JPH1195273A - Laser apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to generate the light of four kinds of wavelengths on the same optical axis and to improve efficiency by installing the nonlinear optical element of a second optical parameteric oscillator(OPO) within an optical resonator common to the first and second OPOs. SOLUTION: Fresh signal light and idler light are generated by the nonlinear type interaction of a first nonlinear optical element 16a of the second OPO 13 with the signal light from the first OPO 6 as exciting light. The fresh signal light and idler light are generated as well in the second nonlinear crystal 16b in the second OPO 13 even by the idler light from the first OPO 6. The light generated by the first nonlinear crystal 16a and the exciting light are generally not phase matched in the second nonlinear crystal 16b and, therefore, there is substantially no interaction. The action with respect to the light generated in the second nonlinear optical element 16b and the exciting light is similar to the action in the first nonlinear optical element 16a. As a result thereof, the light rays of total four kinds from the second OPO 13 are generated on the same optical axis from the common optical resonator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device having an optical parametric oscillator (OPO) for generating a laser beam whose wavelength is converted by a nonlinear optical effect, and more particularly to a laser device having a plurality of OPOs. The present invention relates to a laser device that emits light from the same optical axis and has improved generation efficiency of wavelength-converted light.

[0002]

2. Description of the Related Art Generally, an optical parametric oscillator (OP)
O) is constructed by placing a non-linear optical element such as KTP having a parametric gain in an optical resonator composed of two reflecting mirrors in the same way as a laser resonator, and exciting it with an appropriate laser beam. These optical parametric resonators are configured so that signal light (signal wave light) and / or idler light (auxiliary wave light) resonate. When the pumping input exceeds a certain threshold, the signal light and idler light are used. Parametric oscillation occurs.

[0003] Explaining these with reference to FIG. 2, a laser beam generated from an excitation laser oscillator 1 passes through condensing optical systems 2 a and 2 b and an input mirror 3 and enters a nonlinear optical element 4. In a nonlinear optical element, two lights (signal light,
Idler light) is generated. One or both of the lights are reflected by the output mirror 5, return on the optical axis, reciprocate with the incident mirror 3, and resonate and amplified. A part of the light is transmitted through the output mirror 5 and extracted outside as laser output light. Since the energy conservation law is established between the wavelengths of the excitation light, the signal light, and the idler light, the following relationship is established.

1 / λp = 1 / λs + 1 / λi (1) where λp is the wavelength of the pump light, λs is the wavelength of the signal light, and λi is the wavelength of the idler light.

For example, in a configuration using KTP for the nonlinear optical element 4 using an Nd: YAG laser as excitation light, λp
= 1.06 μm, λs = 1.6 μm, λi =
A light of 3.2 μm is obtained. In a special case (degenerate oscillation) in which λs = λi, λi = λ
Light of s = 2.12 μm is obtained.

However, in order for the OPO 6 to efficiently convert the wavelength of the excitation light energy to generate light, the following vector equation called a phase matching condition must be established in the nonlinear optical element 4.

Kp = Ks + Ki (2) This condition is generally realized by a method called angular phase matching for adjusting the inclination of the crystal axis with respect to the wave vector by utilizing the birefringence of the crystal. It is.

In recent years, in order to efficiently generate light of a longer wavelength, a second OPO using light from the OPO as excitation light has been proposed.
Are introduced. Figure 3
Explaining based on this, the pump laser 1 and the first OPO
The configuration and operation up to 6 are the same as those in FIG. 2, and one of the two beams generated from the first OPO 6 is one of the beam splitters 7.
Then, the remaining light is input to the input mirror 9 of the second OPO 8, and the non-linear optical element 10 is activated second by this light. Thereby, the first OPO 8 is output from the output mirror 11 of the second OPO 8 by the same process as that of the first OPO 6.
2 light having a longer wavelength than the light generated by the OPO6 is generated.

Further, as shown in FIG. 4, on the optical path of the light separated by the beam splitter 7, another OPO 12
And the optical path is formed by each of the mirrors m1, m2, and m3, the efficiency is further improved.

[0010]

Generally, in a laser device having an optical parametric oscillator, only one wavelength is intended for output, and it is difficult to simultaneously output two lights (signal light and idler light). Almost no. Therefore, of the two lights generated by the optical parametric oscillator, only one light is required, and the energy of the other light is often wasted. Therefore, use of only one light is not preferable because the oscillation efficiency of the entire oscillator is limited.

In particular, since the ratio of the energy of the generated light is substantially inversely proportional to the wavelength, when the output of the idler light is intended, for example, the efficiency becomes extremely low.

Also, in order to extract only the light of the desired wavelength from the two lights, an optical mirror for separating the two lights must be installed, and the efficiency does not become 100%. In addition, there is a problem that the output further decreases.

In the method of installing another OPO device on the optical path of the light separated by the beam splitter, the efficiency is improved, but the configuration becomes complicated, and light is generated from two optical axes. It is not practical. in this case,
This problem can be overcome by applying an optical system for synthesizing each generated light, but the apparatus becomes more complicated and it is extremely difficult to completely align the optical axes.

[0014]

According to the present invention, there is provided a first optical parametric oscillator disposed on the optical axis of an excitation laser oscillator and a second optical parametric oscillator disposed on the optical axis in front thereof. Wherein the second optical parametric oscillator includes first and second nonlinear optical elements for wavelength-converting each of signal light and idler light generated from the first optical parametric oscillator. A laser device is provided in an optical resonator common to an optical parametric oscillator.

According to the present invention, there is provided a laser device characterized in that the signal light generated from the first optical parametric oscillator and the idler light have the same wavelength.

According to the present invention, there is provided a laser device wherein the wavelength of the signal light generated from the second optical parametric oscillator is equal to the wavelength of the idler light.

According to the present invention, the nonlinear optical element in the second optical parametric oscillator is characterized in that a device for converting the wavelength of signal light and a device for converting the wavelength of idler light are provided separately. Laser device.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 2 to 4 denote the same components or components having the same functions as those of the conventional technology.

FIG. 1 is a block diagram of the present embodiment, wherein condensing optical systems 2a, 2b,
A first optical parametric oscillator (OPO) 6, a second OPO
PO13 are arranged in this order.

The first OPO is a nonlinear optical element 4
The input mirror 3 is provided at the rear on the optical axis across the TP, and the output mirror 5 is provided at the front. The second OPO 13 has a first nonlinear optical element 16a and a second nonlinear optical element 16b provided between the incident mirror 3 and the output mirror 5 on the optical axis.
Since the signal light from the first OPO 6 and the idler light generally have different wavelengths and often do not have the same polarization direction, the nonlinear light whose angle is adjusted so as to be phase-matched with the signal light of the first OPO 6 is often used. Optical element 16a
And a second non-linear optical element 16b that is phase-matched to the idler light of the first OPO 6. As the nonlinear optical elements 16a and 16b, those having a low absorptance are applied to the two lights from the first OPO 6 and the respective lights generated by the second OPO 13. The incident mirror 14 transmits the signal light and the idler light from the first OPO 6 while reflecting the two signal lights generated by the second OPO 13, and the output mirror 15 having the characteristic of reflecting the two signal lights generated by the second OPO 13 is generated by the second OPO 13. 2
One or both of the two signal lights and the idler light are reflected to reciprocate between the input mirror 14 and resonate to increase the light intensity. Some of these lights are extracted from the output mirror 15 from the same optical axis.

With these configurations, new signal light and idler light are generated by the nonlinear interaction of the first nonlinear optical element 16a in the second OPO 13 with the signal light as the excitation light from the first OPO 6. The first O
The second OPO 13 is also generated by the idler light from the PO 6.
A new signal light and an idler light are generated in the second nonlinear crystal 16b. First nonlinear crystal 16a
The light and the excitation light generated in the second nonlinear optical element 1
In 6b, there is almost no interaction since phase matching is not generally performed. The operation of the light and the excitation light generated by the second nonlinear optical element 16b is the same as that of the first nonlinear optical element 16a.

As a result, a total of four types of light are generated from the second OPO 13. These are emitted from the same optical axis because they are emitted from a common optical resonator.

[0023]

【Example】

Example 1 A case will be described in which a YAG laser having an oscillation wavelength of 1.06 m is used for the excitation laser device 1 to generate mid-infrared light in a 3 to 5 m band. When KTP is used for the first OPO6,
As the generated light satisfying the expression (1), for example, a wavelength of 1.9 μm
m signal light and a 2.4 m wavelength idler light are obtained. AgGaSe ₂ crystal cut to be phase-matched with light of wavelength 2.4 m is used as the _second nonlinear optical element 16 a in the _second OPO 13, and AgGaSe ₂ is cut to be phase-matched with light of wavelength 1.9 m. _Two crystals are arranged as a second nonlinear optical element 16b.

From the former crystal, two lights satisfying the expression (1) for p = 1.9 μm, for example, s = 3.6 μm
And i = 4.1 μm light is generated. Also, from the latter crystal, for s = 2.4 μm, two lights satisfying the expression (1), for example, s = 4.6 μm and i = 5.0 μm.
m are generated, and the wavelengths generated by them are all 3-5 μm.
m.

Embodiment 2 When the first OPO 6 is degenerated, the wavelengths of the signal light and the idler light are both 2.12 μm. In this case, when a crystal such as KTP called type 2 phase matching is used as the two generated lights, the polarization directions are orthogonal, but the wavelength 2.
By arranging _two AgGaSe ₂ crystals cut and processed so as to be phase-matched with light of 12 μm and rotating the crystal directions around the optical axis by 90 degrees with respect to each other, the first OP
The signal light and the idler light from O6 are phase-matched to each other, and two sets of light satisfying the expression (1) can be generated for p = 2.12 μm. In particular, by making the second OPO 13 also degenerate oscillation, it is possible to make all the wavelengths of the four generated lights in the second OPO 13 4.24 μm.

In each of the above embodiments, the nonlinear optical element 4
KTP (KTiOPO ₄ ) was used as the
TiOAsO ₄ ), CTA (CsTiOAsO ₄ ), R
TP (CsTiOAsO ₄ ) can be used in the same manner.

In the above embodiment, the number of OPOs is two. However, it is needless to say that three or more OPOs can be similarly constructed.

In the above embodiment, in the second OPO, the first nonlinear optical element is used for converting the signal light and the second nonlinear optical element is used for converting the wavelength of the idler light. Needless to say, a similar effect can be obtained.

[0029]

As described above, according to the present invention, 2
In a laser device having two optical parametric oscillators (OPOs), the optical energy on one side from the first OPO, which was conventionally wasted, is converted into light of a longer wavelength by the second OPO, so that a maximum of four wavelengths can be obtained. Can be generated on the same optical axis, so that the efficiency of the laser device can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a laser device of the present invention.

FIG. 2 is a configuration diagram of a conventional optical parametric oscillator.

FIG. 3 is a configuration diagram of a modification of the optical parametric oscillator according to the related art.

FIG. 4 is a configuration diagram of another modification of the optical parametric oscillator according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Excitation laser oscillator 2 ... Condensing optical system 3 ... Input mirror 4 ... Nonlinear optical element (of 1st OPO) 5 ... Output mirror 6 ... 1st optical parametric oscillator (OPO) 7 ... Beam splitter 13 ... 2 OPOs 16a, 16b ... nonlinear optical element (of the second OPO)

Claims (4)

[Claims] 1. A laser device comprising: a first optical parametric oscillator disposed in front of an excitation laser on an optical axis; and a second optical parametric oscillator disposed in front of the pumping laser on the optical axis. The second optical parametric oscillator includes a non-linear optical element for wavelength-converting each of signal light and idler light generated from the first optical parametric oscillator in an optical resonator common to the first and second optical parametric oscillators. A laser device, wherein the laser device is installed in a laser device. 2. The laser device according to claim 1, wherein a wavelength of the signal light generated from the first optical parametric oscillator is equal to a wavelength of the idler light. 3. The laser device according to claim 2, wherein the signal light generated from said second optical parametric oscillator and the idler light have the same wavelength. 4. The nonlinear optical element in the second optical parametric oscillator, wherein a nonlinear optical element for converting the wavelength of signal light and a nonlinear optical element for converting the wavelength of idler light are separately provided. A laser device according to claim 1.