A dispersion compensation method for high-energy laser systems based on dual liquid crystal polarization gratings

Abstract

The present invention specifically relates to a dispersion compensation method for a high-energy laser system based on a dual liquid crystal polarization grating. The high-energy laser system includes a main laser emission branch and a beacon light tracking branch. A galvanometer is added to the beacon light tracking branch to perform dispersion compensation. The galvanometer is placed at an angle of 135° with the x-axis on the line where the fast mirror and the wavelength splitter are located, and is placed directly below the second narrowband filter. The deflection angle difference between the two wavelengths of the 1064nm main laser and the 1053nm beacon light is calculated based on the periodic parameters and rotation angle of the first liquid crystal polarization grating and the second liquid crystal polarization grating, and the deflection amount of different axes is sent to the galvanometer of the beacon light branch to control the galvanometer for compensation. The dispersion problem introduced by using dual liquid crystal polarization gratings as beam deflection devices is solved.

Description

Technical Field

[0001] The invention relates to the field of high energy laser systems, and in particular to a dispersion compensation method for high energy laser systems based on double liquid crystal polarization gratings. Background Art

[0002] High-energy laser systems use the thermal effect, photoelectric effect, and thermal coupling of high-power lasers to directly damage or disable targets; high-energy laser weapons have the characteristics of concentrated energy, anti-electromagnetic interference, and fast attack speed, and are widely used in precision strikes, information confrontation, and strategic defense. The new generation of high-energy laser weapons has been increasingly enhanced in terms of miniaturization, lightness, multi-platform, and high power, and thus puts forward higher requirements for the system's beam pointing capability and volume.

[0003] This resulted in a high-energy laser system based on a dual liquid crystal polarization grating. The beam pointing mechanism of a traditional high-energy laser system generally uses two structures: a mechanical turntable and a rotating dual prism. The beam pointing mechanism in the new dual liquid crystal polarization grating uses a new dual liquid crystal polarization grating. Compared with the traditional beam pointing mechanism, it has the advantages of small size, light weight, large scanning range and high pointing accuracy.

[0004] From the grating equation, we know that grating diffraction is related to wavelength. The double grating deflects light beams of different wavelengths differently, resulting in dispersion. Therefore, the application of dual liquid crystal polarization grating improves the beam pointing accuracy but also introduces the dispersion problem. Dispersion will cause the main laser emission branch and the beacon light tracking branch to be out of axial alignment, thereby affecting the accuracy of high-energy laser strikes. Summary of the invention

[0005] In order to solve the dispersion problem introduced by using a double liquid crystal polarization grating as a beam deflection device, the present invention provides a dispersion compensation method for a high-energy laser system based on a double liquid crystal polarization grating.

[0006] The high-energy laser system comprises a main laser emission branch and a beacon light tracking branch. The main laser emission branch comprises a liquid crystal polarization grating 1, a liquid crystal polarization grating 2, a motor 1, a motor 2, a primary mirror 5, a secondary mirror 6, an energy beam splitter 7, a fast mirror 11, a wavelength beam splitter 12, a 1 / 4 wave plate 17, a 1 / 2 wave plate 18, a lens group 3 19 and a main laser emission device 20. The beacon light tracking branch comprises a liquid crystal polarization grating 1, a liquid crystal polarization grating 2, a primary mirror 5, a secondary mirror 6, an energy beam splitter 7, a narrow-band filter 1, a lens group 19, a coarse tracking camera 10, a fast mirror 11, a wavelength beam splitter 12, a narrow-band filter Two 14, lens group two 15 and precision tracking camera 16; characterized in that the beacon light tracking branch adds a galvanometer 13 for dispersion compensation, the galvanometer 13 and the x-axis have an angle of 135°, the galvanometer 13 is placed on the straight line where the fast mirror 11 and the wavelength splitter 12 are located, and is placed directly below the narrowband filter two 14; according to the periodic parameters and rotation angles of the liquid crystal polarization grating one 1 and the liquid crystal polarization grating two 4, the deflection angle difference of the two wavelengths of the 1064nm main laser and the 1053nm beacon light is calculated, the deflection amount of different axes solved is sent to the galvanometer 13 of the beacon light branch, and the galvanometer 13 is controlled to compensate.

[0007] Furthermore, the external light beam is diffracted by the liquid crystal polarization grating 1, the liquid crystal polarization grating 2, reflected by the primary mirror 5 and reflected by the secondary mirror 6, and then enters the energy beam splitter 7. A part of the light passes through the energy beam splitter 7, is filtered by the narrow-band filter 8, and is converged by the lens group 9 to be received by the coarse tracking camera 10. The other part of the light is reflected by the energy beam splitter 7 and reaches the fast reflection mirror 11, and then is transmitted by the wavelength beam splitter 12, reflected by the galvanometer 13, filtered by the narrow-band filter 14 and is converged by the lens group 15 to be received by the fine tracking camera 16.

[0008] Furthermore, in the main laser emission branch, the liquid crystal polarization grating 1 is electrically connected to the motor 1 2 , the liquid crystal polarization grating 2 4 is electrically connected to the motor 2 3 , and the 1 / 4 wave plate 17 , the 1 / 2 wave plate 18 and the main laser emission device 20 share a common optical axis.

[0009] Furthermore, in the main laser emission branch, the laser of the main laser emitting device 20 is converged by the lens group three 19 and then converted by the 1 / 2 wave plate 18, the 1 / 4 wave plate 17, reflected by the wavelength splitter 12, reflected by the fast reflection mirror 11, reflected by the secondary mirror 6, reflected by the primary mirror 5, diffracted by the liquid crystal polarization grating 24 and the liquid crystal polarization grating 11, and then emitted.

[0010] Furthermore, a common optical path design of a 1064nm main laser emission branch and a 1053nm beacon light tracking branch is adopted.

[0011] Furthermore, the liquid crystal polarization grating 1 and the liquid crystal polarization grating 2 4 are both polarization gratings written by orthogonal circular polarization interference.

[0012] Furthermore, the periods of the liquid crystal polarization grating 1 and the liquid crystal polarization grating 4 are both 8 μm.

[0013] The beneficial effects of the present invention are as follows: a galvanometer is used as a dispersion compensation element, and is designed in combination with a beacon light tracking branch, which has a faster response time, a larger scanning range, and more stable accuracy while achieving real-time dispersion compensation. In a high-energy laser system with dual liquid crystal polarization gratings, a galvanometer in the beacon light tracking branch is used to achieve real-time compensation for the chromatic aberration introduced by the dual liquid crystal polarization gratings. The dispersion compensation element galvanometer controls the spot position of the 1053nm beacon light on the precision tracking camera, and then drives the fast reflector to adjust the spot on the precision tracking camera to the center. At this time, the beam deflection angle of the 1053nm beacon light and the 1064nm main laser due to dispersion is compensated, and the 1064nm laser emitted by the main laser coincides with the received 1053nm beacon light path; compared with placing the dispersion compensation element in other positions, the aperture of the optical system in front of the galvanometer in the beacon light branch is relatively small. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of a high-energy laser system and dispersion compensation with dual liquid crystal polarization gratings.

[0015] Among them, 1-liquid crystal polarization grating 1, 2-motor 1, 3-motor 2, 4-liquid crystal polarization grating 2, 5-primary mirror, 6-secondary mirror, 7-energy spectrometer, 8-narrow band filter 1, 9-lens group 1, 10-coarse tracking camera, 11-fast reflection mirror, 12-wavelength spectrometer, 13-galvanometer, 14-narrow band filter 2, 15-lens group 2, 16-fine tracking camera, 17-1 / 4 wave plate, 18-1 / 2 wave plate, 19-lens group 3, 20-primary laser emitting device. DETAILED DESCRIPTION

[0016] 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 scope of protection of the present invention.

[0017] The dispersion compensation method of the high-energy laser system based on the dual liquid crystal polarization grating of the present invention is mainly divided into a main laser emission branch and a beacon light tracking branch. In order to compensate for the dispersion introduced by the dual grating, a galvanometer 13 is added to the beacon light tracking branch as a dispersion compensation element. The dispersion compensation and beacon light tracking branches mainly include: a liquid crystal polarization grating 1, a liquid crystal polarization grating 2 4, a primary mirror 5, a secondary mirror 6 and an energy beam splitter 7. A part of the light is received by a coarse tracking camera 10 through the energy beam splitter 7, a narrow band filter 1 8, and a lens group 1 9; the other part is reflected by the energy beam splitter 7 to reach a fast reflection mirror 11, a wavelength beam splitter 12, a galvanometer 13, a narrow band filter 2 14, and a lens group 2 15 to be received by a fine tracking camera 16. The narrow band filter 1 8, the lens group 1 9, and the coarse tracking camera 10 share an optical axis; the narrow band filter 2 14, the lens group 2 15, and the fine tracking camera 16 share an optical axis.

[0018] The main laser emission branch mainly includes: liquid crystal polarization grating 1, liquid crystal polarization grating 2, motor 1, motor 2, primary mirror 5, secondary mirror 6, energy beam splitter 7, fast mirror 11, wavelength beam splitter 12, 1 / 4 wave plate 17, 1 / 2 wave plate 18, lens group 3 19, and main laser emission device 20. The liquid crystal polarization grating 1 is electrically connected to the motor 1, and the liquid crystal polarization grating 2 is electrically connected to the motor 2. The liquid crystal polarization grating 1 and the liquid crystal polarization grating 2 are placed in parallel with the same optical axis, and the primary mirror 5 and the secondary mirror 6 are placed in parallel; the 1 / 4 wave plate 17, the 1 / 2 wave plate 18, and the main laser emission device 20 are on the same optical axis; the energy beam splitter 7, the fast mirror 11, and the wavelength beam splitter 12 are all at an angle of 45° with the positive direction of the x-axis.

[0019] The liquid crystal polarization grating 1 and the liquid crystal polarization grating 2 4 are both polarization gratings written by orthogonal circular polarization interference; the periods of the liquid crystal polarization grating 1 and the liquid crystal polarization grating 2 4 are both 8 μm.

[0020] The primary mirror 5 and the secondary mirror 6 form a beam expansion / reduction antenna system, which is shared by both transmitting and receiving, expanding the beam aperture during transmission and reducing the beam aperture during reception.

[0021] The 1 / 4 wave plate 17 and the 1 / 2 wave plate 18 are both used to convert the light beam emitted by the laser into circularly polarized light.

[0022] The wavelength of the main laser and beacon light, and the rotation angles of the liquid crystal polarization grating 1 and 2 will affect the deflection angle of the light beam. The wavelength of the light emitted by the main laser emission branch of the system is 1064nm, and the wavelength of the beacon light is 1053nm. From the grating equation, it can be seen that the diffraction angles of different wavelengths of the same order are different. The different diffraction angles of the main laser 1064nm and the beacon light 1053nm produce chromatic aberration. The deflection angle difference of the two wavelengths is calculated based on the period parameter 8μm of the liquid crystal polarization grating. The maximum deflection angle that a single grating can achieve is:

[0023] The double grating rotation angles are θ1 and θ2 respectively, and the deflection angle of the light is: is the beam deflection angle, λ is the wavelength of light, Λ is the grating period of liquid crystal polarization grating 1 and liquid crystal polarization grating 24, θ1 is the rotation angle of liquid crystal polarization grating 1, and θ2 is the rotation angle of liquid crystal polarization grating 24.

[0024] According to the above formula, the relationship between the real-time rotation angle θ1 of the liquid crystal polarization grating 1, the real-time rotation angle θ2 of the polarization grating 2 and the angle deviation caused by dispersion is established, and according to the relationship between the real-time rotation angle information of the dual liquid crystal polarization gratings and the dispersion value, the dispersion compensation element galvanometer 13 of the beacon optical branch is dynamically angle biased to make the 1064nm main laser emission branch coaxial with the 1053nm beacon optical tracking branch.

[0025] The specific implementation process of dispersion compensation includes the following steps:

[0026] Step 1: The capture, ranging and illumination subsystem includes four steps: initial pointing, capture and tracking, laser ranging and laser illumination. According to the external guidance data, the system's single-mirror servo turntable drives the single-swing mirror to point to the target area, uses the medium-wave infrared capture camera to capture the target image, controls the single-mirror servo turntable to complete the capture and the first-level coarse tracking of the system; performs laser ranging on the target to obtain the target distance information; uses the laser illuminator to emit active laser to illuminate the target; and obtains the target's azimuth and pitch angle information.

[0027] Step 2: Secondary pointing: the dual liquid crystal polarization grating servo unit rotates the dual liquid crystal polarization grating to point to the target according to the azimuth and pitch angle information captured and tracked by the ranging lighting subsystem, so that the target enters its coarse tracking field of view.

[0028] Step three: coarse tracking, the captured beacon light enters the main expansion / contraction antenna system composed of the primary mirror 5 and the secondary mirror 6 for constriction, and after constriction, it is received by the coarse tracking camera 10 after passing through the energy beam splitter 7, the narrowband filter 8, and the lens group 9 to form a light spot, and the position of the light spot is converted into the miss amount information and transmitted to the dual liquid crystal polarization grating drive mechanism. The servo unit controls the rotation of the dual grating according to the miss amount, and performs coarse tracking and alignment on the target. The coarse tracking detector and the servo system form a closed-loop tracking to ensure that the coarse tracking accuracy can make the target enter the fine tracking field of view, and ensure the normal operation of the fine tracking subunit.

[0029] Step 4: Precision tracking. The light passes through the energy spectrometer 7, the fast reflector 11, the wavelength spectrometer 12, the galvanometer 13, the narrow band filter 14, and the lens group 15, and is received by the precision tracking camera 16. At this time, the controller calculates the off-target amount Δx and Δy of the light spot, and then calculates the control amount Z of the fast reflector 11.x and Z y ; According to the control quantity Z x and Z y The fast reflector 11 is adjusted to close the light spot stably to the center of the field of view of the CCD imaging sensor, thereby completing the precise tracking of the beacon light.

[0030] Step 5: Dispersion compensation, calculate the deflection angle of the two wavelengths by the following formula:

[0031]

[0032] The period parameter of the dual liquid crystal polarization grating is 8μm, and the rotation angle of the dual liquid crystal polarization grating is used to calculate the deflection angle difference between the two wavelengths of the 1064nm main laser and the 1053nm beacon light. The deflection amount of different axes is sent to the galvanometer 13 of the beacon light branch to control the galvanometer 13 for compensation.

Claims

1. A dispersion compensation method for a high-energy laser system based on dual liquid crystal polarization gratings, the high-energy laser system comprising a main laser emission branch and a beacon light tracking branch, the main laser emission branch comprising a liquid crystal polarization grating 1 (1), a liquid crystal polarization grating 2 (4), a motor 1 (2), a motor 2 (3), a primary mirror (5), a secondary mirror (6), an energy beam splitter (7), a fast mirror (11), a wavelength beam splitter (12), a quarter wave plate (17), a half wave plate (18), a lens group 3 (19) and a main laser emitting device (20), the beacon light tracking branch comprising a liquid crystal polarization grating 1 (1), a liquid crystal polarization grating 2 (2), a primary mirror (5), a secondary mirror (6), an energy beam splitter (7), a narrow band filter 1 (8), a lens group 1 (9), a coarse tracking camera (10), a fast mirror (11), a wavelength beam splitter (12), a narrow band filter 2 (14), a lens group 2 (15) and a fine tracking camera (16); characterized in that: The beacon light tracking branch is added with a galvanometer (13) for dispersion compensation. The angle between the galvanometer (13) and the x-axis is 135 degrees. The galvanometer (13) is placed on a straight line where a fast mirror (11) and a wavelength splitter (12) are located, and is placed directly below a second narrowband filter (14). The deflection angle difference between the two wavelengths of the 1064nm main laser and the 1053nm beacon light is calculated according to the period parameters and rotation angles of the first liquid crystal polarization grating (1) and the second liquid crystal polarization grating (4). The calculated deflection amounts of different axes are sent to the galvanometer (13) of the beacon light branch, and the galvanometer (13) is controlled to perform compensation.

2. The dispersion compensation method according to claim 1, characterized in that: The external light beam is diffracted by the first liquid crystal polarization grating (1), the second liquid crystal polarization grating (2), reflected by the primary mirror (5) and reflected by the secondary mirror (6) in sequence, and then enters the energy beam splitter (7). A portion of the light passes through the energy beam splitter (7), is filtered by the first narrow band filter (8) and converged by the first lens group (9) in sequence, and then is received by the rough tracking camera (10). Another portion of the light is reflected by the energy beam splitter (7) and reaches the fast reflection mirror (11), and then is transmitted by the wavelength beam splitter (12), reflected by the galvanometer (13), filtered by the second narrow band filter (14) and converged by the second lens group (15) in sequence, and then is received by the fine tracking camera (16).

3. The dispersion compensation method according to claim 1, characterized in that: In the main laser emission branch, the liquid crystal polarization grating 1 (1) is electrically connected to the motor 1 (2), the liquid crystal polarization grating 2 (4) is electrically connected to the motor 2 (3), and the 1 / 4 wave plate (17), the 1 / 2 wave plate (18) and the main laser emission device (20) are coaxial.

4. The dispersion compensation method according to claim 3, characterized in that: In the main laser emission branch, laser light from a main laser emission device (20) is converged by a lens group three (19) and then sequentially converted by a 1 / 2 wave plate (18), converted by a 1 / 4 wave plate (17), reflected by a wavelength beam splitter (12), reflected by a fast reflection mirror (11), reflected by a secondary mirror (6), reflected by a primary mirror (5), diffracted by a second liquid crystal polarization grating (4), and diffracted by a first liquid crystal polarization grating (1) before being emitted.

5. The dispersion compensation method according to claim 1, characterized in that: The common optical path design of 1064nm main laser emission branch and 1053nm beacon light tracking branch is adopted.

6. The dispersion compensation method according to claim 1, characterized in that: The liquid crystal polarization grating 1 (1) and the liquid crystal polarization grating 2 (4) are both polarization gratings written by orthogonal circular polarization interference.

7. The dispersion compensation method according to claim 1, characterized in that: The periods of the first liquid crystal polarization grating (1) and the second liquid crystal polarization grating (4) are both 8 μm.

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