High-Resolution Laser-Vibrometer Microscopy

Transcription

1 DO /eno017/B5.3 High-Reolution Lae-Viboete Micocopy Chitian Rebe, Robet Kowach TU Clauthal, E, Clauthal-Zellefeld, Leibniztaße 8, Geany Abtact: Pecie high-fequency electonic, a fo exaple in at phone, equie advanced filte baed on ico- o even nanoelectoechanical (MEM o NEM) eonato. MEM o NEM eonato excite high eonance fequencie in the GHz ange at coplex 3D-ode. The vibation tanfe chaacteitic, the ode hape, and the enegy flow of acoutic wave ae ipotant to undetand electical tanfe chaacteitic and daping influence. Heteodyne ntefeoete Micocope ae an excellent widely ued tool fo out-of-plane vibation. Howeve, fequency ange and vibation aplitude eolution need to be ipoved. The cuent bandwidth i liited to appoxiately 600 MHz fo diect deodulation of the caie detecto ignal and vibation-aplitude eolution i liited to f/ Hz. The patial eolution i liited to the intefeoete wavelength. n thi pape, we peent the cuent liit of available yte and dicu technical olution to beach the liit. Key wod: Lae-Dopple viboety, icocopy, high-fequency vibation, MEM eonato, nanocopy. ntoduction Heteodyne intefeoety cobine with confocal icocopy to a poweful laeviboete icocope [1]. Recently, thi technique ha been advanced to a copletely thee-dienional-vibation eauing yte [] by eploying the diection-dependent Dopple effect. A heteodyne intefeoetic yte up to 1. GHz peented in [3] aue not only high vibation-aplitude eolution but alo vey good accuacy due to a well-analyzed uncetainty budget [4]. A vibation-aplitude eolution without aveaging in the ode of of-the-at. Digitization noie liit the axiu eolution fo highly eflective uface. The detecto ignal of the yte dicued in [3] would povide a hotnoie liited eolution in the ode of 1-3 lae focu diaete of the eauing bea. The vibation ut be unifo within the bea diaete othewie thee-wave-ixing effect falify the eaueent eult daatically. We can aue that the tiniet lae focu of nowaday olution i in the ode of the lae wavelength of appoxiately 500 n. Howeve, highe eolution ae equied to advance the technology to highe fequency ange above 1. GHz. Highe fequencie lead to highe equied powe level to excite a cetain vibation aplitude. Fo exaple, an ocillato with a peak-to-peak diplaceent aplitude of 100 n at 1 khz would have an aplitude of jut 10 f at a vibation with equal velocity aplitude at 10 GHz. The eolution of the eauing yte hould be ubtantially tanveal oundwave in ilicon ha a peed of ound of 5843 / coeponding to a wavelength of 584 n at 10 GHz. Taking into account that the aplitude hould be eaued in an unifoly vibating aea a lateal eolution in the ange below 100 n hould be ealized. n thi pape, we dicu the ecently achieved eeach eult to ipove the vibationaplitude and the lateal eolution of laeviboete icocope. The diplaceent eolution of any diplaceent eno depend on it noie and it ignal enitivity to diplaceent. The allet diplaceent aplitude that exceed the noie in 1 Hz bandwidth define the eolution. Theefoe, only two way exit to advance the eolution: (1) deceaing noie and () inceaing the ignal enitivity to diplaceent. Since the noie i aleady hot-noie-liited, we can gain lowe noie level only with queezed-light technique [5]. Such photon tate can only be geneated with nonlinea expenive optical eleent and degade apidly with light loe. Unfotunately, ealitic eflectivity of a eaueent uface alway eult in ubtantial degadation of queezed-light tate. t ee to be oe feaible to ai fo AMA Confeence 017 SENSOR 017 and RS

2 DO /eno017/B5.3 highe diplaceent enitivity. Multipleeflection intefeoety povide uch highe enitivity a the field of cavity optoechanic deontate [6]. A fit ealization of thi idea [7] deontate aleady eolution below the hot-noie liit of the conventional yte. n ode to achieve lateal eolution beyond the claical diffaction liit we have identified aplitude abobance odulation [8] a a uitable technique to geneate a dynaic pinhole on a uface coveed with a thin (<< 1 µ) photochoic laye. Thi technique ha been exploed fo lithogaphy [9] and tanitted-light icocopy [10] o fa. We have theoetically invetigated the application of thi technique to eflected-light icocopy [11]. To achieve thee eult we have advanced exiting iulation odel by adding the influence of the eflected light in ate equation and by etiating diffaction loe oughly. We expect that an ipoveent of a facto of 10 fo the lateal eolution i feaible in epect to ou iulation. We alo dicu thee eult in thi pape. Open-Optical-Reonato ntefeoete A io integated into the icocope objective at a uface whee no efaction appea ake poible ultiple eflection of the eaueent bea between pecien uface and the additional integated io uface. Fig. 1 how the cheatic of the open-optical-eonato (OOR) etup. pedict eolution below 1 f caefully adapted icocope-io eflectivity. Auing all diplaceent t (<< 1 n) a well a an adjutent of the eonato on the axiu taniion whee the phae deviation i axial and by efeencing to the enitivity of the two-bea intefeoete 4 B t, with wavelength, phae epone R G S 4 B GS (1) yield with the enitivity aplification R 1 R G S R R R R R R () fo the phae of the eflected light that can be evaluated with a tandad heteodyne intefeoete and lae-dopple viboete phae decode. Obviouly, the eflectivity of the OOR in epect to the pecien eflectivity ha a citical influence. The phae gain GS at the opeation point whee the ditance i a ultiple of the wavelength i not defined fo efeence io eflectance and aple eflectance R R. The phae ha a point of dicontinuity at thi point, which lead to an undefined enitivity gain at thi condition. Ou iulation how [7] that a high gain >> 100 i poible. Unfotunately, the eflected light powe i inial at the axiu enitivity gain becaue the optical eonato i lighttaniive at the woking point. Thi eult in a light attenuation gain R 1 R co R R G L, (3) 1 R R R R co whee the phae of the light etuning fo the eonato i B. Thu, caeful election of the paaete i neceay to achieve a eolution ipoveent. The eolution of the OOR i deived in efeence [7] Figue 1: Scheatic of the icocope objective with io to inceae the diplaceent enitivity. n [7] we have hown ecently by expeiental eult that we can achieve eolution on a eflective uface below the hot-noie liit and we have deontated theoetic eult, which OORM G S h B GL P P G P P L. (4) The eolution gain G R eult fo equation (4) and the eolution of the two-bea intefeoete AMA Confeence 017 SENSOR 017 and RS

3 DO /eno017/B5.3 OORM h B P P P P G L P P G R G S. (5) G P P Hee, P i the eflected light powe at the aple and P i the powe of the efeence bea of the intefeoete Many ico- and nanoyte ae ade of ilicon. 53 n ha been identified a welluited wavelength fo a heteodyneintefeoetic icocope becaue a all lae focu i poible a well a hot-noieliited detection. Theefoe, Fig. deontate the ituation fo ilicon with a eflectivity of 0.38 at 53 n. L to Even on plain ilicon, the OOR technique can ipove the eolution by a facto of oe than 1.8. Conideing a pecien with a eflectivity of R Saple invetigated with an OOR eflectivity of R OORM the achievable eolution would eult in epect to equation (10) to 76.6 attoete pe quae-oot-hetz. Thu, attoete eolution i poible with ou appoach fo highly eflecting uface. Howeve, even fo ilicon with R Saple it would be poible with an OOR eflectivity of R OORM 0.4 to achieve with P = 10 W efeence powe and P 0 = 5 W eaueent light powe to achieve 83 attoete pe quae-oot-hetz eolution. Fig. 3 how the ingle-hot eaueent of the piezo-actuato vibation at 50 khz. Figue : Reolution ipoveent of an OOR eflectivity of 0.4, which i lightly highe than the eflectivity of ilicon (0.38) fo 53 n wavelength. A ed line ak the thehold fo eolution ipoveent. The gay ba how the pectu fo a eaueent with a conventional icocope objective. The noie level i too high to allow eauing the piezo-vibation aplitude without aveaging. The eaueent with OOR objective wa calibated and coected in epect to the efeence eaueent. The noie level achieved with the OOR objective i at 56 f fo 50 Hz (coeponding to 3.5 f/ Hz) without aveaging (black ba). Thu, a eolution gain of G R 10 wa achieved fo thi eaueent. The level of the eaueent pefoed with the OOR objective i below the quantu hot noie level of the conventional icocope-objective eaueent fo 100 µw eaueent-light powe and a geen line ak the hot-noielevel at 67 f (4. f/ Hz). n thi cae, 0 coplex aveage of the pectu deceae the noie level to 780 attoete fo 1 Hz eolution bandwidth. Thu, attoete eolution i feaible fo eaonable eaueent condition. AMA Confeence 017 SENSOR 017 and RS

4 DO /eno017/B5.3 Figue 3: Copaion of the diplaceent pectu fo the efeence eaueent with appoxiately 1 p aplitude at 50 khz at RBW = 50 Hz. Fit we eaued the vibation of the piezo pecien wit a conventional icocope objective without aveaging (ed ba). The noie level i too high to allow eauing the piezovibation aplitude. The eaueent with OOR objective wa calibated and coected in epect to the efeence eaueent. The noie level achieved with the OOR objective i at 56 f (coepond to 3.5 f/ Hz ) without aveaging. The level i below the quantu hot noie level of the conventional- icocopeobjective eaueent aked by a ed line. Nanocopy with Abobance Modulation Abobance Modulation ha been intoduced to ipove the eolution of lithogaphy beyond the diffaction liit and the application to taniion-light icocopy ha been exploed by iulation and expeient [8][9][10]. The detection of vibation on icotuctue equie eflected light icocopy in cobination with intefeoetic evaluation of the eaueent light. n ode to exploe theoetically the equieent fo eflected-light nanocopy with abobance odulation we have advanced exiting iulation odel by adding the influence of the eflected light in ate equation of a photochoic laye [11]. Thi polye laye endowed with photochoic olecule cove the uface of the eaueent object. The incopoated bitable photochoic olecule povide a atuable optical tanition, which allow to eveibly odulating the abobance pectu of thee pecial olecule between two tate by iadiation at two diffeent wavelength [1]. n analogy to STED icocopy, one wavelength witche the photochoic laye to an opaque tate poviding only a ingle local zeo whee the abobance popetie eain tanpaent. Thu, thi technique ceate optically a canning ub-wavelength apetue diectly on the uface of the pecien. Fo the geneation of an annula ubwavelength apetue a doughnut-haped lae pot 1 eployed to witch the photochoic laye to an opaque tate fo the eauing wavelength (Fig. 4 (a)). n the cente of thi iadiation patten, the poce geneate the neceay tanpaent local zeo. The focued, diffactionliited aueent bea (Fig. 4 (b)) i abobed anywhee but in the tanpaent zeo and, in tun, educe the abobance in the photochoic laye dependent on the local iadiation. The iultaneou iadiation with both wavelength, thu, initiate a dynaic poce in the photochoic laye until eaching an equilibiu whee the effective pot at the eauing wavelength i beyond the diffaction liit (Fig. 4 (c)). AMA Confeence 017 SENSOR 017 and RS

5 DO /eno017/B5.3 Figue 4: Light intenity ditibution of the diffaction liited eauing pot (a), opaque light-induced, doughnut-haped apetue (b), and effective eauing pot (c) beyond the diffaction liit. Fo odelling bitable photochoic olecule, a ate-equation appoach i convenient. Concentation change c A t of photochoic olecule in the tanpaent tate A ) can be expeed a c t A 1 1 A B c A B A c B, (6) whee ae the bidiectional photon cuent denitie at the diffeent wavelength and i the co ection fo the tanition X Y between the two tate X and Y. With idealization the ate of the concentation of olecule in the opaque tate B i c c B A t t. (7) Fo ino concentation with thin laye an analytical olution fo thi diffeential equation can be found [13]. Howeve, the neceay high aboption fo the application to intefeoetic evaluation equie a diffeent odel and a diffeent atheatic appoach. Hee, the photon cuent denitie tongly change duing the penetation of the laye and, thu, thee i only a nueic olution fo thi dynaic poce. Fo the application with high nueical apetue, a thin photochoic laye i eential due to hot depth of focu. The iulation with thi odel enable u to evaluate of both tepoal and patial popetie with delibeate iadiation patten at both wavelength unde vaiation of deign paaete of the photochoic laye. The ain deign paaete ae the laye thickne, photochoic concentation, pectal popetie of the utilized photochoic olecule and the iadiation patten. The eult how a tong dependency of the achieved ipoveent of the lateal eolution on the powe atio of the incopoated bea. Taniion odel take thi dependency aleady into account. Since ou odel include the eflection on the uface and the back-popagation fo the pecien to the objective, thi dependency on the powe atio i futhe inceaed. Figue 5: Side view of the intenity ditibution of the photochoic laye on the eaueent object fo the geneation of a eveible, opaque apetue. Figue 6: Exeplay coection thought the abobance odulation laye (AML) howing the abobance ditibution at the eaueent wavelength ove the laye depth in equilibiu. We have iulated with ou odel the bea abobance though a photochoic laye of 00 n with a high concentation of a Diaylethen deivate whoe popetie ae publihed in [13]. Unde the iadiation with a doughnut-haped activating pot at 35 n and AMA Confeence 017 SENSOR 017 and RS

6 DO /eno017/B5.3 a diffaction-liited eaueent pot at 63 n with eiion powe in the W egie the iulation how a capability of ipoving the lateal eolution to a tenth of the diffaction liit. Epecially in the cental zeo the eflectivity of the uface influence the width of the ub-wavelength apetue. The inevitable intenity loe of >98 % caue low eaueent intenitie. Howeve, the light loe ee to be acceptable, epecially fo intefeoetic eaueent ethod whee coheent aplification enue high enitivity. Additional loe will occu due to diffaction at the ubwavelength-apetue [14] eulting in light faction, which popagate in aboptive egion of the optical ceated pinhole. Thee diffaction loe ae ubject to ou futhe eeach. Concluion Refeence [7] pove that it i poible to agnify the enitivity and to ipove the eolution of a two-bea intefeoete by eploying an OOR len. We have dicued the theoy fo the OOR intefeoete in thi pape. The phae gain and the eolution ipoveent have been veified by expeient. Noie level below the quantu liit of the two-bea intefeoete ae poible. Expeient deontate attoete eolution with 0 aveage fo 1 Hz eolution bandwidth. n addition, ou theoetical finding how that attoete vibation-aplitude eolution pe Hz i achievable if the alignent i pefect and the intefeoetic detection i quantu liited. The ot ipotant futue goal i the expeiental deontation of attoete eolution pe Hz without aveaging on a vibating icotuctue. n addition, we will exploe the tabilization of the opeation point with a obut electonic contol loop. We have alo uaized ou theoetic wok on lateal eolution ipoveent by eflectance abobance odulation. Ou finding pedict a lateal eolution ipoveent by a facto of 10 facing aboption of 98%. n ou futue wok, we will focu on the additional diffaction loe to deign a nanocopic eaueent yte. Reolution in x, y, and z, Opt. Eng. 53(3), (014) [3] C. Rebe, S. Boedecke, A. Däbentedt, F. - Dopple viboete with low-hea-ode Bagg Poc. of the 8th ntenational Confeence on Vibat SPE 7098, 70980A, (008) [4] M. Winte, H. Füe, M. Biele, G. Siegund, C. - Conf. Poc. 1457, 165 (01) [5] C.M. Cave, Quantu-echanical noie in an intefeoete, Phy. Rev. D, 3, (1981) [6] T.J. Kippenbeg, K.J. Vahala, Cavity optoechanic, Opt. Exp., 15, 5, 1717 (007) [7] C. Rebe, L. Kadne, M, Gieen, Appoaching attoete lae viboety, Rev. Sci. ntu. 87, (016) [8] R. Menon, H.. Sith, Abobance-odulation optical lithogaphy. J. Opt. Soc. A. A 3 (9), S. 90 (006) [9] T. Tujioka, T. Haada, M. Kue, K. Kuoki, M. ie, Supe-Reolution with a Photochoic Mak Laye in an Optical Meoy. OPT REV (3), S (1995) [10] H.-Y. Tai, E. E. Moon, R. Menon, Fa-Field Optical aging at the Nanocale via Abobance Modulation, Poc. of Novel Technique in Micocopy, Vancouve Canada, 6 30 Apil, 009, pp. NMA. [11] R. Kowach, C. Rebe, Modellieung de Auflöungteigeung ittel photochoe Schichten fü die nanokopiche Lae-Dopple- Viboetie, Tagungband de XXX. Metechniche Sypoiu, Hg. v. Zieann, Stefan, De Guyte Oldenbug, S (016). [1] and witing at the nanocale with focued viible Applied Phyic A: Mateial Science & Poceing 77, (003) [13] G. Paiani, R. Catagna, R. Menon, C. Betaelli, A. Bianco, Modeling abobance-odulation optical lithogaphy in photochoic fil. Opt Lett 38 (16), S (013) [14] 66, (1944) Refeence [1] ae-scanning Confocal Viboete Micocope: Theoy and [] C. Rebe, R. Kowach, W. Och, A. Däbentedt, M. Gieen, M. Winte, Optical 3D- Viboete Micocope with Picoete- AMA Confeence 017 SENSOR 017 and RS