Influence Of Spherical Aberration Research Articles

Influence of spherical aberration on the tightly focusing characteristics of vector vortex beams.

For a tightly focusing imaging system, the aberration of the lens will result in a distorted focusing spot and undermine the system performance. In this paper, the expression of the tightly focused light field of Laguerre-Gaussian vector vortex beam (LGVVB) is deduced. Then the intensity distribution, focal shift and spot size that influenced by spherical aberration are calculated in detail. Since the vector vortex beams have multiple degrees of freedom to control the form of the intensity distribution on the focal plane, the effects of aberration on the focal spot are analyzed when some key parameters are changed. The results show the Pancharatnam topological charge is the most influential parameter to change the light distribution on the focal plane. According to the change rule, a scheme is proposed to minimize the effect of aberration by jointly adjusting the parameters of the LGVVB.

Influence of Spherical Aberration on the SNR in Single-Beam Laser Doppler Velocimeter for Remote Measurement

Influence of Spherical Aberration on the SNR in Single-Beam Laser Doppler Velocimeter for Remote Measurement

Optimization of Multi-Layer Data Recording and Reading in an Optical Disc

Storage capacity of a conventional optical disc can be enhanced significantly by recording data within the three-dimensional volume. However, spherical aberrations and light-scattering limit the number of layers that can be efficiently recorded and retrieved. In this paper, we show that by optimizing the multi-layer data recording and reading parameters, the number of fabricated layers could be tripled to 60 in commercial grade poly-methyl-methacrylate polycarbonate and reduce the read laser power by a factor of 7 by the 20th layer. Influence of spherical aberration on write laser spot size was studied by using vector diffraction theory and compared with experimental values obtained by monitoring the threshold energy of the write laser with depth. Scattering losses of the read laser were studied by simulating the propagation of light through multi-layered micro-structured material. The main advantage of our technique is its practical implementation, as it refrains from the use of index-matching liquids and specialized optics during the read–write process.

Influence of spherical aberration on beam quality of high-power laser beams propagating upwards in the atmosphere

For laser ablation propulsion’s applications in space (e.g., space-debris removal, etc.), the laser power is well above the critical power for self-focusing in the atmosphere. Therefore, the self-focusing effect on the beam quality is very significant. In addition, a high-power laser beam is usually accompanied with spherical aberration due to nonlinear effects in its generation process. In this paper, the influence of spherical aberration on the beam quality of high-power laser beams propagating upwards in the atmosphere is studied by using numerical simulation. It is shown that for the large beam size case, the target intensity may be improved by applying the positive spherical aberration. However, for the small beam size case, the target intensity may be improved by using the negative spherical aberration. Furthermore, a laser beam with a large size is more suitable for laser ablation propulsion’s applications in space than that with a small size. Owing to the linear diffraction effect and the nonlinear self-focusing effect, there exists optimal beam power to maximize the target intensity. The formula of the optimal beam power is fitted for the large beam size case in this paper. On the other hand, the focal shift appears due to diffraction, self-focusing and spherical aberration, which results in a degradation of the beam quality on the target. For the large beam size case, to move the actual focus to the target and improve the beam quality on the target, the formula of the modified focal length is also derived in this paper. The results obtained in this paper are of important theoretical significance and practical value.

Paraxial focal length calculation using Strehl definition measurement.

This work describes a method for determination of a paraxial focal length of optical systems using measurements of the Strehl definition. The influence of spherical aberration on the value of the measured effective focal length of an optical system is analyzed, and a method is proposed for an elimination of this influence and determination of the paraxial focus position and the paraxial focal length of a lens from the measurement of the effective focal length and the Strehl definition.

Beam quality improvement by controlling thermal lens spherical aberration in an end-pumped Nd:YVO4 laser.

We present for the first time, to the best of our knowledge, the influence of spherical aberration on the beam quality of a single-stage laser amplifier. We set up an amplifier with a special structure to measure the spherical aberration distribution in the cavity. The output power of the oscillator was controlled, and the pump power of the amplifier was adjusted to improve the beam quality. The results show that there is an optimal amplifier pump power, which maximizes the output laser beam quality. In the presented experiment, an optimal laser beam was achieved with an output power of 10.54W and beam quality of Mx2=1.54, My2=1.39 for a pump power of 9.33W, oscillator output power of 9.2W, and a beam quality of Mx2=2.10, My2=2.03.

Aberration compensation for optical trapping of cells within living mice.

Optical tweezers have been used to trap and manipulate microparticles within living animals. When the optical trap is constructed with an oil-immersion objective, it suffers from spherical aberration. There have been many investigations on the influence of spherical aberration when the particles are trapped in a water medium. However, the dependence of optical force on trapping depth is still ambiguous when the trapped particles are immersed in a high refractive index medium (such as biological tissue, refractive index solution) in experiments. In this paper, the microparticles are immersed in an aqueous solution of glycerol to mimic the cells within biological tissue. As the trapping laser is focused into the specimen, spherical aberration is introduced, degrading the optical trapping performance. It is similar to trapping in water; altering the effective tube length can also compensate for the spherical aberration of the optical trap in a high refractive index medium. Finally, the cells in living mice are trapped by the optical tweezers with the help of spherical aberration compensation.

Influence of spherical aberration, stimulus spatial frequency, and pupil apodisation on subjective refractions.

To test competing hypotheses (Stiles Crawford pupil apodising or superior imaging of high spatial frequencies by the central pupil) for the pupil size independence of subjective refractions in the presence of primary spherical aberration. Subjective refractions were obtained with a variety of test stimuli (high contrast letters, urban cityscape, high and low spatial frequency gratings) while modulating pupil diameter, levels of primary spherical aberration and pupil apodisation. Subjective refractions were also obtained with low-pass and high-pass stimuli and using 'darker' and 'sharper' subjective criteria. Subjective refractions for stimuli containing high spatial frequencies focus a near paraxial region of the pupil and are affected only slightly by level of Seidel spherical aberration, degree of pupil apodisation and pupil diameter, and generally focused a radius of about 1-1.5mm from the pupil centre. Low spatial frequency refractions focus a marginal region of the pupil, and are significantly affected by level of spherical aberration, amount of pupil apodisation, and pupil size. Clinical refractions that employ the 'darker' or 'sharper' subjective criteria bias the patient to use lower or higher spatial frequencies, respectively. In the presence of significant levels of spherical aberration, the pupil size independence of subjective refractions occurs with or without Stiles Crawford apodisation for refractions that optimise high spatial frequency content in the image. If low spatial frequencies are optimised by a subjective refraction, spherical refractive error varies with spherical aberration, pupil size, and level of apodisation. As light levels drop from photopic to scotopic, therefore, we expect a shift from pupil size independent to pupil size dependent subjective refractions. Emphasising a 'sharper' criterion during subjective refractions will improve image quality for high spatial frequencies and generate pupil size independent refractions.

Influence of spherical aberrations on fundamental mode beam quality under different laser resonators

Spherical aberrations of the thermal lens of the active media are severe when solid state lasers are strongly pumped. The fundamental mode profile deteriorates due to the aberrations. Self-consistent modes of a resonator with aberrations are calculated by using the Fox–Li diffraction iterative algorithm. Calculation results show that the aberration induced fundamental mode beam quality deterioration depends greatly on the resonator design. The tolerance of a flat-flat resonator to the aberration coefficient is about 30λ in the middle of stability, where λ is the wavelength of laser beam. But for a dynamically stable resonator, 2λ of spherical aberration will create diffraction loss of more than 40%, if inappropriate design criteria are used. A birefringence compensated laser resonator with two Nd:YAG rods is experimentally studied. The experimental data are in quite good agreement with simulation results.

Influence of spherical aberrations on the performance of dynamically stable resonators

Spherical aberrations of thermal lens of the active media are severe when the solid state lasers are strongly pumped. The aberrations influence the mode profile, the diffraction loss, the output power and other laser beam properties, especially for a dynamically stable resonator with large TEM 00-mode volume. Self-consistent modes in a resonator with aberrations are calculated using Fox–Li diffraction iterative algorithm. There are side lobes with the fundamental mode when the spherical aberration is introduced, hence the beam quality is deteriorated. The calculated results agree well with the experimental data. The beam filling factor plays an important role in the design of a laser system. The optimum value of the beam filling factor should be determined by the experimental results according to the spherical aberration effect.

Influence of aperture lens with spherical aberration on the spectral behavior of polychromatic Gaussian Schell-model beams

Abstract Starting from the propagation law of the cross-spectral density function, the spectral behavior of polychromatic Gaussian Schell-model(GSM) beams passing through an aperture lens with spherical aberration is studied. Emphasis is given on the influence of spherical aberration on the spectral shift and spectral switch of GSM beams. It is shown that there is a spectral shift in comparison with the aberration-free case. The spherical aberration also affects the behavior of spectral switches.

Diffraction-induced spectral switches of spherically aberrated polychromatic Gaussian beams

Starting from the propagation law of the crossspectral density function, an analytical expression for the onaxis spectrum of spherically aberrated pol y chromatic Gaussian beams diffracted at an aperture is derived, the aberration f ree result is obtained as a special case treated in the paper. Detailed numerica l calculations and physical analysis are presented. It is shown that the onaxis spectrum in the near field may be redshifted and blueshifted in co mparison wi th the aberrationfree case, and the spectral switch may also take place. In pa r ticular, the influence of spherical aberration on the behavior of spectral swit ches is illustrated.

Modal Behaviour of Passive, Stable Microcavities

Tunable active and passive components for wavelength division multiplex (WDM) systems like vertical cavity surface emitting lasers (VCSELs) and filters show advanced optical performance at reduced production costs if the cavity structure is of stable, half symmetric type. In this paper we report about the mathematical modelling of the power of sidemodes which appear if beam and cavity geometry do not match. We present experimental data which show that the sidemodes are filtered out up to a certain degree by the fiber coupling optics. A limit for the sidemode suppression even for perfect cavity and beam geometry match was also observed. These aspects raise the question on the influence of spherical aberrations on the performance of fiber coupled devices.

Nano-area electron diffraction pattern reconstructed from three-dimensional Fourier spectrum.

A method to obtain a nano-area electron diffraction pattern in transmission electron microscopy (TEM) was proposed, based on three-dimensional (3D)) image formation theory. This method allows us to reconstruct an electron diffraction pattern from a 3D Fourier spectrum of high-resolution through-focus images. As a test case, an electron diffraction pattern from a tilted Si single crystal was reconstructed using the proposed method and compared with the conventional selected-area electron diffraction pattern. The intensity distribution of the reconstructed electron diffraction pattern was confirmed to be qualitatively equal to that of the selected-area electron diffraction pattern, though the degree of the equivalency between these patterns reduces at the high frequency region and the reproducibility of the intensity degrades when the number of images used in the image processing was decreased. By selecting areas in a reconstructed exit wave field, some electron diffraction patterns were obtained from the nano-areas without the influence of spherical aberration.

Influence of optical aberrations on laser-induced plasma formation in water and their consequences for intraocular photodisruption

The influence of spherical aberrations on laser-induced plasma formation in water by 6-ns Nd:YAG laser pulses was investigated for focusing angles that are used in intraocular microsurgery. Waveform distortions of 5.5lambda and 18.5lambda between the optical axis and the 1/e(2) irradiance values of the laser beam were introduced by replacement of laser achromats in the delivery system by planoconvex lenses. Aberrations of 18.5lambda increased the energy threshold for plasma formation by a factor of 8.5 compared with the optimized system. The actual irradiance threshold for optical breakdown was determined from the threshold energy in the optimized system and the spot size measured with a knife-edge technique. For aberrations of 18.5lambda the irradiance threshold was 48 times larger than the actual threshold when it was calculated by use of the diffraction-limited spot size but was 35 times smaller when it was calculated by use of the measured spot size. The latter discrepancy is probably due to hot spots in the focal region of the aberrated laser beam. Hence the determination of the optical-breakdown threshold in the presence of aberrations leads to highly erroneous results. In the presence of aberrations the plasmas are as much as 3 times longer and the transmitted energy is 17-20 times higher than without aberrations. Aberrations can thus strongly compromise the precision and the safety of intraocular microsurgery. They can further account for a major part of the differences in the breakdown-threshold and the plasma-transmission values reported in previous investigations.

Influence of spherical aberration on axial imaging of confocal reflection microscopy

The influence of spherical aberration on axial imaging of confocal reflection microscopy is investigated. In particular, the effects of lens aperture size and of the first three orders of spherical aberration are inspected. It is shown both theoretically and experimentally that the aberrated axial response can be improved by slightly reducing the lens aperture size. The experimental results concerning the effect of the tube length on the axial response and the aberration compensation are also given.

Influence of spherical aberration and astigmatism on the imaging of extended objects using a holographic lens

Investigations on the imaging of extended objects by a holographic lens in the presence of third-order spherical aberration and astigmatism have been carried out. Light intensity distribution in the aberration spot observed at the Gaussian plane has been evaluated numerically, using a ray-tracing procedure, for different amounts of astigmatism and for a fixed value of spherical aberration. The images of extended coherent and incoherent edges as well as bar objects have been computed and the results have been compared with that for the aberration-free case. All the results are illustrated in graphical form.

Phase-space representation of the Strehl ratio: ambiguity function

The irradiance distribution along the optical axis, or the Strehl ratio versus defocus, of a rotationally symmetric system is described in terms of a phase-space representation: Woodward’s ambiguity function. We show that the Fourier spectrum of the Strehl ratio versus defocus for variable spherical aberration can be analyzed from a single picture. This result is applied to analyze the use of shade pupils for reducing the influence of spherical aberration.

L'image tridimensionnelle du point en présence d'aberration sphérique primaire et de filtrage d'amplitude : unitaire ou modal

We investigate the point diffraction image arising from an objective lens in the vicinity of its paraxial focus, under the combined influence of spherical aberration, defocusing, and an amplitude filtering of modal TEM00 law. The previous literature pertaining to our subject is first reviewed thoroughly and then we outline a new hybrid formalism that permits an easy computation of the total diffraction image everywhere in the focal region. In this formalism the complex pupil amplitude is developed into a series of Zernike polynomials, the coefficients of which are obtained through the Gauss–Chebyshev method of numerical quadrature. A considerable amount of numerical information has thus been obtained, which will be presented here in graphical form and discussed. Notably we show that our modal filter, combined with an appropriate amount of defocusing, does compensate the existing spherical aberration beyond the supposedly ideal situation represented by the Airy pattern.

Ｓｉｎｇｌｅ ａｔｏｍを見る試み ＩＩ 結晶格子像における球面収差の影響

Ｓｉｎｇｌｅ ａｔｏｍを見る試み ＩＩ 結晶格子像における球面収差の影響