CN107132673B - A device for eliminating depolarization of electro-optical crystals - Google Patents
A device for eliminating depolarization of electro-optical crystals Download PDFInfo
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- CN107132673B CN107132673B CN201710589301.6A CN201710589301A CN107132673B CN 107132673 B CN107132673 B CN 107132673B CN 201710589301 A CN201710589301 A CN 201710589301A CN 107132673 B CN107132673 B CN 107132673B
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on magneto-optical elements, e.g. exhibiting Faraday effect
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
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- Optics & Photonics (AREA)
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- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
- Lasers (AREA)
Abstract
The application discloses a device for eliminating depolarization of an electro-optic crystal, which consists of a first electro-optic crystal, a first 90-degree optical rotator, a second electro-optic crystal and a second 90-degree optical rotator. The laser is injected from the first electro-optical crystal switch, sequentially passes through the first 90-degree optical rotator and the second electro-optical crystal and then is output from the second 90-degree optical rotator. The application can eliminate the angle depolarization of the electro-optic crystal caused by the angle inclination of the injected laser, improves the output energy and the beam quality of the laser, and has important application in a laser amplifier.
Description
Technical Field
The application relates to the technical field of lasers, in particular to a device for eliminating depolarization of an electro-optic crystal.
Background
The electro-optic crystal is an important device in the field of lasers, and has very wide application in the fields of high-power Q-switched lasers, laser amplifiers and the like. The working state of the electro-optical crystal can be divided into a static state and a dynamic state, wherein the static state refers to the condition that the electro-optical crystal is not electrified, and the dynamic state refers to the condition that the electro-optical crystal is electrified. Under ideal conditions, the polarization state of the injected laser is not changed during static operation of the electro-optic crystal, and a fixed change amount is generated for the polarization state of the laser during dynamic operation. However, since the electro-optical crystal is usually a birefringent crystal and the laser always has a certain divergence angle, under the static working condition, only the polarization state of the laser light transmitted along the optical axis direction of the electro-optical crystal in the propagation direction is not changed, and the polarization state of the laser light in the propagation direction is changed to different degrees, so that the depolarization effect of the laser light is caused.
Such depolarization effects can have serious consequences in lasers, especially laser amplifiers, such as beam quality degradation and self-excitation. It is therefore necessary to investigate how to eliminate laser depolarization by the electro-optic crystal.
Disclosure of Invention
Aiming at the problems in the prior art, the application provides a device for eliminating the depolarization of an electro-optic crystal, which solves the problem of laser depolarization caused by the electro-optic crystal.
In order to achieve the above purpose, the present application provides the following technical solutions:
the application discloses a device for eliminating depolarization of an electro-optic crystal, which consists of a first electro-optic crystal, a first 90-degree optical rotator, a second electro-optic crystal and a second 90-degree optical rotator. The laser is injected from the first electro-optic switch, sequentially passes through the first 90-degree optical rotatory plate and the second electro-optic crystal and then is output from the second 90-degree optical rotatory plate.
Further, the device for eliminating the depolarization of the electro-optic crystal is characterized in that the materials and the placing postures of the first electro-optic crystal and the second electro-optic crystal are the same.
Further, the device for eliminating depolarization of the electro-optical crystal is characterized in that the first electro-optical crystal and the second electro-optical crystal are cut along the c-axis, and the optical axis direction is a horizontal direction.
Further, the device for eliminating depolarization of the electro-optic crystal is characterized in that the length l of the first electro-optic crystal along the optical axis direction 1 Phase retardation of o-light and e-lightLength l of second electro-optic crystal along optical axis direction 2 Phase retardation amount of o light and e light ∈>The relation of (2) is:Wherein n is o '、n e ' respectively the refractive indexes of o-light and e-light of the electro-optic crystal, alpha is the angle between the injection laser and the optical axis of the electro-optic crystal, m and n are positive integers, l 1 And l 2 The length of (2) is such that ε 1 ＝ε 2 。
Further, the device for eliminating depolarization of the electro-optic crystal is characterized in that the rotation angles of the first 90-degree optical rotator and the second 90-degree optical rotator to the polarization state of the laser are independent of the polarization direction of the polarizer, and the rotation angles are 90 degrees.
Further, the device for eliminating depolarization of the electro-optic crystal is characterized in that the rotation directions of the first 90-degree optical rotator and the second 90-degree optical rotator on the polarization state of the laser are the same.
Further, the device for eliminating depolarization of the electro-optic crystal is characterized in that the first 90-degree optical rotator and the second 90-degree optical rotator are opposite in rotation direction of the polarization state of the laser.
Further, the device for eliminating depolarization of the electro-optic crystal is characterized in that the first 90 DEG optical rotator is a 90 DEG quartz rotor or a 90 DEG Faraday optical rotator, and the second 90 DEG optical rotator is a 90 DEG quartz rotor or a 90 DEG Faraday optical rotator.
The beneficial effects of the application are as follows:
1. the application adopts the combination of two identical PC crystals and two 90-degree rotors, eliminates the laser depolarization phenomenon caused by a single electro-optical crystal and improves the quality of laser beams.
2. The application does not change the polarization state of the injected laser, can directly place the device in a laser system to replace the traditional single electro-optical crystal, and has beneficial effect on system application.
Drawings
FIG. 1 is a schematic view of an apparatus provided in a first embodiment;
fig. 2 is a schematic view of an apparatus according to a second embodiment and a conventional technique.
Fig. 3 shows the relationship between the laser output/input energy ratio and the laser propagation direction after the laser passes through the second embodiment (a) and the conventional technology (b).
In the figure: 11-first electro-optic crystal, 12-first 90 rotor, 13-second electro-optic crystal, 14-second 90 rotor, 201-polarizer, 202-quarter wave plate (202), 203-first electro-optic crystal, 204-first 90 optical rotator, 205-second electro-optic crystal, 206-second 90 optical rotator, 207-total mirror, 208-polarizer, 209-quarter wave plate, 210-electro-optic crystal, 211-mirror.
Detailed Description
In order to make the technical solution of the present application better understood by those skilled in the art, the technical solution of the present application will be clearly and completely described in the following with reference to the accompanying drawings, and based on the embodiments of the present application, other similar embodiments obtained by those skilled in the art without making any inventive effort should be included in the scope of protection of the present application.
Example 1
In this embodiment, as shown in fig. 1, a device for eliminating depolarization of an electro-optic crystal is composed of a first electro-optic crystal (11), a first 90 optical rotator (12), a second electro-optic crystal (13) and a second 90 optical rotator (14). The laser is injected from the first electro-optical light (11), sequentially passes through the first 90 DEG optical rotator (12) and the second electro-optical crystal (13), and then is output from the second 90 DEG optical rotator (14). The first electro-optic crystal (11) and the second electro-optic crystal (12) are KDP crystals, and the placement posture, physical and geometric parameters of the first electro-optic crystal (11) and the second electro-optic crystal (13) are the same. The first 90 DEG optical rotator (12) and the second 90 DEG optical rotator (14) are 90 DEG quartz rotors.
In this embodiment, the horizontal direction is taken as the x-axis, the vertical direction is taken as the y-axis, the electric fields of the x-axis and the y-axis can be decomposed by the laser with any polarization state, and the polarization state expression of the injected laser is assumed to be:wherein E is x And E is y Is the component of the electric field in the x-direction and the y-direction. The electro-optic crystal is KDP crystal, belongs to uniaxial crystal, has double refraction effect, and the o-light refractive index and the e-light refractive index are respectively expressed as n o And n e The length is denoted as l and the effect of this embodiment is analyzed using the jones matrix, which can be written generally as follows:
wherein θ is the included angle between the o-ray direction of the electro-optical crystal and the system coordinate system, δ is the phase delay amount of the electro-optical crystal to the laser in the o-ray direction and the e-ray direction, and the magnitude of the phase delay amount is related to the included angle between the laser propagation direction and the electro-optical crystal, and can be written as follows:
wherein alpha is the included angle between the laser propagation direction and the optical axis of the electro-optic crystal, lambda is the wavelength of the injected laser, n' o And n' e The refractive indexes of o light and e light transmitted in the electro-optical crystal by the laser with the propagation direction and the optical axis included angle alpha are respectively:
after the laser light passes through the first electro-optic crystal (11), the electric field expression of the laser light can be written as:
for the laser light that does not propagate along the optical axis of the electro-optic crystal, as can be seen from expression (3), n o ≠n e When the expression (2) is introduced and the expression (1) is introduced, the matrix A is not an identity matrix, and then E 'can be obtained according to the expression (4)' x /E' y ≠E x /E y That is, the polarization state of the laser is changed, so that the depolarization phenomenon occurs in the conventional single electro-optic crystal.
When the laser light passes through the first electro-optical crystal (11) and sequentially passes through the first 90 DEG optical rotator (12), the second electro-optical crystal (13) and the second 90 DEG optical rotator (14), the polarization states thereof can be expressed as:
wherein, matrix B is the Jones matrix of the 90-degree rotor, and the expression is:
from expressions (1) and (6), it can be calculated that:
then substituting the expression (7) into the expression (5) to obtain E' x ＝E x ，E' y ＝E y That is to say, the polarization state of the output laser is completely consistent with that of the injection laser, eliminating the traditional electro-opticAnd depolarization introduced by the crystal.
Example 2
In this embodiment, as shown in fig. 2, fig. 2 (a) is a device for eliminating depolarization of an electro-optic crystal, and the device is composed of a polarizer (201), a quarter-wave plate (202), a first electro-optic crystal (203), a first 90 ° optical rotator (204), a second electro-optic crystal (205), a second 90 ° optical rotator (206), and a total reflection mirror (207). The laser is injected from the polaroid (201), sequentially passes through the quarter wave plate (202), the first electro-optical crystal (203), the first 90-degree optical rotator (204), the second electro-optical crystal (205) and the second 90-degree optical rotator (206), is reflected by the total reflection mirror (207) and returns along the original light path, and is output from the polaroid (201). The first electro-optic crystal (203) and the second electro-optic crystal (205) are KDP crystals, and the placement posture, physical and geometric parameters of the first electro-optic crystal (203) and the second electro-optic crystal (205) are the same. The first 90 DEG optical rotator (204) and the second 90 DEG optical rotator (205) are 90 DEG quartz rotors. The injection laser being linearly polarized light having a polarization direction in the x-direction, i.eThe polarization direction of the analyzer is the x-direction.
The jones matrix of the analyzer can be expressed as:
the jones matrix for the quarter wave plate is:
according to the matrix in embodiment 1, the polarization state of the output laser light in embodiment 2 can be expressed as:
at this point, the output is in a fully extinction state, i.e., no light output.
Fig. 2 (b) shows a conventional electro-optic crystal device, laser is injected from a polarizer (208), passes through a quarter-wave plate (209) and an electro-optic crystal (210), returns along the original path through a reflecting mirror (211), and is output from the polarizer, and at this time, the expression of the polarization state is:
further, the electric field of the output laser light can be obtained as:
as can be seen from equation (12), the output is not quenched and there is a laser output, and the laser output intensity is related to the amount of phase delay of the electro-optic crystal. For ease of calculation, assume E x =1, then there is:
fig. 3 is a comparison of the present embodiment with the conventional technology, in which the angle represents the included angle between the laser transmission direction and the optical axis of the electro-optic crystal, and the output-input transmittance represents the ratio of the output energy to the input energy. The relationship between the output-input energy ratio and the angle in the present application and the conventional technology is shown in the graph (a) and the graph (b), respectively, and it can be seen from the graph that the output energy is always 0, which plays an isolating role on the backward transmitted laser energy, whereas the output energy ratio in the conventional technology is closely related to the laser transmission angle, the output end cannot be completely extinction, which plays no isolating role, and is disadvantageous in practical laser application, and may cause damage to the front-end device.
Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.
Claims (6)
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| CN108871559B (en) * | 2018-07-13 | 2020-05-12 | 中国工程物理研究院计量测试中心 | Calibration method of light beam quality β factor measurement system |
| CN115469464A (en) * | 2022-09-21 | 2022-12-13 | 广东大湾区空天信息研究院 | Polarization control device and polarization control method |
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