MICROSCOPY RESEARCH AND TECHNIQUE 77:105–109 (2014)
MRT Letter: Experimental Verification of Vectorial Theory to Determine Field at the Geometrical Focus of a Cylindrical Lens KAVYA MOHAN, AND PARTHA PRATIM MONDAL* Nanobioimaging Laboratory, Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India
KEY WORDS
bioimaging; fluorescence microscopy
ABSTRACT We provide experimental evidence supporting the vectorial theory for determining electric field at and near the geometrical focus of a cylindrical lens. This theory provides precise distribution of field and its polarization effects. Experimental results show a close match ( 95% using v2-test) with the simulation results (obtained using vectorial theory). Light-sheet generated both at low and high NA cylindrical lens shows the importance of vectorial theory for further development of light-sheet techniques. Potential applications are in planar imaging systems (such as, SPIM, IML-SPIM, imaging cytometry) and spectroscopy. Microsc. Res. Tech. 77:105–109, 2014. V 2014 Wiley Periodicals, Inc. C
INTRODUCTION Planar illumination based techniques are among the fastest growing imaging techniques in fluorescence microscopy (Greger et al., 2011; Huisken et al., 2004; Keller et al., 2010; Voie et al., 1993). This technique gives several advantages over the existing point-bypoint based imaging techniques such as confocal (Brakenhoff et al., 1979; Sheppard, 1986), two photon excitation (TPE) individual molecule localization-selective plane illumination microscopy (IML-SPIM) Denk et al., 1990), 4pi (Hell, 2007), and stimulated emission depletion (STED) (Bianchini et al., 2012; Hell and Wichmann, 1994). A very recent development in planar illumination is the integration of selective plane illumination microscopy (SPIM) with super-resolution techniques called IML-SPIM (Zanacchi et al., 2011). Overall, planar imaging techniques continue to grow at a rapid pace and are finding new applications ranging from bioimaging to applied physics (Dalgarno et al., 2012; Pampaloni et al., 2013; Purnapatra and Mondal, 2013a; Raju et al., 2013; Zanacchi et al., 2013). As the name suggests, cylindrical lens based lightsheet microscopy uses a sheet of light for sample illumination rather than point-illumination. This technique was first proposed by Voie et al. (1993) and vastly improved by Stelzer and coworkers (2004, 2010). Since then many variants of planar illumination technique has arrived including, digital scanned laser light-sheet fluorescence microscopy (DSLM) (Keller et al., 2008), objective coupled planar illumination microscopy (OCPI) (Holekamp et al., 2008), extended light-sheet microscopy (Purnapatra and Mondal, 2013) and its super-resolution analogue (individual molecule localization SPIM) (Zanacchi et al., 2011). Although rapid development has taken place in light-sheet microscopy technique, very little is known about the field distribution at and near the geometrical focus. This is essential for quantitative understanding of the C V
2014 WILEY PERIODICALS, INC.
field distribution and for developing precise microscopy techniques based on planar imaging. Recently, we published a complete vectorial theory for planar imaging using cylindrical lens system Purnapatra and Mondal, 2013b. In this letter, we provide experimental verification for validating vectorial theory. Specifically, we test the theory at varying numerical aperture (NA) and for both linearly and circularly polarized light illumination. METHODS According to the vectorial theory, the electric field components at the focus of a cylindrical lens for a linearly polarized (polarization angle hP) plane wave illumination are given by (Purnapatra and Mondal, 2013), 2
Ex ðq; /Þ
3
2
coshp
6 7 1a ð6 6 6 7 6 Ey ðq; /Þ 75 6 6 sinhp cosh 6 7 6 4 5 2a4 Ez ½q; / sinhp sinh
3 7 7pffiffiffiffiffiffiffiffiffiffiffiffi 7 7 cosh 7 5
(1)
3exp ½iqkcos ðh2/Þdh where, a is the semi-aperture angle of the cylindrical lens and k is the wavenumber in the image space. The *Correspondence to: Partha P. Mondal, Nanobioimaging Laboratory, Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India. E-mail: [email protected] Received 12 December 2013; accepted in revised form 18 December 2013 REVIEW EDITOR: Prof. Alberto Diaspro Contract grant sponsors: INSA, Department of Science and Technology BRNS (DAE) and Edmund Optics (EO) Higher Education Grant Program 2013. DOI 10.1002/jemt.22332 Published online 5 January 2014 in Wiley Online Library (wileyonlinelibrary.com).
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radial distance from the x-axis and the polar inclinapffiffiffiffiffiffiffiffiffiffiffiffiffi tion are denoted by q5 y2 1z2 and /5tan21 ðy=zÞ respectively. The resultant field at and near the geometrical focus is given by, I5jEj2 5jEx j2 1jEy j2 1jEz j2
(2)
RESULTS AND DISCUSSIONS To characterize the light-sheet and its polarization properties, we have carried out experiments by
directly placing the camera at the focus. The incident light is x-polarized and the wavelength is chosen as 532 nm. We have used both low (a 5 0.43 , focal length5 250 mm) and high (a 5 0.71 , focal length 5 150 mm) numerical aperture lens for understanding the characteristics of light-sheet. The scan range along the optical z-axis was from 24.25 mm to 14.25 mm passing through the focus (z 5 0) and a total of 850 2D scans were taken along z-axis. Figure 1 shows the experimental scheme for mapping the electric field distribution at and near the focus. The incident light beam is allowed to pass
Fig. 1. Schematic diagram of the optical setup for mapping the field at and nearby the focus of a cylindrical lens. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Fig. 2. A,B: The field distribution (system PSF) obtained by computational simulation (vectorial theory) and experimentation for cylindrical lens with low numerical aperture (a 5 0.43 and f 5 250 mm). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Microscopy Research and Technique
EXPERIMENTAL VERIFICATION FOR VALIDATING VECTORIAL THEORY
through a liquid crystal variable retarder (Thorlabs, LCR-1-VIS). This facilitates the control of polarization state of light and the state can be switched from linear to circular by applying the external voltage. Subsequently, the beam is expanded 2.5 times using a beamexpander to fill the back-aperture of the cylindrical lens. One dimensional focusing of the cylindrical lens results in the generation of light-sheet. A CCD camera (Chameleon, Pointgrey) is placed about the focus and the field is scanned by translating the camera along the optical z-axis to acquire several 2D snap-shots of the field and subsequently merged to generate 3D field distribution. The camera is setup with an exposure time of 0.82 ms, and gain of 25.34 dB. The field for low NA lens (a 5 0.43 and f 5 250 mm) is shown in Figure 2. The computational and experimental realization of the 3D field is shown in Figures 2A and 2B respectively. Visually, a good match is found between the computationally simulated field (using master Eqs. (1) and (2)) and the measured field (see, YZ and XZ planes in Fig. 2). To validate the theory at larger NA lens, we have also studied the field distribution at large NA (a 5 0.71 and f 5 150 mm). The correspond-
ing field along with the computationally simulated field is shown in Figure 3. Figures 3A and 3B respectively show the computationally simulated and experimentally obtained field distribution. Visual inspection for both low and high NA shows a good match. To further strengthen the theory, we have carried out intensity plots along predetermined lines passing through the system Point Spread Function (PSF). Figure 4 show the intensity variation along Y and Z axis. Alongside the theoretical plot is also shown depicting close resemblance. For low NA case (top row in Fig. 4), the full width at half maxima (FWHM) along Y and Z axis is about 26.25 lm and 7.2 mm, respectively. This reduces to 16.87 lm and 3 mm along Y and Z, respectively, for high NA lens (bottom row in cylindrical X ðO 2E Þ2 2 i i 2 Fig. 4). v -Value v 5 is used to compare Ei i experimental result (O) with the theoretically calculated result (E). The corresponding v2-values are 0.2 (Y-profile) and 1.2 (Z-profile) for low NA, whereas for high NA case, the values are 0.4 (Y-profile) and 1.6 (Z-profile). These v2-value reveal 95%-fit between experimental and theoretical value. Finally, we show the field distribution for circularly-polarized light
Fig. 3. A,B: The system PSF for relatively high numerical aperture (a 5 0.71 and f 5 150 mm), obtained by both computational simulation (vectorial theory) and experimentation. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Microscopy Research and Technique
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and compare it with linearly-polarized light illumination. We employed a liquid-crystal retarder to change the polarization state from linear to circular. Figure 5 does not show significant change in the field distribution. This is due to the fact that the polarization
dependent change is observable only at large NA (aperture angle > 1 ). With the availability of large NA cylindrical lens, this theory may play vital role for understanding field distribution at the geometrical focus.
Fig. 4. A, B: Comparison (in-terms of v2-test) of both the lateral and axial intensity profile plots of the experimentally obtained PSF and the PSF obtained from the theoretical model for small numerical
aperture (a 5 0.43 ). C, D: Comparison for large numerical aperture (a 5 0.71 ) of the cylindrical lens. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Fig. 5. A, B: The experimentally measured field distribution for circular and linear polarized light illumination. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Microscopy Research and Technique
EXPERIMENTAL VERIFICATION FOR VALIDATING VECTORIAL THEORY
CONCLUSION AND COMMENTS In this letter, we have experimentally verified the vectorial theory for determining the field distribution at and near the focus of a cylindrical lens. This is significant for probing polarization sensitive fluorescent molecules and precision imaging using light-sheet microscopy technique. Close resemblance between experimental and theoretical values reveal the significance of vectorial theory for field calculation in cylindrical lens geometry. This will lay the foundation for further development of light-sheet technique for both fluorescence-labeled and label-free imaging. REFERENCES Bianchini P, Harke B, Galiani S, Vicidomini G, Diaspro A. 2012. Single-wavelength two-photon excitation-stimulated emission depletion (SW2PE-STED) Superresolution imaging. Proc Natl Acad Sci USA 109:6390–6393. Brakenhoff GJ, Blom P, Barends P. 1979. Confocal scanning light microscopy with high aperture immersion lenses. J Microsc 117: 219–232. Dalgarno HIC, Cizmar T, Vettenburg T, Nylk J, Gunn-Moore FJ, Dholakia K. 2012. Wavefront corrected light sheet microscopy in turbid media. Appl Phys Lett 100:191108. Denk W, Strickler JH, Webb WW. 1990. Two-photon laser scanning fluorescence microscopy. Science 248:73. Greger K, Neetz MJ, Reynaud EG, Stelzer EH. 2011. Three dimensional fluorescence lifetime imaging with a single plane illumination microscope provides and improved signal to noise ratio. Opt Express 19:20743–20750. Hell SW, Wichmann J. 1994. Breaking the diffraction resolution limit by stimulated emission: Stimulated-emission-depletion fluorescence microscopy. Opt Lett 19:780–782.
Microscopy Research and Technique
109
Hell SW. 2007. Far field nanoscopy. Science 316:1153–1158. Holekamp TF, Turaga D, Holy TE. 2008. Fast three-dimensional fluorescence imaging of activity in neural populations by objective-coupled planar illumination microscopy. Neuron 57: 661–672. Huisken J, Swoger J, Del Bene F, Wittbrodt J, Stelzer EHK. 2004. Optical sectioning deep inside live embryos by selective plane illumination microscopy. Science 305:1007–1009. Keller PJ, Schmidt AD, Santella A, Khairy K, Bao Z, Wittbrodt J, Stelzer EH. 2010. Fast, high-contrast imaging of animal development with scanned light sheet-based structured-illumination microscopy. Nat Methods 7:637. Keller PJ, Schmidt AD, Wittbrodt J, Stelzer EHK. 2008. Reconstruction of zebrafish early embryonic development by scanned light sheet microscopy. Science 322:1065–1069. Pampaloni F, Ansari N, Stelzer EH. 2013. High resolution deep imaging of cellular spheroids with light-sheet based fluorescence microscopy. Cell Tissue Res 352:161–177. Purnapatra SB, Mondal PP. 2013a. Generation of extended light sheet for single and multi-photon fluorescence microscopy. Appl Phys Lett 103:043701. Purnapatra SB, Mondal PP. 2013b. Determination of electric field at and near the focus of a cylindrical lens for applications in fluorescence microscopy, AIP Adv 3:052124. Raju R, Kavya M, Mondal PP. 2013. Light sheet based imaging flow cytometry on a microfluidic platform. Micros Res Tech 76:1101– 1107. Sheppard CJR. 1986. Aberrations in high aperture conventional and confocal imaging systems. Appl Opt 27:4782–4786. Voie AH, Burns DH, Spelman FA. 1993. Orthogonal-plane fluorescence optical sectioning: Three-dimensional imaging of macroscopic biological specimens. J Microsc 170:229. Zanacchi FC, Lavagnino Z, Donnorso MP, Bue AD, Furia L, Faretta M, Diaspro A. 2011. Live-cell 3D super-resolution imaging in thick biological samples. Nat Methods 8:1047–1049. Zanacchi FC, Lavagnino Z, Faretta M, Furia L, Diaspro A. 2013. Light-sheet confined super-resolution using two-photon photoactivation. PLoS One 7:e67667.
MRT Letter: Experimental Verification of Vectorial Theory to Determine Field at the Geometrical Focus of a Cylindrical Lens KAVYA MOHAN, AND PARTHA PRATIM MONDAL* Nanobioimaging Laboratory, Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India
KEY WORDS
bioimaging; fluorescence microscopy
ABSTRACT We provide experimental evidence supporting the vectorial theory for determining electric field at and near the geometrical focus of a cylindrical lens. This theory provides precise distribution of field and its polarization effects. Experimental results show a close match ( 95% using v2-test) with the simulation results (obtained using vectorial theory). Light-sheet generated both at low and high NA cylindrical lens shows the importance of vectorial theory for further development of light-sheet techniques. Potential applications are in planar imaging systems (such as, SPIM, IML-SPIM, imaging cytometry) and spectroscopy. Microsc. Res. Tech. 77:105–109, 2014. V 2014 Wiley Periodicals, Inc. C
INTRODUCTION Planar illumination based techniques are among the fastest growing imaging techniques in fluorescence microscopy (Greger et al., 2011; Huisken et al., 2004; Keller et al., 2010; Voie et al., 1993). This technique gives several advantages over the existing point-bypoint based imaging techniques such as confocal (Brakenhoff et al., 1979; Sheppard, 1986), two photon excitation (TPE) individual molecule localization-selective plane illumination microscopy (IML-SPIM) Denk et al., 1990), 4pi (Hell, 2007), and stimulated emission depletion (STED) (Bianchini et al., 2012; Hell and Wichmann, 1994). A very recent development in planar illumination is the integration of selective plane illumination microscopy (SPIM) with super-resolution techniques called IML-SPIM (Zanacchi et al., 2011). Overall, planar imaging techniques continue to grow at a rapid pace and are finding new applications ranging from bioimaging to applied physics (Dalgarno et al., 2012; Pampaloni et al., 2013; Purnapatra and Mondal, 2013a; Raju et al., 2013; Zanacchi et al., 2013). As the name suggests, cylindrical lens based lightsheet microscopy uses a sheet of light for sample illumination rather than point-illumination. This technique was first proposed by Voie et al. (1993) and vastly improved by Stelzer and coworkers (2004, 2010). Since then many variants of planar illumination technique has arrived including, digital scanned laser light-sheet fluorescence microscopy (DSLM) (Keller et al., 2008), objective coupled planar illumination microscopy (OCPI) (Holekamp et al., 2008), extended light-sheet microscopy (Purnapatra and Mondal, 2013) and its super-resolution analogue (individual molecule localization SPIM) (Zanacchi et al., 2011). Although rapid development has taken place in light-sheet microscopy technique, very little is known about the field distribution at and near the geometrical focus. This is essential for quantitative understanding of the C V
2014 WILEY PERIODICALS, INC.
field distribution and for developing precise microscopy techniques based on planar imaging. Recently, we published a complete vectorial theory for planar imaging using cylindrical lens system Purnapatra and Mondal, 2013b. In this letter, we provide experimental verification for validating vectorial theory. Specifically, we test the theory at varying numerical aperture (NA) and for both linearly and circularly polarized light illumination. METHODS According to the vectorial theory, the electric field components at the focus of a cylindrical lens for a linearly polarized (polarization angle hP) plane wave illumination are given by (Purnapatra and Mondal, 2013), 2
Ex ðq; /Þ
3
2
coshp
6 7 1a ð6 6 6 7 6 Ey ðq; /Þ 75 6 6 sinhp cosh 6 7 6 4 5 2a4 Ez ½q; / sinhp sinh
3 7 7pffiffiffiffiffiffiffiffiffiffiffiffi 7 7 cosh 7 5
(1)
3exp ½iqkcos ðh2/Þdh where, a is the semi-aperture angle of the cylindrical lens and k is the wavenumber in the image space. The *Correspondence to: Partha P. Mondal, Nanobioimaging Laboratory, Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India. E-mail: [email protected] Received 12 December 2013; accepted in revised form 18 December 2013 REVIEW EDITOR: Prof. Alberto Diaspro Contract grant sponsors: INSA, Department of Science and Technology BRNS (DAE) and Edmund Optics (EO) Higher Education Grant Program 2013. DOI 10.1002/jemt.22332 Published online 5 January 2014 in Wiley Online Library (wileyonlinelibrary.com).
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radial distance from the x-axis and the polar inclinapffiffiffiffiffiffiffiffiffiffiffiffiffi tion are denoted by q5 y2 1z2 and /5tan21 ðy=zÞ respectively. The resultant field at and near the geometrical focus is given by, I5jEj2 5jEx j2 1jEy j2 1jEz j2
(2)
RESULTS AND DISCUSSIONS To characterize the light-sheet and its polarization properties, we have carried out experiments by
directly placing the camera at the focus. The incident light is x-polarized and the wavelength is chosen as 532 nm. We have used both low (a 5 0.43 , focal length5 250 mm) and high (a 5 0.71 , focal length 5 150 mm) numerical aperture lens for understanding the characteristics of light-sheet. The scan range along the optical z-axis was from 24.25 mm to 14.25 mm passing through the focus (z 5 0) and a total of 850 2D scans were taken along z-axis. Figure 1 shows the experimental scheme for mapping the electric field distribution at and near the focus. The incident light beam is allowed to pass
Fig. 1. Schematic diagram of the optical setup for mapping the field at and nearby the focus of a cylindrical lens. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Fig. 2. A,B: The field distribution (system PSF) obtained by computational simulation (vectorial theory) and experimentation for cylindrical lens with low numerical aperture (a 5 0.43 and f 5 250 mm). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Microscopy Research and Technique
EXPERIMENTAL VERIFICATION FOR VALIDATING VECTORIAL THEORY
through a liquid crystal variable retarder (Thorlabs, LCR-1-VIS). This facilitates the control of polarization state of light and the state can be switched from linear to circular by applying the external voltage. Subsequently, the beam is expanded 2.5 times using a beamexpander to fill the back-aperture of the cylindrical lens. One dimensional focusing of the cylindrical lens results in the generation of light-sheet. A CCD camera (Chameleon, Pointgrey) is placed about the focus and the field is scanned by translating the camera along the optical z-axis to acquire several 2D snap-shots of the field and subsequently merged to generate 3D field distribution. The camera is setup with an exposure time of 0.82 ms, and gain of 25.34 dB. The field for low NA lens (a 5 0.43 and f 5 250 mm) is shown in Figure 2. The computational and experimental realization of the 3D field is shown in Figures 2A and 2B respectively. Visually, a good match is found between the computationally simulated field (using master Eqs. (1) and (2)) and the measured field (see, YZ and XZ planes in Fig. 2). To validate the theory at larger NA lens, we have also studied the field distribution at large NA (a 5 0.71 and f 5 150 mm). The correspond-
ing field along with the computationally simulated field is shown in Figure 3. Figures 3A and 3B respectively show the computationally simulated and experimentally obtained field distribution. Visual inspection for both low and high NA shows a good match. To further strengthen the theory, we have carried out intensity plots along predetermined lines passing through the system Point Spread Function (PSF). Figure 4 show the intensity variation along Y and Z axis. Alongside the theoretical plot is also shown depicting close resemblance. For low NA case (top row in Fig. 4), the full width at half maxima (FWHM) along Y and Z axis is about 26.25 lm and 7.2 mm, respectively. This reduces to 16.87 lm and 3 mm along Y and Z, respectively, for high NA lens (bottom row in cylindrical X ðO 2E Þ2 2 i i 2 Fig. 4). v -Value v 5 is used to compare Ei i experimental result (O) with the theoretically calculated result (E). The corresponding v2-values are 0.2 (Y-profile) and 1.2 (Z-profile) for low NA, whereas for high NA case, the values are 0.4 (Y-profile) and 1.6 (Z-profile). These v2-value reveal 95%-fit between experimental and theoretical value. Finally, we show the field distribution for circularly-polarized light
Fig. 3. A,B: The system PSF for relatively high numerical aperture (a 5 0.71 and f 5 150 mm), obtained by both computational simulation (vectorial theory) and experimentation. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Microscopy Research and Technique
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and compare it with linearly-polarized light illumination. We employed a liquid-crystal retarder to change the polarization state from linear to circular. Figure 5 does not show significant change in the field distribution. This is due to the fact that the polarization
dependent change is observable only at large NA (aperture angle > 1 ). With the availability of large NA cylindrical lens, this theory may play vital role for understanding field distribution at the geometrical focus.
Fig. 4. A, B: Comparison (in-terms of v2-test) of both the lateral and axial intensity profile plots of the experimentally obtained PSF and the PSF obtained from the theoretical model for small numerical
aperture (a 5 0.43 ). C, D: Comparison for large numerical aperture (a 5 0.71 ) of the cylindrical lens. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Fig. 5. A, B: The experimentally measured field distribution for circular and linear polarized light illumination. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Microscopy Research and Technique
EXPERIMENTAL VERIFICATION FOR VALIDATING VECTORIAL THEORY
CONCLUSION AND COMMENTS In this letter, we have experimentally verified the vectorial theory for determining the field distribution at and near the focus of a cylindrical lens. This is significant for probing polarization sensitive fluorescent molecules and precision imaging using light-sheet microscopy technique. Close resemblance between experimental and theoretical values reveal the significance of vectorial theory for field calculation in cylindrical lens geometry. This will lay the foundation for further development of light-sheet technique for both fluorescence-labeled and label-free imaging. REFERENCES Bianchini P, Harke B, Galiani S, Vicidomini G, Diaspro A. 2012. Single-wavelength two-photon excitation-stimulated emission depletion (SW2PE-STED) Superresolution imaging. Proc Natl Acad Sci USA 109:6390–6393. Brakenhoff GJ, Blom P, Barends P. 1979. Confocal scanning light microscopy with high aperture immersion lenses. J Microsc 117: 219–232. Dalgarno HIC, Cizmar T, Vettenburg T, Nylk J, Gunn-Moore FJ, Dholakia K. 2012. Wavefront corrected light sheet microscopy in turbid media. Appl Phys Lett 100:191108. Denk W, Strickler JH, Webb WW. 1990. Two-photon laser scanning fluorescence microscopy. Science 248:73. Greger K, Neetz MJ, Reynaud EG, Stelzer EH. 2011. Three dimensional fluorescence lifetime imaging with a single plane illumination microscope provides and improved signal to noise ratio. Opt Express 19:20743–20750. Hell SW, Wichmann J. 1994. Breaking the diffraction resolution limit by stimulated emission: Stimulated-emission-depletion fluorescence microscopy. Opt Lett 19:780–782.
Microscopy Research and Technique
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Hell SW. 2007. Far field nanoscopy. Science 316:1153–1158. Holekamp TF, Turaga D, Holy TE. 2008. Fast three-dimensional fluorescence imaging of activity in neural populations by objective-coupled planar illumination microscopy. Neuron 57: 661–672. Huisken J, Swoger J, Del Bene F, Wittbrodt J, Stelzer EHK. 2004. Optical sectioning deep inside live embryos by selective plane illumination microscopy. Science 305:1007–1009. Keller PJ, Schmidt AD, Santella A, Khairy K, Bao Z, Wittbrodt J, Stelzer EH. 2010. Fast, high-contrast imaging of animal development with scanned light sheet-based structured-illumination microscopy. Nat Methods 7:637. Keller PJ, Schmidt AD, Wittbrodt J, Stelzer EHK. 2008. Reconstruction of zebrafish early embryonic development by scanned light sheet microscopy. Science 322:1065–1069. Pampaloni F, Ansari N, Stelzer EH. 2013. High resolution deep imaging of cellular spheroids with light-sheet based fluorescence microscopy. Cell Tissue Res 352:161–177. Purnapatra SB, Mondal PP. 2013a. Generation of extended light sheet for single and multi-photon fluorescence microscopy. Appl Phys Lett 103:043701. Purnapatra SB, Mondal PP. 2013b. Determination of electric field at and near the focus of a cylindrical lens for applications in fluorescence microscopy, AIP Adv 3:052124. Raju R, Kavya M, Mondal PP. 2013. Light sheet based imaging flow cytometry on a microfluidic platform. Micros Res Tech 76:1101– 1107. Sheppard CJR. 1986. Aberrations in high aperture conventional and confocal imaging systems. Appl Opt 27:4782–4786. Voie AH, Burns DH, Spelman FA. 1993. Orthogonal-plane fluorescence optical sectioning: Three-dimensional imaging of macroscopic biological specimens. J Microsc 170:229. Zanacchi FC, Lavagnino Z, Donnorso MP, Bue AD, Furia L, Faretta M, Diaspro A. 2011. Live-cell 3D super-resolution imaging in thick biological samples. Nat Methods 8:1047–1049. Zanacchi FC, Lavagnino Z, Faretta M, Furia L, Diaspro A. 2013. Light-sheet confined super-resolution using two-photon photoactivation. PLoS One 7:e67667.
