Narrow linewidth subnanosecond laser

Abstract

The invention relates to the technical field of lasers, and discloses a narrow-linewidth subnanosecond laser. The narrow-linewidth subnanosecond laser comprises a pumping source, a resonant cavity and a coupling system, the pumping source, the resonant cavity and the coupling system are arranged along the same optical axis, and the pumping source serves as gain laser. A laser crystal, a polaroid, a quarter-wave plate, an electro-optical modulator and a Bragg grating are sequentially arranged in the resonant cavity along an optical axis. The end face of the Bragg grating away from the coupling system is plated with a beam-splitting film. Laser forms oscillation in the resonant cavity, and the Bragg grating plays a role in screening longitudinal modes, so that narrow linewidth output is realized. The polaroid and the quarter-wave plate are matched to play roles of polarization analysis and light splitting. The voltage on the electro-optical modulator is periodically adjusted to periodically adjust the loss in the resonant cavity so as to output the subnanosecond pulse laser.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and particularly to a narrow linewidth sub-nanosecond laser. Background Art

[0002] Sub-nanosecond lasers can release high energy in an extremely short time, making them have the characteristics of high energy and high peak power. Therefore, they can ensure processing accuracy and reduce the thermal impact on the surrounding area. This makes sub-nanosecond lasers have significant advantages in the field of fine processing.

[0003] The laser linewidth is the full width at half maximum of the emission spectrum of a laser light source, that is, the width between two frequencies corresponding to half the peak height (sometimes also taking 1 / e). It reflects the purity and coherence of the laser spectrum and is an important parameter in laser performance evaluation. The characteristics of the laser linewidth are mainly reflected in the purity and coherence of the laser spectrum it reflects. The smaller the linewidth value, the higher the purity of the spectrum and the better the monochromaticity of the laser. Such lasers usually have extremely small phase or frequency noise and very small relative intensity noise, thus ensuring the stability and reliability of the laser output. At the same time, the smaller the linewidth value, the stronger the corresponding coherence, manifested as an extremely long coherence length. This characteristic makes narrow linewidth lasers have significant advantages in applications requiring high coherence.

[0004] In the scientific research field, narrow linewidth lasers are the core components of precision measurement systems such as optical atomic clocks and gravitational wave detection. Their high stability and high coherence provide strong support for scientific research. In the industrial field, narrow linewidth lasers play an important role in fiber optic communication, lidar, laser processing, etc. For example, in fiber optic communication, narrow linewidth lasers can provide a stable light source, improving the transmission efficiency and stability of the communication system; in lidar, narrow linewidth lasers can enhance the detection accuracy and anti-interference ability of the radar; in laser processing, narrow linewidth lasers can achieve more precise processing effects, improving the processing quality and efficiency.

[0005] To narrow the laser pulse width, it is usually necessary to shorten the resonator length or increase the transmittance of the output coupling mirror. However, the length of the resonator is limited by the size of the gain medium and the components inside the cavity. It is very difficult to achieve sub-nanosecond high-energy laser output under high repetition rate conditions by using the method of shortening the resonator length. By using the method of increasing the transmittance of the output mirror, although the laser pulse width can be narrowed by increasing the pump power, there are problems such as a high threshold, easy thermal cracking of the laser crystal, and broadening of the rising edge of the laser pulse. Summary of the Invention

[0006] Based on the above, the purpose of the present invention is to provide a narrow linewidth sub-nanosecond laser to solve the above technical problems.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A narrow linewidth sub-nanosecond laser, comprising: a pump source, a resonant cavity and a coupling system, wherein the pump source, the resonant cavity and the coupling system are arranged along the same optical axis; Inside the resonant cavity, along the optical axis, there are sequentially arranged: a laser crystal, a polarizer, a quarter-wave plate, an electro-optic modulator and a Bragg grating; The end face of the Bragg grating away from the coupling system is coated with a beam splitting film.

[0008] As a preferred solution of the narrow linewidth sub-nanosecond laser, the end face of the laser crystal close to the coupling system is coated with a reflective film.

[0009] As a preferred solution of the narrow linewidth sub-nanosecond laser, a mirror is provided between the laser crystal and the coupling system.

[0010] As a preferred solution of the narrow linewidth sub-nanosecond laser, the resonant cavity further includes a Peltier thermoelectric module, and the Peltier thermoelectric module is fixedly connected to the Bragg grating.

[0011] As a preferred solution of the narrow linewidth sub-nanosecond laser, the output mode of the pump source is spatial light output or fiber-coupled output, and the pumping mode is pulsed pumping or continuous pumping.

[0012] As a preferred solution of the narrow linewidth sub-nanosecond laser, the coupling system adopts a single lens or a lens group structure to couple the pump light to the laser crystal with a certain spot size.

[0013] As a preferred solution of the narrow linewidth sub-nanosecond laser, the laser crystal is a laser crystal capable of outputting laser with a wavelength of 1064 nm, including but not limited to: Nd:YVO4 crystal, Nd:GdVO4 crystal, Nd:YAG crystal and Nd:YLF crystal.

[0014] As a preferred solution of the narrow linewidth sub-nanosecond laser, it operates in an electro-optic Q-switching mode, and the Q-switching mode is pressure-type electro-optic Q-switching or voltage-drop type electro-optic Q-switching.

[0015] As a preferred solution of the narrow linewidth sub-nanosecond laser, the electro-optic modulator is one of an RTP electro-optic modulator, a BBO electro-optic modulator, an LGS electro-optic modulator, an LN electro-optic modulator or a KD*P electro-optic modulator.

[0016] As a preferred solution of the narrow linewidth sub-nanosecond laser, the Bragg grating is one of a bulk Bragg grating or a fiber Bragg grating.

[0017] The beneficial effects of the present invention are: The present invention provides a narrow linewidth sub-nanosecond laser, which includes: a pump source and a resonant cavity. The pump source and the resonant cavity are arranged along the same optical axis, and the pump source serves as the gain laser. Inside the resonant cavity, along the optical axis, there are successively arranged: a coupling system, a laser crystal, a polarizer, a quarter-wave plate, an electro-optic modulator, and a Bragg grating. The end face of the Bragg grating far from the coupling system is coated with a beam-splitting film. The laser forms oscillations in the resonant cavity, where the Bragg grating plays a role in screening longitudinal modes to achieve narrow linewidth output. The polarizer and the quarter-wave plate cooperate to play the roles of polarization detection and beam splitting. By periodically adjusting the voltage on the electro-optic modulator, the loss in the resonant cavity is periodically adjusted, thereby achieving the output of sub-nanosecond pulsed laser. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the content of the embodiments of the present invention and these drawings.

[0019] Figure 1 It is a schematic diagram of the narrow linewidth sub-nanosecond laser provided in the first specific embodiment of the present invention; Figure 2 It is a schematic diagram of the narrow linewidth sub-nanosecond laser provided in the second specific embodiment of the present invention; Figure 3 It is a schematic diagram of the narrow linewidth sub-nanosecond laser provided in the third specific embodiment of the present invention.

[0020] In the figure: 100 - pump source; 300 - coupling system; 200 - resonant cavity; 201 - laser crystal; 202 - polarizer; 203 - quarter-wave plate; 204 - electro-optic modulator; 205 - Bragg grating; 206 - mirror; 207 - Peltier thermoelectric module. Specific Embodiments

[0021] To make the technical problems solved by the present invention, the technical solutions adopted, and the achieved technical effects clearer, the following will further describe in detail the technical solutions of the embodiments of the present invention with reference to the drawings. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention. Embodiment

[0022] As Figure 1 shown, this embodiment provides a narrow linewidth sub-nanosecond laser, and the device includes: A pump source 100, a resonant cavity 200, and a coupling system 300 are arranged along the same optical axis. Inside the resonant cavity 200, a laser crystal 201, a polarizer 202, a quarter-wave plate 203, an electro-optic modulator 204, and a Bragg grating 205 are sequentially arranged along the optical axis. A beam-splitting film is coated on the end face of the Bragg grating 205 away from the coupling system 300.

[0023] The output light forms an oscillation inside the resonant cavity 200. Specifically, a reflective film is coated on the end face of the laser crystal 201 close to the coupling system 300. A beam-splitting film is coated on the end face of the Bragg grating 205 away from the coupling system 300. The laser forms an oscillation between the end face of the laser crystal 201 close to the coupling system 300 and the end face of the Bragg grating 205 away from the coupling system 300. The function of the beam-splitting film is to shorten the cavity length, thereby achieving two effects. First, the pulse width of the laser can be compressed to the sub-nanosecond level; second, the line width is further reduced.

[0024] Among them, the Bragg grating 205 plays a role in screening longitudinal modes to achieve narrow line-width output. The polarizer 202 and the quarter-wave plate 203 cooperate to play the roles of polarization detection and beam splitting. By periodically adjusting the voltage on the electro-optic modulator 204, the loss inside the resonant cavity 200 is periodically adjusted, thereby achieving the output of sub-nanosecond pulsed laser.

[0025] In this embodiment, a fiber-coupled output semiconductor laser is used as the pump source 100, and the pumping method is pulsed pumping. The pump source 100 outputs a laser with a wavelength of 878.6 nm as the gain laser. The gain laser enters the coupling system 300 through an optical fiber and is incident on the laser crystal 201 after being shaped by the coupling system 300.

[0026] It should be noted that using spatial light output can replace fiber-coupled output to achieve the same technical effect. And according to the required output light parameters, the pumping method can also use continuous pumping instead of pulsed pumping.

[0027] The coupling system 300 adopts a single-lens or lens-group structure. An anti-reflection film for the pump source 100 is coated on the lens surface, and the laser generated by the pump source 100 is coupled to the laser crystal 201 with a certain spot size, realizing the mode matching between the pump light and the oscillating light inside the resonator. Specifically, in this embodiment, the coupling system 300 includes a collimating lens and a focusing lens.

[0028] After the laser crystal 201 absorbs the pump light from the pump source 100, population inversion is achieved. When the gain in the laser crystal 201 is greater than the loss of the resonant cavity, a laser oscillation can be established, which is a necessary component for generating laser. The laser crystal 201 is a laser crystal capable of outputting laser with a wavelength of 1064 nm, including but not limited to: Nd:YVO4 crystal, Nd:GdVO4 crystal, Nd:YAG crystal, and Nd:YLF crystal. In this embodiment, the laser crystal 201 is an Nd:YVO4 crystal.

[0029] The polarizer 202 is used to select light with a specific polarization direction and block other polarized light. The linearly polarized light forms a 45° angle with the fast axis direction of the quarter-wave plate 203, and the quarter-wave plate 203 converts the linearly polarized light into circularly polarized light. The quarter-wave plate 203 and the electro-optic modulator 204 play a role in polarization conversion in the resonant cavity 200 to achieve Q-switched pulse output.

[0030] In this embodiment, the narrow linewidth sub-nanosecond laser operates in a pressurized electro-optic Q-switching mode. It should be noted that a similar technical effect can also be achieved by using a step-down electro-optic Q-switching method. However, by using the step-up electro-optic Q-switching method, the working time of the electro-optic crystal can be effectively reduced, and the laser life can be improved. The electro-optic modulator 204 is an RTP electro-optic modulator. It should be noted that a similar technical effect can also be achieved by using a BBO electro-optic modulator, an LGS electro-optic modulator, an LN electro-optic modulator, or a KD*P electro-optic modulator.

[0031] The quarter-wave plate 203 and the electro-optic modulator 204 play a role in polarization conversion in the resonant cavity 200 to achieve Q-switched pulse output. In this embodiment, the laser uses pressurized electro-optic Q-switching. The linearly polarized light generated by the laser crystal 201 and the polarizer 202 forms a 45° angle with the fast axis direction of the quarter-wave plate 203, converting the linearly polarized light into circularly polarized light. When no λ / 4 voltage is applied to the electro-optic modulator 204, it has no effect on the laser polarization state. The circularly polarized light is reflected by the Bragg grating 205 and then passes through the quarter-wave plate 203 again and becomes linearly polarized light again. At this time, the polarization direction rotates by 90°, and it cannot pass through the polarizer 202, so the resonant cavity 200 cannot output laser, achieving the "closed door" effect. When a λ / 4 voltage is applied to the electro-optic modulator 204, the quarter-wave plate 203 converts it into circularly polarized light. After being reflected by the Bragg grating 205, it passes through the electro-optic modulator 204 and the quarter-wave plate 203 again, and is restored to linearly polarized light with the same polarization direction as the original. It passes through the polarizer 202 to form an oscillation and output high-energy pulses, and the resonant cavity achieves the "open door" effect and outputs Q-switched pulses. The electro-optic modulator 204 in this embodiment is an RTP electro-optic switch. The output mirror of the resonant cavity 200 is the Bragg grating 205, and its reflection surface is flat, mainly to achieve the reflection of the fundamental frequency light. Its surface can also be processed into a concave surface or a convex surface.

[0032] The Bragg grating 205 is one of a volume Bragg grating or an optical fiber Bragg grating. An optical Bragg grating is a transparent device with a periodically varying refractive index, and has a high reflectivity in a wavelength region (bandwidth) near a specific wavelength.

[0033] In this embodiment, the Bragg grating 205 is a volume Bragg grating. Using the volume Bragg grating as the output mirror of the resonator 200 to filter longitudinal modes and achieve the output of narrow-linewidth laser. Embodiment

[0034] The basic structure of the laser provided in this embodiment is the same as that of the first embodiment, only some structures are different. This embodiment only describes the structures different from those of the first embodiment.

[0035] As Figure 2 shown, in this embodiment, the resonator 200 further includes a mirror 206. The mirror 206 transmits the pump light and reflects the output light, and the output light forms an oscillation between the mirror 206 and the end face of the Bragg grating 205 far from the coupling system 300. Adding the mirror 206 reduces the debugging difficulty. Embodiment

[0036] The basic structure of the laser provided in this embodiment is the same as that of the first embodiment, only some structures are different. This embodiment only describes the structures different from those of the first embodiment.

[0037] As Figure 3 shown, in this embodiment, the resonator 200 further includes a Peltier thermoelectric module 207. The Peltier thermoelectric module 207 is fixedly connected to the Bragg grating 205. The Peltier thermoelectric module 207 includes a metal heat sink and a Peltier thermoelectric cooler, and the Peltier thermoelectric cooler is embedded inside the metal heat sink. By energizing the Peltier thermoelectric cooler, the temperature of the metal heat sink is adjusted, and then the temperature of the Bragg grating 205 is adjusted. Adjusting the temperature of the Bragg grating 205 will adjust the effective refractive index of the crystal and the grating period, and further the wavelength of the output light can be adjusted within the picometer level. In the field of lidar, adjusting the wavelength of the output light can better match the central wavelength required by the receiving end, thereby effectively improving the accuracy and resolution of the lidar.

[0038] Further preferably, a thermal conductive material, such as thermal conductive silicone grease and soft metal, etc., is further installed between the Peltier thermoelectric module 207 and the Bragg grating 205, which is used to fill the tiny gap between the Peltier thermoelectric module 207 and the Bragg grating 205, enhance the thermal conductivity effect, and thus optimize the temperature control effect.

[0039] Note that the above is only a preferred embodiment of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein. Various obvious changes, re-adjustments, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, it may also include more other equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.

[0040] 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. It 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. Therefore, it should not be understood as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions.

[0041] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "mounted", "connected", and "coupled" 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.

Claims

1. A narrow linewidth sub-nanosecond laser, characterized in that: include: A pump source (100), a resonant cavity (200) and a coupling system (300), wherein the pump source (100), the resonant cavity (200) and the coupling system (300) are arranged along the same optical axis; The resonant cavity (200) is provided with the following in sequence along the optical axis: a laser crystal (201), a polarizing plate (202), a quarter-wave plate (203), an electro-optic modulator (204), and a Bragg grating (205); The end surface of the Bragg grating (205) away from the coupling system (300) is coated with a beam splitting film.

2. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: The end face of the laser crystal (201) close to the coupling system (300) is coated with a reflective film.

3. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: A reflecting mirror (206) is provided between the laser crystal (201) and the coupling system (300).

4. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: The resonant cavity (200) further comprises a Peltier thermoelectric module (207), and the Peltier thermoelectric module (207) is tightly connected to the Bragg grating (205).

5. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: The output mode of the pump source (100) is spatial light output or optical fiber coupling output, and the pumping mode is pulse pumping or continuous pumping.

6. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: The coupling system (300) adopts a single lens or a lens group structure to couple the pump light to the laser crystal (201) with a certain spot size.

7. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: The laser crystal (201) is a laser crystal capable of outputting a wavelength of 1064 nm, including but not limited to: Nd:YVO4 crystal, Nd:GdVO4 crystal, Nd:YAG crystal and Nd:YLF crystal.

8. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: It works by electro-optical Q-switching, and the Q-switching method is voltage-added electro-optical Q-switching or voltage-down electro-optical Q-switching.

9. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: The electro-optic modulator (204) is one of an RTP electro-optic modulator, a BBO electro-optic modulator, a LGS electro-optic modulator, a LN electro-optic modulator or a KD*P electro-optic modulator.

10. The narrow linewidth sub-nanosecond laser according to claim 1, characterized in that: The Bragg grating (205) is a volume Bragg grating or a fiber Bragg grating.

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