A mid-infrared thermal depolarization compensation laser based on trapezoidal electro-optical crystal

Abstract

A mid-infrared thermal depolarization compensation laser based on a trapezoidal electro-optical crystal. The invention belongs to the field of laser technology, and specifically to the technical field of vortex spot ring pulse continuous laser system. The invention solves the problems of the increase of the cavity length of the resonant cavity, the complexity of the cavity structure, and the limited compensation effect in the previous thermal depolarization compensation method. The laser comprises a trapezoidal photoelectric Q-switched crystal, a 45° total reflection mirror, a 45° polarization beam splitter, an LD side pump module, and a total reflection mirror; one side of the trapezoidal photoelectric Q-switched crystal shares a common optical path with the 45° polarization beam splitter, the LD side pump module, and the total reflection mirror, and the other side of the trapezoidal photoelectric Q-switched crystal shares a common optical path with the 45° total reflection mirror; the 45° total reflection mirror and the 45° polarization beam splitter share a common optical path.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to the technical field of mid-infrared thermal depolarization compensation lasers. Background Art

[0002] Mid-infrared 3-micron pulsed lasers have great application potential and demand in scientific research, medicine, military and other fields. At present, the method of using rare earth ion doping as laser gain medium to directly achieve mid-infrared laser output has been widely studied. This type of crystal itself has a self-termination effect and poor thermal performance. During the operation of the laser, most of the pumping energy is converted into heat dissipated in the laser crystal. Uneven pumping and heat transfer cause uneven temperature distribution inside the crystal, forming thermal stress and causing uneven distribution of crystal refractive index, making the isotropic laser medium anisotropic. When the laser passes through an anisotropic refractive index medium, the laser wavefront will be distorted, and the linearly polarized light will produce a depolarization effect after being incident on the laser medium with stress birefringence. The depolarized beam cannot pass completely through the polarizer, so it will lead to the loss of light energy and the deterioration of the quality of the hot spot. Therefore, it is necessary to compensate for the thermal depolarization loss to meet the needs of high beam quality and high peak power mid-infrared lasers in practical applications.

[0003] At present, the main methods for achieving thermal depolarization compensation include the quarter-wave plate method, the dual laser crystal rod series method, the dual electro-optical Q-switching method, etc. Among them, the dual laser crystal series method and the dual electro-optical Q-switching method can achieve complete compensation for thermal depolarization, but the use of these two methods for compensation will inevitably lead to an increase in the length of the resonant cavity and a complication of the resonant cavity structure. Although the quarter-wave plate method has a simple cavity structure, its compensation effect is limited and can only achieve partial compensation. Summary of the invention

[0004] In order to solve the problems of increased cavity length, complicated cavity structure and limited compensation effect in the previous thermal depolarization compensation methods, the present invention proposes a mid-infrared thermal depolarization compensation laser based on a trapezoidal electro-optical crystal.

[0005] The laser comprises a trapezoidal photoelectric Q-switched crystal, a 45° total reflection mirror, a 45° polarization beam splitter, an LD side pump module and a total reflection mirror;

[0006] One side of the trapezoidal photoelectric Q-switched crystal shares a common optical path with a 45° polarization beam splitter, an LD side pump module and a total reflection mirror, and another side of the trapezoidal photoelectric Q-switched crystal shares a common optical path with a 45° total reflection mirror; the 45° total reflection mirror and the 45° polarization beam splitter share a common optical path;

[0007] The trapezoidal photoelectric Q-switched crystal is an isosceles trapezoid with a base and waist at an angle of 45 degrees, and is used to connect the optical path and cooperate with a 45-degree polarization beam splitter to play the role of cavity dumping pulse modulation.

[0008] Furthermore, the LD side pump module comprises a plurality of groups of LD target bars uniformly surrounding the gain medium for pumping, and the number of the LD target bar groups is an odd number.

[0009] Furthermore, both sides of the 45° polarization beam splitter are coated with P light high transmittance and S light high reflectivity films.

[0010] Furthermore, the trapezoidal photoelectric Q-switched crystal, the 45° total reflection mirror, the 45° polarization beam splitter and the total reflection mirror form a resonant cavity.

[0011] Furthermore, the laser emitted by the LD side pump module enters a 45° polarization beam splitter and is decomposed into P polarized light and S polarized light that are perpendicular to each other.

[0012] Further, the P polarized light is incident on the trapezoidal photoelectric Q-switched crystal through a 45° polarization beam splitter, a half-wave voltage is applied to the trapezoidal photoelectric Q-switched crystal, the P polarized light is converted into S polarized light through the trapezoidal photoelectric Q-switched crystal, the S polarized light is incident on a 45° total reflection mirror, is reflected to the 45° polarization beam splitter, and then is reflected into the total reflection mirror through the 45° polarization beam splitter, the laser is confined in the resonant cavity to form oscillation, the light field in the resonant cavity is gradually enhanced, and energy is stored in the resonant cavity, when the energy in the resonant cavity reaches the expected value, the half-wave voltage is stopped on the trapezoidal photoelectric Q-switched crystal, the P polarized light passes through the trapezoidal photoelectric Q-switched crystal without changing the polarization characteristics, is emitted from the trapezoidal photoelectric Q-switched crystal and then incident on a 45° total reflection mirror, is reflected to the 45° polarization beam splitter, and then is emitted through the 45° polarization beam splitter.

[0013] Further, the S polarized light is reflected to the 45° total reflection mirror through the 45° polarization beam splitter, and the 45° total reflection mirror reflects the S polarized light into the trapezoidal photoelectric Q-switched crystal, and a half-wave voltage is applied to the trapezoidal photoelectric Q-switched crystal. The S polarized light is converted from S polarized light to P polarized light through the trapezoidal photoelectric Q-switched crystal, and then enters the total reflection mirror through the 45° polarization beam splitter. The laser is confined in the resonant cavity to form oscillation, and the light field in the resonant cavity is gradually enhanced, and energy is stored in the resonant cavity. When the energy in the resonant cavity reaches the expected value, the half-wave voltage is stopped on the trapezoidal photoelectric Q-switched crystal, and the S polarized light passes through the trapezoidal photoelectric Q-switched crystal without changing the polarization characteristics, and is emitted from the trapezoidal photoelectric Q-switched crystal and then emitted into the 45° polarization beam splitter.

[0014] The beneficial effects of the laser of the present invention are:

[0015] The thermal depolarization effect is fully compensated while reducing the complexity of the cavity structure; and the cavity dumping technology is used to store laser energy in the laser resonant cavity and release it quickly at a specific moment, further reducing the loss and making the energy in the cavity more effectively converted into output pulse energy.

[0016] A trapezoidal electro-optical crystal is used, so that it can realize electro-optical pulse modulation while taking into account the function of connecting the return optical path, and it is applied to thermal depolarization compensation, simplifying the cavity structure, and reducing the inherent loss of the resonant cavity. At present, due to the nature of the Er laser crystal in the mid-infrared band, there is a self-termination effect, which leads to its limited energy and storage energy. Compared with the Q-switching technology, the cavity dumping technology stores energy in the resonant cavity, so its energy existence limit will be higher. The output laser performance finally obtained will be better. At present, due to the nature of the Er laser crystal in the mid-infrared band, there is a self-termination effect, which leads to its limited energy and storage energy. Compared with the Q-switching technology, the cavity dumping technology stores energy in the resonant cavity, so its energy existence limit will be higher. The output laser performance finally obtained will be better. The structure designed by the present invention can simultaneously combine the cavity dumping technology to realize high-energy pulsed laser. Compared with the conventional electro-optical Q-switched laser output, the obtained laser peak power is higher, the pulse width is narrower, and the energy utilization rate is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The structure diagram of the mid-infrared thermal depolarization compensation laser based on the trapezoidal electro-optical crystal in the embodiment of the present invention;

[0018] Figure 2 Schematic diagram of the optical path propagation of the P-polarized component laser separated by a 45° polarization beam splitter in an embodiment of the present invention;

[0019] Figure 3 Schematic diagram of the optical path propagation of the S-polarized component laser separated by a 45° polarization beam splitter in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0021] Embodiment 1,

[0022] This embodiment provides a mid-infrared thermal depolarization compensation laser based on a trapezoidal electro-optical crystal.

[0023] A trapezoidal electro-optical crystal is used to achieve electro-optical pulse modulation while also taking into account the function of connecting the return optical path. It is used for thermal depolarization compensation, simplifies the cavity structure, and reduces the inherent loss of the resonant cavity. At the same time, the cavity dumping technology is combined to achieve high-energy pulsed laser. Compared with conventional electro-optical Q-switched laser output, the obtained laser peak power is higher, the pulse width is narrower, and the energy utilization rate is higher.

[0024] The laser comprises a trapezoidal photoelectric Q-switched crystal 1, a 45° total reflection mirror 2, a 45° polarization beam splitter 3, an LD side pump module 4 and a total reflection mirror 6;

[0025] One side of the trapezoidal photoelectric Q-switched crystal 1 shares an optical path with a 45° polarization beam splitter 3, an LD side pump module 4 and a total reflection mirror 6, and another side of the trapezoidal photoelectric Q-switched crystal 1 shares an optical path with a 45° total reflection mirror 2; the 45° total reflection mirror 2 shares an optical path with a 45° polarization beam splitter 3.

[0026] The trapezoidal photoelectric Q-switched crystal 1 is an isosceles trapezoid with a base and waist at an angle of 45 degrees, and is used to connect the optical path and cooperate with the 45-degree polarization beam splitter 3 to play the role of cavity dumping pulse modulation.

[0027] The LD side pump module 4 is composed of multiple groups of LD target bars uniformly surrounding the gain medium 5 for pumping. To prevent the LD target bars from being damaged by collinearity, the number of LD target bar groups is an odd number.

[0028] The 45° polarization beam splitter 3 is coated with P light high transmittance and S light high reflectivity films on both sides, and is used to split the laser into two beams of light with different polarization components, and has the function of polarization beam combining.

[0029] The trapezoidal photoelectric Q-switched crystal 1, the 45° total reflection mirror 2, the 45° polarization beam splitter 3 and the total reflection mirror 6 form a resonant cavity.

[0030] The laser light emitted by the LD side pump module 4 enters the 45° polarization beam splitter 3 and is decomposed into P polarized light and S polarized light that are perpendicular to each other.

[0031] The mid-infrared thermal depolarization compensation laser based on trapezoidal electro-optical crystal uses a trapezoidal electro-optical crystal to connect in series the oscillation light paths of the two polarization characteristics P polarization and S polarization after being polarized by a 45° polarization beam splitter 3 without overflowing the cavity, thereby compensating for the thermal depolarization loss and realizing pulse modulation of the laser; because the cavity structure makes the optical path of the light with two polarization characteristics in the cavity the same, it is also conducive to realizing the orthogonal polarization laser output.

[0032] Principle of thermal depolarization loss: During the operation of the laser, most of the pumping energy is converted into heat and dissipated in the laser crystal. Uneven pumping and heat transfer cause uneven temperature distribution inside the crystal, forming thermal stress that causes uneven distribution of the crystal refractive index, making the isotropic laser medium anisotropic. When the laser passes through an anisotropic refractive index medium, the laser wavefront will be distorted, and a depolarization effect will occur when the linearly polarized light is incident on the laser medium with stress birefringence. The depolarized light beam cannot pass completely through the polarizer, so it will lead to loss of light energy.

[0033] Embodiment 2,

[0034] This embodiment is a further limitation of the first embodiment, and describes the optical path propagation of the P polarized component laser separated by a 45° polarization beam splitter. The schematic diagram of the propagation is shown in FIG. Figure 2 shown.

[0035] The P polarized light passes through the 45° polarization beam splitter 3 and enters the interior of the trapezoidal photoelectric Q-switched crystal 1. A half-wave voltage is applied to the trapezoidal photoelectric Q-switched crystal 1. The P polarized light passes through the trapezoidal photoelectric Q-switched crystal 1 and is converted from P polarized light to S polarized light. The S polarized light enters the 45° total reflection mirror 2, is reflected to the 45° polarization beam splitter 3, and then is reflected to the total reflection mirror 6 through the 45° polarization beam splitter 3. The laser is confined in the resonant cavity to form oscillation, the light field in the resonant cavity is gradually enhanced, and energy is stored in the resonant cavity. When the energy in the resonant cavity reaches the expected value, the half-wave voltage is stopped on the trapezoidal photoelectric Q-switched crystal 1. The P polarized light passes through the trapezoidal photoelectric Q-switched crystal 1 without changing the polarization characteristics. After being emitted from the trapezoidal photoelectric Q-switched crystal 1, it enters the 45° total reflection mirror 2, is reflected to the 45° polarization beam splitter 3, and then is emitted through the 45° polarization beam splitter 3.

[0036] Embodiment 3,

[0037] This embodiment is a further limitation of the embodiment 1, and describes the optical path propagation of the S polarized component laser separated by a 45° polarization beam splitter. The schematic diagram of the propagation is shown in FIG. Figure 3 shown.

[0038] The S polarized light is reflected to the 45° total reflection mirror 2 through the 45° polarization beam splitter 3, and the 45° total reflection mirror 2 reflects the S polarized light into the trapezoidal photoelectric Q-switched crystal 1, and a half-wave voltage is applied to the trapezoidal photoelectric Q-switched crystal 1. The S polarized light is converted from S polarized light to P polarized light through the trapezoidal photoelectric Q-switched crystal 1, and then enters the total reflection mirror 6 through the 45° polarization beam splitter 3. The laser is confined in the resonant cavity to form oscillation, and the light field in the resonant cavity is gradually enhanced, and energy is stored in the resonant cavity. When the energy in the resonant cavity reaches the expected value, the half-wave voltage is stopped on the trapezoidal photoelectric Q-switched crystal 1, and the S polarized light passes through the trapezoidal photoelectric Q-switched crystal 1 without changing the polarization characteristics. After being emitted from the trapezoidal photoelectric Q-switched crystal 1, it is emitted into the 45° polarization beam splitter 3 and then emitted.

[0039] Since the optical paths of the two polarization components of light oscillating in the resonant cavity are the same, the electro-optical crystal achieves synchronous cavity inversion modulation of P and S light at the same time.

[0040] The present invention designs the electro-optical crystal into a trapezoidal structure and uses it to realize the return connection of the optical path, which not only realizes the complete compensation of thermal depolarization loss and the pulse modulation of the laser, but also improves the energy conversion efficiency. In addition, since the optical path of the laser P and S light in the cavity is the same, the gain amplification is realized at the gain medium at the same time, and the output laser has orthogonal polarization characteristics.

Claims

1. A mid-infrared thermal depolarization compensation laser based on a trapezoidal electro-optical crystal, characterized in that: The laser comprises a trapezoidal photoelectric Q-switched crystal (1), a 45° total reflection mirror (2), a 45° polarization beam splitter (3), an LD side pump module (4) and a total reflection mirror (6); One side of the trapezoidal photoelectric Q-switched crystal (1) shares a light path with a 45° polarization beam splitter (3), an LD side pump module (4) and a total reflection mirror (6); another side of the trapezoidal photoelectric Q-switched crystal (1) shares a light path with a 45° total reflection mirror (2); and the 45° total reflection mirror (2) and the 45° polarization beam splitter (3) share a light path; The trapezoidal photoelectric Q-switched crystal (1) is an isosceles trapezoid with a bottom and side angled at 45 degrees, and is used to connect the optical path and cooperate with the 45-degree polarization beam splitter (3) to play the role of cavity dumping pulse modulation; The two sides of the trapezoidal photoelectric Q-switched crystal (1) respectively reflect polarized light, thus playing the functions of folding back the light path and connecting the light path; The 45° polarization beam splitter (3) is coated on both sides with a P light high transmittance film and an S light high reflectance film.

2. The mid-infrared thermal depolarization compensation laser based on trapezoidal electro-optical crystal according to claim 1, characterized in that: The LD side pump module (4) comprises a plurality of groups of LD target bars uniformly surrounding the gain medium (5) for pumping, and the number of the LD target bar groups is an odd number.

3. The mid-infrared thermal depolarization compensation laser based on trapezoidal electro-optical crystal according to claim 2, characterized in that: The trapezoidal photoelectric Q-switched crystal (1), the 45° total reflection mirror (2), the 45° polarization beam splitter (3) and the total reflection mirror (6) form a resonant cavity.

4. The mid-infrared thermal depolarization compensation laser based on trapezoidal electro-optical crystal according to claim 3, characterized in that: The laser light emitted by the LD side pump module (4) is incident on a 45° polarization beam splitter (3) and is decomposed into P polarized light and S polarized light that are perpendicular to each other.

5. The mid-infrared thermal depolarization compensation laser based on trapezoidal electro-optical crystal according to claim 4, characterized in that: The P polarized light passes through a 45° polarization beam splitter (3) and enters the interior of a trapezoidal photoelectric Q-switched crystal (1). A half-wave voltage is applied to the trapezoidal photoelectric Q-switched crystal (1). The P polarized light passes through the trapezoidal photoelectric Q-switched crystal (1) and is converted from P polarized light to S polarized light. The S polarized light enters a 45° total reflection mirror (2) and is reflected to the 45° polarization beam splitter (3). Then, it passes through the 45° polarization beam splitter (3) and is reflected to the total reflection mirror (6). The laser is confined in the resonant cavity to form oscillation. The light field in the resonant cavity is gradually enhanced and energy is stored in the resonant cavity. When the energy in the resonant cavity reaches a desired value, the half-wave voltage is stopped from being applied to the trapezoidal photoelectric Q-switched crystal (1). The P polarized light passes through the trapezoidal photoelectric Q-switched crystal (1) without changing its polarization characteristics. After being emitted from the trapezoidal photoelectric Q-switched crystal (1), it enters a 45° total reflection mirror (2), is reflected to the 45° polarization beam splitter (3), and then is emitted through the 45° polarization beam splitter (3).

6. The mid-infrared thermal depolarization compensation laser based on trapezoidal electro-optical crystal according to claim 5, characterized in that: The S polarized light passes through a 45° polarization beam splitter (3) and is reflected to a 45° total reflection mirror (2). The 45° total reflection mirror (2) reflects the S polarized light into a trapezoidal photoelectric Q-switched crystal (1). A half-wave voltage is applied to the trapezoidal photoelectric Q-switched crystal (1). The S polarized light passes through the trapezoidal photoelectric Q-switched crystal (1) and is converted into P polarized light. The light then passes through the 45° polarization beam splitter (3) and enters a total reflection mirror (6). The laser is confined in the resonant cavity to form oscillations. The light field in the resonant cavity is gradually enhanced, and energy is stored in the resonant cavity. When the energy in the resonant cavity reaches a desired value, the half-wave voltage is stopped from being applied to the trapezoidal photoelectric Q-switched crystal (1). The S polarized light passes through the trapezoidal photoelectric Q-switched crystal (1) without changing its polarization characteristics. The light is emitted from the trapezoidal photoelectric Q-switched crystal (1) and then enters the 45° polarization beam splitter (3) and then is emitted.

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