CN109270764B - Femtosecond laser filamentation regulation and control device and method based on feedback iteration wavefront shaping technology - Google Patents
Femtosecond laser filamentation regulation and control device and method based on feedback iteration wavefront shaping technology Download PDFInfo
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- CN109270764B CN109270764B CN201811420182.2A CN201811420182A CN109270764B CN 109270764 B CN109270764 B CN 109270764B CN 201811420182 A CN201811420182 A CN 201811420182A CN 109270764 B CN109270764 B CN 109270764B
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- 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
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Abstract
The invention discloses a femtosecond laser filamentation regulation and control device and a method based on a feedback iteration wavefront shaping technology. The invention adopts a feedback iteration technology, calculates a feedback signal by the super-continuum spectrum collected by the CCD camera, and controls the spatial light modulator to modulate the phase of the initial laser pulse by using a genetic algorithm, thereby realizing the control of the filamentation process. The invention can realize the accurate control of the filamentation process when the femtosecond laser pulse is transmitted in the transparent medium, including the formation of single-filament or multi-filament arrays and the filamentation position, and has the characteristics of simplicity and effectiveness.
Description
Technical Field
The invention belongs to the field of intense field laser physics, and relates to a device and a control method for controlling a filamentation process when femtosecond laser pulses are transmitted in a transparent medium.
Background
When the femtosecond laser is transmitted in a transparent medium, when the peak power of the femtosecond laser exceeds a certain value, namely critical power, the femtosecond laser pulse with ultrahigh peak power can generate self-focusing effect and form plasma in the optical medium; when the defocusing effect and the self-focusing effect of the plasma reach dynamic balance, the femtosecond laser pulse forms a long and narrow plasma channel in the propagation direction, which is called as a femtosecond laser optical filament, and the phenomenon is called as filament formation. The filamentation phenomenon attracts people's extensive attention once discovered, and the filamentation method is widely applied to the fields of atmospheric remote sensing, laser lightning, air laser, traceless cutting of hard and brittle materials and the like.
The femtosecond laser filamentation process relates to a series of nonlinear effects, and the light intensity of the laser and slight disturbance of the wave front of the laser can influence the filamentation process, so that the number of optical fibers, the filamentation length and the like in the femtosecond laser filamentation process are unstable. In order to ensure the application of femtosecond laser filamentation, a series of control means for realizing femtosecond laser filamentation are developed, such as changing the intensity distribution (such as elliptical distribution) of the initial laser pulse, adjusting the numerical aperture of the system, and controlling the phase of the initial laser pulse by using a phase mask or a spatial light modulator. The method for adjusting the phase of the front of the incident laser wave has less laser energy loss and is a very promising adjustment and control method, however, most of the existing methods utilize a fixed phase template to control the front of the femtosecond laser wave so as to further realize the adjustment and control of the filamentation process of the femtosecond laser, the method strongly depends on the wave front parameters of the incident laser, and the adaptability is poor after the laser wave front is distorted. The femtosecond laser wave front shaping method based on feedback iteration has the advantages of precise regulation and control and less requirement on laser parameters, but the femtosecond laser wave front shaping method based on feedback iteration reported in the prior art (opt. Commun.259, (2006); opt. express 24, (2016)) still has the problems of complex iteration algorithm, incapability of regulating monofilament size, poor monofilament contrast and the like.
Disclosure of Invention
The invention aims to provide a device and a method for controlling a filamentation process when femtosecond laser pulses are transmitted in a transparent medium, which can realize the accurate control of forming a plurality of filaments when the femtosecond laser pulses are transmitted in the transparent medium, include that the filaments are changed into monofilaments at any positions, and have the characteristics of simplicity and effectiveness.
The core idea of the invention is to optimize the femtosecond laser wavefront by utilizing wavefront shaping equipment such as a spatial light modulator and the like and adopting a feedback iteration mode, thereby regulating and controlling the filamentation process of the femtosecond laser pulse when the femtosecond laser pulse is transmitted in a transparent medium.
In order to achieve the purpose, the invention adopts the technical scheme that:
a device for regulating and controlling a femtosecond laser filamentation process based on a feedback iteration wavefront shaping technology comprises a femtosecond laser, wherein a diaphragm and a continuous attenuator are arranged on a transmission light path of the femtosecond laser, femtosecond laser pulses pass through the diaphragm and the continuous attenuator and then irradiate on a spatial light modulator, a first convex lens, a water pool filled with distilled water, the diaphragm, a second convex lens, a low-pass filter and a CCD (charge coupled device) are sequentially arranged on a light path of the femtosecond laser pulses after being reflected by the spatial light modulator, a super-continuous spectrum generated after the femtosecond laser pulses pass through the water is collected on the CCD camera, and the CCD camera and the spatial light modulator are both connected on a computer (personal computer).
A femtosecond laser filamentation process regulation and control method based on feedback iteration wavefront shaping technology utilizes a computer to monitor light intensity in a specific range of a super-continuum spectrum collected on a CCD camera to calculate a feedback signal IfeedbackAnd the spatial light modulator is controlled by a genetic algorithm to modulate the phase of the initial laser pulse, so that the aim of controlling the filamentation process of the femtosecond laser pulse when the femtosecond laser pulse is transmitted in a transparent medium is fulfilled. In the process of controlling the random multifilaments to become monofilaments by the feedback signals,
wherein
The average intensity of the supercontinuum in a particular range is chosen,
other supercontinuum average intensities collected for CCD cameras outside the particular range selected. In the process of controlling random multi-filament into multi-filament array by the feedback signal,
wherein
For the average intensity of the supercontinuum in the selected focus range of each object,
other supercontinuum average intensities collected by the CCD camera outside the selected focus range of all targets.
The invention has the following advantages: the initial laser pulse is regulated and controlled by combining a spatial light modulator with a genetic algorithm, the operation method is relatively simple, and the control of the filamentation process can be finished only by selecting a specific range of a CCD camera to be monitored on a computer. Compared with other methods for controlling the filamentation process, the method can more effectively utilize the supercontinuum energy to concentrate the supercontinuum energy on a certain monofilament or form a multifilament array.
Drawings
Fig. 1 is a schematic diagram of an apparatus for controlling a filament forming process when femtosecond laser pulses are propagated in a transparent medium.
FIG. 2 is a graph showing the result of changing the optical filament from random multifilaments to single filament at any position while controlling the femtosecond laser pulse to propagate in a transparent medium.
FIG. 2(a) is a supercontinuum of femtosecond laser pulses through distilled water when the spatial light modulator is not phase-loaded.
Fig. 2(b) -2 (d) show the supercontinuum of any position after modulation by the spatial light modulator.
FIG. 3 is a graph showing the result of changing the random multi-filament array into a multi-filament array of the optical filament formed by the femtosecond laser pulse controlled to propagate in a transparent medium according to the present invention.
FIG. 3(a) is a supercontinuum of femtosecond laser pulses through distilled water when the spatial light modulator is not phase-loaded.
FIG. 3(b) shows the supercontinuum formed after modulation by the spatial light modulator.
FIG. 3(c) is a three-dimensional diagram of the supercontinuum formed after modulation by the spatial light modulator.
Wherein: 1 is a femtosecond laser, 2 is a first diaphragm, 3 is a reflector, 4 is a variable continuous attenuator, 5 is a spatial light modulator, 6 is a first convex lens, 7 is distilled water, 8 is a second diaphragm, 9 is a second convex lens, 10 is a low-pass filter, 11 is a CCD camera, and 12 is a computer.
Detailed Description
The present invention will be further described with reference to the following examples and drawings, but the scope of the present invention should not be limited thereto.
Referring to fig. 1, fig. 1 is an experimental schematic diagram of a filamentation process of the invention when a spatial light modulator is combined with a genetic algorithm to control a femtosecond laser pulse to propagate in a transparent medium, as can be seen from the figure, an output laser of the femtosecond laser 1 irradiates on the spatial light modulator 5 after passing through a first diaphragm 2 and a variable continuous attenuator 4, the femtosecond laser pulse is focused in distilled water 7 through a first convex lens 6 after being phase-modulated by the spatial light modulator 5 to generate a filamentation effect, and is collected by a CCD camera 11 through a second diaphragm 8, a second convex lens 9 and a low-pass filter 10, and a computer 12 monitors a light intensity calculation feedback signal I in a specific range of a supercontinuum collected by the CCD camera 11 at the same timefeedbackThe spatial light modulator 5 is controlled by using a genetic algorithm to change the phase of the initial laser pulse so as to realize the control of the filamentation process when the femtosecond laser pulse propagates in the transparent medium.
The spatial light modulator is a reflective phase type spatial light modulator.
Said feedback signal
Wherein
The average intensity of the supercontinuum in a particular range is chosen,
other supercontinuum average intensities collected for CCD cameras outside the particular range selected.
The genetic algorithm is realized by Matlab software.
Example 1: the invention controls the transmission of femtosecond laser pulse in transparent mediumThe formed light silk is changed into single silk at any position from random multifilaments. Monitoring the light intensity of the super-continuum spectrum in a specific range collected by the CCD camera by using a computer, and calculating a feedback signal
Using genetic algorithm to feedback signal I simultaneouslyfeedbackMonitoring and continuously optimizing the phase of the initial laser pulse to make IfeedbackGradually increase in value to finally form the monofilament. Referring to fig. 2(a) to fig. 2(d), (a) shows the supercontinuum of femtosecond laser pulses passing through distilled water when the spatial light modulator is not in phase, and (b) (c) (d) shows the supercontinuum of any position after modulation by the spatial light modulator.
Example 2: the invention controls the light silk formed when the femtosecond laser pulse is transmitted in the transparent medium to be changed from random multi-silk into multi-silk array. Monitoring light intensity of the supercontinuum collected by the CCD camera in a plurality of specific ranges by using a computer, and calculating a feedback signal
Using genetic algorithm to feedback signal I simultaneouslyfeedbackMonitoring and continuously optimizing the phase of the initial laser pulse to make IfeedbackGradually increasing in value to finally form a multifilament array. Referring to fig. 3(a) -3 (c), (a) shows the supercontinuum generated by the femtosecond laser pulse passing through distilled water when the spatial light modulator is not loaded with phase, and (b) shows the supercontinuum generated after modulation by the spatial light modulator. (c) Is a three-dimensional graph of the supercontinuum formed after the spatial light modulator is modulated.
Experiment results show that the feedback iteration technology is used for modulating the phase of the initial femtosecond laser pulse by using the spatial light modulator, so that the filamentation process of the femtosecond laser pulse in the transparent medium can be effectively controlled.
Claims (1)
1. A feedback iteration method for controlling the filamentation process when femtosecond laser pulses are transmitted in a transparent medium is characterized in that: monitoring the supercontinuum collected on the CCD camera (11) with a computer (12)Calculating the feedback signal I from the light intensity of the spectrumfeedbackAnd using a genetic algorithm to control the spatial light modulator (5) to modulate the phase of the initial laser pulse so that the feedback signal IfeedbackThe value of the signal I is gradually increased, the control of the filamentation process of the femtosecond laser pulse in the transparent medium is finally realized, the CCD camera and the spatial light modulator are both connected to a computer, and the computer is utilized to monitor the light intensity in the specific range of the super-continuum spectrum collected on the CCD camera to calculate the feedback signal IfeedbackAnd a genetic algorithm is used for controlling a spatial light modulator to modulate the phase of the initial laser pulse, and a feedback signal is fed back in the process of controlling the random multifilaments to become monofilaments at any positions
Wherein
For the average intensity of the supercontinuum within the selected focus range of the target,
for the average intensity of other super-continuum collected by CCD camera outside the selected target focusing range, its feedback signal is used in the process of controlling random multi-filament to become multi-filament array
Wherein
For the average intensity of the supercontinuum in the selected focus range of each object,
other supercontinuum average intensities collected by the CCD camera outside the selected focus range of all targets.
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| CN101291041A (en) * | 2008-06-04 | 2008-10-22 | 中国科学院上海光学精密机械研究所 | Rapid filament forming method in atmosphere of femto-second laser pulse |
| CN102411246A (en) * | 2011-08-11 | 2012-04-11 | 中国科学院上海光学精密机械研究所 | Device and method for shortening length of filament of femtosecond laser in air |
| CN104339088A (en) * | 2013-08-02 | 2015-02-11 | 罗芬-新纳技术公司 | System FOR PERFORMING LASER FILAMENTATION WITHIN TRANSPARENT MATERIALS |
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| CN101291041A (en) * | 2008-06-04 | 2008-10-22 | 中国科学院上海光学精密机械研究所 | Rapid filament forming method in atmosphere of femto-second laser pulse |
| CN102411246A (en) * | 2011-08-11 | 2012-04-11 | 中国科学院上海光学精密机械研究所 | Device and method for shortening length of filament of femtosecond laser in air |
| CN104339088A (en) * | 2013-08-02 | 2015-02-11 | 罗芬-新纳技术公司 | System FOR PERFORMING LASER FILAMENTATION WITHIN TRANSPARENT MATERIALS |
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