 forwards excitation light p generated by an excitation light source 5 which is a Nd:YAG laser laser-oscillating at a wavelength of 1.0642 μm, in a horizontal direction. A nonlinear optical element 3 formed of the crystal of HgGaSis arranged in a position adjacent to an input-output mirror 2 positioned on an optical axis L of the excitation light p. The nonlinear optical element 3 on the optical axis L emits signal light s and idler light i as infrared. A non-coated MgFrectangular prism 4 made of MgFin the position adjacent to the nonlinear optical element 3 reflects the excitation light p and infrared from the nonlinear optical element 3, and sends the excitation light p and the infrared as light parallel to the incident light back to the optical element.

Description

  The present invention relates to an infrared solid-state laser oscillation device that oscillates coherent infrared rays by optical parametric oscillation, and is particularly suitable for oscillating infrared rays in a wavelength range of 4 to 7 μm.

  Conventionally, an optical parametric oscillator that outputs coherent light of two different wavelengths as output light by inputting coherent excitation light into the crystal of the nonlinear optical element is known as one based on the nonlinear optical system. Yes. In general, this optical parametric oscillator is roughly constituted by a nonlinear optical element and a pair of reflecting mirrors arranged on both sides of the pumping light source in addition to the excitation light source. These two coherent lights that are output lights are called signal light and idler light, and the following equations 1 and 2 are used between the excitation light, signal light, and idler light. A relationship is established.

(Equation 1)
1 / λ _s + 1 / λ _i = 1 / λ _p

(Equation 2)
n _s / λ _s + n _i / λ _i = n _p / λ _p

Where λ _p is the wavelength of the excitation light, λ _s is the wavelength of the signal light, λ _i is the wavelength of the idler light, and _np is the refractive index of the excitation light and n _s is the refractive index of the signal light. , N _i is the refractive index of idler light.

In a laser oscillation apparatus having such an optical parametric oscillator, for example, an Nd: YAG (Nd ³⁺ : Y ₃ Al ₅ O ₁₅ ) laser that oscillates at a wavelength of 1.0642 μm is used as an excitation light source, and a nonlinear optical element is used. As an example, a material composed of AgGaS ₂ (AGS) crystal is known.
On the other hand, in particular, infrared rays having a wavelength of, for example, 6.45 μm within infrared rays having a wavelength in the range of 4 to 7 μm have recently been used in the medical technical field, and high-output infrared rays having this wavelength range are obtained. That is needed.

JP-A-11-95271 JP 2003-280055 A JP 2008-40293 A

  However, for example, conventional laser oscillators that are excited with an Nd: YAG laser and generate infrared light with a wavelength of 4 to 7 μm as idler light include single-pass (single-pass) optical parametric oscillators and double-pass (double-pass) optical parametrics. Although an oscillator is considered, even if a nonlinear optical element capable of high output is obtained, it has the following problems.

  That is, the single-pass optical parametric oscillator has a drawback in that the conversion efficiency into infrared of 4 to 7 μm, which is idler light, is low because the pump light only pumps the nonlinear optical element once.

In the double-pass optical parametric oscillator, the input mirror, which is one of the reflecting mirrors, has not only a high transmittance of 90 to 99% at the excitation light wavelength (1.0642 μm) but also a signal light of 4 to 7 μm. Unless the reflectance at is high, high output with idler light cannot be obtained. In other words, in order to obtain high output with idler light, the signal light (1.25 to 1.45 μm) has high reflectivity with high idler light and withstands high output exceeding 100 MW / cm ^2. It is necessary to adopt an input mirror with a high damage threshold.

  On the other hand, as a reflection mirror that has been used conventionally, there is a metal mirror such as gold or silver having a reflectivity of almost 100% with idler light and signal light, but there is a defect that it deteriorates due to use. Yes, it could not be adopted substantially. For this reason, it is extremely difficult to manufacture a reflector having a high damage threshold as described above, and there is a drawback that the manufacturing cost increases.

  On the other hand, the above-mentioned patent documents 1 to 3 are listed as those using a parametric oscillator. For example, Patent Document 1 discloses a structure in which the ratio of energy converted from excitation light to signal light and idler light in degenerate oscillation in which the wavelengths of signal light and idler light are equal is improved by a quarter wavelength plate. ing. Japanese Patent Application Laid-Open No. H10-228561 discloses a device that generates coherent and stable output vacuum ultraviolet rays using an optical parametric oscillator. Similarly, in Patent Document 3, the incident angle of the light to be converted incident on the wavelength conversion element body is changed, the light incident on the wavelength conversion element body is reflected by the side surface of the wavelength conversion element body, and the inside of the wavelength conversion element body is reflected. A zigzag progression is disclosed.

However, none of these Patent Documents 1 to 3 can obtain high-output infrared rays at low cost.
The present invention has been made in view of the above-described background, and an object thereof is to provide an infrared solid-state laser oscillation device that can obtain high-output infrared rays at low cost.

The invention according to claim 1, which has solved the above problems, includes an excitation light source that generates laser light,
An input / output mirror that receives the laser light and transmits the laser light and transmits infrared rays of at least one of predetermined wavelengths;
A nonlinear optical element that receives the laser light transmitted through the input / output mirror and outputs coherent infrared light having two wavelengths that are longer than the laser light and different from each other;
A MgF ₂ right angle prism that totally reflects these two coherent infrared and laser beams emitted from the nonlinear optical element back to the nonlinear optical element;
An infrared solid-state laser oscillation device characterized by comprising:

According to the infrared solid-state laser oscillation device of the first aspect, excitation light, which is laser light generated from the excitation light source, passes through the input / output mirror and is incident on the nonlinear optical element, and has a longer wavelength than the laser light. The nonlinear optical element outputs signal light and idler light, which are coherent infrared rays having two different wavelengths. Then, the two coherent infrared rays and the laser light emitted from the nonlinear optical element are totally reflected by the MgF ₂ right angle prism and incident on the nonlinear optical element and returned.

As a result, of these two coherent infrared rays emitted from the nonlinear optical element to the input / output mirror side, the input / output mirror reflects, for example, one coherent infrared ray which is an infrared ray having a predetermined wavelength, Only the remaining coherent infrared rays can be transmitted. Accordingly, in this claim, the signal light and the idler light are double-pass optical parametric oscillation in which the nonlinear optical element is generated twice, and at least a high output with the idler light can be obtained.

Further, in the present claims, an MgF ₂ right angle prism having a high damage threshold that can withstand a high output exceeding 100 MW / cm ² as well as being manufactured at a low cost is employed as a substitute for the reflecting mirror. From this, according to the infrared solid-state laser oscillation device according to the present claims, high-power signal light and idler light can be obtained at low cost. In other words, in addition to non-linear optical elements, an input / output mirror is integrated, and this is combined with a MgF ₂ right-angle prism to make a double-pass optical parametric oscillator. It will also solve the damage problem.

Accordingly, the infrared solid-state laser device according to the present invention uses, for example, an Nd: YAG laser that oscillates excitation light having a wavelength of 1.0642 μm as an excitation light source and is arranged in a positional relationship of a double-pass optical parametric oscillator. By pumping the optical element again with a MgF ₂ right angle prism instead of a special and expensive reflector, an output approximately twice that of a single-pass optical parametric oscillator can be obtained specifically.

Although the invention of claim 2 has substantially the same configuration as that of claim 1, it can be manufactured at a low cost in the same manner as described above instead of the MgF ₂ right angle prism and can withstand a high output exceeding 100 MW / cm ^2. A CaF ₂ right angle prism with a high damage threshold is employed. Therefore, according to the infrared solid-state laser oscillation device of the present invention, high-output signal light and idler light can be obtained at low cost as in the case of Claim 1.

The invention according to claim 3 is the infrared solid-state laser oscillation device according to claim 1 or ₂ , wherein an HgGa ₂ S ₄ (HGS) crystal is used as the nonlinear optical element. That is, by using this element material that can be used even at high output, the effects of the inventions of claims 1 and 2 can be more reliably exhibited.
The HgGa ₂ S ₄ crystal is a transparent nonlinear optical crystal in the range of 0.4 to 13 μm, and has a nonlinear optical constant of about 2.2 times that of AgGaS ₂ , and has a damage threshold with an Nd: YAG laser. Is about 2-3 times that of AgGaS ₂ . Further, unlike AgGaSe ₂ and ZnGeP ₂ which are other nonlinear optical crystals, this HgGa ₂ S ₄ crystal has a great merit that the most common Nd: YAG laser can be used as an excitation light source. Incidentally, AgGaSe ₂ and ZnGeP ₂ mainly use a laser with a wavelength of 2 μm because of the absorption band, but a laser with a wavelength of 2 μm has a major drawback that must be cooled to 77K.

  According to the present invention, there is an excellent effect that an infrared solid-state laser oscillation device capable of obtaining high-output infrared rays at low cost is provided.

It is a figure which shows embodiment of the infrared solid-state laser oscillation apparatus of this invention. FIG. 2 is a sectional view taken along line 2-2 in FIG. 1. It is a figure showing the graph which shows the change along the wavelength of the transmittance | permeability of the input-output mirror applied to embodiment of the infrared solid-state laser oscillation apparatus of this invention.

A first embodiment of an infrared solid-state laser oscillation apparatus according to the present invention will be described below with reference to the drawings.
As shown in FIGS. 1 and 2, the infrared solid-state laser oscillation device 10 according to the present embodiment has an excitation light source 5 that is an Nd: YAG laser that oscillates at a wavelength of 1.0642 μm. In the upper part in FIG. 1 of the excitation light source 5 as the basic light source, a bending reflector 1 made of CaF ₂ for sending the excitation light p, which is a laser beam generated by the excitation light source 5, in the horizontal direction in the figure is 45 °. It is arranged at an angle. Note that the reflectance R of the bending reflector 1 is about 90 to 99% at a wavelength of 1.0642 μm. Further, the bending reflector 1 has a transmittance T≈90% at a wavelength of 1.25 to 1.45 μm and a transmittance T≈90% at a wavelength of 4 to 7 μm.

A position of the right side of the bending reflecting mirror 1, the position on the optical axis L is the optical path of the excitation light p which is bent by the bending reflecting mirror 1, CaF ₂ made of the input and output mirror 2 is arranged Yes. As shown in the graph of FIG. 3, the transmittance T of the input / output mirror 2 is about 90 to 99% at a wavelength of 1.0642 μm, and the reflectance R is about 1.25 to 1.45 μm. About 90% or 85% (transmittance T is about 10% or 15%), and the transmittance T is about 90 to 99% at a wavelength of 4 to 7 μm. As a result, the input / output mirror 2 reflects infrared light having a predetermined wavelength of 1.25 to 1.45 μm and transmits infrared light having a wavelength of 1.0642 μm and a wavelength of 4 to 7 μm.

At a position adjacent to the input / output mirror 2 on the optical axis L, a non-linear optical element 3 having a length of, for example, 8 mm formed of a crystal of HgGaS ₄ (HGS) is disposed. However, the nonlinear optical element 3 is supported by a support jig or the like (not shown) so that the tilt angle (phase matching angle) with respect to the optical axis L can be adjusted. Further, antireflection films 3A for preventing reflection of infrared rays having a wavelength of 1.0642 μm and a wavelength of 1.25 to 1.45 μm are attached to both end faces of the nonlinear optical element 3. The reflectance R is set to 1 to 2%. Accordingly, when the 1.0642 μm excitation light p is incident, the nonlinear optical element 3 emits the signal light s and the idler light i.

An adjacent position of the nonlinear optical element 3 on the optical axis L is made of MgF ₂ and has no coating for reflecting the excitation light p or infrared light from the nonlinear optical element 3 and returning it as light parallel to the incident light. An MgF ₂ right angle prism 4 is arranged. The reflectance R of the MgF ₂ right angle prism 4 is about 90 to 99% at any wavelength of 1.0642 μm, 1.25 to 1.45 μm, and 4 to 7 μm.

As described above, the bending reflector 1, the input / output mirror 2, the nonlinear optical element 3, and the MgF ₂ right angle prism 4 constitute a double-pass optical parametric oscillator 9. Accordingly, the infrared solid-state laser oscillation device 10 of the present embodiment shown in FIGS. 1 and 2 includes an excitation light source 5 that is an Nd: YAG laser that oscillates at a wavelength of 1.0642 μm, and the excitation light source 5. The optical parametric oscillator 9 is arranged.

  An energy meter or an IR spectrum is provided at a position adjacent to the left of the bending reflector 1 through a filter 6 for removing the signal light s and the excitation reflected light p ′ (2 to 5%) that has not been phase matched. A meter 7 is arranged so that the IR spectrum meter 7 can detect the wavelength and intensity of infrared rays transmitted through the bending reflector 1. However, the filter 6 and the IR spectrum meter 7 are merely for measuring the wavelength and intensity of infrared rays, and need not be present.

Next, the operation of the infrared solid-state laser oscillation device 10 of the present embodiment will be described.
According to the infrared solid-state laser oscillating device 10 according to the present embodiment, the excitation light p that is laser light emitted from the excitation light source 5 is folded back by the bending mirror 1 and the input / output mirror 2 is moved along the optical axis L. Further, it passes through while exciting the nonlinear optical element 3 of the HgGa ₂ S ₄ crystal. Accordingly, the signal light s having a wavelength of 1.25 to 1.45 μm and the idler light i having a wavelength of 4 to 7 μm, which are coherent infrared rays having wavelengths longer than the excitation light p and different from each other, The nonlinear optical element 3 emits.

After that, the two coherent infrared rays and the excitation light p emitted from the nonlinear optical element 3 are reflected by the MgF ₂ right-angle prism 4 in parallel with the incident light, and again enter the nonlinear optical element 3 to be excited. The excitation light p is transmitted through the input / output mirror 2, reflected by the bending mirror 1, and emitted downward from the optical parametric oscillator 9. For this reason, in this embodiment, as a result of exciting the nonlinear optical element 3 again, the nonlinear optical element 3 generates more signal light s and idler light i than the single path in accordance with these two excitations. Although the optical parametric oscillation occurs, the input / output mirror 2 reflects the signal light s and transmits only the remaining idler light i, whereby high output with the idler light i can be obtained.

As a result of the above, the signal light s and idler light i generated by exciting the nonlinear optical element 3 in the optical parametric oscillator 9 are amplified between the input / output mirror 2 and the MgF ₂ rectangular prism 4, Only the idler light i is transmitted through the input / output mirror 2 and the bending mirror 1 and separated from the excitation light p. Then, by passing through the filter 6 and entering the IR spectrum meter 7, data on the wavelength and intensity of the idler light i, which is infrared, can be obtained.

  From the above, although the nonlinear optical element 3 of the optical parametric oscillator 9 of the present embodiment is excited by the excitation light p from the Nd: YAG laser used as the excitation light source 5, the inclination angle of the nonlinear optical element 3 is indicated by the arrow at this time. By adjusting in the R direction, it is also possible to stably obtain infrared rays having a wavelength of 6.45 μm, for example, among the wavelengths of 4 to 7 μm with maximum efficiency.

Further, in the present embodiment, the MgF ₂ right angle prism 4 having a high damage threshold that can withstand a high output exceeding 100 MW / cm ² as well as being manufactured at a low cost is employed as a substitute for the reflecting mirror. From this, according to the infrared solid-state laser oscillating device 10 according to the present embodiment, the high-output signal light s and idler light i can be stably obtained at low cost. That is, in addition to the nonlinear optical element 3, the input / output mirror 2 is integrated, and the MgF ₂ right angle prism 4 is combined with this to form a double-pass optical parametric oscillator 9, thereby improving deformation efficiency and output characteristics. In addition, the problem of reflector damage will be solved.

Accordingly, the infrared solid-state laser oscillation device 10 of the present embodiment uses, for example, an Nd: YAG laser that oscillates excitation light p having a wavelength of 1.0642 μm as the excitation light source 5, and makes the nonlinear optical element 3 special and expensive. Exactly twice the output of the single-pass optical parametric oscillator 9 could be obtained specifically by exciting again with the MgF ₂ right angle prism 4 instead of a simple reflecting mirror.

Specifically, in the infrared solid-state laser oscillation device 10 as shown in FIGS. 1 and 2, an Nd: YAG laser having an average output of 2.4 W (output per pulse: 80 mJ, pulse width: 5 ns) is employed as the excitation light source 5. When an optical parametric oscillator 9 adopting an HgGa ₂ S ₄ crystal having a length of 8 mm as the nonlinear optical element 3 is excited with an Nd: YAG laser, an HgGa ₂ S ₄ crystal (cut angle θ = 56 °, φ = 0 °; θ and φ are z (= c) and the angle of x (= a) axis) are tilted by ± 9 ° as shown by dotted lines, and are tuned so that the wavelength range of 4.5 to 7.5 μm can be obtained. In particular, for example, a maximum average output of 210 mW (output of 7 mJ per pulse, pulse width of 3.5 ns) was obtained at a wavelength of 6.45 μm.

Next, a second embodiment of the infrared solid-state laser oscillation device according to the present invention will be described.
The apparatus of the present embodiment has the same structure as that of the first embodiment. However, a rectangular prism instead of MgF ₂ right-angle prism 4, in the present embodiment has a CaF ₂ made of CaF ₂ rectangular prism.
Thus, according to the infrared solid-state laser oscillation device 10 according to the present embodiment, high-output signal light s and idler light i can be obtained at low cost as in the first embodiment.

In the above embodiment, only the high-power idler light i is derived outside the infrared solid-state laser oscillation device. However, the high-output signal light s and idler light i are derived outside the infrared solid-state laser oscillation device. May be. In the above embodiment, the bending reflecting mirror and the input / output mirror are made of CaF ₂ , but other known materials may be used.

  The embodiment according to the present invention has been described above, but the present invention is not limited to the embodiment, and various modifications can be made without departing from the spirit of the present invention.

  The present invention can be applied to various technical fields that require high-output infrared rays, and can be applied not only to medical use but also to other technical fields such as industrial use.

DESCRIPTION OF SYMBOLS 1 Bending reflecting mirror 2 Input / output mirror 3 Nonlinear optical element 4 MgF ₂ right angle prism 5 Excitation light source 6 Filter 7 IR spectrum meter 9 Optical parametric oscillator 10 Infrared solid-state laser oscillation device p Excitation light s Signal light i Idler light

Claims (3)

An excitation light source that generates laser light;
An input / output mirror that receives the laser light and transmits the laser light and transmits infrared rays of at least a predetermined wavelength; and
A nonlinear optical element that receives the laser light transmitted through the input / output mirror and outputs coherent infrared light having two wavelengths that are longer than the laser light and different from each other;
A MgF ₂ right angle prism that totally reflects these two coherent infrared and laser beams emitted from the nonlinear optical element back to the nonlinear optical element;
An infrared solid-state laser oscillation device comprising: An excitation light source that generates laser light;
An input / output mirror that receives the laser light and transmits the laser light and transmits infrared rays of at least one of predetermined wavelengths;
A nonlinear optical element that receives the laser light transmitted through the input / output mirror and outputs coherent infrared light having two wavelengths that are longer than the laser light and different from each other;
A CaF ₂ right angle prism that totally reflects these two coherent infrared and laser beams emitted from the nonlinear optical element back to the nonlinear optical element;
An infrared solid-state laser oscillation device comprising: The infrared solid-state laser oscillation apparatus according to claim 1 or ₂ , wherein an HgGa ₂ S ₄ crystal is used as the nonlinear optical element.

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