Commercial Objective Lens Research Articles

A Practical Apertometer for Solid Immersion Objective

A solid immersion objective is generally composed of a truncated solid ball and a commercial objective lens. It features higher numerical aperture (NA) than oil-immersion objectives and thus shows capabilities in some applications requiring higher NA or spatial resolutions. Different from commercial products of oil-immersion objectives and their pre labeled NA values, solid immersion objective is generally home-designed/developed, and the theoretical NA is taken as its practical value, which is not suggested. So far, there has been no proper and commercial apparatus to measure this NA value especially for bare solid immersion objectives. In this work, we propose an extremely simple but very practical approach for the measurement, which inherits the concept of Fourier optics but offers some specific features. Furthermore, we specifically propose an algorithm of multipoint reference to achieve high accuracy of NA value. Detailed comparisons between the proposed algorithm and the previous algorithm of single-point reference are elaborated. An experimental prototype of apertometer for solid immersion objective is built up to verify the proposed approach and algorithm. To the best of the authors’ knowledge, this is the simplest, cheapest, and most practical approach and apparatus for the NA measurement of bare solid immersion objective.

Compact conical beam shaper and freeform segmented reflector for SERS analysis.

We present a Raman spectroscopy setup containing a conical beam shaper in combination with a freeform segmented reflector for surface enhanced Raman scattering (SERS) analysis. The freeform segmented reflector and the conical beam shaper are designed by numerical approaches and fabricated by means of ultra-precision diamond tooling. The segmented reflector has a numerical aperture of 0.984 and a working distance of 1mm for SERS measurements. We perform systematic simulations using non-sequential ray tracing to assess the detecting abilities of the designed SERS-based system. We implement a proof-of-concept setup and demonstrate the confocal behavior by measuring the SERS signal of 10µM rhodamine B solution. The experimental results agree well with the simulations concerning the misalignment tolerances of the beam shaper with respect to the segmented reflector and the misalignment tolerances of the collecting fiber. In addition, we conduct benchmark SERS measurements by using a 60× objective lens with a numerical aperture of 0.85. We find that the main Raman intensity of rhodamine B at 1502 cm-1 obtained by our segmented reflector working together with the conical beam shaper is approximately 30% higher compared to the commercial objective lens.

Metalens With Artificial Focus Pattern

Metalens as one of the most popular applications of emmerging optical metasurfaces has raised widspread interest recently. With nano structures fully controlling phase, polarization and transmission, metalens has achieved comparable performance of commercial objective lenses. While recent studies seeking for the accomplishment of traditional focusing behaviors through metalens are successful, inthis work, we have discovered that instead of focusing light to a point, metasurface further enables shaping the focus into a flexibly designed pattern, with more promises and potentials. New mechanism and generalizations of conventional point-focused metalens guiding principles have been proposed with metalens concentrating light to artificial focus pattern. As proving examples, we have demonstrated the engineering of metalens with artificial focus pattern by creating line and ring-shaped focus as 'drawing tools'. The metalens with 'U' and 'M' shaped focus are characterized for the proof of concepts. These metalens are fabricated through a single layer of silicon-based material through CMOS compatible nano fabrication process. The mechanism to generate artificial focus pattern can be applied to a plethora of future on-chip optical devices with applications ranging from beam engineering to next generation nano lithography.

Quantifying distortions in two-photon remote focussing microscope images using a volumetric calibration specimen

Remote focussing microscopy allows sharp, in-focus images to be acquired at high speed from outside of the focal plane of an objective lens without any agitation of the specimen. However, without careful optical alignment, the advantages of remote focussing microscopy could be compromised by the introduction of depth-dependent scaling artifacts. To achieve an ideal alignment in a point-scanning remote focussing microscope, the lateral (XY) scan mirror pair must be imaged onto the back focal plane of both the reference and imaging objectives, in a telecentric arrangement. However, for many commercial objective lenses, it can be difficult to accurately locate the position of the back focal plane. This paper investigates the impact of this limitation on the fidelity of three-dimensional data sets of living cardiac tissue, specifically the introduction of distortions. These distortions limit the accuracy of sarcomere measurements taken directly from raw volumetric data. The origin of the distortion is first identified through simulation of a remote focussing microscope. Using a novel three-dimensional calibration specimen it was then possible to quantify experimentally the size of the distortion as a function of objective misalignment. Finally, by first approximating and then compensating the distortion in imaging data from whole heart rodent studies, the variance of sarcomere length (SL) measurements was reduced by almost 50%.

Optimal Integral Force Feedback and Structured PI Tracking Control: Application for High Speed Confocal Microscopy.

In this paper, an improvement to Integral Force Feedback (IFF) damping control is proposed. The main limitation of Integral Force Feedback is that the maximum modal damping depends on the system's parameters. Hence, for some system achievable damping is insignificant. The proposed improvement allows any arbitrary damping ratio to be achieved for a system by introducing a new feed-through term in the system. To achieve displacement tracking, one technique is to enclose the system in an integral feedback loop. However, the bandwidth is limited due to the effects of an additional pole in the damping loop. The proposed Structured PI controller is parameterised so that it contains a zero that cancel the additional pole. Experiment was conducted on a commercial objective lens positioner. The results show an exceptional tracking and damping performance and the system's insensitivity to changes in resonance frequency. The maximum bandwidth achievable with a commercial PID controller is 26.1 Hz. In contrast, with the proposed method, the bandwidth is increased to 255 Hz.

MEMS-based handheld confocal microscope for in-vivo skin imaging

This paper describes a handheld laser scanning confocal microscope for skin microscopy. Beam scanning is accomplished with an electromagnetic MEMS bi-axial micromirror developed for pico projector applications, providing 800x600 (SVGA) resolution at 56 frames per second. The design uses commercial objective lenses with an optional hemisphere front lens, operating with a range of numerical aperture from NA=0.35 to NA=1.1 and corresponding diagonal field of view ranging from 653 μm to 216 μm. Using NA=1.1 and a laser wavelength of 830 nm we measured the axial response to be 1.14 μm full width at half maximum, with a corresponding 10%-90% lateral edge response of 0.39 μm. Image examples showing both epidermal and dermal features including capillary blood flow are provided. These images represent the highest resolution and frame rate yet achieved for tissue imaging with a MEMS bi-axial scan mirror.

Compatibility between Compact Read Only Memory Reader and Recording System

To achieve the practical use of holographic data storage (HDS) as a consumer product, it is necessary to develop devices taking into consideration the compatibility among HDS systems and to reconstruct the margin of these systems. This time, we developed a compact read-only-memory (ROM) reader using a commercial objective lens, and we try to ensure the compatibility between our angle multiplexing recording system and the ROM reader, and the readout tolerance of shifting in the X- and Z-directions and tilting of a medium. The results obtained show the possibility for commercialization of HDS technology.

Three-dimensional confocal fluorescence imaging under ultrashort pulse illumination

Three-dimensional (3-D) image performance of confocal single-photon and two-photon fluorescence microscopy under ultrashort pulse illumination is analysed in terms of the 3-D optical transfer function. It is found that the material dispersion does not affect the imaging performance if a well-corrected commercial objective lens is used. The finite spectral bandwidth of an ultrashort pulse of a temporal duration shorter than 10 fs may result in significant improvement in resolution. The improvement becomes less pronounced in two-photon fluorescence imaging.