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Sample records for laser photorefractive keratectomy

  1. Corneal topography of excimer laser photorefractive keratectomy.

    PubMed

    Klyce, S D; Smolek, M K

    1993-01-01

    The application of the 193 nm excimer laser for keratorefractive surgery promises to deliver a higher degree of precision and predictability than traditional procedures such as radial keratotomy. The development and evaluation of keratorefractive surgery have benefited from the parallel advances made in the field of corneal topography analysis. We used the Computed Anatomy Topography Modeling System (TMS-1) to analyze a Louisiana State University (LSU) Eye Center series of patients who had photorefractive keratectomy for the treatment of myopia with the VISX Twenty/Twenty excimer laser system. The excimer ablations were characterized by a relatively uniform distribution of surface powers within the treated zone. In the few cases that exhibited marked refractive regression, corneal topography analysis showed correlative changes. With topographical analysis, centration of the ablations relative to the center of the pupil could be evaluated. Marked improvement in centration occurred in the patients of LSU Series IIB in which the procedure to locate the point on the cornea directly over the pupil's center during surgery was refined. Corneal topographical analysis provides objective measures of keratorefractive surgical results and is able to measure the precise tissue removal effect of excimer laser ablation without the uncertainties caused by measuring visual acuity alone. Our observations forecast the need for improved aids to center the laser ablations and for the development of a course of treatment to prevent post-ablation stromal remodeling. PMID:8450433

  2. Excimer laser photorefractive keratectomy with different ablation zones.

    PubMed

    Hassan, Z; Lampé, Z; Békési, L; Berta, A

    1997-01-01

    In this study we would like to introduce the excimer laser, and to demonstrate our results and complications by using different ablation zones during photorefractive keratectomy (PRK) in the correction of myopia and astigmatismus. In 1996 we performed photorefractive keratectomy on 100 myopic eyes of 52 patients (28 females, 24 males). Mean age was 26.21 years (ranged from 19 to 54 years). The preoperative refraction ranged from -1.0 D to -18.0 Diopters. The diameter of the ablation zones were between 5 and 6.5 mm. We evaluated the results and the complications of the surgeries of 100 eyes which were performed with Schwind keratom F excimer laser. After 2 days, 1 week, 1 month, 3 months, and 6 months postoperatively we tested the best uncorrected and corrected visual acuities, and performed intraocular pressure measurement, slit lamp examination as well as corneal topography. The postoperative refractions were between +/- 0.5 to +/- 1.0 Diopters. After six months postoperatively the slit lamp examination showed that 80% of the patients had no corneal haze while 20% had stage I (Hanna) corneal haze. The smaller the diameter of the ablation zone was, the more pronounced the corneal haze and the night-glare were. The photorefractive excimer laser keratectomy is judged to be a safe method, although it might have some side-effects. The different ablation zones of this treatment means an important modification, that not only allows the method to meet the individual requirements, but reduces the chance of the complications as well. Based on the authors' experiences PRK for moderate myopia with large diameter ablation zones appears more predictable than than with smaller ablation zone diameters. PMID:9408312

  3. Photorefractive Keratectomy in Keratoconus

    PubMed Central

    Tambe, Deepali Sandeep; Ivarsen, Anders; Hjortdal, Jesper

    2015-01-01

    Purpose To assess the efficacy and safety of topography-guided photorefractive keratectomy (PRK) for keratoconus and to estimate the subsequent risk of progression. Methods This is a retrospective follow-up study. Between 1998 and 2013, 28 eyes of 23 patients (age 17–60) with grade 1–3 keratoconus received topography-guided PRK. Corrected-distance visual acuity (CDVA), keratometry, pachymetry, and corneal topography were assessed before, after 3 months, and at a late follow-up of a median of 7 years after the procedure. Postoperative complications including subsequent keratoplasty were noted. Results Of the 28 eyes, 5 (18%percnt;) had undergone corneal transplantation at a median of 7 years (range 3–10) after PRK. Four eyes were not available for follow-up. In the remaining 19 eyes, CDVA was improved in 16 eyes (84.3%percnt;), reduced in 2 eyes (10.5%percnt;), and unchanged in 1 eye (5.2%percnt;). Thus, average CDVA had improved from 0.49 logMAR before PRK to 0.27 logMAR at 3 months, and to 0.24 at the long-term follow-up. The mean spherical equivalent was reduced from − 6.2 to −3.7 dpt after 3 months and to −2.1 dpt at the late follow-up. Similarly, the mean cylinder was reduced from −4.2 to −3.0 dpt after 3 months and at the late follow-up. Conclusion Topography-guided PRK in keratoconus may be effective for reducing myopia and astigmatism and may offer a temporary or permanent alternative to keratoplasty in contact lens-intolerant keratoconus. In the present study, we found a low risk of keratoconus progression after PRK. PMID:26327912

  4. Glare sensitivity and visual acuity after excimer laser photorefractive keratectomy for myopia

    PubMed Central

    Niesen, U.; Businger, U.; Hartmann, P.; Senn, P.; Schipper, I.

    1997-01-01

    BACKGROUND—Following excimer laser photorefractive keratectomy (PRK), an increase in glare sensitivity and a reduction in contrast sensitivity can occur owing to changes in the cornea (structure and topography). In this study, an attempt was made to quantify and document objectively a change in those subjective perceptual factors.
METHODS—Snellen visual acuity and disability glare were measured with the Berkeley glare test preoperatively as well as 1, 3, 6, 9, and 12 months postoperatively, after excimer laser photorefractive keratectomy (PRK) on 32 myopic patients (46 eyes). During the postoperative progress checks, haze was graded and contrast sensitivity was measured with the Vistech chart. All the data were statistically analysed by multiple regression.
RESULTS—One year after PRK, a reduction in visual acuity (VA) measured with the low acuity contrast chart (10%) with and without glare could still be found, despite the fact that acuity measurements with a high contrast Snellen chart showed the same VA 6 months postoperatively as well as before the treatment. The lowest VA could be measured 1 month postoperatively; thereafter, the acuity increased despite the increase in haze that occurred during the first 3 months.
CONCLUSION—Disability glare and a reduction in contrast sensitivity could be observed in most patients after PRK treatment with the Meditec laser system with its scanning slit. The future will show if new technology and a broader flattening area of 6 to 7 mm can minimise these postoperative complications.

 PMID:9059248

  5. Results of excimer laser photorefractive keratectomy for the correction of myopia at Cedars-Sinai Medical Center: 1993

    NASA Astrophysics Data System (ADS)

    Maguen, Ezra I.; Salz, James J.; Nesburn, Anthony B.; Warren, Cathy; Macy, Jonathan I.; Papaioannou, Thanassis; Hofbauer, John; Berlin, Michael S.

    1994-06-01

    This report summarizes the authors' 3-year experience with excimer laser photorefractive keratectomy (PRK) on 240 eyes of 161 patients. With constant laser emission parameters, nitrogen (N2) flow across the cornea was used on 79 eyes while 161 eyes had no N2 flow. 74 eyes were operated on without fixation with a suction ring. Postoperative pain management included patching and oral analgesics in 77 eyes and the use of topical Diclofenac or Ketorolac, and a therapeutic soft contact lens in 163 eyes. Follow up ranged from 1 month (206 eyes) to 36 months (10 eyes).

  6. Long term results of no-alcohol laser epithelial keratomileusis and photorefractive keratectomy for myopia

    PubMed Central

    Spadea, Leopoldo; Verboschi, Francesca; De Rosa, Vittoria; Salomone, Mariella; Vingolo, Enzo Maria

    2015-01-01

    AIM To evaluate the long term clinical results of mechanical no-alcohol-assisted laser epithelial keratomileusis (LASEK) versus standard photorefractive keratectomy (PRK) for low-moderate myopia. METHODS Twenty-five eyes treated with LASEK and twenty-five eyes treated with PRK were evaluated with a mean follow-up duration of 60mo. Mechanical separation of the epithelium was performed with blunt spatula and without application of alcohol. Laser ablation was performed with the MEL-70 excimer laser. All patients were examined daily until epithelial closure; at 1, 3, 6, and 12mo, and every year subsequently. Main outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction, haze, efficacy and safety indexes. RESULTS Twenty-one eyes and 22 eyes completed follow-up of 60mo in LASEK and PRK group respectively. Manifest refraction at 60mo follow-up was -0.01 and 0.26 in LASEK and PRK group respectively. In the LASEK group mean UDVA and mean CDVA after 60mo were 20/22 and 20/20 respectively (P>0.01). In the PRK group mean UDVA and mean CDVA at 60mo follow-up were 20/20 and 20/20 after 60mo (P>0.01). The efficacy indexes were 0.87 and 0.95, and the safety indexes were 1.25 and 1.4 respectively for LASEK group and PRK group. CONCLUSION Both standard PRK and no-alcohol LASEK offer safe and effective correction of low-moderate myopia in the long term without any statistically significant difference between the two groups. PMID:26086011

  7. How predictable are the results of excimer laser photorefractive keratectomy? A review.

    PubMed

    Grosvenor, T

    1995-10-01

    At the close of 1994, the AOA News reported that at least 14 companies were preparing to market equipment for excimer laser photorefractive keratectomy (PRK). More than a dozen PRK centers had been formed for the purpose of recruiting optometrists to co-manage PRK patients. Because the surgery is a "no-touch" computer-driven procedure whose duration is measured in seconds, the preoperative and postoperative care of PRK patients will assume major importance. Optometrists who will be asked to take part in the management of PRK patients must be able to counsel patients on matters such as the predictability of the procedure in terms of postoperative refractive error and visual acuity, as well as the possibility of unintended consequences such as difficulty in night driving. Information currently available, mainly as a result of studies conducted in other countries, shows that the results of PRK are highly predictable for preoperative myopia up to about -3.00 D and somewhat less predictable for myopia between -3.00 and -6.00 D, whereas for myopia greater than -6.00 D the probability of achieving a full correction decreases rapidly with increasing amounts of myopia. As compared to radial keratotomy (RK) in which the postoperative refractive error drifts relentlessly in the hyperopic direction, PRK brings about an initial hyperopic shift followed by regression leading to increasing myopia. Researchers disagree on the cause of the postoperative hyperopic shift and regression, and on the value of various methods of controlling regression including the use of wider and deeper ablation profiles and the postoperative use of corticosteroids and nonsteroid anti-inflammatory drugs. It is too early to determine whether the myopic creep in PRK will be as persistent as the hyperopic creep in RK, but it is likely that whereas presbyopic post-RK patients may have adequate distance vision but require corrective lenses for reading, presbyopic post-PRK patients may be sufficiently myopic

  8. Corneal modeling for analysis of photorefractive keratectomy

    NASA Astrophysics Data System (ADS)

    Della Vecchia, Michael A.; Lamkin-Kennard, Kathleen

    1997-05-01

    Procedurally, excimer photorefractive keratectomy is based on the refractive correction of composite spherical and cylindrical ophthalmic errors of the entire eye. These refractive errors are inputted for correction at the corneal plane and for the properly controlled duration and location of laser energy. Topography is usually taken to correspondingly monitor spherical and cylindrical corneorefractive errors. While a corneal topographer provides surface morphologic information, the keratorefractive photoablation is based on the patient's spherical and cylindrical spectacle correction. Topography is at present not directly part of the procedural deterministic parameters. Examination of how corneal curvature at each of the keratometric reference loci affect the shape of the resultant corneal photoablated surface may enhance the accuracy of the desired correction. The objective of this study was to develop a methodology to utilize corneal topography for construction of models depicting pre- and post-operative keratomorphology for analysis of photorefractive keratectomy. Multiple types of models were developed then recreated in optical design software for examination of focal lengths and other optical characteristics. The corneal models were developed using data extracted from the TMS I corneal modeling system (Computed Anatomy, New York, NY). The TMS I does not allow for manipulation of data or differentiation of pre- and post-operative surfaces within its platform, thus models needed to be created for analysis. The data were imported into Matlab where 3D models, surface meshes, and contour plots were created. The data used to generate the models were pre- and post-operative curvatures, heights from the corneal apes, and x-y positions at 6400 locations on the corneal surface. Outlying non-contributory points were eliminated through statistical operations. Pre- and post- operative models were analyzed to obtain the resultant changes in the corneal surfaces during PRK

  9. Bilateral Nocardia Keratitis after Photorefractive Keratectomy

    PubMed Central

    Faramarzi, Amir; Feizi, Sepehr; Javadi, Mohammad-Ali; Rezaei Kanavi, Mozhgan; Yazdizadeh, Forouzan; Moein, Hamid-Reza

    2012-01-01

    Purpose To report the clinical, confocal scan, and histopathologic features of nocardia keratitis in a patient who developed bilateral infection following photorefractive keratectomy (PRK). Case Report A 23-year-old woman underwent bilateral PRK for low myopia. On postoperative day 3, dense central stromal infiltrates were noticed in both eyes. Empirical antibiotic therapy was initiated which was converted into specific therapy after a definite diagnosis was made based on clinical features and confirmed by confocal scan and histopathologic findings. Clinical and confocal scan features were consistent with the diagnosis of Nocardia keratitis, and topical 2% amikacin eye drops were started. Because of poor response to medical therapy, lamellar keratectomy was performed in both eyes which shortened the treatment course. Histopathologic examination reconfirmed the initial diagnosis. Conclusion Familiarity with clinical and confocal scan features facilitates early diagnosis of Nocardia keratitis leading to proper management and hence a rapid therapeutic response. PMID:23275825

  10. Epipolis-laser in situ keratomileusis versus photorefractive keratectomy for the correction of myopia: a meta-analysis.

    PubMed

    Wu, Wenjing; Wang, Yan; Xu, Lulu

    2015-10-01

    It is unclear whether epipolis-laser in situ keratomileusis (Epi-LASIK) has any significant advantage over photorefractive keratectomy (PRK) for correcting myopia. We undertook this meta-analysis of randomized controlled trials and cohort studies to examine possible differences in efficacy, predictability, and side effects between Epi-LASIK and PRK for correcting myopia. A system literature review was conducted in the PubMed, Cochrane Library EMBASE. The statistical analysis was performed by RevMan 5.0 software. The results included efficacy outcomes (percentage of eyes with 20/20 uncorrected visual acuity post-treatment), predictability (proportion of eyes within ±0.5 D of the target refraction), epithelial healing time, and the incidence of significant haze and pain scores after surgery. There are seven articles with total 987 eyes suitable for the meta-analysis. There is no statistical significance in the predictability between Epi-LASIK and PRK, the risk ratio (RR) is 1.03, 95% confidence interval (CI) [0.92, 1.16], p = 0.18; with respect to efficacy, the odds ratio is 1.43, 95% CI = [0.85, 2.40], p = 0.56 between Epi-LASIK and PRK, there is no statistical significance either. The epithelial cell layer healing time and the pain scores and the incidence of significant haze showed no significance between these two techniques although more pains can be found in Epi-LASIK than PRK at the early-stage post-operation. According to the above analysis, Epi-LASIK has good efficacy and predictability as PRK. In addition, both techniques have low pain scores and low incidence of significant haze. PMID:26253460

  11. Topography and raytracing analysis of patients with excellent visual acuity 3 months after excimer laser photorefractive keratectomy for myopia.

    PubMed

    Maguire, L J; Zabel, R W; Parker, P; Lindstrom, R L

    1991-01-01

    We performed topography and raytracing analysis 3 months after surgery on five consecutive eyes of five patients, which had excimer laser photorefractive keratectomy for myopia. Three of the five eyes had uncorrected postoperative visual acuity of 20/20 or better. Two eyes had an uncorrected vision of 20/40. In three of five eyes, the area of excimer ablation was centered within 1.0 mm of the optical axis. Three other eyes showed decentration that ranged from 1.1 to 1.5 mm. The range of surface power seen within 2 mm of the central keratoscope ring was as follows: patient CK = 37.50 to 39.50 diopters; patient CA = 40.50 D to 44.80 D; patient CW = 37.90 D to 42.20 D; patient AC = 35.50 D to 39.00 D; patient DT = 34.50 D to 41.40 D. Topography patterns differed from eye to eye. A raytracing program modeled refraction of 20/80 and 20/20 "E" of 100%, 50%, 25%, 12.5% and 6.25% contrast through all measured points on the central 10 keratoscope rings of the five postoperative corneas. The five computer-derived images were ranked subjectively according to the observed degree of image degradation by three observers. Two eyes showed discernible 20/20 E's even at the 12.5% contrast level. Little to no ghost image was seen. Two eyes showed degraded but discernible 20/20 letters at higher levels of contrast only. These eyes showed moderate ghost images that were most apparent in the high-contrast 20/80 letters. One eye showed poor resolution of the 100% contrast 20/20 letter and moderately severe ghost images.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2043557

  12. Corneal Regeneration After Photorefractive Keratectomy: A Review.

    PubMed

    Tomás-Juan, Javier; Murueta-Goyena Larrañaga, Ane; Hanneken, Ludger

    2015-01-01

    Photorefractive keratectomy (PRK) remodels corneal stroma to compensate refractive errors. The removal of epithelium and the ablation of stroma provoke the disruption of corneal nerves and a release of several peptides from tears, epithelium, stroma and nerves. A myriad of cytokines, growth factors, and matrix metalloproteases participate in the process of corneal wound healing. Their balance will determine if reepithelization and stromal remodeling are appropriate. The final aim is to achieve corneal transparency for restoring corneal function, and a proper visual quality. Therefore, wound-healing response is critical for a successful refractive surgery. Our goal is to provide an overview into how corneal wounding develops following PRK. We will also review the influence of intraoperative application of mitomycin C, bandage contact lenses, anti-inflammatory and other drugs in preventing corneal haze and post-PRK pain. PMID:25444646

  13. Corneal Regeneration After Photorefractive Keratectomy: A Review☆

    PubMed Central

    Tomás-Juan, Javier; Murueta-Goyena Larrañaga, Ane; Hanneken, Ludger

    2014-01-01

    Photorefractive keratectomy (PRK) remodels corneal stroma to compensate refractive errors. The removal of epithelium and the ablation of stroma provoke the disruption of corneal nerves and a release of several peptides from tears, epithelium, stroma and nerves. A myriad of cytokines, growth factors, and matrix metalloproteases participate in the process of corneal wound healing. Their balance will determine if reepithelization and stromal remodeling are appropriate. The final aim is to achieve corneal transparency for restoring corneal function, and a proper visual quality. Therefore, wound-healing response is critical for a successful refractive surgery. Our goal is to provide an overview into how corneal wounding develops following PRK. We will also review the influence of intraoperative application of mitomycin C, bandage contact lenses, anti-inflammatory and other drugs in preventing corneal haze and post-PRK pain. PMID:25444646

  14. Role of epithelial hyperplasia in regression following photorefractive keratectomy.

    PubMed Central

    Gauthier, C. A.; Holden, B. A.; Epstein, D.; Tengroth, B.; Fagerholm, P.; Hamberg-Nyström, H.

    1996-01-01

    AIM--To determine the relation between epithelial hyperplasia and regression of effect after photorefractive keratectomy (PRK). METHODS--Seventy unilaterally treated patients with PRK were examined. All eyes had been treated with the Summit excimer laser 27 (SD 7) months previously with zone diameters of 4.1 to 5.0 mm. The untreated fellow eyes served as controls. Epithelial thickness was measured centrally with a thin slit optical pachometer and manifest subjective refraction was performed. RESULTS--The epithelium was 21% thicker in the treated eye (p < 0.0001). The relation between refractive regression and epithelial hyperplasia was significant (r = 0.41; p < 0.001). CONCLUSIONS--Epithelial hyperplasia after PRK correlated with the myopic shift (including hyperopia reduction) after treatment with the Summit laser. A model is proposed suggesting that both subepithelial and epithelial layers contribute to regression in the Summit treated eyes with 18 microns of epithelial hyperplasia contributing each dioptre of regression. PMID:8759267

  15. Corneal Aberrations Before and After Photorefractive Keratectomy

    PubMed Central

    Rosa, Nicola; De Bernardo, Maddalena; Lanza, Michele; Borrelli, Maria; Fusco, Fabrizia; Flagiello, Antimo

    2010-01-01

    Purpose To determine whether - and which - higher-order corneal aberrations, up to the sixth order, are induced by photorefractive keratectomy (PRK). Methods 197 eyes of 197 patients have been examined with a corneal aberrometer for a 3.5 and a 6.0 mm pupil simulation, both before and 1, 3, 6 months after myopic PRK treatment ranging from −15.25 D to -0.5 D (mean −5.31±2.95 D). The statistical evaluation was performed using a paired Student's T-test. Results After PRK there is a clear-cut increase in almost all the higher-order corneal aberrations for both a 3.5 and a 6.0 mm pupil simulation. These aberrations tend to normalize after 3 and 6 months mainly for a 3.5 mm simulation, whereas such normalization is not present for a 6.0 mm simulation. Conclusions PRK induces significant aberrations both for 3.5 and 6 mm pupils, 1 month after PRK, but a trend towards normalization is evident at the 6 month follow-up for the smaller pupil size.

  16. Effect of ablation profile on wound healing and visual performance 1 year after excimer laser photorefractive keratectomy.

    PubMed Central

    Corbett, M C; Verma, S; O'Brart, D P; Oliver, K M; Heacock, G; Marshall, J

    1996-01-01

    BACKGROUND: Early photorefractive keratectomy ablations were of limited diameter and depth to maintain the integrity of the globe and to minimise postoperative haze. This study evaluated the effects of deeper, larger diameter wounds on refractive stability and corneal haze, and investigated the effects of ablation profile on wound healing and visual performance. METHODS: One hundred patients undergoing -3.00D and -6.00D corrections were randomised to receive 5 mm, 6 mm, or multizone treatments. The multizone treatment was 6 mm in diameter, but only the depth of the 5 mm treatment. Outcome was measured by Snellen visual acuity, residual refractive error, objective techniques for haze and halos, pupil diameter, subjective night vision, and requirement for retreatment. RESULTS: Overall, the results of 6 mm treatments were superior to those of 5 mm and multizone treatments: they had a smaller hyperopic shift (p < 0.01), a more predictable (p < 0.001) and stable refractive outcome, less haze (p < 0.05), smaller halos (p < 0.05), fewer subjective night vision problems, and fewer patients required retreatment. CONCLUSIONS: Analysis of these data and a literature review of corneal wound healing demonstrated that the improved outcome associated with the 6 mm beam did not relate to the depth of ablation. The factor with greatest apparent influence on the development of haze and regression was the slope of the wound surface over the entire area of the ablation. Tapering the wound edge provided no additional benefit, and contributed to night vision problems. It is, therefore, recommended that small diameter or multizone treatments should not be used in low and moderate myopia. PMID:8703860

  17. High-speed photorefractive keratectomy with femtosecond ultraviolet pulses

    NASA Astrophysics Data System (ADS)

    Danieliene, Egle; Gabryte, Egle; Vengris, Mikas; Ruksenas, Osvaldas; Gutauskas, Algimantas; Morkunas, Vaidotas; Danielius, Romualdas

    2015-05-01

    Femtosecond near-infrared lasers are widely used for a number of ophthalmic procedures, with flap cutting in the laser-assisted in situ keratomileusis (LASIK) surgery being the most frequent one. At the same time, lasers of this type, equipped with harmonic generators, have been shown to deliver enough ultraviolet (UV) power for the second stage of the LASIK procedure, the stromal ablation. However, the speed of the ablation reported so far was well below the currently accepted standards. Our purpose was to perform high-speed photorefractive keratectomy (PRK) with femtosecond UV pulses in rabbits and to evaluate its predictability, reproducibility and healing response. The laser source delivered femtosecond 206 nm pulses with a repetition rate of 50 kHz and an average power of 400 mW. Transepithelial PRK was performed using two different ablation protocols, to a total depth of 110 and 150 μm. The surface temperature was monitored during ablation; haze dynamics and histological samples were evaluated to assess outcomes of the PRK procedure. For comparison, analogous excimer ablation was performed. Increase of the ablation speed up to 1.6 s/diopter for a 6 mm optical zone using femtosecond UV pulses did not significantly impact the healing process.

  18. Preliminary results of tracked photorefractive keratectomy (T-PRK) for mild to moderate myopia with the autonomous technologies excimer laser at Cedars-Sinai Medical Center

    NASA Astrophysics Data System (ADS)

    Maguen, Ezra I.; Salz, James J.; Nesburn, Anthony B.

    1997-05-01

    Preliminary results of the correction of myopia up to -7.00 D by tracked photorefractive keratectomy (T-PRK) with a scanning and tracking excimer laser by Autonomous Technologies are discussed. 41 eyes participated (20 males). 28 eyes were evaluated one month postop. At epithelization day mean uncorrected vision was 20/45.3. At one month postop, 92.8 of eyes were 20/40 and 46.4% were 20/20. No eye was worse than 20/50. 75% of eyes were within +/- 0.5 D of emmetropia and 82% were within +/- 1.00 D of emmetropia. Eyes corrected for monovision were included. One eye lost 3 lines of best corrected vision, and had more than 1.00 D induced astigmatism due to a central corneal ulcer. Additional complications included symptomatic recurrent corneal erosions which were controlled with topical hypertonic saline. T-PRK appears to allow effective correction of low to moderate myopia. Further study will establish safety and efficacy of the procedure.

  19. Wound healing anomalies after excimer laser photorefractive keratectomy: correlation of clinical outcomes, corneal topography, and confocal microscopy.

    PubMed Central

    Steinert, R F

    1997-01-01

    PURPOSE: To further the understanding of wound healing anomalies affecting visual function after myopic photorefractive keratectomy (PRK). METHOD: Analysis of a clinical database of PRK on 133 eyes with myopia of -1.5 to -7.0 D and 43 eyes with myopia of -6.0 to -12.0 D. Visual function was analyzed by subgroups of 1) no topographic anomalies; 2) topographic central islands; and 3) topographic keyhole patterns. The natural course of healing was documented over 6 months with visual acuity measurements, clinical observation, and corneal topography. In vivo clinical-pathologic correlations were made by scanning confocal microscopy. RESULTS: Topographic anomalies were identified 1 month post-PRK in 48 eyes (40.3%) with low-moderate myopia and in 14 eyes (32.5%) with moderate-high myopia. For patients with 6 month follow-up, these rates declined to 25% and 23%, respectively. At 1 month post-PRK, topographic anomalies significantly reduced uncorrected and best-corrected visual acuity and refractive predictability. By 6 months post-PRK, the small number of eyes with persistent anomalies had visual outcomes similar to patients with normal topography. A simple approach to anti-island pre-treatment reduced islands slightly and keyhole anomalies significantly (anti-island pre-treatment vs no pretreatment: islands 25% vs 31.8%; keyholes 2.3% vs 17.6%; p = 0.021) but with decreased predictability of induced refractive change at 1 month post-PRK. Confocal microscopy in vivo demonstrated prominent deposition of subepithelial extracellular material 1 to 2 months after PRK that diminished by 6 to 8 months, but persisted in the presence of central islands. Scar formation appeared to represent an elevated plaque of new collagen with active keratocytes. CONCLUSIONS: Topographic anomalies of wound healing are common after PRK. Vision and predictability are reduced by anomalies 1 month post-PRK but anomalies often resolve by 6 months. Marked improvement of vision occurs even when

  20. Spherical and aspherical photorefractive keratectomy and laser in-situ keratomileusis for moderate to high myopia: two prospective, randomized clinical trials. Summit technology PRK-LASIK study group.

    PubMed Central

    Steinert, R F; Hersh, P S

    1998-01-01

    OBJECTIVE: Determine the outcomes of single-zone photorefractive keratectomy (SZPRK), aspherical photorefractive keratectomy (ASPRK), and laser in-situ keratomileusis (LASIK) for the correction of myopia between -6 and -12 diopters. DESIGN: Two simultaneous prospective, randomized, multi-center clinical trials. PARTICIPANTS: 286 first-treated eyes of 286 patients enrolled in one of two studies. In Study I, 134 eyes were randomized to SZPRK (58 eyes) or ASPRK (76 eyes). In Study II, 152 eyes were randomized to ASPRK (76 eyes) or to LASIK (76 eyes). INTERVENTION: All eyes received spherical one-pass excimer laser ablation as part of PRK or LASIK performed with the Summit Technologies Apex laser under an investigational device exemption, with attempted corrections between -6 and -12 diopters. MAIN OUTCOME MEASURES: Data on uncorrected and best spectacle-corrected visual acuity, predictability and stability of refraction, and complications were analyzed. Follow-up was 12 months. RESULTS: At 1 month postoperatively, more eyes in the LASIK group achieved 20/20 and 20/25 or better uncorrected visual acuity than PRK-treated eyes; at the 20/25 or better level, the difference was significant for LASIK (29/76 eyes, 38%) over SZPRK (10/58 eyes, 17%) (P = .0064). At all subsequent postoperative intervals, no difference was seen between treatment groups. Similarly, best corrected visual acuities were better for LASIK than all PRK eyes at 1 month postoperatively, and LASIK was better than SZPRK at 3 months follow-up (e.g., for 20/20 or better at 1 month, LASIK 50/76 eyes (66%) versus SZPRK 24/57 eyes (42%), P = .0066). PRK eyes had a mean loss of BCVA through 6 months, while LASIK eyes had a slight gain of mean BCVA through month 6; at 12 months, both ASPRK groups but not SZPRK continued to have a small mean loss of BCVA (e.g., compared to preoperative, mean BCVA at 12 months for SZPRK was + 0.3, LASIK was +.21, ASPRK I was -0.11, and ASPRK II -0.31 (SZPRK versus ASPRK II, P

  1. Excimer laser photorefractive surgery of the cornea

    NASA Astrophysics Data System (ADS)

    Gaster, Ronald N.

    1998-09-01

    The 193 nm argon fluoride (ArF) excimer laser can effectively be used to change the radius of curvature of the cornea and thus alter the refractive state of the eye. This change allows myopic (nearsighted) patients to see well with less dependence on glasses or contact lenses. The two major techniques of laser refractive surgery currently in effect in the United States are photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). This paper will discuss these refractive cornea surgical techniques.

  2. Wavefront-Guided Laser in Situ Keratomileusis (Lasik) versus Wavefront-Guided Photorefractive Keratectomy (Prk): A Prospective Randomized Eye-to-Eye Comparison (An American Ophthalmological Society Thesis)

    PubMed Central

    Manche, Edward E.; Haw, Weldon W.

    2011-01-01

    Purpose To compare the safety and efficacy of wavefront-guided laser in situ keratomileusis (LASIK) vs photorefractive keratectomy (PRK) in a prospective randomized clinical trial. Methods A cohort of 68 eyes of 34 patients with −0.75 to −8.13 diopters (D) of myopia (spherical equivalent) were randomized to receive either wavefront-guided PRK or LASIK in the fellow eye using the VISX CustomVue laser. Patients were evaluated at 1 day, 1 week, and months 1, 3, 6, and 12. Results At 1 month, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), 5% and 25% contrast sensitivity, induction of higher-order aberrations (HOAs), and subjective symptoms of vision clarity, vision fluctuation, ghosting, and overall self-assessment of vision were worse (P<0.05) in the PRK group. By 3 months, these differences had resolved (P>0.05). At 1 year, mean spherical equivalent was reduced 94% to −0.27 ± 0.31 D in the LASIK group and reduced 96% to −0.17 ± 0.41 D in the PRK group. At 1 year, 91% of eyes were within ±0.50 D and 97 % were within ±1.0 D in the PRK group. At 1 year, 88% of eyes were within ±0.50 D and 97% were within ±1.0 D in the LASIK group. At 1 year, 97% of eyes in the PRK group and 94% of eyes in the LASIK group achieved an UCVA of 20/20 or better (P=0.72). Refractive stability was achieved in both PRK and LASIK groups after 1 month. There were no intraoperative or postoperative flap complications in the LASIK group. There were no instances of corneal haze in the PRK group. Conclusions Wavefront-guided LASIK and PRK are safe and effective at reducing myopia. At 1 month postoperatively, LASIK demonstrates an advantage over PRK in UCVA, BSCVA, low-contrast acuity, induction of total HOAs, and several subjective symptoms. At postoperative month 3, these differences between PRK and LASIK results had resolved. PMID:22253488

  3. A retrospective analysis of the postoperative use of loteprednol etabonate gel 0.5% following laser-assisted in situ keratomileusis or photorefractive keratectomy surgery

    PubMed Central

    Salinger, Clifford L; Gordon, Michael; Jackson, Mitchell A; Perl, Theodore; Donnenfeld, Eric

    2015-01-01

    Background While loteprednol etabonate ophthalmic gel 0.5% (LE gel) is approved for treatment of postoperative ocular inflammation and pain, there have been no reported studies in patients undergoing laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). Methods This was a retrospective chart review conducted at five refractive surgical centers in the USA. Data were collected from primary LASIK or PRK surgery cases in which LE gel was used postoperatively as the clinician’s routine standard of care and in which patients were followed-up for up to 6 months. Data extracted from charts included patient demographics, surgical details, LE gel dosing regimen, pre- and postsurgical refractive characteristics, intraocular pressure (IOP) measurements, and visual acuity. Primary outcomes included postoperative IOP elevations, adverse events, and early discontinuations. Results Data were collected on 189 LASIK eyes (96 patients) and 209 PRK eyes (108 patients). Mean (standard deviation [SD]) years of age at surgery was 36.0 (11.7) and 33.9 (11.3) in LASIK and PRK patients. LE gel was prescribed most often four times daily during the first postoperative week, regardless of procedure; the most common treatment duration was 7–14 days in LASIK and ≥30 days in PRK patients. No unusual corneal findings or healing abnormalities were reported. Mean postoperative uncorrected distance visual acuity was 20/24 in LASIK and 20/30 in PRK eyes. Mild/trace corneal haze was reported in 20% of PRK patients; two PRK patients with moderate/severe corneal haze were switched to another corticosteroid. Mean postoperative IOP did not increase over time in either LASIK or PRK eyes (P≥0.331); clinically significant elevations from baseline in IOP (≥10 mmHg) were noted in only three eyes of two PRK patients. Conclusion LE gel appears to have a high level of safety and tolerability when used for the management of postoperative pain and inflammation following LASIK

  4. Optical comparison of multizone and single-zone photorefractive keratectomy

    NASA Astrophysics Data System (ADS)

    Gonzalez-Cirre, Xochitl; Manns, Fabrice; Rol, Pascal O.; Parel, Jean-Marie A.

    1997-05-01

    The purpose is to calculate and compare the point-spread function and the central ablation depth (CAD) of a paraxial eye model after photo-refractive keratectomy (PRK), with single and multizone treatments. A modified Le Grand-El Hage paraxial eye model, with a pupil diameter ranging from 2 to 8 mm was used. Ray-tracing was performed for initial myopia ranging from 1 to 10D; after single zone PRK; after double zone PRK; and after tripe zone PRK. The ray-tracing of a parallel incident beam was calculated by using the paraxial matrix method. At equal CAD, the optical image quality is better after single zone treatments. Multizone treatments do not seem to be advantageous optically.

  5. Infectious keratitis after photorefractive keratectomy in a comanaged setting.

    PubMed

    Heidemann, D G; Clune, M; Dunn, S P; Chow, C Y

    2000-01-01

    A 48-year-old man had simultaneous bilateral photorefractive keratectomy (PRK). The surgeon who performed the PRK did not see the patient in follow-up, and there was confusion regarding the comanaging doctor. Therefore, the patient was not examined immediately postoperatively. Several days later, he was hospitalized for an unrelated, painful orthopedic problem and heavily sedated. Seven days after the PRK, an ophthalmologist was consulted for ocular irritation and discharge. Examination showed bilateral, purulent conjunctivitis and severe infectious keratitis in the left eye. The patient was treated with periocular and topical antibiotics. Corneal cultures yielded Staphylococcus aureus. The keratitis resolved slowly, leaving the patient with hand motion visual acuity. A corneal transplant and cataract extraction was performed 15 months later, resulting in a best corrected visual acuity of 20/400 because of glaucomatous optic nerve damage. Severe infectious keratitis may occur after PRK. Poor communication between the surgeon, comanaging doctor, and patient may result in treatment delay. PMID:10646160

  6. The results of photorefractive keratectomy with Mitomycin-C in myopia correction after 5 years

    PubMed Central

    Hashemi, Masih; Amiri, Mohammad Aghazadeh; Tabatabaee, Mehdi; Ayatollahi, Ali

    2016-01-01

    Objective: To evaluate the results of photorefractive keratectomy (PRK) with mitomycin C in myopia correction after five years. Methods: This is a cross sectional study which included 145 eyes of 74 patients in 18 to 51 years age group that were undergoing Photorefractive keratectomy with mitomycin C using Allegretto Wave Eye-Q 400-Hz excimer laser platform in Markazi Eye Center, Tehran, Iran. All the surgical procedures were performed by the same surgeon. After five years follow-up evaluation including BCVA, UCVA, Refractive error measurement and external eye examination was performed. Results: The mean diopter of spherical equivalent before surgery was -3.40±1.73. The following findings were obtained after 5 years follow up visit: The mean spherical equivalent value: -0.08±0.40, the mean: Log MARUCVA: 0.02±0.07, the mean Log MAR BCVA: 0.00±0.04. Conclusion: PRK is an effective, safe and predictable method used to correct myopia. The wave front-optimized algorithm of the Allegretto Wave Eye-Q 400-Hz excimer laser platform demonstrated good refractive and visual results. Presence of variables such as gender, age and astigmatism before operation have no significant impact on the result of this operation. PMID:27022380

  7. Complications after procedures of photorefractive keratectomy

    NASA Astrophysics Data System (ADS)

    Gierek-Ciaciura, Stanislawa

    1998-10-01

    Purpose: The aim of this study was to investigate the saveness of the PRK procedures. Material and method: 151 eyes after PRK for correction of myopia and 112 after PRK for correction of myopic astigmatism were examined. All PRK procedures have been performed with an excimer laser manufactured by Aesculap Meditec. Results: Haze, regression, decentration infection and overcorrection were found. Conclusions: The most often complication is regression. Corneal inflammation in the early postoperative period may cause the regression or haze. The greater corrected refractive error the greater haze degree. Haze decreases with time.

  8. [Corneal reinnervation after lamellar keratoplasty in comparison with epikeratophakia and photorefractive keratectomy].

    PubMed

    Böhm, A; Kohlhaas, M; Kliefoth, U; Draeger, J; Lombardi, M; Abbondanza, M; Zuppardo, M; Görne, M

    1994-10-01

    Corneal sensitivity was examined with the Draeger aesthesiometer in 8 patients after lamellar keratoplasty, 7 patients after epikeratophakia and 82 patients after photorefractive keratectomy. We examined 9 different points in each cornea. The corneal sensitivity of patients after lamellar keratoplasty was normal 1 year after operation. A correlation with the depth of the lamellar dissection was demonstrated. Patients with lamellar keratoplasty with pterygium showed a sensitivity decrease in the nasal parts of the lenticule even after one year. Three years after epikeratophakia the corneal center was still not sensitive. After photorefractive keratectomy of more than 10 D, corneal hyposensitivity was shown even 2 years after operation. PMID:7812096

  9. Use of angle kappa in myopic photorefractive keratectomy

    PubMed Central

    Khakshoor, Hamid; McCaughey, Michael V; Vejdani, Amir Hossein; Daneshvar, Ramin; Moshirfar, Majid

    2015-01-01

    Purpose To explore utilization of the coaxially sighted corneal light reflex (CSCLR) for centration during myopic photorefractive keratectomy (PRK) for patients with relatively high angle kappa (κ) values. Methods Patients were stratified into two groups preoperatively, on the basis of angle κ values. Group A was composed of 166 eyes with an angle κ value <5°. Group B consisted of 182 eyes with an angle κ value >5°. Intraoperative centering of ablation was performed within group A by utilizing the pupillary center, and within group B by using the CSCLR. Visual acuities were evaluated and compared at 6 months and 12 months postoperatively between groups. Results Mean uncorrected visual acuities (UCVA) for all patients at 6 months and 12 months were −0.073 logMAR and −0.080 logMAR, respectively. A total of 98.9% of patients had a UCVA of 0.00 logMAR (≈20/20 Snellen) 12 months postoperatively. There was not a significant between-group difference in regard to residual refractive error at 6 months or 12 months (P=0.53 and P=0.97), or in UCVA at 6 months and 12 months (P=0.76 and P=0.17). There were no subjective complaints of monocular diplopia, glare, or haloes within either group at any time during follow-up. Conclusion Availing use of the CSCLR for centration of ablation within myopic patients with high angle κ values may aid in providing better refractive outcomes after performance of PRK. PMID:25678767

  10. [Effects some drugs of re-epithelialization in the early postoperative period after photorefraction keratectomy].

    PubMed

    Kurenkov, V V; Smirennaia, E V; Polunin, G S; Makarov, I A

    1999-01-01

    Terms of re-epithelialization, severity of the painful syndrome, intensity of corneal "crepe" (opacity) are assessed in myopic patients treated by maxitrol, eubetal, colbiocin ointments and maxitrol eyedrops in the early postoperative period after photorefraction keratectomy. The crepe intensity was assessed routinely according to a clinical score: 0) transparent cornea, 1) trace crepe; 2) moderate crepe; and 3) intensive crepe. Biomicroscopy on day 4 after photorefraction keratectomy showed complete epithelialization in 91.7% patients after colbiocin ointment, in 91.% after maxitrol eyedrops, 87% after eubetal ointment, and 82.6% after maxitrol ointment. The least corneal opacity (0 and 0-1) was observed after eubetal ointment and maxitrol eyedrops. The mean score for pain was virtually the same in all groups; in the colbiocin ointment group more patients complained of pain for more than 24 h in comparison with other groups. PMID:10665290

  11. Effectiveness of Scraping and Mitomycin C to Treat Haze After Myopic Photorefractive Keratectomy

    PubMed Central

    Spadea, Leopoldo; Verrecchia, Valerio

    2011-01-01

    To report the possibility of post myopic photorefractive keratectomy (PRK) haze treatment in a patient with expressed reluctance for any additional laser therapy. Seven months after bilateral PRK with subsequent development of corneal haze and refractive regression in both eyes, a 37-old-year male patient presented a best-spectacle corrected visual acuity (BSCVA) of 20/30 in the right eye and of 20/22 in the left eye. Both eyes were sequentially treated by scraping the stromal surface and application of mitomycin C (MMC) for 2 minutes. Both eyes had significant improvement in corneal transparency. Eighteen months after this treatment BSCVA had improved to 20/20 in each eye. No toxic effects were observed during either re-epithelialization or follow-up periods. In conclusion scraping and application of MMC could be considered a good tool in the treatment of selected cases of haze after myopic PRK, especially with patients that are reluctant to undergo a secondary laser procedure. PMID:22262990

  12. Risk factors of regression and undercorrection in photorefractive keratectomy: a case-control study

    PubMed Central

    Mohammadi, Seyed-Farzad; Nabovati, Payam; Mirzajani, Ali; Ashrafi, Elham; Vakilian, Banafsheh

    2015-01-01

    AIM To determine risk factors of regression and undercorrection following photorefractive keratectomy (PRK) in myopia or myopic astigmatism. METHODS A case-control study was designed in which eyes with an indication for re-treatment (RT) were defined as cases; primary criteria for RT indication, as assessed at least 9mo postoperatively, included an uncorrected distance visual acuity (UDVA) of 20/30 or worse and a stable refraction for more than 3mo. Additional considerations included optical quality symptoms and significant higher order aberrations (HOAs). Controls were chosen from the same cohort of operated eyes which had complete post-operative follow up data beyond 9mo and did not need RT. The cohort included patients who had undergone PRK by the Tissue-Saving (TS) ablation profile of Technolas 217z100 excimer laser (Bausch & Lomb, Rochester, NY, USA). Mitomycin C had been used in all of the primary procedures. RESULTS We had 70 case eyes and 158 control eyes, and they were comparable in terms of age, sex and follow-up time (P values: 0.58, 1.00 and 0.89, respectively). Pre-operative spherical equivalent of more than -5.00 diopter (D), intended optical zone (OZ) diameter of less than 6.00 mm and ocular fixation instability during laser ablation were associated with RT indications (all P values <0.001). These factors maintained their significance in the multiple logistic regression model with odd ratios of 6.12, 6.71 and 7.89, respectively. CONCLUSION Higher refractive correction (>-5.00 D), smaller OZ (<6.00 mm) and unstable fixation during laser ablation of PRK for myopia and myopic astigmatism were found to be strong predictors of undercorrection and regression. PMID:26558204

  13. Impact of corneal cross-linking combined with photorefractive keratectomy on blurring strength

    PubMed Central

    Labiris, Georgios; Sideroudi, Haris; Angelonias, Dimitris; Georgantzoglou, Kimonas; Kozobolis, Vassilios P

    2016-01-01

    Purpose The aim of this study was to evaluate the impact of corneal cross-linking combined with photorefractive keratectomy (PRK) on blurring strength. Methods A total of 63 patients with keratoconus were recruited for this study, and two study groups were formed according to the therapeutic intervention: corneal collagen cross-linking (CxL) group (33 patients) received corneal cross-linking according to the Dresden protocol, while the rest additionally received topography-guided photorefractive keratectomy (tCxL). The impact of surgical procedure on blurring strength was assessed by power vector analysis. Potential association between blurring strength and vision-specific quality of life was assessed using the National Eye Institute Visual Function Questionnaire (NEI-VFQ) 25 instrument. Results Blurring strength presented excellent correlation with NEI-VFQ scores both preoperatively and postoperatively (all P<0.01). Both groups demonstrated nonsignificant changes in best-corrected visual acuity; however, only the tCxL group had significant reduction in blurring strength (13.48+10.86 [preoperative], 4.26+7.99 [postoperative], P=0.042). Conclusion Only the combined treatment (tCxL) resulted in significant reduction in blurring strength. Moreover, the excellent correlation of blurring strength with NEI-VFQ scores indicates its reliability as an index of self-reported quality of life in keratoconus, since it seems to address the nonsignificant changes in best-corrected visual acuity following CxL treatments that are conceived as subjective improvement by the patient. PMID:27099464

  14. Corneal Complications During and After Vitrectomy for Retinal Detachment in Photorefractive Keratectomy Treated Eyes.

    PubMed

    Tosi, Gian Marco; Baiocchi, Stefano; Balestrazzi, Angelo; Martone, Gianluca; Marigliani, Davide; Neri, Giovanni; Caporossi, Tomaso

    2015-12-01

    To evaluate the occurrence of late-onset corneal haze (LOCH) after vitrectomy for rhegmatogenous retinal detachment (RRD) in photorefractive keratectomy (PRK)-treated eyes. This observational cohort study comprised 13 eyes of 13 patients who underwent vitrectomy for RRD and who had been subjected to PRK years earlier. The occurrence of LOCH was evaluated together with all the preoperative, intraoperative, and postoperative factors that could affect final corneal status. LOCH developed in 2 eyes. Both patients had undergone PRK for high myopia--one 3 years and the other 9 years prior to RRD. Both patients presented with RRD due to giant retinal tear and were subjected to scleral buckle, 20-gauge vitrectomy, and silicone oil tamponade. Three months after vitrectomy and 1 month after silicone oil removal they both developed LOCH. During vitreoretinal surgery neither of the 2 patients needed mechanical epithelial debridement. Intraoperative epithelial debridement was performed in 2 of the other patients of the series, who had undergone previous PRK for high myopia and had clear corneas at presentation; in 1 of them this manoeuvre hampered intraoperative visualization. Follow-up after retinal detachment surgery ranged from 6 to 156 months (mean, 37.5 months). Subepithelial corneal scarring may be reactivated many years after PRK. In our series this happened after vitrectomy. PMID:26683931

  15. Long Term Followup of Photorefractive Keratectomy with Adjuvant Use of Mitomycin C

    PubMed Central

    Diakonis, Vasilios F.; Kankariya, Vardhaman P.; Kymionis, George D.; Kounis, Georgios; Kontadakis, George; Gkenos, Eirineos; Grentzelos, Michael A.; Hajithanasis, George; Yoo, Sonia H.; Pallikaris, Ioannis G.

    2014-01-01

    Purpose. To study the long term refractive and visual outcomes of photorefractive keratectomy (PRK) with intraoperative application of mitomycin C (MMC). Methods. This study included 37 eyes who received myopic PRK; after photoablation, a sponge soaked in 0.02% MMC solution was applied in all corneas for 2 minutes. Efficacy, safety, predictability, and stability of PRK MMC were evaluated. Endothelial cell density was evaluated at the last postoperative interval. Results. Mean preoperative spherical equivalent (SEQ) was −6.03 ± 1.87 D (diopters) and reduced to −0.09 ± 0.53 D at the last postoperative examination. Mean followup was 44.73 ± 18.24 months. All the eyes were in the ±1.00 D of attempted versus achieved SEQ at the one-year follow-up interval. Furthermore, 95% of the eyes did not lose lines or gained 1 to 2 lines of CDVA, while 5% lost 1 line. At the third postoperative month, 89% of the eyes either were clear or had trace haze, while 4 eyes had mild haze; by the 12-month postoperative interval, none of the eyes demonstrated haze. Mean endothelial cell density (ECD) at the last postoperative interval was 2658 ± 153 cells/mm2. Conclusions. PRK, with intraoperative use of MMC, demonstrates stable refractive and visual outcomes up to 44 months after surgery. PMID:24868456

  16. Customized photorefractive keratectomy to correct high ametropia after penetrating keratoplasty: A pilot study

    PubMed Central

    De Rosa, Giuseppe; Boccia, Rosa; Santamaria, Carmine; Fabbozzi, Lorenzo; De Rosa, Luigi; Lanza, Michele

    2014-01-01

    Purpose To evaluate preliminarily the safety and efficacy of customized photorefractive keratectomy (PRK) to correct ametropia and irregular astigmatism after penetrating keratoplasty (PK). Methods This pilot study included five eyes of five patients with a mean spherical equivalent of −5.1 ± 1.46 D (range from −2.75 to −6.50 D). In all cases, ametropia and irregular astigmatism was corrected with topography-guided customized PRK. Ocular examinations with topographic analysis were performed preoperatively as well as at 1, 3 and 6 months after surgery. Results All eyes gained postoperatively at least three Snellen lines of uncorrected visual acuity. Mean refractive spherical equivalent was 0.62 ± 0.63 D (range from −0.25 to −1.75 D) at 6 months postoperatively. Conclusion Our pilot study suggests that customized PRK can be a safe and effective method for treating ametropia and irregular astigmatisms after PK. Future studies with larger samples and longer follow-ups should be performed to confirm these results. PMID:25151176

  17. Photorefractive keratectomy in patients with mild to moderate stable keratoconus: a five-year prospective follow-up study

    PubMed Central

    Chelala, Elias; Rami, Hala El; Dirani, Ali; Fadlallah, Ali; Fakhoury, Omar; Warrak, Elias

    2013-01-01

    Background The purpose of this study was to evaluate the visual outcome of photorefractive keratectomy (PRK) in patients with mild to moderate stable keratoconus and to assess the risk of progression of the disease after the excimer laser procedure. Methods In this prospective study, carried out at the Clemenceau Medical Center, an affiliate of Johns Hopkins International, in Beirut, Lebanon, 119 eyes from 72 patients with grade 1–2 keratoconus (Amsler–Krumeich classification) underwent PRK. Forty-seven patients had both eyes treated and 25 patients had one eye treated. The procedure was done using the Wavelight Eye Q Excimer laser. Uncorrected and best-corrected visual acuity, corneal topography, and pachymetry were assessed before the procedure and 3, 6, 12, 36, and 60 months after the procedure. Results Mean uncorrected visual acuity showed a statistically significant improvement (P < 0.05) at one, 3, and 5 years follow-up. One hundred and seventeen eyes (98.3%) showed no progression while two eyes (1.7%) showed progression of the disease at 5 years follow-up, as documented by corneal topography and pachymetry. These two eyes were treated with corneal collagen crosslinking. Conclusion PRK in mild to moderate keratoconus is a safe and effective procedure for improving uncorrected vision in patients with mild refractive errors. However, close follow-up of patients is needed to detect any progression of the disease. Longer follow-up is needed to assess the overall effect of this procedure on progression of the disease. PMID:24109172

  18. Comparative Study of Two Silicone Hydrogel Contact Lenses used as Bandage Contact Lenses after Photorefractive Keratectomy

    PubMed Central

    Razmjoo, Hasan; Abdi, Elham; Atashkadi, Sayna; Reza, Akhlaghi M; Reza, Peyman A; Akbari, Mojtaba

    2012-01-01

    Background: Silicon hydrogel bandage contact lenses are used to enhance epithelial healing, control surface-generated pain, and prevent epithelial erosions after refractive surgery. Considering the importance of faster reepithelialization in preventing complications of photorefractive keratectomy (PRK) and the fact that the features and specifications of these commercially-available lenses are different and their performance as a postoperative bandage lenses would be different also, the aim of this study was comparison the efficacy of senofilcon A and lotrafilcon A after PRK. Methods: In this prospective study, 44 patients with PRK in both eyes randomly received a silicon hydrogel contact lens of senofilcon A in one eye and lotrafilcon A in other eye. Then the epithelial defect size, visual acuity and subjective level of pain and discomfort were measured for both eyes and compared on day 1, 3 and 5 postoperatively. Results: There was no statistical difference in rate of reepithelialization between senofilcon A and lotrafilcon A (P > 0.05). The mean pain and discomfort index was significantly lower in eyes with senofilcon A (P < 0.05). The mean subjective visual scores were similar with both bandage contact lenses (BCLs) (P > 0.05). Conclusion: Silicon hydrogel BCLs are safe and effective for corneal reepithelialization and have great therapeutic outcome on visual outcomes after PRK. But, senofilcon A had better effect on postoperative pain and discomfort which made it superior than lotrafilcon A. However for more conclusive results, it is recommended to study larger sample size with evaluation the possible factors responsible for the obtained findings regarding postoperative pain and discomfort. PMID:23112899

  19. Excimer laser system Profile-500

    NASA Astrophysics Data System (ADS)

    Atejev, V. V.; Bukreyev, V. S.; Vartapetov, Serge K.; Semenov, A. D.; Sugrobov, V. A.; Turin, V. S.; Fedorov, Sergei N.

    1999-07-01

    The description of ophthalmological excimer laser system 'PROFILE-500' for photorefractive and physiotherapeutic keratectomy is presented. Excimer Laser Systems 'PROFILE- 500' are optical system that use ArF excimer lasers to perform photorefractive keratectomy or LASIK; surgical procedures used to correct myopia, hyperopia and astigmatism.

  20. Analysis of glycosaminoglycans in rabbit cornea after excimer laser keratectomy

    PubMed Central

    Kato, T.; Nakayasu, K.; Ikegami, K.; Obara, T.; Kanayama, T.; Kanai, A.

    1999-01-01

    BACKGROUND/AIMS—The biochemical basis for the development of subepithelial opacity of the cornea after excimer laser keratectomy has yet to be fully defined. The aim of this study was to evaluate the alterations of glycosaminoglycans (GAGs) after excimer laser keratectomy.
METHODS—Rabbit corneas were harvested on days 5, 10, 20, and 30 after excimer laser photoablation. The amount of main disaccharide units was determined by high performance liquid chromatography (HPLC). In addition, immunohistochemical studies were performed on corneal sections 20 days after the ablation.
RESULTS—The concentrations of ΔDi-0S at 5 and 10 days were significantly lower than before the ablation. ΔDi-6S showed a significant increase 5 days after the ablation but ΔDi-4S did not show any significant change. There was a significant increase in ΔDi-HA at 20 and 30 days after ablation. In immunohistochemistry, the positive staining for ΔDi-6S and hyaluronic acid was observed in the subepithelial region. These immunohistochemical results were well correlated with the HPLC findings.
CONCLUSIONS—The increase in chondroitin-6 sulphate and hyaluronic acid may be related to corneal subepithelial opacity after excimer laser keratectomy.

 PMID:10216064

  1. Laser-induced corneal cross-linking upon photorefractive ablation with riboflavin

    PubMed Central

    Kornilovskiy, Igor M; Kasimov, Elmar M; Sultanova, Ayten I; Burtsev, Alexander A

    2016-01-01

    Aim To estimate the biomechanical effect of the laser-induced cross-linking resulting from photorefractive ablation of the cornea with riboflavin. Methods Excimer laser ablation studies were performed ex vivo (32 eyes of 16 rabbits) by phototherapeutic keratectomy (PTK) and in vivo (24 eyes of 12 rabbits) by transepithelial photorefractive keratectomy (TransPRK), with and without riboflavin saturation of the stroma. Then, we performed corneal optical coherence tomography on 36 eyes of 18 patients with varying degrees of myopia at different times after the TransPRK was performed with riboflavin saturation of the stroma. Results Biomechanical testing of corneal samples saturated with riboflavin revealed cross-linking effect accompanied by the increase in tensile strength and maximum strength. PTK showed increase in tensile strength from 5.1±1.4 to 7.2±1.6 MPa (P=0.001), while Trans-PRK showed increase in tensile strength from 8.8±0.9 to 12.8±1.3 MPa (P=0.0004). Maximum strength increased from 8.7±2.5 to 12.0±2.8 N (P=0.005) in PTK and from 12.8±1.6 to 18.3±1.2 N (P=0.0004) in TransPRK. Clinical optical coherence tomography studies of the biomicroscopic transparent cornea at different times after TransPRK showed increased density in the surface layers of the stroma and membrane-like structure beneath the epithelium. Conclusion Photorefractive ablation of the preliminary corneal stroma saturation with riboflavin causes the effect of laser-induced cross-linking, which is attended with an increase in corneal tensile strength, maximum strength, increased density in the surface layers of the stroma, and formation of a membrane-like structure beneath the epithelium after TransPRK. PMID:27099467

  2. Efficacy of Wavefront-guided Photorefractive Keratectomy with Iris Registration for Management of Moderate to High Astigmatism by Advanced Personalized Treatment Nomogram

    PubMed Central

    Mohammadpour, Mehrdad; Hashemi, Hassan; Jabbarvand, Mahmoud; Rahmatnejad, Kamran; Sabet, Fatemeh Alsadat

    2016-01-01

    Purpose: To evaluate the efficacy of photorefractive keratectomy (PRK) using the advanced personalized treatment (APT) nomogram for correction of moderate to high astigmatism. Methods: This prospective interventional case series included 60 consecutive eyes of 30 patients undergoing wavefront-guided PRK (Zyoptix 217 Z100 excimer laser, Bausch & Lomb, Munich, Germany) using the APT nomogram and iris registration for myopic astigmatism. Mitomycin-C was applied intraoperatively in all eyes. Ophthalmic examination was performed preoperatively and 1, 3 and 6 months postoperatively. Results: Preoperatively, mean sphere was -1.68 ± 2.08 diopters (D), mean refractive astigmatism was -3.04 ± 1.05 D and mean spherical equivalent (SE) was -3.12 ± 1.77 D. Six months postoperatively, mean sphere was + 0.60 ± 0.64 D (P < 0.005), mean cylinder was -0.43 ± 0.46 D (P < 0.005) and mean SE was + 0.28 ± 0.48 D (P < 0.005). Hyperopic overcorrection (≥ +1.0 D) occurred in 3 (5%) eyes. Postoperatively, root mean square (RMS) of higher order aberrations (HOAs) was significantly increased (P = 0.041). RMS of spherical aberration (Z [4, 0]) showed no significant change after surgery (P = 0.972). Conclusion: Considering the acceptable residual refractive error, low rate of hyperopic overcorrection, acceptable uncorrected visual acuity, and low risk of postoperative corneal haze, PRK using the APT nomogram with iris registration and mitomycin-C use is a safe and effective modality for treatment of moderate to high astigmatism. PMID:27413491

  3. Clinical outcomes between optical path difference custom aspheric treatment and optimized prolate ablation photorefractive keratectomy in myopia exceeding 8 diopters

    PubMed Central

    Choi, B J; Park, Y M; Lee, J S

    2015-01-01

    Purpose Comparison of visual acuity, refractive, and wavefront outcomes associated with optimized prolate ablation (OPA) and optical path difference custom aspheric treatment (OPDCAT) algorithms for correction of myopia exceeding 8 diopters (D). Patients and Methods Patients were randomly assigned to have photorefractive keratectomy (PRK) with OPA (n=32) or OPDCAT (n=21) algorithms. Visual acuity, manifest refraction, ocular and corneal higher-order aberrations, corneal asphericity, modulated-transfer function, and point-spread function were compared 1, 3, and 6 months postoperatively. Results Mean manifest-refraction spherical equivalents at 6 months were −0.24 D in both groups. All patients in both groups had an uncorrected-distance visual acuity of 20/20 or better. Predictability (±1 D from intended refraction) at 6 months was 94% in the OPA group, and in the OPDCAT group it was 86%. The OPA group had less induced corneal and ocular spherical aberrations (SAs) than the OPDCAT group. Postoperative corneal asphericity change was lowest in the OPA group. Both the groups exhibited significantly-improved AreaRatio-Total value and insignificantly deteriorated AreaRatio-HO value throughout the postoperative period. The OPA group had significantly-higher AreaRatio-Total compared with OPDCAT group at both 1 and 6 months after the operation. Six months after surgery, the Strehl ratio had decreased in both groups, and there was no significant difference between the groups. Conclusion The OPA algorithms yielded higher-objective visual quality and predictability, induced less corneal and ocular SAs, and preserved more preoperative-corneal asphericity than the OPDCAT algorithms. PMID:25397788

  4. Military target task performance after wavefront-guided (WFG) and wavefront-optimized (WFO) photorefractive keratectomy (PRK)

    NASA Astrophysics Data System (ADS)

    Maurer, Tana; Deaver, Dawne; Howell, Christopher; Moyer, Steve; Nguyen, Oanh; Mueller, Greg; Ryan, Denise; Sia, Rose K.; Stutzman, Richard; Pasternak, Joseph; Bower, Kraig

    2014-06-01

    Major decisions regarding life and death are routinely made on the modern battlefield, where visual function of the individual soldier can be of critical importance in the decision-making process. Glasses in the combat environment have considerable disadvantages: degradation of short term visual performance can occur as dust and sweat accumulate on lenses during a mission or patrol; long term visual performance can diminish as lenses become increasingly scratched and pitted; during periods of intense physical trauma, glasses can be knocked off the soldier's face and lost or broken. Although refractive surgery offers certain benefits on the battlefield when compared to wearing glasses, it is not without potential disadvantages. As a byproduct of refractive surgery, elevated optical aberrations can be induced, causing decreases in contrast sensitivity and increases in the symptoms of glare, halos, and starbursts. Typically, these symptoms occur under low light level conditions, the same conditions under which most military operations are initiated. With the advent of wavefront aberrometry, we are now seeing correction not only of myopia and astigmatism but of other, smaller optical aberrations that can cause the above symptoms. In collaboration with the Warfighter Refractive Eye Surgery Program and Research Center (WRESP-RC) at Fort Belvoir and Walter Reed National Military Medical Center (WRNMMC), the overall objective of this study is to determine the impact of wavefront guided (WFG) versus wavefront-optimized (WFO) photorefractive keratectomy (PRK) on military task visual performance. Psychophysical perception testing was conducted before and after surgery to measure each participant's performance regarding target detection and identification using thermal imagery. The results are presented here.

  5. Wavefront-Guided Photorefractive Keratectomy with the Use of a New Hartmann-Shack Aberrometer in Patients with Myopia and Compound Myopic Astigmatism

    PubMed Central

    Schallhorn, Steven C.; Venter, Jan A.; Hannan, Stephen J.; Hettinger, Keith A.

    2015-01-01

    Purpose. To assess refractive and visual outcomes and patient satisfaction of wavefront-guided photorefractive keratectomy (PRK) in eyes with myopia and compound myopic astigmatism, with the ablation profile derived from a new Hartmann-Shack aberrometer. Methods. In this retrospective study, 662 eyes that underwent wavefront-guided PRK with a treatment profile derived from a new generation Hartmann-Shack aberrometer (iDesign aberrometer, Abbott Medical Optics, Inc., Santa Ana, CA) were analyzed. The preoperative manifest sphere ranged from −0.25 to −10.75 D, and preoperative manifest cylinder was between 0.00 and −5.25 D. Refractive and visual outcomes, vector analysis of the change in refractive cylinder, and patient satisfaction were evaluated. Results. At 3 months, 91.1% of eyes had manifest spherical equivalent within 0.50 D. The percentage of eyes achieving uncorrected distance visual acuity 20/20 or better was 89.4% monocularly and 96.5% binocularly. The mean correction ratio of refractive cylinder was 1.02 ± 0.43, and the mean error of angle was 0.00 ± 14.86° at 3 months postoperatively. Self-reported scores for optical side effects, such as starburst, glare, halo, ghosting, and double vision, were low. Conclusion. The use of a new Hartmann-Shack aberrometer for wavefront-guided photorefractive keratectomy resulted in high predictability, efficacy, and patient satisfaction. PMID:26504595

  6. Early outcomes after small incision lenticule extraction and photorefractive keratectomy for correction of high myopia

    PubMed Central

    Chan, Tommy C. Y.; Yu, Marco C. Y.; Ng, Alex; Wang, Zheng; Cheng, George P. M.; Jhanji, Vishal

    2016-01-01

    We prospectively compared visual and refractive outcomes in patients with high myopia and myopic astigmatism after small-incision lenticule extraction (SMILE) and photorefractive keratetctomy (PRK) with mitomycin C. Sixty-six eyes of 33 patients (mean age, 29.7 ± 5.6 years) were included (SMILE: 34 eyes, PRK 32 eyes). Preoperatively, no significant difference was noted in manifest spherical equivalent (p = 0.326), manifest sphere (p = 0.277), and manifest cylinder (p = 0.625) between both groups. At 1 month, there were significant differences in logMAR uncorrected distance visual acuity, efficacy index and manifest refraction spherical equivalent between SMILE and PRK (p ≤ 0.029). At 6 months, the logMAR corrected distance visual acuity (p = 0.594), logMAR uncorrected visual acuity (p = 0.452), efficacy index (p = 0.215) and safety index was (p = 0.537) was comparable between SMILE and PRK. Significant differences were observed in postoperative manifest spherical equivalent (p = 0.044) and manifest cylinder (p = 0.014) between both groups. At the end of 6 months, 100% of the eyes in SMILE group and 69% of the eyes in PRK group were within ±0.50 D of the attempted cylindrical correction. The postoperative difference vector, magnitude of error and absolute angle of error were significantly smaller after SMILE compared to PRK (p ≤ 0.040) implying a trend towards overcorrection of cylindrical correction following PRK. PMID:27601090

  7. Early outcomes after small incision lenticule extraction and photorefractive keratectomy for correction of high myopia.

    PubMed

    Chan, Tommy C Y; Yu, Marco C Y; Ng, Alex; Wang, Zheng; Cheng, George P M; Jhanji, Vishal

    2016-01-01

    We prospectively compared visual and refractive outcomes in patients with high myopia and myopic astigmatism after small-incision lenticule extraction (SMILE) and photorefractive keratetctomy (PRK) with mitomycin C. Sixty-six eyes of 33 patients (mean age, 29.7 ± 5.6 years) were included (SMILE: 34 eyes, PRK 32 eyes). Preoperatively, no significant difference was noted in manifest spherical equivalent (p = 0.326), manifest sphere (p = 0.277), and manifest cylinder (p = 0.625) between both groups. At 1 month, there were significant differences in logMAR uncorrected distance visual acuity, efficacy index and manifest refraction spherical equivalent between SMILE and PRK (p ≤ 0.029). At 6 months, the logMAR corrected distance visual acuity (p = 0.594), logMAR uncorrected visual acuity (p = 0.452), efficacy index (p = 0.215) and safety index was (p = 0.537) was comparable between SMILE and PRK. Significant differences were observed in postoperative manifest spherical equivalent (p = 0.044) and manifest cylinder (p = 0.014) between both groups. At the end of 6 months, 100% of the eyes in SMILE group and 69% of the eyes in PRK group were within ±0.50 D of the attempted cylindrical correction. The postoperative difference vector, magnitude of error and absolute angle of error were significantly smaller after SMILE compared to PRK (p ≤ 0.040) implying a trend towards overcorrection of cylindrical correction following PRK. PMID:27601090

  8. Excimer laser superficial keratectomy for proud nebulae in keratoconus.

    PubMed

    Moodaley, L; Liu, C; Woodward, E G; O'Brart, D; Muir, M K; Buckley, R

    1994-06-01

    Contact lens intolerance in keratoconus may be due to the formation of a proud nebula at or near the apex of the cone. Excimer laser superficial keratectomy was performed as an outpatients with proud nebulae as treatment patients with proud nebulae as treatment for their contact lens intolerance. The mean period of contact lens wear before the development of intolerance was 13.4 years (range 2 to 27 years). Following the development of intolerance, three patients abandoned contact lens wear in the affected eye while the remainder experienced a reduction in comfortable wearing time (mean = 3.75 hours; range: 0-14 hours). All patients had good potential Snellen visual acuity with a contact lens of 6/9 (nine eyes) and 6/12 (one eye). The proud nebulae were directly ablated with a 193 nm ArF excimer laser using a 1 mm diameter beam. Between 100-150 pulses were sufficient to ablate the raised area. Patients experienced no pain during the procedure and reported minimal discomfort postoperatively. In all cases flattening of the proud nebulae was achieved. Seven patients were able to resume regular contact lens wear (mean wearing time = 10.17 hours; range 8 to 16 hours). In three patients, resumption of contact lens wear was unsuccessful because of cone steepness. All patients achieved postoperative Snellen visual acuity of 6/12 or better with a contact lens. Four patients experienced a loss of one line in Snellen acuity. The mean follow up period was 8.3 months (range 2 to 17 months). Excimer laser superficial keratectomy is a useful technique for the treatment of contact lens intolerance caused by proud nebulae in patients with keratoconus. Penetrating keratoplasty is thus avoided. PMID:8060928

  9. Excimer laser superficial keratectomy for proud nebulae in keratoconus.

    PubMed Central

    Moodaley, L; Liu, C; Woodward, E G; O'Brart, D; Muir, M K; Buckley, R

    1994-01-01

    Contact lens intolerance in keratoconus may be due to the formation of a proud nebula at or near the apex of the cone. Excimer laser superficial keratectomy was performed as an outpatients with proud nebulae as treatment patients with proud nebulae as treatment for their contact lens intolerance. The mean period of contact lens wear before the development of intolerance was 13.4 years (range 2 to 27 years). Following the development of intolerance, three patients abandoned contact lens wear in the affected eye while the remainder experienced a reduction in comfortable wearing time (mean = 3.75 hours; range: 0-14 hours). All patients had good potential Snellen visual acuity with a contact lens of 6/9 (nine eyes) and 6/12 (one eye). The proud nebulae were directly ablated with a 193 nm ArF excimer laser using a 1 mm diameter beam. Between 100-150 pulses were sufficient to ablate the raised area. Patients experienced no pain during the procedure and reported minimal discomfort postoperatively. In all cases flattening of the proud nebulae was achieved. Seven patients were able to resume regular contact lens wear (mean wearing time = 10.17 hours; range 8 to 16 hours). In three patients, resumption of contact lens wear was unsuccessful because of cone steepness. All patients achieved postoperative Snellen visual acuity of 6/12 or better with a contact lens. Four patients experienced a loss of one line in Snellen acuity. The mean follow up period was 8.3 months (range 2 to 17 months). Excimer laser superficial keratectomy is a useful technique for the treatment of contact lens intolerance caused by proud nebulae in patients with keratoconus. Penetrating keratoplasty is thus avoided. Images PMID:8060928

  10. One-Year Results of Simultaneous Topography-Guided Photorefractive Keratectomy and Corneal Collagen Cross-Linking in Keratoconus Utilizing a Modern Ablation Software

    PubMed Central

    Sherif, A. M.; Ammar, M. A.; Mostafa, Y. S.; Gamal Eldin, S. A.; Osman, A. A.

    2015-01-01

    Purpose. To evaluate effectiveness of simultaneous topography-guided photorefractive keratectomy and corneal collagen cross-linking in mild and moderate keratoconus. Methods. Prospective nonrandomized interventional study including 20 eyes of 14 patients with grade 1-2 keratoconus that underwent topography-guided PRK using a Custom Ablation Transition Zone (CATz) profile with 0.02% MMC application immediately followed by standard 3 mw/cm2 UVA collagen cross-linking. Maximum ablation depth did not exceed 58 μm. Follow-up period: 12 months. Results. Progressive statistically significant improvement of UCVA from 0.83 ± 0.37 logMAR preoperative, reaching 0.25 ± 0.26 logMAR at 12 months (P < 0.001). Preoperative BCVA (0.27 ± 0.31 logMAR) showed a progressive improvement reaching 0.08 ± 0.12 logMAR at 12 months (P = 0.02). Mean Kmax reduced from 48.9 ± 2.8 to 45.4 ± 3.1 D at 12 months (P < 0.001), mean Kmin reduced from 45.9 ± 2.8 D to 44.1 ± 3.2 D at 12 months (P < 0.003), mean keratometric asymmetry reduced from 3.01 ± 2.03 D to 1.25 ± 1.2 D at 12 months (P < 0.001). The safety index was 1.39 at 12 months and efficacy index 0.97 at 12 months. Conclusion. Combined topography-guided PRK and corneal collagen cross-linking are a safe and effective option in the management of mild and moderate keratoconus. Precis. To our knowledge, this is the first published study on the use of the CATz ablation system on the Nidek Quest excimer laser platform combined with conventional cross-linking in the management of mild keratoconus. PMID:26366293

  11. Effect of Photorefractive Keratectomy on Optic Nerve Head Topography and Retinal Nerve Fiber Layer Thickness Measured by Heidelberg Retina Tomograph 3

    PubMed Central

    Nilforushan, Naveed; Azadi, Pejvak; Soudi, Reza; Shaheen, Yahya; Sheibani, Kourosh

    2016-01-01

    Purpose: To determine whether photorefractive keratectomy (PRK) has a significant effect on optic nerve head (ONH) parameters and peripapillary retinal nerve fiber layer (RNFL) thickness measured by the Heidelberg Retina Tomograph 3 (Heidelberg Engineering GmbH, Heidelberg, Germany) in eyes with low to moderate myopia. Methods: This prospective, interventional case series, includes 43 consecutive myopic eyes which were assessed on the day of PRK and 3 months postoperatively using the HRT3. Among the stereometric parameters, we compared disc area, linear cup disc ratio, cup shape measure, global rim area, global rim volume, RNFL height variation contour and mean RNFL thickness; out of the Glaucoma Probability Score (GPS) we assessed changes in global value, rim steepness temporal/superior, and temporal/inferior, as well as cup size and cup depth before and after PRK. Results: Mean refractive error before and after PRK were −3.24 ± 1.31 and −0.20 ± 0.42 diopters, respectively. No significant change occurred in disc area, linear cup disc ratio, cup shape measure, rim area and rim volume among the stereometric parameters; and in rim steepness temporal/superior and rim steepness temporal/inferior in the GPS before and after PRK using the default average keratometry. However, RNFL height variation contour, mean RNFL thickness, and cup size and depth were significantly altered after PRK (P < 0.05). Conclusion: PRK can affect some HRT3 parameters. Although the most important stereometric parameters for differentiating normal, suspect or glaucomatous patients such as rim and cup measurements in stereometric parameters were not changed. PMID:27413492

  12. Automated superficial lamellar keratectomy augmented by excimer laser masked PTK in the management of severe superficial corneal opacities

    PubMed Central

    Alio, J L; Javaloy, J; Merayo, J; Galal, A

    2004-01-01

    Aim: To assess superficial lamellar keratectomy augmented by excimer laser smoothening with sodium hyaluronate 0.25%, for the management of superficial corneal opacities. Methods: Consecutive procedure performed in 14 eyes (13 patients) with an automated microkeratome and excimer laser phototherapeutic keratectomy (PTK) smoothening using sodium hyaluronate 0.25%. Main outcome measures: UCVA, BCVA, pachymetry, degree of haze, ray tracing analysis, and complications. Mean follow up was 12 (SD 1.6) months. Results: Mean preoperative haze from previous corneal refractive surgeries was 3.5 (SD 0.5) (11/14 cases). In one case, opacity was caused by ocular trauma and in two by infectious keratitis. The mean preoperative UCVA was 0.7 logMAR (0.2 (SD 0.13) decimal value). BCVA was 0.4 logMAR (0.4 (SD 0.17) decimal value). Mean preoperative corneal pachymetry was 508 (SD 62.5) µm and mean opacity depth measured by corneal confocal microscopy was 115.2 (SD 49.4) µm. At 6 months, 71.4% of the eyes with previous corneal refractive surgery showed grade I haze or less. Mean postoperative corneal pachymetry at 6 months was 352.36 (SD 49.05) µm. Conclusions: Automated superficial lamellar keratectomy combined with excimer laser PTK smoothening assisted by sodium hyaluronate 0.25% induces a significant improvement of corneal transparency and visual acuity in cases of corneal opacity caused by previous refractive surgery, ocular trauma, and keratitis. PMID:15377553

  13. Efficient local fixing of photorefractive polymer hologram using a laser beam.

    PubMed

    Li, Guoqiang; Wang, Peng

    2010-03-15

    We propose and demonstrate a novel technique for efficient local fixing of photorefractive polymer hologram using a laser beam. In the technique, a CO(2) laser beam is used to heat the sample and a local hologram can be fixed easier than previous methods. By using thinner glass substrates for the photorefractive device, the hologram can be fixed efficiently and at much faster speed. The fixation efficiency can be greater than 80% and the hologram can be fixed in the order of a second. This technique is critical for dynamic holographic three-dimensional display and holographic data storage. PMID:20383297

  14. Phototherapeutic keratectomy

    PubMed Central

    Rathi, Varsha M; Vyas, Sharadini P; Sangwan, Virender S

    2012-01-01

    Phototherapeutic keratectomy (PTK) is done regularly for anterior corneal diseases such as corneal dystrophies, corneal degenerations, scars, and band-shaped keratopathy. The various indications include both therapeutic and visual. The aim of this article is to discuss the therapeutic indications for PTK, the specific technique pertaining to a specific etiology, the various other procedures like amniotic membrane graft combined with PTK or PTK being done for recurrences in the grafts, and PTK done before cataract surgery when the anterior corneal pathology coexists with the cataract. Post PTK management such as healing of an epithelial defect, use of steroids in the post PTK period, recurrences of primary disease pathology, and infections, will be discussed. Methods of literature search: A Medline search was carried out for articles in the English language, with the keywords, phototherapeutic keratectomy, band-shaped keratopathy, spheroidal degeneration, scars, bullous keratopathy, and corneal dystrophy. The relevant references are mentioned here. PMID:22218239

  15. Photorefractive Semiconductors and Applications

    NASA Technical Reports Server (NTRS)

    Chen, Li-Jen; Luke, Keung L.

    1993-01-01

    Photorefractive semiconductors are attractive for information processing, becuase of fast material response, compatibility with semiconductor lasers, and availability of cross polarization diffraction for enhancing signal-to-noise ration. This paper presents recent experimental results on information processing using photorefractive GaAs, InP and CdTe, including image processing with semiconductor lasers.

  16. The photorefractive effect

    SciTech Connect

    Pepper, D.M. ); Kukhtarev, N.V. )

    1990-10-01

    When Arthur Ashkin and his colleagues at Bell Laboratories first noticed the photorefractive effect some 25 years ago, they considered the phenomenon a curiosity at best and a complete nuisance at worst. Today photorefractive materials are being shaped into components for a new generation of computers that exploit light instead of electricity. During the past 25 years investigators have discovered a wide variety of photorefractive materials, including insulators, semiconductors and organic compounds. Photorefractive materials, like film emulsions, change rapidly when exposed to bright light, respond slowly when subjected to dim light and capture sharp detail when struck by some intricate pattern of light. Unlike film, photorefractive materials are erasable: images can be stored or obliterated at whim or by design. By virtue of their sensitivity, robustness, and unique optical properties, photorefractive materials have the potential to be fashioned into data-processing elements for optical computers. In theory, these devices would allow optical computers to process information at much faster rates than their electronic counterparts. Employing photorefractive materials, workers have already developed the optical analogue to the transistor: if two laser beams interact within a photorefractive material, one beam can control, switch or amplify the second beam. Photorefractive materials also lie at the heart of devices that trace the edges of images, that connect networks of lasers and that store three-dimensional images.

  17. Optical trapping/modification of nano-(micro)particles by gradient and photorefractive forces during laser illumination

    NASA Astrophysics Data System (ADS)

    Kukhtarev, N.; Kukhtareva, T.; Okafor, F.

    2010-08-01

    In this paper we describe photo-induced trapping/redistribution of silver nano-(micro) particles near the surface of photorefractive crystal LiNbO3:Fe. This type of optical trapping is due to combined forces of direct gradient-force trapping and asymmetric photorefractive forces of electro-phoresis and dielectro-phoresis. The silver nanoparticles were produced through extracellular biosynthesis on exposure to the fungus, Fusarium oxysporum (FO) and to the plant extracts. Pulsed and CW visible laser radiation lead to significant modification of nanoparticle clusters. This study indicates that extracellular biosynthesis can constitute a possible viable alternative method for the production of nanoparticles. In addition, the theoretical modeling of asymmetric photorefractive electric field grating has been presented and compared with the experimental results.

  18. Ultrasound-modulated optical imaging using a photorefractive interferometer and a powerful long pulse laser

    NASA Astrophysics Data System (ADS)

    Rousseau, Guy; Blouin, Alain; Monchalin, Jean-Pierre

    2009-02-01

    Ultrasound-modulated optical imaging is an emerging biodiagnostic technique which provides the optical spectroscopic signature and the spatial localization of an optically absorbing object embedded in a strongly scattering medium. The transverse resolution of the technique is determined by the lateral extent of ultrasound beam focal zone while the axial resolution is obtained by using short ultrasound pulses. The practical application of this technique is presently limited by its poor sensitivity. Moreover, any method to enhance the signal-to-noise ratio must satisfy the biomedical safety limits. In this paper, we propose to use a pulsed single-frequency laser source to raise the optical peak power applied to the scattering medium and to collect more ultrasonically tagged photons. Such a laser source allows illuminating the tissues mainly during the transit time of the ultrasonic wave. A single-frequency Nd:YAG laser emitting 500-μs pulses with a peak power superior to 100 W was used. Tagged photons were detected with a GaAs photorefractive interferometer characterized by a large optical etendue. When pumped by high intensity laser pulses, such an interferometer provides the fast response time essential to obtain an apparatus insensitive to the speckle decorrelation encountered in biomedical applications. Consequently, the combination of a large-etendue photorefractive interferometer with a high-power pulsed laser could allow obtaining both the sensitivity and the fast response time necessary for biomedical applications. Measurements performed in 30- and 60-mm thick optical phantoms made of titanium dioxide particles dispersed in sunflower oil are presented. Results obtained in 30- and 60-mm thick chicken breast samples are also reported.

  19. Successful treatment of Fusarium keratitis after photo refractive keratectomy.

    PubMed

    Cavallini, Gian Maria; Ducange, Pietro; Volante, Veronica; Benatti, Caterina

    2013-11-01

    A 39-year-old woman presented to our hospital with a history of photorefractive keratectomy (PRK), performed two weeks prior; slit-lamp examination revealed diffuse conjunctival congestion, corneal ulcer and stromal infiltration. After 5 days of antifungal and antibacteric treatment, the infiltrate progressively increased so that a therapeutic penetrating keratoplasty was necessary. The microbiological analyses revealed the presence of fungal filaments. Twenty days after surgery the patient had recurrent fungal infiltrate in the donor cornea with wound dehiscence. We performed a second penetrating keratoplasty. With the matrix-assisted-laser-desorption-ionization-time-of-flight analysis (MALDI-TOF) we identified a Fusarium solani. Intravenous amphothericine B, a combination of intracameral and intrastromal voriconazole and intracameral amphotericine B were administered. After 6 months from the last surgery the infection was eradicated. The management of fungal keratitis after PRK depends on many factors: In our experience, a prompt keratoplasty and the use of intracameral antifungal medication proved to be very effective. PMID:24178402

  20. Successful treatment of Fusarium keratitis after photo refractive keratectomy

    PubMed Central

    Cavallini, Gian Maria; Ducange, Pietro; Volante, Veronica; Benatti, Caterina

    2013-01-01

    A 39-year-old woman presented to our hospital with a history of photorefractive keratectomy (PRK), performed two weeks prior; slit-lamp examination revealed diffuse conjunctival congestion, corneal ulcer and stromal infiltration. After 5 days of antifungal and antibacteric treatment, the infiltrate progressively increased so that a therapeutic penetrating keratoplasty was necessary. The microbiological analyses revealed the presence of fungal filaments. Twenty days after surgery the patient had recurrent fungal infiltrate in the donor cornea with wound dehiscence. We performed a second penetrating keratoplasty. With the matrix-assisted-laser-desorption-ionization-time-of-flight analysis (MALDI-TOF) we identified a Fusarium solani. Intravenous amphothericine B, a combination of intracameral and intrastromal voriconazole and intracameral amphotericine B were administered. After 6 months from the last surgery the infection was eradicated. The management of fungal keratitis after PRK depends on many factors: In our experience, a prompt keratoplasty and the use of intracameral antifungal medication proved to be very effective. PMID:24178402

  1. Lensometry by two-laser holography with photorefractive Bi12TiO20

    NASA Astrophysics Data System (ADS)

    Barbosa, Eduardo A.; Preto, André O.

    2008-04-01

    Refractive and profilometric measurements of lenses were performed through holography with a photorefractive Bi12TiO20 crystal as the recording medium. Two properly aligned diode lasers emitting in the red region were employed as light sources. Both lasers were tuned in order to provide millimetric and sub-millimetric synthetic wavelengths. The surfaces of the test lens were covered by a 25-μm opaque plastic tape in order to allow the lens profilometry upon illuminating them with a collimated beam. The resulting holographic images appear covered by interference fringes corresponding to the wavefront geometry of the wave scattered by the lens. For refractive index measurement a diffusely scattering flat surface was positioned behind the uncovered lens which was also illuminated by a plane wave. The resulting contour interferogram describes the form of the wavefront after the beam traveled back and forth through the lens. The fringe quantitative evaluation was carried out through the four-stepping technique and the resulting phase map and the Branch-cut method was employed for phase unwrapping. The only non-optical procedure for lens characterization was the thickness measurement, made by a dial caliper. Exact ray tracing calculation was performed in order to establish a relation between the output wavefront geometry and the lens parameters like radii of curvature, thickness and refractive index. By quantitatively comparing the theoretical wavefront geometry with the experimental results relative uncertainties bellow 3% for refractive index and 1 % for focal length were obtained.

  2. Photorefractivity in WGM resonators

    NASA Technical Reports Server (NTRS)

    Matsko, Andrey; Savchenkov, Anatoliy; Strekalov, Dmitry; Ilchenko, Vladimir; Maleki, Lute

    2006-01-01

    We report on observation of photorefractive effects in whispering gallery mode resonators made of as-grown and magnesium doped lithium niobate and lithium tantalate in the near as well as far infrared. The effects manifested themselves as dynamic modification of the spectra as well as quality factors of the resonators coupled to the laser radiation. We have observed a significant (exceeding 10-4) change of the ordinary index of refraction of all the materials exposed with 780 nm light. Photorefractive effects have also been detected at 1550 nm. Our experiments support the conclusion that the photorefractivity does not have a distinct red boundary. We show that the maximum saturated refractive index change in the infrared is of the same order of magnitude as in the visible light.

  3. Factors Affecting Long-term Myopic Regression after Laser In Situ Keratomileusis and Laser-assisted Subepithelial Keratectomy for Moderate Myopia

    PubMed Central

    Lim, Sung A; Park, Yooyeon; Cheong, Yu Jin; Na, Kyung Sun

    2016-01-01

    Purpose High myopia is known to be a risk factor for long-term regression after laser refractive surgery. There have been few studies about the correction of moderate myopias that did not need retreatment after long-term follow-up. We evaluated 10 years of change in visual acuity and refractive power in eyes with moderate myopia after laser refractive surgery. Methods We included patients that had undergone laser in situ keratomileusis (LASIK) or laser-assisted subepithelial keratectomy (LASEK) to correct their myopia and that had at least 10 years of follow-up. We evaluated the stability of visual acuity in terms of safety, efficacy, and refractive changes at examinations 6 months and 1, 2, 5, 7, and 10 years after surgery. Results The study evaluated 62 eyes (36 eyes in LASIK patients and 26 eyes in LASEK patients). In both groups, the efficacy index tended to decrease, and it was consistently higher in the LASEK group compared to the LASIK group over the 10 years of follow-up. The safety index improved over 10 years and was always higher than 0.9 in both groups. The difference between the spherical equivalent at 6 months postoperatively and later periods was statistically significant after 5, 7, and 10 years in both groups (LASIK, p = 0.036, p = 0.003, and p < 0.001, respectively; LASEK, p = 0.006, p = 0.002, and p = 0.001, respectively). Ten years after surgery,26 eyes (66.7%) in the LASIK group and 19 eyes (73.1%) in the LASEK group had myopia greater than 1 diopter. In comparison with the thickness at 6 months postoperatively, central corneal thickness was significantly increased after 5, 7, and 10 years in both LASIK and LASEK groups (LASIK, p < 0.001, p < 0.001, and p < 0.001, respectively; LASEK, p = 0.01, p < 0.001, and p < 0.001, respectively). Conclusions Moderately myopic eyes showed progressive myopic shifting and corneal thickening after LASIK and LASEK during 10 years of follow-up. We also found that early refractive regression may indicate the long

  4. Propagation characteristics of a focused laser beam in a strontium barium niobate photorefractive crystal under reverse external electric field.

    PubMed

    Guo, Q L; Liang, B L; Wang, Y; Deng, G Y; Jiang, Y H; Zhang, S H; Fu, G S; Simmonds, P J

    2014-10-01

    The propagation characteristics of a focused laser beam in a SBN:75 photorefractive crystal strongly depend on the signal-to-background intensity ratio (R=Is/Ib) under reverse external electric field. In the range 20>R>0.05, the laser beam shows enhanced self-defocusing behavior with increasing external electric field, while it shows self-focusing in the range 0.03>R>0.01. Spatial solitons are observed under a suitable reverse external electric field for R=0.025. A theoretical model is proposed to explain the experimental observations, which suggest a new type of soliton formation due to "enhancement" not "screening" of the external electrical field. PMID:25322227

  5. Digital photorefraction

    NASA Astrophysics Data System (ADS)

    Costa, Manuel F.; Jorge, Jorge M.

    1997-12-01

    The early evaluation of the visual status of human infants is of a critical importance. It is of utmost importance to the development of the child's visual system that she perceives clear, focused, retinal images. Furthermore if the refractive problems are not corrected in due time amblyopia may occur. Photorefraction is a non-invasive clinical tool rather convenient for application to this kind of population. A qualitative or semi-quantitative information about refractive errors, accommodation, strabismus, amblyogenic factors and some pathologies (cataracts) can the easily obtained. The photorefraction experimental setup we established using new technological breakthroughs on the fields of imaging devices, image processing and fiber optics, allows the implementation of both the isotropic and eccentric photorefraction approaches. Essentially both methods consist on delivering a light beam into the eyes. It is refracted by the ocular media, strikes the retina, focusing or not, reflects off and is collected by a camera. The system is formed by one CCD color camera and a light source. A beam splitter in front of the camera's objective allows coaxial illumination and observation. An optomechanical system also allows eccentric illumination. The light source is a flash type one and is synchronized with the camera's image acquisition. The camera's image is digitized displayed in real time. Image processing routines are applied for image's enhancement and feature extraction.

  6. Digital photorefraction

    NASA Astrophysics Data System (ADS)

    Costa, Manuel F. M.; Jorge, Jorge M.

    1998-01-01

    The early evaluation of the visual status of human infants is of a critical importance. It is of utmost importance to the development of the child's visual system that she perceives clear, focused, retinal images. Furthermore if the refractive problems are not corrected in due time amblyopia may occur. Photorefraction is a non-invasive clinical tool rather convenient for application to this kind of population. A qualitative or semi-quantitative information about refractive errors, accommodation, strabismus, amblyogenic factors and some pathologies (cataracts) can the easily obtained. The photorefraction experimental setup we established using new technological breakthroughs on the fields of imaging devices, image processing and fiber optics, allows the implementation of both the isotropic and eccentric photorefraction approaches. Essentially both methods consist on delivering a light beam into the eyes. It is refracted by the ocular media, strikes the retina, focusing or not, reflects off and is collected by a camera. The system is formed by one CCD color camera and a light source. A beam splitter in front of the camera's objective allows coaxial illumination and observation. An optomechanical system also allows eccentric illumination. The light source is a flash type one and is synchronized with the camera's image acquisition. The camera's image is digitized displayed in real time. Image processing routines are applied for image's enhancement and feature extraction.

  7. Therapeutic keratectomy for Mycobacterium abscessus keratitis after LASIK.

    PubMed

    Sun, Yi-Chen; Wang, I-Jong; Chen, Wei-Li; Hu, Fung-Rong

    2003-11-01

    We report successful treatment of a case of Mycobacterium abscessus keratitis after laser in situ keratomileusis (LASIK) with therapeutic lamellar keratectomy. A 34-year-old woman developed a 2 x 2 mm feathery infiltration within the interface inferior to the pupil margin with mild inflammation of the conjunctiva in her left eye 40 days after LASIK surgery. Bacterial culture from the infiltrates of the interface of the stromal bed revealed Mycobacterium abscessus. After combination antibiotic therapy including amikacin and ciprofoxacin was given for 6 weeks, infiltration persisted despite the development of necrosis in the flap tissue. Therapeutic lamellar keratectomy combined with flap removal was performed. No recurrence was found 1 year after the surgery. Therapeutic lamellar keratectomy with flap removal can provide an effective treatment modality for the management of post-LASIK Mycobacterium abscessus keratitis that is unresponsive to medical treatment. PMID:14724729

  8. Excimer laser phototherapeutic keratectomy in eyes with anterior corneal dystrophies: preoperative and postoperative ultrasound biomicroscopic examination and short-term clinical outcomes with and without an antihyperopia treatment.

    PubMed Central

    Rapuano, Christopher J

    2003-01-01

    PURPOSE: To evaluate the use of high-frequency ultrasound biomicroscopy (UBM) in determining the depth of corneal pathology in eyes undergoing excimer laser phototherapeutic keratectomy (PTK) for primary or recurrent anterior stromal corneal dystrophies. Corneal clarity, visual acuity and refractive changes in eyes with and without an antihyperopia treatment were also analyzed. METHODS: Twenty eyes of 14 patients with anterior stromal corneal dystrophies were treated with PTK. Eyes were evaluated preoperatively and 6 to 8 weeks postoperatively with slit-lamp biomicroscopy, manifest refraction, keratometry, computerized corneal topography, ultrasound pachymetry, and UBM. RESULTS: Nineteen of 20 corneas (95%) had greatly improved corneal clarity after PTK. Mean uncorrected Snellen vision improved from 20/102 to 20/69 and best corrected vision improved from 20/62 to 20/38. Nine eyes (45%) improved 2 or more lines of uncorrected vision, and 13 eyes (65%) improved 2 or more lines of best corrected vision. Mean change in spherical equivalent was just -0.92 diopters (D); however, the range was large (-13 to +3.88 D). UBM measurement of central corneal pathology did not correlate with the actual PTK ablation depth (P = .07). The amount of antihyperopia treatment did not correlate with changes in manifest refraction spherical equivalent, keratometry, or computerized corneal topography readings, but did correlate with length of time until corneal reepithelialization after PTK (P = .003). CONCLUSIONS: PTK resulted in improvements in corneal clarity and visual acuity in most patients with superficial corneal stromal dystrophies. UBM was not an effective tool to accurately measure the depth of corneal pathology preoperatively. The combined approach of minimizing ablation depth and selective use of an antihyperopia treatment resulted in minimal mean change in spherical equivalent; however, the range was large. PTK is a very good minimally invasive technique to improve vision in

  9. Phototherapeutic keratectomy for bullous keratopathy.

    PubMed Central

    Thomann, U; Meier-Gibbons, F; Schipper, I

    1995-01-01

    AIMS--This study was designed to investigate the therapeutic potential of excimer laser for recurrent painful erosions in patients not suited to treatment with penetrating keratoplasty. METHODS--Phototherapeutic keratectomy (PTK) with the excimer laser was performed prospectively on a series of 13 eyes of 12 patients with recurrent corneal erosions in connection with bullous keratopathy of varied aetiology. The main complaint of the patients before the treatment was frequent attacks of pain. The patients selected either refused corneal grafting or could not for a variety of reasons expect to profit visually from an operation. The treatment was performed with the MEL 60 Aesculap Meditec excimer laser using either a spot mode (five cases), a scanning mode (three cases), or a combination of both (five cases). RESULTS--All patients responded well to the treatment, and the pain subsided after a couple of weeks. In five cases (38.5%) a second treatment was necessary because of persistent pain, which was, however, much less than before the initial treatment. In four of these five patients small corneal bullae persisted. The visual performance of the seven patients with visual acuity better than 20/200 ameliorated in two cases and remained unchanged in four cases. One patient lost two Snellen lines after the laser treatment for terminal glaucoma. The mean follow up was 14.1 months (range 1-28 months). No complications were seen so far. CONCLUSION--It was concluded that PTK is a very promising and effective outpatient treatment for patients with bullous keratopathy. This therapeutic approach is not thought to have been described before. Images PMID:7742278

  10. Comparison of retina damage thresholds simulating the femtosecond-laser in situ keratomileusis (fs-LASIK) process with two laser systems in the CW- and fs-regime

    NASA Astrophysics Data System (ADS)

    Sander, M.; Minet, O.; Zabarylo, U.; Müller, M.; Tetz, M. R.

    2012-04-01

    The femtosecond-laser in situ keratomileusis procedure affords the opportunity to correct ametropia by cutting transparent corneal tissue with ultra-short laser pulses. Thereby the tissue cut is generated by a laser-induced optical breakdown in the cornea with ultra-short laser pulses in the near-infrared range. Compared to standard procedures such as photorefractive keratectomy and laser in-situ keratomileusis with the excimer laser, where the risk potential for the eye is low due to the complete absorption of ultraviolet irradiation from corneal tissue, only a certain amount of the pulse energy is deposited in the cornea during the fs-LASIK process. The remaining energy propagates through the eye and interacts with the retina and the strong absorbing tissue layers behind. The objective of the presented study was to determine and compare the retina damage thresholds during the fs-LASIK process simulated with two various laser systems in the CW- and fs-regime.

  11. EDITORIAL: Photorefractive materials and effects for photonics

    NASA Astrophysics Data System (ADS)

    Vlad, V. I.; Fazio, E.; Damzen, M.

    2003-11-01

    This special issue of Journal of Optics A: Pure and Applied Optics is devoted to a mature field of nonlinear optics: photorefractive materials and effects for photonics. Photorefractivity was discovered long time ago by A Ashkin et al in 1966 and since then much work has been performed to characterize the phenomenon and to apply it. Nevertheless, research in this field remain very active and productive, in both basic and applied directions. Some leading groups worldwide present their most up-to-date investigations of photorefractive materials and effects, as well as their applications in photonics. Thus, the papers in this issue report new results in three directions: photorefractive material researches, wave propagation (particularly solitons) through these nonlinear optical materials, and various applications and devices using photorefractive effects. The challenging goal of photorefractive material research is to find sensitive and fast materials for information transmission and processing. P M Johansen studies the fundamental problem of space--charge field formation in photorefractives. V Marinova et al show that light-induced properties of Ru-doped Bi12TiO20 (BTO) crystals has an extended sensitivity in the near infrared region. H A Al-Attar and O Taqatqa introduce a new photorefractive polymer composite for their interesting properties for optical data storage. R Ramos-Garcia et al perform measurements of absorption coefficient and refractive index changes in photorefractive quantum wells of GaAs. A Radoua et al characterize by two-wave mixing the photorefractive Ba0.77Ca0.23TiO3:Rh crystals (BCT) at 1.06 mum, and M K Balakirev et al study the photorefractive effect upon all optical poling of glass. Wave propagation and solitons are intensively studied in photorefractive crystals due to the possibility of obtaining steady-state spatial solitons, dynamic waveguiding and soliton interactions at low laser intensity. W Ramadan et al introduce a new procedure to

  12. Photorefraction of the Eye

    ERIC Educational Resources Information Center

    Colicchia, Giuseppe; Wiesner, Hartmut; Zollman, Dean

    2015-01-01

    Photorefraction is a method to easily estimate the refractive state of the eye. The principle of photorefraction involves projecting light into the eye during flash photography and then examining the paths of light that emerge from the pupil after scattering on the back portion of the interior of the eyeball (fundus). We will explain the optical…

  13. A sensitive observation of the photo-refraction effects in BIBO and LBO crystals basing on the loss modulation of laser intracavity

    NASA Astrophysics Data System (ADS)

    Xu, Shixiang; Gao, Yanxia

    2012-11-01

    We present a sensitive scheme basing on the sensitive intracavity loss modulation to observe photo-refraction (PR) effects of some nonlinear crystals usually used for optical parametric chirped pulse amplification (OPCPA), e.g. BIBO and LBO, pumped by the second harmonic (SH) of intense 800 nm ultrashort laser pulse chain. Our results show that the dynamical PR effects of BIBO and LBO crystals need about 10 s to reach a steady state or to fade away after their pumping switch on or off. These data imply that using these kinds of crystals for multi-stages OPCPA with the repetition rate from some Hz to tens of Hz, it may be necessary to consider the deterioration of the OPCPA stability due to the PR effects. However, if the repetition rate is high (˜kHz) or low enough (<0.1 Hz), the PR effects become negligible for the stability.

  14. Net Photorefractive Gain In Gallium Arsenide

    NASA Technical Reports Server (NTRS)

    Liu, Tsuen-Hsi; Cheng, Li-Jen

    1990-01-01

    Prerequisite includes applied electric field. Electric field applied to GaAs crystal in which two infrared beams interfere. Depending on quality of sample and experimental conditions, net photorefractive gain obtained. Results offer possibility of new developments in real-time optical processing of signals by use of near-infrared lasers of low power.

  15. Photorefraction of the Eye

    NASA Astrophysics Data System (ADS)

    Colicchia, Giuseppe; Wiesner, Hartmut; Zollman, Dean

    2015-02-01

    Photorefraction is a method to easily estimate the refractive state of the eye. The principle of photorefraction involves projecting light into the eye during flash photography and then examining the paths of light that emerge from the pupil after scattering on the back portion of the interior of the eyeball (fundus). We will explain the optical principles underlying the method for eccentric photorefraction and describe how students can perform it using current digital cameras. Our purpose is not to diagnose refractive errors reliably, but to use devices popular among young people that, in combination with an important ophthalmic context, may be successful in improving students' interest for learning optical concepts.

  16. Photorefractive Interferometers for Ultrasonic Measurements on Paper

    SciTech Connect

    Lafond, E. F.; Brodeur, P. H.; Gerhardstein, J. P.; Habeger, C. C.; Telschow, Kenneth Louis

    2002-12-01

    Photorefractive interferometers have been employed for the detection of ultrasound in metals and composites since 1991 [1–4]. Instances of laser-generated ultrasound and laser-based detection in paper were reported in 1996 [5]. More recently, bismuth silicon oxide (BSO) photorefractive interferometers were adapted to detect ultrasound in paper [6]. In this article we discuss BSO and GaAs photorefractive detection of ultrasound on different paper grades and present the resulting waveforms. Compared to contact piezoelectric transducer methods, laser interferometry offers signifcant advantages. One of these is that it is a noncontact technique. This is especially important for on-line application to lightweight papers which could be marked or damaged by contact transducers. Broadband ultrasonic laser generation matched with the broadband sensitivity of laser interferometers is another beneft. This is important for obtaining narrow pulses in nondispersive time-of-fight determinations and for measuring the phase velocity of dispersive modes over a wide frequency band. Also, laser ultrasonic techniques provide a measure of bending stiffness through the analysis of low frequency A0 waves.

  17. Photorefractive polymers: Materials science, thin-film fabrication, and experiments in volume holography

    NASA Astrophysics Data System (ADS)

    McGee, David J.; Matlin, Mark D.

    2001-10-01

    When exposed to low power laser light, photorefractive materials can function as dynamic diffraction gratings, making them attractive for applications in holography and optical image processing. Conventional crystalline photorefractive materials are useful in demonstrations of basic nonlinear optical phenomena at the advanced undergraduate level, although the fabrication of such crystals is beyond the reach of most undergraduate facilities. Within the last five years, however, polymeric photorefractive materials have been developed that can be fabricated by collaborative teams of undergraduate physics and chemistry students. We have found that the study of photorefractive polymers provides an excellent framework to emphasize connections among optics, chemistry, and materials science at a level accessible to undergraduates. We provide an overview of photorefractive polymers, describe the fabrication of a typical photorefractive polymeric system, and discuss experiments in volume holography.

  18. [Analysis of images in the prophylaxis and treatment of complications after kerato-refractive excimer laser surgeries].

    PubMed

    Makarov, I A

    2003-01-01

    A total of 236 eyes of patients with myopia and hypermetropia of different severity degrees after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) were observed. The densitometry and planimetry analysis of corneal images, obtained through storing them in the computer memory, was used to evaluate postoperatively the corneal condition. Planimetry was used to forecast the time of epithelization and to assess the efficiency of drug therapy. The optic density was found to increase, after excimer-laser surgeries, in all patients and it depended on a type of refraction and its degree. The optic-density dynamics of corneal images also depended on a degree and type of refraction as well as on a type of drug therapy. Hence, densitometry and planimetry, as objective methods used to follow up the patients after keratorefractive excimer-laser surgeries, make it possible to diagnose early enough the presence of complications related with disorders in transparency and healing of the cornea. PMID:12698885

  19. Photorefractive properties of doped cadmium telluride

    NASA Astrophysics Data System (ADS)

    Bylsma, R. B.; Bridenbaugh, P. M.; Olson, D. H.; Glass, A. M.

    1987-09-01

    The first study of the photorefractive properties of doped CdTe has demonstrated high sensitivity for optical processing applications. Of the binary II-VI and III-V semiconductors, CdTe has the highest electro-optic coefficient r41 in the infrared, some three times larger than that of GaAs and InP. Deep levels introduced into CdTe exhibit appropriate absorption and photoconductivity at 1.06 μm by doping with V and Ti impurities. Photorefractive beam coupling experiments in CdTe:V gave small signal gains of 0.7 cm-1, and diffraction efficiencies with no applied electrical field of 0.7%. Thus, CdTe appears to be superior to previously studied III-V semiconductors, in the near-infrared spectrum. Optimization of doping and trap densities is expected to result in gain which exceeds the absorption loss, thereby allowing phase conjugation with infrared injection lasers.

  20. The photorefractive characteristics of bismuth-oxide doped lithium niobate crystals

    SciTech Connect

    Zheng, Dahuai; Yao, Jiaying; Kong, Yongfa; Liu, Shiguo; Zhang, Ling; Chen, Shaolin; Xu, Jingjun

    2015-01-15

    Bismuth-doped lithium niobate (LN:Bi) crystals were grown by Czochralski method and their optical damage resistance, photorefraction, absorption spectra, and defect energy levels were investigated. The experimental results indicate that the photorefractive properties of LN:Bi were enhanced as compared with congruent one, the photorefractive response time was greatly shortened, the photorefractive sensitivity was increased, and the diffraction efficiency of near-stoichiometric LN:Bi (SLN:Bi) reached 31.72% and 49.08% at 532 nm and 488 nm laser, respectively (light intensity of 400 mW/cm{sup 2}). An absorption peak at about 350 nm was observed in the absorption spectrum of LN:Bi. And the defect energy levels simulation indicates new defect levels appear in the forbidden gap of LN:Bi crystals. Therefore bismuth can act as photorefractive centers in LN crystals.

  1. CALL FOR PAPERS: Photorefractive Materials and Effects for Photonics

    NASA Astrophysics Data System (ADS)

    2003-01-01

    Guest editors: Professor Valentin Vlad National Institute for Laser, Plasma and Radiation Physics, Bucharest, Romania Professor Eugenio Fazio Università di Roma `La Sapienza', Italy Professor Mike Damzen Imperial College, London, UK A topical issue of Journal of Optics A: Pure and Applied Optics will be devoted to papers reporting new results in the field of photorefractive effects and their applications in photonics. The topics to be covered will include, but are not limited to: bulletnew photorefractive materials (fast, sensitive in IR) bulletwave mixing in photorefractives bulletphotorefractive phase conjugators bulletholographic storage in photorefractive materials bulletphotorefractive spatial solitons bulletadaptive interconnection with photorefractive devices bulletphase conjugate interferometry bulletoptical analogue and digital computing (including optical correlators) bulletother applications and devices using photorefractive effects. The topical issue is scheduled for publication in November 2003. All papers will be peer reviewed and the normal refereeing standards of Journal of Optics A: Pure and Applied Optics will be maintained. Manuscripts should be prepared according to the general guidelines for authors published in the journal. Full details on how to structure an article, including specific information on figures, tables and references, are available from our Web site at www.iop.org/journals/authors/jopa. There are no page charges. In addition to the usual 25 free offprints, the contributing author of each paper published will receive a complimentary copy of the topical issue. Manuscripts should be submitted to the Publisher by 1 May 2003, although authors are strongly encouraged to submit their work as soon as possible. Please include a covering letter stating that the submission is intended for the Photorefractive Materials and Effects for Photonics special issue, to avoid treatment as a regular submission. Submission address: Dr Claire Blay

  2. Photorefractive effect at 775 nm in doped lithium niobate crystals

    SciTech Connect

    Nava, G.; Minzioni, P.; Cristiani, I.; Degiorgio, V.; Argiolas, N.; Bazzan, M.; Ciampolillo, M. V.; Pozza, G.; Sada, C.

    2013-07-15

    The photorefractive effect induced by 775-nm laser light on doped lithium niobate crystals is investigated by the direct observation in the far field of the transmitted-beam distortion as a function of time. Measurements performed at various Zr-doping concentrations and different light intensities show that the 775-nm light beam induces a steady-state photorefractive effect comparable to that of 532-nm light, but the observed build-up time of the photovoltaic field is longer by three-orders of magnitude. The 775-nm photorefractivity of lithium niobate crystals doped with 3 mol. % ZrO{sub 2} or with 5.5 mol. % MgO is found to be negligible.

  3. REVIEW: Optical neural computers based on photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Bel'dyugin, Igor'M.; Zolotarev, M. V.; Sviridov, K. A.

    1992-05-01

    The results are given of recent investigations of the feasibility of using photorefractive crystals in the construction of optical neural computers and of associative memories. The physical basis of the interaction of laser radiation with photorefractive crystals is given and the principles governing the formation of an all-optical neuron and of links (synapses) between neurons in such crystals are discussed. An analysis is made of the learning capabilities of various models of neural networks (Boltzmann machine, perceptron, associatron, neural networks with competition, etc.) and optical systems implementing these models with the aid of photorefractive crystals are described. Extensive experimental data are reported and the results are given of modeling of various tasks (multidimensional optimization, image recognition, etc.) by optical neural computers.

  4. Femtosecond all-solid-state laser for refractive surgery

    NASA Astrophysics Data System (ADS)

    Zickler, Leander; Han, Meng; Giese, G.'nter; Loesel, Frieder H.; Bille, Josef F.

    2003-06-01

    Refractive surgery in the pursuit of perfect vision (e.g. 20/10) requires firstly an exact measurement of abberations induced by the eye and then a sophisticated surgical approach. A recent extension of wavefront measurement techniques and adaptive optics to ophthalmology has quantitatively characterized the quality of the human eye. The next milestone towards perfect vision is developing a more efficient and precise laser scalpel and evaluating minimal-invasive laser surgery strategies. Femtosecond all-solid-state MOPA lasers based on passive modelocking and chirped pulse amplification are excellent candidates for eye surgery due to their stability, ultra-high intensity and compact tabletop size. Furthermore, taking into account the peak emission in the near IR and diffraction limited focusing abilities, surgical laser systems performing precise intrastromal incisions for corneal flap resection and intrastromal corneal reshaping promise significant improvement over today's Photorefractive Keratectomy (PRK) and Laser Assisted In Situ Keratomileusis (LASIK) techniques which utilize UV excimer lasers. Through dispersion control and optimized regenerative amplification, a compact femtosecond all-solid-state laser with pulsed energy well above LIOB threshold and kHz repetition rate is constructed. After applying a pulse sequence to the eye, the modified corneal morphology is investigated by high resolution microscopy (Multi Photon/SHG Confocal Microscope).

  5. Dynamic photorefractive self-amplified angular-multiplex 2-D optical beam-array generation

    NASA Technical Reports Server (NTRS)

    Zhou, Shaomin; Yeh, Pochi; Liu, Hua-Kuang

    1993-01-01

    A real-time 2-D angular-multiplex beam-array holographic storage and reconstruction technique using electrically-addressed spatial light modulators(E-SLM's) and photorefractive crystals is described. Using a liquid crystal television (LCTV) spatial light modulator (SLM) for beam steering and lithium niobate photorefractive crystal for holographic recording, experimental results of generating large and complicated arrays of laser beams with high diffraction efficiency and good uniformity are presented.

  6. Bilateral methicillin-resistant Staphylococcus aureus keratitis following hyperopic photorefractive surgery.

    PubMed

    Magli, Adriano; Forte, Raimondo; Rombetto, Luca; Carelli, Roberta

    2012-02-01

    To report clinical manifestations of a female patient with bilateral bacterial keratitis following photorefractive keratectomy (PRK). Bilateral PRK was performed for moderate hyperopia. Bandage contact lenses were fitted at the conclusion of the surgery. Bilateral infectious keratitis with hypopion was diagnosed within 4 days after surgery. Smear and culture were obtained and showed the presence of methicillin-resistant Staphylococcus aureus (MRSA). The patient was treated with systemic prednisone and topical antibiotics (vancomycin, tobramycin and netylmicin) and betamethasone. After 1 month corneal leukoma was still present and remained unchanged during the following 7 months. Infectious keratitis is a rare complication of PRK that appears early in the postoperative period. MRSA keratitis may determine long-term visual impairment despite prompt therapeutic intervention. PMID:22215418

  7. The Recovery of Optical Quality after Laser Vision Correction

    PubMed Central

    Jung, Hyeong-Gi

    2013-01-01

    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. Results This study included 51 eyes that underwent LASIK and 57 that underwent PRK. The optical quality three months post-surgery did not differ significantly between these laser vision correction techniques. Furthermore, the preoperative and postoperative optical quality did not differ significantly in either group. Optical quality recovered within one week after LASIK but took between one and three months to recover after PRK. 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 correction, so laser vision correction is efficacious for correcting myopia. The double-pass system is a useful tool for clinical assessment of optical quality. PMID:23908570

  8. Recent advancements in photorefractive holographic imaging

    NASA Astrophysics Data System (ADS)

    Lynn, B.; Blanche, P.-A.; Bablumian, A.; Rankin, R.; Voorakaranam, R.; St. Hilaire, P.; LaComb, L., Jr.; Yamamoto, M.; Peyghambarian, N.

    2013-02-01

    We have recently demonstrated several improvements in material properties and optical design to increase the resolution, size, brightness, and color range of updatable holograms using photorefractive materials. A compact system has been developed that is capable of producing holograms with brightness in excess of 2,500 cd/m2 using less than 20mW of CW laser power. The size of the hologram has been increased to 300mm × 150mm with a writing time of less than 8 seconds using a 50 Hz pulse laser. Optical improvements have been implemented to reduce the hogel size to less than 200 μm. We have optimized the color gamut to extend beyond the NTSC CIE color space through a combination of spatial and polarization multiplexing. Further improvements could bring applications in telemedicine, prototyping, advertising, updatable 3D maps and entertainment.

  9. Photorefraction demonstrations using electrooptic PLZT ceramics modulators

    NASA Astrophysics Data System (ADS)

    Ozolinsh, Maris; Hanstorp, Dag

    2003-11-01

    PLZT ceramics electrooptic (EO) modulator was designed for demonstrations and student's laboratory works to study photorefraction using Ar+ laser (λ = 514 nm). PLZT element had an aperture of 1.5 x 8 mm2 and thickness of 1.5 mm. Reading of recorded patterns was realized by applying to the element the biasing electric field. The most efficient writing took place for ceramics composition PLZT 8.75/65/35. The total intensity of two writing beams was up to 300 mW, the applied electric field during writing -- up to 20 kV/cm. The diffraction efficiency depended on the applied biasing reading electric field EBR. For the reading He-Ne laser the diffraction efficiency η ~ 0.48 was obtained at the bias field values EBR = 13 kV/cm. The simplicity of the modulator alignment and writing and reading processes promote the use of such modulators in the teaching process.

  10. Indications, results, and complications of refractive corneal surgery with lasers.

    PubMed

    Brancato, R; Carones, F

    1994-08-01

    The applications of the current laser technology in refractive surgery have developed during the past year. Several techniques to correct ametropia with various laser sources have been proposed and investigated. To date, using the myopic photorefractive keratectomy excimer laser is the most common technique; it has already been performed on more than 100,000 eyes worldwide. Refractive results on large series of patients with long-term follow-up indicate that the technique is safe, effective, and highly predictable in the correction of low to moderate myopia. Concerns about the treatment of high myopia still arise, especially regarding regression toward myopia and stability of achieved refraction; multizone treatments have been proposed to reach better results. The correction of compound myopic astigmatism with the excimer laser seems to be promising, although long-term results on large series are still pending. Among the patients treated, very few complications occurred. We believe that laser technology will play the most important role in refractive surgery in the future. PMID:10147334

  11. Fast adaptive interferometer with a photorefractive GaP crystal

    NASA Astrophysics Data System (ADS)

    Kamshilin, Alexei A.; Prokofiev, Victor V.

    2002-10-01

    The performance of an adaptive interferometer based on mixing of light waves with different polarization states in a photorefractive GaP crystal at λ = 0.633 μm is described. Both high sensitivity and fast response time are achieved with a low-power He-Ne laser. The parameters of the interferometer are appropriate for remote ultrasound detection in an industrial environment.

  12. White Light Photorefractive Phase Zone Plates

    NASA Astrophysics Data System (ADS)

    Gao, Yuan-Mei; Liu, Si-Min

    2008-02-01

    Incoherent white light from an incandescent source is employed to fabricate volume phase zone plates in LiNbO3: Fe, for the first time to our knowledge, which can guide and modulate the input white light or laser light. The diffractive efficiency of the white light volume phase zone plates fabricated can reach as high as 12%. In addition, we test the volume phase zone plates by a probe beam and find that the volume phase zone plate is present in the direction perpendicular to the c-axis and absent in the direction parallel to the c-axis. This directly proves the existence of photovoltaic photorefractive anisotropy of white light.

  13. Holographic Optical Storage Using Photorefractive Polymers

    NASA Technical Reports Server (NTRS)

    Hayden, L. Michael; Strutz, Shane J.; Harris, Kristi; Ayachitula, Rajani

    2000-01-01

    The task for this report is to perform the basic research and develop a prototype benchtop holographic optical storage system based on photochromic and/or photorefractive polymers so that both permanent and erasable images may be stored and retrieved in the same mixed polymer medium. The task consist of: assembly and setup of the benchtop holographic storage system, including lasers, optics, and other ancillary equipment in a laboratory setting; and research and development of a suitable polymer matrix that will allow practical storage and retrieval of digital data. This will necessitate molecular design of the matrices involved and subsequent physics test to verify the characteristics of the matrices provide practical storage and retrieval.

  14. The 2014 Bowman Lecture—Bowman's and Bruch's: a tale of two membranes during the laser revolution

    PubMed Central

    Marshall, J

    2015-01-01

    To describe the historical evolution of the role of lasers in effecting therapeutic changes in the four acellular membranes of the eye. Over the past 50 years, iterative developments have been instituted in lasers used for various forms of eye surgery predominately on the basis of data generated in early experiments in the 1960s to determine thresholds for damage and their incorporation in codes of practice for laser safety. The evolutionary steps are described. Excimer laser technology resulted in the generation of the new field of laser refractive surgery with over 40 million individuals now having undergone procedures such as photorefractive keratectomy and LASIK. Developments in lasers used for various forms of retinal surgery have undergone changes involving shorter and shorter pulse durations together with changes in beam energy distribution with implications for potential intervention in AMD prophylactically. Lasers have made a major impact on surgical treatment on all four acellular membranes of the eye but particularly Bowman's membrane in refractive surgery, where it has been demonstrated that it can be removed without significant consequences for eye health or vision. PMID:25567376

  15. The 2014 Bowman Lecture-Bowman's and Bruch's: a tale of two membranes during the laser revolution.

    PubMed

    Marshall, J

    2015-01-01

    To describe the historical evolution of the role of lasers in effecting therapeutic changes in the four acellular membranes of the eye. Over the past 50 years, iterative developments have been instituted in lasers used for various forms of eye surgery predominately on the basis of data generated in early experiments in the 1960s to determine thresholds for damage and their incorporation in codes of practice for laser safety. The evolutionary steps are described. Excimer laser technology resulted in the generation of the new field of laser refractive surgery with over 40 million individuals now having undergone procedures such as photorefractive keratectomy and LASIK. Developments in lasers used for various forms of retinal surgery have undergone changes involving shorter and shorter pulse durations together with changes in beam energy distribution with implications for potential intervention in AMD prophylactically. Lasers have made a major impact on surgical treatment on all four acellular membranes of the eye but particularly Bowman's membrane in refractive surgery, where it has been demonstrated that it can be removed without significant consequences for eye health or vision. PMID:25567376

  16. Perspectives of using the 223-nm wavelength of the KrCl excimer laser for refractive surgery and for the treatment of some eye diseases

    NASA Astrophysics Data System (ADS)

    Bagayev, Sergei N.; Chernikh, Valery V.; Razhev, Alexander M.; Zhupikov, Andrey A.

    2000-06-01

    The new surgical UV ophthalmic laser system Medilex based on the KrCl (223 nm) excimer laser for refractive surgery was created. The comparative analysis of using the UV ophthalmic laser systems Medilex based on the ArF (193 nm) and the KrCl (223 nm) excimer lasers for the correction of refractive errors was performed. The system with the radiation wavelength of 223 nanometer of the KrCl excimer laser for refractive surgery was shown to have several medical and technical advantages over the system with the traditionally used radiation wavelength of 193 nanometer of the ArF excimer laser. In addition the use of the wavelength of 223 nanometer extends functional features of the system, allowing to make not only standard for this type systems surgical and therapeutic procedures but also to treat such ocular diseases as the glaucoma and herpetic keratities. For the UV ophthalmic laser systems Medilex three variations of the beam delivery system including special rotating masks and different beam homogenize systems were developed. All created beam delivery systems are able to make the correction of myopia, hyperopia, astigmatism and myopic or hyperopic astigmatism and may be used for therapeutic procedures. The results of the initial treatments of refractive error corrections using the UV ophthalmic laser systems Medilex for both photorefractive keratectomy (PRK) and LASIK procedures are presented.

  17. Two-Step Processes and IR Recording in Photorefractive Crystals

    NASA Astrophysics Data System (ADS)

    Kraetzig, Eckhard; Buse, Karsten

    Two-step excitation processes have been used for hologram storage in photorefractive crystals. By this means the interference pattern can be formed with red or near-IR light and nondestructive readout of information is possible. Often shallow levels are involved in the holographic recording process in photorefractive crystals. The shallow levels can be populated by illumination with visible or UV pulses forming states with relatively long lifetimes, thus sensitizing the crystals for holographic recording with IR pulses. In LiNbO3 and LiTaO3 the most important shallow levels have been identified. They result from NbLi^5+ and TaLi^5+ antisite defects (Nb5+ or Ta5+ on Li+ site). The crystals can also be pre-illuminated with visible light from a cw argon laser or a xenon lamp and holograms can be recorded with red light from a laser diode. The sensitization process is possible for other photorefractive crystals, too. The holograms can be read nondestructively with IR light and can be erased with green light. The hologram lifetime is limited by electron tunneling or by an ionic conductivity. Lifetimes up to years can be achieved. Recording of components for telecommunication applications with IR light allows one to create reconfigurable and thus more versatile devices.

  18. Future of photorefractive based holographic 3D display

    NASA Astrophysics Data System (ADS)

    Blanche, P.-A.; Bablumian, A.; Voorakaranam, R.; Christenson, C.; Lemieux, D.; Thomas, J.; Norwood, R. A.; Yamamoto, M.; Peyghambarian, N.

    2010-02-01

    The very first demonstration of our refreshable holographic display based on photorefractive polymer was published in Nature early 20081. Based on the unique properties of a new organic photorefractive material and the holographic stereography technique, this display addressed a gap between large static holograms printed in permanent media (photopolymers) and small real time holographic systems like the MIT holovideo. Applications range from medical imaging to refreshable maps and advertisement. Here we are presenting several technical solutions for improving the performance parameters of the initial display from an optical point of view. Full color holograms can be generated thanks to angular multiplexing, the recording time can be reduced from minutes to seconds with a pulsed laser, and full parallax hologram can be recorded in a reasonable time thanks to parallel writing. We also discuss the future of such a display and the possibility of video rate.

  19. Recent advances in photorefractive polymers

    NASA Astrophysics Data System (ADS)

    Thomas, Jayan; Christenson, C. W.; Lynn, B.; Blanche, P.-A.; Voorakaranam, R.; Norwood, R. A.; Yamamoto, M.; Peyghambarian, N.

    2011-10-01

    Photorefractive composites derived from conducting polymers offer the advantage of dynamically recording holograms without the need for processing of any kind. Thus, they are the material of choice for many cutting edge applications, such as updatable three-dimensional (3D) displays and 3D telepresence. Using photorefractive polymers, 3D images or holograms can be seen with the unassisted eye and are very similar to how humans see the actual environment surrounding them. Absence of a large-area and dynamically updatable holographic recording medium has prevented realization of the concept. The development of a novel nonlinear optical chromophore doped photoconductive polymer composite as the recording medium for a refreshable holographic display is discussed. Further improvements in the polymer composites could bring applications in telemedicine, advertising, updatable 3D maps and entertainment.

  20. Nonvolatile photorefractive properties in triply doped stoichiometric Mg:Fe:Mn:LiTaO3 crystals

    NASA Astrophysics Data System (ADS)

    Sun, Ting; Zhang, Xiao-Dong; Sun, Liang; Wang, Rui

    2014-01-01

    We have grown triply doped Mg:Fe:Mn:LiTaO3 crystals with near stoichiometry using the top seeded solution growth technique. The defect structure was investigated by infrared absorption spectra and Curie temperature. Using a blue laser as the source, excellent photorefractive properties were obtained. Nonvolatile holographic storage properties were investigated using the dual wavelength technique. We got a very high fixed diffraction efficiency and nonvolatile holographic storage sensitivity. The blue light has more than enough energy to excite holes of deep (Mn) and shallow (Fe) trap centers with the same phase, which enhance dramatically the blue photorefractive properties and the nonvolatile holographic storage. Mg2+ ion is no longer damage resistant at blue laser, but enhances photorefractive characteristics.

  1. Air assisted lamellar keratectomy for the corneal haze model

    PubMed Central

    Kim, Soohyun; Park, Young Woo; Lee, Euiri; Park, Sang Wan; Park, Sungwon; Kim, Jong Whi; Seong, Je Kyung

    2015-01-01

    To standardize the corneal haze model in the resection depth and size for efficient corneal haze development, air assisted lamellar keratectomy was performed. The ex vivo porcine corneas were categorized into four groups depending on the trephined depth: 250 µm (G1), 375 µm (G2), 500 µm (G3) and 750 µm (G4). The stroma was equally ablated at the five measurement sites in all groups. Significant differences were observed between the trephined corneal depths for resection and ablated corneal thickness in G1 (p < 0.001). No significant differences were observed between the trephined corneal depth for resection and the ablated corneal thickness in G2, G3, and G4. The resection percentage was similar in all groups after microscopic imaging of corneal sections. Air assisted lamellar keratectomy (AK) and conventional keratectomy (CK) method were applied to six beagles, after which development of corneal haze was evaluated weekly until postoperative day 28. The occurrence of corneal haze in the AK group was significantly higher than that in the CK group beginning 14 days after surgery. Alpha-smooth muscle actin expression was significantly higher in the AK group (p < 0.001) than the CK group. Air assisted lamellar keratectomy was used to achieve the desired corneal thickness after resection and produce sufficient corneal haze. PMID:25797296

  2. Temperature and intensity dependence of photorefractive effect in GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Partovi, Afshin

    1986-01-01

    The photorefractive effect in semi-insulating Cr-doped GaAs as measured by the beam coupling technique was investigated as functions of temperature (295-386 K) and intensity (0.15-98 mW/sq cm of 1.15-micron light beams from a He-Ne laser). Results show that the photorefractive effect deteriorates rapidly over a narrow range of temperature as temperature rises, and that this characteristic temperature increases with the logarithm of beam intensity. The observed phenomenon is attributed to the competing effects of the dark- and light-induced conductivities.

  3. Scanning mid-IR laser apparatus with eye tracking for refractive surgery

    NASA Astrophysics Data System (ADS)

    Telfair, William B.; Yoder, Paul R., Jr.; Bekker, Carsten; Hoffman, Hanna J.; Jensen, Eric F.

    1999-06-01

    A robust, real-time, dynamic eye tracker has been integrated with the short pulse mid-infrared laser scanning delivery system previously described. This system employs a Q- switched Nd:YAG laser pumped optical parametric oscillator operating at 2.94 micrometers. Previous ablation studies on human cadaver eyes and in-vivo cat eyes demonstrated very smooth ablations with extremely low damage levels similar to results with an excimer. A 4-month healing study with cats indicated no adverse healing effects. In order to treat human eyes, the tracker is required because the eyes move during the procedure due to both voluntary and involuntary motions such as breathing, heartbeat, drift, loss of fixation, saccades and microsaccades. Eye tracking techniques from the literature were compared. A limbus tracking system was best for this application. Temporal and spectral filtering techniques were implemented to reduce tracking errors, reject stray light, and increase signal to noise ratio. The expanded-capability system (IRVision AccuScan 2000 Laser System) has been tested in the lab on simulated eye targets, glass eyes, cadaver eyes, and live human subjects. Circular targets ranging from 10-mm to 14-mm diameter were successfully tracked. The tracker performed beyond expectations while the system performed myopic photorefractive keratectomy procedures on several legally blind human subjects.

  4. Photorefractivity in liquid crystalline composite materials

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R.

    1997-09-01

    We report recent improvements in the photorefractive of liquid crystalline thin film composites containing electron donor and acceptor molecules. The improvements primarily result from optimization of the exothermicity of the intermolecular charge transfer reaction and improvement of the diffusion characteristics of the photogenerated ions. Intramolecular charge transfer dopants produce greater photorefractivity and a 10-fold decrease in the concentration of absorbing chromophores. The mechanism for the generation of mobile ions is discussed.

  5. Two-color photorefractive properties in near-stoichiometric lithium tantalate crystals

    NASA Astrophysics Data System (ADS)

    Liu, Youwen; Kitamura, Kenji; Takekawa, Shunji; Nakamura, Masaru; Furukawa, Yasunori; Hatano, Hideki

    2004-06-01

    The two-color photorefractive properties in undoped as-grown near-stoichiometric lithium tantalate crystals were investigated, where a near-infrared laser and a cw ultraviolet beam were used for writing and gating, respectively. The key parameters in characterizing two-color photorefractive effect, light-induced absorption change, two-color sensitivity, refractive index change, readout characteristics, and dark decay were measured by changing intensities of gating and writing beams, wavelengths of gating and writing beams for the crystals with different near-stoichiometric crystal compositions, and proton concentrations. The results showed that there exists an optimal crystal composition of around 49.65% for both sensitivity and refractive index change together with moderate lifetime of small polarons. The achieved refractive index change was on the order of 10-4, and the obtained maximum sensitivity was 0.18 cm/J. The extrapolated lifetime of holograms at room temperature in the crystals without observable OH- absorption was longer than 50 yr. The measurements of UV-induced absorption change at room temperature and low temperature of 77.3 K suggested that the unintentional impurity of Fe and intrinsic defects were responsible for two-color photorefractive effect. The excellent two-color photorefractive properties of undoped as-grown near-stoichiometric lithium tantalate crystals were discussed based on this mechanism and the physical properties of lithium tantalate.

  6. Nanostructured holographic recording utilizing InOx photorefractive thin films

    NASA Astrophysics Data System (ADS)

    Kiriakidis, George

    2003-04-01

    Photorefractive materials consistute a fast growing branch of nonlinear optics. The materials most commonly designated as photorefractive involve a charge-transport-induced non-linearity. Recent work on simple oxides such as InOx, prepared by dc sputtering, has demonstrated changes in their conductivity of more than six orders of magnitude after low power UV illumination and subsequent oxidation in and Ozon atmosphere. The structural changes on these films induced by growth parameters were studied by x-ray diffraction and Atomic Force Microscopy (AFM). Between Room Temperature (BRT) and 300°C it was found that there is a preferred growth along the (222) axis while AFM revealed a roughness increase as a function of film thickness and a tendency for nanoscale grains to be overgrown by larger neighbors. Based on these light induced charge-transport changes of InOx, ambient holographic recording process characteristics were obtained using a UV laser radiation at 325nm. It was realized that there exists a direct correlation of the recording efficiency with conductivity changes under ambient conditions. Evidence is provided for the presence of two coexisting processes in the recording regime.

  7. Luminescence-induced photorefractive spatial solitons

    NASA Astrophysics Data System (ADS)

    Fazio, E.; Alonzo, M.; Devaux, F.; Toncelli, A.; Argiolas, N.; Bazzan, M.; Sada, C.; Chauvet, M.

    2010-03-01

    We report the observation of spatial confinement of a pump beam into a photorefractive solitonic channel induced by luminescence [luminescence induced spatial soliton (LISS)]. Trapped beams have been obtained in erbium doped lithium niobate crystals at concentrations as high as 0.7 mol % of erbium. By pumping at 980 nm, erbium ions emit photons at 550 nm by two-step absorption, wavelength which can be absorbed by lithium niobate and originates the photorefractive effect. The luminescence at 550 nm generates at the same time the solitonic channel and the background illumination reaching a steady-state soliton regime.

  8. Imaging of transient surface acoustic waves by full-field photorefractive interferometry

    SciTech Connect

    Xiong, Jichuan; Xu, Xiaodong E-mail: christ.glorieux@fys.kuleuven.be; Glorieux, Christ E-mail: christ.glorieux@fys.kuleuven.be; Matsuda, Osamu; Cheng, Liping

    2015-05-15

    A stroboscopic full-field imaging technique based on photorefractive interferometry for the visualization of rapidly changing surface displacement fields by using of a standard charge-coupled device (CCD) camera is presented. The photorefractive buildup of the space charge field during and after probe laser pulses is simulated numerically. The resulting anisotropic diffraction upon the refractive index grating and the interference between the polarization-rotated diffracted reference beam and the transmitted signal beam are modeled theoretically. The method is experimentally demonstrated by full-field imaging of the propagation of photoacoustically generated surface acoustic waves with a temporal resolution of nanoseconds. The surface acoustic wave propagation in a 23 mm × 17 mm area on an aluminum plate was visualized with 520 × 696 pixels of the CCD sensor, yielding a spatial resolution of 33 μm. The short pulse duration (8 ns) of the probe laser yields the capability of imaging SAWs with frequencies up to 60 MHz.

  9. Bifurcating optical pattern recognition in photorefractive crystals

    NASA Technical Reports Server (NTRS)

    Liu, Hua-Kuang

    1993-01-01

    A new concept and experimental demonstration of a bifurcating optical pattern recognizer that uses a nonlinear gain saturation memory medium such as a high-gain photorefractive crystal are presented. A barium titanate crystal is used as a typical example of the nonlinear medium for the demonstration of the bifurcating optical pattern recognizer.

  10. Incoherently coupled dark-bright photorefractive solitons

    NASA Astrophysics Data System (ADS)

    Chen, Zhigang; Segev, Mordechai; Coskun, Tamer H.; Christodoulides, Demetrios N.; Kivshar, Yuri S.; Afanasjev, Vsevolod V.

    1996-11-01

    We report the observation of incoherently coupled dark-bright spatial soliton pairs in a biased bulk photorefractive crystal. When such a pair is decoupled, the dark component evolves into a triplet structure, whereas the bright one decays into a self-defocusing beam.

  11. Photorefractive Laser Ultrasound Spectroscopy for Materials Characterization

    SciTech Connect

    Telschow, K.L.; Deason, V.A.; Ricks, K.L.; Schley, R.S.

    1997-12-31

    Ultrasonic elastic wave motion is often used to measure or characterize material properties. Through the years, many optical techniques have been developed for applications requiring noncontacting ultrasonic measurement. Most of these methods have similar sensitivities and are based on time domain processing using interferometry. Wide bandwidth is typically employed to obtain real- time surface motion under transient conditions. However, some applications, such as structural analysis, are well served by measurements in the frequency domain that record the randomly or continuously excited vibrational resonant spectrum. A significant signal-to-noise ratio improvement is achieved by the reduced bandwidth of the measurement at the expense of measurement speed compared to the time domain methods. Complications often arise due to diffuse surfaces producing speckle that introduces an arbitrary phase component onto the optical wavefront to be recorded. Methods that correct for this effect are actively being investigated today.

  12. Diffused holographic information storage and retrieval using photorefractive optical materials

    NASA Astrophysics Data System (ADS)

    McMillen, Deanna Kay

    Holography offers a tremendous opportunity for dense information storage, theoretically one bit per cubic wavelength of material volume, with rapid retrieval, of up to thousands of pages of information simultaneously. However, many factors prevent the theoretical storage limit from being reached, including dynamic range problems and imperfections in recording materials. This research explores new ways of moving closer to practical holographic information storage and retrieval by altering the recording materials, in this case, photorefractive crystals, and by increasing the current storage capacity while improving the information retrieved. As an experimental example of the techniques developed, the information retrieved is the correlation peak from an optical recognition architecture, but the materials and methods developed are applicable to many other holographic information storage systems. Optical correlators can potentially solve any signal or image recognition problem. Military surveillance, fingerprint identification for law enforcement or employee identification, and video games are but a few examples of applications. A major obstacle keeping optical correlators from being universally accepted is the lack of a high quality, thick (high capacity) holographic recording material that operates with red or infrared wavelengths which are available from inexpensive diode lasers. This research addresses the problems from two positions: find a better material for use with diode lasers, and reduce the requirements placed on the material while maintaining an efficient and effective system. This research found that the solutions are new dopants introduced into photorefractive lithium niobate to improve wavelength sensitivities and the use of a novel inexpensive diffuser that reduces the dynamic range and optical element quality requirements (which reduces the cost) while improving performance. A uniquely doped set of 12 lithium niobate crystals was specified and

  13. Photorefractive properties of cobalt-doped strontium barium niobate crystals

    SciTech Connect

    Bogodaev, N V; Ivleva, Lyudmila I; Lykov, P A; Polozkov, N M; Osiko, Vyacheslav V

    1999-05-31

    The two-wave interaction (at {lambda} = 488 nm) in strontium barium niobate crystals doped with cobalt ions (Co:SBN) was studied. The experimental dependences of the gain coefficient on the grating period and of the grating response time on the writing beam intensity were used to calculate the Debye screening length, the diffusion length, the dark conductivity, and the effective concentration of carrier traps for a series of Co:SBN crystals with different dopant concentrations. The crystals were shown to have high coupling coefficients ({Gamma} = 33 cm{sup -1}) and short optical response times ({tau} = 140 ms for I = 1 W cm{sup -2} ). This, in combination with a high photorefractive sensitivity (S = 39 cm{sup 2} J{sup -1} ), determines the efficiency of their use in the storage of optical information and in laser phase conjugation. (nonlinear optical phenomena)

  14. Phenol adsorption using holographic interferometry in photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Kurzeluk, Mona; Guzun, Anicuta; Petris, Adrian; Vlad, Valentin I.

    2001-06-01

    Phenol is a major pollutant under strict effluent restriction. Its toxicity is well known, both in aquatic environment and human health. Among the purification technologies, adsorption is widely used in ecological procedures for chemical industry, for water and air purification. In order to check up the adsorbent properties of different adsorbent materials, it is necessary to determine some modeling parameters as the diffusion constants and concentration profiles in the vicinity of the adsorbent. The visualization and measuring method used in this work is double-exposure holographic interferometry using a Bi12TiO20 (BTO) photorefractive crystal (PRC) as reusable recording material and a low cost laser diode, as coherent light source. By holographic methods, we are studying phenol adsorption on granulated active coal and active coal powder. The visualization of the diffusion layer and measurements of its dynamics have been performed.

  15. Time-gated holographic imaging using photorefractive materials

    NASA Astrophysics Data System (ADS)

    Hyde, Sam C. W.; Barry, Nicholas P.; Jones, Richard; Dainty, Christopher; French, Paul M. W.; Wechsler, Barry A.; Klein, Marvin B.

    1995-05-01

    We present results for real-time holographic imaging in the medical imaging window (approximately 650 to 1000 nm) using photorefractive media. By recording holograms of a USAF test chart using a Ti:sapphire laser, we have selected the coherent)mostly ballistic) light and formed an image through a scattering medium which simulates biological tissue. The advantage of this approach is that a 2D image may be acquired in 'real time', i.e. without scanning. This will permit electronic signal processing and averaging, which may be used to reduce the deleterious effects of speckle. If the holograom is written with ultrashort pulses, then time-gated imaging is possible. This may be used to provide depth information by recording the 'time of flight' of the image light. We have recorded such holograms with picosecond pulses and present time-gated image data.

  16. Picosecond dynamics of free carrier populations, space- charge fields, and photorefractive nonlinearities in zincblende semiconductors

    NASA Astrophysics Data System (ADS)

    Stark, Thomas Spencer

    Generally, nonlinear optics studies investigate optically-induced changes in refraction or absorption, and their application to spectroscopy or device fabrication. The photorefractive effect is a nonlinear optical effect that occurs in solids, where transport of an optically-induced free-carrier population results in an internal space-charge field, which produces an index change via the linear electrooptic effect. The photorefractive effect has been widely studied for a variety of materials and device applications, mainly because it allows large index changes to be generated with laser beams having only a few milliwatts of average power. Compound semiconductors are important photorefractive materials because they offer a near-infrared optical response, and because their carrier transport properties allow the index change to be generated quickly and efficiently. While many researchers have attempted to measure the fundamental temporal dynamics of the photorefractive effect in semiconductors using continuous-wave, nanosecond- and picosecond-pulsed laser beams, these investigations have been unsuccessful. However, studies with this goal are of clear relevance because they provide information about the fundamental physical processes that produce this effect, as well as the material's speed and efficiency limitations for device applications. In this dissertation, for the first time, we time-resolve the temporal dynamics of the photorefractive nonlinearities in two zincblende semiconductors, semi- insulating GaAs and undoped CdTe. While CdTe offers a lattice-match to the infrared material HgxCd1-xTe, semi-insulating GaAs has been widely used in optoelectronic and high- speed electronic applications. We use a novel transient- grating experimental method that allows picosecond temporal resolution and high sensitivity. Our results provide a clear and detailed picture of the picosecond photorefractive response of both materials, showing nonlinearities due to hot

  17. Optical diagnostics for turbulent and multiphase flows: Particle image velocimetry and photorefractive optics

    SciTech Connect

    O`Hern, T.J.; Torczynski, J.R.; Shagam, R.N.; Blanchat, T.K.; Chu, T.Y.; Tassin-Leger, A.L.; Henderson, J.A.

    1997-01-01

    This report summarizes the work performed under the Sandia Laboratory Directed Research and Development (LDRD) project ``Optical Diagnostics for Turbulent and Multiphase Flows.`` Advanced optical diagnostics have been investigated and developed for flow field measurements, including capabilities for measurement in turbulent, multiphase, and heated flows. Particle Image Velocimetry (PIV) includes several techniques for measurement of instantaneous flow field velocities and associated turbulence quantities. Nonlinear photorefractive optical materials have been investigated for the possibility of measuring turbulence quantities (turbulent spectrum) more directly. The two-dimensional PIV techniques developed under this LDRD were shown to work well, and were compared with more traditional laser Doppler velocimetry (LDV). Three-dimensional PIV techniques were developed and tested, but due to several experimental difficulties were not as successful. The photorefractive techniques were tested, and both potential capabilities and possible problem areas were elucidated.

  18. Area scalable optically induced photorefractive photonic microstructures

    NASA Astrophysics Data System (ADS)

    Jin, Wentao; Xue, Yan Ling; Jiang, Dongdong

    2016-07-01

    A convenient approach to fabricate area scalable two-dimensional photonic microstructures was experimentally demonstrated by multi-face optical wedges. The approach is quite compact and stable without complex optical alignment equipment. Large-area square lattice microstructures are optically induced inside an iron-doped lithium niobate photorefractive crystal. The induced large-area microstructures are analyzed and verified by plane wave guiding, Brillouin-zone spectroscopy, angle-dependent transmission spectrum, and lateral Bragg reflection patterns. The method can be easily extended to generate other more complex area scalable photonic microstructures, such as quasicrystal lattices, by designing the multi-face optical wedge appropriately. The induced area scalable photonic microstructures can be fixed or erased even re-recorded in the photorefractive crystal, which suggests potential applications in micro-nano photonic devices.

  19. Comparison of non-cycloplegic photorefraction, cycloplegic photorefraction and cycloplegic retinoscopy in children

    PubMed Central

    Ozdemir, Ozdemir; Özen Tunay, Zuhal; Petriçli, Ikbal Seza; Ergintürk Acar, Damla; Erol, Muhammet Kazım

    2015-01-01

    AIM To compare the results of noncycloplegic photorefraction, cycloplegic photorefraction and cycloplegic refraction in preschool and non-verbal children. METHODS One hundred and ninety-six eyes of 98 children (50 females, 48 males) were included in the study. Firstly, non-cycloplegic photorefraction was achieved with Plusoptix A09; secondly, cycloplegic photorefraction was carried out with Plusoptix A09 after 10 min cyclopentolate. Finally, 30min after instillation of twice cyclopentolate, cycloplegic refraction was obtained with autorefraction and/or standard retinoscopy. Spheric equivalent, spheric power, cylindric power and cylindrical axis measurements were statistically compared. RESULTS The mean age was 28.8±18.5mo (range 12-72mo). The differences in spherical equivalent, spheric power and cylindrical power measured by the three methods were found statistically significant (P<0.05). The spherical equivalent and spheric power measured by cycloplegic photorefraction were statistically higher than the measurements of the other methods (P<0.05). The cylindrical power measured by cycloplegic refraction was statistically lower than the measurements of the photorefraction methods (P<0.05). There was no significant difference in cylindrical axis measurements between three methods (P>0.05). CONCLUSION For the determination of refractive errors in children, the Plusoptix A09 measurements give incorrect results after instillation of cyclopentolate. Additionally, the cylindrical power measured by Plusoptix A09 with or without cycloplegia is higher. However, the non-cycloplegic Plusoptix A09 measures spheric equivalent and spheric power similar to cycloplegic refraction measurements in preschool and non-verbal children. PMID:25709922

  20. Composite waveguide on a photorefractive crystal

    SciTech Connect

    Usievich, B A; Nurligareev, D Kh; Sychugov, V A; Ivleva, Lyudmila I

    2011-10-31

    A new waveguiding structure (composite waveguide) has been proposed, which has the form of a linear dielectric layer on the surface of a photorefractive crystal and supports spatially confined modes propagating along its surface. We demonstrate that the modal properties of the composite waveguide are determined by those of a Bragg waveguide and the properties of nonlinear surface waves and the leaky modes of the thin-film waveguide. Various schemes of mode excitation in the composite waveguide are examined.

  1. Photorefractive conjugated polymer-liquid crystal composites

    SciTech Connect

    Wasielewski, M. R.; Yoon, B. A.; Fuller, M.; Wiederrecht, G. P.; Niemczyk, M. P.; Svec, W. A.

    2000-05-15

    A new mechanism for space-charge field formation in photorefractive liquid crystal composites containing poly(2,5-bis(2{prime}-ethylhexyloxy)-1,4-phenylenevinylene) (BEH-PPV) and the electron acceptor N,N{prime}-dioctyl-1,4:5,8-naphthalenediimide, NI, is observed. Using asymmetric energy transfer (beam coupling) measurements that are diagnostic for the photorefractive effect, the direction of beam coupling as a function of grating fringe spacing inverts at a spacing of 5.5 {micro}m. The authors show that the inversion is due to a change in the dominant mechanism for space-charge field formation. At small fringe spacings, the space-charge field is formed by ion diffusion in which the photogenerated anion is the more mobile species. At larger fringe spacings, the polarity of the space charge field inverts due to dominance of a charge transport mechanism in which photogenerated holes are the most mobile species due to hole migration along the BEH-PEV chains coupled with interchain hole hopping. Control experiments are presented, which use composites that can access only one of the two charge transport mechanisms. The results show that charge migration over long distances leading to enhanced photorefractive effects can be obtained using conjugated polymers dissolved in liquid crystals.

  2. Photorefractive phase-conjugation digital holographic microscopy

    NASA Astrophysics Data System (ADS)

    Chang, Chi-Ching; Chan, Huang-Tian; Shiu, Min-Tzung; Chew, Yang-Kun

    2015-05-01

    In this work, we propose an innovative method for digital holographic microscopy named as photorefractive phaseconjugation digital holographic microscopy (PPCDHM) technique based on the phase conjugation dynamic holographic process in photorefractive BaTiO3 crystal and the retrieval of phase and amplitude of the object wave were performed by a reflection-type digital holographic method. Both amplitude and phase reconstruction benefit from the prior amplification by self-pumped conjugation (SPPC) as they have an increased SNR. The interest of the PPCDHM is great, because its hologram is created by interfered the amplified phase-conjugate wave field generated from a photorefractive phase conjugator (PPC) correcting the phase aberration of the imaging system and the reference wave onto the digital CCD camera. Therefore, a precise three-dimensional description of the object with high SNR can be obtained digitally with only one hologram acquisition. The method requires the acquisition of a single hologram from which the phase distribution can be obtained simultaneously with distribution of intensity at the surface of the object.

  3. Resonance running hologram velocity nonlinearity dependence upon light intensity in photorefractive crystals

    NASA Astrophysics Data System (ADS)

    de Oliveira, Ivan; Carvalho, Jesiel F.; Frejlich, Jaime

    2013-06-01

    We report on the nonlinear relation between the resonance hologram velocity and the recording light irradiance in fringe-locked running hologram experiments carried out on a nominally undoped photorefractive Bi12TiO20 crystal using 532 nm wavelength laser light. Such nonlinearity is due to the dependence of the material diffusion length on the light irradiance. Experimental data show a good agreement with the theoretical equations thus supporting the mathematical model here reported and allowing to compute the quantum efficiency for photoelectron generation, the dependence of the diffusion length upon the recorded light irradiance, and the far from saturation diffusion length.

  4. Nonlinear photorefractive response at high modulation depths

    NASA Technical Reports Server (NTRS)

    Vachss, Frederick; Hesselink, Lambertus

    1988-01-01

    The response of photorefractive materials to sinusoidal intensity patterns of high modulation depths is considered. It is shown that the induced refractive-index response in this regime is highly nonlinear. Concise analytic expressions for the various nonlinear harmonics of the photorefractive response field are developed and compared with exact numerical solutions of the underlying charge-transport equations as well as with the results of previous theoretical models over a broad range of physical parameters. We show that the nonlinear response characteristics are strongly dependent on both the magnitude of applied electric fields and the relative concentrations of charge donor and acceptor sites in the material. For drift dominated recording, in particular, we determine analytically that in the limit of a minimal acceptor/donor ratio, the amplitudes of higher spatial harmonics of the response reach a maximum and eventually decay as functions of increasing applied field, whereas these amplitudes reach a nonzero limit in the case of a near-unity acceptor/donor ratio. Finally, we generalize our results to account for diffusion effects in an appended derivation.

  5. Photorefractive surface nonlinearly chirped waveguide arrays

    NASA Astrophysics Data System (ADS)

    Qi, Pengfei; Feng, Tianrun; Wang, Sainan; Han, Rong; Hu, Zhijian; Zhang, Tianhao; Tian, Jianguo; Xu, Jingjun

    2016-05-01

    We report an alternate type of nonlinear waveguides, photorefractive surface nonlinearly chirped waveguide arrays, which can be directly induced by photorefractive surface waves in virtue of diffusion and drift nonlinearities. The amplitude of such nonlinearly chirped waveguide arrays has an apodized envelope owing to the diffusion nonlinearity. The refractive-index change of the apodized tails converges to a nonzero value which can be handily adjusted by an external electric field. Moreover, the chirp parameters such as amplitude, sign (positive or negative), and initial position can be conveniently adjusted by an external electric field, background illumination, incident beam, etc. Then the guided-wave properties of this type of waveguide arrays are analyzed by using the transfer matrix method. Owing to the flexible tail and the nonlinear chirp, the dispersion curves of the index-guided modes can be tailored by an external electric field and the dispersion curves of ordinary and extraordinary Bragg guided modes couple, intertwine, and anticross with each other. Meanwhile, there is a clear "competition" in the coupling hybrid mode near anticrossing.

  6. Photorefraction Screens Millions for Vision Disorders

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Who would have thought that stargazing in the 1980s would lead to hundreds of thousands of schoolchildren seeing more clearly today? Collaborating with research ophthalmologists and optometrists, Marshall Space Flight Center scientists Joe Kerr and the late John Richardson adapted optics technology for eye screening methods using a process called photorefraction. Photorefraction consists of delivering a light beam into the eyes where it bends in the ocular media, hits the retina, and then reflects as an image back to a camera. A series of refinements and formal clinical studies followed their highly successful initial tests in the 1980s. Evaluating over 5,000 subjects in field tests, Kerr and Richardson used a camera system prototype with a specifically angled telephoto lens and flash to photograph a subject s eye. They then analyzed the image, the cornea and pupil in particular, for irregular reflective patterns. Early tests of the system with 1,657 Alabama children revealed that, while only 111 failed the traditional chart test, Kerr and Richardson s screening system found 507 abnormalities.

  7. Fiber sensing with photorefractive fiber

    NASA Astrophysics Data System (ADS)

    Yu, Francis T. S.; Guo, Ruyan; Wang, Bo; Liu, Yuexin

    2002-11-01

    Optical fibers have been widely used for transmitting temporal signal. However, the transmission of spatial signal has not been fully exploited. Although multimode fiber has a large space-bandwidth product, transmitting spatial signals by using a fiber is rather difficult. When a laser beam is lached into a multimode fiber, the exit light field produces a complicated speckle pattern caused by the modal phasing of the fiber. It is difficult to recover the transmitted informati from the speckle field. However, the fiber speckle field can be used to fiber sensing with a hologrpahic method. In other words, if a hologram is made with the speckle fiber field, the information of the fiber status can be recovered. Thus by reading the hologram by the same speckle field, the reference beam can be reconstructed, which represents the detection of the speckle field. In other words, instead of exploiting the temporal content, the spatial content from a multimode fiber can be exploited for sensing. Our analyses and experimentations have shown that the fiber specklegram sensor (FSS) is highly senstiive to perturbation, and it is less vulnerable to the environment factors. Applications of the FSS to temperature, transversal displacement, and dynamic sensing are also included.

  8. Improving sensitivity of photorefractive polymer composites for holographic display applications

    NASA Astrophysics Data System (ADS)

    Christenson, Cory W.

    This work presents recent progress in the area of organic photorefractive polymer composites. These materials have been previously shown to be a suitable medium for dynamic holographic displays, with multiple colors and single frame writing times on the order of seconds. However, these materials still require large electric fields and high intensity lasers to function effectively. Recent advancements in improving these areas are discussed, including a review of the history and state-of-the-art in photorefractive polymer composites. The addition of electron traps via low loading of the electron-transporting molecule Alq3 is shown to dramatically improve the diffraction efficiency and reduce the required field. The grating formation also proceeds faster by more than one order of magnitude, leading to an increase in sensitivity by a factor of 3. The dynamics of these materials also show evidence of competing gratings indicative of bipolar charge transport and trapping. The addition of an amorphous polycarbonate (APC) buffer layer is reported to have a similar effect on the steady-state diffraction efficiency, and the further doping with a fullerene derivative (PCBM) allows a 3x increase in the efficiency in the reflection geometry, which is normally poor due to the small grating spacing. These composites reveal the fundamental limits of the reflection geometry, based on the physics of high frequency gratings. A reversal in the direction and increase in the magnitude of the two-beam coupling energy transfer is also observed. The use of interdigitated coplanar electrodes, instead of the standard uniform electrodes in a parallel-plate geometry, is shown to result in large diffraction efficiency with symmetric writing beams due to the increased projection field. The efficiency is similar to that achieved in the standard samples with large slant angles and much better than those geometries typically used in applications, with the benefit that the writing beams do not have

  9. Analysis of photoastigmatic keratectomy with the cross-cylinder ablation

    PubMed Central

    Rosa, Nicola; De Bernardo, Maddalena; Romano, Mario R; Scarfato, Gianluca; Verdoliva, Francesco; Mastropasqua, Rodolfo; Lanza, Michele

    2012-01-01

    Aim: The aim was to evaluate the safety and efficacy of the “cross-cylinder” technique in the correction of astigmatism. Setting and Design: A prospective interventional study from a university eye department was conducted. Material and Methods: The photoastigmatic refractive keratectomy (PARK) using the “cross-cylinder” technique was performed in 102 eyes of 84 patients with at least 0.75 D of astigmatism. The study population was divided into two groups: in the first group the preoperative astigmatic power ranged from –0.75 D to –3.00 D (group 1), in the second group it ranged from –3.25 D to –6.00 D (group 2). Group 1 included 82 eyes of 67 patients (29 males and 38 females) with a mean cylinder power of –1.90 ± 0.63 D, group 2 included 20 eyes of 17 patients (13 males and 4 females) with a mean cylinder power of -4.28 ± 0.76 D. All eyes were targeted for emmetropia. The results were evaluated using Calossi's vector analysis method. Six-month postoperative outcomes are presented. Results: Six months after PARK the mean sphere for the entire cohort was +0.28 ± 0.75 D (range +2.5 to –2 D), the mean cylindrical power was +0.33 ± 0.51 D (range +2.5 to –1.25 D) and the mean spherical equivalent refraction was +0.73 ± 0.81 D (range +1.75 to –2 D). Conclusions: The cross-cylinder technique may be safely used with predictable results for the correction of astigmatism. PMID:22824597

  10. Phototherapeutic keratectomy for recurrent granular dystrophy in postpenetrating keratoplasty eyes

    PubMed Central

    Rathi, Varsha M; Taneja, Mukesh; Murthy, Somasheila I; Bagga, Bhupesh; Vaddavalli, Pravin Krishna; Sangwan, Virender S

    2016-01-01

    Purpose: The purpose is to assess the clinical and visual outcome after phototherapeutic keratectomy (PTK) procedure in eyes with prior penetrating keratoplasty (PKP) for granular corneal dystrophy (GCD) and the time of performance of repeat PTK for recurrence. Methods: PTK was performed for visually significant recurrence: A reduction in best-corrected visual acuity (BCVA) by >2 lines over BCVA before recurrence was considered as visually significant recurrence. Three eyes had amniotic membrane patch performed with PTK. The main outcome measures were a recurrence of GCD, clinical course, and visual outcome. Intervals between repeat PTK procedures were noted. Results: Six patients (n = 10 eyes; males: 4, mean age 39 ± 13.97 years) underwent PTK. The mean pachymetry before first PTK was 527.1 ± 34 microns. The mean duration between PKP and first PTK was 85.1 months (range: 37–108 months). Two and three PTK procedures were done for seven and five eyes, respectively. Mean duration between first and second and second and third PTK was 62.12 ± 34.41 and 42.8 ± 13.54 months respectively. The average cut depth was 43.66 ± 19.57, 75 ± 43.30 and 39 ± 19.79 microns after the first, second and third PTK procedures, respectively. All eyes had a corneal haze. Prefirst PTK mean BCVA was 20/200 and improved significantly after the first two PTK procedures to 20/40 and after the third PTK procedure to 20/32 (P < 0.001). Five eyes had hyperopia. One acute graft rejection was managed successfully at 5 months with medical therapy. Conclusion: Multiple PTK procedures can be performed safely with improved visual acuity in grafts without compromising graft survival. PMID:27050350

  11. Spatial Rogue Waves in Photorefractive Ferroelectrics

    NASA Astrophysics Data System (ADS)

    Pierangeli, D.; Di Mei, F.; Conti, C.; Agranat, A. J.; DelRe, E.

    2015-08-01

    Rogue waves are observed as light propagates in the extreme nonlinear regime that occurs when a photorefractive ferroelectric crystal is undergoing a structural phase transition. The transmitted spatial light distribution contains bright localized spots of anomalously large intensity that follow a signature long-tail statistics that disappears as the nonlinearity is weakened. The isolated wave events form as out-of-equilibrium response and disorder enhance the Kerr-saturated nonlinearity at the critical point. Self-similarity associable to the individual observed filaments and numerical simulations of the generalized nonlinear Schrödinger equation suggests that dynamics of soliton fusions and scale invariance can microscopically play an important role in the observed rogue intensities and statistics.

  12. Simulation of keratoconus observation in photorefraction

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Ling; Tan, B.; Baker, K.; Lewis, J. W. L.; Swartz, T.; Jiang, Y.; Wang, M.

    2006-11-01

    In the recent years, keratoconus (KC) has increasingly gained attention due to its treatment options and to the popularity of keratorefractive surgery. This paper investigates the potential of identification of KC using photorefraction (PR), an optical technique that is similar to objective retinoscopy and is commonly used for large-scale ocular screening. Using personalized eye models of both KC and pre-LASIK patients, computer simulations were performed to achieve visualization of this ophthalmic measurement. The simulations are validated by comparing results to two sets of experimental measurements. These PR images show distinguishable differences between KC eyes and eyes that are either normal or ametropic. The simulation technique with personalized modeling can be extended to other ophthalmic instrument developments. It makes possible investigation with the least number of real human subjects. The application is also of great interest in medical training.

  13. Analysis of eccentric photorefraction by Fourier optics

    NASA Astrophysics Data System (ADS)

    Liu, Yong; Chen, Jiabi

    2007-03-01

    Eccentric photorefraction usually is used as early eyesight diagnostic test of infants and small children. Unlike currently approved geometrical optical model of eccentric photorefractometer, the crescent formation and the light-intensity distribution in the pupil image of a myopic eye are analyzed by Fourier optics with the assumption of an isotropic scattering retina. In the case of little circular light source and rectangular slit, the simulation results of different myopic diopters are obtained by geometrical optical theory and Fourier optics respectively. It is found that the simulation results by Fourier optics are similar as those obtained by geometrical optics, and all simulations are almost corresponding to the experimental result. The result demonstrates that the new method presented here is feasible.

  14. Imaging of transient surface acoustic waves by full-field photorefractive interferometry.

    PubMed

    Xiong, Jichuan; Xu, Xiaodong; Glorieux, Christ; Matsuda, Osamu; Cheng, Liping

    2015-05-01

    A stroboscopic full-field imaging technique based on photorefractive interferometry for the visualization of rapidly changing surface displacement fields by using of a standard charge-coupled device (CCD) camera is presented. The photorefractive buildup of the space charge field during and after probe laser pulses is simulated numerically. The resulting anisotropic diffraction upon the refractive index grating and the interference between the polarization-rotated diffracted reference beam and the transmitted signal beam are modeled theoretically. The method is experimentally demonstrated by full-field imaging of the propagation of photoacoustically generated surface acoustic waves with a temporal resolution of nanoseconds. The surface acoustic wave propagation in a 23 mm × 17 mm area on an aluminum plate was visualized with 520 × 696 pixels of the CCD sensor, yielding a spatial resolution of 33 μm. The short pulse duration (8 ns) of the probe laser yields the capability of imaging SAWs with frequencies up to 60 MHz. PMID:26026514

  15. Orientational photorefractive effects observed in poly(vinyl alcohol)/liquid crystal composites

    NASA Astrophysics Data System (ADS)

    Ono, Hiroshi; Saito, Isao; Kawatsuki, Nobuhiro

    1998-04-01

    We successfully observed orientational photorefractive gratings generated in poly(vinyl alcohol) (PVA)/liquid crystal (LC) composites doped with a fullerene (C60) as a photoconductive sensitizer under an applied dc field. Orientational photorefractivity was demonstrated by observing Raman-Nath diffraction beams with an external dc field. The photorefractive gratings were partially memorized even in the absence of the applied dc field.

  16. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.

    1993-01-01

    During the period covered by this report, October 11, 1991 through October 10, 1992, the research has progressed in a number of different areas. The sol-gel technique was initially studied and experimentally evaluated for depositing films of BaTiO3. The difficulties with the precursors and the poor quality of the films deposited lead to the investigation of pulsed laser deposition as an alternative approach. The development of the pulsed laser deposition technique has resulted in continuous improvements to the quality of deposited films of BaTiO3. The initial depositions of BaTiO3 resulted in amorphous films, however, as the pulsed laser deposition technique continued to evolve, films were deposited in the polycrystalline state, then the textured polycrystalline state, and most recently heteroepitaxial films have also been successfully deposited on cubic (100) oriented SrTiO3 substrates. A technique for poling samples at room temperature and in air is also undergoing development with some very preliminary but positive results. The analytical techniques, which include x-ray diffraction, ferroelectric analysis, UV-Vis spectrophotometry, scanning electron microscopy with x-ray compositional analysis, optical and polarized light microscopy, and surface profilometry have been enhanced to allow for more detailed evaluation of the samples. In the area of optical characterization, a pulsed Nd:YAG laser has been incorporated into the experimental configuration. Now data can also be acquired within various temporal domains resulting in more detailed information on the optical response of the samples and on their photorefractive sensitivity. The recent establishment of collaborative efforts with two departments at Johns Hopkins University and the Army Research Lab at Fort Belvoir has also produced preliminary results using the metallo-organic decomposition technique as an alternative method for thin film processing of BaTiO3. RF and DC sputtering is another film deposition

  17. Laser in-situ keratomileusis in patients with diabetes mellitus: a review of the literature

    PubMed Central

    Simpson, Rachel G; Moshirfar, Majid; Edmonds, Jason N; Christiansen, Steven M

    2012-01-01

    Purpose A growing number of diabetic patients request laser in situ keratomileusis (LASIK) for elective vision correction each year. While the United States Food and Drug Administration considers diabetes a relative contraindication to LASIK surgery, there are several reports in the literature of LASIK being performed safely in this patient population. The purpose of this review was to examine whether diabetes should still be considered a contraindication to LASIK surgery by reviewing the ocular and systemic complications of diabetes, and examining the existing data on the outcomes of LASIK in diabetic patients. Methods A literature review was conducted through PubMed, Medline, and Ovid to identify any study on LASIK surgery in patients with diabetes mellitus. This search was conducted without date restrictions. The search used the Medical Subject Headings (MeSH®) term LASIK linked by the word “and” to the following MeSH and natural language terms: diabetes, diabetes mellitus, systemic disease, and contraindications. Abstracts for all studies meeting initial search criteria were reviewed for relevance. There were no prospective clinical studies identified. Three retrospective studies were identified. Key sources from these papers were identified, reviewed, and included as appropriate. An additional literature search was conducted to identify any study of ocular surgery on patients with diabetes using the MeSH terms refractive surgery, photorefractive keratectomy, radial keratotomy, cataract surgery, vitrectomy, and iridectomy linked by the word “and” to the following MeSH terms: diabetes, diabetes mellitus, and systemic disease. This search was conducted without date restrictions. Abstracts of studies meeting the initial search criteria were reviewed and articles deemed relevant to the subject were included in this review. Conclusion LASIK may be safe in diabetic patients with tight glycemic control and no ocular or systemic complications. PMID:23109803

  18. Microwave signal processing with photorefractive dynamic holography

    NASA Astrophysics Data System (ADS)

    Fotheringham, Edeline B.

    Have you ever found yourself listening to the music playing from the closest stereo rather than to the bromidic (uninspiring) person speaking to you? Your ears receive information from two sources but your brain listens to only one. What if your cell phone could distinguish among signals sharing the same bandwidth too? There would be no "full" channels to stop you from placing or receiving a call. This thesis presents a nonlinear optical circuit capable of distinguishing uncorrelated signals that have overlapping temporal bandwidths. This so called autotuning filter is the size of a U.S. quarter dollar and requires less than 3 mW of optical power to operate. It is basically an oscillator in which the losses are compensated with dynamic holographic gain. The combination of two photorefractive crystals in the resonator governs the filter's winner-take-all dynamics through signal-competition for gain. This physical circuit extracts what is mathematically referred to as the largest principal component of its spatio-temporal input space. The circuit's practicality is demonstrated by its incorporation in an RF-photonic system. An unknown mixture of unknown microwave signals, received by an antenna array, constitutes the input to the system. The output electronically returns one of the original microwave signals. The front-end of the system down converts the 10 GHz microwave signals and amplifies them before the signals phase modulate optical beams. The optical carrier is suppressed from these beams so that it may not be considered as a signal itself to the autotuning filter. The suppression is achieved with two-beam coupling in a single photorefractive crystal. The filter extracts the more intense of the signals present on the carrier-suppressed input beams. The detection of the extracted signal restores the microwave signal to an electronic form. The system, without the receiving antenna array, is packaged in a 13 x 18 x 6″ briefcase. Its power consumption equals that

  19. Holographic light scattering in photorefractive crystals with local response

    NASA Astrophysics Data System (ADS)

    Goulkov, M.; Odoulov, S.; Woike, Th.; Imbrock, J.; Imlau, M.; Krätzig, E.; Bäumer, C.; Hesse, H.

    2002-05-01

    Strong polarization-isotropic wide-angle light scattering in photorefractive crystals with dominating photovoltaic response is explained referring to different experimental results obtained for LiTaO3:Fe crystals. It is shown experimentally that the steady-state amplification of the light scattering results from a nonzero shift in the temporal frequency between the coherent optical noise and the pump beam. Competition of photovoltaic and diffusion contributions in the photorefractive effect leads to a spatial and temporal asymmetry of nonlinear scattering. Contributions of ``hot'' electrons in the diffusion process have to be assumed.

  20. Photorefractivity in polymer-stabilized liquid crystals films.

    SciTech Connect

    Wasielewski, M. R.

    1998-05-08

    We have shown that PSLCs are capable of forming photorefractive gratings that operate in the thick grating regime. Polymer stabilization alters the charge transport and trapping characteristics of LCs, resulting in longer lived gratings, while maintaining the advantages of high orientational birefringence within LCs. Furthermore, very low applied electric fields (800 V/cm) and low optical intensities (100 mW/cm{sup 2}) are required to create large photorefractive effects in these materials. It is expected that optimization of the redox potentials of the chromophores within the PSLCs will continue to improve the performance of these materials.

  1. Spatial rogue waves in a photorefractive pattern-forming system.

    PubMed

    Marsal, N; Caullet, V; Wolfersberger, D; Sciamanna, M

    2014-06-15

    We have experimentally analyzed pattern formation in an optical system composed of a bulk photorefractive crystal subjected to a single optical feedback. In a highly nonlinear regime far above the modulational instability threshold, we are reporting on turbulent spatiotemporal dynamics that leads to rare, intense localized optical peaks. We have proven that the statistics and features of those peaks correspond to the signatures of two-dimensional spatial rogue events. These optical rogue waves occur erratically in space and time and live typically the same amount of time as the response time of the photorefractive material. PMID:24978569

  2. Adaptive fringe-locked running hologram in photorefractive crystals.

    PubMed

    Frejlich, J; Garcia, P M; Cescato, L

    1989-11-01

    We have recorded running holograms in a photorefractive crystal with an applied electric field, using a 90 degrees phase-shift fringe-locked interference pattern of light. This method provides a simple way to obtain optimal conditions for nonstationary holographic recording. The experiment that we describe allows us to calculate the crystal diffusion length L(D) and provides direct evidence of the occurrence of running holograms in photorefractive crystals. Experimental results for a Bi(12)SiO(20) sample are reported. PMID:19759637

  3. Modulation Z-scan technique for characterization of photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Aguilar, P. A. Marquez; Sanchez-Mondragon, J. J.; Stepanov, S.

    1996-10-01

    We propose a simple single-beam configuration for characterization of the amplitude, speed of growth, and polarization properties of the photoinduced refractive-index change that is due to a drift photorefractive mechanism of nonlinearity in crystals, namely, the modulation Z-scan technique, based on the modulation of an externally applied electric field. The results of a simple theoretical model developed for one-dimensional parabolic photorefractive lens formation in this configuration are illustrated by original experiments with a semi-insulating GaAs crystal at lambda =1.06 mu m .

  4. Spatial solitons in two-photon photorefractive media

    NASA Astrophysics Data System (ADS)

    Hou, Chunfeng; Pei, Yanbo; Zhou, Zhongxiang; Sun, Xiudong

    2005-05-01

    We provide a theory for spatial solitons due to the two-photon photorefractive effect based on the Castro-Camus model [Opt. Lett. 28, 1129 (2003)]. We present the evolution equation of one-dimensional spatial solitons in two-photon photorefractive media. In steady state and under appropriate external bias conditions, we obtain the dark and bright soliton solutions of the optical wave evolution equation, and also discuss the self-deflection of the bright solitons theoretically by taking into account the diffusion effect.

  5. Spatial solitons in two-photon photorefractive media

    SciTech Connect

    Hou Chunfeng; Pei Yanbo; Zhou Zhongxiang; Sun Xiudong

    2005-05-15

    We provide a theory for spatial solitons due to the two-photon photorefractive effect based on the Castro-Camus model [Opt. Lett. 28, 1129 (2003)]. We present the evolution equation of one-dimensional spatial solitons in two-photon photorefractive media. In steady state and under appropriate external bias conditions, we obtain the dark and bright soliton solutions of the optical wave evolution equation, and also discuss the self-deflection of the bright solitons theoretically by taking into account the diffusion effect.

  6. Imaging of Lamb Waves in Plates for Quantitative Determination of Anisotropy using Photorefractive Dynamic Holography

    SciTech Connect

    Telschow, Kenneth Louis; Deason, Vance Albert; Schley, Robert Scott; Watson, Scott Marshall

    1998-06-01

    Anisotropic properties of sheet materials can be determined by measuring the propagation of Lamb waves in different directions. Electromagnetic acoustic transduction and laser ultrasonic methods provide noncontacting approaches that are often desired for application to industrial and processing environments. This paper describes a laser imaging approach utilizing the adaptive property of photorefractive materials to produce a real-time measurement of the antisymmetric Lamb wave mode in all directions simultaneously. Continuous excitation is employed enabling the data to be recorded and displayed by a CCD camera. Analysis of the image produces a direct quantitative determination of the phase velocity in all directions showing plate anisotropy in the plane. Many optical techniques for measuring ultrasonic motion at surfaces have been developed for use in applications such as vibration measurement and laser ultrasonics. Most of these methods have similar sensitivities and are based on time domain processing using homodyne, Fabry-Perot [1], and, more recently, photorefractive interferometry [2]. Generally, the methods described above do not allow measurement at more than one surface point simultaneously, requiring multiple beam movements and scanning in order to produce images of surface ultrasonic motion over a large area. Electronic speckle interferometry, including shearography, does provide images directly of vibrations over large surface areas. This method has proven very durable in the field for large displacement amplitudes of several wavelengths. In addition, a sensitivity of ë/3000 has been demonstrated under laboratory conditions [3]. Full-field imaging of traveling ultrasonic waves using digital shearography has been recently reported with sensitivity in the nanometer range [4]. With this method, optical interference occurs at the photodetector

  7. Holographic digital data storage in a photorefractive polymer.

    PubMed

    Lundquist, P M; Poga, C; Devoe, R G; Jia, Y; Moerner, W E; Bernal, M P; Coufal, H; Grygier, R K; Hoffnagle, J A; Jefferson, C M; Macfarlane, R M; Shelby, R M; Sincerbox, G T

    1996-06-15

    We report high-contrast storage of 64-kbit digital data pages in a photorefractive polymer material. Singlepage writing, reading, and erasing operations were demonstrated with a dual-function-dopant polymeric material having a dark lifetime of several days. Data were reconstructed without error by use of several simple readout algorithms. PMID:19876193

  8. Talbot effect by a photorefractive volume phase grating.

    PubMed

    Forte, Gustavo; Lencina, Alberto; Tebaldi, Myrian; Bolognini, Néstor

    2012-02-01

    In our proposal a light intensity distribution generated by an incoherently illuminated planar amplitude grating is projected into a photorefractive crystal. This 3D distribution is mapped as an index refractive perturbation via the photorefractive effect thereby generating a volume phase grating. The self-imaging phenomenon in the Fresnel field of this volume phase grating coherently illuminated is theoretically and experimentally analyzed. A model to simulate this volume grating that considers the 3D light intensity distribution formed in the crystal combined with the photorefractive grating formation theory is proposed. A path-integral approach to calculate the self-image patterns which account for the inhomogeneous propagation through the photorefractive grating is employed. The experimental and theoretical results show that the self-images location coincides with that of the self-images generated by planar phase grating of the same period. Moreover, the self-images visibility depends on three parameters: the exit pupil diameter of the incoherent recording optical system, the external electric field applied on the crystal, and the crystal thickness. To study the visibility behavior, a phase parameter which includes the three mentioned parameters is proposed. The self-images visibility shows the typical sinusoidal dependence found in planar phase grating. A good agreement between theoretical and experimental results is observed. PMID:22307118

  9. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.; Potember, Richard S.

    1991-01-01

    The principle objectives of this ongoing research involve the preparation and characterization of polycrystalline single-domain thin films of BaTiO3 for photorefractive applications. These films must be continuous, free of cracks, and of high optical quality. The two methods proposed are sputtering and sol-gel related processing.

  10. Holographic gratings in photorefractive polymers without external electric field

    NASA Astrophysics Data System (ADS)

    Kukhtarev, Nickolai V.; Lyuksyutov, Sergei F.; Buchhave, Preben; Volodin, Boris L.

    1997-09-01

    Using anomalous large diffusion we report a recording of reflection type gratings in a PVK-based photorefractive polymer without any external electric field. Diffraction efficiency of the gratings was measured to be 7%. An efficient modulation of beams during two-beam coupling up to 12% was demonstrated by using phase mutilation technique. This practical scheme can be used in dynamic vibration measurements.

  11. Electro- and magneto-optic properties of photorefractive semiconductors

    NASA Astrophysics Data System (ADS)

    Dinu, Mihaela

    The photorefractive effect is a low intensity, nonlocal optical nonlinearity which has been studied extensively because of its potential uses. Photorefractive quantum wells exhibit record sensitivities and speeds, and are prime candidates for optical processing applications, both in the spatial (for images) and in the time domain (for the shaping of femtosecond pulses). For this latter application, multiple quantum well devices have to overcome a large bandwidth mismatch with femtosecond pulses, which arises from the resonant nature of photorefractivity at the bandgap. By engineering the excitonic transition spectrum of multiple quantum wells, the bandwidth of photorefractive multiple quantum well devices is increased to match that of ultrafast pulses. In superlattices, breaking of the spatial periodicity leads to the emergence of a wide distribution of critical points and transition energies; we have explored the effect of quasiperiodicity in Fibonacci superlattices, where excitonic interactions concentrate the oscillator strength at low energies and limit the useful diffractive bandwidth. Multiple quantum well structures in which the quantum wells are isolated and the quantum confinement can be tuned along the thickness of the device offer a wide parameter space for bandwidth design. In quantum well devices, almost dispersion-free diffraction can be achieved due to the Kramers-Kronig relationship between the real and imaginary parts of the electro-refraction, which makes the phase of the diffracted pulse linear in frequency. The second part of the thesis concentrates on the photorefractive effect in diluted magnetic semiconductors. In ZnMnSe epilayers, we demonstrate resonant photorefractive diffraction in the blue spectral region. Wide-gap II-VI semiconductors have characteristic properties (such as high absorption coefficients at the gap and low sensitivity to electric fields) which make the fabrication of resonant photorefractive devices in the transverse

  12. Diamond burr superficial keratectomy with mitomycin C for corneal scarring and high corneal astigmatism after pterygium excision

    PubMed Central

    Ozgurhan, Engin Bilge; Kara, Necip; Yildirim, Aydin; Alkin, Zeynep; Bozkurt, Ercument; Demirok, Ahmet

    2013-01-01

    Background The purpose of this paper is to report the successful treatment of corneal scarring and high corneal astigmatism secondary to previous pterygium surgery with diamond burr superficial keratectomy using mitomycin C. Methods Four patients with corneal scarring and high corneal astigmatism related to previous pterygium surgery underwent diamond burr superficial keratectomy with application of mitomycin C. Anterior segment photography and corneal topographic analysis were obtained preoperatively and postoperatively in all patients. Results Six months after surgery, corneal astigmatism and corneal aberrations were reduced in all patients. A clear cornea was achieved in all cases. No complications were noted during the follow-up period. Conclusion Diamond burr superficial keratectomy with application of mitomycin C is a potentially effective and simple procedure for treating patients with corneal scarring and high corneal astigmatism secondary to previous pterygium surgery. PMID:23737657

  13. Real-time contrast-enhanced holographic imaging using phase coherent photorefractive quantum wells.

    PubMed

    Dongol, A; Thompson, J; Schmitzer, H; Tierney, D; Wagner, H P

    2015-05-18

    We demonstrate wide-field real-time and depth-resolved contrast enhanced holographic imaging (CEHI) using the all-optical phase coherent photorefractive effect in ZnSe quantum wells. Moving objects are imaged at large depth-of-field by the local enhancement of a static reference hologram. The high refresh rate of the holographic films enables direct-to-video monitoring of floating glass beads and of living Paramecium and Euglena cells moving in water. Depth resolution is achieved by tilting the incident laser beam with respect to the normal of the cuvette. This creates double images of the objects, which are analyzed geometrically and with Fresnel diffraction theory. A two-color CEHI set-up further enables the visualization of a concealed 95 µm thick wire behind a thin layer of chicken skin. PMID:26074534

  14. Photovoltaic effect in Bi{sub 2}TeO{sub 5} photorefractive crystal

    SciTech Connect

    Oliveira, Ivan de Capovilla, Danilo Augusto

    2015-10-12

    We report on the presence of a strong photovoltaic effect on nominally undoped photorefractive Bi{sub 2}TeO{sub 5} crystals and estimated their Glass photovoltaic constant and photovoltaic field for λ = 532 nm illumination. We directly measured the photovoltaic-based photocurrent in this material under λ = 532 nm wavelength laser light illumination and compared its behavior with that of a well known photovoltaic Fe-doped Lithium Niobate crystal. We also show the photovoltaic current to strongly depend on the polarization direction of light. Holographic diffraction efficiency oscillation during recording and the behavior of fringe-locked running holograms in self-stabilized experiments are also demonstrated here as additional indirect proofs of the photovoltaic nature of this material.

  15. Observation of photorefractive effects in blue-phase liquid crystal containing fullerene-C60.

    PubMed

    Khoo, Iam Choon; Chen, Chun-Wei; Ho, Tsung-Jui

    2016-01-01

    Photorefractive effects manifested in two beam coupling and side diffractions are observed in fullerene-C60 doped blue-phase liquid crystals (BPLC-C60) upon application of a DC bias field. The mechanism at work here is attributed to BPLC lattice distortion by the combined DC (Edc)+ photorefractive space-charge (Ephoto) fields, in addition to the DC + optical field induced effects reported in previous studies of dye-doped system. The first order diffraction efficiency of ∼2×10-3 and beam coupling gain of over 2% are observed in a 55 μm thick sample with input laser beam power of 5 mW at an applied DC voltage of 160 V. The effective nonlinear index coefficient n2 of BPLC-C60 is measured to be on the order of 10-2  cm2/W, which is slightly lower than their NLC counterparts. Owing to the isotropy of BPLC optical properties, these effects can be observed with more relaxed requirements on the laser polarizations, directions of incidence, and sample orientations. PMID:26696174

  16. Waveguides formed by quasi-steady-state photorefractive spatial solitons

    NASA Astrophysics Data System (ADS)

    Morin, Matthew; Duree, Galen; Salamo, Gregory; Segev, Mordechai

    1995-10-01

    We show that a quasi-steady-state photorefractive spatial soliton forms a waveguide structure in the bulk of a photorefractive material. Although the optically induced waveguide is formed by a very low-power (microwatts) soliton beam, it can guide a powerful (watt) beam of a longer wavelength at which the medium is nonphotosensitive. Furthermore, the waveguide survives, either in the dark or when guiding the longer-wavelength beam, for a long time after the soliton beam is turned off. We take advantage of the solitons' property of evolution from a relatively broad input beam into a narrow channel and show that the soliton induces a tapered waveguide (an optical funnel) that improves the coupling efficiency of light into the waveguiding structure.

  17. Phase-shifting real-time holography with photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Gesualdi, M. R. R.; Soga, D.; Muramatsu, M.

    2006-01-01

    The phase-shifting interferometry techniques is a well-known technique which has been used with great success in optical profilers, micro-displacements, micro-deformations and others applications in Non-Destructive Test in basic research, engineering and biotechnology areas. This work presents our Advances in Phase-Shifting Real-Time Holography using Photorefractive Sillenite. And we have obtained quantitative results in many applications in measurements of micro-rotation, micro-displacements, deformation, surface contouring and whole lens wave-optics. The real-time holography process is doing using the photorefractive Bi 12SiO 20 crystal recording medium, where the phase-shifting 4-frames method for obtained the phase map, this was filtered by sin/cos filter and was applied the unwrapping process. The experimental results agree with the expected one in these applications and with promises potentialities of this method for studies with in situ visualization, monitoring and analysis.

  18. Photorefractivity in a Titanium Doped ZnCdTe Crystal

    NASA Technical Reports Server (NTRS)

    Davis, M.; Collins, L.; Dyer, K.; Tong, J.; Ueda, A.; Chen, H.; Chen, K.-T.; Burger, A.; Pan, Z.; Morgan, S. H.

    1997-01-01

    Single crystals of Zn(.04)Cd(.96)Te was grown by horizontal physical vapor transport (PVT) method and doped by annealing with TiTe2 powder at 600 C for six days. Photorefractive two-beam coupling, along with photoluminescence and absorption spectroscopy, were used to characterize the ZnCdTe:Ti crystal. At 1.32 micrometers, the photorefractive gain has been measured as a function of the grating period. A gain of about 0.16/cm was obtained at an intensity of about 0.1 W/sq cm. The results of this titanium doped ZnCdTe crystal are compared to that of vanadium-doped CdTe crystals reported previously.

  19. Photoconductivity and photoconversion at a photorefractive thin crystal plate

    NASA Astrophysics Data System (ADS)

    Frejlich, Jaime; de Oliveira, Ivan; de Araujo, William R.; Carvalho, Jesiel F.; Montenegro, Renata; Georges, Marc; Fleury-Frenette, Karl

    2016-05-01

    We report on the photoconductivity and the photoelectric conversion measured on a thin photorefractive sillenite crystal plate, between transparent electrodes, in the longitudinal configuration where the current is measured along the same direction of the light beam through the sample. Its behavior is based on the already reported light-induced Schottky effect. The wavelength for optimal photoconductivity is determined. A specific parameter is formulated here for quantitatively determining the photoelectric conversion efficiency of the sandwiched material.

  20. Near-infrared sensitive organic-inorganic photorefractive device

    NASA Astrophysics Data System (ADS)

    Marinova, Vera; Liu, Ren-Chung; Lin, Shiuan-Huei; Chen, Ming-Syuan; Lin, Yi-Hsin; Hsu, Ken-Yuh

    2016-07-01

    Organic-inorganic hybrid structure, assembled by Rh-doped Bi12TiO20 crystal and liquid crystal (LC) layer, operating at near-infrared range is proposed and demonstrated. Due to the photorefractive properties of inorganic substrate, light illumination caused a space charge field which acts as a driving force for LC molecules re-alignment and subsequent refractive index modulation. All optically controlled phase retardation ability has been demonstrated supporting possibilities for further infrared applications.

  1. Output behavior based on writing occupancy in a photorefractive converter

    NASA Astrophysics Data System (ADS)

    Zerbino, Lia M.; Tebaldi, M.; Bolognini, N.

    2007-05-01

    In this paper, a one-dimensional image distribution is stored as modulation of birefringence in a BSO photorefractive crystal in an incoherent to coherent converter arrangement. The features of the read-out image under different write-in image magnifications of an input object are analyzed. In particular, characteristic parameters are introduced to assess the feasibility of an adequate recognition of the converted image. Experimental results under extinction configuration obtained by using intensity-normalized images are described.

  2. Phase-modulated beams technique for thin photorefractive films characterization

    NASA Astrophysics Data System (ADS)

    Barmenkov, Yu. O.; Kir'yanov, A. V.; Starodumov, A. N.; Kozhevnikov, N. M.; Lemmetyinen, H.

    2000-04-01

    The phase-modulated beams technique is developed for nonlinear thin photorefractive films characterization. In the Raman-Nath diffraction approximation, the formulas are deduced, allowing us to measure the amplitude of phase grating recorded in a film and its nonlinear refractive index n2. The method is applied for studying Langmuir-Blodgett multilayer thin (˜0.6 μm) films of Bacteriorhodopsin at wavelength 633 nm.

  3. Improvements in the data fidelity of photorefractive memories

    NASA Astrophysics Data System (ADS)

    Neifeld, Mark A.

    1995-08-01

    Parallel error decoding is discussed for 2D page access optical memory. Both parallel space- domain and parallel spectral-domain Reed-Solomon decoders are discussed and compared with conventional serial decoding implementations. The parallel approach is found to yield information rates of nearly 1012 bps. A methodology is also presented for 4f optical storage system design. This approach allows the photorefractive crystal volume to be minimized while maintaining the maximum storage capacity that is consistent with a given SNR requirement.

  4. Photorefractivity in liquid crystals doped with a soluble conjugated polymer.

    SciTech Connect

    Niemczyk, M. P.; Svec, W. A.; Wasielewski, M. R.; Wiederrecht, G. P.

    1999-07-07

    Photoconductive polymers are doped into liquid crystals to create a new mechanism for space-charge field formation in photorefractive liquid crystal composites. The composites contain poly(2,5-bis(2{prime}-ethylhexyloxy)-1,4-phenylenevinylene) (BEH-PPV) and the electron acceptor N,N{prime}-dioctyl-1,4:5,8-naphthalenediimide, NI. Using asymmetric energy transfer (beam coupling) measurements that are diagnostic for the photorefractive effect, the direction of beam coupling as a function of grating fringe spacing inverts at a spacing of 5.5 {micro}m. We show that the inversion is due to a change in the dominant mechanism for space-charge field formation. At small fringe spacings, the space-charge field is formed by ion diffusion in which the photogenerated anion is the more mobile species. At larger fringe spacings, the polarity of the space charge field inverts due to dominance of a charge transport mechanism in which photogenerated holes are the most mobile species due to hole migration along the BEH-PPV chains coupled with interchain hole hopping. Control experiments are presented, which use composites that can access only one of the two charge transport mechanisms. The results show that charge migration over long distances leading to enhanced photorefractive effects can be obtained using conjugated polymers dissolved in liquid crystals.

  5. Vibration modal analysis using all-optical photorefractive processing

    SciTech Connect

    Hale, T.; Telschow, K.

    1996-12-31

    A new experimental method for vibration modal analysis based on all- optical photorefractive processing is presented. The method utilizes an optical lock-in approach to measure phase variations in light scattered from optically rough, continuously vibrating surfaces. In this four-wave mixing technique, all-optical processing refers to mixing the object beam containing the frequency modulation due to vibration with a single frequency modulated pump beam in the photorefractive medium that processes the modulated signals. This allows for simple detection of the conjugate wavefront image at a CCD. The conjugate intensity is shown to be a function of the first-order ordinary Bessel function and linearly dependent on the vibration displacement induced phase. Furthermore, the results demonstrate the unique capabilities of the optical lock-in vibration detection technique to measure vibration signals with very narrow bandwidth (< 1 Hz) and high displacement sensitivity (sub-Angstrom). This narrow bandwidth detection can be achieved over a wide frequency range from the photorefractive response limit to the reciprocal of the photoinduced carrier recombination time. The technique is applied to determine the modal characteristics of a rigidly clamped circular disc from 10 kHz to 100 kHz.

  6. Photorefractivity in liquid crystals doped with a soluble conjugated polymer

    NASA Astrophysics Data System (ADS)

    Wiederrecht, Gary P.; Svec, Walter A.; Niemczyk, Mark P.; Wasielewski, Michael R.

    1999-10-01

    Photoconductive polymers are doped into liquid crystals to create a new mechanism for space-charge field formation in photorefractive liquid crystal composites. The composites contain poly(2,5-bis(2'-ethylhexyloxy)-1,4- phenylenevinylene) (BEH-PPV) and the electron acceptor N,N'- dioctyl-1,4:5,8-naphthalenediimide, NI. Using asymmetric energy transfer (beam coupling) measurements that are diagnostic for the photorefractive effect, the direction of beam coupling as a function of grating fringe spacing inverts at a spacing of 5.5 micrometers . We show that the inversion is due to a change in the dominant mechanism for space-charge field formation. At small fringe spacings, the space-charge field is formed by ion diffusion in which the photogenerated anion is the more mobile species. At larger fringe spacings, the polarity of the space charge field inverts due to dominance of a charge transport mechanism in which photogenerated holes are the most mobile spaces due to hole migration along the BEH-PPV chains coupled with interchain hole hopping. Control experiments are presented, which use composites that can access only one of the two charge transport mechanisms. The results show that charge migration over long distances leading to enhanced photorefractive effects can be obtained using conjugated polymers dissolved in liquid crystals.

  7. Effect of onion extract on corneal haze suppression after air assisted lamellar keratectomy

    PubMed Central

    KIM, Soohyun; PARK, Young Woo; LEE, Euiri; PARK, Sang Wan; PARK, Sungwon; NOH, Hyunwoo; KIM, Jong Whi; SEONG, Je Kyung; SEO, Kangmoon

    2015-01-01

    This study evaluated the effect of onion extract on corneal haze suppression after applying the air assisted lamellar keratectomy. The air assisted lamellar keratectomy was performed on 24 canine eyes. They were treated with an artificial tear (group C), prednisolone acetate (group P), onion extract (group O) and TGF-β1 (group T) three times per day from 7 to 28 days after the surgery. Corneal haze occurred on the all eyes and was observed beginning 7 days after the surgery. The haze was significantly decreased in groups P and O from day 14 compared with the group C using the clinical (group P; P=0.021, group O; P=0.037) and objective evaluation method (group P; P=0.021, group O; P=0.039). In contrast, it was significantly increased in group T from day 14 compared with group C based on the clinical (P=0.002) and objective evaluation method (P<0.001). Subsequently, these eyes were enucleated after euthanasia, and immunohistochemistry with α-SMA antibodies was done. The total green intensity for α-SMA was significantly more expressed in group T and significantly less expressed in groups P and O than in group C. Onion extract could have potential as a therapeutic in preventing corneal haze development by suppressing the differentiation of fibroblasts into myofibroblasts. PMID:26607134

  8. Effect of onion extract on corneal haze suppression after air assisted lamellar keratectomy.

    PubMed

    Kim, Soohyun; Park, Young Woo; Lee, Euiri; Park, Sang Wan; Park, Sungwon; Noh, Hyunwoo; Kim, Jong Whi; Seong, Je Kyung; Seo, Kangmoon

    2016-04-01

    This study evaluated the effect of onion extract on corneal haze suppression after applying the air assisted lamellar keratectomy. The air assisted lamellar keratectomy was performed on 24 canine eyes. They were treated with an artificial tear (group C), prednisolone acetate (group P), onion extract (group O) and TGF-β1 (group T) three times per day from 7 to 28 days after the surgery. Corneal haze occurred on the all eyes and was observed beginning 7 days after the surgery. The haze was significantly decreased in groups P and O from day 14 compared with the group C using the clinical (group P; P=0.021, group O; P=0.037) and objective evaluation method (group P; P=0.021, group O; P=0.039). In contrast, it was significantly increased in group T from day 14 compared with group C based on the clinical (P=0.002) and objective evaluation method (P<0.001). Subsequently, these eyes were enucleated after euthanasia, and immunohistochemistry with α-SMA antibodies was done. The total green intensity for α-SMA was significantly more expressed in group T and significantly less expressed in groups P and O than in group C. Onion extract could have potential as a therapeutic in preventing corneal haze development by suppressing the differentiation of fibroblasts into myofibroblasts. PMID:26607134

  9. Vector interactions of steady-state planar solitons in biased photorefractive media

    NASA Astrophysics Data System (ADS)

    Singh, S. R.; Carvalho, M. I.; Christodoulides, D. N.

    1995-11-01

    A theory describing the steady-state propagation of orthogonally polarized planar bright beams in biased photorefractive media is developed. Interactions between soliton states of each polarization in a strontium barium niobate photorefractive crystal are then investigated numerically. Our results indicate that such vector interactions can lead to a number of interesting effects such as beam compression and beam steering.

  10. Photorefractive and computational holography in the experimental generation of Airy beams

    NASA Astrophysics Data System (ADS)

    Suarez, Rafael A. B.; Vieira, Tarcio A.; Yepes, Indira S. V.; Gesualdi, Marcos R. R.

    2016-05-01

    In this paper, we present the experimental generation of Airy beams via computational and photorefractive holography. Experimental generation of Airy beams using conventional optical components presents several difficulties and a practically infeasible. Thus, the optical generation of Airy beams has been made from the optical reconstruction of a computer generated hologram implemented by a spatial light modulator. In the photorefractive holography technique, being used for the first time to our knowledge, the hologram of an Airy beam is constructed (recorded) and reconstructed (read) optically in a nonlinear photorefractive medium. The Airy beam experimental realization was made by a setup of computational and photorefractive holography using a photorefractive Bi12 TiO20 crystal as holographic recording medium. Airy beams and Airy beam arrays were obtained experimentally in accordance with the predicted theory; with excellent prospects for applications in optical trapping and optical communications systems.

  11. Diffraction response of photorefractive polymers over nine orders of magnitude of pulse duration

    PubMed Central

    Blanche, Pierre-Alexandre; Lynn, Brittany; Churin, Dmitriy; Kieu, Khanh; Norwood, Robert A.; Peyghambarian, Nasser

    2016-01-01

    The development of a single mode fiber-based pulsed laser with variable pulse duration, energy, and repetition rate has enabled the characterization of photorefractive polymer (PRP) in a previously inaccessible regime located between millisecond and microsecond single pulse illumination. With the addition of CW and nanosecond pulse lasers, four wave mixing measurements covering 9 orders of magnitudes in pulse duration are reported. Reciprocity failure of the diffraction efficiency according to the pulse duration for a constant energy density is observed and attributed to multiple excitation, transport and trapping events of the charge carriers. However, for pulses shorter than 30 μs, the efficiency reaches a plateau where an increase in energy density no longer affects the efficiency. This plateau is due to the saturation of the charge generation at high peak power given the limited number of sensitizer sites. The same behavior is observed in two different types of devices composed of the same material but with or without a buffer layer covering one electrode, which confirm the origin of these mechanisms. This new type of measurement is especially important to optimize PRP for applications using short pulse duration. PMID:27364998

  12. Diffraction response of photorefractive polymers over nine orders of magnitude of pulse duration

    NASA Astrophysics Data System (ADS)

    Blanche, Pierre-Alexandre; Lynn, Brittany; Churin, Dmitriy; Kieu, Khanh; Norwood, Robert A.; Peyghambarian, Nasser

    2016-07-01

    The development of a single mode fiber-based pulsed laser with variable pulse duration, energy, and repetition rate has enabled the characterization of photorefractive polymer (PRP) in a previously inaccessible regime located between millisecond and microsecond single pulse illumination. With the addition of CW and nanosecond pulse lasers, four wave mixing measurements covering 9 orders of magnitudes in pulse duration are reported. Reciprocity failure of the diffraction efficiency according to the pulse duration for a constant energy density is observed and attributed to multiple excitation, transport and trapping events of the charge carriers. However, for pulses shorter than 30 μs, the efficiency reaches a plateau where an increase in energy density no longer affects the efficiency. This plateau is due to the saturation of the charge generation at high peak power given the limited number of sensitizer sites. The same behavior is observed in two different types of devices composed of the same material but with or without a buffer layer covering one electrode, which confirm the origin of these mechanisms. This new type of measurement is especially important to optimize PRP for applications using short pulse duration.

  13. Diffraction response of photorefractive polymers over nine orders of magnitude of pulse duration.

    PubMed

    Blanche, Pierre-Alexandre; Lynn, Brittany; Churin, Dmitriy; Kieu, Khanh; Norwood, Robert A; Peyghambarian, Nasser

    2016-01-01

    The development of a single mode fiber-based pulsed laser with variable pulse duration, energy, and repetition rate has enabled the characterization of photorefractive polymer (PRP) in a previously inaccessible regime located between millisecond and microsecond single pulse illumination. With the addition of CW and nanosecond pulse lasers, four wave mixing measurements covering 9 orders of magnitudes in pulse duration are reported. Reciprocity failure of the diffraction efficiency according to the pulse duration for a constant energy density is observed and attributed to multiple excitation, transport and trapping events of the charge carriers. However, for pulses shorter than 30 μs, the efficiency reaches a plateau where an increase in energy density no longer affects the efficiency. This plateau is due to the saturation of the charge generation at high peak power given the limited number of sensitizer sites. The same behavior is observed in two different types of devices composed of the same material but with or without a buffer layer covering one electrode, which confirm the origin of these mechanisms. This new type of measurement is especially important to optimize PRP for applications using short pulse duration. PMID:27364998

  14. Controlling and synchronizing the spatiotemporal chaos of photorefractive ring oscillators with coupling

    NASA Astrophysics Data System (ADS)

    Chen, Xiaoxiao; Feng, Xiuqin; Tian, Zuolin; Yao, Zhihai

    2016-06-01

    We present the control and synchronization of spatiotemporal chaos in the photo-refractive ring oscillator systems with coupling technology. First, we realize the synchronization of spatiotemporal chaos in the two photorefractive ring oscillator systems via mutual coupling by choosing a suitable coupling strength. With the mutual coupling strength enlarging, the two mutual coupling photorefractive ring oscillator systems are controlled into periodic state, period number differs on account of the coupling strength and lattice coordinates. By increasing the coupling strength, the photorefractive ring oscillator is converted into period 8, subsequently it is converted into periods 4 and 2, periodic synchronization of the photorefractive ring oscillator systems is achieved at the same time. Calculation results show that period 1 is impossible by mutual coupling technology. Then, we investigate the influence of noise and parameter deviation on chaotic synchronization. We find that mutual coupling chaotic synchronization method can synchronize two chaotic systems with the weak noise and parameter deviation and has very good robustness. Given that the weak noise and parameter deviation have a slight effect on synchronization. Furthermore, we investigate two dimension control and synchronization of spatiotemporal chaos in the photorefractive ring osillator systems with coupling technology and get successful results. Mutual coupling technology is suitable in practical photorefractive ring oscillator systems.

  15. Valacyclovir for the prevention of recurrent herpes simplex virus eye disease after excimer laser photokeratectomy.

    PubMed Central

    Asbell, P A

    2000-01-01

    PURPOSE: A variety of factors have been reported as inducing the reactivation of latent herpes simplex virus (HSV), among them stress, trauma, and UV radiation. Excimer laser photorefractive keratectomy (PRK) is a surgical procedure utilizing a 193 nm ultraviolet light to alter the curvature of the cornea and hence correct vision. Reactivation of ocular herpes simplex keratitis following such excimer laser PRK has been reported. All published cases of HSV reactivation following excimer laser treatment in humans are reviewed. The present study evaluates whether stress, trauma of the corneal de-epithelialization prior to the laser, or the excimer laser treatment itself to the stromal bed induces this ocular reactivation of the latent HSV, and whether a systemic antiviral agent, valacyclovir, would prevent such laser PRK-induced reactivation of the HSV. METHODS: Forty-three normal 1.5- to 2.5-kg New Zealand white rabbits were infected on the surface of the cornea with HSV-1, strain RE. The animals were monitored until resolution, and then all animals were divided into 5 treatment groups: (1) de-epithelialization only, intraperitoneal (i.p.) saline for 14 days; (2) de-epithelialization plus laser, i.p. saline for 14 days; (3) de-epithelialization plus laser, valacyclovir 50 mg/kg per day i.p. for 14 days; (4) de-epithelialization plus laser, valacyclovir 100 mg/kg per day i.p. for 14 days; (5) de-epithelialization plus laser, valacyclovir 150 mg/kg per day i.p. for 14 days. Animals were evaluated in a masked fashion by clinical examination biweekly and viral cultures biweekly through day 28. RESULTS: The reactivation rates were as follows: group 1, 0%; group 2, 67%; group 3, 50%; group 4, 17%; and group 5, 0%. Viral titers were negative in animals that had no reactivation but persistently positive in those that had reactivation (day 6 through day 28). CONCLUSIONS: Excimer laser (193 nm) treatment can trigger reactivation of ocular herpes disease (67%) and viral

  16. The acute phase of inflammatory response involved in the wound-healing process after excimer laser treatment

    PubMed Central

    Resan, Mirko; Vukosavljevic, Miroslav; Vojvodic, Danilo; Pajic-Eggspuehler, Brigitte; Pajic, Bojan

    2016-01-01

    Purpose To evaluate the participation of proinflammatory cytokines in the acute phase of corneal wound-healing response after excimer laser treatment. Methods The study included 68 myopic eyes up to −3.0 diopters divided into two groups: 1) eyes treated with laser in situ keratomileusis (LASIK) (n=31) and 2) eyes treated with photorefractive keratectomy (PRK) (n=37). Each group was then divided into three subgroups based on tear sampling times: before (0 hours), 1 hour after, and 24 hours after treatment. The tear fluid was sampled from lower lateral tear meniscus using a cellulose microsurgical sponge. The levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and IL-8 in tear fluid were determined by flow cytometry method. Results Statistical significance was observed in the concentrations of TNF-α (P=0.0421) and IL-1β (P=0.0225) between samples collected 1 and 24 hours after PRK treatment in favor of samples collected 1 hour after treatment. IL-6 concentration changes showed a significant increase in the PRK group in both time intervals following treatment compared to pretreatment (0 hour/1 hour, P=0.0031; 0 hour/24 hours, P=0.0059). For IL-8 concentrations, significant differences were observed between control and experimental groups in samples collected 1 hour after LASIK and 1 hour after PRK treatment (P<0.001 for both groups), and IL-8 concentrations between control and experimental groups in samples collected 24 hours after LASIK and 24 hours after PRK treatment were greater after PRK treatment (P=0.0005). Comparison of average concentration values of proinflammatory cytokines in all the tested samples between LASIK and PRK groups showed significantly higher levels of IL-1β in the LASIK group 24 hours after treatment (P=0.0134), and of IL-6 in the PRK group 24 hours after treatment (P=0.0031). Conclusion The acute phase of corneal wound healing after excimer laser treatment is defined by an intensive inflammatory response. After PRK

  17. Photorefractive properties of iron-doped lithium tantalate crystals

    NASA Astrophysics Data System (ADS)

    Imbrock, J.; Bäumer, C.; Hesse, H.; Kip, D.; Krätzig, E.

    Iron-doped lithium tantalate crystals are grown by the Czochralski method and their photorefractive properties are examined with holographic methods. Dynamic range, holographic sensitivity, photoconductivity, and dark storage time are measured in dependence on the iron concentration and light intensity. The largest refractive-index change for ordinarily polarized light is 3.5×10-4, in comparison with 6.2×10-4 for iron-doped lithium niobate. Due to a small mobility of protons the dark storage time of holograms in lithium tantalate is larger than that in lithium niobate.

  18. Surface multipole solitons on photorefractive media with Bessel optical lattices

    NASA Astrophysics Data System (ADS)

    Hong, Woo-Pyo

    2015-03-01

    We find the existence conditions for new surface crescent, dipole, tripole, and quadrupole solitons formed at the interface of a focusing photorefractive medium and a medium imprinted with a Bessel optical lattice. We demonstrate by using numerical simulations that the crescent and the dipole solitons show oscillatory behaviors in their amplitude and shape while the tripole and the quadrupole solitons maintain a remarkable rigidity during propagation. Based on a linear stability analysis, we classify the stability region of the tripole and the quadrupole surface solitons in terms of the Bessel optical lattice strength and the Bessel index.

  19. Nonlinear dynamic theory for photorefractive phase hologram formation

    NASA Technical Reports Server (NTRS)

    Kim, D. M.; Shah, R. R.; Rabson, T. A.; Tittle, F. K.

    1976-01-01

    A nonlinear dynamic theory is developed for the formation of photorefractive volume phase holograms. A feedback mechanism existing between the photogenerated field and free-electron density, treated explicitly, yields the growth and saturation of the space-charge field in a time scale characterized by the coupling strength between them. The expression for the field reduces in the short-time limit to previous theories and approaches in the long-time limit the internal or photovoltaic field. Additionally, the phase of the space charge field is shown to be time-dependent.

  20. Selective properties of volume phase holograms in photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Pencheva, T. G.; Petrov, M. P.; Stepanov, S. I.

    1982-01-01

    The paper deals with the selective properties (both angular and spectral) of volume phase holograms in birefringent and cubic optically active photorefractive crystals. It is shown that in birefringent crystals of LiNbO 3 type, the spectral selectivity of the grating depends remarkably on the type of diffraction (isotropic or anisotropic) and the polarization of the reconstructing plane light wave. In cubic optically active crystals the peculiarities of diffraction reveal themselves in a fine structure of differently polarized peaks in the Bragg maximum that can be easily observed, in particular in Bi 12SiO 20 samples with a thickness d ≈ 8 mm.

  1. Defect-mediated discrete solitons in optically induced photorefractive lattices

    SciTech Connect

    Li Yongyao; Pang Wei; Chen Yongzhu; Yu Zhiqiang; Zhou Jianying; Zhang Huarong

    2009-10-15

    Theoretical analysis to the defect mediated discrete solitons in one- and two-dimensional periodical waveguide lattices is presented. The waveguide arrays with these functional defects are assumed to respond to the light field as an optically induced photorefraction and they are patterned by a holographic technique. It is found that the spatial energy distributions of the solitary waves can be controlled by the defects in the waveguide arrays, and this gives rise to an additional freedom to externally shaping the light field distribution to a special shape.

  2. Photorefractive effect in CdMnTe:V Crystal

    NASA Technical Reports Server (NTRS)

    Pour, K. M.; Chattopadahyay, K.; Chen, H.; Chen, K. T.; Morgan, S.; Burger, A.

    1998-01-01

    We present two-wave mixing result obtained with a CdMnTe:V crystal. A photorefractive gain coefficient of 0.20 /cm was observed at 633 nm with the signal-to-pump ratio being of the order of 10(exp -3). This crystal was grown by vertical Bridgman Technique and doped with Vanadium during the growth. The crystal were of good optical quality and showed high resistivity. Room temperature absorption and low temperature photoluminescence studies comparing the band edge and defect center at the doped and undoped CdMnTe crystal will also be discussed.

  3. A design study of a photorefractive page composer

    NASA Technical Reports Server (NTRS)

    1975-01-01

    A laboratory demonstration and preliminary system analysis of a page composer designed to have the dual advantages of low optical loss and small size, were reported. The current page composer is optically addressed and functions by virtue of optically induced refractive index changes in the active material. Laboratory demonstrations of the device were successfully performed using 10 x 10 bit and 128 x 128 bit data arrays. It was established that the only significant obstacle to the construction of a brass-board model working at megabit data rates is the lack of sensitivity of the photorefractive materials which were considered during the course of this study. Possible materials for future consideration are the photoplastics. While they have more than the required sensitivity, their stability and suitability for double exposure holography was not investigated. If a sufficiently sensitive material is found, then the photorefractive page composer could be built to perform in a highly efficient fashion which would result in a overall reduction of the size of the memory system and an easing of the requirements upon the sensitivity of the holographic recording material.

  4. Geometrical theory to predict eccentric photorefraction intensity profiles in the human eye

    NASA Astrophysics Data System (ADS)

    Roorda, Austin; Campbell, Melanie C. W.; Bobier, W. R.

    1995-08-01

    In eccentric photorefraction, light returning from the retina of the eye is photographed by a camera focused on the eye's pupil. We use a geometrical model of eccentric photorefraction to generate intensity profiles across the pupil image. The intensity profiles for three different monochromatic aberration functions induced in a single eye are predicted and show good agreement with the measured eccentric photorefraction intensity profiles. A directional reflection from the retina is incorporated into the calculation. Intensity profiles for symmetric and asymmetric aberrations are generated and measured. The latter profile shows a dependency on the source position and the meridian. The magnitude of the effect of thresholding on measured pattern extents is predicted. Monochromatic aberrations in human eyes will cause deviations in the eccentric photorefraction measurements from traditional crescents caused by defocus and may cause misdiagnoses of ametropia or anisometropia. Our results suggest that measuring refraction along the vertical meridian is preferred for screening studies with the eccentric photorefractor.

  5. Fault tolerant all-optical router with photorefractive all-optical switch

    NASA Astrophysics Data System (ADS)

    Kaino, Toshiya; Okamoto, Atsushi; Honma, Satoshi

    2003-08-01

    We propose a new type of the fault tolerant all-optical router (FTAR) by using an all-optical switch with photorefractive two-wave mixing. FTAR can detect a cutoff of a main transmitting line and automatically reroute a signal beam from the main line to a backup line. These functions can increase communication reliability of optical wireless. FTAR is composed of ony all-optical devices without any electronic devices or any mechanical operations. In the new type of FTAR, the routing of the signal beam is controlled by a control beam transmitting on the main line from a different light source at a receiver in the opposite direction with the signal beam. Compared with the previous type of FTAR composed of two photorefractinve crystals, the new configuration offers the simplification of the construction and high transmission efficiency of the signal beam. In this report, we experiment on the FTAR by usign a BaTiO3 and Ar+ laser whose wavelength is 514.5nm, and confirm the fundamental fucntin of FTAR. We give comparison of the result with the numerical analysis. We also analyze the dependence of the switching time on the input beam intensity of the crystal by a numerical analysis and an experiment.

  6. Holographic three-dimensional telepresence using large-area photorefractive polymer.

    PubMed

    Blanche, P-A; Bablumian, A; Voorakaranam, R; Christenson, C; Lin, W; Gu, T; Flores, D; Wang, P; Hsieh, W-Y; Kathaperumal, M; Rachwal, B; Siddiqui, O; Thomas, J; Norwood, R A; Yamamoto, M; Peyghambarian, N

    2010-11-01

    Holography is a technique that is used to display objects or scenes in three dimensions. Such three-dimensional (3D) images, or holograms, can be seen with the unassisted eye and are very similar to how humans see the actual environment surrounding them. The concept of 3D telepresence, a real-time dynamic hologram depicting a scene occurring in a different location, has attracted considerable public interest since it was depicted in the original Star Wars film in 1977. However, the lack of sufficient computational power to produce realistic computer-generated holograms and the absence of large-area and dynamically updatable holographic recording media have prevented realization of the concept. Here we use a holographic stereographic technique and a photorefractive polymer material as the recording medium to demonstrate a holographic display that can refresh images every two seconds. A 50 Hz nanosecond pulsed laser is used to write the holographic pixels. Multicoloured holographic 3D images are produced by using angular multiplexing, and the full parallax display employs spatial multiplexing. 3D telepresence is demonstrated by taking multiple images from one location and transmitting the information via Ethernet to another location where the hologram is printed with the quasi-real-time dynamic 3D display. Further improvements could bring applications in telemedicine, prototyping, advertising, updatable 3D maps and entertainment. PMID:21048763

  7. Nonresonant four-wave mixing in photorefractive CdTe crystals using a picosecond parametric generator

    NASA Astrophysics Data System (ADS)

    JarašiÅ«nas, Kestutis; Gudelis, Vytautas; Delaye, Philippe; Roosen, Gerald

    1998-11-01

    We demonstrate that a parametrically pumped picosecond laser has enough coherence and energy to write transient phase gratings at nonresonant interaction, thus allowing a study of time-resolved carrier transport in CdTe crystals to be made. Autocorrelation trace of light diffraction efficiency on transient grating allowed us to measure a coherence length of the parametric generator. Carrier diffusion, recombination, and drift in light-created internal space-charge (SC) electric fields have been studied in vanadium or germanium doped semi-insulating CdTe crystals by nonresonant four-wave mixing technique at 940 nm wavelength. It was found that modification of the deep level charge state in CdTe:V by As codoping has changed the sign of majority carriers, responsible for the creation of SC field. Dynamics of free carrier grating decay in CdTe:Ge revealed an electron-governed very fast initial grating decay which develops with time into the double-exponential hole-governed grating decay. Time-resolved transient grating technique described in this article provides a powerful tool for investigation of the role of deep traps in photorefractive semiconductors and optimization of their photoelectric properties in a required temporal and spectral range.

  8. Picosecond enhancement of photorefractive beam coupling in CdTe:V at 960 nm

    NASA Astrophysics Data System (ADS)

    Andreas Schroeder, W.; Stark, Thomas S.; Smirl, Arthur L.; Valley, George C.

    1991-08-01

    Photorefractive beam coupling in CdTe:V is observed with single 1 ps pulses at a wavelength of 960 nm. Coupling coefficients are substantially larger than observed with 30 ps pulses at 1.06 μm and nearly a factor of 100 larger than calculations based on conventional transport properties of CdTe. We consider anomalously large carrier diffusion (hot carriers) as a possible mechanism for the production of this nonlocal photorefractive grating.

  9. Change in the refractive index of a photorefractive crystal during formation of a spatially screened soliton

    SciTech Connect

    Assel'born, Sergei A; Kundikova, Nataliya D; Novikov, Igor' V

    2010-02-28

    A change in the refractive index of a photorefractive barium-sodium niobate crystal in an alternating electric field during the propagation of intensity-modulated coherent radiation in it is studied. It is shown experimentally that a change in the refractive index in the soliton regime in a photorefractive crystal with a small nonlocal response is independent of the external-field amplitude and intensity-modulation depth. (nonlinear-optics phenomena)

  10. Non-contact measurements of ultrasonic waves on paper webs using a photorefractive interferometer

    DOEpatents

    Brodeur, Pierre H.; Lafond, Emmanuel F.

    2000-01-01

    An apparatus and method for non-contact measurement of ultrasonic waves on moving paper webs employs a photorefractive interferometer. The photorefractive interferometer employs an optical head in which the incident beam and reflected beam are coaxial, thus enabling detection of both in-plane and out-of-plane waves with a single apparatus. The incident beam and reference beams are focused into a line enabling greater power to be used without damaging the paper.

  11. Photorefractive and photochromic effects in undoped GaP at high temperature

    NASA Astrophysics Data System (ADS)

    Horiuchi, Kenji; Kuroda, Kazuo

    1995-01-01

    Photorefractive and photochromic effects are investigated in undoped semi-insulating GaP at high temperature. The photochromic effect takes place at the temperature above 340 K and the depreciation of the photorefractive coupling coefficient is observed above 385 K. These results suggest the existence of additional donor and acceptor levels. The binding energy of the donor level is estimated to be 420 meV.

  12. Surface defect lattice solitons in biased photovoltaic-photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Hui, Juanli; Lu, Keqing; Zhang, Baoju; Zhang, Jun; Xing, Haiying

    2015-12-01

    We show that surface defect lattice solitons (SDLSs) at the interface with a defect between the photonic lattices and the uniform photovoltaic-photorefractive (PP) crystals with external applied field are possible. These SDLSs exist only in the semi-infinite gap for positive defect strength, and in the semi-infinite, first, and second gaps for negative defect strength. In the semi-infinite gap, SDLSs are stable in the low power region and unstable in the high power region. In the first and second gaps, SDLSs are stable in the all power region. We find that these SDLSs are those studied previously in biased non-PP crystals when the bulk photovoltaic effect is negligible and are those in PP crystals when the external bias field is absent.

  13. Photorefractive materials for nonvolatile volume holographic data storage

    PubMed

    Hesselink; Orlov; Liu; Akella; Lande; Neurgaonkar

    1998-11-01

    Optically gated recording and nonvolatile readout in a digital volume holographic data storage system that uses a pair of mutually incoherent light sources during recording and only one for readout were demonstrated recently. This approach used stoichiometric lithium niobate, which after post-growth processing gave rise to an at least two orders of magnitude improvement in sensitivity over the best materials reported previously. It is also shown that by adding certain dopants (iron and manganese) to near-stoichiometric lithium niobate, the dark storage time and gating efficiency can be increased compared with previous work. The underlying physical mechanisms of gated recording and the effectiveness of the gating process responsible for this manifold improved performance are discussed, and bipolarons and small polarons are identified as the responsible photorefractive species. PMID:9804540

  14. Structural homogeneity of photorefractive LiNbO3 crystals doped with 0.03-4.5 mol % of ZnO

    NASA Astrophysics Data System (ADS)

    Sidorov, N. V.; Palatnikov, M. N.; Teplyakova, N. A.; Gabain, A. A.; Efremov, I. N.

    2016-04-01

    Using the electronic spectroscopy method, the laser-conoscopy method, and the Raman light-scattering method, we have studied the structural homogeneity of LiNbO3 crystals doped with 0.03-4.5 mol % of ZnO. We have found that, as the laser radiation power is increased to 90 mW, the conoscopic patterns of crystals show additional distortions, which are attributed to the manifestation of the photorefractive effect. For the LiNbO3 crystal doped with 4.5 mol % of ZnO, in which the photorefractive effect is low, we have revealed a considerable shift (compared to the remaining crystals) of the optical absorption edge toward the shortwavelength range, which indicates a high structural homogeneity of this crystal. We have shown that, in the LiNbO3 crystal doped by 0.05 mol % ZnO, due to the displacement of NbLi and Li□ structural defects by Zn2+ cations, the crystal structure is ordered and, simultaneously, the number of defects with localized electrons decreases.

  15. Effects of Lamellar Keratectomy and Intrastromal Injection of 0.2% Fluconazole on Fungal Keratitis

    PubMed Central

    You, Xinying; Li, Jun; Li, Suxia; Shi, Weiyun

    2015-01-01

    Purpose. To evaluate effects of lamellar keratectomy and intrastromal injection of 0.2% fluconazole (LKIIF) on fungal keratitis. Methods. Data for 54 eyes of consecutive patients with fungal keratitis treated with LKIIF were retrospectively analyzed. The lesions in these eyes did not heal or were aggravated after antifungal chemotherapy for 7 days. The maximum lesion diameters were ≤5 mm and maximum depth was not more than half of full corneal thickness. Cases were followed up for at least 90 days. Results. Forty-six eyes were cured (85.2%). The wound healing times were 3–16 days and were less than 7 days in 28 cases (51.9%). In cured eyes, uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) were both 20/250–20/20. The UCVA improved in 38 eyes and was unchanged in seven eyes. BCVA improved in 44 eyes and was unchanged in two eyes. When followed up for more than 90 days, 89% (41 of 46 eyes) showed improvement in UCVA and 11% were unchanged. Regarding BCVA, 98% improved and one eye was unchanged. No other complications were observed except neovascularization in one eye and thinner corneas. Conclusions. LKIIF was quick and effective for small fungal keratitis confined to half of the corneal thickness. PMID:26064673

  16. Topological dynamics of optical singularities in speckle-fields induced by photorefractive scattering in a LiNbO{sub 3} : Fe crystal

    SciTech Connect

    Vasil'ev, Vasilii I; Soskin, M S

    2013-02-28

    A natural singular dynamics of elliptically polarised speckle-fields induced by the 'optical damage' effect in a photorefractive crystal of lithium niobate by a passing beam of a helium - neon laser is studied by the developed methods of singular optics. For the polarisation singularities (C points), a new class of chain reactions, namely, singular chain reactions are discovered and studied. It is shown that they obey the topological charge and sum Poincare index conservation laws. In addition, they exist for all the time of crystal irradiation. They consist of a series of interlocking chains, where singularity pairs arising in a chain annihilate with singularities from neighbouring independently created chains. Less often singular 'loop' reactions are observed where arising pairs of singularities annihilate after reversible transformations in within the boundaries of a single speckle. The type of a singular reaction is determined by a topology and dynamics of the speckles, in which the reactions are developing. (laser optics 2012)

  17. Lasers.

    ERIC Educational Resources Information Center

    Schewe, Phillip F.

    1981-01-01

    Examines the nature of laser light. Topics include: (1) production and characteristics of laser light; (2) nine types of lasers; (3) five laser techniques including holography; (4) laser spectroscopy; and (5) laser fusion and other applications. (SK)

  18. Photorefractive nonlinearities caused by the Dember space-charge field in undoped CdTe

    NASA Astrophysics Data System (ADS)

    Schroeder, W. Andreas; Stark, Thomas S.; Boggess, Thomas F.; Smirl, Arthur L.; Valley, George C.

    1991-06-01

    The decay of a photorefractive grating in undoped CdTe produced by subband-gap picosecond excitation has been isolated and temporally resolved. The grating is observed to decay completely at the same rate as the free-carrier grating, a rate consistent with the decay of a 1.7 micron-period grating by ambipolar diffusion. This provides convincing evidence that the source of the photorefractive grating is the Dember space-charge field that is established between electron-hole pairs created by band-to-band two-photon absorption. This establishes the Dember field as a source for the photorefractive space-charge field that can be turned on in the dielectric relaxation time and turned off in the ambipolar diffusion time. It also allows the material to recover fully in the recombination lifetime which can be adjusted by doping or damaging the material.

  19. Orientational photorefractive properties in polymer-dispersed liquid crystals with different polymer matrixes

    NASA Astrophysics Data System (ADS)

    Ono, Hiroshi; Saito, Isao; Kawatsuki, Nobuhiro

    1998-10-01

    We report orientational photorefractive effects observed in photoconductive liquid crystals (LCs) contained with three kinds of polymer, i.e., poly(methyl methacrylate) (PMMA), poly(vinyl alcohol) (PVA) and a side-chain liquid crystalline polymer (SLCP1). The morphology of the photorefractive composites depended on the kind of polymer strongly. In both PMMA and PVA cases, LC and polymer were phase-separated and the composite showed memory effects. In SLCP1 case, the phase-separation in the composite dose not occur and the high resolution could be achieved. In this case, the photorefractive Bragg gratings were generated and a high two-beam coupling gain coefficient with a low applied field of 4 V/micrometers was observed.

  20. Photorefractive Bragg gratings in nematic liquid crystals aligned by a magnetic field

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R. |

    1999-06-01

    Photorefractive Bragg gratings are observed in low-molar-mass nematic liquid crystals doped with electron donor and acceptor molecules. This is accomplished by alignment of the nematic liquid crystals in a 0.3 T magnetic field, which produces thicker homeotropic aligned samples than traditional surfactant techniques. Grating fringe spacings as low as 3.7 {mu}m are achieved with 176-{mu}m-thick samples, producing grating {ital Q} values of 33. Up to this point, low molar mass nematic liquid crystals have exhibited photorefractive gratings with Q{le}1. Asymmetric two-beam coupling and photoconductivity experiments are performed to verify the photorefractive origin of the gratings. {copyright} {ital 1999 American Institute of Physics.}

  1. Effects of the induced birefringence in photorefractive crystals on speckle optical vortices

    NASA Astrophysics Data System (ADS)

    Gómez, Jorge A.; Rueda, Edgar; Salazar, Ángel; Tebaldi, Myriam; Bolognini, Nestor; Lencina, Alberto

    2012-03-01

    In this work, we show that it is possible to change the properties of an optical vortex formed in a speckle pattern by the control of an external electric field applied to a sillenite-type photorefractive material in a non-holographic configuration. To show it, a scheme that allows the recovering of both, the polarization state and the phase distribution of an optical field was implemented. Changes in the polarization state of the light in the neighborhood of the vortex were observed with the application of an external electric field. Likewise, changes in the phase structure around the vortex and displacements of the vortices themselves were measured. These displacements have a fairly linear dependence on the applied field to the photorefractive crystal. Experimental results are qualitatively explained with the theoretical treatment of non-holographic recording in photorefractive crystals.

  2. Optical distributed sensors for feedback control: Characterization of photorefractive resonator

    NASA Technical Reports Server (NTRS)

    Indebetouw, Guy; Lindner, D. K.

    1992-01-01

    The aim of the project was to explore, define, and assess the possibilities of optical distributed sensing for feedback control. This type of sensor, which may have some impacts in the dynamic control of deformable structures and the monitoring of small displacements, can be divided into data acquisition, data processing, and control design. Analogue optical techniques, because they are noninvasive and afford massive parallelism may play a significant role in the acquisition and the preprocessing of the data for such a sensor. Assessing these possibilities was the aim of the first stage of this project. The scope of the proposed research was limited to: (1) the characterization of photorefractive resonators and the assessment of their possible use as a distributed optical processing element; and (2) the design of a control system utilizing signals from distributed sensors. The results include a numerical and experimental study of the resonator below threshold, an experimental study of the effect of the resonator's transverse confinement on its dynamics above threshold, a numerical study of the resonator above threshold using a modal expansion approach, and the experimental test of this model. A detailed account of each investigation, including methodology and analysis of the results are also included along with reprints of published and submitted papers.

  3. Photorefractivity in polymer-stabilized nematic liquid crystals

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R. |

    1998-07-01

    Polymer-stabilized liquid crystals, consisting of low concentrations of a polymeric electron acceptor, are shown to exhibit significantly enhanced photorefractive properties. The charge generation and transport properties of these composite systems are strongly modified from nematic liquid crystals doped with electron donors and acceptors. The new composites are produced by polymerizing a small quantity of a 1,4:5,8-naphthalenediimide electron acceptor functionalized with an acrylate group in an aligned nematic liquid crystal. Photopolymerization creates an anisotropic gel-like medium in which the liquid crystal is free to reorient in the presence of a space charge field, while maintaining charge trapping sites in the polymerized regions of the material. The presence of these trapping sites results in the observation of longer lived, higher resolution holographic gratings in the polymer-stabilized liquid crystals than observed in nematic liquid crystals alone. These gratings display Bragg regime diffraction. Asymmetric beam coupling, photo-conductivity, and four-wave mixing experiments are performed to characterize the photophysics of these novel materials.

  4. Photorefractivity in polymer-stabilized nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Wiederrecht, Gary P.; Wasielewski, Michael R.

    1998-10-01

    Polymer-stabilized liquid crystals, consisting of low concentrations of a polymeric electron acceptor, are shown to exhibit significantly enhanced photorefractive properties. The charge generation and transport properties of these composite systems are strongly modified from nematic liquid crystals doped with electron donors and acceptors. The new composites are produced by polymerizing a small quantity of a 1,4:5,8-naphthalenediimide electron acceptor functionalized with an acrylate group in an aligned nematic liquid crystal. Photopolymerization creates an anisotropic gel-like medium in which the liquid crystal is free to reorient in the presence of a space charge field, while maintaining charge trapping sites in the polymerized regions of the material. The presence of these trapping sites results in the observation of longer lived, higher resolution holographic gratings in the polymer-stabilized liquid crystals than observed in nematic liquid crystals alone. These gratings display Bragg regime diffraction. Asymmetric beam coupling, photo-conductivity, and four-wave mixing experiments are performed to characterize the photophysics of these novel materials.

  5. Numerical solution for Nagumo's equation for the electron density in photorefractive materials

    NASA Astrophysics Data System (ADS)

    Magaña, Fernando

    2005-03-01

    We study the distribution of the electron density in a photorefractive material, using a set of nonlinear partial differential equations, that describes the physical response of photorefractive systems under inhomogeneous ilumination based on the band transport model, proposed by Kukhtarev et al. (Ferroelectrics, vol. 22, 949 (1979)). Assuming that the electron density only depends of x coordinate and taking a constant external electric field E in the same x coordinate we find that the electron density obeys a Nagumo's equation whose solution is soliton type.

  6. IR sensitive photorefractive polymers, the first updateable holographic three-dimensional display

    NASA Astrophysics Data System (ADS)

    Tay, Savas

    This work presents recent advances in the development of infra-red sensitive photorefractive polymers, and updateable near real-time holographic 3D displays based on photorefractive polymers. Theoretical and experimental techniques used for design, fabrication and characterization of photorefractive polymers are outlined. Materials development and technical advances that made possible the use of photorefractive polymers for infra-red free-space optical communications, and 3D holographic displays are presented. Photorefractive polymers are dynamic holographic materials that allow recording of highly efficient reversible holograms. The longest operation wavelength for a photorefractive polymer before this study has been 950nm, far shorter than 1550nm, the wavelength of choice for optical communications and medical imaging. The polymers shown here were sensitized using two-photon absorption, a third order nonlinear effect, beyond the linear absorption spectrum of organic dyes, and reach 40% diffraction efficiency with a 35ms response time at this wavelength. As a consequence of two-photon absorption sensitization they exhibit non-destructive readout, which is an important advantage for applications that require high signal-to-noise ratios. Holographic 3D displays provide highly realistic images without the need for special eyewear, making them valuable tools for applications that require "situational awareness" such as medical, industrial and military imaging. Current commercially available holographic 3D displays employ photopolymers that lack image updating capability, resulting in their restricted use and high cost per 3D image. The holographic 3D display shown here employs photorefractive polymers with nearly 100% diffraction efficiency and fast writing time, hours of image persistence, rapid erasure and large area, a combination of properties that has not been shown before. The 3D display is based on stereography and utilizes world's largest photorefractive

  7. Photorefractive nonlinearities caused by the Dember space-charge field in undoped CdTe.

    PubMed

    Schroeder, W A; Stark, T S; Boggess, T F; Smirl, A L; Valley, G C

    1991-06-01

    The photorefractive nonlinearity associated with the Dember space-charge field between electrons and holes produced by two-photon absorption is unambiguously isolated and studied in undoped CdTe by using a nondegenerate, forward-probing, polarization-sensitive, transient-grating technique with a temporal resolution of <5 ps. PMID:19776789

  8. Implementation of a photorefractive correlator based on a fake zoom lens

    NASA Astrophysics Data System (ADS)

    Rueda, Jorge Enrique; Tebaldi, Myrian; Granieri, Sergio; Bolognini, Nestor

    A space-variant optical correlator is experimentally implemented based on the fractional Fourier transform. The proposed arrangement employs a fake zoom lens that enables to vary the degree of the fractional Fourier transform continuously between -1 to +1. The optical device uses as a recording medium for the holographic filter a photorefractive BTO crystal. The experimental results confirm the shift-variance properties.

  9. Image processing by four-wave mixing in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Gheen, Gregory; Cheng, Li-Jen

    1987-01-01

    Three image processing experiments were performed by degenerate four-wave mixing in photorefractive GaAs. The experiments were imaging by phase conjugation, edge enhancement, and autocorrelation. The results show that undoped, semiinsulating, liquid-encapsulated Czochralski-grown GaAs crystals can be used as effective optical processing media despite their small electrooptic coefficient.

  10. Sub-Millisecond Response Time in a Photorefractive Composite Operating under CW Conditions

    NASA Astrophysics Data System (ADS)

    Moon, Jong-Sik; Stevens, Tyler E.; Monson, Todd C.; Huber, Dale L.; Jin, Sung-Ho; Oh, Jin-Woo; Winiarz, Jeffrey G.

    2016-08-01

    Extensive study of photorefractive polymeric composites photosensitized with semiconductor nanocrystals has yielded data indicating that the inclusion of such nanocrystals enhances the charge-carrier mobility, and subsequently leads to a reduction in the photorefractive response time. Unfortunately, the included nanocrystals may also act as a source of deep traps, resulting in diminished diffraction efficiencies as well as reduced two beam coupling gain coefficients. Nonetheless, previous studies indicate that this problem is mitigated through the inclusion of semiconductor nanocrystals possessing a relatively narrow band-gap. Here, we fully exploit this property by doping PbS nanocrystals into a newly formulated photorefractive composite based on molecular triphenyldiamine photosensitized with C60. Through this approach, response times of 399 μs are observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency, with internal diffraction efficiencies of 72% and two-beam-coupling gain coefficients of 500 cm‑1 being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of enhanced charge mobility without the accompaniment of superfluous traps. It is anticipated that this approach can play a significant role in the eventual commercialization of this class of materials.

  11. Sub-millisecond response time in a photorefractive composite operating under CW conditions

    DOE PAGESBeta

    Moon, Jong -Sik; Stevens, Tyler E.; Monson, Todd C.; Huber, Dale L.; Jin, Sung -Ho; Oh, Jin -Woo; Winiarz, Jeffrey G.

    2016-08-01

    Extensive study of photorefractive polymeric composites photosensitized with semiconductor nanocrystals has yielded data indicating that the inclusion of such nanocrystals enhances the charge-carrier mobility, and subsequently leads to a reduction in the photorefractive response time. Unfortunately, the included nanocrystals may also act as a source of deep traps, resulting in diminished diffraction efficiencies as well as reduced two beam coupling gain coefficients. Nonetheless, previous studies indicate that this problem is mitigated through the inclusion of semiconductor nanocrystals possessing a relatively narrow band-gap. Here, we fully exploit this property by doping PbS nanocrystals into a newly formulated photorefractive composite based onmore » molecular triphenyldiamine photosensitized with C60. Through this approach, response times of 399 μs are observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency, with internal diffraction efficiencies of 72% and two-beam-coupling gain coefficients of 500 cm–1 being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of enhanced charge mobility without the accompaniment of superfluous traps. As a result, it is anticipated that this approach can play a significant role in the eventual commercialization of this class of materials.« less

  12. Sub-Millisecond Response Time in a Photorefractive Composite Operating under CW Conditions

    PubMed Central

    Moon, Jong-Sik; Stevens, Tyler E.; Monson, Todd C.; Huber, Dale L.; Jin, Sung-Ho; Oh, Jin-Woo; Winiarz, Jeffrey G.

    2016-01-01

    Extensive study of photorefractive polymeric composites photosensitized with semiconductor nanocrystals has yielded data indicating that the inclusion of such nanocrystals enhances the charge-carrier mobility, and subsequently leads to a reduction in the photorefractive response time. Unfortunately, the included nanocrystals may also act as a source of deep traps, resulting in diminished diffraction efficiencies as well as reduced two beam coupling gain coefficients. Nonetheless, previous studies indicate that this problem is mitigated through the inclusion of semiconductor nanocrystals possessing a relatively narrow band-gap. Here, we fully exploit this property by doping PbS nanocrystals into a newly formulated photorefractive composite based on molecular triphenyldiamine photosensitized with C60. Through this approach, response times of 399 μs are observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency, with internal diffraction efficiencies of 72% and two-beam-coupling gain coefficients of 500 cm−1 being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of enhanced charge mobility without the accompaniment of superfluous traps. It is anticipated that this approach can play a significant role in the eventual commercialization of this class of materials. PMID:27478156

  13. Sub-Millisecond Response Time in a Photorefractive Composite Operating under CW Conditions.

    PubMed

    Moon, Jong-Sik; Stevens, Tyler E; Monson, Todd C; Huber, Dale L; Jin, Sung-Ho; Oh, Jin-Woo; Winiarz, Jeffrey G

    2016-01-01

    Extensive study of photorefractive polymeric composites photosensitized with semiconductor nanocrystals has yielded data indicating that the inclusion of such nanocrystals enhances the charge-carrier mobility, and subsequently leads to a reduction in the photorefractive response time. Unfortunately, the included nanocrystals may also act as a source of deep traps, resulting in diminished diffraction efficiencies as well as reduced two beam coupling gain coefficients. Nonetheless, previous studies indicate that this problem is mitigated through the inclusion of semiconductor nanocrystals possessing a relatively narrow band-gap. Here, we fully exploit this property by doping PbS nanocrystals into a newly formulated photorefractive composite based on molecular triphenyldiamine photosensitized with C60. Through this approach, response times of 399 μs are observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency, with internal diffraction efficiencies of 72% and two-beam-coupling gain coefficients of 500 cm(-1) being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of enhanced charge mobility without the accompaniment of superfluous traps. It is anticipated that this approach can play a significant role in the eventual commercialization of this class of materials. PMID:27478156

  14. Growth, Spectroscopy and Photorefractive Investigation of Vanadium Doped CdSSe

    NASA Technical Reports Server (NTRS)

    Davis, Michelle; Pan, Zhengda; Chen, Kuo-Tong; Chen, Henry; Davis, Swanson L.; Burger, Arnold; Morgan, Steven H.

    1997-01-01

    We present two-wave mixing results obtained with a CdS(0.8)Se(0.2):V crystal. The CdS(0.8)Se(0.2):V crystal was grown by physical vapor transport (PVT) along with a concentration of 150 ppm (nominal) vanadium for creating trap centers. The as-grown crystal has a large crystal size, good optical quality, and a medium resistivity of 10(exp 6) - 108 ohms-cm. A large photorefractive gain coefficient of ().24 cm-' was observed at 633 nm with an optical intensity of 60 mW/cm(exp 2) and a grating period of 1.6 microns. To our knowledge, this is the first observation of the photorefractive effect in a vanadium doped CdSSe crystal. Room temperature absorption and low temperature photoluminescence spectroscopy measurements are also discussed. With a significant photorefractive effect, the CdSSe:V crystals are promising for device applications based on photorefractive effect, in the wavelength range of 600-700 nm.

  15. Dynamic Photorefractive Memory and its Application for Opto-Electronic Neural Networks.

    NASA Astrophysics Data System (ADS)

    Sasaki, Hironori

    This dissertation describes the analysis of the photorefractive crystal dynamics and its application for opto-electronic neural network systems. The realization of the dynamic photorefractive memory is investigated in terms of the following aspects: fast memory update, uniform grating multiplexing schedules and the prevention of the partial erasure of existing gratings. The fast memory update is realized by the selective erasure process that superimposes a new grating on the original one with an appropriate phase shift. The dynamics of the selective erasure process is analyzed using the first-order photorefractive material equations and experimentally confirmed. The effects of beam coupling and fringe bending on the selective erasure dynamics are also analyzed by numerically solving a combination of coupled wave equations and the photorefractive material equation. Incremental recording technique is proposed as a uniform grating multiplexing schedule and compared with the conventional scheduled recording technique in terms of phase distribution in the presence of an external dc electric field, as well as the image gray scale dependence. The theoretical analysis and experimental results proved the superiority of the incremental recording technique over the scheduled recording. Novel recirculating information memory architecture is proposed and experimentally demonstrated to prevent partial degradation of the existing gratings by accessing the memory. Gratings are circulated through a memory feed back loop based on the incremental recording dynamics and demonstrate robust read/write/erase capabilities. The dynamic photorefractive memory is applied to opto-electronic neural network systems. Module architecture based on the page-oriented dynamic photorefractive memory is proposed. This module architecture can implement two complementary interconnection organizations, fan-in and fan-out. The module system scalability and the learning capabilities are theoretically

  16. Photorefractive properties of paraelectric potassium lithium tantalate niobate crystal doped with iron

    NASA Astrophysics Data System (ADS)

    Tian, Hao; Zhou, Zhongxiang; Gong, Dewei; Wang, Haifeng; Jiang, Yongyuan; Hou, Chunfeng

    2008-03-01

    We report the successful growth of paraelectric potassium lithium tantalate niobate (KLTN) single crystal doped with iron. Detailed investigations have been made on the photorefractive properties of the as-grown crystal. The key parameters such as space-charge field, grating response time, photorefractive sensitivity and sign of the dominant charge carrier were obtained by two-wave mixing technique. 1.7 mm thick sample exhibits a high diffraction efficiency of 78% at the external field of 3.3 kV/cm and a sensitivity of 1.49 × 10-10E0 cm2/J. The two-wave mixing gain coefficient increases linearly with external field, and reaches a large value of 19.4 cm-1 at 4 kV/cm. Based on experimental results, iron is an effective dopant to KLTN which shows high diffraction efficiency and two-wave mixing gain coefficient.

  17. Growth and photorefractive properties of Zn, Fe double-doped LiTaO 3 crystal

    NASA Astrophysics Data System (ADS)

    Fang, Shuangquan; Wang, Biao; Zhang, Tao; Ling, Furi; Wang, Rui

    2006-02-01

    Zn, Fe double-doped LiTaO3 crystals have been grown by the Czochralski method. The photorefractive properties and optical damage resistance were measured by the two-beam coupling experiments and transmitted facula distortion method, respectively. The results showed that the photorefractive response speed of Zn:Fe:LiTaO3 was about four times faster than that of Fe:LiTaO3, whereas the optical damage resistance was two orders of magnitude higher than that of Fe:LiTaO3. In this paper, site occupation mechanism of impurities was also discussed to explain the high optical damage resistance and fast response speed of Zn:Fe:LiTaO3 crystal.

  18. Photorefractive holographic moiré-like patterns for secure numerical code generation.

    PubMed

    de Oliveira, G N; Oliveira, M E; dos Santos, P A M

    2013-03-15

    In this Letter, low-frequency photorefractive holographic moiré fringe patterns are proposed as secure numerical code generators that could be useful for storage or data transmission. These dynamic moiré patterns are holographically obtained by the superposition of two or more sinusoidal gratings with slightly different pitches. The Bi(12)TiO(20) photorefractive crystal sample is used as holographic medium. An optical numerical base was defined with patterns representing the 0, 1 and -1 digits as bits. Then, the complete set of these optical bits is combined to form bytes, where a numerical sequence is represented. The results show that the proposed numerical code is simple, robust and extremely secure, then could be used efficiently as standard numerical identification in robotic vision or eventually in storage or transmission of secure numerical data. PMID:23503288

  19. Optical correlation of spatial-frequency-shifted images in a photorefractive BSO correlator.

    PubMed

    Tavassoli, Abtine; Becker, Michael F

    2004-03-10

    The optical cross correlation of an image with another image that was spatial-frequency shifted in one dimension was demonstrated in a photorefractive VanderLugt correlator. The first image was stored as a Fourier-transform hologram in a photorefractive Bi12SiO20 crystal (BSO) and was successively correlated with different spatial-frequency-shifted versions of a second image. We implemented the spatial-frequency shift by rotating a galvanometer mirror in an image plane, causing the Fourier transform to be shifted laterally in the BSO. We verified that the resulting operation in the BSO was an accurate complex multiplication of the shifted and the stored Fourier transforms. As many as 20 successive readouts were conducted without measurable erasure of the stored hologram. The dynamic range, saturation behavior, and other performance parameters were measured and are discussed. PMID:15046173

  20. Photorefractive moiré-like patterns for the multifringe projection method in Fourier transform profilometry.

    PubMed

    de Oliveira, M E; de Oliveira, G N; de Souza, J C; dos Santos, P A M

    2016-02-10

    In the present paper, the method of simultaneous moiré-like fringe pattern projection for Fourier transform profilometry is described. The photorefractive holographic interferometric process produces controlled moiré-like patterns with two or more different variation directions. Each low spatial frequency fringe pattern is experimentally obtained as a result of the superposition of two high spatial frequency sinusoidal gratings, with slightly different pitches, for each fringe variation direction. These dynamic moiré-like patterns are induced due to an optical holographic beating of the sinusoidal induced gratings in the volume of the photorefractive Bi₁₂TiO₂₀ (BTO) crystal sample used as dynamic holographic medium. Two or more moiré-like fringe patterns, with at least two different variation directions, simultaneously (or not), are projected onto the object surface. Thus, this is the 2D fringe projection stage of our proposed Fourier transform procedure to determine the profile of a simple object. PMID:26906374

  1. Optical signal processing on photorefractive crystal substrate and bacteriorhodopsin thin film

    NASA Astrophysics Data System (ADS)

    Azimipour, Mehdi; Pashaie, Ramin

    2013-03-01

    In this article we present a new approach for implementation of computation algorithms to perform nonlinear signal processing with light on the surface of a photorefractive crystal and Bacteriorhodopsin thin film. Using the developed mathematical models for the photodynamics of these materials, we demonstrate a specific operation mode and a design procedure to obtain nonlinear response which can be used for implementation of high-performance photonic computers.

  2. Incoherent collisions between two-dimensional bright steady-state photorefractive spatial screening solitons

    NASA Astrophysics Data System (ADS)

    Shih, Ming-Feng; Segev, Mordechai

    1996-10-01

    We report the observation of incoherent collisions between two-dimensional bright photorefractive screening solitons. The solitons remain intact and do not exchange energy whenever the collision angle exceeds the critical angle for guidance in the waveguide that each soliton induces, which is, in turn, fully controlled by the soliton parameters. When the collision angle is much smaller than the critical angle the solitons fuse to form a single beam.

  3. Growth and characterization of high-performance photorefractive BaTiO3 crystals

    NASA Technical Reports Server (NTRS)

    Warde, C.; Garrett, M. H.; Chang, J. Y.; Jenssen, H. P.; Tuller, H. L.

    1991-01-01

    Barium titanate has been used for many nonlinear optical applications primarily because it has high grain and high self-pumped phase conjugate reflectivities. However, barium titanate has had a relatively slow response time, and thus low sensitivity. Therefore, it has not been suited to real-time operations. In this report we will describe the modifications in crystal growth, doping, reduction, and poling that have produced barium titanate crystals with the fastest photorefractive response time reported to date, approximately 21 microseconds with a beam-coupling gain coefficient of 38.7 cm(exp -1) and the highest sensitivity reported to date of 3.44 cm(exp 3)/kJ. The sensitivity of these barium titanate crystals is comparable to or greater than other photorefractive oxides. We will show, for the first time, beam-coupling in barium titanate at video frame rates. We infer from response time measurements that barium titanate has a phonon limited mobility. Also, photorefractive response time measurements as a function of the crystallographic orientation and grating wave vector for our cobalt-doped oxygen reduced crystals indicate that their faster response time arise because of an increase in the free carrier lifetime.

  4. NONLINEAR OPTICS: Energy exchange between optical waves due to self-diffraction by photorefractive gratings in a CdTe crystal

    NASA Astrophysics Data System (ADS)

    Borshch, A. A.; Brodin, M. S.; Burin, O. M.; Volkov, V. I.; Kukhtarev, N. V.; Semenets, T. I.; Smereka, Z. N.

    1990-07-01

    Theoretical and experimental investigations were made of a photorefractive nonlinearity of CdTe semiconductor crystals. Photorefractive gratings were formed in undoped CdTe and used to provide efficient energy exchange between nanosecond pulsed light beams (λ approx 1.06 μm) characterized by an exchange gain of ~ 0.13 cm - 1.

  5. Line sensing device for ultrafast laser acoustic inspection using adaptive optics

    DOEpatents

    Hale, Thomas C.; Moore, David S.

    2003-11-04

    Apparatus and method for inspecting thin film specimens along a line. A laser emits pulses of light that are split into first, second, third and fourth portions. A delay is introduced into the first portion of pulses and the first portion of pulses is directed onto a thin film specimen along a line. The third portion of pulses is directed onto the thin film specimen along the line. A delay is introduced into the fourth portion of pulses and the delayed fourth portion of pulses are directed to a photorefractive crystal. Pulses of light reflected from the thin film specimen are directed to the photorefractive crystal. Light from the photorefractive crystal is collected and transmitted to a linear photodiode array allowing inspection of the thin film specimens along a line.

  6. Photorefractive performance of a CdSe /ZnS core/shell nanoparticle-sensitized polymer

    NASA Astrophysics Data System (ADS)

    Aslam, Farzana; Binks, David J.; Rahn, Mark D.; West, David P.; O'Brien, Paul; Pickett, Nigel; Daniels, Steve

    2005-05-01

    We report the photorefractive performance of a polymer composite sensitized by CdSe /ZnS core/shell nanoparticles, and also comprising poly(N-vinylcarbazole) and an electro-optic chromophore. The nanoparticles are characterized by absorption and photoluminescence spectroscopy, elemental analysis, transmission electron microscopy, and powder x-ray diffraction. The electro-optic response of the composite is measured independently of the photorefractive effect by transmission ellipsometry. An asymmetric two-beam coupling gain of 30.6±0.4cm-1 is obtained, confirming photorefractivity. Degenerate four-wave mixing is used to assess photorefractive performance and, at a poling field of 70Vμm-1, yields a diffraction efficiency of 4.21%±0.03%, a holographic contrast of 3.05×10-4±1×10-6, a space-charge rise time of 25±2s, and a sensitivity of 4.7×10-5±4×10-6cm3J-1. These results constitute a significant improvement on the performance of previous nanoparticle-sensitized photorefractive polymer composites.

  7. Multiple limbal haemangiosarcomas in a border collie dog: management by lamellar keratectomy/sclerectomy and strontium-90 beta plesiotherapy.

    PubMed

    Donaldson, D; Sansom, J; Murphy, S; Scase, T

    2006-09-01

    An eight-year-old, neutered, male border collie dog was presented with a six-week history of left ocular discomfort and a raised, red mass at the lateral limbus. The right eye had been enucleated approximately 12 months previously following suspected trauma when the eye had become red and painful. The mass was excised using superficial keratectomy/sclerectomy and the surgery site was treated with strontium-90 beta radiation. Histopathological findings were consistent with a diagnosis of haemangiosarcoma. Immunohistochemical staining showed uniform expression of CD31 in neoplastic cells, confirming their endothelial origin. Two further treatments with strontium-90 beta radiation were applied to the surgical site at weekly intervals. Twenty-six weeks after surgery, a second, raised, red limbal mass became apparent at the medial limbus of the left eye. Surgical excision and adjuvant strontium-90 beta plesiotherapy were performed as described for the initial tumour. Routine histopathological analysis confirmed haemangiosarcoma at this site. Eighty-six weeks following the initial presentation, no recurrence of ocular haemangiosarcoma was evident. PMID:16961474

  8. Sulfur vacancies in photorefractive Sn{sub 2}P{sub 2}S{sub 6} crystals

    SciTech Connect

    Golden, E. M.; Giles, N. C.; Basun, S. A.; Grabar, A. A.; Stoika, I. M.; Evans, D. R.; Halliburton, L. E.

    2014-12-28

    A photoinduced electron paramagnetic resonance (EPR) spectrum in single crystals of Sn{sub 2}P{sub 2}S{sub 6} (SPS) is assigned to an electron trapped at a sulfur vacancy. These vacancies are unintentionally present in undoped SPS crystals and are expected to play an important role in the photorefractive behavior of the material. Nonparamagnetic sulfur vacancies are formed during the initial growth of the crystal. Subsequent illumination below 100 K with 442 nm laser light easily converts these vacancies to EPR-active defects. The resulting S = 1/2 spectrum shows well-resolved and nearly isotropic hyperfine interactions with two P ions and two Sn ions. Partially resolved interactions with four additional neighboring Sn ions are also observed. Principal values of the g matrix are 1.9700, 1.8946, and 1.9006, with the corresponding principal axes along the a, b, and c directions in the crystal. The isotropic parts of the two primary {sup 31}P hyperfine interactions are 19.5 and 32.6 MHz and the isotropic parts of the two primary Sn hyperfine interactions are 860 and 1320 MHz (the latter values are each an average for {sup 117}Sn and {sup 119}Sn). These hyperfine results suggest that singly ionized sulfur vacancies have a diffuse wave function in SPS crystals, and thus are shallow donors. Before illumination, sulfur vacancies are in the doubly ionized charge state because of compensation by unidentified acceptors. They then trap an electron during illumination. The EPR spectrum from the sulfur vacancy is destroyed when a crystal is heated above 120 K in the dark and reappears when the crystal is illuminated again at low temperature.

  9. Enhanced photorefractive performance in CdSe quantum-dot-dispersed poly(styrene-co-acrylonitrile) polymers

    SciTech Connect

    Li Xiangping; Embden, Joel van; Chon, James W. M.; Gu Min; Evans, Richard A.

    2010-06-21

    This paper reports on the enhanced photorefractive behavior of a CdSe quantum-dot-dispersed less expensive polymer of poly(styrene-co-acrylonitrile). The capability of CdSe quantum dots used as photosensitizers and the associated photorefractive performance are characterized through a photocurrent experiment and a two-beam coupling experiment, respectively. An enhanced two-beam coupling gain coefficient of 12.2 cm{sup -1} at 46 V/mum was observed owning to the reduced potential barrier. The photorefractive performance per CdSe quantum dot is three orders of magnitude higher than that in the sample sensitized by trinitrofluorenone in poly(styrene-co-acrylonitrile), and almost ten times higher than that in the CdSe quantum-dot-sensitized poly(N-vinylcarbazole) polymers.

  10. Human excimer laser corneal surgery: preliminary report.

    PubMed Central

    L'Esperance, F A; Taylor, D M; Del Pero, R A; Roberts, A; Gigstad, J; Stokes, M T; Warner, J W; Telfair, W B; Martin, C A; Yoder, P R

    1988-01-01

    The first human trial utilizing the argon fluoride excimer laser at 193 nm to produce a superficial keratectomy in ten human eyes has been described with the histopathological evaluation of four eyes and the longer gross appearance of six eyes at intervals extending to 10 months post-excimer laser treatment. The process of laser superficial keratectomy has proved to be one of the promising areas of surgical intervention for reconstructive or refractive keratoplasty in the future. Intensive investigations need to be undertaken on the corneal wound healing process following laser ablation as well as the nature, and long-term stability of the corneal excisions or induced refractive corrections. It is essential that the optimal laser parameters be established for the various refractive corrections and other corneal surgical techniques, and that pathophysiologic and histopathologic changes that have been induced by the excimer laser-corneal tissue interaction in animals and humans be critically and extensively analyzed. Images FIGURE 1 FIGURE 19 A FIGURE 19 B FIGURE 20 A FIGURE 20 B FIGURE 21 A FIGURE 21 B FIGURE 22 A FIGURE 22 B FIGURE 23 FIGURE 24 FIGURE 25 FIGURE 26 FIGURE 27 FIGURE 28 FIGURE 29 A FIGURE 29 B FIGURE 29 C FIGURE 29 D FIGURE 30 A FIGURE 30 B FIGURE 31 A FIGURE 31 B FIGURE 32 FIGURE 33 FIGURE 34 FIGURE 35 FIGURE 36 FIGURE 37 A FIGURE 37 B FIGURE 37 C FIGURE 38 A FIGURE 38 B FIGURE 39 A FIGURE 39 B FIGURE 39 C FIGURE 40 A FIGURE 40 B PMID:2979049

  11. Dark current and light illumination effects on grating formation during periodic long-term operation in photorefractive polymers

    SciTech Connect

    Fujihara, T.; Mamiya, J.; Kawamoto, M.; Sassa, T.

    2014-01-14

    Photorefractive grating formation dynamics in long-timescale writing and the effects of periodic writing through the control of writing beam irradiation or electric field application were investigated using typical photorefractive polymers. Both dark current and writing beam irradiation affected grating formation dynamics. Dark current in polymers changed the effective trap density over time through deep trap filling and/or detrapping and thus affected grating formation considerably. The writing beam irradiation also affected grating development in the presence of an electric field owing to the accumulation of filled deep traps. However, grating development recovered after the elimination of the electric field freed up the filled deep traps.

  12. Electro-optic and dielectric properties of photorefractive BaTiO3 and KNbO3

    NASA Astrophysics Data System (ADS)

    Zgonik, Marko; Nakagawa, Kiyoshi; Günter, Peter

    1995-08-01

    Recently determined complete sets of materials parameters describing the dielectric, elastic, piezoelectric, elasto-optic, and electro-optic properties of BaTiO3 and KNbO3 crystals at room temperature are used to calculate the effective electro-optic coefficients and dielectric constants required for describing photorefractive phenomena. We show a substantial deviation of the new values from the electro-optic coefficients for homogeneously applied electric fields that were used previously in describing the photorefractive effects. We derive angular dependences of the effective electro-optic coefficients and the effective dielectric constants relevant for grating recording in both crystals and verify them experimentally.

  13. Carrier Dynamics and Application of the Phase Coherent Photorefractive Effect in ZnSe Quantum Wells

    NASA Astrophysics Data System (ADS)

    Dongol, Amit

    The intensity dependent diffraction efficiency of a phase coherent photorefractive (PCP) ZnSe quantum well (QW) is investigated at 80 K in a two-beam four-wave mixing (FWM) configuration using 100 fs laser pulses with a repetition rate of 80 MHz. The observed diffraction efficiencies of the first and second-order diffracted beam are on the order of 10-3 and 10-5, respectively, revealing nearly no intensity dependence. The first-order diffraction is caused by the PCP effect where the probe-pulse is diffracted due to a long-living incoherent electron density grating in the QW. The second-order diffraction is created by a combination of diffraction processes. For negative probe-pulse delay, the exciton polarization is diffracted at the electron grating twice by a cascade effect. For positive delay, the diffracted signal is modified by the destructive interference with a chi(5) generated signal due to a dynamical screening effect. Model calculations of the signal traces based on the optical Bloch equations considering inhomogeneous broadening of exciton energies are in good agreement with the experimental data. To study the carrier dynamics responsible for the occurrence of the PCP effect, threebeam FWM experiments are carried out. The non-collinear wave-vectors k1 , k2 and k3 at central wavelength of 441 nm (~2.81 eV) were resonantly tuned to the heavy-hole exciton transition energy at 20 K. In the FWM experiment the time coincident strong pump pulses k1 and k2 create both an exciton density grating in the QW and an electron-hole pair grating in the GaAs while the delayed weak pulse k3 simultaneously probes the exciton lifetime as well as the electron grating capture time. The model calculations are in good agreement with the experimental results also providing information about the transfer delay of electrons arriving from the substrate to the QW. For negative probe-pulse delay we still observe a diffracted signal due to the long living electron density grating in

  14. Beam coupling in hybrid photorefractive inorganic-cholesteric liquid crystal cells: Impact of optical rotation

    SciTech Connect

    Reshetnyak, V. Yu.; Pinkevych, I. P.; Sluckin, T. J.; Cook, G.; Evans, D. R.

    2014-03-14

    We develop a theoretical model to describe two-beam energy exchange in a hybrid photorefractive inorganic-cholesteric cell. A cholesteric layer is placed between two inorganic substrates. One of the substrates is photorefractive (Ce:SBN). Weak and strong light beams are incident on the hybrid cell. The interfering light beams induce a periodic space-charge field in the photorefractive window. This penetrates into the cholesteric liquid crystal (LC), inducing a diffraction grating written on the LC director. In the theory, the flexoelectric mechanism for electric field-director coupling is more important than the LC static dielectric anisotropy coupling. The LC optics is described in the Bragg regime. Each beam induces two circular polarized waves propagating in the cholesteric cell with different velocities. The model thus includes optical rotation in the cholesteric LC. The incident light beam wavelength can fall above, below, or inside the cholesteric gap. The theory calculates the energy gain of the weak beam, as a result of its interaction with the pump beam within the diffraction grating. Theoretical results for exponential gain coefficients are compared with experimental results for hybrid cells filled with cholesteric mixture BL038/CB15 at different concentrations of chiral agent CB15. Reconciliation between theory and experiment requires the inclusion of a phenomenological multiplier in the magnitude of the director grating. This multiplier is cubic in the space-charge field, and we provide a justification of the q-dependence of the multiplier. Within this paradigm, we are able to fit theory to experimental data for cholesteric mixtures with different spectral position of cholesteric gap relative to the wavelength of incident beams, subject to the use of some fitting parameters.

  15. The simultaneous enhancement of photorefraction and optical damage resistance in MgO and Bi2O3 co-doped LiNbO3 crystals.

    PubMed

    Zheng, Dahuai; Kong, Yongfa; Liu, Shiguo; Chen, Muling; Chen, Shaolin; Zhang, Ling; Rupp, Romano; Xu, Jingjun

    2016-01-01

    For a long time that optical damage was renamed as photorefraction, here we find that the optical damage resistance and photorefraction can be simultaneously enhanced in MgO and Bi2O3 co-doped LiNbO3 (LN:Bi,Mg). The photorefractive response time of LN:Bi,Mg was shortened to 170 ms while the photorefractive sensitivity reached up to 21 cm(2)/J. Meanwhile, LN:Bi,Mg crystals could withstand a light intensity higher than 10(6)  W/cm(2) without apparent optical damage. Our experimental results indicate that photorefraction doesn't equal to optical damage. The underground mechanism was analyzed and attributed to that diffusion dominates the transport process of charge carriers, that is to say photorefraction causes only slight optical damage under diffusion mechanism, which is very important for the practical applications of photorefractive crystals, such as in holographic storage, integrated optics and 3D display. PMID:26837261

  16. The simultaneous enhancement of photorefraction and optical damage resistance in MgO and Bi2O3 co-doped LiNbO3 crystals

    PubMed Central

    Zheng, Dahuai; Kong, Yongfa; Liu, Shiguo; Chen, Muling; Chen, Shaolin; Zhang, Ling; Rupp, Romano; Xu, Jingjun

    2016-01-01

    For a long time that optical damage was renamed as photorefraction, here we find that the optical damage resistance and photorefraction can be simultaneously enhanced in MgO and Bi2O3 co-doped LiNbO3 (LN:Bi,Mg). The photorefractive response time of LN:Bi,Mg was shortened to 170 ms while the photorefractive sensitivity reached up to 21 cm2/J. Meanwhile, LN:Bi,Mg crystals could withstand a light intensity higher than 106  W/cm2 without apparent optical damage. Our experimental results indicate that photorefraction doesn’t equal to optical damage. The underground mechanism was analyzed and attributed to that diffusion dominates the transport process of charge carriers, that is to say photorefraction causes only slight optical damage under diffusion mechanism, which is very important for the practical applications of photorefractive crystals, such as in holographic storage, integrated optics and 3D display. PMID:26837261

  17. Generation of Squeezed Light Using Photorefractive Degenerate Two-Wave Mixing

    NASA Technical Reports Server (NTRS)

    Lu, Yajun; Wu, Meijuan; Wu, Ling-An; Tang, Zheng; Li, Shiqun

    1996-01-01

    We present a quantum nonlinear model of two-wave mixing in a lossless photorefractive medium. A set of equations describing the quantum nonlinear coupling for the field operators is obtained. It is found that, to the second power term, the commutation relationship is maintained. The expectation values for the photon number concur with those of the classical electromagnetic theory when the initial intensities of the two beams are strong. We also calculate the quantum fluctuations of the two beams initially in the coherent state. With an appropriate choice of phase, quadrature squeezing or number state squeezing can be produced.

  18. Energy transfer in two-wave mixing quasi-degenerated in photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Barrera, B.; Arias Hernández, N. A.; Molina Prado, M. L.; Tebaldi, M.

    2016-02-01

    Wave equations describing the quasi-degenerated two-beam coupling in the photorefractive crystals for high frequency gratings have been solved. In the case of the quasi-degenerate two-beam coupling, equations depend upon the coupling coefficient, the response time of the medium, the input beams frequencies, the absorption coefficient and the input intensity ratio. The response time of the medium is function of the diffusion field, the drift field, the saturation field and the concentration ratio, i.e., the ratio between NA density of acceptor impurities and ND density of donor impurities. The effect of these parameters on the gain has been studied in details.

  19. Sequential formation of multiple lattice gap solitons in defocusing photovoltaic-photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Hui, Juanli; Lu, Keqing; Zhao, Chong; Gao, Lixu; Chen, Weijun

    2016-05-01

    We show that an odd- or even-numbered sequence of multiple gap solitons (MGSs) supported by optical lattices imprinted in defocusing photovoltaic-photorefractive (PP) crystals is possible. The side lobes of MGSs are the small intensity, which can be controlled by changing the propagation constant. The lobes of MGSs are the same intensity except for the side lobes. The existence domain of MGSs decreases with decreasing the lattice depth and vanishes when the lattice depth decreases to below a certain threshold. The stability of MGSs has been investigated numerically and it has been found that they are stable.

  20. Depth-resolved holographic optical coherence imaging using a high-sensitivity photorefractive polymer device

    NASA Astrophysics Data System (ADS)

    Salvador, M.; Prauzner, J.; Köber, S.; Meerholz, K.; Jeong, K.; Nolte, D. D.

    2008-12-01

    We present coherence-gated holographic imaging using a highly sensitive photorefractive (PR) polymer composite as the recording medium. Due to the high sensitivity of the composite holographic recording at intensities as low as 5 mW/cm2 allowed for a frame exposure time of only 500ms. Motivated by regenerative medical applications, we demonstrate optical depth sectioning of a polymer foam for use as a cell culture matrix. An axial resolution of 18 μm and a transverse resolution of 30 μm up to a depth of 600 μm was obtained using an off-axis recording geometry.

  1. Raman Study of Photorefractive Nonlinearity in TITANIUM:LITHIUM Niobate and of Silicon Crystallite Formation in Silicon Dioxide

    NASA Astrophysics Data System (ADS)

    Ramabadran, Uma B.

    1990-01-01

    Photorefractive non-linearities in electro-optic crystals have been widely investigated in a variety of materials including LiNbO_3. This phenomenon is also observed in the Ti:LiNbO_3 channel waveguide which is typically a few microns in thickness and width and therefore experiences high power densities which gives rise to this effect. The non-linearity is observed in the unidirectional energy transfer from one waveguide mode to an orthogonal one causing a polarization rotation. A threshold value of power necessary to initiate the polarization rotation can be obtained and used to calculate a value of beta_{15 }, an asymmetric component of the photovoltaic tensor. Elastic scattered light is collected over a distance of the propagating guided wave and the scattering loss as a function of distance is calculated. The Raman spectrometer was used in a novel way to measure inelastic scattered light from the waveguide surface as a function of propagatory distance and this data used to calculate the loss coefficient. In this way, the contributions due to surface inhomogeneities were neglected and a value of the loss characteristic of the guiding medium alone was obtained. The measurements were carried out in the channel waveguides of Ti:LiNbO _3 described above and in planar waveguides of Si^+/N^+ implanted in SiO_2 thermally grown on silicon substrates. In the latter case, the Raman macrochamber was used with a large collection lens to obtain sufficient signal. Different annealing cycles were performed to optimize the waveguide quality. This thesis also reports the investigation of diffusion characteristics of silicon when samples of high -dose silicon ion-implanted in crystalline quartz were subjected to rapid thermal or laser annealing. Characterization techniques included differential interference microscopy, Rutherford backscattering spectroscopy and Raman microprobe spectroscopy. The data obtained indicated that rapid thermal annealing results in the formation of

  2. Amplification of optical signals in Bi{sub 12}TiO{sub 20} crystal by photorefractive surface waves

    SciTech Connect

    Khomenko, A.V.; Garcia-Weidner, A.; Kamshilin, A.A.

    1996-07-01

    We have demonstrated experimentally beam amplification by coupling between the signal beam and the photorefractive surfaces wave in Bi{sub 12}TiO{sub 20} crystal. A gain of 16,000 has been measured, with an output signal-to-noise ratio of {approx_gt}20 for weak input signals. {copyright} {ital 1996 Optical Society of America.}

  3. Off-Resonance Photosensitization of a Photorefractive Polymer Composite Using PbS Nanocrystals

    SciTech Connect

    Moon, Jong-Sik; Liang, Yichen; Stevens, Tyler E.; Monson, Todd C.; Huber, Dale L.; Mahala, Benjamin D.; Winiarz, Jeffrey G.

    2015-05-26

    The photosensitization of photorefractive polymeric composites for operation at 633 nm is accomplished through the inclusion of narrow band gap semiconductor nanocrystals composed of PbS. Unlike previous studies involving photosensitization of photorefractive polymer composites with inorganic nanocrystals, we employ an off-resonance approach where the first excitonic transition associated with the PbS nanocrystals lies at ~1220 nm and not the wavelength of operation. Using this methodology, internal diffraction efficiencies exceeding 82%, two-beam-coupling gain coefficients of 211 cm–1, and response times of 34 ms have been observed, representing some of the best figures of merit reported for this class of materials. Furthermore, these data demonstrate the ability of semiconductor nanocrystals to compete effectively with traditional organic photosensitizers. In addition to superior performance, this approach also offers an inexpensive and easy means by which to photosensitize composite materials. Additionally, the photoconductive characteristics of the composites used for this study will also be considered.

  4. Off-Resonance Photosensitization of a Photorefractive Polymer Composite Using PbS Nanocrystals

    DOE PAGESBeta

    Moon, Jong-Sik; Liang, Yichen; Stevens, Tyler E.; Monson, Todd C.; Huber, Dale L.; Mahala, Benjamin D.; Winiarz, Jeffrey G.

    2015-05-26

    The photosensitization of photorefractive polymeric composites for operation at 633 nm is accomplished through the inclusion of narrow band gap semiconductor nanocrystals composed of PbS. Unlike previous studies involving photosensitization of photorefractive polymer composites with inorganic nanocrystals, we employ an off-resonance approach where the first excitonic transition associated with the PbS nanocrystals lies at ~1220 nm and not the wavelength of operation. Using this methodology, internal diffraction efficiencies exceeding 82%, two-beam-coupling gain coefficients of 211 cm–1, and response times of 34 ms have been observed, representing some of the best figures of merit reported for this class of materials. Furthermore,more » these data demonstrate the ability of semiconductor nanocrystals to compete effectively with traditional organic photosensitizers. In addition to superior performance, this approach also offers an inexpensive and easy means by which to photosensitize composite materials. Additionally, the photoconductive characteristics of the composites used for this study will also be considered.« less

  5. Three-dimensional holographic imaging of living tissue using a highly sensitive photorefractive polymer device.

    PubMed

    Salvador, M; Prauzner, J; Köber, S; Meerholz, K; Turek, J J; Jeong, K; Nolte, D D

    2009-07-01

    Photorefractive materials are dynamic holographic storage media that are highly sensitive to coherent light fields and relatively insensitive to a uniform light background. This can be exploited to effectively separate ballistic light from multiply-scattered light when imaging through turbid media. We developed a highly sensitive photorefractive polymer composite and incorporated it into a holographic optical coherence imaging system. This approach combines the advantages of coherence-domain imaging with the benefits of holography to form a high-speed wide-field imaging technique. By using coherence-gated holography, image-bearing ballistic light can be captured in real-time without computed tomography. We analyzed the implications of Fourier-domain and image-domain holography on the field of view and image resolution for a transmission recording geometry, and demonstrate holographic depth-resolved imaging of tumor spheroids with 12 microm axial and 10 microm lateral resolution, achieving a data acquisition speed of 8 x 10(5) voxels/s. PMID:19582098

  6. Temporal modulation instability, transition to chaos in non-feedback biased photorefractive media

    NASA Astrophysics Data System (ADS)

    Sharif, Morteza A.; Borjkhani, Mehdi; Ghafary, Bijan

    2014-05-01

    This paper surveys the theoretical dynamic model of chaotic regime in optical delayed feedback system; chaotic control parameters of optical input intensity and externally applied bias electric field are investigated. It is also shown that quasi-periodic state identified as temporal modulation instability can be deeply considered as a route to chaos through the evolution equation. Numerical solution of nonlinear Schrödinger equation as the universal model of modulation instability approves such claim. Pre-experiment based on optical delayed feedback system confirms theoretical model results and clarifies the crucial role of critical frequency as the competition point between optical bistability and the chaotic regime. Then, the simple experiment of non-feedback chaos control in Lithium Niobate photorefractive medium without delay indicates that quasi-periodic state -implies on temporal modulation instability- is also attainable and thus chaotic control can be achieved. The causal explanation of such behavior in slow response time Lithium Niobate photorefractive medium is analytically discussed as the generation of the internal feedback inside the medium.

  7. Dynamic range compression/expansion of light beams by photorefractive crystals

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen (Inventor); Liu, Hua-Kuang (Inventor)

    1988-01-01

    An apparatus is provided which greatly reduces the intensity of bright portions of an image while only moderately reducing the brightness of dimmer portions of the image, to thereby compress the range of light intensities to facilitate detection of the image. The apparatus includes a light detector device formed by a chip of photorefractive material. A 2-D array of light beams from an object to be detected passes through a beam splitter to form two arrays of light beams. The two arrays are directed at different angles against a surface of the chip of photorefractive material, the two arrays of light beams forming coincident images on the surface. One of the 2-D arrays of beams emerging from an opposite surface of the chip has a lower range of intensities, to facilitate detection of the object despite very bright spots in its image. The other array of light beams emerging from the chip has a greater range of intensities than the unprocessed image of the object.

  8. Photorefractivity in nematic liquid crystals doped with a conjugated polymer: Mechanisms for enhanced charge transport

    SciTech Connect

    Wiederrecht, G.P.; Niemczyk, M.P.; Svec, W.A.; Wasielewski, M.R. |

    1999-06-01

    New organic materials that exhibit photorefractive effects are of wide interest for potential optical signal processing applications. The authors report on a photorefractive nematic liquid crystal composite containing the conjugated polymer poly(2,5-bis(2{prime}-ethylhexyloxy)-1,4-phenylenevinylene), BEH-PPV that exhibits a novel fringe spacing dependent inversion of the polarity of the space-charge field due to competition between the ionic diffusion and charge drift transport mechanisms. A eutectic mixture of 35% (wt %) 4{prime}-(n-octyloxy)-4-cyanobiphenyl, 8OCB, and 65% 4{prime}(n-pentyl)-4-cyanobiphenyl, 5CB, was doped with 10{sup {minus}5} M BEH-PPV (200 kD by GPC), as the electron donor. The molecular weight of the BEH-PPV polymer implies that 500 repeat units of the monomer are present with an extended chain length of 0.35 {micro}m. N,N{prime}-Dioctyl-1,4:5,8-naphthalenediimide, NI, 8 {times} 10{sup {minus}3} M, was added as the electron acceptor. The free energy change for the photoinduced electron-transfer reaction, (BEH-PPV) + NI {yields} (BEH-PPV){sup +} + NI{sup {minus}}, is {minus}1.0 eV. Two other liquid-crystal composites were also studied as controls.

  9. Energy transfer between injection-locked single-mode diode lasers by two-beam coupling in BaTiO/sub 3/

    SciTech Connect

    Christian, W.R.; Beckwith, P.H.; McMichael, I.

    1989-01-01

    Two-beam coupling in photorefractive BaTiO/sub 3/ is used to combine beams coherently from two injection-locked single-mode diode lasers operating at 830 nm. We are able to transfer more than 70% of the power in one beam to the other beam with this method.

  10. ISS-Crystal Growth of Photorefractive Materials (BSO): Critical Design Issues for Optimized Data Extraction from Space Experiments

    NASA Technical Reports Server (NTRS)

    Hyers, Robert W.; Motakef, S.; Witt, A. F.; Wuensch, B.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Realization of the full potential of photorefractive materials in device technology is seriously impeded by our inability to achieve controlled formation of critical defects during single crystal growth and by difficulties in meeting the required degree of compositional uniformity on a micro-scale over macroscopic dimensions. The exact nature and origin of the critical defects which control photorefractivity could not as yet be identified because of gravitational interference. There exists, however, strong evidence that the density of defect formation and their spatial distribution are adversely affected by gravitational interference which precludes the establishment of quantifiable and controllable heat and mass transfer conditions during crystal growth. The current, NASA sponsored research at MIT is directed at establishing a basis for the development of a comprehensive approach to the optimization of property control during melt growth of photorefractive materials, making use of the m-g environment, provided in the International Space Station. The objectives to be pursued in m-g research on photorefractive BSO (Bi12SiO20) are: (a) identification of the x-level(s) responsible for photorefractivity in undoped BSO; (b) development of approaches leading to the control of x-level formation at uniform spatial distribution; (c) development of doping and processing procedures for optimization of the critical, application specific parameters, spectral response, sensitivity, response time and matrix stability. The presentation will focus on: the rationale for the justification of the space experiment, ground-based development efforts, design considerations for the space experiments, strategic plan of the space experiments, and approaches to the quantitative analysis of the space experiments.