Focus grid geeratio by i-lie holography Jigag Wu, 1,* Lap Ma Lee, 2 ad Chaghuei Yag 1,2 1 Departmet of Electrical Egieerig, Califoria Istitute of Techology, 1200 E Califoria Blvd., Pasadea, CA 91125, USA 2 Departmet of Bioegieerig, Califoria Istitute of Techology, 1200 E Califoria Blvd., Pasadea, CA 91125, USA *jigag@caltech.edu Abstract: We describe a simple way to geerate a wide-area highresolutio focus grid by i-lie holography ad study the factors that impacts its quality. I our holographic recordig setup, the referece beam was the direct trasmissio of the icomig collimated laser beam through a mask coatig with thi metal film, ad the sample beam was the trasmissio of the laser through small apertures fabricated o the mask. The iterferece of the two beams was the recorded by a holographic plate positioed behid the mask. Compared with other recordig schemes, the i-lie holography scheme has may distict advatages ad is more suitable for geeratig a wide-area focus grid. We explored the depedece of diffractio quality, icludig recostructed focus spot itesity ad spot size, o differet parameters for recordig, such as optical desity of the metal film, size of the apertures, ad focal legths. A wide-area focus grid (170 x 138 spots with area 5.1 mm x 4.1 mm) was recorded usig the i-lie holography scheme for a demostratio. 2010 Optical Society of America OCIS codes: (090.0900) Holography; (090.2890) Holographic optical elemet. Refereces ad liks 1. R. Gräf, J. Rietdorf, ad T. Zimmerma, Live cell spiig disk microscopy, Adv. Biochem. Eg. Biotechol. 95, 57 75 (2005). 2. J. Bewersdorf, R. Pick, ad S. W. Hell, Multifocal multiphoto microscopy, Opt. Lett. 23(9), 655 657 (1998). 3. P. M. Ludquist, C. F. Zhog, P. Zhao, A. B. Tomaey, P. S. Peluso, J. Dixo, B. Bettma, Y. Lacroix, D. P. Kwo, E. McCullough, M. Maxham, K. Hester, P. McNitt, D. M. Grey, C. Heriquez, M. Foquet, S. W. Turer, ad D. Zaccari, Parallel cofocal detectio of sigle molecules i real time, Opt. Lett. 33(9), 1026 1028 (2008). 4. J. Ho, A. V. Parwai, D. M. Jukic, Y. Yagi, L. Athoy, ad J. R. Gilbertso, Use of whole slide imagig i surgical pathology quality assurace: desig ad pilot validatio studies, Hum. Pathol. 37(3), 322 331 (2006). 5. M. Oheim, High-throughput microscopy must re-ivet the microscope rather tha speed up its fuctios, Br. J. Pharmacol. 152(1), 1 4 (2007). 6. J. Wu, X. Cui, G. Zheg, Y. M. Yag, L. M. Lee, ad C. Yag, A wide field-of-view microscope based o holographic focus grid illumiatio, (accepted by Opt. Lett.). 7. F. Kalkum, S. Broch, T. Brads, ad K. Buse, Holographic phase cojugatio through a sub-wavelegth hole, Appl. Phys. B 95(3), 637 645 (2009). 8. W. Liu, ad D. Psaltis, Pixel size limit i holographic memories, Opt. Lett. 24(19), 1340 1342 (1999). 9. D. Gabor, A ew microscopic priciple, Nature 161(4098), 777 778 (1948). 10. J. J. Barto, Removig multiple scatterig ad twi images from holographic images, Phys. Rev. Lett. 67(22), 3106 3109 (1991). 11. W. Xu, M. H. Jericho, I. A. Meiertzhage, ad H. J. Kreuzer, Digital i-lie holography for biological applicatios, Proc. Natl. Acad. Sci. U.S.A. 98(20), 11301 11305 (2001). 12. V. Moreo, J. F. Roma, ad J. R. Salgueiro, High efficiecy diffractive leses: deductio of kioform profile, Am. J. Phys. 65(6), 556 562 (1997). 13. M. H. Horma, ad H. H. M. Chau, Zoe plate theory based o holography, Appl. Opt. 6(2), 317 322 (1967). 14. J. W. Goodma, Itroductio to Fourier Optics (Roberts & Compay Publishers, 3 rd editio, 2004), Chap. 9. 15. C. Geet, ad T. W. Ebbese, Light i tiy holes, Nature 445(7123), 39 46 (2007). 16. A. K. Richter, ad F. P. Carlso, Holographically geerated les, Appl. Opt. 13(12), 2924 2930 (1974). 17. H. I. Bjelkhage, Silver-halide recordig materials for holography ad their processig (Spriger, 2 d editio, 1995), Chap. 5. #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14366
1. Itroductio Focus grid illumiatios has bee used for multi-beam cofocal microscopy [1], multifocal microscopy [2], ad sigle molecule detectio [3], etc. I such applicatios, it is importat to geerate a tight focus spot for high-resolutio imagig, ad a small spacig betwee the focus spots for fast image acquisitio speed. Previously, the focus grid is usually geerated by usig microles array, diffractive optical elemets, or holographic optical elemets, alog with a microscope objective to achieve the abovemetioed characteristics. Oe disadvatage of these methods is that the area of the focus grid illumiatio will be limited by the field-ofview of microscope objective, ad is thus usuitable for applicatios that require wide fieldof-view imagig, e.g., whole-slide imagig [4] or high-throughput imagig ad sesig [5]. Obviously, to achieve a wider field-of-view, the microscope objective has to be elimiated whe geeratig the focus grid illumiatio. A appropriately desiged microles array provides a good alterate solutio. The umber of elemets i such a array ca be scaled up arbitrarily. However, there is a sigificat dowside to such a solutio the grid desity is typically low. This is because the required umerical apertures for high resolutio spots (< 1 µm) ecessarily require the focus spot separatio ad the focal legth to be high. For example, to accomplish a focused spot size of 1 µm at a focal distace of 10 mm, each microles i the array would have to be at least 5 mm i diameter (assumig wavelegth of 500 m). Sice the pitch of the focus grid is equal to microles diameter, this implies that such a array would have a pitch of 5 mm. This sparse grid desity is a sigificat impedimet for most applicatios. The grid desity ca potetially be icreased by usig smaller leses with shorter focal legths. However, the required optical surfaces would be more difficult to fabricate ad the shorter focal legths may be restrictive for certai applicatios. Iterestigly, it is worth otig that the physical leses are ot the oly meas by which we ca focus light. It is also possible to implemet a virtual microles array via holographic recordig. A appropriately pattered piece of holographic plate should be able to trasform a uiform iput coheret light field ito a grid of tightly focused light spots. The holographic projectio-base approach has two advatages. First, implemetatio would be simpler ad cheaper, as log as we ca write the appropriate patter ito the holographic plate. Secod, the effective holographic leses ca overlap to a great extet, ad, as such, we would be able to achieve a higher focus grid desity. Recetly, we showed that a appropriately pattered holographic plate ca geerate light spots of diameter 0.74 µm at a focal distace of 6 mm with a pitch of 30 µm [6]. The correspodig holographic les diameter is 4.3 mm. This implies that the les overlap ratio (les diameter divided by pitch) is 140 (for covetioal leslet array, this ratio is at most 1). The use of holography to geerate a high-resolutio focus spot has bee demostrated by several groups via well-desiged schemes [7, 8]. I their schemes, the trasmissio of a tiy aperture was iterfered with a referece beam ad recorded by holographic materials. This approach ca provide high-quality ad well-cotrolled recordig. I-lie holography was origially proposed by Gabor more tha half a cetury ago [9] ad has bee studies extesively sice the [10, 11]. I this paper, we show that a i-lie holography scheme ca be used for geeratig a wide-area focus grid. I our scheme, as show i Fig. 1(a), the direct trasmissio of a collimated laser beam through a semitrasparet mask iterferes with the trasmissio of the laser through a aperture grid fabricated o the semi-trasparet mask, ad the iterferece patter is recorded by a holographic plate. The advatages of our scheme ca be summarized as follows: (1) The ilie scheme make the setup isesitive to vibratios ad perturbatios i the system; (2) The focal legth of the focus grid ca be adjusted easily ad ca be short with relative ease; (3) The scheme is suitable for recordig large-area aperture grid ad thus suitable for achievig large-area focus grid. This paper reports our experimetal fidigs regardig the impact of various implemetatio parameters o the quality of the recordig. #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14367
The quality of the holographic recordig depeds o the aperture size, the opacity of the mask ad the focal legth. The parameter choices for creatig a optimal recordig are ot apparet by simply dissectig the problem aalytically. Here, we experimetally show the impact of each major desig choice o the recordig s properties. This paper will hopefully serves as a guide for researchers lookig to create such holographic grids for their respective experimets. I sectio 2, we will describe the i-lie holography setup for recordig the hologram for geeratig a focus grid ad preset a theory for calculatig the recostructed focus spot itesity. I sectio 3, we show a series of experimet that studies the depedece of hologram quality, icludig recostructed spot size ad diffractio efficiecy, o experimet parameters, such as optical desity (OD) of the mask, the aperture size, ad the focal legth. Fially, we summarize our work i sectio 4. 2. I-lie holography setup The i-lie holography setup for recordig a hologram that ca geerate a focus spot (a holographic les) is show i Fig. 1(a). The holographic les is also called a siusoidal zoe plate [12] or a Garbor zoe plate [13]. The mask i the setup cosists of a aperture pattered o a layer of metal film. Whe a collimated laser beam shies o the mask, the trasmissio through the aperture serves as sample wave. The metal film is deliberately made to be thi so that the collimated laser beam ca directly trasmit through it ad be atteuated. The direct trasmissio of the beam through the metal film the serves as referece wave ad iterferes with the sample beam ad the iterferece is recorded by a holographic plate positioed at a certai distace behid the mask. I the experimet, we used a silver halide holographic plate. After exposure, the holographic plate was developed ad bleached to produce a phase hologram. A focus spot ca the be geerated by the holographic recostructio process, as show i Fig. 1(b), where a cojugated collimated beam is trasformed ito a focus spot by the hologram. The focal legth of the holographic les is the same as the distace betwee the mask ad the holographic plate durig the recordig process. By replacig the mask with oe that is pattered with a grid of apertures, the same process will yield a phase hologram that ca reder a grid of focus spots. Fig. 1. I-lie holography scheme for fabricatig a holography les. (a) Recordig of the hologram; (b) Recostructio of the focus spot. Cosiderig the sesitivity dyamic rage of holographic materials, it is preferable to make the itesity of referece beam comparable to that of the sample beam. This is true if we have oly oe aperture o the mask. However, for aperture grid o the mask, the iterferece betwee the trasmissios of differet apertures will cotribute to the hologram patter ad affect diffractio if the trasmissios are comparable to the referece beam trasmissio. Thus i the recordig scheme, it is importat to make the itesity of the referece beam much stroger tha that of the sample beam so that a reasoable recostructio ca be achieved [14]. The trasmissio through tiy apertures is geerally a complicated problem ad defies simple solutio without some approximatios [15]. A approximate theory for calculatig holographically geerated les ca be foud i Ref [16], where the Frauhoffer diffractio was used to approximate the trasmissio through the aperture. Similar to Ref [13], our #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14368
calculatio below is based o the simpler assumptio that the sample beam is a combiatio of spherical waves ad the referece beam is a plae wave, sice the apertures i our experimet is comparable to the wavelegth ad much smaller tha the focal legth. Usig paraxial approximatio, the sample wave, i.e., the trasmissio through the aperture grid, ca be writte as A1 π exp i [( x x y ) ] f (1) where f is the focal legth, A 1 /f is the amplitude of oe hole, (x,y ) is the coordiate of the ceter of the aperture, ad λ is the laser wavelegth. Here we eglect the costat phase shift from propagatio alog z-directio. Figure 1(a) shows the scheme with aperture. Thus the iterferogram itesity o the holographic plate ca be writte as: A π I x A i x x y y 1 ( ) 0 + exp [( ) + ( ) ] f 2 A1 π = A0 + 2A0 cos [( x x y ) ] f (2) 2 A1 π π + exp i [( x x ) ( ) ] exp [( ) ( ) ] 2 + y y i x x + y y f A A + 2A f 2 1 0 0 π cos [( x x y ) ] where A 0 is referece wave amplitude. Here we use the approximatio that A 1 << A 0. After developig ad bleachig, we will get a phase hologram [17] ad the trasmissio ca be writte as 2 2 A π 1 t( x) = exp ik A0 + 2A0 cos( [( x x y ) ]) f 2 π = exp( ika0 ) exp iβ cos( [( x x y ) ]) (3) where K is a costat, ad β = 2 KA0 A1 / f is the modulatio amplitude. The modulatio term ca be further expaded as π π (4) l exp i β cos( [( x x ) + ( y y ) ]) ( i ) J l ( β )exp[ il [( x x ) ( y y ) ]] = + l= where J l (β) is the lth order Bessel fuctio of the first kid. Whe β is small ad l 0, J l 1 β ( β ) Γ ( l+ 1) 2 l (5) Neglectig higher order terms, we have #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14369
π π π J 0 ( β ) + ij1( β )exp[ i [( x x y ) ]] + ij 1( β )exp[ i [( x x y ) ]] (6) exp iβ cos( [( x x y ) ]) iβ π iβ π + i x x + y y + i x x + y y 2 Γ(2) 2 Γ(2) 1 exp[ [( ) ( ) ]] exp[ [( ) ( ) ]] where we use the relatio J -1 (β) = J 1 (β). Thus Eq. (3) becomes iβ π iβ π t x i x x y y i x x y y iβ π iβ π + + + + ( ) 1+ exp[ [( ) + ( ) ]] + exp[ [( ) + ( ) ]] 2 Γ(2) 2 Γ(2) 1 exp[ i [( x x ) ( y y ) ]] exp[ i [( x x ) ( y y ) ]] 2 Γ(2) 2 Γ(2) (7) We eglect higher order terms i this aalysis. The first term correspods to the 0 order of the trasmitted beam, ad the secod ad third terms correspod to the + 1 ad 1 order of the diffractio. Comparig with Eq. (1), we ca see that the + 1 ad 1 order diffractio will geerate the focus grid ad its cojugate image. The amplitude of the + 1 order diffractio, which is the diffractio order that we are iterested, ca be writte as 2 iβ 2 / 2 β A0 A1 f (8) 2 Γ(2) Thus, the recostructed focus spot itesity will be proportioal to the itesity of referece beam, the itesity of sample beam behid the mask, ad iversely proportioal to the square of focal legth. Note that the above equatio is a approximatio ad is ot valid for comparable referece ad sample beam itesities. For the focus spot size, a perfectly recostructed focus spot will be comparable i size to the origial aperture i the mask. However, for small apertures that are comparable to the wavelegth, the recostructed spot size will also deped o other factors, such as the resolutio of the holographic material, uiformity of the holographic emulsio, the focal legth, ad the relative itesity betwee sample ad referece beams. I the ext sectio, we show the result of a series of experimet, where we fabricated holograms usig masks with differet ODs, differet sizes of the apertures, ad differet focal legths. The experimetal results agree well with the above theoretical aalysis. 3. Experimets ad Aalysis I the experimet, we used chrome masks with OD = 2.1, 3.2, 4.2, ad 5.3. A lie of apertures were puched through the metal film o each mask usig focused io beam, ad the sizes of the apertures were 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, ad 2.0 µm. The separatio betwee adjacet apertures was 60 µm. For each mask, holograms were recorded at focal legths of f = 3, 6, 9, 12 mm. We used a gree laser with wavelegth of 532 m ad power of 200 mw (Excelsior-532-200, Spectra-Physics) for recordig the hologram. The holographic material was silver halide (VRP, Itegraf). I the recostructio, we set the itesity of the collimated beam icidet o the hologram to be 17 µw/cm 2. With icreasig ODs, the referece beam was atteuated more ad the itesity was closer to that of the sample beam. Accordig to the previous discussio, we should expect to see better diffractio ad stroger focus spots for larger OD, sice the itesities of the sample beam will be more comparable to that of the referece beam. So it is ot surprisig that for OD 2.1, ad 3.2, the recostructed spots ca be observed clearly for all the aperture sizes except 0.2 µm, ad for OD 4.2, all the recostructed spots ca be observed. However, for OD 5.3, we ca observe multiple diffractios of the hologram, which prevet a clear correspodece betwee focus spots ad the apertures o the mask. #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14370
Figure 2 shows the microscope image of masks ad recostructed spots of holograms with OD 4.2 ad OD 5.3. Figure 2(a), 2(b) show the images for OD-4.2 mask, where the recostructed spots is a exact replicatio of the apertures. Figure 2(c), 2(d) show the images for OD-5.3 mask, where we ca see that the umber of recostructed spots is more tha that of the apertures. This is because for OD 5.3, the iterferece betwee the trasmissios of differet apertures is comparable to the iterferece betwee the trasmissio of apertures ad the referece beam. Thus uwated iterferece betwee the aperture trasmissios would be pattered oto the hologram ad ad prevet a clearly recostructio of the focus spots that correspod to the origial apertures. For OD 2.1, 3.2 ad 4.2, the itesity of referece beam is much higher tha that of the sample beam, ad the correspodece of recostructed focus spots ad origial apertures ca be clearly see. Fig. 2. Microscope image of masks ad recostructed spots of holograms uder 4X objective. (a) Mask with OD 4.2; (b) Recostructed spots of hologram correspodig to OD-4.2 mask; (c) Mask with OD 5.3; (d) Recostructed spots of hologram correspodig to OD-5.3 mask. The recostructed spot itesities ad the full-width-half-maximum (FWHM) spot sizes were measured, usig a microscope with 60X/NA0.95 objective, for OD 2.1, 3.2, ad 4.3 ad plotted i Fig. 3, where Fig. 3(a), 3(b) show the plots for OD 2.1, Fig. 3(c), 3(d) show the plots for OD 3.2, ad Fig. 3(e), 3(f) show the plots for OD 4.3. From Fig. 3(a), 3(c), ad 3(e), we ca observe the followig importat features regardig the recostructed spot itesity: (I1) For same OD ad same focal legth, the recostructed spot itesity decreases with smaller aperture size. This could be explaied by less trasmissio through smaller apertures ad Eq. (8). (I2) The recostructed spot itesity is roughly iversely proportioal to the atteuatio coefficiet of referece beam through the mask, ad thus stroger for larger OD. This is because i the experimet, the total exposure o the holographic plate is set to be the optimal value of 80 µj/cm 2 for the holographic material VRP. Assumig that the referece beam itesity is much larger tha the sample beam itesity, the icrease i OD of the mask will result i icrease i sample beam exposure durig recordig as the exposure time will be loger. Thus accordig to Eq. (8), the spot itesity will icrease to the same amout as OD decreases. The experimet shows that for the same aperture size, the spot itesities of OD-3.2 holograms are roughly 10 times of the spot itesities of OD-2.1 holograms, ad the spot itesities of OD- 4.2 holograms are roughly 5-8 times of the spot itesities of OD-3.2 holograms. This agrees well with the theory #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14371
Fig. 3. Recostructed spot itesity ad FWHM spot size versus aperture size at differet ODs ad differet focal legths. (a)(b) OD = 2.1; (c)(d) OD = 3.2; (e)(f) OD = 4.2. From Fig. 3(b), 3(d), ad 3(f), we ca observe the followig importat features regardig recostructed spot size: (S1) For same OD ad same aperture, the spot size decreases with smaller focal legth. This could be explaied by the effective holographic les area o the hologram. As the focal legth decreases, the effective holographic les area also decreases, thus the impact of possible o-uiformity of the holographic recordig material o the les quality would be less, ad the recostructed spot size ca be closer to the origial aperture size. (S2) For same OD ad same focal legth, the spot size decreases with smaller aperture size ad fially reaches a asymptotic value. The decrease i spot size is cosistet with our logical expectatio. The existece of a asymptotic value is usurprisig as well the holographic material ca oly record feature size dow to a certai limit. Recostructio of a small spot requires the patterig of fier diffractio features. Oce we have reached that limit, we caot expect the recostructio spot size to taper to a asymptotic value ad ay further decrease i the mask s aperture size would have o impact. #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14372
We ca see that the recostructio spot ca have a FWHM spot size as small as 0.6 µm. Note that this ca be smaller tha the aperture diameter sice we measured the FWHM spot size, which was related to the diffractio of the aperture. (S3) For differet OD ad same aperture size, we ca obtai similar recostructed spot size, especially for small apertures ad small focal legths. This idicates that the spot size is less sesitive to the relative itesity betwee referece ad sample beam, ad more depedig o the effective holographic les area. This implies that the uiformity of the holographic material is a importat quality-determiig factor. Accordig to these experimetal observatios, we ca see that to get a optimal hologram quality, we would first eed to choose a optimal OD for the mask. A OD of 4 works well for holographic grid desigs that are similar to the oe we have here. We ote that choosig a OD beyod 4 ca potetially provide eve better efficiecy. However, a excessively high OD would sigificatly atteuate the referece itesity. I our experimets, the direct trasmissio through the mask becomes exceedigly weak for a OD beyod 5. I this situatio, the diffractio trasmissios through adjacet apertures would iterfere sigificatly ad lead to sigificat cross-talks. Next a appropriate aperture size should be chose accordig to (I1) ad (S2), which show that there is a trade-off betwee spot itesity ad spot size. Fially we ca see that for small apertures, the spot itesity ad spot size will geerally get better as focal legth decreases, thus we would wat to choose the smallest possible focal legth as log as it is compatible with the system desig. I the fabricatio of our demostratio focus grid, we chose to use a aperture size of 0.8 µm for small eough recostructed spot size based o the reasos listed above. Figure 4 shows the recostructed spot itesity vs. focal legth ad OD for the 0.8-µm aperture size. We ca see that there is a optimal parameter set for gettig the best spot itesity. Fig. 4. Recostructed spot itesity vs. focal legth ad OD for 0.8-µm aperture size. The squares idicate the experimet data poits. Usig the i-lie holography method, we fabricated a hologram that ca geerate a focus grid of 170 x 138, with 30-µm separatio betwee the focus spots. The hologram was recorded with a OD 4 mask with apertures of 0.8-µm diameter, ad at a focal legth of 5 mm. Figure 5 shows a small part of the recostructed spots observed uder microscope with a 20X objective. The FWHM spot size was measured to be aroud 0.7 µm. The focus grid ca be readily used i a wide-field microscope system. #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14373
Fig. 5. Microscope image of a small part of the recostructed focus grid uder a 20X objective. While this set of experimets did ot study the impact of aperture separatio o the focus grid quality, the observed depedecy treds of the other desig parameters ca help iform us o this relatioship. Specifically, a icrease i grid desity would lead to higher total trasmissios through the apertures. This i tur would lead to more iterferece betwee the trasmissios through differet apertures. I this case, we expect a lower OD mask would be required so that the i-lie holography iterferece is stroger tha the cross-talk terms. The exact impact of aperture separatio is well worth a future detailed experimetal study. 4. Summary I coclusio, we have show a i-lie holography scheme for recordig a hologram to geerate a wide-area focus grid. Compare with other methods for geeratig focus grid, our scheme is relatively simple, robust, ad have may other advatages. We have studied the effect of mask OD, aperture size, ad focal legth o recordig process ad showed that a set of appropriate parameters is importat for fabricatig the hologram. A hologram was fabricated to geerate a wide-area focus grid for demostratio of priciple. The hologram ca be potetially used for wide field-of-view imagig or parallel detectig ad sesig applicatios. Ackowledgemet The authors ackowledge Yig Mi Wag, Guoa Zheg, ad Dr. Xiqua Cui for helpful discussios. This work is supported by Departmet of Defese grat #W81XWH-09-1-0051. #128026 - $15.00 USD Received 5 May 2010; revised 27 May 2010; accepted 10 Ju 2010; published 21 Ju 2010 (C) 2010 OSA 5 July 2010 / Vol. 18, No. 14 / OPTICS EXPRESS 14374