CN102411246B - Device and method for shortening length of filament of femtosecond laser in air - Google Patents
Device and method for shortening length of filament of femtosecond laser in air Download PDFInfo
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- CN102411246B CN102411246B CN 201110229222 CN201110229222A CN102411246B CN 102411246 B CN102411246 B CN 102411246B CN 201110229222 CN201110229222 CN 201110229222 CN 201110229222 A CN201110229222 A CN 201110229222A CN 102411246 B CN102411246 B CN 102411246B
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Abstract
The invention relates to a device and method for shortening the length of the filament of femtosecond laser in air. The device consists of a plano-convex cylindrical lens, a plano-concave cylindrical lens, a first optical grating, a second optical grating and a condenser lens which are arranged on an output optical path of the femtosecond laser in sequence, the first optical grating and the second optical grating are opposite to each other and are arranged in parallel, the distance between the plano-convex cylindrical lens and the plano-concave cylindrical lens is the difference between focal distances of the plano-convex cylindrical lens and the plano-concave cylindrical lens. The device and method provided by the invention have the advantages of simpleness and effectiveness; the length of the optical filament formed by the device and method provided by the invention is shortened greatly by over ten times as compared with the length of the optical filament formed by a condenser lens only; the short optical filament is beneficial to the improvement of the resolution ratio of remote detection, the position of the optical filament can be changed through changing the distance between the optical gratings, and the optical filament can be applied to scanning detection; moreover, the short optical filament is capable of greatly reducing noise in the process of remote detection, thereby improving the signal to noise ratio of detection. The method is very important for accurate remote scanning detection.
Description
Technical field
The present invention relates to the high field laser physics, particularly a kind ofly shorten femtosecond laser becomes the filament length degree in air apparatus and method, long-range accurate scanning probe is of great importance.
Background technology
The appearance of femtosecond pulse has greatly promoted the development of research fields such as femtochemistry, the detection of atom and molecule dynamics, bio-imaging.Yet owing to be subjected to the influence of factors such as diffraction and GVD (Group Velocity Dispersion) in the laser propagation process, once a very long time it is believed that ultrashort laser pulse was not suitable for long-distance transmissions in air.But in the experiment, can stable transfer in the air tens of rice of strong femtosecond laser in addition on km, and the peak light intensity of its inside remains on 10
13～10
14W/cm
2Constant, i.e. so-called " become silk " phenomenon.Generally believe that at present this is because the result of the self-defocusing mobile equilibrium that the plasma that the self-focusing that optical Kerr effect causes and multiphoton ionization or ionization above threshold produce causes (can consult document Braun, etal. Opt. Lett. 20,73,1995 and A. Couairon, A. Mysyrowicz, Phys. Rep. 441,47, and 2007).Femtosecond pulse can propagate into larger distance by becoming silk, and this is in remote probe significant meaning being arranged.
Yet though it is more remote to become in the silk process laser can propagate, the chevilled silk of formation is longer usually, and this has greatly limited the resolution of remote probe process.Simultaneously, the super continuous white light that long silk produces forms ground unrest, reduces the signal to noise ratio (S/N ratio) of surveying.Form short chevilled silk, a kind of simple way is to adopt big numerical aperture to focus on.Yet, wanting at remote one-tenth silk, this needs the condenser lens of very big size.As to adopt numerical aperture be that 0.1 condenser lens becomes silk at a distance at 5m, and then needing diameter is the lens of 1m.Large-sized lens like this are all very difficult at aspects such as processing, assemblings, and expensive.
Summary of the invention
The present invention aims to provide a kind of femtosecond laser becomes the filament length degree in air apparatus and method that shorten, and these apparatus and method have simple and more effective characteristics, and the long-range accurate scanning probe of atmosphere is had important effect.
The basic thought that technology of the present invention solves is:
Focus on after making ultrashort laser pulse produce spatial dispersion by grating pair, allow the light of different frequency only overlap at the focus place, thereby form strong ultrashort, super strong laser pulse.In the place of off-focal, because the light of different frequency does not overlap on time and space, make pulse width increase sharply, cause laser intensity to descend, Rayleigh length reduces, thereby shortens the length of chevilled silk.
Technical solution of the present invention is as follows:
A kind ofly shorten femtosecond laser becomes the filament length degree in air device, be characterized in and directly exported without compressor reducer by the femtosecond laser that chirped pulse amplification produces, light path in described femtosecond laser output sets gradually plano-convex cylindrical lens, plano-concave cylindrical lens, first grating, second grating and condenser lens formation, relative with second grating and the parallel placement of described first grating, the distance between described plano-convex cylindrical lens and the plano-concave cylindrical lens is poor for both focal lengths.
Utilize above-mentioned shortening femtosecond laser in air, to become the device of filament length degree to shorten into the method for filament length degree, comprise the following steps:
1. open femto-second laser, femtosecond laser is derived without compressor reducer, adjust light path, make described femtosecond laser in air, form chevilled silk;
2. mobile described plano-convex cylindrical lens or plano-concave cylindrical lens overlap the focus of described plano-convex cylindrical lens and plano-concave cylindrical lens, and then described chevilled silk reaches the shortest.
Technique effect of the present invention is as follows:
Experiment shows that apparatus and method of the present invention have simple and more effective characteristics, adopts the length of apparatus of the present invention and the formed chevilled silk of method, significantly shortens than the chevilled silk that only produces with condenser lens, and shortening amount is more than 10 times.Short chevilled silk is conducive to improve the resolution of remote probe, and by changing the position that distance between grating changes chevilled silk, can be used for scanning probe.Short chevilled silk also will reduce noise in the remote probe process greatly, thereby improve the signal to noise ratio (S/N ratio) of surveying.This method has important meaning for long-range accurate scanning probe.
Description of drawings
Fig. 1 is the principle schematic of the inventive method.
Fig. 2 shortens the index path of laser pulse filament forming device in air for the present invention;
Wherein: 1 is without the overcompression device, direct laser pulse of from amplifier, deriving, and 2 is the plano-convex cylindrical lens, and 3 is the plano-concave cylindrical lens, and 4 is first grating, and 5 is second grating, and 6 is condenser lens, and 7 is that laser focuses on the back chevilled silk that forms in air.
Embodiment
The invention will be further described below in conjunction with embodiment and accompanying drawing, but should not limit protection scope of the present invention with this.
See also Fig. 1 earlier, Fig. 1 is the principle schematic of the inventive method.The present invention aims to provide a kind of femtosecond laser becomes the filament length degree in air apparatus and method that shorten.Key is to adopt the time-space focusing technology, the laser pulse that will produce without the chirped pulse amplification of overcompression device will be warbled behind grating pair and be converted space chirp to the time, scioptics focus on then, make the light of different frequency only overlap at the focus place, form strong ultrashort, super strong laser pulse, and in the place of off-focal, because the light of different frequency does not overlap on time and space, make pulse width increase sharply, cause laser intensity to descend, Rayleigh length reduces, thereby has shortened the length of chevilled silk.
See also Fig. 2 again, Fig. 2 shortens the index path of laser pulse filament forming device in air for the present invention.As seen from the figure, the present invention shortens femtosecond laser becomes the filament length degree in air device, and this device comprises contracting bundle part, spatial dispersion part and focusing block:
Contracting bundle part is by forming at plano-convex cylindrical lens 2 and the plano-concave cylindrical lens 3 placed successively on the light path behind the collimation.Laser is through after the contracting bundle part, the light beam bundle that contracts in the horizontal direction, contracting beam ratio by between the focal length of plano-convex post lens 2 peaceful concave cylindrical lenses 3 and two cylindrical lenses apart from decision.
The spatial dispersion part is made up of with second grating, 5 grating pairs parallel and staggered relatively first grating 4, by the incident angle of regulating grating and time and the spatial dispersion that the distance between two gratings is regulated laser.After the laser process spatial dispersion part, the time warbles and is compensated, and produces space chirp.
Focusing block is made up of condenser lens 6.Laser focuses on through producing behind the focusing block, and becomes silk near focus.
A kind ofly shorten femtosecond laser becomes the filament length degree in air device, it is characterized in that the femtosecond laser that will be produced by chirped pulse amplification 1 directly exports without compressor reducer, light path in described femtosecond laser 1 output sets gradually plano-convex cylindrical lens 2, plano-concave cylindrical lens 3, first grating 4, second grating 5 and condenser lens 6 formations, described first grating 4 and the 5 relative and parallel placements of second grating, the distance between described plano-convex cylindrical lens 2 and the plano-concave cylindrical lens 3 is poor for both focal lengths.
Utilize above-mentioned shortening femtosecond laser in air, to become the device of filament length degree to shorten into the method for filament length degree, comprise the following steps:
1. open femto-second laser, femtosecond laser 1 is derived without compressor reducer, adjust light path, make described femtosecond laser in air, form chevilled silk 7;
2. mobile described plano-convex cylindrical lens 2 or plano-concave cylindrical lens 3 overlap the focus of described plano-convex cylindrical lens 2 and plano-concave cylindrical lens 3, and then described chevilled silk reaches the shortest.
Be a specific embodiment below, femtosecond laser 1 is that centre wavelength is 800 nanometers, and pulse width is 30 femtoseconds, single pulse energy is 6 millijoules, spot size (full width at half maximum) is the light of 6mm, and when adopting 1 meter condenser lens 6 to focus on, the length of chevilled silk can reach 10 centimetres.When adopting apparatus of the present invention, the focal length of plano-convex cylindrical lens 2 is 50 centimetres, and the focal length of plano-concave cylindrical lens 3 is 10 centimetres, and the distance between two lens is 40 centimetres.The incident angle of first grating 4 is 53 degree, and the distance between first grating 4 and second grating 5 is 73 centimetres, and when the focal length of condenser lens 6 was similarly 1 meter, the length of chevilled silk was 4 millimeters.The chevilled silk that focuses on 10 centimeter length that produce than direct employing condenser lens has shortened 25 times.
Claims (2)
1. one kind is shortened femtosecond laser becomes the filament length degree in air device, it is characterized in that and directly to be exported without compressor reducer by the femtosecond laser (1) that chirped pulse amplification produces, light path in described femtosecond laser (1) output sets gradually plano-convex cylindrical lens (2), plano-concave cylindrical lens (3), first grating (4), second grating (5) and condenser lens (6), described first grating (4) and the relative and parallel placement of second grating (5), the distance between described plano-convex cylindrical lens (2) and the plano-concave cylindrical lens (3) is poor for both focal lengths.
2. utilize the described shortening femtosecond laser of claim 1 in air, to become the device of filament length degree to shorten into the method for filament length degree, be characterised in that to comprise the following steps:
1. open femto-second laser, femtosecond laser (1) is derived without compressor reducer, adjust light path, make described femtosecond laser in air, form chevilled silk (7);
2. mobile described plano-convex cylindrical lens (2) or plano-concave cylindrical lens (3) overlap the focus of described plano-convex cylindrical lens (2) and plano-concave cylindrical lens (3), and then described chevilled silk reaches the shortest.
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| CN 201110229222 CN102411246B (en) | 2011-08-11 | 2011-08-11 | Device and method for shortening length of filament of femtosecond laser in air |
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| CN 201110229222 CN102411246B (en) | 2011-08-11 | 2011-08-11 | Device and method for shortening length of filament of femtosecond laser in air |
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| CN102411246A CN102411246A (en) | 2012-04-11 |
| CN102411246B true CN102411246B (en) | 2013-08-14 |
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| CN104659645A (en) * | 2013-11-18 | 2015-05-27 | 中国科学院大连化学物理研究所 | RTP electrooptical modulating Q airflow hydrogen fluoride laser |
| CN104570544B (en) * | 2015-01-04 | 2017-07-14 | 中国科学院上海光学精密机械研究所 | Based on air into silk multicolor femto-second laser pulse generation |
| CN105487320B (en) * | 2015-11-17 | 2019-05-10 | 长春理工大学 | Array filament forming device and method of the femtosecond laser in transparent optical medium |
| CN108302465A (en) * | 2016-09-30 | 2018-07-20 | 长城汽车股份有限公司 | Laser assisted far lighting module |
| CN107024850B (en) * | 2017-05-26 | 2019-11-01 | 清华大学 | High-speed structures light 3-D imaging system |
| CN108363217B (en) * | 2018-04-20 | 2020-04-24 | 中国科学院物理研究所 | Method for adjusting and monitoring grating parallelism by utilizing automatic leveling laser striping machine and application |
| CN109270764B (en) * | 2018-11-26 | 2021-01-19 | 西安交通大学 | Femtosecond laser filamentation regulation and control device and method based on feedback iteration wavefront shaping technology |
| CN112290358B (en) * | 2020-09-21 | 2022-06-24 | 山东师范大学 | Device and method for generating supercontinuum radiation with adjustable spectral peak |
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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 | Method for quickly forming filaments in femtosecond laser pulse air |
| CN101718937A (en) * | 2009-11-04 | 2010-06-02 | 中国科学院上海光学精密机械研究所 | Device and method for prolonging filamentation length of femtosecond laser in air |
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