CN113612107B - Pockels cell-based phase modulation-free pulse pickup method and device - Google Patents

Pockels cell-based phase modulation-free pulse pickup method and device Download PDF

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CN113612107B
CN113612107B CN202110916590.2A CN202110916590A CN113612107B CN 113612107 B CN113612107 B CN 113612107B CN 202110916590 A CN202110916590 A CN 202110916590A CN 113612107 B CN113612107 B CN 113612107B
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pockels cell
laser
phase modulation
pulse
analyzer
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CN113612107A (en
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程文雍
宋琛
李大振
杨厚文
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Shandong University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10061—Polarization control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/115—Q-switching using intracavity electro-optic devices

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  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
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  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Lasers (AREA)

Abstract

The invention relates to a method and a device for picking up pulse without phase modulation based on a Pockels cell, wherein the device comprises the following steps: the device comprises a laser with high repetition frequency, a half-wave plate, a polarizer, a Pockels cell and an analyzer which are sequentially arranged along a light path. The method comprises the following steps: after passing through a half-wave plate, a laser pulse sequence with high repetition frequency is injected into the system; separating the laser of the P polarization component and the laser of the S polarization component through a polarizer; laser pulses of the P polarization component enter the Pockels cell, and when the Pockels cell is not added with high voltage, a pulse sequence of the P polarization component is output through the Pockels cell and the analyzer without any phase modulation; when the Pockels cell is applied with high voltage, the polarization state of the laser rotates by 90 degrees and then is reflected to a bypass through an analyzer; by adjusting the pressurizing time of the Pockels cell, a single pulse to high repetition frequency pulse sequence with linear polarization, high signal-to-noise ratio, high stability and no phase modulation can be obtained.

Description

Pockels cell-based phase modulation-free pulse pickup method and device
Technical Field
The invention relates to the technical field of lasers, in particular to a Pockels cell-based phase-modulation-free pulse pickup method and device.
Background
High repetition frequency lasers have been widely used in the fields of laser fiber communication, laser space telecommunications, laser marking, laser cutting, etc., but the low single pulse energy caused by the high repetition frequency is also a necessary result. Because the single pulse energy directly generated from the laser oscillation cavity cannot meet the requirement of laser processing, the single pulse energy can be amplified by some optical pulse energy amplification methods, such as a cavity dumping technology, a regenerative amplification technology, a traveling wave amplification technology and the like, and the first is to reduce the repetition frequency of the high-repetition-frequency laser and pick up a single pulse or a pulse train; in the field related to material analysis, the measurement of material properties may be interfered by the thermal influence caused by the high repetition frequency light pulse, so that the application of the low repetition frequency light pulse is necessary; in the related field of information storage based on laser application, the number, phase, polarization state and the like of light pulses of a laser play a crucial role in storage capacity and storage stability.
With the continuous improvement of the requirements of industrial and scientific research application on the number, the phase and the polarization degree of laser pulses, the market has higher and higher requirements on laser pulse picking.
The pockels cell-based electro-optical modulator has been widely used in the industrial and scientific research fields, most operating schemes adopt single-pass half-wave voltage or double-pass quarter-wave voltage to realize pulse pickup, and the selected pulse sequence is intercepted during high-voltage work. A limitation is that additional phase modulation may be generated based on the pulse train picked up at high voltage operation. The extra phase modulation is, for example, a crystal using transverse electro-optic modulation, as shown in fig. 1, the length of the crystal in the light passing direction is L, the thickness is d, i.e. the distance between the pressurizing electrodes, and the applied electric field is V ═ E z d, the phase delay of the emergent crystal is,
Figure BDA0003205793450000011
Figure BDA0003205793450000012
wherein λ is the wavelength of incident light, n 0 Is the refractive index of o light in the crystal when no electric field is applied, gamma is the electro-optic coefficient, E z Is the electric field strength parallel to the z-axis. The theory of electro-optic phase modulation shows that when the crystal works at high voltage, if the electric field in the crystal is uniformly distributed, the phases of all points on the wave surface of a light beam are necessarily equal, because factors such as electrode spacing selection can influence the uniformity of the electric field of the cross section of the crystal to a certain extent, the actual electric field distribution is not uniform, the wave surface has phase distortion after the light beam passes through the electro-optic crystal, the phase delay of all points is not equal, and the accuracy of phase modulation is influenced. On the other hand, ideally, driven by pockels cellsThe high-voltage signal sent by the device is a square wave signal, the actual high-voltage signal has a rising edge and a falling edge, the electrical signal has the problems of instability of amplitude and the like, and the phase modulation of the pulse sequence picked up in the same pressurizing time is different, so that additional phase modulation is generated. Such additional phase modulation can have adverse effects on pulse picking applications including increased instability of energy amplification systems based on the pulse picking technique, reduced accuracy in applications such as laser storage using pulse phase information, etc.
Pulse selection based on acousto-optic modulators is also a common method in existing pulse picking technologies, for example: CN 107210572A; the method is to apply short radio frequency pulse signals on an acousto-optic modulator to spatially separate beams with different diffraction orders. The limitation is that the pulse selection method based on the acousto-optic modulator needs additional optical elements to focus the light beam to a smaller light spot, so the damage-resistant threshold is low, and the pulse selection method cannot be applied to the pulse picking scheme of a high-power laser.
Therefore, the pulse picking device has a simple development structure, is suitable for the pulse picking technology of a high repetition frequency laser, avoids the additional modulation of the high-voltage electric field nonuniformity and the fluctuation of an output signal on the phase, and has important significance. The invention is therefore proposed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a pulse picking method and a device without phase modulation based on a Pockels cell. The pulse picking based on the Pockels cell can be well suitable for the pulse picking of a high repetition frequency laser, and has the characteristic of simple structure. The invention utilizes the twice pressurizing gaps to output the pulse sequence, thereby avoiding the additional modulation of the phase caused by the nonuniformity of the high-voltage electric field and the fluctuation of the output signal of the Pockels cell driver.
The technical scheme of the invention is as follows:
a pockels cell based phase modulation free pulse picking apparatus comprising: the device comprises a laser with high repetition frequency, a half-wave plate, a polarizer, a Pockels cell and an analyzer which are sequentially arranged along a light path.
According to the present invention, preferably, an angle formed by the fast axis direction of the half-wave plate and the polarization direction of the incident laser of the laser is half of an included angle formed by the linear polarization direction of the incident laser and the horizontal polarization direction, so that the polarizer transmittance is the highest.
According to the invention, preferably, the polarizer and the analyzer are polarizing plates coated with films corresponding to the incident laser wavelength, and further preferably, the incident angle of the incident laser of the polarizer and the analyzer is brewster angle or 45 degrees corresponding to the incident laser wavelength.
According to the invention, the pockels cell preferably uses beta-phase barium metaborate (BBO) crystal, lithium niobate (LiNbO) 3 ) Crystals, Rubidium Titanyl Phosphate (RTP) crystals, and the like as electro-optic crystals.
According to the present invention, preferably, the pockels cell further comprises an actuator.
According to the invention, the pockels cell-based phase modulation-free pulse picking method comprises the following steps of using the device:
a laser with high repetition frequency sends out a laser pulse sequence with high repetition frequency, and the laser pulse sequence is injected into the system through a half-wave plate; separating the laser of the P polarization component and the laser of the S polarization component through a polarizer; when the Pockels cell is not applied with high voltage, the pulse sequence of the P polarization component is output from the main optical path through the Pockels cell and the analyzer without any phase modulation; when the pockels cell is applied with high voltage, the polarization state of the laser rotates by 90 degrees, and then the laser is reflected out of a main optical path by an analyzer; and adjusting the pressurizing time of the trigger signal of the Pockels cell driver according to the actual requirement, thereby realizing the pickup of the pulse sequence without phase modulation.
According to the invention, it is preferred that the pockels cell is subjected to a high voltage using a pockels cell driver.
According to the present invention, preferably, the high voltage is a half-wave voltage.
According to the present invention, preferably, the pockels cell driver output waveform is a square wave.
According to the invention, the pockels cell driver trigger signal is preferably triggered by a signal generator or a laser output synchronous frequency divider board.
The technical scheme provided by the invention has the beneficial effects that:
1. the pulse picking method provided by the invention is to penetrate through the laser pulse sequence of the Pockels cell in the gap of twice high voltage application, so that additional phase modulation is not needed, and the pulse picking method is more suitable for subsequent application.
2. The pulse picking method provided by the invention is simple, reliable and easy to operate, and can accurately pick up the repetition frequency and the number of pulses of the required pulse sequence.
3. The pulse pickup device without phase modulation based on the Pockels cell has a simple structure, and all used devices are common devices in the market and are easy to obtain.
Drawings
FIG. 1 is a schematic view of an electro-optic crystal under the action of a z-direction electric field.
Fig. 2 is a schematic structural diagram of a pockels cell-based pulse pickup apparatus without phase modulation in embodiment 1 of the present invention.
FIG. 3 is a pulse sequence chart of the output without phase modulation at a repetition frequency of 10kHz and a pressurization time of 50 μ s in example 3;
FIG. 4 is a pulse sequence chart of the output without phase modulation with a repetition frequency of 10kHz and a pressurization time of 98.4 μ s in example 3;
FIG. 5 is a pulse sequence chart showing the output of the pulse sequence without phase modulation in example 3, with a repetition frequency of 10kHz and a pressing time of 99.84. mu.s.
Wherein: 1-high repetition frequency laser, 2-half wave plate, 3-polarizer, 4-Pockels cell, 5-analyzer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the technical solutions of the present invention are described in detail below with reference to the accompanying drawings and examples.
Example 1
As shown in fig. 2, a pockels cell based phase modulation free pulse picking apparatus includes: the high repetition frequency laser 1, half-wave plate 2, polarizer 3, Pockels cell 4 and analyzer 5 that set up sequentially along the light path, the said Pockels cell 4 also includes the driver, Pockels cell driver output waveform is square wave;
the center wavelength of the laser 1 with high repetition frequency is 1064nm, the output power is 200W, the repetition frequency is 6.25MHz, and the pulse width is 3 ns.
The angle formed by the fast axis direction of the half-wave plate 2 and the incident laser polarization direction of the laser 1 is half of the included angle between the linear polarization direction of the incident laser 1 and the horizontal polarization direction, so that the transmittance of the polarizer 3 is the highest.
The polarizer 3 and the analyzer 5 are polarizing films plated with film layers corresponding to the incident laser wavelength;
the polarizer 3 transmits the laser pulse sequence of the P-polarization component and reflects the laser pulse sequence of the S-polarization component, the incident angle of the polarizer 3 is 45 degrees, and the incident angle of the incident laser of the analyzer 5 is 45 degrees.
The pockels cell 4 adopts beta-phase barium metaborate (BBO) crystal.
Example 2
As described in example 1, except that:
the incident angles of the incident laser of the polarizer 3 and the polarization analyzer 5 are the Brewster angle of the corresponding incident laser wavelength.
The Pockels cell 4 adopts lithium niobate (LiNbO) 3 ) Crystals or Rubidium Titanyl Phosphate (RTP) crystals.
Example 3
A pockels cell based phase modulation free pulse picking method comprising using the apparatus described in embodiment 1:
the laser 1 with high repetition frequency sends out a laser pulse sequence with high repetition frequency, and the laser pulse sequence is injected into a system through a half-wave plate 2; separating the laser of the P polarization component and the laser of the S polarization component through a polarizer 3;
when the pockels cell 4 is not applied with high voltage, the pulse sequence of the P-polarized component is output from the main optical path through the pockels cell 4 and the analyzer 5 without any phase modulation;
when the pockels cell 4 is applied with high voltage, the polarization state of the laser rotates by 90 degrees, and then the laser is reflected out of a main optical path by the analyzer 5;
in this embodiment, the high voltage is a half-wave voltage, and 3600V is applied by the pockels cell driver.
And adjusting the pressurizing time of the trigger signal of the Pockels cell driver according to the actual requirement, thereby realizing the pickup of the pulse sequence without phase modulation. The pockels cell trigger signal is triggered by a signal generator.
The pulse picking steps are as follows:
firstly, adding 3600V high pressure to a Pockels cell 4;
secondly, adjusting a signal generator and setting a repetition frequency;
thirdly, adjusting the signal generator and setting the pressurizing time;
the desired pulse sequence without phase modulation is output as shown in fig. 3-5 below.
Wherein, FIG. 3 is a pulse sequence diagram without phase modulation output with a repetition frequency of 10kHz and a pressurization time of 50 μ s;
FIG. 4 is a pulse sequence diagram of output without phase modulation with a repetition frequency of 10kHz and a pressurization time of 98.4 mus;
FIG. 5 is a pulse sequence chart of output without phase modulation with a repetition frequency of 10kHz and a pressurization time of 99.84 μ s.
The present invention provides an efficient method for pockels cell based phase modulation free pulse picking. By reasonably controlling the pressurizing time of the trigger signal, the pulse pickup of the high repetition frequency laser can be realized.
The above-described embodiments are only a part of the embodiments of the present invention, rather than the whole embodiments, and are not intended to limit the present invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (8)

1. A pockels cell based phase-free modulated pulse picking method comprising using a pockels cell based phase-free modulated pulse picking apparatus, the apparatus comprising: the high-repetition-frequency laser, the half-wave plate, the polarizer, the Pockels cell and the analyzer are sequentially arranged along a light path, wherein the fast axis direction of the half-wave plate and the incident laser polarization direction of the laserThe included angle between the linear polarization direction and the horizontal polarization direction of the incident laser is half of that of the incident laser, so that the transmittance of the polarizer is highest; the pockels cell adopts beta-phase barium metaborate (BBO) crystal and lithium niobate (LiNbO) 3 ) Crystal or Rubidium Titanyl Phosphate (RTP) crystal as electro-optic crystal;
the method comprises the following steps:
a laser with high repetition frequency sends out a laser pulse sequence with high repetition frequency, and the laser pulse sequence is injected into the system through a half-wave plate; separating the laser of the P polarization component and the laser of the S polarization component through a polarizer; when the Pockels cell is not applied with high voltage, the pulse sequence of the P polarization component is output from the main optical path through the Pockels cell and the analyzer without any phase modulation; when the pockels cell is applied with high voltage, the polarization state of the laser rotates by 90 degrees, and then the laser is reflected out of a main optical path by an analyzer; and adjusting the pressurizing time of the trigger signal of the Pockels cell driver according to the actual requirement, thereby realizing the pickup of the pulse sequence without phase modulation.
2. The pockels cell-based phase modulation-free pulse picking method of claim 1, wherein the polarizer and analyzer are polarizers coated with film layers corresponding to the incident laser wavelength.
3. The pockels cell based phase modulation free pulse picking method of claim 1, wherein the incident angle of the incident laser light of the polarizer and the analyzer is brewster angle or 45 degrees corresponding to the incident laser wavelength.
4. The pockels cell based phase modulation free pulse picking method of claim 1, wherein the pockels cell further comprises a driver.
5. Pockels cell based phase modulation free pulse picking method according to claim 1, characterized in that a high voltage is applied to the pockels cell with a pockels cell driver.
6. Pockels cell based phase modulation free pulse picking method as claimed in claim 5, characterized in that the high voltage is a half wave voltage.
7. Pockels cell based phase modulation free pulse picking method according to claim 1, wherein the pockels cell driver output waveform is a square wave.
8. Pockels cell based phase modulation free pulse picking method as claimed in claim 1, characterized in that the pockels cell driver trigger signal is triggered by a signal generator or a laser output synchronized divider board.
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