JPH02123776A - Solid laser device - Google Patents

Abstract

PURPOSE:To improve the efficiency of optical pumping, and to increase an output by applying irradiation light to an optical conversion means composed of a semiconductor, generating fluorescence and optically pumping a laser active substance in a laser medium by the fluorescence. CONSTITUTION:An optical conversion means 10 consisting of a semiconductor absorbing irradiation light 1R and generating fluorescence having a wavelength proper to the optical pumping of a laser active substance is provided, and irradiation light 1R is applied to the optical conversion means 10 and the laser active substance in a laser medium 1 is optically pumped while using fluorescence generated from the optical conversion means 10 as excitation light EL. Not only a wavelength component within a wavelength range having the excellent efficiency of the optical pumping of the laser active substance in irradiation light but also a wavelength component within a wavelength range shorter than the wavelength component are absorbed by previously conforming the wavelength of fluorescence emitted from the optical conversion means 10 within the wavelength range having the excellent efficiency of the optical pumping of the laser active substance, and the wavelength, component which has not been used is utilized effectively for optically pumping the laser active substance. Accordingly, the efficiency of optical pumping is improved, and a large output can be acquired.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state laser device that uses YAG, glass, or the like doped with transition metal ions or rare earth element ions as a solid-state laser medium, and emits laser light through optical excitation.

[Conventional technology]

As is well known, in solid-state laser devices, YA
G (YJfsO+x), G G G (GdsGa
sOtt) + G S G G (GdsGasOtt)
An optical crystal or glass base material containing transition metal ions such as CS' or rare earth element ions such as Nd'' as a laser active substance is used as a laser medium, and excitation light for this has conventionally been used as a laser medium. Light from an excitation light source such as a tungsten halogen lamp or krypton discharge lamp, or in some cases sunlight, is used.The shape of the laser medium is usually rod-shaped, but recently, so-called slab-shaped ones are also used for high output. As is well known, FIG. 5 shows the basic structure of a conventional solid-state laser device using rod-shaped YAG as a laser medium.

As shown in FIG. 5(a), a partial reflection mirror 2 and a total reflection mirror 3 are arranged opposite to each end face of a rod-shaped laser medium 1, and together with the laser medium 1, a laser resonant system is constructed.
The output of the laser beam LL is extracted from the partial reflecting mirror 2 side. The light source 4 for the excitation light EL is, for example, a krypton discharge lamp, and is disposed in a closed container 5 facing the laser medium 1, and the laser medium is heated by a cooling medium CM flowing into the closed container 5 through an inlet/outlet 5a. 1 and excitation light source 4 are strongly cooled. As shown in Figure (b), the closed container 5 has an elliptical cylinder shape with both ends closed, and its inner surface is mirror-finished, and the excitation light EL from the excitation light source 4 placed at one focal point of the ellipse is It is focused on the laser medium t1 located at the other focal point.

[To be solved by the invention &1IB] However, in general, in optically pumped solid-state lasers, only a small part of the excitation light EL given to the laser medium contributes to the excitation of the laser active substance or ions, and most of it contributes to the excitation of the laser active substance or ions. There is a problem that energy efficiency is very low because the energy is lost in the process. This will be explained with reference to FIG.

Figure 4 (al is Y with Nd'' as the laser active ion)
In the AG laser medium, this shows the correlation between the relative value of the efficiency η at which the pumping light contributes to the excitation of Nd'' and the wavelength λ of the pumping light.
It has high excitation efficiency in the wavelength range of 20n-. The same figure (b
) shows the wavelength characteristics of the emission intensity I of a krypton discharge lamp as an excitation light source, and as can be seen from the figure, it is very convenient that it has a high emission intensity in the wavelength range A mentioned above.
However, if the excitation light source is in a range other than this, especially in the short wavelength range B
However, while it has a considerable emission intensity, the excitation efficiency of the laser medium is extremely low in this wavelength range B, so
When viewed over the entire wavelength range, it is only 5% of the energy of the excitation light.
The laser contributes only to a limited extent to the excitation of active ions.

In this way, the efficiency of optical excitation is about 5%, and the remaining 9596
is all converted into heat within the laser medium, so solid-state lasers have a high density of active ions, which is due to the density of the laser medium. In reality, however, there is a problem in that it is not possible to operate at a sufficiently high output due to thermal constraints.

From the viewpoint of improving optical pumping efficiency, solid-state laser devices that use a semiconductor laser as a pumping light source have recently attracted attention. The oscillation wavelength can be adjusted by changing the wavelength, for example, Nd"
By adjusting the excitation efficiency to around 810n-, where the excitation efficiency peaks at .degree., the optical excitation efficiency can be greatly improved, and the problem of heat generation in the laser medium can be almost completely eliminated. However, as is well known, the maximum output per semiconductor laser is as low as IW, so even if you configure a pumping light source by using a large number of semiconductor lasers, you will only be able to obtain a solid-state laser output of several watts to several tens of watts. Although solid-state laser devices pumped by semiconductor lasers are suitable for low-output applications, the power of several hundred watts currently obtained with lamp pumping is
It is unlikely that it will reach high output levels.

An object of the present invention is to solve these problems and provide a solid-state laser device with high optical pumping efficiency and suitable for high output.

[Means to solve the problem]

According to the present invention, this purpose is achieved by absorbing irradiated light and emitting fluorescence at a wavelength suitable for optical excitation of laser active materials in a solid-state laser device that optically excites a laser active substance in a solid laser medium to emit laser light. This is achieved by providing a light conversion means made of a semiconductor, applying irradiation light to the light conversion means, and using the fluorescence emitted from the light conversion means as excitation light to optically excite the laser active substance in the laser medium.

The light conversion means referred to in the above configuration converts the irradiated light that it receives into fluorescence, and the semiconductor used therein is one that can easily adjust the wavelength of the fluorescence or the wavelength range ζ to the wavelength range where the light excitation efficiency of the laser active substance is high. is desirable, and in this sense it is 41. Using Ga and □As, the content of Al is
It is preferable that the wavelength of fluorescence can be adjusted by adjusting the wavelength of the fluorescence. In addition, in order to narrow the wavelength range of fluorescence as much as possible so that it can accurately match the peak of the optical excitation efficiency of the laser active material, it is desirable that the semiconductor has a direct transition type energy band structure, and AlGaAs has this type of energy band structure. In this respect, it is suitable as a semiconductor for the light conversion means in the present invention. When AlGaAs is used, the light conversion means may of course have a single layer structure, but in some cases, it may have a composite layer structure with a so-called double heterojunction structure.

As for the actual form of the light conversion means, it is preferable to form a semiconductor in the form of a thin layer or film, and to form the light conversion means in the form of a plate-like body sandwiched between a pair of transparent holding plates, for example, glass plates. It is suitable to configure and incorporate it into a solid-state laser device.

[Function] As is well known, semiconductors have an energy band structure consisting of a valence band with a low energy level and a conduction band above it, and when exposed to irradiation light, electrons in the valence band move to the conduction band. When the excited electrons transition or fall back into the valence band, they emit fluorescence with a wavelength λ determined by the energy gap Eg between the conduction band and the valence band. The wavelength of this fluorescence is expressed as λ-Eg/h c (1). However, h is a blank constant and C is the speed of light. Furthermore, this semiconductor hardly absorbs wavelength components longer than the wavelength λ in the above equation in the irradiation light it receives, but it absorbs wavelength components shorter than that very well.

The present invention utilizes this principle, and for example, to explain the emission intensity distribution of the light source shown in FIG. 4(b),
The wavelength λ of the fluorescence emitted by the light conversion means using the semiconductor described above
By aligning the wavelength component within the wavelength range A where the optical excitation efficiency of the laser active substance is high, the wavelength components within this range A of the irradiation light received by the light conversion means from this light source as well as the wavelength components within the shorter wavelength range B are included. By absorbing the wavelength component, converting it to fluorescence within wavelength range A, and applying it to the laser medium as excitation light, wavelength range B, which has not been used until now, can be generated.
The wavelength components within the wavelength range are effectively used for optical excitation of a laser active substance.

If we look at the energy band structure of the semiconductor described above in more detail in terms of the amount of interlocking electrons or the wave number vector, we can see that the valence band has an upwardly convex band shape, and the conduction band has a downwardly convex band shape, but they are not directly transitioned. A type of semiconductor has a band structure in which the top of the valence band and the bottom of the conduction band almost coincide. In this case, the electrons excited by the irradiation light from the valence band to conduction dispersion relax their momentum within a very short relaxation time and fall to the bottom of the conduction band, and from there they transition to the top of the valence band and fluoresce. to occur. In direct transition type semiconductors, there is almost no change in the amount of interlocking electrons during this transition, so
Indirect i! ! The quantum efficiency of fluorescence generation is high, almost 100%, compared to the shape transfer, and the wavelength range of the fluorescence is also narrow, so this has very advantageous advantages for the present invention.

By selecting the component ratio of At and Go, the aforementioned AIGαAs can generate fluorescence in a wavelength range where the optical excitation efficiency of the laser active substance is high, and has a direct transition type energy band structure within this component range. have.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
This figure corresponds to the previous FIG. 5 and illustrates the general configuration of a solid-state laser device according to the present invention, and corresponding parts are given the same reference numerals. In the following, explanations of parts that overlap with the previous ones will be omitted.

In the embodiment shown in FIG. 1, the laser medium 1 is a so-called slab-shaped plate suitable for a high-output solid-state laser device, and has a slightly flat rectangular cross section as seen from the cross section in FIG. 1(b). The material is, for example, Nd.
"Doped YAG is used. As mentioned above, this laser medium has a wavelength characteristic of optical excitation efficiency η shown in FIG. 4(a).
has.

In a solid-state laser device using such a slab-shaped laser medium 1, as shown in FIG. The laser beam travels in a zigzag pattern while being totally reflected by the pair of plate surfaces, thereby reducing the so-called thermal lens effect of the laser medium ft1. Furthermore, as shown in FIG.
b is applied to eliminate the temperature gradient in the left-right direction of the cross section and reduce the thermal lens effect by -N.

In order to apply excitation light EL to this slab-shaped laser medium 1 from the pair of plate surfaces, in this embodiment, light conversion means 1O according to the present invention are provided above and below, respectively, as shown in the figure. The converting means 10 is formed into a plate-like body in which a thin layer or film of AtGaAS is sandwiched between a pair of glass plates, and is fixed to the left and right side walls of the closed container 5 in FIG. 1(a) by appropriate means. In order to provide the irradiation light IR to the pair of light conversion means 10, in this example, irradiation light sources 6 are respectively disposed in the upper and lower parts of the closed container 5, and a cooling medium is passed through the closed container 5. Cooled by CM. As this irradiation light source 6, in addition to various high-output discharge lamps and incandescent lamps, sunlight can also be used as described above, but in this embodiment, the emission intensity I of the wavelength characteristic shown in Fig. 4 0)) can be used. Assume that a krypton discharge lamp with a distribution of is used.

Now, the laser medium 1 with the optical excitation efficiency η shown in FIG. 4(a)
For this reason, it is advantageous to use a light conversion means 10 that emits fluorescence with a wavelength within the range A shown in the figure, especially at a wavelength of 810 nm, where the maximum peak of the light excitation efficiency l occurs. The composition ratio of AI and Ga in the material is selected to match this. Now, if the component ratio of AI is X, then the energy gap I of A, Ga, and I1As semiconductors is I! , is expressed by the following formula.

8g-1,424+ 1.247x (eV)
(21 The energy gap Eg when the wavelength λ in equation (1) above is 81on- is 1.53 eV, so if this is inserted into equation (2) above, it becomes x-0,086, and this composition is By holding it, Nd”
AlG in a composition range that can cause the laser medium 10 to generate fluorescence with a wavelength that matches the maximum optical excitation efficiency of the laser medium 11 using doped YAG, and has a low component ratio of A1.
aAs is the aforementioned direct transition type semiconductor. However, the wavelength λ of the fluorescence emitted from this actually has some temperature dependence, but the degree is usually 0.3 nm/' (:
Therefore, in Fig. 4 (1100n of the width of the wavelength range of al
Compared to this, the range of change in fluorescence wavelength is sufficiently small and poses no practical problem.

In the solid-state laser device according to the present invention configured as described above, the semiconductor of the light conversion means 10 absorbs the wavelength components within the ranges A and B in FIG. 4(b) in the irradiation light IR from the irradiation light source 6. Then, the fluorescent light can be converted into fluorescence having a wavelength corresponding to the highest peak of the optical excitation efficiency η shown in FIG. 4(a), and can be applied to the laser medium ffl. The optical conversion means IO effectively utilizes the wavelength component in range B, which could not be used conventionally, and converts it into fluorescence of a wavelength corresponding to the highest optical excitation efficiency of the laser active substance, so that the optical excitation efficiency of the solid-state laser device is lower than that of the conventional one. In addition, unlike a conventional semiconductor laser, the light conversion means 10 has a role of converting the irradiation light IR into fluorescence as the excitation light EL, so it can excite with a large amount of energy. Light can be applied to the laser medium l, and therefore, the present invention can provide a high-output solid-state laser device.

FIG. 2 shows an example of the configuration of the light conversion means 10 using a single layer of semiconductor, and FIG.
The completed state is shown in partially enlarged cross-section. As shown in FIG. 2A, first, an AlGaAs layer 14 having the above-mentioned composition is grown on a GaAs substrate 11 to a thickness of, for example, 0.3 cm by, for example, a liquid phase epitaxial method.
After removing a portion of the As substrate 11 by polishing or etching, the shape is adjusted to a predetermined size, and as shown in FIG. The light conversion means 10 is constructed by arranging and sandwiching them between 110aO and 11OaO.

FIG. 3 shows a light conversion means 10 using a composite layer semiconductor having a double heterojunction structure in the same manner as FIG. 2. In FIG. As shown in the same figure (al), first an AlGaAs layer 12 having a composition of x-0.2 is grown thickly on the GaAs-based fill by liquid phase epitaxial method, and then x=0.2 is grown by vapor phase epitaxial method. AIGa with composition of 45
AsFfJ 13. AlG with a composition of x −0,08
aAs layer 14 and AlGaAs composition with an X ratio of 0.45
The layers 15 are grown one after another, and the total thickness of the AlGaAs layers 12 to 15 is about 0.3 mm, which is the same as before, and then the GaAs layers are grown.
Substrate 12 is removed as before.

Similarly to the case of FIG. 2, this composite semiconductor layer is sandwiched between a pair of transparent plates 10a and 10b to constitute the light conversion means IO.

The composite semiconductor layer configured as described above is a double heterojunction in which a heterojunction is formed between the AIGaAsq 14 which has been subjected to a hatchet lug and the AlGaAs layers 13 and 15 above and below which have different AI component ratios. ARGaAsN has a small energy gap structure, and when irradiation light is received from the side of the transparent plate 10a, excited electrons or carriers generated in the composite semiconductor layer by absorption of the light are
14, and the fluorescence emitted during the transition to the valence band is applied to the laser medium 1 as excitation light from, for example, the transparent plate tab side. This excited electron AlGaAs layer 14
The concentration can also be promoted by appropriately applying a potential difference between each layer in the composite semiconductor layer.

Although the quantum efficiency of the composite semiconductor layer in the embodiment shown in FIG. 3 is not necessarily as good as that in FIG.
Since the components can be managed as a container, it has advantages in manufacturing semiconductors for light conversion means.

As can be inferred from the embodiments described above, the present invention is not limited to these embodiments, and can be implemented in various embodiments.

(Effects of the Invention) As explained above, according to the present invention, in a solid-state laser device that optically excites a laser active substance in a solid laser medium to emit laser light, a wavelength suitable for optical excitation of the laser active substance by absorbing irradiation light is provided. A light conversion means made of a semiconductor that emits fluorescence is provided, and irradiation light is applied to this light conversion means, and the fluorescence emitted from the light conversion means is used as excitation light to optically excite the laser active substance in the laser medium. By making the semiconductor of the light conversion means absorb wavelength components that could hardly be absorbed due to the low optical excitation efficiency of the laser active material of the laser medium, and by matching the type and composition of this semiconductor to the laser active material, this can be achieved. The absorbed irradiation light can be converted into fluorescence having a wavelength with good optical excitation efficiency and can be applied to the laser medium as excitation light. By effectively utilizing the wavelength components of this irradiation light and improving the optical excitation efficiency of the laser active substance, solid-state The optical excitation efficiency of the laser device can be significantly improved compared to the conventional method.

Furthermore, since the entire surface of the light conversion means in the present invention serves to convert the irradiation light into fluorescence for optical excitation, excitation light with large energy can be applied to the laser medium from the light conversion means, and this excitation light can be applied to the laser medium. is efficiently used for optical excitation of the laser active substance, the heat generated by the excitation light in the laser medium can be significantly reduced compared to the conventional method, and the present invention provides a high-output solid-state laser device by combining these effects. This becomes possible through the implementation of

Furthermore, by using a direct transition type semiconductor for the light conversion means, the above-mentioned effects can be further enhanced.

[Brief explanation of the drawing]

1 to 4 relate to the present invention; FIG. 1 is a longitudinal and cross-sectional view of an embodiment of a solid-state laser device according to the invention, and FIGS. 2 and 3 are views of different embodiments of the light conversion means. FIG. 4, a partially enlarged sectional view, is a diagram illustrating the optical excitation efficiency of a laser active substance and the wavelength characteristics of the light intensity distribution of irradiated light. FIG. 5 is a longitudinal and cross-sectional view of a typical conventional solid-state laser device.
Closed container of solid-state laser device, 6: Irradiation light source, 10: Light conversion means, 10a, 10b: Transparent plate for light conversion means, 1
1: GaAs substrate, 12.13.15: AlG
aAs layer, 14] AlGa as semiconductor for light conversion means
As layer, BL: excitation light, ■: light intensity of irradiation light, ■R: irradiation light, LLj laser light, λ: wavelength, η: zero photoexcitation effect of laser active material Figure 1 Figure 2 '$3 Figure

Claims (1)

[Claims] In a solid-state laser device that optically excites a laser active material in a solid laser medium to emit laser light, a light conversion means made of a semiconductor that absorbs irradiated light and emits fluorescence at a wavelength suitable for optical excitation of the laser active material is provided to perform optical conversion. A solid-state laser device characterized in that a means is provided with irradiation light and fluorescence emitted from the means is used as excitation light to optically excite a laser active substance in a laser medium.