CN112525494B - Device and method for improving and measuring high repetition rate ultrafast laser filament pointing stability - Google Patents

Abstract

An apparatus for detecting pointing stability of a high repetition frequency ultrafast laser light filament, comprising: the laser comprises an ultrafast laser, a ceramic wafer, a microscope and a focusing lens arranged along the laser emitting direction of the ultrafast laser; device for improving the pointing stability of high-frequency ultrafast laser light wires, comprising: the laser comprises an ultrafast laser, a ceramic wafer, a microscope, a metal electrode connected with a high-voltage power supply and a focusing lens arranged along the laser emitting direction of the ultrafast laser; and a method for improving and measuring the pointing stability of the high-repetition-frequency ultrafast laser light wire. The invention applies an external electric field on an ultrafast laser gas filament forming area by using a high-voltage loaded metal electrode, and achieves the aim of improving the pointing stability of the high-frequency ultrafast laser filament by utilizing the guiding effect of laser plasma on the subsequent pulse of the high-frequency laser based on the strong interaction between the external electric field and the plasma in the ultrafast laser filament.

Description

Device and method for improving and measuring high repetition rate ultrafast laser filament pointing stability

technical field

The invention relates to high-voltage discharge and the coupling effect between the external electric field and the nonlinear filament formation of the ultrafast strong laser. Repetitive ultrafast laser filaments are used to improve the pointing stability of ultrafast laser filaments.

Background technique

During the transmission of ultrafast and intense laser in the air, when the self-focusing effect caused by the Kerr effect and the defocusing effect caused by the laser plasma reach a dynamic balance, a uniform and slender plasma channel can be formed in the air, that is, the light Silk. Ultrafast laser filamentation has important applications in processing and imaging, ultrashort pulse compression and supercontinuum spectrum generation, terahertz and harmonic radiation sources, air lasers, remote atmospheric detection, air lasers and other fields. In these applications, high repetition frequency (>100Hz) laser ultrafast gas filaments are generally used, but for high repetition frequency laser gas filaments, the self-heating effect of the filaments will have a serious negative impact on the pointing stability of the filaments, reducing many Measurement accuracy and resolution based on laser gas filament applications. Improving the pointing stability of high repetition rate laser gas is an urgent problem that needs to be solved, which is of great significance to the application of optical filaments.

The traditional technology of controlling fiber transmission mainly relies on laser pulse wavefront modulation, which has limited improvement in the pointing stability of ultrafast laser filaments, and is limited by conditions such as laser energy, laser spot size, and material damage threshold. Some methods even It is at the cost of sacrificing the energy of the ultrafast laser filament, and the influence of the thermal effect of the filament itself on the pointing stability of the filament cannot be reduced, and the long-distance stable transmission of high-energy, high-repetition-frequency laser gas filament cannot be realized.

Contents of the invention

The purpose of the present invention is to propose a new and effective method for the bottleneck problem of thermally induced jitter in high-repetition-frequency ultrafast laser filamentation and the shortcomings and limitations of traditional methods for improving the pointing stability of high-repetition-frequency laser gas filaments. Based on the strong coupling between the external electric field and the plasma in the ultrafast laser filament, the pointing stability of the ultrafast laser filament is improved by using the laser plasma to guide the subsequent pulses of the high repetition frequency laser. Under the action of an external electric field, the recombination process of electrons and ions in the ultrafast laser filament is suppressed, thereby weakening the thermal effect of the high repetition rate laser gas filament itself; Under the action, the energized metal electrode tip has a Coulomb force on it, thereby "fixing" the position of the ultrafast laser filament, so the pointing stability of the ultrafast laser filament is improved. This is for applications based on ultrafast femtosecond laser gas filaments with laser repetition rates >100Hz, such as femtosecond filament micromachining and imaging, ultrashort pulse compression and supercontinuum spectroscopy generation, terahertz and harmonic radiation sources, air In applications such as laser, remote atmospheric detection, air laser and artificial lightning, it is of great significance to improve the stability of the light filament pointing and improve the accuracy and resolution of related applications.

Technical solution of the present invention is as follows:

A device for detecting the pointing stability of a high-repetition-frequency ultrafast laser filament, which is characterized in that it includes: an ultrafast laser, a ceramic sheet, a microscope, and a focusing lens placed along the laser emitting direction of the ultrafast laser;

The laser light emitted by the ultrafast laser is focused by a focusing lens and then formed into filaments in the gas, and the ceramic sheet is placed in the filamentation area for ablation to form an ablation pattern;

The microscope is used to observe the ablation pattern. When the area of the ablation pattern is larger, the pointing stability of the ultrafast laser filament is worse, so as to calibrate the pointing stability of the ultrafast laser filament.

A device for improving the pointing stability of a high-repetition ultrafast laser filament, which is characterized in that it includes: an ultrafast laser, a ceramic sheet, a microscope, a metal electrode connected to a high-voltage power supply, and an Placed focusing lens;

The laser light emitted by the ultrafast laser is focused by a focusing lens and then formed into filaments in the gas, and the ceramic sheet is placed in the filamentation area for ablation to form an ablation pattern;

The metal electrode is close to the wire-forming area, and the electrostatic field at the metal electrode is changed by changing the voltage of the high-voltage power supply, and the ceramic sheet is replaced every time the voltage value is changed;

The microscope is used to observe the ablation pattern. When the area of the ablation pattern is larger, the pointing stability of the laser light filament is worse, so as to calibrate the pointing stability of the ultrafast laser filamentation.

Preferably, an insulating component is also included, the metal electrode is fixed at one end of the insulating component, and the other end of the insulating component is fixed on a grounded working platform.

The insulating assembly is formed by connecting an insulating support and an insulating plastic rod, and the metal electrode is fixed on the insulating support.

Preferably, the pulse width of the ultrafast laser is on the order of fs to ps, the repetition rate>100Hz, and the peak power of the laser pulse generated is greater than the self-focusing filamentation critical power P _cr of the laser pulse in the gas environment (P _cr = 3.77λ ² /8πn ₂ n ₀ , λ is the center wavelength of the laser pulse, n ₀ and n ₂ are the linear refractive index and Kerr nonlinear refractive index in air respectively).

Preferably, the ultrafast laser is a titanium sapphire ultrafast laser, a Yb ³⁺ doped all-solid-state ultrafast laser, a fiber ultrafast laser, and the like.

8. The device for improving the pointing stability of high-repetition-frequency ultrafast laser filaments according to claim 3, wherein said metal electrodes include tip electrodes, linear arrays of tip metal electrodes, and wedge-shaped metal electrodes. The power connection generates a static external electric field and loads the external electric field on the ultrafast laser filament.

Preferably, the ceramic sheets are insulating materials such as silicon nitride and silicon carbide ceramic sheets, and the diameter of the effective range is larger than several millimeters, and the thickness is on the order of millimeters.

Preferably, the resolution of the microscope is 0.001mm.

A method for improving and measuring the pointing stability of a high-repetition-frequency ultrafast laser filament is characterized in that the steps are as follows:

(1) The ultrafast laser pulse emitted by the ultrafast laser with a repetition rate > 100 Hz is focused by the focusing lens, and then filaments are formed in the gas to produce ultrafast laser filaments;

(2) Insert the ceramic sheet into the light filament, and after a certain number of super laser light filaments ablate the ceramic sheet, use a microscope to photograph the ablation pattern on the ceramic sheet. The larger the ablation area, the more stable the ultrafast laser light filament pointing. Poor, to calibrate the ultrafast laser filamentation pointing stability;

(3) Put the metal electrode connected to the high-voltage power supply close to the ultrafast laser filament, and change the electrostatic field at the metal electrode by adjusting the voltage of the high-voltage power supply. Every time the voltage value is changed, a new ceramic chip is replaced, and each firing is guaranteed. The number of laser pulses of the etched ceramic sheet is the same to measure the pointing stability of the light filament under different applied electric fields.

Further, steps are also included:

(4) Fix the voltage of the high-voltage power supply, adjust the output laser pulse repetition frequency of the ultrafast laser, so that the laser light wire with different repetition frequencies can ablate the ceramic sheet, and ensure that the number of ablation pulses is the same. Pointing stability of an ultrafast laser filament with an applied electric field.

Compared with prior art, the advantages of the present invention:

The existing technology relies on the wavefront modulation of the pump beam, and the optical path is relatively complicated. Due to the limitations of laser energy and material damage threshold, it is impossible to suppress the disturbance caused by the thermal effect of the high repetition frequency laser filament itself. The effect of improving the stability of the filament pointing is very limited, and it is impossible to achieve long-distance stable transmission of high-energy, high-repetition-frequency laser gas filaments.

The optical path is simple and the implementation is convenient. Based on the strong coupling between the external electric field and the plasma in the ultrafast laser filament, the laser plasma can be used to guide the subsequent pulses of the high repetition frequency laser, which can significantly improve the pointing of the high repetition frequency laser filament. Stability, and lower requirements for the strength of the applied electric field. Due to the variability of electrode shape and optical path, the coupling efficiency between the applied electric field and the optical filament can be increased, thereby further improving the stability of the optical filament pointing. At the same time, since it is not limited by the damage threshold of the medium, it can realize stable transmission of high-energy, high-repetition-frequency ultrafast laser filaments in any scale. This is useful for applications of ultrafast femtosecond laser gas filaments based on laser repetition rates, such as femtosecond filament micromachining and imaging, ultrashort pulse compression and supercontinuum spectroscopy generation, terahertz and harmonic radiation sources, air lasers, In applications such as remote atmospheric detection, air lasers, and artificial lightning induction, it is of great significance to improve the pointing stability of the light filament and improve the accuracy and resolution of related applications.

The experimental device and light path are very simple, and after improvement, it can have a wider application prospect.

Description of drawings

Fig. 1 is a kind of structure schematic diagram of the device of promoting and measuring the pointing stability of high repetition frequency ultrafast laser light filament of the present invention;

Fig. 2 is in the embodiment 1 of the present invention, ultrafast laser repetition rate is 1kHz, pulse width is 32fs, pulse energy is 3.4mJ, when there is no external electric field, the pattern ablated by ultrafast laser light filament on the ceramic sheet, the number of pulses is 3500, the ablation area is about 3.5×8 ^-3 mm ² , the picture is taken by microscope;

Fig. 3 shows that in Example 1 of the present invention, the ultrafast laser repetition frequency is 1kHz, the pulse width is 32fs, the pulse energy is 3.4mJ, and when the high-voltage power supply indication is 5kV (the electric field is 6×8 ⁶ V/m), the ceramic sheet The pattern ablated by the ultrafast laser filament, the number of pulses is 3500, the ablation area is about 3×8 ^-3 mm ² , the picture is taken by microscope.

Detailed ways

The present invention is described in detail below in conjunction with embodiment and accompanying drawing, but should not limit protection scope of the present invention with this:

Example 1

As shown in Figure 1, the present invention provides a device for improving and measuring the pointing stability of high-repetition-frequency ultrafast laser filaments, including an ultrafast laser 1, a focusing lens 2, a metal electrode 3, a high-voltage power supply 9, and a ceramic sheet 6 , Microscope 10;

The metal electrode 3 is installed on the insulating conversion body 4, and is fixedly connected with one end of the insulating plastic screw rod 5, and the other end of the insulating plastic rod 5 is fixed on a grounded workbench, and the metal electrode 3 is connected to the The high-voltage power supply 9 is connected;

The laser light emitted by the titanium sapphire laser 1 is focused by the focusing lens 2, and then becomes filaments in the gas, and the ceramic sheet 6 is placed in the filamentation area for ablation to form an ablation pattern. The ceramic sheet 6 is fixed on the insulating support 7 and It is connected with the insulating plastic rod 8, and the other end of the insulating plastic rod 8 is fixed on the grounded workbench. The morphology of the ceramic sheet 6 after ultrafast laser filament ablation is observed and recorded by a microscope 10 .

Using a method for improving and measuring the pointing stability of the femtosecond laser filament, the specific steps are as follows:

First, adjust the repetition frequency of the Ti:Sapphire laser to 1kHz, the pulse width to 32fs, and the energy to 3.4mJ. The laser pulse passes through a focusing lens with a focal length of 50cm to form a femtosecond laser filament near the tip of the metal electrode. The distance between the tip of the electrode and the filament is about 1mm;

Secondly, suspend the incident laser first, fix the ceramic sheet on the insulating bracket and connect it with the insulating plastic rod, fix the other end of the insulating plastic rod on the workbench, and place the ceramic sheet at the end of the optical fiber;

Then, when the high-voltage power supply shows 0kV, run the Ti:Sapphire laser so that the light filament hits the ceramic sheet, and then suspend the incident laser again after accumulating 3,500 pulses;

Then the ceramic sheet was removed, and the morphology of the ablated ceramic was measured and recorded using a microscope, as shown in FIG. 2 . The larger the ablation area, the worse the pointing stability of the ultrafast laser filament;

After that, adjust the voltage value of the high-voltage power supply according to the above steps, 0kV, 1kV, 2kV, 3kV, 4kV, 5kV, 3.5kV, 8kV, 9.5kV, 15kV, 13.5kV, 20kV, 25kV, 30kV, 35kV, 40kV, 45kV, 50kV, Under each high-voltage condition, the number of laser pulses is fixed at 3500, and the ceramic sheets are ablated separately, and photographed with a microscope, which can improve the pointing stability of the femtosecond laser filament under different applied electric fields;

Secondly, when the high-voltage power supply is fixed at 0kV and 50kV, change the laser repetition frequency to 50Hz, 100Hz, 200Hz, 300Hz, 500Hz, and 800Hz, and fix the number of laser pulses to 3500. Measure the ablation area of the ceramic sheet separately, and you can get different repetition frequencies. , the effect of external electric field on the pointing stability of femtosecond laser filament;

After that, the laser repetition frequency is fixed at 1kHz, the high-voltage power supply reading is 5kV, the laser pulse energy is changed to 3mJ, 4mJ, 5mJ, 6mJ, 3mJ, and 6mJ, and the number of laser pulses is fixed at 3500. Measure the ablation area of the ceramic sheet respectively, and you can get different Ultrafast laser filaments for stable delivery of energy.

Experiments show that, for the first time, the invention successfully utilizes an external electric field to improve and enhance the pointing stability of the high repetition frequency light filament. The invention is based on the strong coupling effect between the external electric field and the plasma in the ultrafast laser filament, and utilizes the guiding effect of the laser plasma on the follow-up pulse of the high repetition frequency laser to improve the pointing stability of the ultrafast laser filament. The high-repetition-frequency ultrafast laser filament can be stably transmitted under different conditions, and the experimental device and experimental method are simple and effective.

Claims (10)

1. A device for improving the pointing stability of a high-repetition-frequency ultrafast laser filament, characterized in that it comprises: an ultrafast laser (1), a ceramic sheet (6), a microscope (10), and a high-voltage power supply (9) A connected metal electrode (3), and a focusing lens (2) placed along the laser emission direction of the ultrafast laser (1); The laser light emitted by the ultrafast laser (1) is focused by the focusing lens (2) and then filaments are formed in the gas, and the ceramic sheet (6) is placed in the filamentation area for ablation to form an ablation pattern; The metal electrode (3) is close to the filament forming area, and under the action of an external electric field, the recombination process of electrons and ions in the ultrafast laser filament is suppressed, which weakens the thermal effect of the high repetition rate laser gas filament itself; the tip of the electrified metal electrode It has a Coulomb force effect on the light filament plasma channel, which improves pointing stability; by changing the voltage of the high-voltage power supply (9), the magnitude of the electrostatic field at the electrode of the pole (3) is changed, and every time the voltage value is changed, the Replace the ceramic sheet once; The microscope (10) is used to observe the ablation pattern. When the area of the ablation pattern is larger, the pointing stability of the ultrafast laser light filament is worse, so as to calibrate the pointing stability of the ultrafast laser light filament. 2. The device for improving the pointing stability of high-repetition-frequency ultrafast laser filament according to claim 1, characterized in that, it also includes an insulating assembly, and said metal electrode (3) is fixed at one end of the insulating assembly, and the insulating assembly The other end of the assembly is fixed on a grounded work platform. 3. The device for improving the pointing stability of the high-repetition-frequency ultrafast laser filament according to claim 1, wherein the insulating assembly is formed by connecting an insulating support (4) with an insulating plastic rod (5), The metal electrodes (3) are fixed on the insulating support (4). 4. The device for promoting high repetition rate ultrafast laser filament pointing stability according to claim 1, characterized in that, the pulse width of the ultrafast laser (1) is on the order of fs to ps, and the repetition rate > 100Hz, the peak power of the generated laser pulse is greater than the self-focusing filamentation critical power P _cr of the laser pulse in the gas environment (P _cr =3.77λ ² /8πn ₂ n ₀ , where λ is the center wavelength of the laser pulse, n ₀ and n ₂ respectively linear and Kerr nonlinear indices of refraction in air). 5. the device of promoting high repetition frequency ultrafast laser light filament pointing stability according to claim 4, is characterized in that, described ultrafast laser (1) is titanium sapphire ultrafast laser, doping Yb ³⁺ all-solid-state Ultrafast lasers, fiber ultrafast lasers, etc. 6. The device for improving the pointing stability of high-repetition-frequency ultrafast laser filament according to claim 1, wherein said metal electrode (5) comprises a tip electrode, a linear array of tip metal electrodes, and a wedge-shaped metal electrode, A static external electric field is generated by being connected with a high-voltage power supply (9), and the external electric field is loaded on the ultrafast laser light filament. 7. the device for promoting high repetition frequency ultrafast laser light filament pointing stability according to claim 1, is characterized in that, described ceramic sheet (6) is insulating materials such as silicon nitride, silicon carbide ceramic sheet, effectively The diameter of the range of action is greater than a few millimeters, and the thickness is on the order of millimeters. 8. The device for improving the pointing stability of high-repetition-frequency ultrafast laser filaments according to claim 1, characterized in that, the resolution of the microscope (10) is 0.001 mm. 9. A method for promoting and measuring the pointing stability of high-repetition-frequency ultrafast laser light filaments, characterized in that the steps include: (1) The ultrafast laser pulse emitted by the ultrafast laser with a repetition rate > 100 Hz is focused by the focusing lens, and then filaments are formed in the gas to produce ultrafast laser filaments; (2) Insert the ceramic sheet into the light filament, and after a certain number of super laser light filaments ablate the ceramic sheet, use a microscope to photograph the ablation pattern on the ceramic sheet. The larger the ablation area, the worse the pointing stability of the laser light filament. This is used to calibrate the pointing stability of ultrafast laser filamentation; (3) Put the metal electrode connected to the high-voltage power supply close to the ultrafast laser filament, and change the electrostatic field at the metal electrode by adjusting the voltage of the high-voltage power supply. Every time the voltage value is changed, a new ceramic chip is replaced, and each firing is guaranteed. The number of laser pulses of the etched ceramic sheet is the same to measure the pointing stability of the light filament under different applied electric fields. 10. the method for promoting and measuring high repetition rate ultrafast laser light filament pointing stability according to claim 9, is characterized in that, also comprises the step: (4) Fix the voltage of the high-voltage power supply, adjust the output laser pulse repetition frequency of the ultrafast laser, so that the laser light wire with different repetition frequencies can ablate the ceramic sheet, and ensure that the number of ablation pulses is the same. Pointing stability of an ultrafast laser filament with an applied electric field.