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An improved laser correction mirror 10 for correcting aberrations in a laser beam wavefront having a rectangular mirror body 12 with a plurality of legs 14, 16, 18, 20, 22, 24, 26, 28 arranged into opposing pairs 34, 36, 38, 40 along the long sides 30, 32 of the mirror body Vector force pairs 49, 50, 52, 54 are applied by adjustment mechanisms 42, 44, 46, 48 between members of the opposing pairs 34, 36, 38, 40 for bending a reflective surface 13 of the mirror body 12 into a shape defining a function which can be used to correct for comatic aberrations.
Excimer laser is the best and the more used technique for Astigmatism correction. Lasik is generally preferred to PRK and must be the choice for hyperopic and mix astigmatisms. Myopic astigmatisms are the easier cases to treat: Hyperopic and mix astigmatisms are more difficult to correct because they are more technically demanding and because the optical zone of the photoablation must be large. Flying spots lasers are the best for these cases.
The most important point is to trace the photoablation very precisely on the astigmatism axis. The use of eye trackers with iris recognition or a preoperative marking of the reference axis avoid cyclotorsion or a wrong position of the head. Irregular astigmatism are better corrected with topoguided or wavefront guided photoablations. Device for wavefront correction in an ultra high power laser. A system for wavefront correction in an ultra high power laser. As the laser medium flows past the optical excitation source and the fluid warms its index of refraction changes creating an xmk wedge.
A system is provided for correcting the thermally induced optical phase errors. Purpose To evaluate the optical quality after laser in situ keratomileusis LASIK or serial photorefractive keratectomy PRK using a double-pass system and to follow the recovery of optical quality after laser vision correction.
Methods This study measured the visual acuity, manifest refraction and optical quality before and one day, one week, one month, and three months after laser vision correction. Optical quality parameters including the modulation transfer function, Strehl ratio and intraocular scattering were evaluated with a double-pass system. The optical quality three cprrection post-surgery did not differ significantly between ccorrection laser vision correction techniques. Furthermore, the preoperative and postoperative optical quality did not differ significantly in either group.
The optical quality of patients in the PRK group seemed to recover slightly more slowly than their uncorrected distance visual acuity. Conclusions Optical quality recovers to the preoperative level after laser vision correctionso laser vision correction is efficacious for correcting myopia.
The double-pass system is a useful tool for clinical assessment of optical quality. Correction for spatial averaging in laser speckle contrast analysis. Practical laser speckle contrast analysis systems face a problem of spatial averaging of speckles, due to the pixel size in the cameras used.
Existing practice is to use a system factor in speckle contrast analysis to account for spatial averaging. The dtdd of the system factor correction has not previously been confirmed. The problem of spatial averaging is illustrated using computer simulation of time-integrated dynamic speckle, and the linearity of the correction confirmed using both computer simulation and experimental results.
The valid linear correction allows various useful compromises in the system design.
ACTIVITES ET TRAVAUX
Holographic optical system for aberration corrections in laser Doppler velocimetry. An optical system containing multifaceted holographic optical elements HOEs has been developed to correct for aberrations introduced by nonflat windows in laser Doppler velocimetry. The multifacet aberration correction approach makes it possible to record on one plate many sets of adjacent HOEs that address different measurement volume locations.
By using 5-mm-diameter facets, it is practical to place sets of holograms on one 10 x The holograms are recorded in dichromated gelatin and therefore are nonabsorptive and suitable for use with high-power argon laser beams. Low f-number optics coupled with a percent efficient distortion- correcting hologram in the collection side of the system yield high optical efficiency.
Un projet d’horloge atomique spatiale utlilsant le refroidissement des atomes par faisceaux laser: This paper, “Un projet d’horloge atomique spatiale utlilsant le refroidissement des atomes par faisceaux laser: Full-thickness skin grafts FTSGs are frequently used to treat patients with burn injuries and to repair defects rendered by excisional including Mohs surgery.
The evidence for corrective laser surgery after scar formation is well established. With regard to laser treatment of FTSG, the evidence is sparse. Laser treatment exerclce FTSG is a novel concept, with minimal literature. We present a case series, one of the first to our knowledge, of the treatment of FTSG with fractional CO 2 laser in five patients after Mohs surgery.
This initiative is part of the strategy of the “Route des Lasers ” center which aims to promote exetcice developed in the areas of photonics, targeting in particular children and teenagers and their awareness acec this particular industrial and scientific topic. High density, optically correctedmicro-channel cooled, v-groove monolithic laser diode array.
This optically correctedmicro-channel cooled, high density laser is usable in all solid state laser systems which require efficient, directional, narrow bandwidth, high optical power density pump sources.
Laser -induced retinal injury studies with wavefront correction. Exrrcice ability of a laser beam to damage the retina of the eye depends on the accuracy to which the optics of the eye focuses the beam onto the retina.
A possible explanation is that uncompensated aberrations of the eye of the anesthetized NHP are larger than predicted. Focus is a dynamic process which is purposely defeated while performing measurements of retinal injury thresholds.
GILLES HUNAULT (giluno)
Optical wavefront correction systems have become available which have the capability to compensate for ocular aberrations. This paper will report on an injury threshold experiment which incorporates an adaptive optics system to compensate for the aberrations of a NHP eye during exposure to a collimated laser beam, therefore producing a near diffraction limited beam spot on the retina.
To evaluate the outcomes of corneal laser ablation with Q factor modification for vision correction in patients with progressive keratoconus.
All patients underwent a detailed ophthalmic examination including uncorrected distance visual acuity UDVAcorrected distance visual acuity CDVAsubjective acceptance and corneal topography using the Pentacam. The topolyzer was used to measure the corneal asphericity Ckrrection. Ablation was performed based on the preoperative Q values and thinnest pachymetry to obtain a target of near normal Q.
This was followed by corneal collagen crosslinking to stabilize the progression. The improvement in higher-order aberrations and total aberrations were statistically significant in both groups; however, the spherical aberration showed statistically significant improvement only in Group II.
lasers correction des: Topics by
Ablation based on the preoperative Q and pachymetry for a near normal postoperative Q value appears to be an effective method to improve the visual acuity and quality in patients with keratoconus. Ablation algorithms and corneal asphericity in myopic correction with excimer lasers. The purpose of this work is studying a corneal asphericity change after a myopic refractive correction by mean of excimer lasers. As the ablation profile shape plays a key role in the post-op corneal asphericity, ablation profiles of recent lasers should be studied.
The other task of this research was to analyze operation LASIK outcomes of one of the lasers with generic spherical ablation profile and to compare an asphericity change with theoretical predictions. The several correction methods, like custom generated aspherical profiles, may be utilized for mitigation of unwanted effects of asphericity avecc.
Here we also present preliminary results of such correction for one of the excimer lasers. Excimer laser correction of hyperopia, hyperopic and mixed astigmatism: The broad acceptance of “spot scanning” or “flying spot” excimer lasers in the last decade has enabled the domination of corneal ablative laser surgery over other refractive surgical procedures for the correction of hyperopia, hyperopic and mixed astigmatism.
This review outlines the most important reasons why the ablative laser correction of hyperopia, hyperopic and mixed astigmatism for many years lagged behind that of myopia. Most of today’s scanning laser systems, exerrcice in the LASIK and PRK procedures, can safely and effectively perform low, moderate and high hyperopic and hyperopic astigmatic corrections. The introduction of these laser platforms has also significantly dorrection the long term refractive stability of hyperopic treatments.
In the future, further improvements in femtosecond and nanosecond technology, eye-tracker systems, and the development of new customized algorithms, such as the ray-tracing method, could additionally increase the upper limit for the safe and predictable corneal ablative laser correction ofhyperopia, hyperopic and mixed astigmatism.
Differential correction system of laser beam directional dithering based on symmetrical beamsplitter. This paper proposes a differential correction system with a differential optical path and a symmetrical beamsplitter for correcting the directional dithering of the laser beams. This system can split a collimated laser beam into two laser beams with equal and opposite movements. Thus, the positional averages of the two split laser beams remain constant irrespective of the dithering angle.
The symmetrical beamsplitter designed based on transfer matrix principle is to balance the optical paths and irradiances of the two laser beams. Experimental results show that the directional dithering is reduced to less than one-pixel value. Finally, two examples show that this system can be widely used in one-dimensional measurement. Controversial opinions exist regarding optimum laser beam characteristics for achieving smoother ablations in laser -based vision correction.
The purpose of the study was to outline a rigorous simulation model avef simulating shot-by-shot ablation process. The impact of laser beam characteristics like super Gaussian order, truncation radius, spot geometry, spot overlap, and lattice exefcice were tested on ablation smoothness. Given the super Gaussian order, the theoretical beam profile was determined following Corrrection model. The intensity beam profile originating from an excimer laser was measured with a beam profiler camera.
For both, the measured and theoretical beam profiles, two spot geometries round and square spots were considered, and two types of lattices reticular and triangular were simulated with varying spot overlaps and ablated material cornea or polymethylmethacrylate [PMMA]. The roughness in ablation was determined by the root-mean-square per square root of layer depth. Truncating the beam profile increases the roughness in ablation, Gaussian profiles theoretically result in smoother ablations, round spot geometries produce lower roughness in ablation compared to square geometry, triangular lattices theoretically produce lower roughness in ablation compared to mxl reticular lattice, theoretically modeled beam profiles show lower roughness in ablation compared to the measured beam profile, and the simulated roughness in ablation on PMMA tends to be lower than on human cornea.
For given input parameters, proper optimum parameters for minimizing the roughness have been found. Theoretically, the proposed model can be used for achieving smoothness with laser systems used for ablation processes at relatively low cost.
This model may improve the quality of results and could be directly applied for improving postoperative surface quality. Designing multifocal corneal models to correct presbyopia by laser ablation. Two multifocal corneal models and an aspheric model designed dgd correct presbyopia by corneal photoablation were evaluated. The design of each model was optimized to achieve the best visual quality possible for both near and distance vision.
In addition, we evaluated the effect of myosis and pupil decentration on visual quality. The corrected model with the central zone for near vision provides better results since it requires less ablated corneal surface area, permits higher addition values, presents stabler visual quality with pupil-size variations and lower high-order aberrations.
Airborne Laser Systems Testing and Analysis essals et analyse des systemes laser embarques. To briefly summarise the fundamental concepts involved A method for corrections of measurements of points of interests measured by beams of radiation propagating through stratified media including performance of ray-tracing of at least one ray lunched from a metrology instrument in a direction of an apparent point of interest, calculation a path length of the ray through stratified medium, and determination of coordinates of true position of the point interest using the at least one path length and the direction of propagation of the ray.
Generalized Alvarez lens for correction of laser aberrations. The original design emphasized in the patent consists of a pair of adjacent optical elements that provide a variable focus.
A lens system with a variable effective focal length is nothing new. Such systems are widely used in cameras, for example.