The laser direct writing method of micro-light variation image and device
Technical field
The present invention relates to a kind of digitalized laser method of producing of micro-optic variable image, be particularly suitable for making low latitude achromatic Optical Variable Imaging frequently.
Background technology
Hologram and based on Optical Variable Imaging (the OpticalVariable Device of dot matrix (dot matrix) diffraction grating, OVD) as advanced anti-counterfeiting technology, be widely used on the physical supports such as currency, visa, ID card, topsecret papers and wrappage, the cycle of the interference fringe that light variation image is contained is about 1 micron, the degree of depth is the 0.1-0.25 micron, be easy to mold pressing and duplicate, become a kind of very ripe application technology.Along with the lifting of industry to the technology application, research to the application technology of low-light variable image begins to receive publicity, so-called micro-light variation image (micro-optical variable device), be often referred to the feature dimension at the 2-40 micron, have the microstructure (low latitude is grating frequently) of refraction, diffraction and reflection characteristic simultaneously, its design, manufacture method are different from hologram image and dot matrix diffraction light change image fully.
General low frequency raster unit can adopt the laser direct-writing method to carve by linear light, but the straight-writing system of x-y cartesian co-ordinate type difficulty when making the complex orientation grating, operational efficiency is low simultaneously.Need first construction drawing as mask for directed speckle type unit, the cycle is long, and the orientation of unit is single relatively, is not suitable for making complicated OVD.
Employing has the two-beam interference type straight-writing system of rotating mechanism, can make high frequency OVD easily and quickly, the two-beam interference optical head as shown in Figure 1, select different grating and orientation thereof by rotation beam splitter 21, thereby on the photoresist face, interfere the little grating of different empty frequencies, different orientation, beam splitter is that the optical grating element by one group of different qualities constitutes, the light intensity of incident light is mainly concentrated on the positive and negative first-order diffraction light, but still have zero order light, therefore need to use light barrier 22 with its elimination.Consider the rationality of system mechanics structure, general lens 24 and lens 23 parfocals.Can find out from accompanying drawing 1 light path, on the photoresist face 25 angle of twin-beam and beam splitter tell ± angle theta of 1 grade of light equates.Angle between two-beam satisfies 2sin (θ/2)=λ/A.When light source lambda is 405nm, to above-mentioned light variation image, when for example interfere forming the little grating of 1000 lines per millimeters, θ=23 °, at this moment, the light barrier structure of zero order light is easy to realize; But for micro-light variation image, empty frequently lower, if will form the little grating of 100 lines per millimeters the time, this moment is eliminated very difficulty of zero order light in θ=2.3 °.Like this, the straight literary style of twin-beam is not suitable for the OVD of low frequency optical grating construction.
Summary of the invention
The object of the invention provides a kind of laser direct writing method of micro-light variation image, solution is difficult when having the laser direct writing method making complex orientation grating of carving by linear light now, the low problem of while operational efficiency is so that micro-light variation image enters the actual industrial application more conveniently.
For achieving the above object, the technical solution used in the present invention is: a kind of laser direct writing method of micro-light variation image comprises the steps:
(1) make up low latitude Grating Digital template frequently, be spacedly distributed with the grating orientation angles, each unit grating is expressed with data structure, be recorded in the Computer Database, the interval of described grating orientation angles is not less than 5 °;
(2) according to the required micro-light variation image of scribing, frequently choose corresponding optical grating construction the Grating Digital template from the low latitude, be presented on the spatial light modulator, utilize laser beam that the raster pattern that shows on the spatial light modulator is projected on the recording medium, the unit picture is dwindled in formation, and imprinting becomes corresponding raster unit on recording medium;
(3) relative position of change light path and recording medium is answered empty frequency and the raster pattern that is orientated according to the micro-light variation image difference transfer pair of required imprinting, repeating step (2), and each raster unit of imprinting obtains required micro-light variation image successively.
Further technical scheme, in the described optical grating mold plate, the grating orientation angles of storage be spaced apart 1 °.
In the technique scheme, the two-dimensional structure storage is adopted in described low latitude Grating Digital template frequently.
Low latitude in the technique scheme is the Grating Digital template frequently, is used to provide the unit of different orientation striped, and each unit is made of chequered with black and white grating lines, and the feature dimension is at the 2-40 micron, and lines have different orientations.For example, the orientation range φ of regulation grating lines is-89 °~90 °, and per 1 ° of change once then has 180 kinds of unit orientation, and the sequence of unit of different orientation is arranged in two dimension pattern plate.Accompanying drawing 2 is the template synoptic diagram that are made of low latitude frequency raster unit, and this synoptic diagram has 36 unit orientation, and per 5 ° of changes once.
We know that during the white-light illuminating diffraction grating, diffracted ray satisfies grating equation:
Λ(sin?i±sinθ)=kλ (1)
Λ is a grating constant in the formula; I is an incident angle; θ is an angle of diffraction; K is an interference level.Angle between the different wave length diffracted ray is,
sinθ1-sinθ2=(λ1-λ2)/Λ (2)
Calculate with white light vertical illumination condition, can find out from formula (2), under equal lighting condition, grating constant is big more, and dispersion angle is just more little.If the grid stroke number is 100 lines/mm, purple light 400nm only is 2.5 ° to the dispersion angle of ruddiness 760nm in+1 order diffraction light, the distance of distinct vision of human eye is 25cm, the linear dispersion of visible light is about 1cm in the diffraction light, the color change of diffraction light is very not obvious, almost present white, therefore, adopt the low frequency grating can realize the light variation image of low chromatic dispersion.The fringe contrast height of low frequency optical grating mold plate, the directionality that the light of composition becomes figure is good.But under the certain condition of the thickness of photoresist, bigger fringe period causes the dutycycle of striped less, is unfavorable for duplicating of relief pattern, otherwise if adopt littler fringe period, it is big that grating dispersion will become.
The low latitude frequently unit of optical grating mold plate also can adopt the lines of random structure to constitute, and referring to accompanying drawing 4, because this speckle of bar shaped at random structure is when the dialogue optical diffraction, the light of each chromatic dispersion mixes, and forms achromatic characteristic.
Realize the laser direct-writing device of a kind of micro-light variation image of said method, comprise laser instrument, collimated light path, imaging optical path, motion platform and control system, described control system is a computer control system, motion platform and described imaging optical path are in X, the relative motion of Y two-dimensional direction, described imaging optical path comprises spatial light modulator, semi-transparent semi-reflecting lens and the miniature light path of two heart projections far away, described spatial light modulator is positioned at the object plane of imaging optical path, by its display image of computer control, described motion platform is positioned at the imaging optical path image planes.
In the technique scheme, described spatial light modulator both can be a transmissive spatial light modulator; It also can be reflective slms.
When making the method for light variation image, laser instrument give off laser beam (royal purple light), behind collimated light path, lighting space photomodulator SLM, computer system reads a unit figure from low latitude frequency Grating Digital template according to the data structure of light variation image at every turn, sends into spatial light modulator, behind the light beam process spatial light modulator SLM, by semi-transparent semi-reflecting lens, the miniature light path of two heart projections far away, dwindle the unit picture being placed on the photoresist dry plate of motion platform to form.Read the grating line cell of different orientation according to the unit orientation of different light variation images, finally the different orientation microstructure that on the photoresist dry plate, forms.The focusing monitoring that CCD is used for focus point can also be set.The Min. of microstructure depends on the size of the numerical aperture of the Pixel Dimensions of SLM, the reduction magnification of two telecentric beam paths, especially microcobjective, influences the microstructure dimension on the photoresist dry plate.
Because the technique scheme utilization, the present invention compared with prior art has following advantage:
1. because the present invention adopts the method for direct imaging rather than the method for interference imaging, the manufacturing process of whole light variation image does not need the mode of mechanical rotation to obtain the striped orientation, as long as on template, read the unit of different orientation by computing machine, can realize the rotation of grating lines on the input SLM, therefore, precision height.
2. by changing the interval of lines in the template, can change the spatial frequency and the dispersive power of the micro-light variation image that finally on the photoresist dry plate, forms.
3. owing to taked to pursue the mode of unit photoetching, the time of the making of whole micro-light variation image shortens greatly.If the unit size of input low frequency optical grating mold plate, 1.6mm, 20 times of projection minification, then the size of the unit on the photoresist dry plate is 80 microns, kinematic system can reach 100 points/s, like this, finishes about about 1 hour of the time of the micro-light variation image of width of cloth 50mm * 50mm area.Equally, if by by the lines photoetching, same system motion speed is 8mm/s, and the empty of lines is 4 microns/mm frequently, like this, finishes about at least 22 hours time of micro-light variation image of width of cloth 50mm * 50mm area.
4. by having taked the mode by the unit photoetching, time of photoetching is only relevant with the speed of the size of modular unit and kinematic system, and is irrelevant with the fine structure of micro-light variation image.
5. by adjusting the empty structure of template frequently, can obtain the micro-optic device of various smooth variant effects.
Description of drawings
Accompanying drawing 1 is the structural representation of two-beam interference optical head in the prior art;
Accompanying drawing 2 digitizing low latitudes are the formwork structure synoptic diagram frequently;
Accompanying drawing 3 is the laser direct writing system structural representation of the embodiment of the invention one
Accompanying drawing 4 is the enlarged diagram of the micro-light variation image optical grating construction of lines at random;
The laser direct writing system structural representation of accompanying drawing 5 embodiment of the invention two;
Accompanying drawing 6 is for having the photo that the zooming effect micro-light variation image is made;
Accompanying drawing 7 and accompanying drawing 8 are the enlarged diagram of micro-light variation image microstructure.
Wherein, [1], LASER Light Source; [2], beam-expanding collimation mirror; [3], catoptron; [4], spatial light modulator; [5], spectroscope; [6], computing machine; [7], final minification projection objective; [8], photoresist face; [9], motion platform; [10], Control Component; [11], CCD; [21], beam splitter; [22], light barrier; [23,24], optical lens; [25], photoresist face.
Embodiment
Below in conjunction with drawings and Examples the present invention is further described:
Embodiment one: a kind of laser direct writing method of micro-light variation image comprises the steps:
(1) make up low latitude Grating Digital template frequently, be spacedly distributed with the grating orientation angles, each unit grating is expressed with data structure, be recorded in the Computer Database, the interval of described grating orientation angles is not less than 5 °;
(2) according to the required micro-light variation image of scribing, frequently choose corresponding optical grating construction the Grating Digital template from the low latitude, be presented on the spatial light modulator, utilize laser beam that the raster pattern that shows on the spatial light modulator is projected on the recording medium, the unit picture is dwindled in formation, and imprinting becomes corresponding raster unit on recording medium;
(3) relative position of change light path and recording medium is answered empty frequency and the raster pattern that is orientated according to the micro-light variation image difference transfer pair of required imprinting, repeating step (2), and each raster unit of imprinting obtains required micro-light variation image successively.
In the low latitude frequently in the Grating Digital template, the OVD data can be expressed as f (x, y, φ, ∧), on behalf of grating, φ be orientated, ∧ represents grating constant, referring to accompanying drawing 6.As shown in Figure 3, make light variation image with laser direct writing system, by the required different empty frequency of Computer Design, the optical grating construction of different orientation, according to the φ in the OVD data, the empty modular unit structure frequently of the numeral that the ∧ value will design in advance outputs on the spatial light modulator, link to each other with computing machine by video driver, by computer control and incoming video signal, project to the photoresist face through the final minification projection objective, owing on template, carried out the orientation design of unit figure in advance, therefore said method can realize arbitrary orientation unit figure photoetching and need not grating rotating mechanism in the two-beam interference, thereby realize low latitude that the two-beam interference system can't the make design and fabrication of micro-light variation image frequently.
Accompanying drawing 3 is a kind of direct-writing devices of making light variation image, laser instrument 1 give off laser beam (royal purple light), through beam-expanding collimation device 2 and catoptron 3, lighting space photomodulator SLM 4, computing machine 5 reads a unit figure from low latitude frequency Grating Digital template according to the data structure of light variation image at every turn, sends into spatial light modulator, behind the light beam process spatial light modulator SLM, by semi-transparent semi-reflecting lens 6, the miniature light path 7 of two heart projections far away, on photoresist dry plate 8, form and dwindle the unit picture.The photoresist dry plate places on the motion platform 9, reads the grating line cell of different orientation according to the unit orientation of different light variation images, finally the different orientation microstructure that forms on the photoresist dry plate.CCD 10 is used for the focusing monitoring of focus point.The Min. of microstructure depends on the size of the numerical aperture of the Pixel Dimensions of SLM, the reduction magnification of two telecentric beam paths, especially microcobjective, influences the microstructure dimension on the photoresist dry plate.
Spatial light modulator (SLM) the Pixel Dimensions 12-25.9 micron that adopts in the laser direct-writing system, miniature through the final minification projection optical system, the smallest spot resolution on photoresist sheet is 2 microns.Therefore, laser direct writing system carries out the minimal characteristic structure that micro-light variation image makes and reaches 2 microns.The low frequency grating constant can reach 250lines/mm.Therefore elementary microstructure on the light variation image is of a size of 40 μ m * 40 μ m, and the resolution of the micro-light variation image of above-mentioned laser direct writing system support is 635dpi.Perhaps the resolution of 80 μ m * 80 μ m micro-light variation images is 317dpi.
By low frequency grating two dimension pattern plate, the OVD of making has the empty structure frequently of 100lines/mm, observes from different perspectives shown in the accompanying drawing 7, and the size of figure changes;
The accompanying drawing 8 usefulness low frequencies colour killing of the light variation image of the lines structure fabrication effect of loosing at random are better than the micro-light variation image with the low frequency preparing grating of accompanying drawing 7.
From accompanying drawing 7 and 8 as can be seen, the realization of the digitizing low frequency grating two dimension pattern plate structure success of design the making of low chromatic dispersion micro-light variation image OVD.It is to be noted, in the technological process that micro-light variation image is made, need the embossment structure of photoresist face is copied on the plastic films material, in hot pressing, frequently optical grating construction is because the dutycycle of embossment (degree of depth and width ratio) less than 1: 10, has resilience in plastic material hot pressing in low latitude shown in the accompanying drawing 2, and print effect is poor slightly, influence the diffraction efficiency of duplicating micro-light variation image, caused glossiness to descend.And linear is owing to have littler feature structure at random, and the striped dutycycle can reach 1: 2.5~1: 5 like this, and therefore, linear is more suitable for and the hot pressing duplication process at random.
Embodiment two: shown in accompanying drawing 5, and a kind of direct-writing device of making light variation image, its structure and embodiment one are similar, but spatial light modulator wherein adopts reflective slms, thus the light path arrangement direction is different with embodiment one.