JP5681022B2 - Laser amplifier - Google Patents

Description

  The present invention relates to a laser amplification device that amplifies and outputs seed light.

  As a conventional laser amplifying apparatus, a seed light source that outputs seed light, an excitation light source that outputs excitation light, and seed light that is input in a state where excitation light is input amplify and output the seed light. What is provided with a laser medium is known (for example, refer patent document 1). For such a laser amplifying apparatus, there is a strong demand for higher output light (higher output) from the industry and the like to which lasers are applied.

Japanese Patent Application Laid-Open No. 2004-241531

  However, if the laser medium is increased in size and the energy of the excitation light is increased in order to increase the energy of the output light, parasitic oscillation is likely to occur in the laser medium. When this parasitic oscillation occurs, the energy stored in the laser medium is reduced, so that the seed light input to the laser medium cannot be efficiently amplified. Parasitic oscillation is a phenomenon that occurs when spontaneously emitted light generated in a laser medium by the input of excitation light is amplified in the laser medium by an unintentionally configured optical resonator.

  Accordingly, an object of the present invention is to provide a laser amplifying apparatus capable of efficiently amplifying seed light.

The laser amplifying apparatus of the present invention amplifies and outputs seed light by inputting seed light with a seed light source that outputs seed light, an excitation light source that outputs excitation light, and seed light in a state where excitation light is input A plurality of laser medium portions each having a solid laser medium to transmit, part of the spontaneous emission light generated in the solid laser medium when the seed light is transmitted and excitation light is input to the solid laser medium A plurality of first saturable absorbers, wherein the plurality of laser medium portions are disposed along the optical path of the seed light, and the plurality of first saturable absorbers are disposed along the optical path of the seed light. Thus , they are alternately arranged with at least one laser medium portion.

  In this laser amplifying device, when excitation light is input to the laser medium portion, spontaneous emission light is generated in the laser medium portion, but a part of the spontaneous emission light is absorbed by the first saturable absorber and becomes parasitic. Oscillation is suppressed. In this state, the excitation light continues to be input to the laser medium portion, so that energy of spontaneous emission light is accumulated in the laser medium portion. At this time, when seed light is input to the laser medium portion, the light transmittance of the first saturable absorber increases (compared to when no seed light is input). Therefore, the seed light is amplified by obtaining energy from the spontaneous emission light in the laser medium portion, and is transmitted to the outside through the first saturable absorber. As described above, in the laser medium portion, the occurrence of parasitic oscillation is suppressed and the energy of spontaneous emission light is increased. Therefore, according to this laser amplifier, the seed light can be efficiently amplified.

In laser amplifier of the present invention, the laser medium unit is more disposed along the optical path of the seed light, the first saturable absorber that has a plurality of alternately arranged at least one laser medium portion . According to this configuration, even if a plurality of laser medium portions are arranged along the optical path of the seed light, the first saturable absorber suppresses the occurrence of parasitic oscillation. It is possible to efficiently amplify and increase the energy of the output light.

The laser amplifying apparatus of the present invention further includes a second saturable absorber that transmits seed light and absorbs part of spontaneous emission light, and the second saturable absorber is in the optical path of the seed light. The laser medium portion may be provided so as to divide the laser medium portion into a plurality when viewed from the direction along the direction. According to this configuration, even if the laser medium portion is enlarged in the direction perpendicular to the optical path of the seed light, the second saturable absorber suppresses the occurrence of parasitic oscillation. Amplifying well, the energy of the output light can be increased.

The laser amplifying apparatus of the present invention further includes a third saturable absorber that transmits seed light and absorbs part of spontaneous emission light, and the third saturable absorber is disposed in the optical path of the seed light. It may be provided in the laser medium part so as to surround the outer edge of the laser medium part when viewed from the direction along. According to this configuration, even if the laser medium portion is enlarged in the direction perpendicular to the optical path of the seed light, the third saturable absorber suppresses the occurrence of parasitic oscillation. Amplifying well, the energy of the output light can be increased.

  According to the present invention, seed light can be efficiently amplified.

1 is a perspective view of a laser amplification device according to an embodiment of the present invention. It is sectional drawing of the optical amplification part of the laser amplification apparatus of FIG. It is a perspective view of the laser medium part of the laser amplifier of FIG. It is a graph which shows the relationship between the input energy and relative light transmittance in a saturable absorber. It is a conceptual diagram for demonstrating the principle of generation | occurrence | production of a parasitic oscillation, and the principle of the suppression. 2 is a graph showing the relationship between input energy and output energy and the relationship between input energy and energy extraction efficiency in the laser amplification device of FIG. 1. It is sectional drawing of the optical amplification part of the laser oscillation apparatus as a reference form.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same or an equivalent part, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 1, the laser amplification device 1 includes a seed light source 2, an excitation light source 3, and an optical amplification unit 10. The seed light source 2 is a solid laser oscillator, for example, and outputs seed light L1 that is a pulse wave. The pumping light source 3 is a semiconductor laser stack, for example, and outputs pumping light L2 that is a continuous wave or a pseudo continuous wave (pulse wave). The optical amplifying unit 10 amplifies the seed light L1 along the optical axis A, and outputs the amplified seed light L1 as output light L3. Here, the energy of the seed light L1 input to the optical amplification unit 10 is, for example, about 100 J, and the energy of the output light L3 output from the optical amplification unit 10 is, for example, about 1 kJ.

  The seed light source 2 is disposed on the optical axis A so as to face the optical amplification unit 10. The pumping light source 3 is off the optical axis A, and the input side of the seed light L1 (hereinafter simply referred to as “input side”) and the output side of the seed light L1 (hereinafter simply referred to as “input side”). (Referred to as “output side”). On the optical axis A, the wavelength selection mirror 4 is disposed on each of the input side and the output side of the optical amplification unit 10. The wavelength selective mirror 4 on the input side is located between the seed light source 2 and the optical amplifying unit 10.

  The seed light L1 output from the seed light source 2 passes through the wavelength selector mirror 4 on the input side, travels along the optical axis A, and is input to the optical amplification unit 10. The excitation light L 2 output from the input-side excitation light source 3 is reflected by the input-side wavelength selection mirror 4, travels along the optical axis A, and is input to the optical amplification unit 10. The excitation light L 2 output from the output-side excitation light source 3 is reflected by the output-side wavelength selection mirror 4, travels along the optical axis A, and is input to the optical amplification unit 10. The output light L3 output from the optical amplifying unit 10 passes through the output-side wavelength selection mirror 4, travels along the optical axis A, and is output to the outside.

  As illustrated in FIG. 2, the optical amplification unit 10 includes a laser medium unit 5 and a saturable absorber (first saturable absorber) 6. The laser medium unit 5 amplifies and outputs the seed light L1 when the seed light L1 is input in a state where the excitation light L2 is input. The saturable absorber 6 has a high light transmittance when the seed light L1 is input. That is, in the saturable absorber 6, the light transmittance when the seed light L1 is input is higher than the light transmittance when the seed light L1 is not input.

  A plurality of (here, 10) laser medium portions 5 are arranged along the optical axis A (that is, along the optical path of the seed light L1). Similarly, a plurality (four in this case) of saturable absorbers 6 are arranged along the optical axis A. The laser medium portion 5 and the saturable absorber 6 are formed in a rectangular plate shape, and are arranged so that the optical axis A passes through the center thereof. Here, one saturable absorber 6 is alternately arranged with a predetermined number (here, two) of laser medium portions 5. As described above, the saturable absorbers 6 are adjacent to the laser medium unit 5 along the optical axis A and are arranged in parallel.

  Each laser medium portion 5 is held by a holder 7, and each saturable absorber 6 is held by a holder 8. More specifically, the holder 7 is made of a material having high thermal conductivity and a mechanical buffering effect (for example, indium or the like) in a state where the input side and output side surfaces of the laser medium unit 5 are exposed. The outer edge of the laser medium portion 5 is held. Similarly, the holder 8 can be passed through a material having high thermal conductivity and a mechanical buffering effect (for example, indium or the like) with the input side and output side surfaces of the saturable absorber 6 exposed. The outer edge of the saturated absorber 6 is held. On the optical axis A, a light transmission window 11 that transmits the seed light L1, the excitation light L2, and the output light L3 is disposed so as to sandwich the laser medium portion 5 and the saturable absorber 6. The transmission window 11 is held by a holder 12. The holder 12 also has a light transmission window 11 through a material (for example, indium or the like) having a high thermal conductivity and a mechanical buffering effect in a state where the input side and output side surfaces of the light transmission window 11 are exposed. Holding the outer edge of.

  Each holder 7, 8, 12 is made of a material having high thermal conductivity (for example, copper or the like), and water, helium gas, fluorine-based material is provided in a gap between adjacent holders 7, 8, 12 in a housing (not shown). A refrigerant C, such as an inert liquid, is circulated. Thereby, the laser medium unit 5 and the saturable absorber 6 can be cooled during the operation of the laser amplifying apparatus 1. Each holder 7, 8, 12 is a rectangular plate whose thickness gradually decreases (that is, gradually decreases) from one side to the other side (from the lower side to the upper side in FIG. 1). It is formed in an airfoil shape, and the refrigerant C is circulated from one side to the other side. Thereby, the refrigerant | coolant C can be distribute | circulated smoothly.

  As shown in FIG. 3, the laser medium unit 5 includes a laser medium 13 and a saturable absorber 14. The laser medium 13 is a fixed laser medium such as Nd: YAG or titanium sapphire. For example, the same type as the solid laser medium of the seed light source 2 is used. The saturable absorber 14 has a high light transmittance when the seed light L1 is input. That is, in the saturable absorber 14, the light transmittance when the seed light L1 is input is higher than the light transmittance when the seed light L1 is not input.

  A plurality of laser media 13 are arranged in a matrix (here, 5 rows and 5 columns), and each laser medium 13 is formed in a rectangular plate shape (for example, an outer shape of 3 cm × 3 cm and a thickness of 1 cm). The saturable absorber 14 includes a saturable absorber (second saturable absorber) 14a and a saturable absorber (third saturable absorber) 14b. The saturable absorber 14 a is arranged in a lattice shape along the gap between the adjacent laser media 13. The saturable absorber 14b is disposed in a rectangular ring shape along the outer edge of the aggregate of all the laser media 13.

  That is, the saturable absorber 14a is provided in the laser medium unit 5 so as to divide the laser medium unit 5 into a plurality of parts when viewed from the optical axis A direction (that is, the direction along the optical path of the seed light L1). . The saturable absorber 14b is provided in the laser medium unit 5 so as to surround the outer edge of the laser medium unit 5 when viewed from the optical axis A direction. In each laser medium unit 5, the laser medium 13 and the saturable absorber 14 are integrated by an optical adhesive, an optical contact, or the like.

The saturable absorbers 6 and 14 described above will be described in more detail. In general, in a saturable absorber, the light transmittance greatly changes with respect to input energy (that is, energy of input light). In the saturable absorber shown in FIG. 4, when the input energy is changed from 1 mJ to 1 μJ, the light transmittance is reduced by two orders of magnitude. Usually, in a laser amplification apparatus, seed light is input at a fluence of several J / cm ² to perform optical amplification. At this time, the flux of spontaneous emission light generated in the laser medium is assumed to be nJ to μJ level.

  Here, since the flux of spontaneously emitted light generated in the laser medium is lower than the saturated fluence of the saturable absorber, the light transmittance of the saturable absorber with respect to the spontaneously emitted light is as low as 1%, for example. On the other hand, since the fluence of the seed light input to the laser medium is higher than the saturation fluence of the saturable absorber, the transmittance of the saturable absorber with respect to the seed light is as high as 99%, for example.

  Therefore, the saturable absorbers 6 and 14 described above absorb the spontaneous emission light generated in the laser medium 13 while propagating the seed light L1 input to the laser medium unit 5 with low loss. be able to. In addition, as a material of the saturable absorbers 6 and 14, a glass filter (BG850, RG1000, etc.), Cr: YAG, a semiconductor saturable absorber, a carbon nanotube, a nonlinear optical material, etc. can be used. The light transmittance characteristics of the saturable absorbers 6 and 14 can be adjusted by the thickness of the saturable absorbers 6 and 14 and the concentration of impurities added.

  As described above, in the laser amplifying apparatus 1, a plurality of laser medium parts 5 are arranged along the optical path of the seed light L 1, and a plurality of saturable absorbers 6 are arranged alternately with a predetermined number of laser medium parts 5. Has been. Further, each laser medium portion 5 is provided with a saturable absorber 14a so as to divide the laser medium portion 5 into a plurality of parts when viewed from the direction along the optical path of the seed light L1, and is viewed from the direction. In this case, a saturable absorber 14b is provided so as to surround the outer edge of the laser medium portion 5. Thereby, when the excitation light L2 that is a continuous wave or a pseudo continuous wave (pulse wave) is input to each laser medium unit 5, spontaneous emission light is generated in the laser medium 13 of each laser medium unit 5, Part of spontaneously emitted light is absorbed by the saturable absorbers 6 and 14, and the occurrence of parasitic oscillation is suppressed. In this state, since the excitation light L2 is continuously input to each laser medium unit 5, the energy of spontaneous emission light increases (that is, accumulates) in each laser medium unit 5. At this time, when the seed light L1 which is a pulse wave is input to each laser medium unit 5, the light transmittance of the saturable absorbers 6 and 14 increases rapidly. Therefore, the seed light L1 is amplified by obtaining energy from spontaneously emitted light in each laser medium unit 5, and is transmitted to the outside through the saturable absorbers 6 and 14. As described above, in the laser amplifying apparatus 1, even if a plurality of laser medium portions 5 are arranged along the optical path of the seed light L1, each laser medium portion 5 is further enlarged in a direction perpendicular to the optical path of the seed light L1. However, in each laser medium portion 5, the occurrence of parasitic oscillation is suppressed, and the energy of spontaneous emission light increases. Therefore, according to the laser amplifying apparatus 1, it is possible to efficiently amplify the seed light L1 in each laser medium unit 5 and increase the energy of the output light L3.

  FIG. 5 is a conceptual diagram for explaining the principle of occurrence of parasitic oscillation and the principle of suppression thereof. As shown in FIG. 5A, in the case where the optical amplifying unit is composed only of the laser medium 13, the laser medium 13 is enlarged and the energy of the pumping light L2 is realized in order to realize high output light energy. The higher the is, the easier the parasitic oscillation L10 occurs. That is, the spontaneous emission light L0 generated in the laser medium 13 by the input of the excitation light L2 is amplified in the laser medium 13 by the optical resonator configured unintentionally, and the parasitic oscillation L10 occurs. When the parasitic oscillation L10 occurs, the stored energy in the laser medium 13 decreases, so that the seed light input to the laser medium 13 cannot be amplified efficiently.

  On the other hand, as shown in FIG. 5B, in the optical amplifying unit 10, the laser medium 13 is divided into a plurality in the direction along the optical path of the seed light L1, and the saturable absorber is interposed between the adjacent laser media 13. 6 is disposed, the spontaneous emission light L0 is generated in the laser medium 13 by the input of the excitation light L2, but a part of the spontaneous emission light L0 is absorbed by the saturable absorber 6 to cause parasitic oscillation. Occurrence is suppressed. Then, since the seed light L1 is input to the laser medium 13 in which energy loss due to parasitic oscillation is suppressed, the energy accumulated in the laser medium 13 is extracted to efficiently amplify the seed light L1 as output light L3. Can be output.

  Here, when the saturable absorbers 6 and 14 are provided (that is, in the case of the laser amplification apparatus 1), and when the saturable absorbers 6 and 14 are not provided, the laser amplification calculation is performed. went. In designing a high energy Ghee laser, when considering the presence or absence of parasitic oscillation, a parameter g01 is used, and parasitic oscillation occurs when g01 is 3 or more.

  First, in the rectangular plate-like (outside 3 cm × 3 cm, thickness 1 cm) laser medium 13 arranged in 25 rows and 5 columns, when the saturable absorber 14 is not provided, g01 is 11.7. As a result, parasitic oscillation occurs. On the other hand, when saturable absorber 14 is provided in a rectangular plate-like (outer shape 3 cm × 3 cm, thickness 1 cm) laser medium 13 arranged in 5 rows and 5 columns, g01 is 2 .8, and the occurrence of parasitic oscillation can be suppressed.

  Next, in the laser medium section 5 arranged along the optical path of the seed light L1, when the saturable absorber 6 is not provided, g01 in the optical axis A direction becomes 7.8, and parasitic oscillation Will happen. On the other hand, when the saturable absorber 6 is provided alternately with the two laser medium portions 5 in the laser medium portions 5 arranged along the optical path of the seed light L1, the optical axis A The direction g01 is 1.7, and the occurrence of parasitic oscillation can be suppressed. FIG. 6 shows the relationship between the input energy and the output energy and the relationship between the input energy and the energy extraction efficiency when the saturable absorbers 6 and 14 are provided (that is, in the case of the laser amplification device 1). It is a graph.

  Generally, it is not practical to dispose a light absorber on the optical path of the seed light L1 because the energy of the seed light L1 is lost. However, by using a saturable absorber, the light transmittance varies depending on the intensity (energy) even at the same wavelength, and thus the above-described configuration can be realized.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, the saturable absorber 6 is not limited to a case where a plurality of saturable absorbers 6 are alternately arranged with a plurality of laser medium units 5, and a plurality of saturable absorbers 6 may be alternately arranged with one laser medium unit 5. Further, the number of saturable absorbers 6 is not limited to a plurality, and one saturable absorber 6 may be provided as long as the saturable absorbers 6 are arranged in parallel with the laser medium unit 5 along the optical path of the seed light L1.

  Further, the saturable absorber 14a may not be arranged in a lattice form as long as the laser medium portion 5 is divided into a plurality of parts when viewed from the direction along the optical path of the seed light L1. In addition, the saturable absorber 14b may not be arranged in a rectangular ring shape as long as it surrounds the outer edge of the laser medium portion 5 when viewed from the direction along the optical path of the seed light L1. Furthermore, even if a cladding material is applied in place of the saturable absorber 14, it is effective in suppressing the occurrence of parasitic oscillation. Here, the cladding material is a material having a characteristic of absorbing the accumulated light in the laser medium 13 having the same wavelength as the seed light L1 (however, the saturable absorber 6 is also essential in this case). .

  Finally, a laser oscillation apparatus as a reference form will be described. As shown in FIG. 7, the configuration of the optical amplification unit 100 of this laser oscillation device is that a wavelength selective total reflection mirror 15 and a wavelength selective output coupling mirror 16 are used instead of the light transmission window 11. This is different from the configuration of the optical amplification unit 10 of the laser amplification device 1 described above. That is, the wavelength selective total reflection mirror 15 transmits the excitation light L2 and totally reflects the oscillated light (emitted light). The wavelength selective output coupling mirror 16 transmits the excitation light L2 and transmits the oscillated light (emitted light) with a transmittance suitable for laser oscillation.

  In the optical amplifying unit 100 configured as described above, when the excitation light L <b> 2 that is a continuous wave is input to each laser medium unit 5, spontaneous emission light is generated in the laser medium 13 of each laser medium unit 5. At this time, a part of spontaneous emission light is absorbed by the saturable absorbers 6 and 14, and the occurrence of parasitic oscillation is suppressed. In this state, since the excitation light L2 is continuously input to each laser medium unit 5, the energy of spontaneous emission light increases (that is, accumulates) in each laser medium unit 5. When the flux of spontaneously emitted light exceeds the saturation fluence of the saturable absorbers 6 and 14, the emitted light is transmitted through the saturable absorbers 6 and 14 and stimulated emission occurs, and the mirrors 15 and 16 are irradiated with light. As a result, the output light L3, which is a pulse wave with a high peak intensity, is output from the wavelength selective output coupling mirror 16 to the outside. Such an optical amplifying unit 100 can also be applied to a general Q-switch pulse oscillator using an active optical switch using an electro-optic effect or an acousto-optic effect.

  DESCRIPTION OF SYMBOLS 1 ... Laser amplifier, 2 ... Seed light source, 3 ... Excitation light source, 5 ... Laser medium part, 6 ... Saturable absorber (1st saturable absorber), 14a ... Saturable absorber (2nd saturable absorber) Absorber), 14b ... saturable absorber (third saturable absorber), L1 ... seed light, L2 ... excitation light.

Claims (4)

A seed light source that outputs seed light;
An excitation light source that outputs excitation light;
A plurality of laser medium units each having a solid-state laser medium that amplifies and outputs the seed light when the seed light is input in a state where the excitation light is input;
A plurality of first saturable absorbers that transmit the seed light and absorb part of spontaneously emitted light generated in the solid-state laser medium when the excitation light is input to the solid-state laser medium ; With
The plurality of laser medium portions are arranged along the optical path of the seed light,
A plurality of the first saturable absorbers are arranged alternately with at least one of the laser medium portions along the optical path of the seed light. A second saturable absorber that transmits the seed light and absorbs part of the spontaneously emitted light ;
The second saturable absorber is provided in the laser medium part so as to divide the laser medium part into a plurality of parts when viewed from a direction along the optical path of the seed light. 1 Symbol placement laser amplifier of the. A third saturable absorber that transmits the seed light and absorbs part of the spontaneous emission light ;
The third saturable absorber is provided in the laser medium portion so as to surround an outer edge of the laser medium portion when viewed from a direction along an optical path of the seed light. 3. The laser amplification device according to 1 or 2 . A seed light source that outputs seed light;
An excitation light source that outputs excitation light;
A plurality of laser medium units each having a solid-state laser medium that amplifies and outputs the seed light when the seed light is input in a state where the excitation light is input;
A first saturable absorber that transmits the seed light and absorbs part of spontaneously emitted light generated in the solid-state laser medium when the excitation light is input to the solid-state laser medium; Prepared,
The plurality of laser medium portions are arranged along the optical path of the seed light,
The laser amplifying apparatus, wherein the first saturable absorber is disposed between the adjacent laser medium portions along the optical path of the seed light.

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