Influence of Aberrations on Modal Decomposition for LMA Fiber Laser Systems

Understanding the mode components is of great importance to manipulate the optical modes and to improve the optical system performance. However, various forms of aberrations, stemming from misalignment and imperfect optical components and system design, degrade the performance of the modal decomposition (MD) system. Here we analyze the influence of various Zernike aberrations on MD performance in large-mode-area fiber laser systems. Using computer-generated optical correlation filter together with angular multiplexing technique, we can simultaneously measure multi-modal contents. Among the common aberrations, we find that the MD results are least sensitive to vertical astigmatism aberration. However, the vertical coma aberration and horizontal coma aberration have a large impact on MD results under the same aberration strength, which show a rather large change in modal weight and intermodal phase. Our analysis is useful to construct a precise MD system applicable for high-power optical fiber modal analysis and mode control.

Evaluation of a new nomogram for Ferrara ring segment implantation in keratoconus

AIM: To evaluate the short-term clinical outcomes of Ferrara rings in keratoconus using an optimized nomogram developed after several years of research and retrospective analysis of clinical data. METHODS: This prospective longitudinal non-comparative clinical trial evaluated 88 eyes of 88 patients (age 18-62y) with keratoconus diagnosis from two Spanish centers. Ferrara ring segment (AJL Ophthalmic) implantation was performed in all cases, using the mechanical procedure in 25 eyes (28.4%) and a femtosecond laser-assisted procedure in 63 eyes (71.6%). The ring segments implanted in each case were selected using a new optimized nomogram that considered variables such as anterior corneal asphericity and astigmatism or the discrepancy among astigmatism and coma orientations. Visual, refractive, corneal topographic, aberrometric, and pachymetric changes after surgery were evaluated during a 3-month follow-up. RESULTS: The implants induced a significant refractive change as well as an improvement in uncorrected (UDVA) and corrected distance visual acuity (CDVA; P<0.001). Postoperative CDVA of 0.10 logMAR or better was achieved in 28.4% and 46.5% of eyes, respectively. Two eyes (2.3%) lost two or more lines of CDVA whereas a total of 53.5% of eyes gained lines of CDVA. A significant central anterior and posterior corneal flattening was induced (P≤0.003), with a significant reduction of anterior (P<0.001) and posterior corneal astigmatisms (P=0.048), and a change in anterior asphericity (P<0.001). Total primary coma (6 mm pupil) change was also statistically significant (preoperative 3.66±3.04 µm vs postoperative 2.33±2.26 µm, P<0.001). No significant differences were found in the effect of ring segments between cases implanted using the mechanical and femtosecond techniques (P≥0.101). CONCLUSION: The implantation of Ferrara rings based on the nomogram evaluated is safe and effective for promoting a visual rehabilitation in keratoconus, with a relevant control of primary coma aberration.

Comparison of the optical quality after SMILE and FS-LASIK for high myopia by OQAS and iTrace analyzer: a one-year retrospective study

Background To compare the correction effect and optical quality after small-incision lenticule extraction (SMILE) and femtosecond laser assisted laser in situ keratomileusis (FS-LASIK) for high myopia. Methods 51 high myopia eyes after SMILE and 49 high myopia eyes after FS-LASIK were enrolled and divided into two groups retrospectively. The OQAS and iTrace analyzer were used for optical quality inspection. Between the two groups the spherical equivalent (SE), astigmatism, uncorrected distant visual acuity (UDVA), strehl ratio (SR), modulation transfer function cutoff frequency (MTF cutoff), objective scatter index (OSI) and wavefront aberrations were analyzed and compared before surgery and at 1, 6 and 12 months after surgery. Results After the operation: (1) SE and astigmatism declined and UDVA increased significantly in both groups, and UDVA was better after SMILE than FS-LASIK. (2) SR and MTF cutoff reduced and OSI increased significantly after SMILE and FS-LASIK. SR and MTF cutoff were significantly higher after SMILE than FS-LASIK. OSI was significantly lower after SMILE than FS-LASIK. (3) The total wavefront aberration, total low-order wavefront aberration, defocus and astigmatism aberration as well as trefoil aberration reduced significantly in both groups. The total high-order wavefront aberration increased significantly after FS-LASIK. The spherical and coma aberration increased significantly in both groups. The total high-order wavefront aberration and coma aberration at 1 month were higher after FS-LASIK than SMILE. Conclusion The optical quality descended after SMILE and FS-LASIK. SMILE was superior to FS-LASIK at the correction effect and optical quality for high myopia. The combination of OQAS and iTrace analyzer is a valuable complementary measurement in evaluating the optical quality after the refractive surgery. Trial registration This is a retrospective study. This research was approved by the ethics committee of Xiangya Hospital and the IRB approval number is 201612074.

IMPROVE POINT SPREAD FUNCTION BY USING GAUSSIAN FILTER WITH SINGLE HEXAGONAL APERTURE

We study the effect of Gaussian filter on the point spread function (psf) for a single hexagonal aperture for diffraction limit system and by inserting a coma aberration (w31=0.25 and 0.5). Also we derived the point spread function for a single hexagonal aperture and when there is a Gaussian filter with different values in width used. the different values of coma aberration was study ,we notice a decrease in intensity and secondary peaks of psf . The pulse to noise ratio increases with the width of the Gaussian filter increases.

Cryo-EM Performance Testing of Hardware and Data Acquisition Strategies

The increasing popularity and adoption rate of cryo-electron microscopy is evidenced by a growing number of new microscope installations around the world. The quality and reliability of the instruments improved dramatically in recent years, but site-specific issues or unnoticed problems during installation could undermine productivity. Newcomers to the field may also have limited experience and/or low confidence in the capabilities of the equipment or their own skills. Therefore, it is recommended to perform an initial test of the complete cryo-EM workflow with an ‘easy’ test sample, such as apoferritin, before starting work with real and challenging samples. Analogous test experiments are also recommended for quantification of new data acquisition approaches or imaging hardware. Here, we present the results from our initial tests of a recently installed Krios G4 electron microscope equipped with two latest generation direct electron detector cameras—Gatan K3 and Falcon 4. Three beam-image shift-based data acquisition strategies were also tested. We detail the methodology and discuss the critical parameters and steps for performance testing. The two cameras performed equally, and the single and multi-shot per-hole acquisition schemes produced comparable results. We also evaluated the effects of environmental factors and optical flaws on data quality. Our results reaffirmed the exceptional performance of the software aberration correction in Relion in dealing with severe coma aberration. We hope that this work will help cryo-EM teams in their testing and troubleshooting of hardware and data collection approaches.

The Effect of adding First Order Aberrations To Third Order Aberrations on Point Spread Function for Triangular Aperture

In this work, Point Spread Function (PSF) for triangular aperture was studied, in case of ideal optical system, also in case of presence first order aberrations )focal error and tilt aberration) and third order aberrations (spherical ,coma, and astigmatism aberrations) individually, and for the same values of aberration factor )W=0.1λ …..0.5 λ ) for angle of rotation (ѱ =0). First order aberrations were added to third order aberrations, to obtain the best balance and to reduce the curve width of the (PSF), and to increase the Strehl ratio, like adding a tilt aberration to the coma aberration and adding focal error to spherical aberration and astigmatism aberration. There are some aberrations effects impact negatively on point spread function, such as focal error with coma aberration and tilt aberration with spherical aberration.

The effect of different optical zone diameters on the results of high-order aberrations in femto-laser-assisted in situ keratomileusis

Purpose: To evaluate the postoperative high-order aberration differences of femto-LASIK surgery in 6.5 and 7 mm optic zones. Patients and Methods: We retrospectively reviewed 80 eyes of 40 patients with myopia or myopia with astigmatism who underwent femtosecond LASIK surgery. Q values, z3, 3 (h. trefoil), z3, –3 (v. trefoil), z3, 1 (h. coma), z3, –1 (vertical coma), z4, 0 (spherical aberration), z5, –1 (second other v. coma), aberration coefficients were evaluated 3 months after surgery. Central corneal thicknesses, intraocular pressures, patient ages and genders, optical zone diameters and ablation depths are collected from patients’ medical records. Results: The mean age was 28.4 ± 0.69 years (range, 20–47 years). Lower z4, 0 spherical aberrations and aberration coefficient values were associated with larger optical zones (7 mm) (z4, 0 spherical aberrations = 1.25, p = 0.01; coefficient value = –1.21, p < 0.01). Although a smaller optical zone (6.5 mm) was associated with an increase in most of the wave-front aberration variables, measurements were not statistically different between the two groups other than z4, 0 spherical aberrations and aberration coefficients. Discussion: LASIK treatment with 6.5 and 7 mm optical zones is safe and effective for correcting myopia and myopic astigmatism and has statistically similar visual outcomes. Moreover, larger optical zone (7 mm) was found to be associated with lower spherical aberration induction and smaller aberration coefficient values compared to 6.5 mm optical zone. This can be important for decision-making in femto-LASIK surgery for better postoperative results.

Comparison of Visual Outcomes for Myopia after Refractive Surgery using Femtosecond Laser-assisted and Epipolis LASIK

Purpose This study was to clinically evaluate the visual outcomes after refractive surgery for myopia using femtosecond laser-assisted in situ keratomileusis (femto-LASIK) and epipolis LASIK (flap-off epi-LASIK). Methods Forty eyes of 27 patients were divided into 2 groups in a retrospective study. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction (MR),corneal asphericity (Q-value) and corneal higher-order aberrations (HOAs) were assessed pre- and postoperatively. Results The pre- and postoperative changes in flattest keratometry reading(K1), steepest keratometry reading(K2), central corneal thickness(CCT), and only Q-value of the anterior surface was statistically significant for both groups (femto-LASIK: P=0.014, P=0.03, P<0.001, P=0.001, respectively; epi-LASIK: all P<0.001). The postoperative corneal thickness spatial profile (CTSP) were statistically significant thinner than preoperative CTSP in both procedures (all P<0.05), and the epi-LASIK was significant thinner than femto-LASIK at 6 mm ring of CTSP (P=0.039). The improvement in LogMAR UDVA after refractive surgery was statistically significant for both groups (P<0.001 for all groups); it was significantly improved for femto-LASIK on day 1 and at 1 week postoperatively (P<0.001, P=0.019, respectively). In analysis of corneal HOAs, there were significant reduction of vertical coma aberration and horizontal secondary astigmatism aberration, and induction of spherical aberration in the front corneal HOAs after femto-LASIK (P=0.021, P=0.001, P=0.001, respectively); in the total corneal HOAs changes were the same pattern as the front corneal HOAs (P=0.007, P=0.004, P<0.001, respectively), but in the back corneal HOAs changes, a few significant induction of vertical coma aberration, and reduction of oblique trefoil aberration and oblique tetrafoil aberration (all P<0.05). In flap-off epi-LASIK, there were only significant induction of SA in the front and total corneal HOAs after surgery (all P<0.05); in the back corneal HOAs, a few significant induced horizontal secondary astigmatism aberration and reduced SA aberration (P=0.027, P=0.011, respectively), however, the back corneal HOAs changes were not significant effect on the total corneal HOAs changes. Conclusion Femto-LASIK showed better early visual outcomes than that noted by epi-LASIK, but there was no significant difference between the outcomes of the 2 procedures 1 week postoperatively.