Narrow linewidth pulse laser

Abstract

The invention provides a narrow linewidth pulse laser, and the pulse laser comprises a laser gain chip (2) which comprises a first reflection end face (1) and a second reflection end face (3) and is used for forming population inversion and lasing light emission; the reflecting mirror (6) is positioned on the light emitting side; the reflecting mirror (6) and the first reflecting end surface (1) form a resonant cavity; the lithium niobate modulation module (4) is positioned in the resonant cavity and is used for regulating and controlling an optical path; and the filter (5) is positioned in the resonant cavity and is used for filtering light deviating from the central wavelength. According to the pulse laser, the Q value of the resonant cavity is adjusted through the combination of the lithium niobate electro-optical crystal and the filter, the complexity of the system is reduced, the stability is improved, and meanwhile the frequency spectrum width is narrowed.

Description

Technical Field

[0001] The present disclosure relates to the field of laser technology, and in particular to a narrow linewidth pulse laser. Background Art

[0002] Pulsed lasers have high peak power and can release a large amount of energy in a very short time. They can perform precise time and space control and are suitable for micro-machining. They can generate femtosecond to nanosecond pulses for fine processing and time-resolved measurement. They are often used in precision manufacturing processes such as laser cutting, marking and welding, laser surgery, ophthalmic treatment and cell imaging, pulse modulation and signal transmission in fiber-optic communications, ultrafast process research, time-resolved spectroscopy and nonlinear optical experiments. They can also be used in lidar for atmospheric monitoring and pollution detection.

[0003] Among them, Q-switching can achieve the pulse output of the laser. Generally speaking, Q-switching technology can be achieved by rotating prisms, using saturable absorbing materials, electro-optical switches and other methods. For the rotating prism method, the Q value of the resonant cavity is modulated every time the prism rotates to align the mirror surface with the axis of the resonant cavity; for saturable absorbing materials, their ability to absorb energy decreases with the increase of light intensity, and they only become transparent at high light intensity, thereby reducing the Q value and achieving Q-switching; for electro-optical switches, electro-optical crystals are used in combination with polarizers. This method can achieve nanosecond pulse width output. Among electro-optical crystals, the growth technology of lithium niobate crystals is relatively mature, easy to grow into large-sized crystals, and not easy to deliquesce, with high temperature stability and low cost, so it has been widely used. The shorter the pulse length, the wider the spectrum will be, and the electro-optical switch generally requires the combination of two polarizers and electro-optical crystals, which increases the complexity of the structure. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above problems, the present disclosure provides a narrow linewidth pulse laser, which is used to at least partially solve the technical problems of traditional pulse lasers such as wide spectrum width and complex structure.

[0006] (II) Technical solution

[0007] In view of this, the present disclosure provides a narrow linewidth pulse laser, including: a laser gain chip, including a first reflective end face and a second reflective end face, for forming a particle number inversion and lasing light; a reflector, located on the light output side; the reflector and the first reflective end face form a resonant cavity; a lithium niobate modulation module, located in the resonant cavity, for performing optical path control; a filter, located in the resonant cavity, for filtering out light that deviates from the central wavelength.

[0008] According to an embodiment of the present disclosure, the laser gain chip is connected to an electrical driver to form a population inversion and emit lasing light.

[0009] According to an embodiment of the present disclosure, the reflectivity of the first reflective end surface is greater than or equal to 90%; the reflectivity of the second reflective end surface is less than or equal to 0.05%.

[0010] According to an embodiment of the present disclosure, the light emitted by the laser gain chip is emitted through the second reflective end face.

[0011] According to an embodiment of the present disclosure, the reflectivity of the reflector is less than or equal to 10%.

[0012] According to an embodiment of the present disclosure, a wavelength that meets the resonance condition and has a gain greater than a loss will be emitted from the reflector.

[0013] According to an embodiment of the present disclosure, a lithium niobate modulation module includes a lithium niobate electro-optical crystal and a thin film electrode disposed thereon, and the lithium niobate electro-optical crystal is electrically connected to the thin film electrode.

[0014] According to an embodiment of the present disclosure, the electric field loaded on the lithium niobate modulation module is parallel to the polarization plane of light, and the electric field changes rapidly and periodically.

[0015] According to an embodiment of the present disclosure, the filter is a grating filter, and the filter is located in the optical axis direction of the resonant cavity.

[0016] According to the embodiments of the present disclosure, the filter finely separates light of different wavelengths, and the wavelength that the filter can pass is the wavelength of light of the center wavelength of the laser that meets the resonance condition.

[0017] (III) Beneficial effects

[0018] The narrow linewidth pulse laser provided by the present disclosure, on the one hand, finely separates light of different wavelengths through the filter in the resonant cavity, the light of the central wavelength of the laser meets the resonance condition, and the light of the remaining wavelengths deviates from the optical path and is lost; this Q-switching method realizes pulsed laser emission, and has a simpler structure than the electro-optical Q-switched laser. On the other hand, the shortening of the pulse length in the present disclosure widens the spectrum, and the structure of the present disclosure can generate a narrow linewidth pulse laser while basically maintaining the pulse length. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0020] Figure 1 The structure of a narrow linewidth pulse laser according to an embodiment of the present disclosure is schematically shown;

[0021] Figure 2 Schematically shows an XY cross-sectional view of a refractive index ellipsoid of a lithium niobate modulation module according to an embodiment of the present disclosure;

[0022] Figure 3 A schematic diagram showing the polarization state and phase change of a light beam incident into a lithium niobate electro-optical crystal according to an embodiment of the present disclosure is shown;

[0023] Description of Figure Numbers:

[0024] 1, first reflective end face; 2, laser gain chip; 3, second reflective end face; 4, lithium niobate modulation module; 5, filter; 6, reflector. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0026] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0027] Various directional words in the present disclosure, such as "front", "back", "left", "right", "up", "down", etc., are only for the convenience of description and are used to describe the relative position relationship between the various components, rather than to limit the present disclosure. Different product placement methods of the present disclosure may result in changes in the various directional descriptions.

[0028] Figure 1 A schematic diagram of the structure of a narrow linewidth pulse laser according to an embodiment of the present invention is schematically given.

[0029] like Figure 1 As shown, a narrow linewidth pulse laser includes: a laser gain chip 2, including a first reflective end face 1 and a second reflective end face 3, which are used to form a particle number inversion and emit light; a reflector 6, located on the light output side; the reflector 6 and the first reflective end face 1 form a resonant cavity; a lithium niobate modulation module 4, located in the resonant cavity, used for optical path control; a filter 5, located in the resonant cavity, used to filter out light that deviates from the central wavelength.

[0030] The present invention utilizes the electro-optical effect of lithium niobate crystal to adjust the optical path in the resonant cavity, and adjusts the Q value of the resonant cavity with a filter to achieve the generation of Q-switched pulsed laser. At the same time, the structure of the Q-switched laser is simplified, and the pulse length of the ultrashort pulse laser achieved by the electro-optical switch is basically maintained while the spectrum width of the pulsed laser is narrowed.

[0031] On the basis of the above embodiment, the laser gain chip 2 is connected to an electrical drive to form a population inversion and emit light. The reflectivity of the first reflective end face 1 is greater than or equal to 90%; the reflectivity of the second reflective end face 3 is less than or equal to 0.05%.

[0032] Exemplarily, the laser gain chip 2 is connected to an electrical drive, and the two end faces of the laser gain chip 2 are respectively a first reflective end face 1 with a reflectivity of 95% and a second reflective end face 3 with a reflectivity of 0.05%; the output light enters the lithium niobate modulation module 4, and the lithium niobate modulation module 4 changes the refractive index ellipsoid of the lithium niobate crystal; the filter 5 is in the direction of the optical axis of the resonant cavity and is located inside the resonant cavity; the reflector 6 and the first reflective end face 1 of the laser gain chip 2 with a reflectivity of 95% together constitute an optical resonant cavity.

[0033] In the present disclosure, the reflectivity of the first reflective end surface 1 is greater than or equal to 90% and the reflectivity of the second reflective end surface 3 is less than or equal to 0.05%. The reflectivity of the first reflective end surface 1 is, for example, 93%, 95%, 97%, 98%, 99%, 99.5%, etc., and the reflectivity of the second reflective end surface 3 is, for example, 0.05%, 0.04%, 0.03%, 0.02%, 0.01%, etc. This setting is conducive to efficient lasing and emission.

[0034] On the basis of the above embodiment, the light emitted by the laser gain chip 2 is emitted through the second reflective end face 3. The light emitted from the second reflective end face 3 with a reflectivity less than or equal to 0.05% enters the lithium niobate modulation module 4.

[0035] Based on the above embodiment, the lithium niobate modulation module 4 includes a lithium niobate electro-optical crystal and a thin film electrode disposed thereon, and the lithium niobate electro-optical crystal is electrically connected to the thin film electrode. The electric field loaded on the lithium niobate modulation module 4 is parallel to the polarization plane of the light, and the electric field changes rapidly and periodically.

[0036] The lithium niobate modulation module 4 is a lithium niobate electro-optical crystal plated thin film electrode, and is electrically connected, such as Figure 1 As shown in the figure, the direction of the electric field is parallel to the polarization plane of the light beam (the y-axis direction in the figure), and the electric field applied to both sides of the electrodes of the lithium niobate electro-optical crystal film changes rapidly and periodically. As a kind of electro-optical uniaxial crystal, lithium niobate will not significantly rotate the other two principal axes when an electric field is applied along the y-axis, but the refractive index of the z-axis cross section will change. Figure 2 As shown, Figure 2 This is the XY cross-sectional diagram of the refractive index ellipsoid of lithium niobate electro-optical crystal. Figure 2 (a) is the cross section of the refractive index ellipsoid of lithium niobate when an electric field is applied. At this time, n1=n2 and the cross section is circular. Figure 2 (b) is the cross section of the refractive index ellipsoid of lithium niobate when an electric field is applied along the y-axis direction. At this time, n1 becomes n1', n2 becomes n2', where n1 is smaller than n1', n2 is larger than n2', and the cross section is elliptical. At this time, light of different polarization states will experience different refractive indices. The change in refractive index changes the optical path, and the resonant wavelength of the resonant cavity shifts. At the same time, due to phase mismatch, the Q value of the resonant cavity decreases.

[0037] Figure 3 is a schematic diagram of the polarization state and phase change of the light beam incident into the lithium niobate crystal. If the polarization direction of the light in the laser cavity is as shown by e, and there is an electric field E in the lithium niobate modulation module 4, the refractive index ellipsoid cross section of the lithium niobate is as follows: Figure 2 As shown, the fast axis and the slow axis are formed. y The optical path is shorter, and the polarization component e along the x-axis x The optical path is longer, and a phase difference occurs after passing through the lithium niobate crystal. The phase mismatch reduces the Q value of the resonant cavity, and the resonant wavelength shifts compared to when there is no electric field.

[0038] On the basis of the above embodiment, the filter 5 finely separates light of different wavelengths, and the wavelength that the filter 5 can pass is the wavelength of light of the center wavelength of the laser that meets the resonance condition.

[0039] Optionally, filter 5 selects a grating filter, and the incident light is diffracted on the grating, and light of different wavelengths propagates at different angles, thereby achieving wavelength separation. The light of the center wavelength of the laser is diffracted into the direction of the laser optical axis, and the light of other wavelengths deviates and is lost due to the optical path. As a result, the Q value of the optical resonant cavity decreases.

[0040] When the Q value of the optical resonant cavity decreases, stimulated radiation is suppressed, the photon density decreases, the working material is pumped and a large particle number inversion occurs, and the degree of particle number inversion is much greater than when the Q value in the cavity is high. When the bias voltage of the lithium niobate modulation module is 0, the optical path is called back, the central wavelength can be reduced through the filter loss, the Q value in the cavity increases, and the high degree of particle number inversion in the cavity will emit high-intensity light radiation to form pulsed light, and then the reversed particle number will fail, and the laser oscillation ends. Repeat this process to achieve Q-switched pulse laser output.

[0041] Based on the above embodiment, the reflectivity of the reflector 6 is less than or equal to 10%. The wavelength that meets the resonance condition and the gain is greater than the loss will be emitted from the reflector 6.

[0042] In the related art, the Q-switched pulse laser realized by using an electro-optical switch requires two polarizers and an electro-optical crystal to be combined, which increases the complexity of the system. The shortening of the pulse length widens the spectrum. The present disclosure proposes a method of using a filter to adjust the Q value of the resonant cavity, which reduces the complexity of the system, increases stability, and narrows the spectrum width.

[0043] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A narrow linewidth pulse laser, characterized in that: include: A laser gain chip (2), comprising a first reflection end face (1) and a second reflection end face (3), used for forming a population inversion and lasing light; A reflector (6) is located on the light-emitting side; the reflector (6) and the first reflective end surface (1) form a resonant cavity; A lithium niobate modulation module (4), located in the resonant cavity and used for optical path control; The filter (5) is located in the resonant cavity and is used to filter out light that deviates from the central wavelength.

2. The narrow linewidth pulse laser according to claim 1, characterized in that: The laser gain chip (2) is connected to an electrical drive to form the particle population inversion and lasing light.

3. The narrow linewidth pulse laser according to claim 1, characterized in that: The reflectivity of the first reflective end surface (1) is greater than or equal to 90%; and the reflectivity of the second reflective end surface (3) is less than or equal to 0.05%.

4. The narrow linewidth pulse laser according to claim 3, characterized in that: The light emitted by the laser gain chip (2) is emitted via the second reflective end face (3).

5. The narrow linewidth pulse laser according to claim 1, characterized in that: The reflectivity of the reflector (6) is less than or equal to 10%.

6. The narrow linewidth pulse laser according to claim 5, characterized in that: The wavelength that meets the resonance condition and has a gain greater than a loss will be emitted from the reflector (6).

7. The narrow linewidth pulse laser according to claim 1, characterized in that: The lithium niobate modulation module (4) comprises a lithium niobate electro-optical crystal and a thin film electrode arranged thereon, and the lithium niobate electro-optical crystal is electrically connected to the thin film electrode.

8. The narrow linewidth pulse laser according to claim 7, characterized in that: The electric field loaded on the lithium niobate modulation module (4) is parallel to the polarization plane of light, and the electric field changes rapidly and periodically.

9. The narrow linewidth pulse laser according to claim 1, characterized in that: The filter (5) is a grating filter, and the filter (5) is located in the optical axis direction of the resonant cavity.

10. The narrow linewidth pulse laser according to claim 9, characterized in that: The filter (5) finely separates light of different wavelengths, and the wavelength that can be passed by the filter (5) is the wavelength of light of the central wavelength of the laser that meets the resonance condition.

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