CN103862171A - Method for preparing two-dimensional periodic metal particle array structure through dual-wavelength femtosecond lasers - Google Patents

Abstract

A method for preparing a two-dimensional periodic metal particle array structure with a dual-wavelength femtosecond laser. The invention proposes a method and device for preparing a two-dimensional periodic particle array structure on a metal surface by using focused two-color femtosecond laser pulses. Two-color femtosecond lasers with different characteristic parameters are realized by using nonlinear frequency doubling technology, and the same optical element is colinearly focused on the sample after the time delay of the common path or the split path, and the formed two-dimensional periodic structure pattern can be changed by changing The azimuth angle of the frequency doubling crystal and the power ratio of the two-color laser are effectively regulated. The invention has the advantage that the preparation of submicron-scale two-dimensional periodic metal particle array structure is realized conveniently and quickly by using the combined design of different wavelengths and polarization characteristics of the femtosecond laser. The new preparation method of the two-color femtosecond laser proposed by the invention has potential important applications in the field of material micro-nano processing.

Description

Method for preparing two-dimensional periodic metal particle array structure with dual-wavelength femtosecond laser

Technical field:

The invention relates to a method and a processing device for preparing a two-dimensional periodic submicron-scale particle array structure on the surface of a metal material with a femtosecond laser. The femtosecond laser pulse is used to induce a periodic subwavelength stripe structure on the metal surface that varies with the incident laser wavelength and polarization state. The changing physical effect belongs to the field of ultrafast laser application and micro-nano processing. It may have important potential applications in the design and preparation of new nano-photonic devices related to surface plasmon polaritons---SPPs in the future. .

Background technique:

In recent years, the rapid development and maturity of femtosecond laser technology and its commercial devices have attracted extensive attention from researchers in many disciplines, especially due to the short pulse time, high peak power and focused power density of femtosecond laser pulses. Large and other characteristics make it widely used in basic scientific research and advanced manufacturing technology development and application such as ultrafast process detection, strong field physics, nonlinear microscopic imaging, laser ablation propulsion, material modification and high precision processing. application prospects.

Especially in the field of ultra-high-precision processing, processing and preparation, femtosecond laser pulses have attracted widespread attention from scientists all over the world as an emerging method that can change the structure of materials and devices at the micro-nano scale and control their functional properties. Compared with the traditional processing technology of optical, electron beam and ion beam exposure for mask etching, femtosecond laser micro-nano processing and preparation technology has the advantages of simple operation, flexibility, high speed, low cost and high precision, and has been gradually developed. Become the frontier research direction in the field of laser, optoelectronics and mechanical engineering. At present, people have successfully realized the processing, preparation and production of metals, semiconductors, polymers and transparent dielectrics on the micron, submicron and even nanometer scales by using femtosecond lasers. In particular, a large number of recent experimental studies have shown that when a single beam of low-energy femtosecond laser is optically focused and irradiates the surface or interior of the sample material in a repetitive or scanning manner, there will be one-dimensional periodic or quasi-periodic arrangements in the area covered by the spot. Stripes, grooves or grating-like structures, whose spatial period changes with the incident femtosecond laser energy and pulse number, and can be much smaller than the incident laser wavelength, while the spatial arrangement direction of the stripes is closely related to the polarization state of the incident laser [Pulse number dependence of laser-induced periodic surface structures for femtosecondlaser irradiation of silicon,Journal of Applied Physics2010,108:034903;Formation ofextraordinarily uniform periodic structures on metals induced by femtosecond laser pulses,Journal of Applied Physics2006,100:023511;Femtosecond-laser-induced nanostructure formed on hard thin films of TiN and DLC, Appl. Phys. A, 2003, 76:983-985]. At the same time, a large number of systematic and in-depth theoretical studies have been given to this peculiar physical phenomenon, and various physical models such as "self-organization, second harmonic and surface wave interference" have been proposed to analyze and simulate [Self- organized pattern formationupon femtosecond laser ablation by circularly polarized light,2006,252:4702-4706;Formationof nanogratings on the surface of a ZnSe crystal irradiated by femtosecond laser pulses,Physical Review B,2005,72:125429;Surface Electromagnetic waves in optics, Optical Engineering, 31:718-730]. In comparison, the interference theory between the incident laser and the plasma waves (SPPs) induced on the material surface can better and reasonably explain the observed experimental phenomena, so it has been accepted by most people at present.

At the same time, a large number of studies have found that these periodic or non-periodic micro-nanostructures induced by femtosecond lasers on the surface of metals and semiconductors can effectively enhance various efficacy and physical and chemical properties of materials [Chen Feng, Zhang Dongshi, etc., femtosecond Method for preparing super-hydrophobic microstructures on metal surfaces by laser, invention patent number: 200910021923; Yang Jianjun, Zhang Nan, Yang Yang, etc., using laser to prepare microstructure targets to improve laser propulsion impulse coupling coefficient, invention patent number:

201110087843; Brighter Light Sources from Black Metal: Significant Increase in Emission Efficiency of Incandescent Light Sources Physical Review Letters, 2009, 102: 234301], thus greatly expanding and enhancing the application potential and value of materials and devices, in solar energy utilization, high sensitivity Photoelectric detection, solid-state lighting and medical device preparation have very broad practical application space.

However, what needs to be emphasized here is that in the previous research on femtosecond laser micro-nano processing, most of the experiments chose to use femtosecond laser pulses with a single central wavelength as the incident light source, and mainly formed on the surface of the material. The periodic stripe structure is distributed in one-dimensional space. In order to further expand the types of surface structures prepared by femtosecond lasers, it has recently been proposed to divide femtosecond pulses of the same wavelength into multi-beam lasers, and then use their spatial interference principle to prepare two-dimensional periodic micro-nano structures on the surface of semiconductor materials [Fabrication of a two-dimensional periodicmicroflower array by three interfered femtosecond laser pulses on Al:ZnO thin films，NewJournal of Physics,2010,12:043025;Enhanced optical absorptance of metals usinginterferometric femtosecond ablation，Optics Express,2007,15:13838-13843；贾鑫, Jia Tianqing, system and method for preparing asymmetric micro-nano composite periodic pattern with femtosecond laser beam, invention patent number: 201310172920; Chen Jianwen, Gao Hongyi, Xie Honglan, etc., working device for forming two-dimensional nanoscale periodic structure by femtosecond laser beam single pulse , Invention Patent No.: 03142107]. Since these experimental methods mainly involve multi-beam interference of a single wavelength, the actual optical path design and working device are relatively complicated, and the spatial period of the two-dimensional structure formed will also be affected by the precise adjustment of the interference optical path.

Invention content:

The technical problem to be solved by the present invention is: how to use femtosecond laser pulses of two different wavelengths to quickly prepare a two-dimensional periodic arrangement of submicron particle array structures on the surface of metal materials, and master the system design ideas, process manufacturing methods, Realize devices and key elements, etc., so as to effectively control the arrangement direction, size and space period of the submicron structure array on the metal surface.

The present invention cleverly utilizes the combined design of different wavelengths and polarization characteristics of femtosecond lasers, and adopts a simple experimental device to conveniently and quickly prepare sub-micron two-dimensional periodic metal lattices on the metal surface that can be changed in arrangement direction and size structure. Compared with the traditional two-dimensional periodic structure manufacturing process, the technical method proposed by the present invention is relatively simple, fast, convenient and highly operable, and overcomes the complicated procedures brought about by the traditional optical path design and manufacturing technical method.

Technical scheme of the present invention:

A method for preparing a two-dimensional periodic metal particle array structure with a dual-wavelength femtosecond laser. The present invention uses BBO crystal frequency doubling technology to realize the mixed output of fundamental frequency and frequency-doubled dual-wavelength femtosecond laser pulses, and the two can be collinear or split. After transmission with a variable time delay, the same optical element is used to focus and irradiate the metal surface in a collinear manner to prepare and form a submicron-scale particle array structure with a two-dimensional periodic distribution. In addition, by changing the key parameters such as the power ratio of the dual-wavelength laser pulse, the amount of time delay, and the phase matching angle of the frequency-doubling crystal, the period, size, and alignment direction of the microstructure array can be regulated, providing a basis for solid materials and device surfaces. Rapid processing of two-dimensional periodic micro-nanostructures provides a new method. The concrete operating steps of the inventive method are:

The first step, the fabrication and fixation of the metal target sample

After the surface of the metal solid target material is mechanically ground and polished, it is ultrasonically cleaned with deionized water to obtain a metal target sample, and then the metal target sample is fixed on a three-dimensional precision mobile platform in an air environment, and the sample is controlled by a computer. Precise movement in three dimensions (x-y-z) in space;

The material of the metal target sample is molybdenum or tungsten metal material.

The second step, the acquisition and transmission of dual-wavelength femtosecond laser

By vertically irradiating the femtosecond laser pulse output by the laser onto the BBO nonlinear crystal, the dual-wavelength femtosecond laser pulse output by mixing the fundamental frequency and frequency-doubled signals is obtained, and then the two pass through a collinear fixed optical path or a variable splitting time After delaying the transmission of the optical path, it passes through the same optical focusing element in a collinear manner and then irradiates vertically on the surface of the metal target sample;

The third step, the adjustment of the surface of the metal target sample

Control the three-dimensional precision moving platform, so that the above-mentioned metal target sample can be precisely moved along the direction perpendicular and parallel to the laser beam, and at the same time adjust the surface inclination of the metal target sample so that the processing surface of the metal target sample is always in line with the laser propagation direction during the entire processing movement process keep perpendicular to each other;

The fourth step is to determine the focus position of the focusing element

Select the incident femtosecond laser power as 10 milliwatts, and then gradually move the sample along the direction parallel to the propagation of the beam to form a series of ablation pits on the surface of the metal target sample, and determine the focus of the femtosecond laser according to the change in the size of the ablation pits. The focal position of the beam;

The fifth step, the positioning of the surface of the metal target sample

Adjust the three-dimensional precision mobile platform so that the surface of the metal target sample moves from the focal position of the focusing element to the range of 300-600 microns in front of the focal point along the reverse beam propagation direction;

The sixth step, preparation of two-dimensional periodic array structure

In the case of ensuring that the two-color femtosecond laser pulse can be irradiated to the sample surface through the focusing element, the three-dimensional precision mobile platform is controlled to make the metal target sample perform two-dimensional mobile scanning in a plane perpendicular to the beam direction, and by adjusting the fundamental frequency and double frequency Laser power, polarization state, and the distance between the sample surface and the focal point are used to prepare different two-dimensional periodic particle array distributions on the surface of the metal target sample.

The specific method for obtaining dual-wavelength femtosecond laser generation in the second step is: based on the BBO crystal nonlinear frequency doubling technology of the I type o+o→e phase matching mode, the femtosecond laser pulse generated by the laser is converted into the fundamental frequency and The dual-wavelength femtosecond laser is simultaneously output by the frequency-doubled signal, and the phase matching angle is changed by rotating the azimuth angle of the BBO crystal. When the phase matching is in the best state, the obtained dual-wavelength femtosecond laser is linearly polarized, and the polarization directions of the two are perpendicular to each other. When the phase matching deviates from the optimal angle, the obtained frequency-doubled laser still maintains linear polarization but The fundamental frequency laser becomes elliptically polarized.

The specific method of using the collinear fixed optical path in the second step to realize dual-wavelength femtosecond laser transmission is: vertically irradiate the femtosecond laser output from the laser onto the BBO frequency doubling crystal to generate and output dual-wavelength femtosecond laser pulses, and then both After being transmitted in a collinear manner and reflected by a dichroic mirror, it is focused by the same optical element and irradiated vertically on the surface of the metal target sample.

The method described in the second step to realize dual-wavelength femtosecond laser transmission by using the branching time variable delay optical path is:

(1) First, the femtosecond laser pulse output by the laser is passed through the beam splitter to form two laser pulses with the same energy, and the two are respectively introduced into different time-delayed optical paths, and BBO frequency doubling and The filtering technology realizes the output of only the frequency doubled femtosecond laser, while the other arm optical path maintains the transmission of the fundamental frequency femtosecond laser;

(2) After the dual-wavelength femtosecond lasers are transmitted through the time-variable delay optical paths of the two arms, after intensity attenuation, the beams are combined by dichroic mirrors, and then reach a common optical focusing element in a collinear transmission mode, and are irradiated vertically on the surface of the metal target sample.

Among them, the optical paths of the two arms are adjusted so that the time delay range of the fundamental-frequency laser irradiated on the surface of the metal target sample relative to the frequency-doubled laser pulse is -50 picoseconds<Δτ<260 picoseconds.

The method for adjusting the power of the fundamental frequency and frequency-doubled femtosecond laser described in the sixth step is to realize the control of the power of the dual-wavelength laser by using a neutral attenuation plate or a combination of a 1/2 wave plate and a polarizer.

The scanning speed of the metal target sample is 0.005 mm/s to 0.4 mm/s.

The optical focusing element is a microscope objective lens or an optical lens.

The reflectivity of the dichroic mirror to the fundamental frequency femtosecond laser is less than 5%, and the reflectivity to the double frequency femtosecond laser is greater than 60%.

In the process of preparing a two-dimensional periodic array structure, when the dual-wavelength femtosecond laser pulses are all linearly polarized, the power ratio range of the required frequency-doubling and fundamental-frequency laser is 1<γ<7; when the frequency-doubling femtosecond laser When the femtosecond laser is linearly polarized and the fundamental frequency femtosecond laser is elliptically polarized, the power ratio range of the required frequency doubling to the fundamental frequency laser is about 0.8<γ<3.

When the phase matching angle of the frequency doubling crystal deviates from the optimal state, the fundamental frequency laser output after him becomes elliptical polarization state, while the frequency doubling laser maintains linear polarization but its polarization direction changes, so as to realize the arrangement of the particle array structure Tilt regulation within the range of ±35°.

The two-dimensional periodic array structure prepared on the surface of the metal target sample is actually formed by two mutually perpendicular periodic stripes intersecting in space. Nano, the size of the metal particles formed by the intersection ranges from 200 to 550 nanometers.

The moving speed of the sample described in the sixth step above ranges from 0.005 to 0.4 mm/s, the minimum movement accuracy is 1 micron, and the distance between two adjacent scanning lines ranges from 2 to 100 microns.

The adjustment of the azimuth angle of the BBO crystal is achieved by rotating the angle θ between the o-axis of the frequency doubling crystal and the polarization direction of the incident fundamental frequency laser in a plane perpendicular to the incident laser. As a reference zero point, its variation range is θ=-35°～35°.

Advantages and beneficial effects of the present invention:

(1) Apply linearly polarized near-infrared femtosecond laser pulses through BBO crystals to generate dual-wavelength femtosecond laser pulses with fundamental frequency and doubled frequency, focus in a collinear manner, and then vertically irradiate on the surface of the metal sample to induce the formation of two-dimensional periodic distribution of sub Microparticle array structure. The invention has the advantages of simple process, low cost and high efficiency, and can be realized in a large area.

(2) Using the BBO frequency doubling crystal to generate different wavelengths and polarization combinations of the fundamental frequency and frequency doubling laser pulses, the two-dimensional periodic structure of the submicron level is written on the sample surface in one step, and the spatial period of the two-dimensional structure differ in both directions.

(3) By rotating the azimuth angle of the frequency doubling crystal in the plane perpendicular to the incident laser, the polarization characteristics and power ratio of the output dual-wavelength laser can be changed, so as to facilitate the formation of a two-dimensional periodic array structure on the surface of the material The shape characteristics such as spatial arrangement direction and period can be effectively controlled.

Description of drawings

Fig. 1 is a diagram of the collinear transmission optical path of the dual-wavelength femtosecond laser designed in the present invention.

Fig. 2 is a diagram of the variable delay optical path of the dual-wavelength femtosecond laser split transmission time designed in the present invention.

The label descriptions in Fig. 1 and Fig. 2 are: 1 represents a femtosecond laser, 2 represents a femtosecond laser with a center wavelength of 800 nanometers, 3 represents a total reflection mirror with a center wavelength of 800 nanometers of a femtosecond laser, and 4 represents a center wavelength of 800 nanometers. Nano neutral attenuator, 5 means BBO frequency doubling crystal, 6 means two-color femtosecond laser, 7 means dichroic mirror, 8 means optical focusing element, 9 means metal target sample, 10 means three-dimensional precision mobile platform, 11 means center The wavelength is a laser beam splitter with a wavelength of 800 nanometers, 12 represents an adjustable time delay line, and 13 represents an optical filter with a center wavelength of 400 nanometers laser.

Figure 3 is the prepared two-dimensional periodic submicron particle array structure, where A is the best matching angle θ=0° for the BBO crystal in Example 3, that is, when the polarization direction of the incident light is parallel to the o-axis direction of the BBO crystal, the metal molybdenum The two-dimensional periodic submicron particle array structure formed on the surface, B is the enlarged detail of A.

Fig. 4 is embodiment 4 when the BBO crystal azimuth angle deviates from the optimal phase matching angle, that is, when θ≠0°, the change of the direction of the two-dimensional periodic array structure formed on the surface of metal molybdenum, the upper left corner of the figure is marked as the frequency doubling crystal o The angle θ between the axis and the polarization direction of the incident fundamental frequency laser, where A is the case where the angle θ=-25°, and B is the case where the angle θ=35°.

Fig. 5 shows the distribution of two-dimensional sub-wavelength periodic structures formed on the surface of metal molybdenum when the total power is 6 milliwatts and the frequency-doubled laser of 400 nanometers is delayed by 56 picoseconds in Example 5.

Detailed ways:

The specific implementation of the "method for preparing a two-dimensional periodic metal particle array structure" by a dual-wavelength femtosecond laser of the present invention will be described in detail below in conjunction with the accompanying drawings.

Example 1

As shown in the optical path structure in Figure 1, after the femtosecond laser 2 generated by the femtosecond laser 1 is incident on the total reflection mirror 3, its reflected light is irradiated vertically to the surface of the BBO frequency-doubling crystal 5 through the neutral attenuation sheet 4, and the resulting double-wavelength The femtosecond laser 6 passes through the dichroic mirror 7 and enters the focusing element 8. The focused two-color femtosecond laser irradiates the surface of the metal target sample 9 fixed on the three-dimensional precision mobile platform 10 to induce the formation of two-dimensional periodic distribution of sub- Microparticle array structure.

Among them, the laser pulse output from the femtosecond laser has the following characteristic parameters: a repetition frequency of 1000 Hz, a pulse width of 50 femtoseconds, a center wavelength of 800 nanometers, and horizontal linear polarization. After passing through the total reflection mirror and the neutral attenuator, they are vertically incident on the BBO nonlinear frequency doubling crystal with a thickness of 1 mm, and based on the type I o+o→e phase matching mode, the output center wavelength is 400 nanometers frequency doubling signal and The remaining hybrid dual-wavelength femtosecond laser pulses centered on the 800 nm fundamental frequency signal. The two are transmitted collinearly and are incident on the dichroic mirror at an angle of 45°. After obtaining different reflection efficiencies, the beam is focused by a 4x microscope objective lens. By controlling the three-dimensional precision mobile platform, the sample surface is moved to a distance of 300-600 microns in front of the laser focus, and the sample is moved in a plane perpendicular to the beam propagation direction at a scanning speed of 0.01-0.4 mm/s, and finally two-dimensional laser beam is achieved on the sample surface. Rapid preparation of dimension-periodic submicron particle array structures.

Example 2

The optical path structure shown in Figure 2, the femtosecond laser 2 generated by the femtosecond laser 1 passes through the beam splitter 11 to form two laser pulses, and then enters two different optical paths respectively, wherein the femtosecond laser in the optical path of one arm only passes through After the neutral attenuator 4 reaches the dichroic mirror 7, the femtosecond laser in the optical path of the other arm enters the adjustable time delay line 12 after passing through the total reflection mirror 3 and the neutral attenuator 4, and then irradiates the BBO vertically after a time delay on the frequency doubling crystal 5, and then reach the dichroic mirror 7 through the filter 13, and the two laser beams are respectively transmitted and reflected by the dichroic mirror 7 to become two-wavelength femtosecond laser pulses of collinear transmission, which pass through the optical element 8 is focused and irradiated vertically onto the surface of the metal target sample 9 fixed on the three-dimensional precision mobile platform 10 to induce the formation of a two-dimensional periodic distribution of submicron particle array structures.

Among them, the horizontal linearly polarized femtosecond laser pulse output from the femtosecond laser has a repetition frequency of 1000 Hz, a pulse width of 50 femtoseconds, and a center wavelength of 800 nanometers. After passing through the beam splitter, two femtosecond laser pulses with equal energy are formed and separated The femtosecond laser in the optical path of one arm only obtains proper intensity regulation through the attenuator, while the femtosecond laser in the optical path of the other arm passes through the adjustable time delay line and irradiates vertically to the On the BBO nonlinear frequency doubling crystal with a thickness of 1 mm, and based on the type I o+o→e phase matching mode, a hybrid dual-wavelength femtosecond laser with an output center wavelength of 400 nm and a center wavelength of 800 nm is generated, and then a 400 nm The optical filter filters out the fundamental frequency laser so as to realize the transmission of only frequency doubled femtosecond laser. The femtosecond laser pulses of different wavelengths propagating in the optical paths of the two arms are finally collinearly transmitted after passing through the beam combiner, and then focused by a 4x microscope objective lens and then irradiated vertically to the sample surface. By controlling the three-dimensional precision mobile platform, the sample surface is moved to a distance of 300-600 microns in front of the laser focus, and the sample is moved in a plane perpendicular to the beam propagation direction at a scanning speed of 0.01-0.4 mm/s, and finally two-dimensional laser beam is achieved on the sample surface. Rapid preparation of dimension-periodic submicron particle array structures.

Example 3

On the basis of the optical path in Example 1, a neutral attenuator is used to attenuate the fundamental frequency femtosecond laser power incident on the BBO crystal, and the azimuth angle of the BBO crystal is rotated to obtain the maximum frequency doubling efficiency, that is, the crystal o The axis is parallel to the polarization direction of the incident fundamental-frequency laser, so that the remaining 800-nm laser output afterwards maintains the original linear polarization, while the 400-nm frequency-doubled laser is also linearly polarized, and the polarization directions of the two are perpendicular to each other. The total power of the dual-wavelength femtosecond laser after reflection by the dichroic mirror is 2 milliwatts, and the sample surface is placed at a position 400 microns in front of the laser focus. Figure 3 shows the scanning electron micrographs of the processing effect obtained when the sample scanning speed is 0.04 mm/s, and the magnifications are 20,000 and 60,000 times, respectively. It can be seen from the figure that the formed elliptical metal particle structure presents an obvious two-dimensional periodic array distribution, that is, the spatial periods arranged along the horizontal and vertical directions are Λ=616 nm and 236 nm, respectively, and the elliptical particles are in two directions The size is about Φ = (448,230) nanometers.

Example 4

On the basis of the device in Example 1, the experimental parameters such as the total power of the dual-wavelength femtosecond laser incident on the surface of the material, the position of the sample, and the scanning speed are kept constant, but at this time by rotating the BBO crystal in the plane perpendicular to the incident laser The azimuth angle makes its o-axis tilt relative to the linear polarization direction of the incident fundamental-frequency laser, which causes the polarization direction of the output frequency-doubled laser to rotate accordingly, and the frequency-doubling efficiency also changes accordingly; in addition, because the frequency-doubling crystal o The angle between the axis and the polarization direction of the incident fundamental frequency laser is not equal to zero, then the incident fundamental frequency laser will generate e-light and o-light components with polarization directions perpendicular to each other in the crystal during the frequency doubling process, thus affecting the remaining fundamental frequency after exiting the crystal The polarization properties of the laser light, i.e. when it becomes elliptically polarized. Therefore, although the total power of the dual-wavelength laser emitted from the BBO crystal does not change in this case, the power ratio and polarization state of the fundamental-frequency and frequency-doubled lasers change. Figure 4 shows the distribution of two-dimensional periodic structures formed on the surface of metal molybdenum when the angles between the o-axis of the rotating BBO crystal and the polarization direction of the incident light are θ=-25° and 35°, respectively, and the spatial arrangement direction of the array structure is The counter/clockwise tilt occurs relative to the case in Example 3, and the two-dimensional spatial periods are Λ=(682,284) nm and (698,290) nm, respectively.

Example 5

On the basis of the optical path in Example 2, the fundamental frequency femtosecond laser pulse output by the laser first passes through the beam splitter and then enters two different time-delayed optical paths, in which a BBO crystal is placed in the optical path of one arm and filtering technology is used to realize only multiple The output and propagation of the femtosecond laser, while the optical path of the other arm maintains the transmission of the original femtosecond laser of the fundamental frequency. sample surface. Adjust the two-arm dual-wavelength femtosecond lasers to be linearly polarized and the polarization directions are perpendicular to each other. The power ratio of the frequency-doubled and fundamental-frequency laser is about 2:1, and the time delay of the fundamental-frequency laser reaching the surface of the sample relative to the frequency-doubled laser The range is -10 picoseconds < Δτ < 220 picoseconds. Figure 5 shows the distribution of two-dimensional subwavelength structures formed on the surface of metal molybdenum when the total power is 6 milliwatts and the frequency-doubled laser of 400 nanometers is delayed by 56 picoseconds. The periods are Λ=654 and 239 nanometers, respectively.

The above descriptions are only preferred implementations of the present invention. It should be pointed out that those skilled in the art may make some improvements and changes without departing from the principle of the original invention. If the basic preparation principle of the design is the same as the method, these improvements and changes should also be considered within the protection scope of the present invention.

Claims (8)

1. dual wavelength femtosecond laser is prepared the method for two-dimension periodic metallic particles array structure, it is characterized in that the concrete steps of the method are as follows:

The first step, the making of metallic target sample and fixing

Metal solid target surfaces is carried out after mechanical grinding and polishing, totally obtain metallic target sample with deionized water ultrasonic cleaning, then in air ambient, metallic target sample is fixed on three-dimensional precise mobile platform, and realizes the precision in space three-dimensional (x-y-z) direction to sample by computer control and move;

Second step, the obtaining and transmit of dual wavelength femtosecond laser

By by the femto-second laser pulse vertical irradiation of laser instrument output to BBO nonlinear crystal, obtain the dual wavelength femto-second laser pulse that fundamental frequency and frequency-doubled signal mix output, then by both through conllinear fixed light path or along separate routes after the transmission of time variable delay light path, by same concentrating element with conllinear mode vertical irradiation at metallic target sample surfaces;

The 3rd step, the adjustment of metallic target sample surfaces

Control three-dimensional precise mobile platform, above-mentioned metallic target sample can be moved along vertically carrying out precision with the direction that is parallel to laser beam, adjust metallic target sample surfaces gradient simultaneously and make metallic target sample finished surface keep mutually vertical with laser propagation direction all the time in whole processing moving process;

The 4th step, concentrating element focal position determine

Selecting incident femtosecond laser power is 10 milliwatts, then, along the progressively mobile example of direction that is parallel to beam propagation, forms serial ablation pit at metallic target sample surfaces, and determines according to the situation of change of ablation dimple size the focal position that focuses on femtosecond laser beam;

The 5th step, the location of metallic target sample surfaces

Regulate three-dimensional precise mobile platform that metallic target sample surfaces is moved in 300～600 micrometer ranges in focus front along contrary direction of beam propagation from the focal position of concentrating element;

The 6th step, the preparation of two-dimension periodic array structure

Guaranteeing that double-colored femto-second laser pulse all can be irradiated in sample surfaces situation through concentrating element, controlling three-dimensional precise mobile platform makes metallic target sample in the plane perpendicular to beam direction, carry out two-dimensional movement scanning, and by regulating the distance between fundamental frequency and double-frequency laser power, polarization state, sample surfaces and focus, distribute thereby prepare different two-dimension periodic array of particles at metallic target sample surfaces.

2. method according to claim 1, is characterized in that exporting and impinge perpendicularly on from laser instrument the femto-second laser pulse that frequency-doubling crystal, laser signal is linear polarization.

3. method according to claim 1, it is characterized in that the concrete grammar that obtains dual wavelength femtosecond laser described in second step is: the femto-second laser pulse of laser instrument output is converted into the dual wavelength femtosecond laser that fundamental frequency and frequency-doubled signal are exported simultaneously by the non-linear frequency doubling technology based on bbo crystal, and realize the regulation and control to double wave laser polarization state by the azimuth of rotation bbo crystal.

4. method according to claim 1, it is characterized in that adopting described in second step conllinear fixed light path to realize the transmission of dual wavelength femtosecond laser and the concrete grammar that focuses on is: after dichroic mirror reflects, obtain energy attenuation in various degree from the dual wavelength femtosecond laser of frequency-doubling crystal output, then both after same optical element focuses on vertical irradiation at metallic target sample surfaces.

5. method according to claim 1, is characterized in that adopting the method for time variable delay light path acquisition dual wavelength femtosecond laser to be along separate routes described in second step:

(1) based on Michelson's interferometer principle, by the time delay light path that enters two different directions after the femto-second laser pulse beam splitting of laser instrument output, wherein in an arm light path, make only to have the output of frequency multiplication femtosecond laser by employing BBO frequency-doubling crystal and spectral filtering technology, and the transmission that another arm light path keeps original incident femtosecond laser; In addition, realize the energy adjustment to dual wavelength femtosecond laser by place attenuator in every arm light path;

(2) dual wavelength femtosecond laser is after two arms time variable delay light path separately, close and be converted into upper separate front and back of time after bundle but the transmission means of conllinear spatially by dichroscope, and focus on and be radiated at metallic target sample surfaces through common optical element;

(3) the variable optical path delay wire system of adjusting two arm light paths, makes the basic frequency laser that is irradiated to metallic target sample surfaces be about-50 psec < Δ τ <260 psecs with respect to double-frequency laser burst length delay scope.

6. according to the method described in any one in claim 1 to 5, it is characterized in that the metallic target sample motion scan speed described in the 5th step is 0.005 mm/second to 0.4 mm/second.

7. according to the method described in any one in claim 1 to 5, it is characterized in that preparing in two-dimensionally periodic structure process, in the time that dual wavelength femtosecond laser is linear polarization, required frequency multiplication and basic frequency laser power ratio scope are 1< γ <7; When frequency multiplication femtosecond laser is linear polarization and fundamental frequency femtosecond laser while being elliptical polarization, the power ratio scope of required frequency multiplication and basic frequency laser is about 0.8< γ <3; And can realize the regulation and control of the inclination within the scope of ± 35 ° to particle array structure orientation.

8. according to the method described in any one in claim 1 to 5, it is characterized in that the two-dimension periodic array structure of preparing at metallic target sample surfaces is actually by the cycle striped of two mutually perpendicular directions formed in space crossed composition, wherein long period variation scope is 230～300 nanometers, variation of short period scope is 580～640 nanometers, and the metal particle size excursion intersecting to form is 200～500 nanometers.

Images