Fig. 1. Two single-objective light sheet illumination methods and the conventional light sheet illumination method. (a) Conventional light sheet microscope consisting of two objective lenses placed orthogonally, one for illumination and another for imaging; (b) tilted planar illumination microscope in which illuminating light is introduced directly into the objective lenses to form a tilted sheet of light on the sample surface, adapted to conventional samples loaded on slides; (c) single-objective light sheet applied to a microdevice channel in which 45°-tilt reflective micromirrors are designed to be placed in the micro device, and the formed sheet of light is directly perpendicular to the optical axis

Fig. 2. Optical path diagram of a oblique plane illumination microscope, with an objective lens used to generate the light sheet and imaging, and the introduction of a remote focusing system to correct the aberration^[5]

Fig. 3. Schematic representation of the scanning modes of several light sheet microscopies^[21]. (a) SCAPE 1.0; (b) OS-2P-LSFM; (c) SOPI, eSPIM, DOPM, and SCAPE 2.0

Fig. 4. Numerical aperture reduction and resolution simulation in OPM. (a) Illustration of illumination angle of the primary objective lens versus collection^[5]; (b) schematic representation of the effective optical pupil area at different tilt angles at NA=1.4 and n=1.52; (c) simulation of PSF with NA=1.30, 1.40, 1.49 and tilt angles of 0°, 30°, 60°, and 90°^[28]

Fig. 5. Several ways to improve OPM performance. (a) Commercial tertiary objective with glass tip; (b) increased resolution by using micromirror array^[32]; (c) incorporation of microlens array for direct imaging by computational methods^[39]; (d) schematic of secondary light cone loss. All the light cones of the low numerical aperture objective are lost. Introduction of grating reflection to redirect the beam^[35]; (e) improvement of the field of view by insertion of ellipsoidal mirrors^[40]

Fig. 6. Oblique plane illumination microscope for fast vital activity imaging. (a) OPM enables 3D imaging of calcium sparks in the heart^[14]; (b) OPM enables observation of calcium wave propagation in cardiac contractions^[30]; (c) SCAPE 2.0 enables hemodynamic observation of the heart and atria at a volumetric imaging speed of 321 volume/s^[19]

Fig. 7. Wide applications of OPM in life science and medical examination scenarios. (a) High-resolution imaging with OPM^[29]; (b) OPM for flow cytometry^[41]; (c) DaXi-OPM realizing simultaneous imaging of 9 zebrafish embryos^[20]; (d) Medi-SCAPE for in vivo tumor detection^[43]; (e) imaging of the fundus retinae using the human eye as a natural objective lens^[44]

Fig. 8. Single objective light sheet microscopewith micromirror reflection^[6]. (a) Optical pathway of a single objective light sheet microscope based on 45° micromirrors, top right is scanning electron micrograph; (b) axial displacement using ETL to ensure constant lateral position of the optical center

Fig. 9. Single-objective light sheet microscope with single-molecule localization methods. (a) soSPIM-PLAM imaging, left is widefield and right is super-resolution^[6]; (b) soSPIM-dSTORM super-resolution imaging, left is widefield, right is super-resolution^[6]; (c) representative volume obSTORM image with a tissue depth of 50 μm, ten images stacked, depth colour coded^[64]; (d) obSTORM high tilt angle of light sheet incidence^[64]; (e) comparison of theoretical and experimental PSFs at different light sheet angles^[64]

Fig. 10. Super resolution structure illumination oblique plane miceoscope^[67]. (a) Comparison of wide-field imaging and super-resolution structure illumination imaging under the same microscope; (b) three orientations, each of which captured three pictures with different phase to reconstruct the obtained super-resolution image; (c) sketch of the SIM-OPM super-resolution structure illumination optical path

Table 1. Scanning modes and characteristics of several typical oblique plane microscopes