Variable optical elements for fast focus control

Abstract

In this article, we survey recent developments in the emerging field of high-speed variable z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. 3D biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modifications methods have made great strides forward in recent years due to precise and fast axial control of light. Three state-of-the-art key optical technologies that enable fast z-focus modulation are reviewed along with a discussion on the implications of what the new variable optical element developments entail and the resulting impact on technologically relevant applications. Box figure. Strategies for axial focus control using a variable optical element. a) Focusing with the varifocal lens as the last focusing element. b) Normal configuration for high-resolution imaging or tight focusing. The varifocal lens is placed at a conjugate plane of the high NA focusing lens.

Fast 3D imaging of giant unilamellar vesicles using reflected light‐sheet microscopy with single molecule sensitivity

“…While the ETL2 was sufficiently fast to shift the detection focal plane and follow the illumination plane, its quadratic defocus is not sufficient for an aberration‐free defocus when using a high‐NA objective 32,50–52 . Also, since we used an oil‐immersion objective and image about 10–20 m away from the surface, we had significant spherical aberrations from the glass–water interface and different sugar solutions inside and outside the GUV.…”

“…Also, since we used an oil‐immersion objective and image about 10–20 m away from the surface, we had significant spherical aberrations from the glass–water interface and different sugar solutions inside and outside the GUV. In principle, all of these aberrations could be corrected for by additional adaptive optics 52 . In general, the defocus and/or change of the tube length can also compensate part of the spherical aberrations 53,54 .…”

Electrically tunable lenses – eliminating mechanical axial movements during high-speed 3D live imaging

“…Other commercially available tunable lenses, in addition to ETLs, are also being used for bioscience microscopy applications (Table 2). For a broader characterisation of tunable optical devices, we direct readers to Kang et al (2020) and Chen et al (2021).…”

In Situ Electrohydrodynamic Jet Printing-Based Fabrication of Tunable Microlens Arrays

“…Some applications, such as cell detection and super-resolution imaging, require arrays with short effective focal lengths and compact sizes. − These impose stringent requirements for added MLA functionalities. Therefore, researchers have been exploring methods to adjust the focal lengths of MLAs to achieve tunable MLAs. − …”