An apparatus and method for expanding the gain bandwidth of an ultrafast laser

Abstract

The present invention provides an apparatus and method for expanding the gain bandwidth of an ultrafast laser. It includes: a phase retarder, a first filter, and a gain medium; the phase retarder is used to adjust the polarization direction of the received initial seed laser to a target seed laser at a predetermined angle with respect to the optical platform; the first filter is used to spatially align the received pump laser and the target seed laser to be completely coincident and then inject them into the gain medium; the gain medium is used to perform birefringence on the received target seed laser so that the target seed laser has optical components on both optical axes of the gain medium. Using the gain medium broadens the gain spectral range, alleviates gain narrowing during the laser amplification process, obtains a narrower pulse output, the overall laser device is more concise, and the gain bandwidth can be broadened and adjusted only by rotating the phase retarder. The output spectral shape of the laser amplifier can be regulated according to actual application requirements, and the application scenarios of the laser are broadened.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast laser technology, and particularly to a device and method for expanding the gain bandwidth of ultrafast laser. Background Art

[0002] To expand the application scenarios of ultrafast lasers, amplification techniques are needed to increase the energy and power of mode-locked seeds. In existing solid-state amplifiers, the gain media used are usually cut and placed in the forward direction, that is, the crystal cut is perpendicular to a certain axis of the crystal, and the polarization direction of the seed laser is parallel to the axis with the largest emission cross-section of the crystal to improve the amplification effect. However, gain narrowing inevitably occurs during the power / energy amplification process of ultrafast lasers, resulting in a narrower output spectrum and a wider pulse. This is not conducive to the development of high-energy laser science research and time-resolved research. For anisotropic (uniaxial and biaxial crystals) gain media, their absorption and emission spectra in different orientations are not the same. Therefore, the difference in emission spectra can be used to compensate for gain narrowing and achieve wide-spectrum amplification. The current solution is to use two gain media placed orthogonally. The seed laser is incident linearly polarized, and the power / energy is amplified using two axes of the two gain media respectively to achieve gain narrowing compensation. However, using two gain media increases the complexity and cost of the laser system. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art, and provides a device and method for expanding the gain bandwidth of ultrafast laser.

[0004] In a first aspect, the present invention provides a device for expanding the gain bandwidth of ultrafast laser, the device comprising: a phase retarder, a first filter, and a gain medium arranged in sequence along the optical path direction;

[0005] The phase retarder is configured to adjust the polarization direction of the received initial seed laser to a target seed laser at a predetermined angle with respect to the optical platform;

[0006] The first filter is configured to spatially align the received pump laser and the target seed laser to be completely coincident and then inject them into the gain medium;

[0007] The gain medium is configured to perform birefringence on the received target seed laser so that the target seed laser has optical components on two optical axes of the gain medium.

[0008] In some embodiments, the phase retarder is a half-wave plate.

[0009] In some embodiments, the first filter is a first dichroic mirror.

[0010] In some embodiments, the gain medium is placed forward, and the a-axis of the gain medium is parallel to the optical platform, and the b-axis is perpendicular to the optical platform.

[0011] In some embodiments, the range of the predetermined angle is 0° to 45°.

[0012] In some embodiments, the gain medium is a ytterbium-doped gain medium.

[0013] In some embodiments, the device further includes a second filter disposed on the light output side of the gain medium;

[0014] The second filter is used to separate the residual pump light and the amplified seed laser.

[0015] In some embodiments, the second filter is a second dichroic mirror.

[0016] In a second aspect, the present invention provides a method for expanding the gain bandwidth of an ultrafast laser. Using the device described above, the method includes:

[0017] The phase retarder adjusts the polarization direction of the received initial seed laser to a target seed laser at a predetermined angle with respect to the optical platform;

[0018] The first filter adjusts the received pump laser and the target seed laser to be completely overlapped in space and then injects them into the gain medium;

[0019] The gain medium performs birefringence on the received target seed laser so that the target seed laser has optical components on both optical axes of the gain medium.

[0020] The beneficial effects of the present invention are as follows:

[0021] The device and method for expanding the gain bandwidth of an ultrafast laser according to the embodiments of the present invention, compared with the previous solutions, use a single gain medium to broaden the gain spectral range, effectively alleviate the gain narrowing in the laser amplification process, and can obtain a narrower pulse output. Since only a single gain medium is used, the overall laser device is more concise. By simply rotating the phase retarder, the gain bandwidth can be broadened and adjusted, and the output spectral shape of the laser amplifier can be regulated according to actual application requirements, thus broadening the application scenarios of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of a device for expanding the gain bandwidth of an ultrafast laser according to an embodiment of the present invention;

[0023] Figure 2Emission spectra of the gain medium (taking Yb:KGW as an example) with different orientations (a represents the Np axis and b represents the Nm axis) according to another embodiment of the present invention. Detailed implementation manners

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0026] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0027] Figure 1 Schematic structural diagram of a device for expanding the gain bandwidth of an ultrafast laser according to an embodiment of the present invention. As Figure 1 shown, a device for expanding the gain bandwidth of an ultrafast laser, the device includes: a phase retarder 110, a first filter 120, and a gain medium 130 sequentially arranged along the optical path direction. The phase retarder 110 is used to adjust the polarization direction of the received initial seed laser to a target seed laser at a predetermined angle with respect to the optical platform. The first filter 120 is used to spatially adjust the received pump laser and the target seed laser to be completely coincident and then inject them into the gain medium 130. The gain medium 130 is used to perform birefringence on the received target seed laser so that the target seed laser has optical components on both optical axes of the gain medium.

[0028] The device for expanding the gain bandwidth of an ultrafast laser in this embodiment controls the polarization of the seed laser by means of a phase retarder so that it has a certain angle with the two optical axes of the gain medium. Due to the birefringence effect, the seed laser will have components on both axes, expanding the gain spectral range, effectively suppressing gain narrowing, and facilitating the obtaining of a narrower compressed pulse.

[0029] Compared with the previous scheme, the device for expanding the gain bandwidth of an ultrafast laser in this embodiment uses a single gain medium to broaden the gain spectral range, effectively alleviates gain narrowing during the laser amplification process, and can obtain a narrower pulse output. Since only a single gain medium is used, the overall laser device is more concise. The gain bandwidth can be broadened and adjusted simply by rotating the phase retarder, and the output spectral shape of the laser amplifier can be regulated according to actual application requirements, expanding the application scenarios of the laser.

[0030] In some embodiments, the phase retarder 110 is a half-wave plate. The first filter 120 is a first dichroic mirror.

[0031] In some embodiments, the gain medium 130 is placed forward, and the a-axis of the gain medium is parallel to the optical platform, and the b-axis is perpendicular to the optical platform.

[0032] In some embodiments, the range of the predetermined angle is 0° to 45°.

[0033] In some embodiments, the gain medium is a ytterbium-doped gain medium.

[0034] In some embodiments, the device further includes a second filter 140 disposed on the light output side of the gain medium. The second filter 140 is used to separate the residual pump light and the amplified seed laser.

[0035] In some embodiments, the second filter is a second dichroic mirror.

[0036] Specifically, in this embodiment, as Figure 1 shown, the polarization direction of the vertically polarized seed laser forms a specific angle with the optical platform after passing through the phase retarder 110. The pump laser and the seed laser are spatially completely overlapped through the first filter 120 and then injected into the anisotropic gain medium 130. The pump light hits the gain medium to generate inverted population. The residual pump light and the amplified laser are separated by the second filter 140. The gain medium 130 is placed forward, the a-axis is parallel to the optical platform, and the b-axis is perpendicular to the optical platform. The seed laser undergoes birefringence after passing through the gain medium 130, and the power components on the a-axis and the b-axis depend on the rotation angle of the half-wave plate. The gain medium is shown taking Yb:KGW as an example, and the emission peak intensities and positions of its Nm axis and Np axis are completely different. As Figure 2As shown, by controlling the polarization of the seed laser incident, the gain spectral components of Yb:KGW in two orientations can be fully utilized, thereby broadening the gain bandwidth, suppressing gain narrowing, and the intensity components of the seed laser on the Nm axis and Np axis can be controlled by adjusting the angle of the half-wave plate, and then the amplified spectral shape can be controlled to achieve the purpose of simple and fast spectral regulation.

[0037] Taking the Yb:KGW gain medium as an example, the emission peak of its Nm axis is at 1025 nm, and the emission peak of its Np axis is at 1040 nm. For a ytterbium-doped mode-locked seed source with a central wavelength near 1030 nm and a spectral range covering 1020 - 1040 nm, if only one axis of the gain medium is used to amplify the power, it will lead to serious gain narrowing. By controlling the polarization of the seed laser to have a certain angle with the Nm / Np axis of the gain medium, due to the birefringence effect, there will be components of the seed laser on both axes, expanding the gain spectral range and effectively suppressing gain narrowing, which is beneficial to obtaining a narrower compressed pulse.

[0038] The following will explain the specific working principle of the device for expanding the ultrafast laser gain bandwidth in the embodiments of the present invention:

[0039] Polarization control principle: When a linearly polarized laser passes through a half-wave plate, due to the fact that the polarization direction of the laser forms a certain angle θ with the optical axis of the wave plate, birefringence occurs, generating an o-ray and an e-ray. The refractive indices of the o-ray and the e-ray are different, resulting in a time delay, that is, a phase difference, inside the wave plate. After exiting, the linearly polarized light is still linearly polarized light, but the polarization direction rotates by 2θ relative to the original. By rotating the wave plate, θ can be changed, and finally the polarization direction after passing through the wave plate can be changed to achieve precise control of the polarization of the seed laser.

[0040] Principle of broadening the gain bandwidth: The polarization direction of the seed laser after passing through the half-wave plate has a certain angle with the optical axis of the gain medium. After the seed laser is incident on the gain medium, birefringence occurs, and there are seed components in both the direction parallel to the optical axis and the direction perpendicular to the optical axis. The gain medium absorbs pump light to generate inverted population. The seed laser extracts the inverted population after passing through the gain medium to achieve power / energy amplification. A dichroic mirror is used to realize the co-propagation of the pump light and the seed light, and a second pump mirror is used to separate the residual pump light and the amplified laser. Since the emission spectra of different orientations of the anisotropic gain medium are not the same, including the inconsistency of the central wavelength and the emission cross-section, this scheme can fully utilize the gain spectral components of different orientations of the gain medium to make up for the gain narrowing in the laser amplification process.

[0041] Principle of amplified spectral regulation: By rotating the half-wave plate, the angle between the seed laser and the optical axis of the gain medium can be controlled, thereby controlling the intensity components of the seed laser in different orientations of the gain medium, that is, the seed intensities of different spectral components. Since laser amplification follows the principle that the stronger the injection, the stronger the extraction, the purpose of amplified spectral regulation can be achieved only by rotating the wave plate.

[0042] In summary, for the device for expanding the gain bandwidth of an ultrafast laser in the embodiments of the present invention, aiming at the gain narrowing effect in the ultrafast laser amplification process, the difference in emission spectra of the anisotropic gain medium in different orientations is utilized to broaden the gain spectral range; aiming at the high technical complexity and cost of a multi-crystal amplifier, by controlling the polarization of the incident laser, the polarization direction of the seed light forms a predetermined angle with the crystal optical axis, so that the seed light has the same components in different axial directions of a single gain medium, thereby broadening the gain bandwidth range of the single gain medium; in addition, the gain components of the seed laser in different orientations of the crystal can be controlled by controlling the angle between the polarization of the seed laser and the optical axis, so as to achieve the effect of regulating the bandwidth and shape of the amplified spectrum.

[0043] Based on the same inventive concept, the embodiments of the present invention also provide a method for expanding the gain bandwidth of an ultrafast laser. The device described above is adopted, and specific reference can be made to the relevant descriptions above, which will not be elaborated here. The method includes:

[0044] The phase retarder adjusts the polarization direction of the received initial seed laser to a target seed laser at a predetermined angle with the optical platform.

[0045] The first filter adjusts the received pump laser and the target seed laser to be completely overlapped in space and then injects them into the gain medium.

[0046] The gain medium performs birefringence on the received target seed laser so that the target seed laser has optical components on both optical axes of the gain medium.

[0047] Compared with the previous solutions, the method for expanding the gain bandwidth of an ultrafast laser in this embodiment uses a single gain medium to broaden the gain spectral range, effectively alleviates the gain narrowing in the laser amplification process, and can obtain a narrower pulse output. Since only a single gain medium is used, the overall laser device is more concise. The gain bandwidth can be broadened and adjusted only by rotating the phase retarder, and the output spectral shape of the laser amplifier can be regulated according to actual application requirements, thus broadening the application scenarios of the laser.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for extending the gain bandwidth of an ultrafast laser, characterized in that: The device comprises: a phase delay plate, a first filter and an anisotropic gain medium which are sequentially arranged along the optical path direction; The phase delay plate is used to adjust the polarization direction of the received initial seed laser to the target seed laser which is at a predetermined angle with the optical platform; The first filter is used to adjust the received pump laser and the target seed laser to completely overlap in space and then inject them into the gain medium; The gain medium is used to perform birefringence on the received target seed laser so that the target seed laser has optical components on the two optical axes of the gain medium, and the intensity of the optical components of the target seed laser on the two optical axes of the gain medium can be controlled by adjusting the angle of the phase delay plate, wherein the gain medium is placed forward, and the a-axis of the gain medium is parallel to the optical platform, and the b-axis is perpendicular to the optical platform.

2. The device according to claim 1, characterized in that The phase retarder is a half-wave plate.

3. The device according to claim 1, characterized in that The first filter is a first dichroic mirror.

4. The device according to any one of claims 1 to 3, characterized in that The predetermined angle ranges from 0° to 45°.

5. The device according to any one of claims 1 to 3, characterized in that: The gain medium is an ytterbium-doped gain medium.

6. The device according to any one of claims 1 to 3, characterized in that The device also includes a second filter arranged on the light-emitting side of the gain medium; The second filter is used to separate the residual pump light and the amplified seed laser.

7. The device according to claim 6, characterized in that The second filter is a second dichroic mirror.

8. A method for extending ultrafast laser gain bandwidth, characterized in that: Using the device according to any one of claims 1 to 7, the method comprises: The phase retarder adjusts the polarization direction of the received initial seed laser to the target seed laser which is at a predetermined angle to the optical platform; The first filter injects the received pump laser and the target seed laser into the gain medium after spatially adjusting them to completely overlap; The gain medium performs birefringence on the received target seed laser so that the target seed laser has optical components on two optical axes of the gain medium.

Images