Contrast transfer function

About: Contrast transfer function is a research topic. Over the lifetime, 934 publications have been published within this topic receiving 26533 citations.

Numerical Spherical Aberration Correction Method using Spatial Light Modulator under Deep-Part Fluorescence Observation

Abstract: We have developed a confocal fluorescence laser scanning microscopy (CFLSM) incorporating a liquid crystal on silicon spatial light modulator (LCOS-SLM). To achieve high-resolution and high-contrast imaging for deeper part of the tissue with CFLSM, high numerical aperture objective lenses are required to tightly focus excitation light to meet Rayleigh limit(criterion) for the specimens. However, mismatch of refractive index at the boundary of interfacing materials, such as atmosphere, glass cover, and biological tissues, causes spherical aberration. Recently, we proposed a numerical method for correcting spherical aberration. In this method a pre-distorted wavefront pattern for aberration correction is calculated by ray tracing from a hypothetical focal point inside a specimen to the pupil plane. The resulting microscope can correct such spherical aberration. We observed 6.0μm fluorescent micro-beads dispersed three-dimensionally in agarose gel to confirm effectiveness of aberration correction. We reconstructed a three-dimensional image by taking 20 images by changing the depth with 1 μm interval and stacking them. It was apparent that the longitudinal/depth resolution was improved and that the intensity of fluorescence image was increased with aberration correction. While this method is applicable to other laser scanning microscopes, it has potential to enhance the signals for various super-resolution microscopic techniques, such as stimulated- emission-depletion (STED) fluorescence microscopy.

High resolution phase imaging with transport of intensity equation and sinusoidal illumination

Abstract: Transport of Intensity equation(TIE) is a non-interferometric method used for quantitative phase imaging. By reformulating the TIE using Contrast Transfer Function, it can be determined that the spatial resolution of the phase retrieved using TIE is limited by the product of imaging system transfer function and a sinc function. In this work, we apply the principles of structured illumination fluorescent microscopy to develop a TIE based super resolved phase imaging technique. The sinusoidal intensity pattern down modulates high frequency spectrum of the phase into the system pass band thereby providing a convenient approach to synthetically enlarge the numerical aperture of the system. Resolution enhancement by two folds is demonstrated using simulations.

Spherical aberration correction of Gaussian beam

Abstract: The relationship between the Strehl ratio and the standard deviation of the wave front aberration of a Gaussian beam is derived from the diffraction integral in the presence of aberrations. Let it be required to develop the spherical aberration of a Gaussian beam into an aberration polynomial. For the maximum value of the Strehl ratio, a set of linear equations is obtained. The optimum configuration of the balanced spherical aberration is obtained from the solution of this set of linear equations. The coefficients of the spherical aberration of a Gaussian beam for the optimum design are illustrated in terms of tables. A comparison is made between the Strehl ratio of the corrected spherical aberration of the Gaussian beam using the optimum design of the uniform beam for the minimum RMS wave front aberration and those for the minimum P-V wave front aberration. The Strehl ratio of the configuration using the optimum design of the uniform beam changes slightly. It turns out that the spherical aberration of the Gaussian beam can be balanced with the optimum configuration of the uniform beam. Finally, the correction of the spherical aberration of the Gaussian beam is illustrated with an example.

Ray transfer matrix perturbation for an optical component with aberration

Abstract: The perturbation theory of matrices is applied to ray transfer matrices (RTMs) to describe an optical component with aberration. A quantitative description of the perturbation extent corresponding to aberration strength is provided using condition numbers and absolute errors for the perturbed RTM. An application to a single small aberration is presented, and the results are compared with those of the diffraction theory of aberrations.

Effect of Quartic Phase Optical Aberration on Laser Beam Quality

Abstract: Laser beam quality is related to the aberration effect. Quartic phase aberration, more commonly known as spherical aberration, can result from aberrated optical components such as beam expanding telescopes, focusing or collimating lenses, or other conventional optical elements; from thermal focusing or thermal blooming in high power laser windows, lenses, amplifier rods, optical isolators, and other absorbing media. In general any kind of quartic aberration will lead to increased far field beam spread, degraded laser beam focusability and increased values of the beam quality. Currently, a well established quality parameter for laser beams is the M2 factor. This paper presents a new mathematical set for the spherical aberration coefficient C4 of Gaussian beams. The main idea comes from the estimation of the laser beam quality factor M2 given by Siegman. We show that this coefficient concerns only the case of geometrical optics.