阅读说明：本技术 一种基于普克尔盒的无相位调制脉冲拾取方法及装置 (Pockels cell-based phase modulation-free pulse pickup method and device ) 是由 程文雍 宋琛 李大振 杨厚文 于 2021-08-11 设计创作，主要内容包括：本发明涉及一种基于普克尔盒的无相位调制脉冲拾取方法及装置,该装置包括：沿光路依次设置的高重复频率的激光器、半波片、起偏器、普克尔盒和检偏器。所述方法包括：高重复频率的激光脉冲序列经过半波片后,注入到系统；通过起偏器对P偏振分量和S偏振分量的激光进行分离；P偏振分量的激光脉冲进入普克尔盒中,当普克尔盒不加高压时,P偏振分量的脉冲序列不经任何相位调制通过普克尔盒和检偏器输出；当普克尔盒加高压时,激光偏振态旋转90度,然后经检偏器反射到旁路；调节普克尔盒的加压时间,能够获得线偏振、高信噪比、高稳定性、无相位调制的单脉冲到高重频脉冲序列。(The invention relates to a phase modulation-free pulse pickup method and a phase modulation-free pulse pickup device based on a Pockels cell, wherein the phase modulation-free pulse pickup device comprises: 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 the laser 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.)

1. A pockels cell based phase modulation free pulse picking apparatus, the 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.

2. The pockels cell-based phase modulation-free pulse picking device according to claim 1, wherein the 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 the angle formed by the linear polarization direction and the horizontal polarization direction of the incident laser, so that the polarizer transmittance is the highest.

3. The pockels cell-based phase modulation-free pulse picking device of claim 1, wherein the polarizer and the analyzer are polarizers coated with films corresponding to the incident laser wavelength;

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.

4. The pockels cell-based phase modulation-free pulse picking apparatus according to claim 1, wherein the pockels cell employs β -phase barium metaborate (BBO) crystal, lithium niobate (LiNbO)₃) Crystal or Rubidium Titanyl Phosphate (RTP)The crystal acts as an electro-optic crystal.

5. A pockels cell based phase modulation free pulse picking device as claimed in claim 1, wherein the pockels cell further comprises a driver.

6. A pockels cell based phase modulation free pulse picking method comprising using the apparatus of any one of claims 1-5, comprising the steps of:

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.

7. Pockels cell based phase modulation free pulse picking method as claimed in claim 6, characterized in that a Pockels cell driver is used to apply high voltage to the Pockels cell.

8. Pockels cell based phase modulation free pulse picking method according to claim 7, characterized in that the high voltage is a half wave voltage.

9. Pockels cell based phase modulation free pulse picking method as claimed in claim 6, characterized in that the Pockels cell driver output waveform is a square wave.

10. Pockels cell based phase modulation free pulse picking method as claimed in claim 6, characterized in that the pockels cell driver trigger signal is triggered by a signal generator or a laser output synchronized divider board.

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 laser fiber communication, laser space telecommunications, laser marking, laser cutting, etc., but the low single pulse energy resulting from 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 used in a large number of applications in the industrial and scientific research fields, most operating schemes use single-pass half-wave voltage or double-pass quarter-wave voltage to achieve pulse pickup, and the selected pulse sequence is intercepted during high-voltage operation. A limitation is that additional phase modulation may be generated based on the pulse train picked up at high voltage operation. The additional phase modulation is to adoptFor example, in the case of a transverse electro-optically modulated crystal, as shown in fig. 1, the crystal length in the light-transmitting direction is L, the thickness is d, i.e., the pitch of the pressurizing electrodes, and the applied electric field is V ═ E_zd, the phase delay of the crystal emergence is, wherein λ is the wavelength of incident light, n₀Is the refractive index of o light in the crystal when no electric field is applied, gamma is the electro-optic coefficient, E_zIs the electric field strength parallel to the z-axis. From the theory of electro-optic phase modulation, when the crystal works at high voltage, if the electric field distribution in the crystal is uniform, the phases of all points on the wave surface of the light beam are necessarily equal, because factors such as electrode spacing selection can influence the uniformity of the electric field of the 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 the phase modulation is influenced. On the other hand, ideally, the high voltage signal emitted by the pockels cell driver should be a square wave signal, while the actual high voltage signal has a rising edge and a falling edge, and the electrical signal has the problem of instability of amplitude, and the phase modulation of the pulse sequence picked up in the same pressurizing time is different, so as to generate additional phase modulation. 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 clearance 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 invention, preferably, the 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 the included angle between the linear polarization direction of the incident laser and the horizontal polarization direction, so that the transmittance of the polarizer 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 invention, the high voltage is preferably 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 phase modulation-free pulse pickup device 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.