A kind of formation method and device based on laser array induced surface thermal deformation effect
Technical field
The present invention relates to photo-thermal detection technique field, specifically a kind of formation method and device based on laser array induced surface thermal deformation effect.
Background technology
The ultimate principle of utilizing induced with laser surface heat deformation effect to detect is to cause local temperature to raise at the effect lower surface of light (hereinafter referred to as pump light) because absorbing luminous energy based on material, thereby deformation occurs.The space distribution of this thermal deformation and being closely related with pump light parameter and material behavior over time.And due to this surface heat deformation, the propagation characteristic of the light reflecting from material surface can change, produce and assemble or effect weakening, just as having newly increased lens.Therefore, this surface heat deformation effect is called again surface thermal lens effect.
The most common method of utilizing surface heat deformation effect to carry out material behavior determination and analysis is to utilize a branch of amplitude to irradiate sample spatial induction through the pump light of ovennodulation to produce thermal deformation, utilizes another bundle to survey light simultaneously and surveys through sample surfaces thermal deformation region the surface heat deformation that pump light causes.When measurement, in the detection light light path reflecting, add a spatial filter, the detection luminous energy that arrives photodetector after spatial filter can be because surface heat deformation changes surveying the convergence of light or effect weakening.In actual measurement, for improving response, conventionally need to utilize phaselock technique.To obtain by sample is carried out to point by point scanning to the two-dimensional imaging of sample.This two-dimensional scan formation method can obtain higher resolution, is similar to and is limited to pump light/detection diffraction of light limit, than being easier to reach sub-micrometer scale under far-field measurement condition.
But this two-dimensional scan formation method is very limited in actual applications.Main cause is that image taking speed is too slow.On the one hand due to signal a little less than, to carry out the phase-locked integration of certain hour to each sample spot; On the other hand, the each movement of sample all needs to spend certain movement and stand-by period, and the latter is in order to make whole system can reach new balance from mechanical shock to local temperature.The image that so generally obtains 500 microns of 500 microns of x of 5 microns of lateral resolutions needs the time of nearly one hour.If absorption of sample is faint, to increase integral time, imaging time will be longer.This shortcoming has greatly limited the application of this technology.
Summary of the invention
The technical problem to be solved in the present invention is to provide a kind of formation method and device based on laser array induced surface thermal deformation effect, and solve and utilize surface thermal lens effect to carry out needing point by point scanning in two-dimensional imaging process, thus long problem consuming time.
Technical scheme of the present invention is:
Based on a formation method for laser array induced surface thermal deformation effect, comprise the following steps:
(1) pump light, pump light source being sent is divided into aplanatic, to be equidistant array distribution pump beam group, pump beam group is irradiated sample surface after assembling, and every a branch of pump light of pump beam group has caused corresponding local surfaces deformation at sample irradiation area;
(2) the detection light, probe source being sent is divided into aplanatic, to be equidistant array distribution detecting light beam group, detecting light beam group is irradiated sample surface after assembling, and every a branch of detection light of detecting light beam group is all corresponding with every a branch of pump light of pump beam group spatially overlaps;
(3), reflex to and survey after light condenser lens again through spatial filter and survey light optical filter by the detecting light beam group of sample outgoing, finally enter photodetector, obtain the two dimensional image of material surface characteristic by measuring the variation of the detecting light beam propagation characteristic that surperficial thermal deformation causes.
The pump beam group obtaining after pump light diffraction light-dividing device in described step (1) is again after modulator, and the modulating frequency of every a branch of pump beam is different, and this pump beam group is irradiated sample surface again after assembling; The described photodetector for detection of surveying light is photodetector array or a photodetector.
Detection to the detecting light beam through spatial filter can have two kinds of diverse ways, specifically describes as follows:
Method one: the detecting light beam group through spatial filter is detected with a photodetector.Like this on single photodetector or signal be the stack of whole detecting light beam group signal, be the simultaneously mixing of tested multiple area informations on sample.Want to utilize a photodetector to realize two-dimensional imaging, the signal that needs every a branch of detection light to produce is distinguishable on detector.。This can be by applying the modulation of different frequency to every a branch of pump light, again in end of probe, utilize phase-locked detection and frequency-scan technique, the surface heat deformation signal (pixel) that just every a branch of pump light can be caused distinguishes, thereby just can not obtain two-dimensional surface thermal deformation signal pattern by point by point scanning.
Method two: to detecting with photodetector array from the detecting light beam array of spatial filter array outgoing, every a branch of detection light respectively correspondence enter a photodetector.Every bit on signal counter sample on each photodetector like this, thus without being scanned, sample just can obtain two-dimensional surface thermal deformation signal pattern.The modulating frequency of pump light can be identical in this case, can be also different.At detecting terminal, utilize parallel processing circuit to process, the surface heat deformation signal (pixel) that just every a branch of pump light can be caused distinguishes.
Described pump light source utilizing emitted light path is different with the radiative path of probe source, described pump beam group is all exported through dichronic mirror output terminal after another input end input of dichronic mirror with described detecting light beam group after dichronic mirror one input end input, and irradiates in sample surface after same focal imaging lens are assembled.
Based on an imaging device for laser array induced surface thermal deformation effect, include pump light source and probe source, be positioned at the sample stage of pump light source and probe source rear end and the spatial filter arranging in turn, survey light optical filter and photodetector; From described pump light source to being provided with in turn pump light diffraction light-dividing device, dichronic mirror and focal imaging lens between sample stage; Survey optical diffraction light-dividing device, polarization spectroscope, quarter-wave plate, dichronic mirror and focal imaging lens from described probe source to being provided with in turn between sample stage; Described quarter-wave plate is arranged at the rear end of polarization spectroscope one output terminal; Described spatial filter is arranged at the rear end of another output terminal of polarization spectroscope; Described photodetector is photodetector array.
Between described pump light diffraction light-dividing device and dichronic mirror, be provided with array photomodulator, described photodetector is photodetector array or a photodetector.
The described imaging device based on laser array induced surface thermal deformation effect also includes surveys light condenser lens, and described detection light condenser lens is arranged between polarization spectroscope and spatial filter or is arranged at the rear end of spatial filter.
Advantage of the present invention:
The present invention carries out point by point scanning method to sample and can improve a lot than traditional on image taking speed, in addition due to without carrying out point by point scanning, concrete detect and Image-forming instrument design can avoid using moving-member, be conducive to improve instrument stability, reduce costs, further miniaturization and broaden application field.
Brief description of the drawings
The structural representation of the embodiment of the present invention.
Embodiment
See Fig. 1, a kind of imaging device based on laser array induced surface thermal deformation effect, include pump light source 1 and probe source 2, be positioned at the sample stage 3 of pump light source 1 and probe source 2 rear ends, be arranged in turn pump light source 1 to the pump light diffraction light-dividing device 4 between sample stage 3, array photomodulator 5, dichronic mirror 6 and focal imaging lens 7, be arranged in turn probe source 2 to the detection optical diffraction light-dividing device 8 between sample stage 3, polarization spectroscope 9, quarter-wave plate 10, dichronic mirror 6 and focal imaging lens 7, be arranged in turn the detection light condenser lens 11 of the rear end of polarization dichronic mirror 9, spatial filter 12, survey light optical filter 13 and photodetector 14, wherein, quarter-wave plate 10 is arranged at the rear end of polarization dichronic mirror 9 transmission output terminals, survey the rear end that light condenser lens 11 is arranged at polarization spectroscope 9 and reflects output terminal.Survey acting as of light optical filter 13 and block parasitic light, only have in theory the light of detection to pass through.
See Fig. 1, a kind of formation method based on laser array induced surface thermal deformation effect: comprise the following steps:
(1), by sample 15 as on sample stage 3;
(2) pump light that, pump light source 1 is sent is divided into aplanatic, to be equidistant array distribution pump beam group through pump light diffraction light-dividing device 4, pump beam group maybe must be modulated after array photomodulator 5 again, the modulating frequency of every light beam can be determined depending on the concrete condition of detecting terminal: if use single electrooptic modulator, the modulating frequency of every light beam is different; If use photodetector array, the modulating frequency of every light beam can be identical; This pump beam group reflects through dichronic mirror 6 again, and by irradiating sample 15 surfaces after focal imaging lens 7 post-concentrations, every a branch of pump light of pump beam group has caused corresponding local surfaces distortion at sample 15 irradiation areas;
(3) the detection light that, probe source 2 sends is divided into aplanatic, to be equidistant array distribution detecting light beam group through surveying optical diffraction light-dividing device 8, detecting light beam group is successively through polarization spectroscope 9, quarter-wave plate 10, dichronic mirror 6, then assemble rear irradiation sample 15 surfaces by focal imaging lens 7, and every a branch of detection light of detecting light beam group all spatially overlaps with every a branch of pump light of pump beam group;
(4) the detecting light beam group, being reflected by sample 15, pass through again focal imaging lens 7, dichronic mirror 6, quarter-wave plate 10, then reflected by polarization spectroscope 9 and through survey light condenser lens 11 assemble adjustments, through spatial filter 12, survey light optical filter 13 laggard enter photodetector 14 record detection light two-dimensional surface thermal deformation signal pattern.The output signal of photodetector 14 utilizes phase-locked detection technique to survey.Now, reference signal using the AC signal identical with the modulating frequency of a certain modulated pump beam as phase-locked detection, the surface heat deformation signal that only has like this this pump beam induction to produce can be measured by lock-in amplifier, and the signal that other pump beam induction produces is all filtered.Change successively the frequency of reference signal, just can obtain the surface heat deformation signal that corresponding pump beam excites.According to the numbering of pump beam and the corresponding signal recording, obtain the two dimensional image of spatial discrimination again.
In actual use, also can utilize multiple analog to digital converters or lock-in amplifier to carry out parallel measurement to every a branch of detection light, to save the time that reference signal is measured that changes successively, further improve image taking speed.