Remote focusing in confocal microscopy by means of a modified Alvarez lens

Abstract

Alvarez lenses are actuated lens-pairs which allow one to tune the optical power by mechanical displacement of subelements. Here, we show that a recently realized modified Alvarez lens design which does not require mechanical actuation can be integrated into a confocal microscope. Instead of mechanically moving them, the sublenses are imaged onto each other in a 4f-configuration, where the lateral image shift leading to a change in optical power is created by a galvo-mirror. The avoidance of mechanical lens shifts leads to a large speed gain for axial (and hence also 3D) image scans compared to classical Alvarez lenses. We demonstrate that the suggested operation principle is compatible with confocal microscopy. In order to optimize the system, we have drawn advantage of the flexibility a liquid-crystal spatial light modulator offers for the implementation. For given specifications, dedicated diffractive optical elements or freeform elements can be used in combination with resonant galvo-scanners or acousto-optic beam deflectors, to achieve even faster z-scans than reported here, reaching video rate.

Full-aperture extended-depth oblique plane microscopy through dynamic remote focusing

“…While RF-OPM can in principle be implemented using any form of incoherent remote focusing, including deformable lenses, 16 deformable mirrors, 17 Alvarez lenses, 18 or optical elements mounted on fast accelerating translation stages, 19 this article reports an ETL based design. While the use of a simple quadratic phase device, such as an ETL, is known to be imperfect for remote focusing, especially in high numerical aperture systems, 19 , 20 the use of ETLs is widespread in remote focusing applications in microscopy 21 – 23 due to their cost effectiveness and compact form factor.…”

Multi-plane remote refocusing epifluorescence microscopy to image dynamic Ca<i/>2+events

“…Methods which carry out the refocussing in another area of the optical setup are generally faster and cause less sample disturbance. One such method is via the use of adaptive optical elements, such as deformable mirrors [3], tunable lenses [4] and spatial light modulators [5]; these have been used to correct defocus aberrations at depth in biological specimens and may also be used for active focus locking in confocal microscopy [6]. Adaptive optical elements, however, add another layer of complexity to the optical train and may be accompanied by a loss of light due to the diffraction efficiency of these elements.…”

Five-dimensional two-photon volumetric microscopy of in-vivo dynamic activities using liquid lens remote focusing

“…Remote focusing is one of the simplest methods of rapidly modulating the focal plane using an active element remotely from the sample to adjust the axial focal plane. A number of technologies and active elements to use this process in point-scanning microscopy have been proposed [9], such as a voice coil motor [10], an acousto-optic modulator [11], a TAG lens [12], a deformable mirror [13,14], a thermal lens [15], an Alvarez lens [16], and a liquid lens [17][18][19][20][21][22][23]. Liquid lens technology is an inexpensive and stable remote focusing technology, and uses either hydraulic pressure [20][21][22] or the electrowetting phenomenon [17][18][19] to change the optical power of the lens.…”