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Abstract
We introduce one-of-a-kind optical microscope that we have developed through optimized integration of wide-field and focused-light microscopies. This new instrument has accomplished operation of the same laser for both wide field illumination and holographic focused beam illumination interchangeably or simultaneously in a way scalable to multiple lasers. We have demonstrated its powerful capability by simultaneously carrying out Epi-fluorescence, total internal reflection fluorescence microscopy, selective plane illumination microscopy, and holographic optical tweezers with five lasers. Our instrument and the optical design will provide researchers across diverse fields, cell-biology and biophysics in particular, with a practical guidance to build an all-around multimodal microscope that will further inspire the development of novel hybrid microscopy experiments.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
While numerous optical microscopy methods currently exist, microscopy can be largely classified into two groups according to how light illuminates specimen. In one scheme, a wide area of sample is simultaneously illuminated to obtain a snapshot of image at once (henceforth defined as ‘wide-field microscopy’). Many common imaging methods, such as brightfield, phase contrast, DIC, Epi-fluorescence, and total internal reflection fluorescence microscopy (TIRFM), are all based on wide-field illumination of light. On the other hand, samples could be locally illuminated by focused light spots (henceforth defined as ‘local-field microscopy’); confocal scanning microscopy and optical tweezers (OT) are some of typical examples. These two microscopy modalities are often complementarily used according to the characteristics of specimen and the type of research.
Wide-field illumination, especially for fluorescence microscopy, is realized by focusing a laser beam on the back focal plane of objective which collimates light on sample plane [Fig. 1(a)]. Local-field illumination scheme, on the contrary, requires a collimated beam upon an objective to create a focused spot on sample plane [Fig. 1(b)]. Because of this disparate optical configuration, the two microscopy methods are typically considered incompatible, and thus they are implemented in different instruments. Integrating them into a single instrument not only would provide a more economical instrumentation but also would offer unusual opportunity for novel hybrid experiments. In fact, there have been tremendous efforts to integrate the two microscopy modalities, especially in biophysics community, for the purpose of combining optical tweezers and fluorescence detection for single-molecule study in various ways: simultaneous single OT and TIRFM [1–4]; simultaneous single OT, TIRFM and confocal [5]; interlaced single OT and TIRFM [6,7]; simultaneous single OT and confocal [8,9]; simultaneous dual OT and TIRFM [10]; interlaced dual OT and confocal [11, 12]; holographic optical tweezers (HOT) and TIRFM [13]; HOT and multiphoton confocal [14]; and dual OT and stimulated emission depletion (STED) microscopy [15]. In all the cases, however, each light source (i.e., laser) had to be exclusively dedicated to either fluorescence excitation or optical trapping, i.e., either wide-or local-field illumination scheme. It would be the most ideal if same laser could be used for both the two microscopy modes interchangeably or simultaneously. Such flexible microscope platforms, however, have not been reported yet.
Fig. 1 Two illumination schemes in microscopy. (a) In ‘wide-field’ scheme, light focused on the back focal plane of objective shines on specimen (e.g., to excite fluorescent molecules) in wide area. Fluorescence emission is shown for only one fluorescent molecule for simplicity. (b) In ’local-field’ scheme, collimated beams enter into objective and get focused on sample plane, which then can be used for trapping microspheres (optical tweezers) or locally exciting fluorescent molecules (confocal microscopy).
Here, we introduce a highly versatile microscope that optimally integrates wide- and local-field illumination for multiple lasers. In this new instrument, the usage of each laser is maximized by flexible choice between the two illumination modes. In addition, a new optical design of wide-field TIRFM illuminator makes it possible to control the laser angle remotely and independently for multiple lasers and thus to easily achieve optimal TIRFM condition in multiple colors. Moreover, holographic optical tweezers technique has been implemented in the local-field illumination mode to generate multiple laser spots in arbitrary patterns for the applications of multiplexed optical trapping [17,18], scanless confocal imaging [19], localized stimulation of cells [20], and localized photobleaching or photoactivation of fluorophores with any choice of lasers. This article describes in details the novel instrument and demonstrates its unique and versatile capability.
2. Optimal integration of wide- and local-field illumination modalities
Our multimodal optical instrument is based on a standard inverted microscope (Nikon Ti-E) with five CW lasers (405nm, 488nm, 532nm, 561nm, and 637nm) as shown schematically in Fig. 2. All the lasers are first combined, using dichroic mirrors, into a single beam, and then the beam enters an acousto-optic tunable filter (AOTF) that functions as fast and independent electronic shutters for multiple lasers. Later, the combined beam is split into individual lasers, with each laser traversing its own optimized optical path for integrated wide- and local-field illuminations. More specifically, each laser is split into two beams through a combination of half-wave plate and polarizing beamsplitter, with each beam being under control of a mechanical shutter. One beam is expanded and focused on the back focal plane of a microscope objective through a series of relay optics for wide-field mode, whereas the other beam gets expanded to illuminate on a spatial light modulator (SLM) whose image is relayed to the back aperture of objective for local-field mode. These two beams, which are perpendicularly polarized, eventually get recombined by a polarizing beamsplitter and delivered to the objective through microscope back port. This optical design makes it possible to distribute laser power between two illumination modes in arbitrary ratio, and also either to choose one mode exclusively or employ both modes simultaneously. The crucial parts of the instrument are listed in Table. 1.
Table 1. Parts list of critical components in Fig. 2.
Fig. 2 Schematics of the multimodal microscope. (M) mirror, (GM) galvo mirror, (SH) shutter, (D1-D4) long-pass dichroic mirrors for 405nm, 488nm, 532nm, and 561nm, (L1-L7) lens, (PBS) polarizing beam splitter, (HWP) half-wave plate, (AOTF) acousto-optic tunable filter, (OBJ) objective, (SLM) spatial light modulator, (TE) lens pair forming a telescope, (FW) filter wheel, (*0) specimen plane and its conjugate images, (*1) objective back aperture plane and its conjugate images, (*2) objective back focal plane and its conjugate images.
3. Optimized multicolor TIRFM
TIRFM is a powerful wide-field fluorescence microscopy technique, due to the substantial enhancement of signal-to-noise ratio that even allows for detection of a single fluorescent molecule on the coverslip surface [21]. It is an essential tool for single-molecule study [22] and various super-resolution fluorescence microscopy [23,24].
In principle, TIRFM is thought to be easily built by focusing a laser beam on the back focal plane of high numerical aperture (NA) objective and then displacing the focused spot off the optical axis to deflect the collimated output beam until it is total internally reflected at glass-water interface. However, the commonly used TIRFM implementations are not optimal in that illumination area and location change according to the beam angle. Furthermore, achieving optimal TIRFM with multiple lasers has been considered nontrivial. Almost all simple home-built multicolor TIRFM microscopes use a single translation mirror or focusing lens by which multiple laser beams are controlled all together. However, optical dispersion and chromatic aberration in the optical system make it almost infeasible to attain the best TIRFM condition for all the lasers in this way [25,26]. Therefore, independent control of multiple lasers would be the best solution for multicolor TIRFM. Such a solution is commercially available indeed (Olympus cellTIRF), but it is a very costly closed-frame system that is not easily compatible with nonproprietary lasers.
We have developed a novel multicolor TIRFM illuminator design that accomplishes optimal TIRFM condition for virtually any number of lasers through independent laser control [Fig. 2]. Briefly, each laser beam is expanded by a telescope made of a pair of two lenses (e.g., L1 and L2 for 405nm in Fig. 2). The front aperture, i.e., front surface of the second lens (L2), is aligned to be a conjugate image plane of the microscope specimen plane through relaying lenses L3, and L4 - L7. In this optical configuration, the sample illumination area is determined by the beam size on the front aperture of L2, which can be easily controlled by the focal length ratio between L1 and L2. Furthermore, the position and angle of laser beam on coverslip surface can be precisely adjusted by xy-position of the 1st (L2) and 2nd lens (L2) of beam expander, respectively. By attaching a single-axis motorized actuator to the 2nd lens, the beam angle adjustment and thus the switching between Epi-illumination and TIRFM can be fully motorized for fast, accurate, and reproducible remote control. Similar illuminators for other lasers can be constructed by appropriately moving the illuminators closer to microscope according to the location of each conjugate plane (*0 in Fig. 2).
To demonstrate the performance of our multicolor TIRFM, we acquired four color luminescence images of 80 nm gold nanospheres (PELCO NanoXact) that are attached to coverslip in water. Epi-fluorescence images show uniform illumination in every colors, but low contrast makes it hard to identify gold nanospheres [Fig. 3(b)]. We then switched to TIRFM mode by tilting all the beam angles by 90 degrees [Fig. 3(c)], which produced high quality images of gold particles in all colors without any compromise in illumination area and uniformity.
Fig. 3 Multi-color luminescence images of 80nm gold nanospheres attached on coverslip. (a) Bright field image. (b) Epi-fluorescence illumination scheme. (c) TIRF illumination scheme. Gold particles were adsorbed to a coverslip by drying gold suspension in air and the coverslip was replenished with water for imaging. Laser beam size was adjusted to fill the whole camera field of view (133µm × 133µm) and the power was adjusted to 2.5mW for 405nm laser and 5mW for others when measured in front of objective. Scale bar: 10µm.
Despite its suboptimal performance, Epi-fluorescence microscopy is still the most commonly used for imaging thick samples (e.g., eukaryotic cells) whose imaging plane cannot be reached by evanescent electric field (< 100 nm). To combine TIRFM and Epi-fluorescence microscopy, separate incoherent light sources (e.g., mercury arc lamp or LEDs) are typically used for Epi-fluorescence detection in addition to lasers for TIRFM. In contrast, our new instrument not only makes such separate light sources unnecessary, but it also allows fast multicolor imaging in flexible combinations of TIRFM and Epi-fluorescence microscopies, e.g., imaging mammalian cell membrane proteins in TIRFM and nucleus in Epi mode, respectively. Furthermore, the instrument’s unique employment of holographic light manipulation, as described in the following sections, facilitates advanced 3-D fluorescence imaging methods, such as selective plane illumination microscopy, for thick specimen.
4. Optimal time-resolved multicolor holographic optical tweezers
Beams of lasers routed for local-field illumination are all combined to be projected on a SLM for wavefront phase modulation [Fig. 2]. Computer-generated holograms projected on the SLM can diffract a single incident beam into multiple focused laser spots on sample plane [17, 18]. Holographic optical tweezers (HOT) use these multiple focused laser spots to trap dielectric microspheres. HOT is a very powerful tool to manipulate microscopic objects by using optical force. With the help of the optimized integration of the two imaging modalities, our microscope is capable of simultaneous wide-field fluorescence imaging and HOT for arbitrary combination of lasers. For example, we could easily trap 0.8µm diameter fluorescent beads (Spherotech, FP-0842-2) with 561nm laser to form a pattern, and simultaneously obtain its Epi-fluorescence image with 405nm excitation or TIRF image of gold nanoparticles on the coverslip surface with 488nm illumination, as demonstrated in Fig. 4 and a supplementary video (see Visualization 1). Such simultaneous optical trapping and fluorescence detection can be applied to the study of single-molecule conformation and mechanics [4].
Fig. 4 Simultaneous holographic optical tweezers and fluorescence imaging. Water-suspended 0.8µm fluorescent beads are trapped by 561nm laser. (a) Simultaneous Epi-fluorescence image of the trapped beads with 405nm laser excitation (see Visualization 1). (b) Simultaneous TIRF image of 100nm gold nanoparticles adsorbed on the coverslip surface using 488nm laser illumination. The signal at the trapped bead position is due to fluorescence bleed-through of the bead by strong 561nm trapping laser.
One issue still remains to be resolved regarding how to holographically control multiple lasers with a single SLM device. Because of the dispersive nature of diffraction, even an identical phase hologram on SLM will project slightly different patterns of light for different laser colors. It was previously proposed to design a single hologram that simultaneously encodes different patterns in multiple colors by separating the axial location of the 1st diffraction order of different lasers [27]. This method, however, introduces undesirable dual patterns either above or below the specimen plane, adversely allowing colors to bleed into one another.
We instead employed a time-resolved multicolor holographic control. In this scheme, on/off of each laser is made to be actively triggered by camera acquisition using camera’s fire-out signal, AOTF, NI-DAQ (NI, PCIe-7852R), and the triggered-acquisition functionality of Nikon NIS Elements software. We also developed a custom LabVIEW virtual instrument (VI) that projects holograms of multiple lasers on SLM in synchrony with sequentially triggered laser colors. As demonstrated in Fig. 5 and a supplementary video (see Visualization 2), multiple lasers can be controlled in a completely independent fashion even with only a single SLM. The major drawback of this scheme is the triggering speed that is limited by the response time of liquid crystal molecules in SLM device chip. In our current setup, subsequent holograms were partially overlapped by afterimages when frame rate exceeded about 20Hz. This issue could be resolved by high speed SLMs that are currently available up to 700Hz [28,29]. For applications requiring higher speed, digital micro-mirror device (DMD) can be alternatively used although the diffraction efficiency of DMD is compromised by its binary phase modulation [30].
Fig. 5 Overlaid image of time-resolved multicolor holographic illumination with 405nm, 488nm, 561nm, and 637nm lasers. Channel-to-channel frame rate: 10Hz, Scale bar: 10µm.
5. Selective plane illumination fluorescence microscopy
The multicolor wavefront phase modulation capability of our instrument allows easy implementation of various advanced imaging modalities other than holographic optical tweezers as well. As an example, we have demonstrated selective plane illumination fluorescence microscopy (SPIM) using 1-D line scan. SPIM is a powerful 3-D fluorescence microscopy for thick specimen through optical sectioning. In contrast to confocal microscopy that uses focused laser spots, SPIM uses a thin light sheet to selectively excite only the fluorophores within the excitation plane, and thus the image acquisition speed is superior to conventional confocal laser scan. Light sheet can be created by either cylindrical optics or 1-D scan of beam in perpendicular to its propagation direction [31,32]. Furthermore, either the detection objective lens itself or a separate objective lens arranged orthogonally to the detection pathway, can be used to illuminate a light sheet. Although the latter case has the advantage of minimal photo-bleaching, its instrumentation is complex and not compatible with high NA objective nor conventional inverted microscope systems.
Without any additional modification to our instrument, we could easily generate a light sheet by holographically creating an optical line tweezers [33, 34] with SLM and scanning it in perpendicular to the line with a galvo mirror [Fig. 6(a)]. The diffraction-limited axial thickness (~500nm for 561nm laser and NA 1.4 objective) of line tweezers renders optical sectioning with the axial resolution on a par with confocal microscopy. By scanning the line (300Hz scan rate) with a galvo mirror asynchronously with image acquisition (20Hz frame rate), we could obtain improved optical sections of thick specimen, such as Arabidopsis stem sections, as compared with Epi-fluorescence images [Fig. 6(b)]. The optical sectioning performance of SPIM can be further improved by rejecting out-of-focus light with confocal slit detection [35,36].
Fig. 6 Selective plane illumination fluorescence microscopy with 1-D scanning of optical line tweezers. (a) Optical line tweezers are created using 561nm and shape phase holography [33,34]. 1-D scanning in perpendicular to the line generates a diffraction-limited thin light sheet for fast optical sectioning fluorescence microscopy. The light image was obtained by placing a mirror in front of microscope objective (Nikon PlanApo VC60X Oil NA 1.4 WD 0.13mm). Scale bar: 10µm. (b) Comparison of line-scan and Epi-fluorescence imaging of Arabidopsis stem section autofluorescence with 561nm excitation. Line-scan imaging shows superior optical sectioning capability when the thick specimen is imaged at 12µm deep inside the surface (red arrow heads). In contrast, Epi-fluorescence image is significantly affected by out-of-focus signal (white arrows), misrepresenting the structures. Scale bar: 10µm.
6. Conclusion
In summary, we have successfully integrated wide-field and local-field illumination schemes into a single microscope platform in the most optimized fashion. Unlike the previously reported multimodal microscopes [1–16], our instrument maximally accomplishes flexible usage of each laser between the two illumination schemes. By building a 5-color laser system, we have demonstrated the scalable design of the instrument that can be easily expanded to any number of lasers in principle. Our instrument is very unique because it features motorized and independent laser angle control in the wide-field mode, which easily realizes optimized multicolor TIRFM imaging in every channel, while it implements time-resolved multicolor HOT into the local-field mode for independent holographic manipulation of multiple lasers with a single SLM.
Our multimodal microscope provides a total-solution for optical microscopy need across many research areas. It allows for economically implementing various microscopy methods, such as Epi-fluorescence, TIRFM, line-scan confocal and HOT, through optimal usage of lasers. Furthermore, as we have demonstrated with simultaneous HOT and fluorescence imaging of microspheres/nanoparticles, combinatorial usages of different microscopy modalities will enable novel hybrid experiments. For instance, cellular mechanics can be studied in a controlled manner by applying force on cell membrane through optically trapped microspheres while imaging cellular response through fluorescently labeled force-transducing proteins [20].
The modular and open-frame design of the instrument provides a sound framework for extending its capability or implementing other advanced imaging techniques, as we have demonstrated with selective plane illumination microscopy using optical line tweezers. It is also possible to add a near-infrared laser such as 1064nm to the instrument for trapping biomolecules; and resonant scanning confocal microscopy can be easily implemented by adding a pair of resonant scanner and galvo scanner into the local-field illumination path of our instrument. It would be also possible to incorporate super-resolution 3-D structured illumination microscopy (SIM) by projecting various grid patterns onto the specimen with the already built-in SLM [37,38]. We expect that our multimodal microscope will inspire the development of novel microscopy methods while providing researchers with practical guidance for building an all-around microscope by themselves.
Funding
Rutgers New Faculty Startup Fund.
Acknowledgments
SHL is grateful to Eric Lam (Rutgers University) for Arabidopsis samples, and Phillip Rechani (Rutgers University) for assistance with holographic optical tweezers experiments and Arabidopsis imaging.
References and links
1. T. Funatsu, Y. Harada, H. Higuchi, M. Tokunaga, K. Saito, Y. Ishii, R. D. Vale, and T. Yanagida, “Imaging and nano-manipulation of single biomolecules,” Biophys. Chem. 68(1–3), 63–72 (1997). [CrossRef]
2. M. J. Lang, P. M. Fordyce, A. M. Engh, K. C. Neuman, and S. M. Block, “Simultaneous, coincident optical trapping and single-molecule fluorescence,” Nat. Methods 1(2), 133–139 (2004). [CrossRef]
3. M. I. Snijder-Van As, B. Rieger, B. Joosten, V. Subramaniam, C. G. Figdor, and J. S. Kanger, “A hybrid total internal reflection fluorescence and optical tweezers microscope to study cell adhesion and membrane protein dynamics of single living cells,” J. Microsc. 233(1), 84–92 (2009). [CrossRef] [PubMed]
4. S. Lee and S. Hohng, “An optical trap combined with three-color FRET,” J. Am. Chem. Soc. 135(49), 18260–18263 (2013). [CrossRef] [PubMed]
5. R. R. Gullapalli, T. Tabouillot, R. Mathura, J. H. Dangaria, and P. J. Butler, “Integrated multimodal microscopy, time-resolved fluorescence, and optical-trap rheometry: toward single molecule mechanobiology,” J. Biomed. Opt. 12(1), 014012 (2007). [CrossRef] [PubMed]
6. R. R. Brau, P. B. Tarsa, J. M. Ferrer, P. Lee, and M. J. Lang, “Interlaced optical force-fluorescence measurements for single molecule biophysics,” Biophys. J. 91(3), 1069–1077 (2006). [CrossRef] [PubMed]
7. P. B. Tarsa, R. R. Brau, M. Barch, J. M. Ferrer, Y. Freyzon, P. Matsudaira, and M. J. Lang, “Detecting force-induced molecular transitions with fluorescence resonant energy transfer,” Angew. Chem. (Int. Ed. Engl.) 46(12), 1999–2001 (2007). [CrossRef]
8. S. Hohng, R. Zhou, M. K. Nahas, J. Yu, K. Schulten, D. M. J. Lilley, and T. Ha, “Fluorescence-force spectroscopy maps two-dimensional reaction landscape of the holliday junction,” Science 318(5848), 279–283 (2007). [CrossRef] [PubMed]
9. R. Zhou, A. G. Kozlov, R. Roy, J. Zhang, S. Korolev, T. M. Lohman, and T. Ha, “SSB functions as a sliding platform that migrates on DNA via reptation,” Cell 146(2), 222–232 (2011). [CrossRef] [PubMed]
10. A. Candelli, G. J. L. Wuite, and E. J. G. Peterman, “Combining optical trapping, fluorescence microscopy and micro-fluidics for single molecule studies of DNA-protein interactions,” Phys. Chem. Chem. Phys. 13(16), 7263–7272 (2011). [CrossRef] [PubMed]
11. M. J. Comstock, T. Ha, and Y. R. Chemla, “Ultrahigh-resolution optical trap with single-fluorophore sensitivity,” Nat. Methods 8(4), 335–340 (2011). [CrossRef] [PubMed]
12. G. Sirinakis, Y. Ren, Y. Gao, Z. Xi, and Y. Zhang, “Combined versatile high-resolution optical tweezers and single-molecule fluorescence microscopy,” Rev. Sci. Instrum. 83(9), 093708 (2012). [CrossRef] [PubMed]
13. M. Kyoung, K. Karunwi, and E. D. Sheets, “A versatile multimode microscope to probe and manipulate nanoparticles and biomolecules,” J. Microsc. 225(2), 137–146 (2007). [CrossRef] [PubMed]
14. R. P. Trivedi, T. Lee, K. A. Bertness, and I. I. Smalyukh, “Three dimensional optical manipulation and structural imaging of soft materials by use of laser tweezers and multimodal nonlinear microscopy,” Opt. Express 18(26), 27658–27669 (2010). [CrossRef]
15. I. Heller, G. Sitters, O. D. Broekmans, G. Farge, C. Menges, W. Wende, S. W. Hell, E. J. G. Peterman, and G. J. L. Wuite, “STED nanoscopy combined with optical tweezers reveals protein dynamics on densely covered DNA,” Nat. Methods 10(9), 910–916 (2013). [CrossRef] [PubMed]
16. H. Li and H. Yang, “A versatile optical microscope for time-dependent single-molecule and single-particle spectroscopy DNA,” J. Chem. Phys. 148(12), 123316 (2018). [CrossRef]
17. J. E. Curtis, B. A. Koss, and D. G. Grier, “Dynamic holographic optical tweezers,” Opt. Commun. 207(1–6), 169–175 (2002). [CrossRef]
18. M. Polin, K. Ladavac, S. H. Lee, Y. Roichman, and D. G. Grier, “Optimized holographic optical traps,” Opt. Express 13(15), 5831–5845 (2005). [CrossRef] [PubMed]
19. V. Nikolenko, B. O. Watson, R. Araya, A. Woodruff, D. S. Peterka, and R. Yuste, “SLM Microscopy: Scanless Two-Photon Imaging and Photostimulation with Spatial Light Modulators,” Front. Neural Circuits 2, 5 (2008). [CrossRef]
20. H. Zhang and K.-K. Liu, “Optical tweezers for single cells,” J. R. Soc., Interface 5(24), 671–690 (2008). [CrossRef]
21. D. Axelrod, “Selective imaging of surface fluorescence with very high aperture microscope objectives,” J. Biomed. Opt. 6(1), 6–13 (2001). [CrossRef] [PubMed]
22. R. Roy, S. Hohng, and T. Ha, “A practical guide to single-molecule FRET,” Nat. Methods 5(6), 507–516 (2008). [CrossRef] [PubMed]
23. E. Betzig, G. H. Patterson, R. Sougrat, O. W. Lindwasser, S. Olenych, J. S. Bonifacino, M. W. Davidson, J. Lippincott-Schwartz, and H. F. Hess, “Imaging intracellular fluorescent proteins at nanometer resolution,” Science 313(5793), 1642–1645 (2006). [CrossRef] [PubMed]
24. M. J. Rust, M. Bates, and X. Zhuang, “Sub-diffraction-limit imaging by stochastic optical reconstruction microscopy (STORM),” Nat. Methods 3(10), 793–795 (2006). [CrossRef] [PubMed]
25. D. S. Johnson, J. K. Jaiswal, and S. Simon, “Total internal reflection fluorescence (TIRF) microscopy illuminator for improved imaging of cell surface events,” Current protocols in cytometry, (Wiley, 2012), Chapter 12, Unit 12.29–12.29.19. [PubMed]
26. A. Yildiz and R. D. Vale, “Total Internal Reflection Fluorescence Microscopy,” Cold Spring Harbor protocols 2015(9), 086348 (2015). [CrossRef] [PubMed]
27. S.-H. Lee and D. Grier, “Robustness of holographic optical traps against phase scaling errors,” Opt. Express 13(19), 7458–7465 (2005). [CrossRef] [PubMed]
28. G. Thalhammer, R. W. Bowman, G. D. Love, M. J. Padgett, and M. Ritsch-Marte, “Speeding up liquid crystal SLMs using overdrive with phase change reduction,” Opt. Express 21(2), 1779–1797 (2013). [CrossRef] [PubMed]
29. S. J. Yang, W. E. Allen, I. Kauvar, A. S. Andalman, N. P. Young, C. K. Kim, J. H. Marshel, G. Wetzstein, and K. Deisseroth, “Extended field-of-view and increased-signal 3D holographic illumination with time-division multiplexing,” Opt. Express 23(25), 32573–32581 (2015). [CrossRef] [PubMed]
30. J. Cheng, C. Gu, D. Zhang, and S.-C. Chen, “High-speed femtosecond laser beam shaping based on binary holography using a digital micromirror device,” Opt. Lett. 40(21), 4875–4878 (2015). [CrossRef] [PubMed]
31. J. Huisken and D. Y. R. Stainier, “Selective plane illumination microscopy techniques in developmental biology,” Development 136(12), 1963–1975 (2009). [CrossRef] [PubMed]
32. T. A. Planchon, L. Gao, D. E. Milkie, M. W. Davidson, J. A. Galbraith, C. G. Galbraith, and E. Betzig, “Rapid three-dimensional isotropic imaging of living cells using Bessel beam plane illumination,” Nat. Methods 8(5), 417–423 (2011). [CrossRef] [PubMed]
33. Y. Roichman, B. Sun, Y. Roichman, J. Amato-Grill, and D. G. Grier, “Optical forces arising from phase gradients,” Phys. Rev. Lett. 100(1), 013602 (2008). [CrossRef] [PubMed]
34. S.-H. Lee, Y. Roichman, and D. G. Grier, “Optical solenoid beams,” Opt. Express 18(7), 6988–6993 (2010). [CrossRef] [PubMed]
35. E. Baumgart and U. Kubitscheck, “Scanned light sheet microscopy with confocal slit detection,” Opt. Express 20(19), 21805–21814 (2012). [CrossRef] [PubMed]
36. L. Silvestri, A. Bria, L. Sacconi, G. Iannello, and F. S. Pavone, “Confocal light sheet microscopy: micron-scale neuroanatomy of the entire mouse brain,” Opt. Express 20(18), 20582–20598 (2012). [CrossRef] [PubMed]
37. M. G. Gustafsson, “Surpassing the lateral resolution limit by a factor of two using structured illumination microscopy,” J. Microsc. 198(Pt 2), 82–87 (2000). [CrossRef] [PubMed]
38. M. G. L. Gustafsson, L. Shao, P. M. Carlton, C. J. R. Wang, I. N. Golubovskaya, W. Z. Cande, D. A. Agard, and J. W. Sedat, “Three-dimensional resolution doubling in wide-field fluorescence microscopy by structured illumination,” Biophys. J. 94(12), 4957–4970 (2008). [CrossRef] [PubMed]
