JP2007227448A - Regenerative amplifier, mode lock laser, and gain smoothing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a regenerative amplifier, or the like capable of obtaining a flat, total gain, and hence obtaining ultra-short pulsed light having high energy and large peak power. <P>SOLUTION: The regenerative amplifier for composing a resonator by two reflectors 3, 4 arranged so that they oppose optically comprises: two solid laser media 21, 22 that are arranged on the light axis of the resonator between the two reflectors 3, 4, generate a gain, and amplify incident light; a polarizer 5 arranged on the light axis of the resonator between the reflector 3 and the solid laser medium 21; and a polarizing switch 8 that is arranged on the light axis in the resonator between the reflector 3 and the polarizer 5 and controls a polarization direction by applying voltage. Light entering from the polarizer 5 is amplified with the flat amplification gain that depends on wavelengths obtained by combining amplification gains having different peak wavelengths generated from the solid laser media 21, 22 each. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a regenerative amplifier, a mode-locked laser, and a gain smoothing method for obtaining a high-peak, short-pulse laser beam in a processing laser apparatus or a measuring apparatus using a laser.

  There is a regenerative amplifier as means for amplifying laser light having a small pulse energy. The regenerative amplifier can amplify a laser beam with a small energy by passing it through a laser medium a plurality of times and extract it as a laser beam with a large energy. The regenerative amplifier is generally composed of a resonator composed of at least two reflecting mirrors, and a laser medium, a polarizer, and a polarization switch arranged in the resonator. The laser beam having a small energy incident on the resonator is rotated in the polarization direction by the polarization switch and confined in the resonator. Since the confined laser beam reciprocates a plurality of times in the resonator, the laser beam passes through the laser medium a plurality of times and the energy is amplified. When it becomes sufficiently large, the polarization direction is rotated again by the polarization switch, so that a laser beam with a large energy is extracted from the polarizer.

  In the regenerative amplifier, even when the gain of the laser medium is small and the amplification factor when the laser light passes through the laser medium once is small, the laser light passes through the laser medium a plurality of times. It can be extracted from the laser medium, and as a result, a laser beam with large energy can be obtained.

  One of the points to be noted in the amplifier is amplification of spontaneous emission light (ASE: Amplified Spontaneous Emission) from the laser medium. ASE is more likely to occur as the gain of the laser medium is higher. In a regenerative amplifier, the ASE is more likely to occur as the number of turns is larger and the amplification factor is larger. ASE is unintentional amplification of light, and the energy stored in the laser medium is extracted by the generation of ASE, so that there is a problem that the amplification output of the laser light is reduced.

  As a solution to such a problem, there is a conventional regenerative amplifier (see, for example, Patent Document 1). In the conventional regenerative amplifier, a saturable absorber is disposed in the resonator of the amplifier. The saturable absorber absorbs light output when small energy is incident and becomes a loss source. When the energy exceeds a certain level, the saturable absorber becomes transparent and has a low loss. For this reason, the weak spontaneous emission light emitted from the laser medium is absorbed by the saturable absorber, so that it does not reciprocate within the resonator and is not amplified one after another. On the other hand, by making the incident energy of the laser light equal to or greater than the threshold value at which the saturable absorber becomes transparent, it is possible to reciprocate in the resonator and extract large energy from the laser medium. For this reason, even when the number of regenerative amplifiers is set to a large number of times and the amplification factor is increased, ASE is not generated, and a laser beam with large energy can be obtained.

Japanese Patent Laid-Open No. 7-94816

  However, in the conventional regenerative amplifier, as the number of rotations increases, the wavelength band of the amplified laser light is more narrowed, and the wavelength band of the output light is narrower than the incident light to the regenerative amplifier. For this reason, there is a problem that the time width of the pulse becomes long and the peak output of the pulse decreases.

  The laser medium is excited to generate a gain having a peak wavelength and a gain band according to the type of the active medium and the host material. Laser light is amplified in accordance with the gain. A high gain is obtained at a peak wavelength with a high gain, and a small gain is obtained at a wavelength with a low gain. In a regenerative amplifier, the peak wavelength that provides high amplification in a single cycle will result in higher amplification in the next cycle. Will be very big. For this reason, the wavelength width is narrowed and the wavelength band is narrowed. Such narrowing of the wavelength band becomes stronger as the number of regenerative amplifiers is increased.

  If the solid-state laser medium is, for example, Ti: Sapphire, the second harmonic of the solid-state laser is required for excitation, so the system is large and complex, but the gain is high, so high-efficiency energy extraction The number of rounds until saturation amplification is performed is relatively small. For this reason, the influence of narrowing of the wavelength band of output light is small. On the other hand, when the active medium is a Yb-based solid-state laser medium, direct excitation by a semiconductor laser is possible, so the system can be made compact and simple. However, since the gain is small, highly efficient energy extraction and In order to perform saturation amplification, a larger number of circulations is required. For this reason, in the regenerative amplifier using the Yb solid-state laser medium, the wavelength band of the output light is more narrowed.

  FIG. 8 shows an example of a calculation result of the frequency dependence of the output light wavelength when a regenerative amplifier is configured using, for example, Yb: KYW as a solid-state laser medium. When the number of turns increases, the wavelength band becomes narrower, and when the wavelength width of incident light is 17 nm, for example, the wavelength width is 15.3 nm in one turn, 8.0 nm in 10 turns, and 3.0 nm in 100 turns. It is narrowed.

  Since the time width and the wavelength bandwidth of the laser light are in a Fourier transform relationship, the laser light with a wide wavelength band becomes a pulse light with a short time, and the laser light with a narrow wavelength band becomes a pulse light with a long time. . Accordingly, the output light whose wavelength band is narrowed by the regenerative amplifier becomes a pulse light that is long in time, and there is a problem that the peak output becomes low.

  The present invention has been made to solve the above-described problems, and its purpose is to obtain a flat total gain, to suppress narrowing of the wavelength band due to many rounds, and to have a wide wavelength width. Reproducing amplifier, mode-locked laser, and gain smoothing capable of obtaining ultrashort pulsed light with high energy and high peak power. Get the method.

  The regenerative amplifier according to the present invention is a regenerative amplifier that constitutes a resonator from first and second reflecting mirrors that are optically opposed to each other, and is arranged between the first and second reflecting mirrors. The first and second solid-state laser media disposed on the optical axis of the resonator, generating gain and amplifying incident light, and the first reflector and the first solid-state laser medium A polarizer disposed on the optical axis of the resonator, and a polarization switch disposed on the optical axis of the resonator between the first reflecting mirror and the polarizer and controlling a polarization direction by applying a voltage; And the light incident from the polarizer is amplified by a flat amplification gain having a wavelength dependency obtained by combining amplification gains having different peak wavelengths generated by the first and second solid-state laser media.

  In the regenerative amplifier according to the present invention, a flat total gain is obtained, narrowing of the wavelength band due to many rounds is suppressed, and output light with a wide wavelength width is obtained. There is an effect that pulsed light is obtained, ultrashort pulsed light having high energy and high peak power can be obtained.

Embodiment 1 FIG.
A regenerative amplifier according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a diagram showing a configuration of a regenerative amplifier according to Embodiment 1 of the present invention. In the following, in each figure, the same reference numerals indicate the same or corresponding parts.

  In FIG. 1, a regenerative amplifier 1 according to the first embodiment includes a reflecting mirror (first reflecting mirror) 3 and a reflecting mirror (second reflecting mirror) 4 that are optically opposed to each other. A polarization switch 8, a polarizer 5, a solid-state laser medium (first solid-state laser medium) 21, and a solid-state laser medium (second solid-state laser medium) 22 on the same axis as the resonator and in the resonator. And are provided.

  The polarization switch 8 is disposed on the optical axis of the resonator between the reflecting mirror 3 and the polarizer 5 and includes, for example, a polarization rotating means 6 and a quarter wavelength plate 7. Incident light 31 enters the resonator from the polarizer 5. The circulating light 32 circulates in the resonator. The output light 33 is extracted from the polarizer 5.

  The reflecting mirror 3 and the reflecting mirror 4 are reflecting mirrors that are totally reflected in the wavelength band of the incident light 31 and the gain bands of the solid-state laser medium 21 and the solid-state laser medium 22. As the reflecting mirror, for example, a dielectric film is laminated on an optical material. The reflecting mirror 3 and the reflecting mirror 4 are optically opposed to each other and constitute a resonator. The reflecting mirror 3 and the reflecting mirror 4 may be curved or flat so as to constitute the resonance mode, and an optical component such as a lens or a curvature mirror is arranged between the reflecting mirror 3 and the reflecting mirror 4 to set the resonance mode. It may be formed.

  The polarization rotation means 6 uses, for example, a Pockels cell that rotates polarized light when a voltage is applied. The quarter-wave plate 7 is an element that rotates polarized light of light passing therethrough, and is rotated to circularly polarized light by a single path of linearly polarized light, and rotated to linearly polarized light that is 90 ° orthogonal to incident light by a reciprocating path. is there.

  The polarizer 5 transmits or reflects depending on the polarization direction, and has a characteristic of transmitting polarized light parallel to the paper surface of FIG. 1 and reflecting vertical polarized light to the paper surface.

  The solid laser medium 21 and the solid laser medium 22 are obtained by adding an active medium to a host material. The host material may be composed of crystal, ceramic, glass, or the like, and the active medium may be a material with a wide gain band such as Yb. For example, Yb: YAG, Yb: KYW, Yb: KGW, Yb: Glass, Yb: YAB, Yb: YCOB, Yb: GdCOB, Yb: LnCOB, Yb: S-FAP can be used.

  Next, the operation of the regenerative amplifier according to the first embodiment will be described with reference to the drawings. FIG. 2 is a diagram showing an example of the wavelength dependence of the amplification gain of the solid-state laser medium of the regenerative amplifier according to Embodiment 1 of the present invention.

  The incident light 31 is a short pulse light polarized in parallel to the paper surface of FIG. For this reason, the incident light 31 passes through the polarizer 5 and is introduced into the resonator. The short pulse light may be chirped pulse light that is extended in time, or may be ultrashort pulse light that is not extended. Ultra-short pulse light has a high peak power even with a small energy because of its short time width. For this reason, when an ultrashort pulse light is amplified, optical components in the amplifier may be damaged at a high peak power before reaching a predetermined energy, and there is a problem that amplified light with high output energy cannot be obtained. is there. For this reason, a method is known in which ultrashort pulse light is extended in time to amplify chirped pulse light with reduced peak power. A high-energy ultrashort pulsed light can be obtained by amplifying chirped pulsed light with a low peak power to a predetermined energy, taking it out as output light, and compressing it temporally with a compressor.

  Incident light 31 incident on the resonator from the polarizer 5 is reflected by the reflecting mirror 3 and passes back and forth between the polarization rotating means 6 and the quarter wavelength plate 7. At this time, the polarization rotation means 6 has no voltage applied, and there is no polarization rotation. On the other hand, in order to pass back and forth through the quarter-wave plate 7, the polarization direction during the reciprocating pass is rotated by 90 °. Therefore, the incident light 31 that has passed through the polarizer 5 and entered the resonator is reflected by the reflecting mirror 3, and when returning to the reflecting mirror 3, the polarization direction is rotated by 90 °, and the vertical direction of FIG. Since it becomes polarized light in the direction, it is reflected by the polarizer 5.

  The light reflected by the polarizer 5 passes through the solid laser medium 21 and the solid laser medium 22 to amplify the light output. Although FIG. 1 shows a configuration in which the back surfaces of the solid-state laser media 21 and 22 are reflective surfaces, a configuration in which light is transmitted may be used. Further, although the configuration using two solid-state laser media 21 and 22 has been shown, the number of the laser media can be used without any limitation.

  The light that has passed through the solid-state laser media 21 and 22 is reflected by the reflecting mirror 4 that is disposed optically facing the reflecting mirror 3, passes through the solid-state laser media 21 and 22 again, and the light output is amplified. Further, the amplified light is reflected by the polarizer 5 again.

  In this way, while the incident light 31 reciprocates once in the resonator, a voltage is applied to the polarization rotation means 6, and the polarization rotation means 6 is ¼ wavelength for single pass and ½ wavelength for reciprocation. Set to rotate. For this reason, the second round of light undergoes 90 ° polarization rotation in the reciprocating passage of the polarization rotating means 6 and 90 ° in the reciprocating passage of the quarter wavelength plate 7, and the polarization direction is rotated by 180 ° in total. When the polarization rotation is 180 °, the polarization in the vertical direction in FIG. 1 becomes the vertical direction again, so that there is no substantial polarization rotation, and the second round of light is reflected by the polarizer 5. The light reflected from the polarizer 5 is amplified by the solid-state laser media 21 and 22 and reflected by the reflecting mirror 4, returns to the polarizer 5 again, is reflected, and takes the third optical path.

  In this way, the incident light 31 incident from the polarizer 5 is confined in the resonator between the reflecting mirror 3 and the reflecting mirror 4 while the polarization rotating means 6 is applied with a voltage to rotate the polarized light. And becomes the circulating light 32. The circling light 32 overlaps the circling light and is amplified every time it passes through the solid-state laser mediums 21 and 22, extracts energy from the solid-state laser media 21 and 22, and becomes high-energy laser light.

  When the laser beam has a large energy, the rotation of the polarization is eliminated by dropping the applied voltage of the polarization rotation means 6. For this reason, the 90 ° polarization rotation caused by the reciprocating passage of the quarter wavelength plate 7 results in the polarization in the horizontal direction of FIG. 1, so that it can pass through the polarizer 5 and take out the output light 33 as the output of the regenerative amplifier 1. .

  The solid-state laser medium 21 and the solid-state laser medium 22 disposed in the resonator may be solid-state laser media having anisotropy. In an anisotropic solid-state laser medium, the peak wavelength and wavelength band of gain may be different for each crystal axis or optical axis of the solid-state laser medium. For example, as shown in FIG. 2, in the a-axis direction of Yb: KYW, the gain peak wavelength is 1025 nm and the gain width (full width at half maximum) is 21 nm, and in the b-axis direction, the gain peak wavelength is 1039 nm and the gain width (half value). Zenpuku) 24nm.

  The crystal axes or optical axes of the solid laser medium 21 and the solid laser medium 22 are arranged in different directions. For example, the optical axis parallel to the polarization direction of the circulating light 32 parallel to the vertical direction of FIG. 1 is the a-axis in the solid-state laser medium 21 and the b-axis in the solid-state laser medium 22. By arranging in this way, the total gain of the solid-state laser medium 21 and the solid-state laser medium 22 having different gain peak wavelengths can be obtained. Since the gain is a combination of gains having different peak wavelengths, the flatness of the gain is high and a wider gain band can be obtained. Since the magnitude of each gain can be adjusted by the concentration of the active medium to be added, the magnitude of the excitation rate, the number of solid-state laser media, etc., the gain between the respective peak wavelengths can be made flat.

  For example, in FIG. 2, a substantially flat gain is obtained from 1025 nm to 1039 nm as the combined gain of Yb: KYW a-axis and b-axis, and a wider bandwidth is obtained with a gain width (full width at half maximum) of 32 nm. With this configuration, a flat and wide gain can be obtained.

  The narrowing of the wavelength band of the amplified light generated by making many rounds in the resonator occurs because the wavelength having a large gain is more strongly amplified. On the other hand, according to the first embodiment, since a flat and wide gain is obtained, narrowing of the wavelength band due to many rounds is suppressed, and output light 33 having a wide wavelength band is obtained.

  As described above, since the anisotropic solid-state laser media 21 and 22 having different axial directions are arranged in the regenerative amplifier 1, a flat total gain is obtained, and the narrowing of the wavelength band due to many rounds is suppressed. As a result, output light 33 having a wide wavelength width is obtained. For this reason, there are features such that ultrashort pulse light with a short time can be obtained, ultrashort pulse light with high energy and high peak power can be obtained.

  As the solid-state laser mediums 21 and 22 arranged in the regenerative amplifier 1 according to the first embodiment, an isotropic solid-state laser medium may be used in addition to the anisotropic solid-state laser medium. Further, both an isotropic medium and an anisotropic medium may be used.

  In an isotropic solid laser medium, there is no difference in gain peak wavelength or gain band depending on the axial direction. However, the total gain can be flattened by using different materials having different peak wavelengths for the solid-state laser medium 21 and the solid-state laser medium 22. For example, the solid laser medium 21 is Yb: YAG having a gain peak wavelength of 1030 nm, and the solid laser medium 22 is Yb: KYW b-axis having a gain peak wavelength of 1039 nm. Since the magnitude of each gain can be adjusted by the concentration of the active medium to be added, the magnitude of the excitation rate, the number of solid-state laser media, etc., the gain between the respective peak wavelengths can be made flat.

  In this way, since a plurality of different solid-state laser media are arranged in the regenerative amplifier 1, a flat total gain is obtained, narrowing of the wavelength band due to many rounds is suppressed, and output light with a wide wavelength width is obtained. 33 is obtained. For this reason, there are features such that ultrashort pulse light with a short time can be obtained, ultrashort pulse light with high energy and high peak power can be obtained.

  In FIG. 1, the configuration in which the incident light 31 is introduced into the resonator by passing through the polarizer 5 is shown. However, the polarization direction of the incident light 31 is set to the vertical direction in FIG. Thus, the configuration may be such that the incident light 31 is introduced into the resonator. In the case of this configuration, the same rotation and amplification are possible by taking the optical axis of the resonator in the direction in which the polarizer 5 passes.

  The polarization rotation means 6 has been described with respect to the case where the polarized light rotates when voltage is applied and the polarized light does not rotate when there is no voltage applied. However, the polarization rotation means 6 does not rotate when the voltage is applied and rotates when the voltage is not applied. Also good.

  The polarization switch 8 has been described with respect to the example constituted by the polarization rotation means 6 set so as to rotate 1/4 wavelength in a single pass and 1/2 wavelength in a reciprocating pass, and the 1/4 wavelength plate 7. Other configurations for operation may be used. For example, the polarization switch 8 may be a polarization rotation unit that is set to rotate by a quarter wavelength by a single pass and by a half wavelength by a round trip by applying a voltage. In this case, an operation similar to the above operation can be obtained by reversing whether or not voltage is applied.

Embodiment 2. FIG.
A regenerative amplifier according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing a configuration of a regenerative amplifier according to Embodiment 2 of the present invention. Note that portions that are not particularly described are the same as those in the first embodiment.

  In FIG. 3, in the regenerative amplifier 1 according to the second embodiment, a plurality of anisotropic solid-state laser media 23 and 24 are arranged in the resonator. At this time, the crystal axes or the optical axes of the solid-state laser media 23 and 24 have the same orientation. A half-wave plate 10 is disposed between the solid-state laser media 23 and 24 on the optical axis of the resonator.

  The incident light 31 that has passed through the polarizer 5 and entered the resonator is reflected by the reflecting mirror 3 and reciprocally passes through the polarization rotating means 6 and the quarter-wave plate 7 to rotate the polarization direction. The direction of polarization reflected in FIG. The light reflected by the polarizer 5 passes through the solid-state laser medium 23 and the light output is amplified. Next, the light passes through the half-wave plate 10, the polarization direction is rotated by 90 °, becomes polarized light in a direction parallel to the plane of FIG. 3, and passes through the solid-state laser medium 24. Further, the light is reflected by the reflecting mirror 4, amplified while passing through the solid laser medium 24 again, and again through the half-wave plate 10, the polarization direction is rotated by 90 °, and the change in the vertical direction in FIG. Become. Further, the light amplified again after passing through the solid-state laser medium 23 is reflected again by the polarizer 5 and makes one round trip. Thereafter, the incident light 31 reciprocated once by the polarization rotation of the polarization rotating means 6 is confined in the resonator to become the circulating light 32, and is amplified one after another, and finally a large amount of energy is solidified. Extracted from the laser media 23 and 24, the output light 33 is obtained.

  As described above, since the half-wave plate 10 is disposed between the solid-state laser medium 23 and the solid-state laser medium 24 and the polarization direction of the circulating light 32 is rotated, the solid-state laser medium 23 and the solid-state laser medium 24 are configured. Even when the crystal axes or the optical axes are arranged in the same direction, the gain peak wavelength and the gain band received by the circulating light 32 in the solid laser medium 23 and the solid laser medium 24 are different from each other. For this reason, since the total gain received when the resonator is circulated once can be flattened, the narrowing of the wavelength band that occurs when the resonator is circulated many times is suppressed, and the broadband output light 33 is reduced. Obtainable. For this reason, there are features such that ultrashort pulse light with a short time can be obtained, ultrashort pulse light with high energy and high peak power can be obtained. Further, since the plurality of solid-state laser media 23 and 24 used in this configuration are made of the same material and can be installed in the same axial direction, it is possible to manufacture an excitation module that excites the solid-state laser media 23 and 24 and gives gain. There is a feature that a regenerative amplifier can be configured more easily.

Embodiment 3 FIG.
A regenerative amplifier according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing the configuration of a regenerative amplifier according to Embodiment 3 of the present invention. Note that portions that are not particularly described are the same as those in the first embodiment.

  In FIG. 4, in the regenerative amplifier 1 according to the third embodiment, an anisotropic solid-state laser medium 25 is disposed in the resonator. A quarter-wave plate (polarization direction rotating element) 11 is disposed between the solid-state laser medium 25 and the reflecting mirror 4 on the optical axis of the resonator. Further, it is coaxial with the optical axis of the resonator from the solid-state laser medium 25 to the polarizer 5, and optically opposes the reflecting mirror 4 at a position where the light from the solid-state laser medium 25 to the polarizer 5 passes through the polarizer 5. Then, a reflecting mirror (third reflecting mirror) 12 is arranged.

  The incident light 31 polarized in parallel with the paper surface of FIG. 4 passes through the polarizer 5 and enters the resonator. The incident light 31 that has entered the resonator is reflected by the reflecting mirror 3, passes back and forth through the polarization rotating means 6 and the quarter wavelength plate 7, rotates in the polarization direction, and is reflected by the polarizer 5. The polarization direction is the vertical direction. The light reflected by the polarizer 5 passes through the solid-state laser medium 25 and the light output is amplified. Next, the light passes through the quarter-wave plate 11, is reflected by the reflecting mirror 4, and passes through the quarter-wave plate 11 again. In order to pass through the quarter-wave plate twice in a reciprocating manner, the polarization direction is rotated by 90 ° to be polarized in a direction parallel to the paper surface of FIG. Again, since the polarization direction of the light incident on the solid-state laser medium 25 is orthogonal to the light incident on the solid-state laser medium 25 from the polarizer 5 side, amplification received by the solid-state laser medium 25 has a different gain peak wavelength. The total gain can be flat because of the superposition of two gains. Since the light that has passed through the solid-state laser medium 25 is polarized in the direction that passes through the polarizer 5, the light passes through the polarizer 5 and is reflected by the reflecting mirror 12 that is optically opposed to the reflecting mirror 4. Then, the light again passes through the polarizer 5 and proceeds again to the solid-state laser medium 25 side. The light that has passed through the solid-state laser medium 25 is reflected by the reflecting mirror 4 and reciprocates through the quarter-wave plate 11 to rotate the polarization direction by 90 ° to become polarized light in the vertical direction in FIG. pass. Furthermore, since it is reflected by the polarizer 5, it can make one round in the resonator. Thereafter, the incident light 31 rotated once by the polarization rotation of the polarization rotating means 6 is confined in the resonator, becomes the circulating light 32, and is amplified one after another, and finally a large energy is transferred to the solid-state laser. By extracting from the medium, output light 33 is obtained.

  With this configuration, even when there is only one solid-state laser medium 25 arranged in the resonator, the polarization direction passing through the solid-state laser medium 25 can be reciprocally rotated. The gain band can be aligned with the two axes of the anisotropic solid-state laser medium 25. For this reason, since the total gain received when the resonator is circulated once can be flattened, the narrowing of the wavelength band that occurs when the resonator is circulated many times is suppressed, and the broadband output light 33 is reduced. Can be obtained. For this reason, there are features such that ultrashort pulse light with a short time can be obtained, ultrashort pulse light with high energy and high peak power can be obtained. Furthermore, since the solid-state laser medium 25 used in this configuration can be configured with at least one, there is a feature that a regenerative amplifier can be configured more easily.

  The same effect can be obtained by using a Faraday rotator having a rotation angle of 90 ° instead of using the quarter-wave plate 11. Furthermore, instead of using the quarter wave plate 11, the same effect can be obtained by using a Faraday rotator having a rotation angle of 45 ° and a half wave plate arranged in an axial direction in which the polarization direction rotates 45 °. is there.

Embodiment 4 FIG.
A regenerative amplifier according to Embodiment 4 of the present invention will be described with reference to FIG. FIG. 5 is a diagram showing the configuration of a regenerative amplifier according to Embodiment 4 of the present invention. Note that portions that are not particularly described are the same as those in the first embodiment.

  In FIG. 5, in the regenerative amplifier 1 according to the fourth embodiment, an anisotropic solid-state laser medium 25 is disposed in the resonator. A quarter-wave plate (first polarization direction rotating element) 11 is disposed between the solid-state laser medium 25 and the reflecting mirror 4 on the optical axis of the resonator. Further, a Faraday rotator 13 and a half-wave plate 14 that are coaxial with the optical axis of the resonator from the solid-state laser medium 25 toward the polarizer 5 and have a rotation angle of 45 ° between the solid-state laser medium 25 and the polarizer 5 are provided. Deploy. The Faraday rotator 13 and the half-wave plate 14 correspond to a second polarization direction rotating element.

  The incident light 31 polarized in parallel with the paper surface of FIG. 5 passes through the polarizer 5 and enters the resonator. The incident light 31 incident on the resonator is reflected by the reflecting mirror 3, passes back and forth through the polarization rotating means 6 and the quarter wavelength plate 7, rotates in the polarization direction, and is reflected by the polarizer 5. The polarization direction is the vertical direction. The light reflected by the polarizer 5 passes through the Faraday rotator 13 and the half-wave plate 14. In the half-wave plate 14, by setting the axial direction of the half-wave plate 14 so as to rotate the polarization by + 45 °, the light passing through the Faraday rotator 13 and the half-wave plate 14 is totaled. The 90 ° polarized light rotates. Therefore, the polarization direction passing through the solid-state laser medium 25 is a direction parallel to the paper surface of FIG. 5, and then the polarization direction is further rotated by 90 ° by the quarter-wave plate 11 and the reflecting mirror 4, and again the solid-state laser Incident on the medium 25. For this reason, the polarization direction on the return path is polarized perpendicular to the paper surface of FIG. For this reason, since the amplification received by the solid-state laser medium 25 is a superposition of two gains having different gain peak wavelengths, the total gain can be made flat.

  The light that has passed through the solid-state laser medium 25 passes through the half-wave plate 14 and the Faraday rotator 13 again. Here, since the Faraday rotator 13 is an irreversible element, when the polarization direction of the light traveling from the polarizer 5 to the solid-state laser medium 25 rotates together with the half-wave plate 14 by 90 ° in total, it is solid. The light traveling from the laser medium 25 to the polarizer 5 passes through without rotating in the polarization direction. For this reason, since the perpendicular polarized light passes through the plane of FIG. 5, it can be reflected by the polarizer 5 to make one round trip. Thereafter, the incident light 31 rotated once by the polarization rotation of the polarization rotating means 6 is confined in the resonator, becomes the circulating light 32, and is amplified one after another, and finally a large energy is transferred to the solid-state laser. By extracting from the medium, output light 33 is obtained.

  The axial direction of the half-wave plate 14 is set so that the polarization rotation of the half-wave plate 14 is −45 ° with respect to the light traveling from the polarizer 5 to the solid-state laser medium 25. Also good. In this case, the light traveling from the polarizer 5 to the solid-state laser medium 25 passes through the half-wave plate 14 and the Faraday rotator 13 so that the total polarization rotation becomes 0 °, and the solid light is polarized perpendicular to the paper surface of FIG. Passes through the laser medium 25. The polarization direction of the light reflected by the reflecting mirror 4 and reciprocally passing through the quarter-wave plate 11 is rotated by 90 °, passes through the solid laser medium 25 in the direction parallel to the paper surface of FIG. It passes through the half-wave plate 14 and the Faraday rotator 13. Here, since the Faraday rotator 13 is an irreversible element, when the polarization direction of light traveling from the polarizer 5 to the solid laser medium 25 is aligned with the half-wave plate 14 and there is no polarization rotation, the solid laser medium Since the polarization of the light traveling from 25 to the polarizer 5 rotates by −90 °, the polarization direction after passing becomes a polarization perpendicular to the paper surface of FIG. 5, and can be reflected by the polarizer 5 and circulate. For this reason, the same feature is obtained.

  With this configuration, even when there is only one solid-state laser medium 25 arranged in the resonator, the polarization direction passing through the solid-state laser medium 25 can be reciprocally rotated. The gain band can be aligned with the two axes of the anisotropic solid-state laser medium 25. For this reason, since the total gain received when the resonator is circulated once can be flattened, the narrowing of the wavelength band that occurs when the resonator is circulated many times is suppressed, and the broadband output light 33 is reduced. Can be obtained. For this reason, there are features such that ultrashort pulse light with a short time can be obtained, ultrashort pulse light with high energy and high peak power can be obtained. Furthermore, since the solid-state laser medium 25 used in this configuration can be configured with at least one, there is a feature that a regenerative amplifier can be configured more easily.

  The same effect can be obtained by using a Faraday rotator having a rotation angle of 90 ° instead of using the Faraday rotator 13 having a rotation angle of 45 ° and the half-wave plate 14.

Embodiment 5 FIG.
A regenerative amplifier according to Embodiment 5 of the present invention will be described with reference to FIG. FIG. 6 is a diagram showing the configuration of a regenerative amplifier according to Embodiment 5 of the present invention. Note that portions that are not particularly described are the same as those in the first embodiment.

  In FIG. 6, in the regenerative amplifier 1 according to the fifth embodiment, a solid-state laser medium 26 (first and second solid-state laser media) is disposed in the resonator. The solid-state laser medium 26 is an isotropic solid-state laser medium or a composite solid-state laser medium shaped into one chip by combining anisotropic solid-state laser media. As a material to be combined, laser media having different peak wavelengths of gain or crystal axis orientations can be obtained, and the total gain can be flattened. For this reason, since the total gain received when the resonator is circulated once can be flattened, the narrowing of the wavelength band that occurs when the resonator is circulated many times is suppressed, and the broadband output light 33 is reduced. Can be obtained. For this reason, there are features such that ultrashort pulse light with a short time can be obtained, ultrashort pulse light with high energy and high peak power can be obtained.

  The solid-state laser medium 26 is desirably optically integrated with different solid-state laser media or solid-state laser media arranged in different crystal axis orientations. For example, they can be integrated by diffusion bonding. It is also possible to join with an optically transparent adhesive. Further, it can be integrated by using a ceramic manufacturing method. Since the composite solid-state laser medium 26 shaped into one chip is used, only one type of pump module for pumping the solid-state laser medium 26 and providing gain is required, and a regenerative amplifier can be configured more easily. There is.

Embodiment 6 FIG.
A mode-locked laser according to Embodiment 6 of the present invention will be described with reference to FIG. FIG. 7 is a diagram showing a configuration of a mode-locked laser according to Embodiment 6 of the present invention. Note that portions that are not particularly described are the same as in the first to fifth embodiments.

  In FIG. 7, the mode-locked laser 50 according to the sixth embodiment is on the same axis as the resonator composed of the output mirror 51 and the reflecting mirror 52 that are optically opposed to each other, and in the resonator. Dispersion compensation means 53, solid laser medium 21, solid laser medium 22, and mode lock means 54 are provided. The resonant light 35 circulates in the resonator. The output light 36 is extracted from the output mirror 51.

  The mode-locked laser 50 is a short-pulse laser oscillator, and is classified into a passive mode-locked laser and an active mode-locked laser. In the passive mode-locked laser, the mode-locked laser 54 is passively generated using, for example, a saturable absorber as the mode-locking means 54. On the other hand, in the active mode-locked laser, the mode-locked laser 54 is actively controlled using, for example, an acousto-optic device that can be controlled by applying a voltage as the mode-locking unit 54 to generate a mode-locked laser. In any case, since the mode-locking means 54 can obtain laser light having a uniform phase in a wide wavelength region, an ultrashort pulse can be obtained.

  In general, in the mode-locked laser 50, the dispersion compensation means 53 is disposed in the resonator. The dispersion compensation unit 53 uses, for example, a prism pair or a grating. Since the dispersion compensation means 53 compensates for the refractive index of the optical components in the resonator and the wavelength dependence of the reflection and transmission characteristics, it is possible to align the phase between wavelengths over a wider band with high accuracy. There is a feature that a pulse output light 36 is obtained.

  In such a mode-locked laser 50, spontaneous emission light generated by a laser medium having a gain circulates a plurality of times in the resonator to increase the light output, and a part of the light is output from the output mirror 51 every turn. 36 is taken out. The output mirror 51 is a partial reflection mirror, which transmits a part of the resonance light 35 incident on the output mirror 51 to become output light 36, reflects a part thereof, and returns to the resonator as the resonance light 35. Since a part of the light is transmitted through the output mirror 51, the output of the resonant light 35 reflected by the output mirror 51 is reduced, but is amplified by the solid-state laser mediums 21 and 22 that pass through the resonator once. A constant output light 36 can be obtained in the round. When a part of the resonance light 35 is reflected and circulates in this way, it can be considered that the light circulates many times on average, and after passing through the solid-state laser media 21 and 22 a plurality of times, the output light 36 can be regarded as being taken out. Here, when the gains of the solid-state laser media 21 and 22 are small and the reflectance of the output mirror 51 is high, it can be considered that, on average, the laser beam is rotated more times, and the gain is small. When the reflectance of the mirror 51 is low, it can be considered that the number of turns is small.

  In the case of a Yb-based solid laser medium, the generated gain is generally small, so that the apparent number of rounds when a mode-locked laser is configured is large. For this reason, the wavelength band of the output light 36 is narrower than the gain band width of the solid-state laser medium due to the effect of gain narrowing.

  Here, according to the sixth embodiment, since the solid-state laser medium 21 and the solid-state laser medium 22 having different gain peak wavelengths are arranged in the resonator, the total gain when the resonator is circulated once is wideband. Makes it flat. For this reason, narrowing of the wavelength band of the resonance light 35 amplified in the resonator is suppressed, and output light 36 having a wide wavelength band is obtained.

  As described above, since the solid-state laser media 21 and 22 having different gain peaks are arranged in the mode-locked laser 50, a flat total gain is obtained, the narrowing of the wavelength band due to many rounds is suppressed, and the wavelength width is reduced. A wide output light 36 is obtained. For this reason, there are features such that ultrashort pulse light with a short time can be obtained, ultrashort pulse light with high energy and high peak power can be obtained.

It is a figure which shows the structure of the regenerative amplifier which concerns on Embodiment 1 of this invention. It is a figure which shows an example of the wavelength dependence of the amplification gain of the solid-state laser medium of the regenerative amplifier which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the regenerative amplifier which concerns on Embodiment 2 of this invention. It is a figure which shows the structure of the regenerative amplifier which concerns on Embodiment 3 of this invention. It is a figure which shows the structure of the regenerative amplifier which concerns on Embodiment 4 of this invention. It is a figure which shows the structure of the regenerative amplifier which concerns on Embodiment 5 of this invention. It is a figure which shows the structure of the mode-locked laser which concerns on Embodiment 6 of this invention. It is a figure which shows an example of the calculation result of the frequency | count dependence of the output light wavelength of the reproduction | regeneration amplifier using a solid state laser medium (Yb: KYW).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Regenerative amplifier, 3 Reflection mirror, 4 Reflection mirror, 5 Polarizer, 6 Polarization rotation means, 7 1/4 wavelength plate, 8 Polarization switch, 10 1/2 wavelength plate, 11 1/4 wavelength plate, 12 Reflection mirror, 13 Faraday rotator, 14 1/2 wavelength plate, 21 Solid laser medium, 22 Solid laser medium, 23 Solid laser medium, 24 Solid laser medium, 25 Solid laser medium, 26 Solid laser medium, 50 Mode-locked laser, 51 Output mirror, 52 reflector, 53 dispersion compensation means, 54 mode lock means.

Claims (12)

A regenerative amplifier that forms a resonator from first and second reflecting mirrors that are optically opposed to each other,
A first and a second solid-state laser medium disposed on the optical axis of the resonator between the first and second reflecting mirrors to generate gain and amplify incident light;
A polarizer disposed on the optical axis of the resonator between the first reflecting mirror and the first solid-state laser medium;
A polarization switch disposed on the optical axis of the resonator between the first reflecting mirror and the polarizer and controlling a polarization direction by applying a voltage;
A regenerative amplifier characterized by amplifying light incident from the polarizer by a wavelength-dependent flat amplification gain obtained by combining amplification gains having different peak wavelengths generated by the first and second solid-state laser media, respectively. . The first and second solid-state laser media are anisotropic;
2. A half-wave plate disposed on the optical axis of the resonator between the first and second solid-state laser media and further rotating a polarization direction of incident light. The regenerative amplifier described. A regenerative amplifier that forms a resonator from first and second reflecting mirrors that are optically opposed to each other,
An anisotropic solid-state laser medium disposed on the optical axis of the resonator between the first and second reflecting mirrors to generate gain and amplify incident light;
A polarizer disposed on the optical axis of the resonator between the first reflecting mirror and the solid-state laser medium;
A polarization switch disposed on the optical axis of the resonator between the first reflecting mirror and the polarizer and controlling a polarization direction by applying a voltage;
A polarization direction rotating element disposed on the optical axis of the resonator between the second reflecting mirror and the solid-state laser medium, and rotating a polarization direction of incident light;
A third reflecting mirror disposed optically opposite to the second reflecting mirror at a position where light directed from the solid-state laser medium toward the polarizer passes through the polarizer;
By changing the polarization direction of the amplified light with respect to the axial direction of the anisotropic solid-state laser medium, the wavelength-dependent flatness obtained by superimposing a plurality of amplification gains with different peak wavelengths generated by the anisotropic solid-state laser medium A regenerative amplifier that amplifies the light incident from the polarizer with a high amplification gain. A regenerative amplifier that forms a resonator from first and second reflecting mirrors that are optically opposed to each other,
An anisotropic solid-state laser medium disposed on the optical axis of the resonator between the first and second reflecting mirrors to generate gain and amplify incident light;
A polarizer disposed on the optical axis of the resonator between the first reflecting mirror and the solid-state laser medium;
A polarization switch disposed on the optical axis of the resonator between the first reflecting mirror and the polarizer and controlling a polarization direction by applying a voltage;
A first polarization direction rotating element disposed on the optical axis of the resonator between the second reflecting mirror and the solid-state laser medium, and rotating a polarization direction of incident light;
A second polarization direction rotating element that is disposed on the optical axis of the resonator between the polarizer and the solid-state laser medium and rotates a polarization direction of incident light;
By changing the polarization direction of the amplified light with respect to the axial direction of the anisotropic solid-state laser medium, the wavelength-dependent flatness obtained by superimposing a plurality of amplification gains with different peak wavelengths generated by the anisotropic solid-state laser medium A regenerative amplifier that amplifies the light incident from the polarizer with a high amplification gain. A regenerative amplifier that forms a resonator from first and second reflecting mirrors that are optically opposed to each other,
A first and a second solid-state laser medium disposed on the optical axis of the resonator between the first and second reflecting mirrors to generate gain and amplify incident light;
A polarizer disposed on the optical axis of the resonator between the first reflecting mirror and the first solid-state laser medium;
A polarization switch disposed on the optical axis of the resonator between the first reflecting mirror and the polarizer and controlling a polarization direction by applying a voltage;
The first and second solid-state laser media are optically integrated, and light incident from the polarizer is amplified by a wavelength-dependent flat amplification gain obtained by combining amplification gains having different peak wavelengths. A regenerative amplifier. A mode-locked laser that constitutes a resonator from an optically opposed output mirror and a reflecting mirror,
A first and a second solid-state laser medium disposed on the optical axis of the resonator between the output mirror and the reflecting mirror to generate gain and amplify incident light;
Dispersion compensation means arranged on the optical axis of the resonator between the output mirror and the first solid-state laser medium to compensate for wavelength dependence;
Mode-locking means disposed on the optical axis of the resonator between the second solid-state laser medium and the reflecting mirror;
A mode lock characterized by amplifying the optical output and performing laser oscillation with a wavelength-dependent flat amplification gain obtained by combining amplification gains having different peak wavelengths generated by the first and second solid-state laser media, respectively. laser. Wavelength-dependent flat synthetic amplification combining the amplification gain having the first peak wavelength generated by the first solid-state laser medium and the amplification gain having the second peak wavelength generated by the second solid-state laser medium A gain smoothing method comprising amplifying incident light by gain. The first and second solid-state laser media are anisotropic;
The gain smoothing method according to claim 7, wherein crystal axes or optical axes of the first and second solid-state laser media are arranged in different directions. The first and second solid-state laser media are anisotropic, are made of the same material and are arranged in the same axial direction,
The gain smoothing method according to claim 7, wherein the polarization direction of the light is rotated by a half-wave plate disposed on an optical axis connecting the first and second solid-state laser media. The gain smoothing method according to claim 7, wherein the first and second solid-state laser media are optically integrated. Gain smoothing characterized by amplifying incident light with a flat, wavelength-dependent combined amplification gain that combines multiple amplification gains with different peak wavelengths generated by a single anisotropic solid-state laser medium Method. The gain smoothing according to claim 11, wherein a plurality of amplification gains having different peak wavelengths are obtained by changing a polarization direction of the amplified light with respect to an axial direction of the anisotropic solid-state laser medium by a polarization direction rotating element. Method.

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